JP5600615B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus including an intermediate transfer belt.

  In a full-color image forming apparatus such as an electrophotographic copying machine or printer, for example, a plurality of drum shapes respectively corresponding to yellow (Y), magenta (M), cyan (C), and black (BK) colors. Photoconductors are available. Then, an electric latent image is formed on the peripheral surface of each photoconductor using a laser scanning unit, and a toner image of each color is generated on the peripheral surface of each photoconductor by the supplied toner of each color. It is configured to be. The toner images of the respective colors generated on the peripheral surfaces of the respective photoconductors are sequentially superimposed and transferred onto an intermediate transfer belt composed of an endless belt that is driven to rotate, whereby a color image is synthesized on the intermediate transfer belt. Next, the color image synthesized on the intermediate transfer belt is transferred to a recording medium such as paper, and is then pressed and heated by a fixing device to be fixed. Further, the toner remaining on the intermediate transfer belt is configured to be removed by the cleaning blade in the same manner as the toner remaining on the photosensitive drum.

  The intermediate transfer belt is stretched around a drive roller and a tension roller. If slip occurs between the drive roller and the intermediate transfer belt, the position of each color is shifted and color shift occurs in printing. Proposed that the roller is made of rubber or a coating rubber member to increase the frictional force between the driving roller and the intermediate transfer belt, or that the frictional force is increased by applying an adhesive to the surface of the intermediate transfer belt in contact with the driving roller. (See Patent Document 1). It has also been proposed to increase the frictional force between the driving roller and the intermediate transfer belt by applying an electrostatic adsorption force between the driving roller and the intermediate transfer belt (see Patent Documents 2 and 3).

JP-A-8-152812 JP 2006-259638 A JP-A-8-146783

  However, in a conventional image forming apparatus equipped with an intermediate transfer belt, in order to prevent color misregistration, when the driving roller is made of a high μ member made of rubber or coating rubber, a rubber layer is processed on a metal cored bar. The advanced technology is required and the cost is high, and the speed of the intermediate transfer belt cannot be kept constant due to the expansion of the rubber due to the environmental change, and the printing quality is deteriorated. Furthermore, when an adhesive is applied to the surface of the intermediate transfer belt that is in contact with the drive roller, the frictional force is reduced due to the aging of the adhesive, and the prevention of color misregistration may be impaired.

In addition, in an image forming apparatus having a conventional intermediate transfer belt, when an electrostatic adsorption force is applied between the drive roller and the intermediate transfer belt to prevent color misregistration, the drive roller can be made of metal. In addition, the electrostatic attraction force of the intermediate transfer belt is small, and therefore there is a drawback that the winding angle of the intermediate transfer belt with respect to the driving roller needs to be 170 degrees or more in order to increase the contact area.
This can be solved by increasing the electrostatic attracting force of the intermediate transfer belt by constantly increasing the voltage (bias voltage) applied to the drive roller. However, constantly increasing the bias voltage not only increases the operating cost, but also increases the influence of the electrostatic attraction force applied to the toner, which may cause color misregistration.
Further, in the image forming apparatus provided with the intermediate transfer belt, the adsorption force of the intermediate transfer belt with respect to each photoconductor varies depending on the printing color. For example, when a so-called three-color release mechanism or four-color release mechanism is incorporated, the tension of the intermediate transfer belt changes depending on whether these release mechanisms are operating or not, thereby preventing color misregistration. There was a risk of damage.

  The present invention has been made in view of the above problems, and in an image forming apparatus provided with an intermediate transfer belt, it is possible to apply an optimum electrostatic attraction force according to the situation between the driving roller and the intermediate transfer belt. The purpose is that.

  The present invention adopts the following configuration as means for solving the above-described problems.

  In the first aspect of the invention, the toner image formed on the image carrier is primarily transferred to an intermediate transfer belt stretched around a driving roller and a tension roller, and the primarily transferred toner image is transferred to the intermediate transfer belt. An image forming apparatus for performing secondary transfer onto a transfer material at a position of a secondary transfer roller provided opposite to the drive roller, wherein the drive roller has a peripheral surface anodized, and the intermediate The bias voltage applied to the secondary transfer roller between the state where the transfer belt is stopped and the transferable speed is made higher than the bias voltage when the intermediate transfer belt is stopped or at the transferable speed. A configuration including a bias voltage applying unit is employed.

  According to a second aspect, in the first aspect, the bias voltage applying unit makes the bias voltage when the intermediate transfer belt is transferable at a higher speed than the bias voltage when the intermediate transfer belt is stopped. Is adopted.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the alumite film thickness on the peripheral surface of the drive roller is 1.0 to 10.0 μm.

  According to a fourth invention, in the invention according to any one of the first to third inventions, the winding angle of the intermediate transfer belt around the drive roller is 130 degrