JP5793898B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, a printer, and the like, which is provided with an intermediate transfer member.

  2. Description of the Related Art Conventionally, an image forming apparatus such as a copying machine, a facsimile machine, a printer or the like, and an intermediate transfer type image forming apparatus provided with an intermediate transfer body such as an intermediate transfer belt is known (for example, [Patent Document 1] to [ Patent Document 10]).

As an intermediate transfer body type image forming apparatus, a so-called tandem type (see, for example, [Patent Document 1] to [Patent Document 3]) and a so-called revolver developing type (for example, see [Patent Document 4] to [Patent Document 10]). ) Is known.
In the former, a plurality of image carriers are provided for the intermediate transfer member, and a desired image is obtained by superimposing images carried on the respective image carriers on the intermediate transfer member. In the latter, one image carrier is provided for the intermediate transfer member, and a plurality of developing devices are provided for the image carrier, and the desired image is superimposed on the image carrier or the intermediate transfer member. It is something to get.

  Such an intermediate transfer type image forming apparatus forms an image on an image carrier, performs primary transfer to transfer the image formed on the image carrier to the intermediate transfer member, and is transferred to the intermediate transfer member. Secondary transfer is performed to transfer the image to a recording material, etc., and the resistance, friction coefficient, and other characteristics of the intermediate transfer member are managed to ensure transferability and prevent abnormal images. .

  For example, in order to prevent the occurrence of so-called discharge traces caused by discharge from the intermediate transfer member to the recording material or the like during secondary transfer, which is a kind of abnormal image, the resistance of the intermediate transfer member is increased. It has proven effective to do.

  However, as a side effect of increasing the resistance of the intermediate transfer member, there is a defect called an afterimage of the intermediate transfer member, that is, after the secondary transfer, charges remain on the intermediate transfer member in a distribution corresponding to the image, and the next primary transfer. It is known that defects that affect the image quality affect the image quality.

  As a measure for preventing this problem, a measure is provided for eliminating the charge between the secondary transfer and the primary transfer of the intermediate transfer member, and the resistance of the intermediate transfer member is set so severe that such a problem does not occur. Measures to manage are known.

  However, in the former method, if a neutralization device dedicated to measures against the afterimage of the intermediate transfer member is provided, the device becomes large and expensive, and the latter method has a problem that the cost is increased. To further describe the latter measure, in order to avoid an increase in cost, the intermediate transfer member must be mass-produced under resistance control at a level where discharge traces and an afterimage of the intermediate transfer member are allowed. Even with countermeasures, there is a problem that an afterimage or the like of the intermediate transfer member may occur even within the guaranteed environment range of the operation of the apparatus due to variations in resistance of the produced intermediate transfer member. As another measure, there is a method of preventing the secondary transfer bias from being excessively high, but this cannot be adopted because it causes a defect of an abnormal image such as defective secondary transfer or transfer dust.

For this reason, it is preferable to eliminate or reduce the residual electrification distribution after the secondary transfer of the intermediate transfer member without using a dedicated device as a direction for countermeasures against the intermediate transfer member afterimage.
In this regard, the revolver type image forming apparatus has a configuration in which the intermediate transfer body after the secondary transfer is idled and a bias is applied by the secondary transfer apparatus (see, for example, [Patent Document 4] and [Patent Document 5]). According to this configuration, there is a possibility that the residual electrification distribution after the secondary transfer is eliminated or alleviated without using a dedicated device. In addition, a configuration provided with a neutralizing device dedicated to measures against an afterimage of an intermediate transfer member has been proposed in a revolver type image forming apparatus (see, for example, [Patent Document 6] and [Patent Document 7]).

  However, when the intermediate transfer member is idled, image formation must be interrupted accordingly, and there is a problem that productivity is reduced when continuous image formation is to be performed. Further, it is necessary to provide a countermeasure against the afterimage of the intermediate transfer body also in the tandem type image forming apparatus.

  The present invention is an image forming apparatus such as a tandem intermediate transfer type copying machine, facsimile, printer, etc., which eliminates or alleviates the residual electrification distribution after secondary transfer of the intermediate transfer member without using a dedicated apparatus. It is another object of the present invention to provide an image forming apparatus that can perform without idling the intermediate transfer member.

In order to achieve the above object, according to the first aspect of the present invention, a plurality of image forming units and an image formed in the plurality of image forming units are transferred to the plurality of image forming units. And an intermediate transfer member that is secondarily transferred to another medium in a secondary transfer unit, and each of the plurality of image forming units carries an image transferred to the intermediate transfer member. A carrier, a transfer means for applying a transfer bias for transferring the image carried on the image carrier to the intermediate transfer member, and the image carrier in the image forming unit in which no image is formed among the plurality of image forming units. A first mode in which a member is separated from the intermediate transfer member, and the image carrier in an image forming unit that does not form an image among the plurality of image forming units is brought into contact with the intermediate transfer member and a second mode in which the state And forming an image in a downstream side image forming unit different from the image forming unit located on the most downstream side of the secondary transfer unit in the moving direction of the intermediate transfer member among the plurality of image forming units. In order to equalize the potential of the intermediate transfer member after the secondary transfer, upstream image formation is located downstream of the secondary transfer portion and upstream of the downstream image forming portion in the movement direction. In the image forming apparatus, a transfer bias can be applied by the transfer means in the section , and an image is formed in the second mode in order to apply the transfer bias .

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect , the image forming apparatus further includes a temperature / humidity detection unit that detects a temperature / humidity of an environment, and the second order is performed on the condition that the temperature / humidity is detected by the temperature / humidity detection unit. In order to apply a transfer bias by the transfer means in the upstream image forming unit in order to equalize the potential of the intermediate transfer member after the transfer, whether or not to perform image formation in the second mode is set. It is characterized by that.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect , the image forming apparatus further comprises unit resistance detecting means for detecting a resistance of a unit including the intermediate transfer member and a member in contact with the intermediate transfer member. In order to apply a transfer bias by the transfer unit in the upstream image forming unit in order to equalize the potential of the intermediate transfer body after the secondary transfer on condition that the resistance detected by the resistance detection unit is used. Whether to perform image formation in the second mode is set.

According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect , the unit includes the intermediate transfer member, the image carrier in contact with the intermediate transfer member, and the transfer unit, and the unit resistance detection unit. Is characterized in that the resistance is detected using the transfer means.

According to a fifth aspect of the present invention, in the image forming apparatus according to the third aspect , the unit is in contact with the intermediate transfer member and the intermediate transfer member in the secondary transfer portion and the image transferred to the intermediate transfer member. Secondary transfer means for applying a secondary transfer bias to the secondary transfer portion for secondary transfer of the image to another medium, and the unit resistance detection means uses the secondary transfer means to reduce the resistance. It is characterized by detecting.

According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, when the next image forming job is input during the image forming operation, the current image forming operation is the first. Whether the image forming operation of the next image forming job is performed in the first mode or the second mode on the condition that it is performed in the second mode and / or in the second mode. It is characterized by setting.

According to a seventh aspect of the present invention, a plurality of image forming units and an image formed at the plurality of image forming units are transferred and two transferred images are arranged opposite to the plurality of image forming units. An intermediate transfer member that is secondarily transferred to another medium in a next transfer portion, and each of the plurality of image forming portions includes an image carrier that carries an image transferred to the intermediate transfer member, and the image carrier. Transfer means for applying a transfer bias for transferring the image carried on the body to the intermediate transfer body, and in the moving direction of the intermediate transfer body among the plurality of image forming sections, more than the secondary transfer section. When forming an image in a downstream image forming unit different from the image forming unit located on the most upstream side in the downstream side, in order to equalize the potential of the intermediate transfer member after the secondary transfer , the secondary in the moving direction Downstream of the transfer section The size of the first transfer bias applied by the transfer means in the upstream image forming unit located upstream from the downstream image forming unit and the image carried on the image carrier are transferred to the intermediate transfer member When there are a plurality of upstream image forming units, the size of the first transfer bias is set to be smaller than the size of the second transfer bias, and the number of the upstream image forming units is single. In this case, the magnitude of the first transfer bias is made larger than the magnitude of the second transfer bias.

  According to the present invention, a plurality of image forming units are arranged opposite to the plurality of image forming units, and images formed in the plurality of image forming units are transferred and the transferred images are transferred to the secondary transfer unit. An intermediate transfer member that is secondarily transferred to another medium, and each of the plurality of image forming units is supported by the image carrier that carries an image to be transferred to the intermediate transfer member. Transfer means for applying a transfer bias for transferring the transferred image to the intermediate transfer member, and the most upstream of the plurality of image forming portions downstream of the secondary transfer portion in the moving direction of the intermediate transfer member. When forming an image in a downstream image forming unit different from the image forming unit located in the downstream, in order to equalize the potential of the intermediate transfer member after the secondary transfer, it is downstream of the secondary transfer unit in the moving direction. Said downstream image on the side Since there is an image forming apparatus in which a transfer bias can be applied by the transfer means in the upstream image forming section located upstream from the image forming section, it is possible to eliminate or alleviate the residual electrification distribution after the secondary transfer of the intermediate transfer member. By applying a transfer bias to reduce the image quality due to residual charge distribution while avoiding the increase in size and cost of the device without using a dedicated device and without idling the intermediate transfer member. It is possible to provide an image forming apparatus that can eliminate or prevent and quickly perform good image formation.

  A first mode in which the image carrier in the image forming unit in which no image is formed among the plurality of image forming units is separated from the intermediate transfer member; A second mode in which the image bearing member in the image forming unit is in contact with the intermediate transfer member, in order to equalize the potential of the intermediate transfer member after secondary transfer If image formation is performed in the second mode in order to apply a transfer bias by the transfer means in the upstream image forming unit, the residual electrification distribution after secondary transfer of the intermediate transfer member can be eliminated or alleviated. Transfer in the second mode of image quality degradation due to residual charge distribution while avoiding the increase in size and cost of the device without using a dedicated device and without idling the intermediate transfer member. To apply a bias Eliminated or prevented I, it is possible to provide an image forming apparatus capable of quickly performing good image formation.

  A temperature / humidity detecting means for detecting the temperature / humidity of the environment, on the upstream side in order to equalize the potential of the intermediate transfer body after the secondary transfer on the condition of the temperature / humidity detected by the temperature / humidity detecting means; In order to apply a transfer bias by the transfer unit in the image forming unit, whether to perform image formation in the second mode or not is set, the residual charge distribution after the secondary transfer of the intermediate transfer member Residual charge distribution generated at different strengths depending on temperature and humidity while eliminating or mitigating without using a dedicated device and without idling the intermediate transfer member, avoiding the increase in size and cost of the device The deterioration of image quality due to the above can be eliminated or prevented by applying a transfer bias in the second mode set as required under the condition of temperature and humidity, and good image formation can be performed quickly. It is possible to provide an image forming apparatus.

  Unit resistance detection means for detecting the resistance of a unit including the intermediate transfer member and a member in contact with the intermediate transfer body, and the intermediate after the secondary transfer, on condition that the resistance is detected by the unit resistance detection means In order to apply a transfer bias by the transfer unit in the upstream image forming unit in order to make the potential of the transfer body uniform, it is determined whether or not to perform image formation in the second mode. It is possible to eliminate or alleviate the residual electrification distribution after the secondary transfer of the intermediate transfer member without using a dedicated device or idling the intermediate transfer member, avoiding the increase in size and cost of the device. At the same time, the transfer bias is applied in the second mode that is set as necessary under the condition of the resistance due to the residual charge distribution generated at different intensities depending on the resistance of the unit. Eliminated or prevented by, it is possible to provide an image forming apparatus capable of quickly performing good image formation.

  The unit includes the intermediate transfer member, the image carrier in contact with the intermediate transfer member, and the transfer unit, and the unit resistance detection unit detects the resistance using the transfer unit. It is possible to eliminate or alleviate the residual electrification distribution after the secondary transfer of the intermediate transfer member without using a dedicated device or idling the intermediate transfer member, avoiding the increase in size and cost of the device. On the other hand, a transfer bias is applied by the transfer means in the second mode set as necessary on the condition that the resistance is deteriorated due to the residual charge distribution generated at different intensities depending on the resistance of the unit. Thus, it is possible to provide an image forming apparatus that can eliminate or prevent the occurrence of the problem and quickly perform good image formation.

  The unit includes a second transfer unit for transferring the image transferred to the intermediate transfer member and the intermediate transfer member in the secondary transfer unit to the second transfer unit for secondary transfer to another medium. Secondary transfer means for applying a secondary transfer bias, and if the unit resistance detection means detects the resistance using the secondary transfer means, residual electrification after secondary transfer of the intermediate transfer member Distribution can be eliminated or alleviated without using a dedicated device and without idling the intermediate transfer member, and it can occur at different strengths depending on the resistance of the unit while avoiding the increase in size and cost of the device. The reduction in image quality due to the residual charge distribution is eliminated or prevented by applying a transfer bias by such secondary transfer means in the second mode set as necessary under the condition of such resistance. The image forming can be provided an image forming apparatus capable of performing quickly.

  When the next image forming job is input during the image forming operation, it is determined whether the current image forming operation is performed in the first mode and / or the second mode. If it is determined whether the image forming operation of the next image forming job is performed in the first mode or the second mode, the residual electrification distribution after the secondary transfer of the intermediate transfer member is eliminated or alleviated. The current image forming operation reduces the image quality due to the residual charge distribution while avoiding the increase in size and cost of the device without using a dedicated device and without idling the intermediate transfer member. Provided is an image forming apparatus capable of eliminating or preventing a transfer bias in a second mode set in accordance with the mode in which the image is being performed and quickly performing good image formation with simple control. be able to

  In order to equalize the potential of the intermediate transfer member after the secondary transfer, the size of the first transfer bias applied by the transfer means in the upstream image forming unit is set so that the image carried on the image carrier is If the size of the second transfer bias transferred to the intermediate transfer member is different from that of the intermediate transfer member, the residual charge distribution after the secondary transfer of the intermediate transfer member can be eliminated or alleviated without using a dedicated device. The intermediate transfer member can be operated without idling, avoiding the increase in size and cost of the apparatus, and the deterioration in image quality due to the residual charge distribution, if necessary, different from the second transfer bias. In addition, it is possible to provide an image forming apparatus which can be eliminated or prevented by applying the first transfer bias and can perform good image formation.

  When there are a plurality of upstream image forming units, the size of the first transfer bias is made smaller than the size of the second transfer bias, and when there is a single upstream image forming unit, the size of the first transfer bias. Is made larger than the magnitude of the second transfer bias, the elimination of the residual electrification distribution after the secondary transfer of the intermediate transfer member is eliminated or alleviated without using a dedicated device and the intermediate transfer member idling. The second transfer bias and the size can be reduced as required based on the number of upstream image forming units, while reducing the image quality due to the residual charge distribution while avoiding the increase in size and cost of the apparatus. It is possible to provide an image forming apparatus which can be eliminated or prevented by applying a different first transfer bias and can perform good image formation.

1 is a schematic front view of an image forming apparatus to which the present invention is applied. FIG. 2 is a schematic front view showing a state in which a first mode is formed in the image forming apparatus shown in FIG. 1. FIG. 3 is a schematic front view illustrating a state in which an example of a second mode is formed in the image forming apparatus illustrated in FIG. 1. 2 is a chart showing each mode that can be formed in the image forming apparatus shown in FIG. 1 and a transfer bias applied in each mode. It is a correlation diagram of a voltage and an electric current for demonstrating the resistance of the unit detected by a unit resistance detection means. 2 is a flowchart illustrating an example of control in Embodiment 1 of the image forming apparatus illustrated in FIG. 1. 6 is a flowchart illustrating another example of control in Embodiment 1 of the image forming apparatus illustrated in FIG. 1. 6 is a flowchart illustrating an example of control in Embodiment 2 of the image forming apparatus illustrated in FIG. 1. 6 is a flowchart illustrating another example of control in Embodiment 2 of the image forming apparatus illustrated in FIG. 1. 2 is a chart of formed images used when evaluating the present invention according to each embodiment of the image forming apparatus shown in FIG. 1.

  FIG. 1 shows an outline of an image forming apparatus to which the present invention is applied. The image forming apparatus 100 is a multifunction peripheral of a copying machine, a printer, and a facsimile machine, and can perform full-color image formation, but other image forming apparatuses, that is, a copying machine, a printer, a facsimile alone, Alternatively, another multifunction device such as a multifunction device of a copying machine and a printer may be used. When used as a printer, the image forming apparatus 100 performs an image forming process based on an image signal corresponding to image information received from the outside. This is the same when the image forming apparatus 100 is used as a facsimile.

  The image forming apparatus 100 can form an image on a sheet-like recording medium using not only plain paper generally used for copying, but also OHP sheets, cardboard, cardboard, cardboard, and envelopes. It is. The image forming apparatus 100 is also a double-sided image forming apparatus capable of forming an image on both sides of a transfer sheet S as a recording material as a recording medium as a sheet as a recording medium.

  The image forming apparatus 100 is a photosensitive member that is a latent image carrier as a drum-like image carrier capable of forming an image as an image corresponding to each color separated into yellow, magenta, cyan, and black. A tandem structure in which the photosensitive drums 20Y, 20M, 20C, and 20BK are arranged in parallel and arranged in a quadruple tandem manner along the stretch direction of the transfer belt 11 as an intermediate transfer belt that is an intermediate transfer body. And tandem method is adopted.

  The photosensitive drums 20Y, 20M, 20C, and 20BK are rotatably supported by a frame (not shown) of the main body 99 that functions as the printer unit of the image forming apparatus 100, and are the moving direction of the transfer belt 11 and are counterclockwise in FIG. Are arranged in this order from the upstream side of the direction A1. Y, M, C, and BK added after the numerals of the respective symbols indicate members for yellow, magenta, cyan, and black.

  Each of the photosensitive drums 20Y, 20M, 20C, and 20BK is an image forming device as a plurality of image forming units for forming yellow (Y), magenta (M), cyan (C), and black (BK) images, respectively. Are provided in the image forming units 60Y, 60M, 60C, and 60BK as image forming stations.

  The photosensitive drums 20Y, 20M, 20C, and 20BK are located on the outer peripheral surface side, that is, the image forming surface side of the endless transfer belt 11 that is configured as an endless belt disposed almost in the center of the main body 99. Yes.

  The transfer belt 11 is movable in the direction of the arrow A1 while facing the photosensitive drums 20Y, 20M, 20C, and 20BK. Visible images, that is, toner images formed and carried on the respective photoconductive drums 20Y, 20M, 20C, and 20BK are respectively superimposed and transferred onto a transfer belt 11 as a transfer medium moving in the direction of arrow A1, and thereafter a transfer paper S It is designed to be transferred in batch. Therefore, the image forming apparatus 100 is a tandem type intermediate transfer type image forming apparatus. Therefore, the image forming apparatus 100 is a tandem indirect transfer type electrophotographic apparatus.

  The lower portion of the transfer belt 11 faces each of the photosensitive drums 20Y, 20M, 20C, and 20BK. The facing position, which is the opposed portion, is on the respective photosensitive drums 20Y, 20M, 20C, and 20BK. A primary transfer portion 58 is formed as a primary transfer region for transferring the toner image to the transfer belt 11.

  In the superimposing transfer to the transfer belt 11, the toner images formed on the photosensitive drums 20Y, 20M, 20C, and 20BK are transferred to the same position on the transfer belt 11 while the transfer belt 11 moves in the A1 direction. As described above, voltage application is performed by primary transfer rollers 12Y, 12M, 12C, and 12BK as first transfer rollers disposed at positions facing the respective photosensitive drums 20Y, 20M, 20C, and 20BK across the transfer belt 11. Thus, the timing is shifted from the upstream side toward the downstream side in the A1 direction.

  The transfer belt 11 has a polyimide base layer and a discharge prevention layer formed on the base layer by coating. Another example of the material of the base layer is PAI. The discharge prevention layer may be made of the same polyimide as the base layer.

  In the main body 99, the image forming apparatus 100 is opposed to image forming units 60Y, 60M, 60C, and 60BK that are image forming stations serving as four image forming apparatuses, and above the photosensitive drums 20Y, 20M, 20C, and 20BK. The transfer belt unit 10 is an intermediate transfer unit as a transfer unit that is an intermediate transfer device provided with the transfer belt 11, and the transfer belt 11 is disposed on the right side of the transfer belt 11 in FIG. As an exposure device serving as a writing device as an optical unit serving as an optical writing unit serving as a latent image forming means disposed below the secondary transfer device 5 and the image forming units 60Y, 60M, 60C, and 60BK. And an optical scanning device 8.

  The image forming apparatus 100 is also transferred below the optical scanning device 8 in the main body 99 toward the secondary transfer portion 57 as a secondary transfer region between the transfer belt 11 and the secondary transfer device 5. A sheet feeding device 61 as a sheet feeding device that is a sheet feeding tray as a sheet feeding unit on which a large number of sheets S can be stacked, and a transfer sheet S conveyed from the sheet feeding device 61 as image forming units 60Y and 60M. , 60C, 60BK, the registration roller pair 4 serving as a conveyance roller that feeds out toward the secondary transfer unit 57 and the leading edge of the transfer paper S reach the registration roller pair 4 at a predetermined timing in accordance with the toner image formation timing. And a sensor (not shown) for detecting this.

  The image forming apparatus 100 also has a fixing device 6 as a fixing unit of a belt fixing system for fixing the toner image on the transfer sheet S on which the toner image is transferred in the main body 99, and a forward rotation. Disposed above the transfer belt unit 10 are a discharge roller 7 as a discharge roller pair that is a discharge roller that discharges the fixed transfer sheet S to the outside of the main body 99, and yellow, cyan, A cylinder on which toner bottles 9Y, 9M, 9C, and 9BK filled with magenta and black toners and a transfer sheet S disposed on the upper side of the main body 99 and discharged to the outside of the main body 99 by the discharge roller 7 are stacked. A paper discharge tray 17 formed by the internal paper discharge unit.

  The image forming apparatus 100 also includes a duplex unit 51 attached to the right side of the main body 99 in the drawing, and a reading device 98 that is an image reading device that is positioned above the main body 99 and reads a document. ing.

  The image forming apparatus 100 is also formed in the main body 99 from the lower side to the upper side on the right side in the figure, and the secondary transfer unit 57, the registration roller pair 4, the fixing device 6, and the paper discharge roller 7 are arranged in the middle. A sheet conveyance path 81 that is a recording material conveyance path through which the transfer sheet S fed from the sheet feeding device 61 enters, and upstream of the registration roller pair 4 in the conveyance direction of the transfer sheet S in the sheet conveyance path 81. A paper feed path 82 that merges from the duplex unit 51 to the sheet conveyance path 81, and a re-distribution branching from the sheet conveyance path 81 toward the duplex unit 51 on the downstream side of the fixing device 6 in the conveyance direction of the transfer sheet S in the sheet conveyance path 81. A paper feed conveyance path 83.

  The image forming apparatus 100 also includes a temperature / humidity detecting unit 97 that detects the temperature and humidity of the environment, a driving device (not shown) that rotationally drives the photosensitive drums 20Y, 20M, 20C, and 20BK, and an image forming apparatus. And a control means 96 including a CPU (not shown), a memory, etc., for controlling the overall operation of 100.

The image forming apparatus 100 also includes a start switch (not shown) for instructing image formation start on the outer surface of the main body 99, a paper type input key as a paper type input unit for inputting the thickness of the transfer paper S, and the like. 100 operation and operation modes can be designated, and an operation panel (not shown) including a liquid crystal display device (not shown) as display means for performing predetermined display is provided.
The image forming apparatus 100 is an in-body discharge type image forming apparatus in which the discharge tray 17 is located above the main body 99 and below the reading device 98.

  In addition to the transfer belt 11, the transfer belt unit 10 includes a plurality of primary transfer rollers 12Y, 12M, 12C, and 12BK that are transfer bias application members as primary transfer bias rollers, and a plurality of transfer belts 11 wound around the transfer belt unit 10. A driving roller 72 as a driving member, a cleaning counter roller 74 as a stretching roller, and a stretching roller 33 as a support roller that stretches the transfer belt 11 together with the driving roller 72 and the cleaning counter roller 74, 34.

  The transfer belt unit 10 is also provided with a cleaning device 13 as a belt cleaning device, which is an intermediate transfer member cleaning device that is disposed facing the transfer belt 11 at a position facing the cleaning counter roller 74 and cleans the surface of the transfer belt 11. A sheet conveyance guide 75 that is disposed at a position facing the stretching roller 33 and guides the transfer sheet S fed from the registration roller 4 toward the secondary transfer unit 57, and a drive (not shown) that drives the drive roller 72 to rotate. System.

  The transfer belt unit 10 also applies a primary transfer bias, which is a transfer bias having the same polarity as the charging polarity of the toner, to the primary transfer rollers 12Y, 12M, 12C, and 12BK, and causes the primary transfer rollers 12Y, 12M, 12C, and 12BK to move. One of the power supply and control means 96 as a bias application means (not shown) that functions as a repulsive roller as a transfer means as a primary transfer means and constitutes a primary transfer device together with the primary transfer rollers 12Y, 12M, 12C, and 12BK. Bias control means realized as a function are included.

  The transfer belt unit 10 is also a known unit that selectively contacts and separates the primary transfer rollers 12Y, 12M, 12C, and 12BK and the photosensitive drums 20Y, 20M, 20C, and 20BK in a set combination that will be described later. It has the contact / separation means of composition.

  The cleaning facing roller 74 and the stretching rollers 33 and 34 are driven rollers that rotate with the transfer belt 11 that is rotationally driven by the driving roller 72. The primary transfer rollers 12Y, 12M, 12C, and 12BK press the transfer belt 11 from the back surface thereof toward the photosensitive drums 20Y, 20M, 20C, and 20BK to form primary transfer nips. The primary transfer nip is formed in a portion of the transfer belt 11 that extends substantially horizontally between the stretching roller 33 and the stretching roller 34. The tension roller 33 functions as a transfer entrance roller for guiding the transfer sheet S fed from the registration roller 4 toward the secondary transfer unit 57.

  The cleaning counter roller 74 is a member that also functions as a tension roller as a pressure member for applying a predetermined tension suitable for transfer to the transfer belt 11. The cleaning counter roller 74 and the stretching rollers 33 and 34 have a function of stabilizing the primary transfer nip.

  In each primary transfer nip, a primary transfer electric field is formed between the photosensitive drums 20Y, 20M, 20C, and 20BK and the primary transfer rollers 12Y, 12M, 12C, and 12BK by the action of the primary transfer bias. . The toner images of the respective colors formed on the photosensitive drums 20Y, 20M, 20C, and 20BK are primarily transferred onto the transfer belt 11 by electrostatic transfer due to the influence of the primary transfer electric field and nip pressure.

The driving roller 72 is in contact with the secondary transfer device 5 via the transfer belt 11 to form a secondary transfer portion 57.
As will be described later, the driving roller 72 is applied with a secondary transfer bias, which is a transfer bias having the same polarity as the charging polarity of the toner, whereby a repulsive roller serving as a transfer means as a secondary transfer means. It is supposed to function as.

  In FIG. 1, the cleaning device 13 is disposed on the lower left side of the transfer belt unit 10, specifically, below the cleaning counter roller 74. Although not shown, the cleaning device 13 includes a cleaning member disposed so as to contact the transfer belt 11 at a position facing the cleaning counter roller 74, a case in which the cleaning member is accommodated therein, and in FIG. A waste toner collection bottle disposed on the front side of the case.

  The cleaning device 13 cleans the transfer belt 11 by scraping and removing foreign matters such as residual toner on the transfer belt 11 with a cleaning member. Such foreign matter removed from the transfer belt 11 is stored in a waste toner recovery bottle. The waste toner collection bottle can be taken out to the front side of the paper in FIG. 1 with the front panel opened, and can be replaced with a new one when the foreign matter inside becomes full. Note that cleaning devices 71Y, 71M, 71C, and 71BK, which will be described later, similarly have replaceable waste toner collection bottles.

  As shown in FIG. 2, the contacting / separating means brings only the primary transfer roller 12BK out of the primary transfer rollers 12Y, 12M, 12C, and 12BK into contact with the transfer belt 11 and causes the primary transfer rollers 12Y, 12M, and 12C to contact each other. The photosensitive drums 20Y, 20M, 20C, and 20BK are separated from the transfer belt 11, and only the photosensitive drum 20BK is brought into contact with the transfer belt 11 to separate the photosensitive drums 20Y, 20M, and 20C from the transfer belt 11. It is possible to form the Bk contact mode.

  As shown in FIG. 1, the contact / separation means causes all of the primary transfer rollers 12Y, 12M, 12C, and 12BK to abut on the transfer belt 11 and also exposes all of the photosensitive drums 20Y, 20M, 20C, and 20BK to light. It is possible to form a full contact mode in contact with the body drum 20BK.

  As shown in FIG. 3, the contact / separation means also contacts only the primary transfer rollers 12C, 12BK of the primary transfer rollers 12Y, 12M, 12C, 12BK with the transfer belt 11 so as to contact the primary transfer rollers 12Y, 12M. Are separated from the transfer belt 11 and only the photosensitive drums 20C, 20BK of the photosensitive drums 20Y, 20M, 20C, 20BK are brought into contact with the transfer belt 11 to separate the photosensitive drums 20Y, 20M from the transfer belt 11. It is possible to form an individual contact mode.

  As shown in FIG. 4, the contact / separation means is formed by selecting any one of the Bk contact mode, the full contact mode, and the individual contact mode in the black mode in which image formation is performed only in black, that is, the Bk mode. In full color mode in which image formation is performed in full color, that is, in FC mode, all contact mode is selected and formed.

  In the Bk mode, the contact / separation means includes the primary transfer rollers 12Y, 12M, 12C and the photosensitive drum 20Y in the image forming units 60Y, 60M, 60C that do not form an image among the image forming units 60Y, 60M, 60C, 60BK. The first mode which is the Bk contact mode in which 20M and 20C are separated from the transfer belt 11, and 1 in the image forming units 60Y, 60M and 60C in which no image is formed among the image forming units 60Y, 60M, 60C and 60BK. Next transfer rollers 12Y, 12M, 12C, all-contact mode in which the photosensitive drums 20Y, 20M, 20C are in contact with the transfer belt 11, or images are not formed in the image forming units 60Y, 60M, 60C, 60BK. The primary transfer roller 12C and the photosensitive drum 20C in the image forming unit 60C are transferred to the transfer base. Has become the second mode is an individual contact mode is brought into contact with bets 11 selectively formable.

  Whether the full contact mode or the individual contact mode is selected as the second mode is set in the initial setting at the time of shipment of the image forming apparatus 100 and may be invariant. It may be selectively set by an operator such as 100 users. If the second mode is the full contact mode and does not change, the contact / separation means only needs to form either the state shown in FIG. 1 or the state shown in FIG. Is done.

  As will be described later, the first mode is selected by the control unit 96 when image formation is performed in the normal Bk mode, in other words, when printing is performed, or when image formation is performed in the Bk afterimage mode. The contact / separation means is driven and controlled under the control of.

  As will be described later, the second mode is selected when the control unit 96 performs image formation, that is, printing in the afterimage mode or the individual afterimage mode, and the contact / separation unit is driven under the control of the control unit 96. Controlled and formed.

  The image forming apparatus 100 forms an image by selecting either the Bk mode for performing monochrome printing or the FC mode for performing color printing by the control unit 96 according to the input image forming job, in other words, the print job. It has become.

  The sheet feeding device 61 accommodates a plurality of transfer sheets S in a state of a stack of transfer sheets, and is disposed below the optical scanning device 8 below the main body 99. In the present embodiment, the sheet feeding device 61 includes a plurality of sheet feeding cassettes 25 arranged in two stages so that a plurality of transfer sheets S can be stacked in a bundle of sheets in the vertical direction. The transfer roller S loaded on the uppermost transfer sheet S is separated from a feeding roller 24 as a paper feed roller that contacts the upper surface of the uppermost transfer paper S, and only one of the transfer sheets S fed by the paper feed roller 24 is separated. And a separation roller (not shown) that further conveys, and the feeding roller 24 is driven to rotate counterclockwise at a predetermined timing, whereby the uppermost transfer sheet S is directed to the registration roller pair 4. To feed.

  In the sheet feeding device 61, the feeding roller 24 is selectively driven to rotate counterclockwise in the figure, and the separation roller acts, so that the uppermost of the transfer sheets S stacked in the sheet feeding cassette 25 is actuated. The transfer paper S is put into the paper transport path 81 and fed toward the registration roller pair 4 so that the transported transfer paper S is stuck and stopped while being sandwiched between the rollers of the registration roller pair 4. It has become.

The secondary transfer device 5 is disposed to face the drive roller 72. The secondary transfer device 5 includes a secondary transfer roller 5a, which is a transfer bias applying member that is pressed toward the drive roller 72 so as to sandwich the transfer belt 11 between the drive roller 72, and toner on the drive roller 72. This is realized as a function of a power supply and control means 96 (not shown) that applies a secondary transfer bias, which is a transfer bias having the same polarity as the charging polarity, and causes the drive roller 72 to function as the configuration of the secondary transfer device 5. Bias control means.
The secondary transfer device 5 also has a sheet conveying function for conveying the transfer sheet S after the toner image is transferred to the fixing device 6 by the secondary transfer roller 5a.

  The power supply and bias control means as the bias applying means may apply a secondary transfer bias as a transfer bias to the secondary transfer roller 5a instead of the driving roller 72. In this case, the secondary transfer bias applied to the secondary transfer roller 5a has the same polarity as the charging polarity of the toner, and the secondary transfer roller 5a functions as an attractive roller which is a transfer unit as a secondary transfer unit.

  The duplex unit 51 includes a manual sheet feeding device 53 disposed on the outer surface side, a part of the sheet feeding path 82 disposed across the duplex unit 51 from the manual sheet feeding device 53, and refeeding. The reversal conveyance path 21 that reverses and conveys the transfer paper S that has passed through the paper conveyance path 83 toward the paper feed path 82, and the transfer paper S that is disposed in the reverse conveyance path 21 is conveyed toward the paper feed path 82. And a conveying roller 23.

  The manual paper feeder 53 includes a manual feed tray 27 as a manual paper feed tray on which the transfer paper S can be stacked, and a paper feed roller that contacts the upper surface of the uppermost transfer paper among the transfer paper S stacked on the manual feed tray 27. And a separation roller (not shown) for separating the transfer paper fed by the feed roller 28 one by one.

  In the manual sheet feeding device 53, the feeding roller 28 is rotated in the clockwise direction in the drawing, and the separation roller acts to feed the uppermost transfer sheet S toward the registration roller pair 4 to be conveyed. The transfer sheet S is abutted and stopped while being sandwiched between the rollers of the registration roller pair 4.

  The fixing device 6 has an endless belt-like fixing belt 64 as a fixing member, a fixing roller 65 wound around the fixing belt 64, and the fixing belt 64 and the fixing belt 64 wound around the fixing belt 64 so that the tension of the fixing belt 64 is constant. A pressure roller 63 as a pressure member for forming a fixing nip as a fixing portion that is a pressure contact portion that presses the transfer sheet S between the tension roller 62 and the fixing roller 65 that press against the fixing belt 64. A halogen heater 66 serving as a first heat source as a first heating unit that is disposed in the fixing roller 65 and heats the fixing belt 64 via the fixing roller 65, and a second heater that heats the pressure roller 63. It has a halogen heater 67 as a second heat source as a heating means and a spring (not shown) as an urging means for forming a fixing nip.

  The material of the fixing belt 64 is polyimide having excellent heat resistance and high durability, and has a thickness of several tens of microns. One rotating shaft of the fixing roller 65 and the pressure roller 63 is fixed, and the other rotating shaft is movably supported so that it can be brought into contact with and separated from one roller. By being biased, a fixing nip is formed between the fixing roller 65 and the pressure roller 63 via the fixing belt 64. The tension roller 62, the fixing belt 64, and the fixing roller 65 constitute a belt unit in which the fixing belt 64 moves endlessly.

  The fixing device 6 fixes the carried toner image on the surface of the transfer paper S by the action of heat and pressure by passing the transfer paper S carrying the toner image in a manner sandwiching the fixing nip. .

  The yellow, cyan, magenta, and black toners in the toner bottles 9Y, 9M, 9C, and 9BK are polymerized toners that are rotated by driving means (not shown) to discharge the toner, and are not shown by a pipe (not shown). A predetermined replenishment amount is supplied to the developing devices 80Y, 80M, 80C, and 80BK provided in the image forming units 60Y, 60M, 60C, and 60BK, as will be described later, through the configured conveyance path.

  Although not shown in detail, the reading device 98 includes a contact glass for placing an original, a light source for irradiating light on the original placed on the contact glass, and a first light that reflects light reflected on the original from the light source. A first traveling body that travels in the left-right direction in FIG. 1, a second traveling body that includes a second reflector that reflects light reflected by the reflector of the first traveling body, and a second traveling body. An image forming lens for forming an image of light from the body, a reading sensor for receiving the light passing through the image forming lens and reading the contents of the document are provided.

  The image forming units 60Y, 60M, 60C, and 60BK have the same configuration. The image forming units 60Y, 60M, 60C, and 60BK are primary transfer rollers as process means around the photosensitive drums 20Y, 20M, 20C, and 20BK along the rotation direction B1 that is clockwise in FIG. 12Y, 12M, 12C, 12BK, cleaning devices 71Y, 71M, 71C, 71BK as cleaning means, a static elimination device (not shown) as a static elimination means, and charging devices 79Y, 79M as a charging means for performing AC charging by a charging bias 79C, 79BK, and developing devices 80Y, 80M, 80C, 80BK as developing means for performing development by applying a developing bias using a two-component developer.

  The photosensitive drum 20Y, the cleaning device 71Y, the charge eliminating device, the charging device 79Y, and the developing device 80Y are integrated to form a process cartridge. The components around the photoconductive drums 20M, 20C, and 20BK are similarly integrated to form a process cartridge. These process cartridges are detachable in the direction of the rotation axis of the photosensitive drums 20Y, 20M, 20C, and 20BK on the front side in FIG. 1 with the front panel opened. Making a process cartridge in this way is very preferable because it can be handled as a replacement part, so that the maintainability is remarkably improved.

In the image forming apparatus 100 having such a configuration, image formation is performed by performing the following image forming processes in the image forming units 60Y, 60M, 60C, and 60BK, respectively, by pressing a start switch or the like.
Specifically, when a signal indicating that a color image should be formed, in other words, an image formation should be performed in the FC mode is input, the document is appropriately read by the reading device 98 or the like. Data corresponding to the power image is acquired, and the contact / separation means is driven by the control means 96 to form the full contact mode. Next, the driving roller 72 is driven, the transfer belt 11, the cleaning counter roller 74, and the stretching rollers 33 and 34 are driven to rotate, and the photosensitive drums 20Y, 20M, 20C, and 20BK are rotationally driven in the B1 direction.

  Each of the photosensitive drums 20Y, 20M, 20C, and 20BK is data corresponding to an image to be formed by uniformly charging the surface by the charging devices 79Y, 79M, 79C, and 79BK in accordance with the rotation in the B1 direction. An electrostatic latent image corresponding to each color of yellow, magenta, cyan, and black is formed by exposure scanning of the laser light from the optical scanning driven by the control means 96 based on the image information, and the electrostatic latent image is developed by the developing device. 80Y, 80M, 80C, and 80BK are developed with a toner that is an image forming material as an image forming material of each color of yellow, magenta, cyan, and black contained in a two-component developer to be visualized, that is, subjected to visible image processing. A single color image composed of toner images of magenta, cyan, and black is formed.

  The yellow, magenta, cyan, and black toner images obtained by development are sequentially superimposed on the same position on the transfer belt 11 rotating in the A1 direction by the primary transfer rollers 12Y, 12M, 12C, and 12BK. As a result, a composite color image is formed on the transfer belt 11. At this time, the transfer bias values applied by the primary transfer rollers 12Y, 12M, 12C, and 12BK are the values in the Y, M, C, and K columns shown in the item of the FC mode in FIG. In the figure, the value in the column “T1” indicates the value of the primary transfer bias.

  On the other hand, with the input of a signal indicating that a color image should be formed, one of the paper feed roller 24 corresponding to each paper feed cassette 25 and the paper feed roller 28 corresponding to the manual feed tray 27 is selected and rotated. The transfer sheet S is fed out and separated and conveyed one by one, and the conveyed transfer sheet S stops in a state where it abuts against the registration roller pair 4. In the case of double-sided image formation, the transfer sheet S on which an image is fixed on one side of the fixing device 6 as described later is abutted against the registration roller pair 4 while being reversed through the reverse conveyance path 21. Stop in the state.

  The registration roller pair 4 rotates in accordance with the timing at which the composite color image superimposed on the transfer belt 11 moves to the secondary transfer unit 57 as the transfer belt 11 rotates in the A1 direction. The combined color image is brought into close contact with the transfer sheet S sent to the secondary transfer unit 57, and is secondarily transferred and recorded on the transfer sheet S by electrostatic transfer under the action of the nip pressure. At this time, the value of the transfer bias applied by the driving roller 72 is the value in the column of T2 shown in the item of the FC mode in FIG. In the figure, the value in the column “T2” indicates the value of the secondary transfer bias.

  The transfer sheet S is conveyed by the secondary transfer device 5 and the transfer belt 11 rotating in the A1 direction and sent to the fixing device 6, and passes through the fixing portion between the heating roller 62 and the pressure roller 63 in the fixing device 6. At this time, the carried toner image, that is, the synthesized color image is fixed by the action of heat and pressure.

  The transfer sheet S on which the composite color image has been fixed, which has passed through the fixing device 6, is discharged out of the main body 99 through the paper discharge roller 7, and is stacked as an image output on the paper discharge tray 17 at the top of the main body 99. . In the case of double-sided image formation, the transfer sheet S that has been fixed on one side is conveyed again toward the registration roller pair 4 through the refeed path 82 and the reverse conveyance path 21.

  In the photosensitive drums 20Y, 20M, 20C, and 20BK, the transfer residual toner remaining after the transfer is removed by the cleaning devices 71Y, 71M, 71C, and 71BK, discharged by the discharging device, and then discharged by the charging devices 79Y, 79M, 79C, and 79BK. Used for charging.

  The surface of the transfer belt 11 after passing the secondary transfer portion 57 after the secondary transfer is cleaned by a cleaning member provided in the cleaning device 13 to prepare for the next transfer.

  When the signal indicating that image formation is to be performed is not the FC mode but the Bk mode, that is, when an image is formed in the image forming unit 60BK, when the above-described belt afterimage, which is an afterimage of the intermediate transfer member, is generated. In order to solve this problem, it is possible to perform an operation for equalizing the potential of the transfer belt 11 after the secondary transfer.

  Specifically, when the signal indicating that image formation is to be performed is the Bk mode and the second mode is the full contact mode, the second mode is formed and the A1 direction is set. In FIG. 5, the transfer bias can be applied by the primary transfer rollers 12Y, 12M, and 12C in the image forming units 60Y, 60M, and 60C that are positioned downstream of the secondary transfer unit 57 and upstream of the image forming unit 60BK. ing. Further, when the signal indicating that image formation is to be performed is the Bk mode and the second mode is the individual contact mode, the second mode is formed, and then the secondary mode is formed in the A1 direction. A transfer bias can be applied by the primary transfer roller 12 </ b> C in the image forming unit 60 </ b> C that is located downstream of the transfer unit 57 and upstream of the image forming unit 60 </ b> BK. Conditions for applying such a transfer bias will be described later.

  As described above, in the second mode, the transfer bias is applied at the position upstream of the image forming unit 60BK in the A1 direction so that the image can be formed by the image forming unit 60BK. The residual charge distribution, that is, the residual potential distribution of the transfer belt 11 is relaxed or eliminated, thereby preventing the occurrence of a belt afterimage during the next primary transfer.

  Therefore, the image formation can be interrupted by utilizing the tandem type without idling the transfer belt 11 and without using a dedicated device for relaxing the residual potential distribution. Therefore, without reducing the productivity when performing image processing, it is possible to eliminate static electricity and form images while ensuring maximum productivity regardless of whether continuous image formation or intermittent image formation is performed, and usability is ensured by maintaining productivity. At the same time, belt afterimage measures are taken without increasing the size and cost of the device.

A condition for applying the transfer bias in the Bk mode, in other words, a condition for image formation in the second mode will be described.
As such conditions, in the image forming apparatus 100, (1) the temperature and humidity of the environment in which the image forming apparatus 100 is used, and (2) the resistance value of a later-described unit including the transfer belt 11 and a later-described member in contact with the transfer belt 11. (3) Whether an image is formed in the second mode when a Bk mode image forming job is input is used. These conditions will be described in order below.

Condition (1) The reason why the temperature and humidity of the environment in which the image forming apparatus 100 is used is used is that the temperature and humidity affect the resistance value of the transfer belt 11 that affects the residual potential distribution. As the resistance value of the transfer belt 11 increases, a residual potential distribution is more likely to occur, and thus a belt afterimage is likely to occur.

  Table 1 shows the correlation between the temperature and humidity and the ease of occurrence of a belt afterimage. In the table, “◯” indicates that no belt afterimage is generated, “×” indicates that a belt afterimage is generated, and “Δ” indicates an intermediate between “◯” and “×”. This also applies to Tables 2 and 3 described later.

  In order to use the temperature and humidity as a condition for image formation in the second mode, the image forming apparatus 100 uses the temperature and humidity detection unit 97 to constantly monitor the temperature and humidity in the main body 99 using the control unit 96. Therefore, it is configured to set whether or not to perform image formation in the second mode using the temperature and humidity detected by the temperature and humidity detection means 97.

As is clear from each example described later, the temperature / humidity threshold value is 18 ° C. as the temperature and 40% RH or 54% RH as the humidity.
Note that the temperature and humidity environment that guarantees belt afterimages is 10 ° C. and 15% RH (see Table 3), and even when the present invention is applied, avoiding belt afterimages is not always necessary for environments below this temperature. It is not guaranteed.

  In addition, as control using the temperature / humidity detected by the temperature / humidity detection means 97, in addition to setting whether or not to perform image formation in the second mode, the image forming conditions such as transfer bias are changed. Independent environmental correction may be added.

Condition (2) The resistance value of the unit including the transfer belt 11 and the member in contact with the transfer belt 11 is used as the condition. The transfer belt 11 in which the magnitude relationship between the resistance values affects the residual potential distribution. The resistance values are correlated in a manner consistent with the magnitude relationship between the resistance values of the primary transfer rollers 12Y, 12M, 12C, and 12BK when the transfer bias is applied. This is to utilize the fact that the current value and the voltage value are relatively easily measured.

Therefore, the member in contact with the transfer belt 11 refers to the primary transfer roller and the photosensitive drum that is in contact with the primary transfer roller when the resistance value is measured using the primary transfer rollers 12Y, 12M, 12C, and 12BK. The unit includes the primary transfer roller, the transfer belt 11, and the photosensitive drum, and the resistance value is a combined resistance value of the primary transfer roller, the transfer belt 11, and the photosensitive drum. is there.
The member in contact with the transfer belt 11 is the drive roller 72 and the secondary transfer roller 5a in contact with the drive roller 72 when the resistance value is measured using the drive roller 72. The roller 72, the transfer belt 11, and the secondary transfer roller are included, and the resistance value is a combined resistance value of the driving roller 72, the transfer belt 11, and the secondary transfer roller 5a.
In this embodiment, the resistance value is measured by the driving roller 72.

  When such a resistor is used as a condition for image formation in the second mode, the image forming apparatus 100 uses the drive roller 72 to cause the bias control unit to use a timing different from that at the time of secondary transfer, that is, to the secondary transfer unit 57. The current value and the voltage value are monitored at the sheet passing timing, and the resistance is calculated by the control unit 96 using the current value and the voltage value detected by the driving roller 72, and the threshold value to be described later is used. Whether to perform image formation in the second mode is set. In this regard, the control unit 96 that functions as a bias control unit functions as a unit resistance detection unit that detects the resistance of the unit using the drive roller 72. However, when the resistance of the unit is detected using the primary transfer roller, the unit functions as a bias control unit that detects the resistance of the unit using the current value and voltage value detected by the primary transfer roller. The control means 96 functions as unit resistance detection means.

  This resistance will be described in more detail. The bias control means applies voltages of 300 V, 500 V, and 700 V to the driving roller 72 as shown in FIG. Measure the value of the current that flows when the voltage is applied. When the current / voltage relationship at these three points is obtained, an approximate curve is drawn to obtain the slope, which becomes the load, that is, the resistance of the unit. This resistance may be measured using one voltage value for simplification, or may be measured using more voltage values for accuracy. However, when one voltage value is used, it is necessary to make the value as close as possible to the bias actually used for the secondary transfer.

  The figure shows the measurement results for two units A and B having different configurations, and the resistances were calculated to be about 26.3 MΩ and about 53.8 MΩ, respectively. Therefore, when these two units A and B are compared, it can be seen that the unit B having a higher resistance is more concerned about the afterimage. Such resistance is a volume resistance. As this value is larger, electric charges are more difficult to escape, and afterimages are more likely to be generated. Also, as the resistance as a unit is larger, the resistance of the transfer belt 11 is greater, so there is a greater concern about afterimages. Because it becomes.

  In this embodiment, 50 MΩ is used as the specific value of the threshold value of resistance. This is because it is determined whether or not the resistance value of the transfer belt 11 has a concern about the afterimage of the belt based on the magnitude relationship between the combined resistance value of the unit and the threshold value. Note that the threshold value depends on the position of the unit for measuring the resistance and the relationship with the members constituting the unit. After measuring the combined resistance value of the unit, various component tolerances are taken into account. Required in advance.

-Condition (3) The reason for using whether or not image formation is being performed in the second mode when a Bk mode image formation job is input is to simplify control and operation. is there. When an image is formed in the second mode when such a job is input, the control, operation, etc. required for driving the contact / separation means is simplified if the job is executed in the second mode as it is. , Productivity is also improved. When image formation is performed in the first mode when such a job is input, it is only necessary to continue image formation as it is, as described later, and to simplify control and the like. Productivity.

  For this reason, in the image forming apparatus 100, when the next image forming job is input as the Bk mode image forming job during the image forming operation, is the current image forming operation being performed in the first mode? Whether or not the image forming operation of the next Bk mode image forming job is performed in the first mode or the second mode is controlled on the condition of whether or not it is performed in the second mode. Means 96 is provided.

  Even if the next mode is determined by referring to the previous state, that is, the mode in this way, for example, when an adjustment operation such as so-called process control is entered midway, the time is used. It is desirable to carry out environmental temperature / humidity detection and unit resistance detection again to accurately select a more suitable mode.

  Here, as shown in FIG. 4, the first mode which is the Bk contact mode includes a normal mode and a Bk afterimage mode. The normal mode is a mode in which image formation is performed when there is little concern about the belt afterimage, and the Bk afterimage mode is a mode in which image formation is performed when there is some concern about the belt afterimage. Comparing T1 and T2 at this time, as can be seen from the table, in the Bk afterimage mode, T1 is set higher and T2 is set lower.

  This is because, as shown in Table 2, the higher the T1 and the lower the T2, the more difficult the belt afterimage tends to occur. In other words, if T1 is low and T2 is high, a belt afterimage is more likely to occur. However, if T2 is high, the amount of residual charge after secondary transfer increases, and if T1 is low, the effect of residual charge is increased. It is because it becomes easy to receive. Thus, the Bk residual mode is a mode in which the bias is shifted in a direction advantageous for the belt afterimage as compared with the normal mode.

  The second mode is a mode that is selected when there is a high possibility of belt afterimages and belt afterimages are likely to occur. In the second mode, there is an image forming unit in which the transfer bias is adjusted as described below. In this image forming unit, although writing by the optical scanning device 8 is stopped, other image forming conditions are set. For example, the charging bias and the developing bias are applied at normal values and operate in the same manner as in normal image formation.

  As shown in FIG. 4, the transfer bias applied by the primary transfer rollers 12Y, 12M, and 12C, that is, the first transfer bias applied as a countermeasure for the belt afterimage in the afterimage mode that is the second mode performed in the full contact mode. The uniform transfer bias is a transfer bias applied by the primary transfer rollers 12Y, 12M, and 12C in order to transfer the toner images carried on the photosensitive drums 20Y, 20M, and 20C to the transfer belt 11 in the FC mode. That is, the transfer bias applied by the driving roller 72, which is set as a countermeasure against the afterimage of the belt in the afterimage mode, is set lower than the toner image transfer bias that is the second transfer bias. Toner image carried on the transfer belt 11 Is set equal to the toner image transfer bias in the transfer bias ie and normal mode lower than the toner image transfer bias is applied by the drive roller 72 to transfer the transfer sheet S.

  Also, as shown in the figure, the uniform transfer bias applied by the primary transfer roller 12C, which is performed as a countermeasure for the belt afterimage in the individual afterimage mode, which is the second mode performed in the individual contact mode, is in the FC mode. This is set lower than the toner image transfer bias applied by the primary transfer roller 12C in order to transfer the toner image carried on the photosensitive drum 20C to the transfer belt 11, and as a countermeasure for the belt afterimage in the individual afterimage mode. The uniform transfer bias applied by the drive roller 72 is lower than the toner image transfer bias applied by the drive roller 72 in order to transfer the toner image carried on the transfer belt 11 to the transfer paper S in the FC mode. And set equal to the toner image transfer bias in the normal mode. That.

  In this way, the size of the uniform transfer bias is different from the size of the toner image transfer bias in consideration of the reduction of energy consumption while considering the above-described tendency according to Table 2. Then, in view of eliminating or mitigating the belt afterimage, it is necessary to apply a bias necessary to reduce the residual potential distribution.

In this respect, since it is sufficient that the total uniform transfer bias is applied to a necessary and sufficient value, the transfer applied by the primary transfer rollers 12Y, 12M, and 12C in the afterimage mode in which the uniform transfer bias is applied at a plurality of locations. The magnitude of the bias, that is, the uniform transfer bias, is smaller than the magnitude of the toner image transfer bias applied by the primary transfer rollers 12Y, 12M, and 12C in the FC mode.
In the individual afterimage mode in which the uniform transfer bias is applied at one place, the magnitude of the transfer bias applied by the primary transfer roller 12C, that is, the uniform transfer bias is applied by the primary transfer roller 12C in the FC mode. The toner image transfer bias is larger than the magnitude.

  As a result, in both the afterimage mode and the individual mode, the bias is shifted in a direction advantageous to the belt afterimage as compared with the Bk mode, and the effect on the belt afterimage can be sufficiently obtained even in the individual afterimage mode.

In both the afterimage mode and the individual afterimage mode, the uniform transfer bias applied by the drive roller 72 is set lower than the toner image transfer bias applied by the drive roller 72 in the FC mode and equal to the toner image transfer bias in the normal mode. The reason for this is that in consideration of the above-mentioned tendency according to Table 2, in the uniform transfer bias, a sufficient bias may be applied to reduce the residual potential distribution in order to eliminate or alleviate the belt afterimage. In view of this.
Although an afterimage can be generated even in the FC mode, it is less likely to occur than in the Bk mode. In the FC mode, the photosensitive drums 20Y, 20M, 20C, 20BK and the primary transfer rollers 12Y, 12M, 12C, 12BK hit the transfer belt 11 in all the image forming units 60Y, 60M, 60C, 60BK. This is because the residual potential distribution is relaxed by sequentially applying a transfer bias at the time of image formation, and at this time, transfer at the time of yellow image formation, which is a relatively inconspicuous color of the residual image, is performed. This is because the residual potential distribution is first reduced by the bias. However, in order to reduce the residual potential distribution with higher accuracy, it is preferable to apply a primary transfer bias higher than the primary transfer bias applied in the normal FC mode when a belt afterimage is likely to occur.

  Hereinafter, each control in which the above conditions (1) to (3) are applied alone or in combination will be described as a first embodiment and a second embodiment with reference to flowcharts. In each flowchart, the afterimage mode is adopted as the second mode, but the individual afterimage mode may be adopted as the second mode.

Example 1
In the present embodiment shown in FIG. 6, the condition (1) described above is applied. In the embodiment shown in the figure, it is assumed that the image forming apparatus 100 is in a standby state in which the image forming operation is not performed.

  As shown in the figure, when a Bk mode print job, that is, an image forming job is inputted and received, and a Bk mode print command, that is, an image forming command is received (S601), the temperature / humidity detecting means 97 is turned on. The temperature and humidity in the main body 99 are read and used to detect them (S602), and it is determined whether the detected humidity is below a certain standard, that is, 40% RH or less (S603). If the detected humidity is not 40% or less, it is assumed that there is no concern about the afterimage of the belt, and printing is performed in the normal Bk mode (S604). If the detected humidity is 40% or less, the detected temperature is It is determined whether the temperature is 18 ° C. or lower (S605). When the detected temperature is not 18 ° C. or less, there is some concern about the afterimage of the belt, so image formation, that is, image formation is performed in the Bk afterimage mode (S606), and when the detected temperature is 18 ° C. or less, a belt afterimage is generated. Therefore, image formation is performed in the afterimage mode (S607).

  In this embodiment, in addition to the above-described condition (1), the control when the above-described condition (3) is applied, that is, when the image forming apparatus 100 determines whether or not the image forming apparatus 100 is on standby. As shown in FIG.

  That is, when a Bk mode print job, that is, an image formation job is input and received, and a Bk mode print command, that is, an image formation command is received (S701), it is confirmed whether the image forming apparatus 100 is in a standby state. (S702) If it is not waiting, that is, if the image forming operation is being performed, it is confirmed whether image formation is being performed in the FC mode (S703). When image formation is performed in the FC mode, since the contact mode is already set, the contact mode is maintained as it is in the next Bk mode image forming job, and image formation is performed in the afterimage mode ( S704). This prevents not only the occurrence of a belt afterimage but also a decrease in productivity. If it is determined in step S703 that image formation is not performed in the FC mode, the image formation operation is being performed in any of the normal Bk mode, the Bk afterimage mode, and the afterimage mode. Since an image forming operation is being performed in an appropriate mode due to a mode determination necessary at the start of the previous opportunity, the next Bk mode image forming job is performed in that mode (S705). . Thereby, the control is made efficient and the next Bk mode is promptly started. If it is confirmed in step S702 that the image forming apparatus 100 is on standby, the following steps S706 to S711 are performed in the same manner as steps S602 to S607 described with reference to FIG.

Example 2
In the present embodiment shown in FIG. 8, the above-described conditions (1) and (2) are applied. In the embodiment shown in the figure, it is assumed that the image forming apparatus 100 is in a standby state in which the image forming operation is not performed.

  These combined resistances, which are the resistances of the units including the driving roller 72, the transfer belt 11, and the secondary transfer roller 5a, which are the conditions of (2), indicate volume resistance as described above. Since it has a characteristic that depends on humidity, the present embodiment determines the necessity of eliminating the belt afterimage more strictly by using the condition (2) in combination with the condition (1). .

  As shown in the figure, when a Bk mode print job, that is, an image forming job is inputted and received, and a Bk mode print command, that is, an image forming command is received (S801), the temperature / humidity detecting means 97 is set. The temperature and humidity in the main body 99 are read and detected to detect them (S802), and it is determined whether the detected humidity is below a certain standard, that is, 54% RH or less (S803). If the detected humidity is not 40% or less, it is determined that there is no concern about the afterimage of the belt and printing is performed in the normal Bk mode (S804). If the detected humidity is 54% or less, unit resistance detection means The unit resistance is detected by the control means 96 functioning as described above by the method described above with reference to FIG. 5 (S805). Next, it is determined whether or not the detected unit resistance is equal to or higher than a certain reference, that is, 50 MΩ or higher (S806). When the detected unit resistance is 50 MΩ or more, a belt afterimage is likely to occur, so image formation is performed in the afterimage mode (S 807). When the detected unit resistance is not 50 MΩ or more, the temperature detected in step S 802 is 18. It is determined whether the temperature is equal to or lower than C (S808). When the detected temperature is 18 ° C. or less, there is some concern about the belt afterimage, so image formation, that is, image formation is performed in the Bk afterimage mode (S809), and when the detected temperature is not 18 ° C. or less, there is a concern about the belt afterimage. If there is no image, image formation is performed in the normal Bk mode (S810).

  In this embodiment, in addition to the above-described conditions (1) and (2), when the above-described condition (3) is applied, that is, it is determined whether or not the image forming apparatus 100 is on standby. The control in this case is as shown in FIG.

  In other words, as shown in the figure, steps S901 to S905 are performed in the appropriate mode by determining the condition relating to the above (3) in the same manner as steps S701 to S705 described with reference to FIG. Image formation is performed, and the conditions regarding (1) and (2) described above are determined in the same manner as steps S802 to S810 described with reference to FIG. 8 in steps S906 to S914, and image formation is performed in an appropriate mode. Do.

  The evaluation results relating to the afterimage of the belt in Example 1, Example 2, and Example 3 in which the second mode is performed in the individual afterimage mode are any of the conditions (1) to (3) described above. Table 3 shows the evaluation results regarding the belt afterimage of the conventional example which is not applied. This evaluation was performed for each example and comparative example in an environment of a temperature of 10 ° C. and a humidity of 15% RH and an environment of a temperature of 23 ° C. and a humidity of 54% RH. This is carried out by performing image formation using each of the charts (a) to (b) shown.

  From the table, it can be seen that in any of Examples 1 to 3, the belt afterimage was improved during image formation in the Bk mode.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments, and the present invention described in the claims is not specifically limited by the above description. Various modifications and changes are possible within the scope of the above.

  For example, in the above-described embodiment, the downstream image forming unit that is different from the image forming unit 60Y that is the most upstream image forming unit downstream of the secondary transfer unit in the moving direction of the intermediate transfer member is the image forming unit 60M. , 60C, 60BK, the image forming unit 60BK is the image forming unit 60BK. However, if the image forming unit 60Y is not the image forming unit 60Y which is the image forming unit located in the uppermost stream, the image forming unit 60BK is used instead of the image forming unit 60BK. Either unit 60M or 60C may be used. Even when the downstream image forming unit is the image forming unit 60BK, the image forming unit to which the uniform transfer bias is applied is located upstream of the downstream image forming unit in the moving direction of the intermediate transfer member. The side image forming unit is selected according to the layout, for example, and for example, any two of the image forming units 60Y, 60M, and 60C or the image forming units 60Y and 60M in the individual contact mode. Any one of them may be used, and even in this way, the same effect can be obtained.

The intermediate transfer member is not limited to a belt shape, and may be a drum shape.
The other medium to which the image is transferred in the secondary transfer portion is not limited to the recording medium, and may be a second intermediate transfer body or the like.
The number of image forming units arranged along the moving direction with respect to the intermediate transfer member is not limited to four as in the above-described form as long as there are a plurality of image forming units. The color is not limited to the combination of the above-described forms.
The application of the present invention is not limited to the case where the intermediate transfer member has a high resistance. Because

The developer used in such an image forming apparatus is not limited to a two-component developer but may be a one-component developer.
The image forming apparatus may be a single unit of these, not a copying machine, a printer, or a facsimile machine, or may be a printing apparatus as long as an afterimage of the intermediate transfer member is generated. Other combinations such as a printer and a printer may be used.

  The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

11 Intermediate transfer member 11, 12Y, 20Y unit 11, 12M, 20M unit 11, 12C, 20C unit 11, 12BK, 20BK unit 11, 5a, 72 unit 12Y, 12M, 12C Transfer means 12Y, 12M in the upstream image forming unit , 12C, 12BK transfer means 20Y, 20M, 20C, 20BK Image carrier 57 Secondary transfer unit 60BK Downstream image forming unit 60Y Uppermost image forming unit 60Y, 60M, 60C Upstream image forming unit 60Y, 60M, 60C, 60BK Multiple image forming units 72 Secondary transfer unit 96 Unit resistance detection unit 97 Temperature / humidity detection unit 100 Image forming apparatus A1 Movement direction of intermediate transfer member S Other medium

JP 2007-264152 A JP 2010-2565 A JP 2006-293198 A JP 2002-214931 A JP 2002-214939 A JP 2000-330391 A JP 2007-140121 A JP 2002-23516 A JP 2000-231286 A Japanese Patent No. 3785911

Claims (7)

A plurality of image forming units;
Intermediate transfer arranged opposite to the plurality of image forming units, and the image formed in the plurality of image forming units is transferred and the transferred image is secondarily transferred to another medium in the secondary transfer unit Having a body,
Each of the plurality of image forming units includes an image carrier that carries an image to be transferred to the intermediate transfer member, and a transfer unit that applies a transfer bias that transfers the image carried on the image carrier to the intermediate transfer member. When,
A first mode in which the image carrier in the image forming unit in which no image is formed among the plurality of image forming units is separated from the intermediate transfer member;
A second mode in which the image carrier in the image forming unit that does not form an image among the plurality of image forming units is in contact with the intermediate transfer member;
When forming an image in the downstream image forming unit different from the image forming unit located on the most upstream side downstream of the secondary transfer unit in the moving direction of the intermediate transfer member among the plurality of image forming units. In order to make the potential of the intermediate transfer body after transfer uniform, the upstream image forming unit located downstream of the secondary transfer unit and upstream of the downstream image forming unit in the moving direction. Transfer bias can be applied by transfer means,
An image forming apparatus that forms an image in a second mode in order to apply the transfer bias. The image forming apparatus according to claim 1.
It has temperature and humidity detection means to detect the temperature and humidity of the environment,
In order to apply a transfer bias by the transfer unit in the upstream image forming unit in order to equalize the potential of the intermediate transfer body after the secondary transfer on the condition of the temperature and humidity detected by the temperature and humidity detection unit. An image forming apparatus for setting whether or not to perform image formation in the second mode. The image forming apparatus according to claim 1 or 2,
Unit resistance detecting means for detecting resistance of a unit including the intermediate transfer member and a member in contact with the intermediate transfer member;
In order to apply a transfer bias by the transfer unit in the upstream image forming unit in order to equalize the potential of the intermediate transfer body after the secondary transfer on condition that the resistance detected by the unit resistance detection unit An image forming apparatus for setting whether or not to perform image formation in the second mode. The image forming apparatus according to claim 3.
The unit includes the intermediate transfer member, the image carrier in contact with the intermediate transfer member, and the transfer unit, and the unit resistance detection unit detects the resistance using the transfer unit. Image forming apparatus. The image forming apparatus according to claim 3.
The unit includes a second transfer unit for transferring the image transferred to the intermediate transfer member and the intermediate transfer member in the secondary transfer unit to the second transfer unit for secondary transfer to another medium. And a secondary transfer unit that applies a secondary transfer bias, wherein the unit resistance detection unit detects the resistance using the secondary transfer unit. The image forming apparatus according to any one of claims 1 to 5,
When the next image forming job is input during the image forming operation, it is determined whether the current image forming operation is performed in the first mode and / or the second mode. An image forming apparatus configured to perform an image forming operation of a next image forming job in the first mode or the second mode. A plurality of image forming units;
Intermediate transfer arranged opposite to the plurality of image forming units, and the image formed in the plurality of image forming units is transferred and the transferred image is secondarily transferred to another medium in the secondary transfer unit Having a body,
Each of the plurality of image forming units includes an image carrier that carries an image to be transferred to the intermediate transfer member, and a transfer unit that applies a transfer bias that transfers the image carried on the image carrier to the intermediate transfer member. And having
When forming an image in a downstream image forming unit different from the image forming unit located on the most upstream side in the moving direction of the intermediate transfer member among the plurality of image forming units on the downstream side of the secondary transfer unit,
In order to equalize the potential of the intermediate transfer member after the secondary transfer, an upstream image forming unit located downstream of the secondary transfer unit and upstream of the downstream image forming unit in the moving direction. The size of the first transfer bias applied by the transfer means and the size of the second transfer bias for transferring the image carried on the image carrier to the intermediate transfer member,
When there are a plurality of upstream image forming units, the size of the first transfer bias is made smaller than the size of the second transfer bias, and when there is a single upstream image forming unit, the size of the first transfer bias. Is larger than the magnitude of the second transfer bias.

Images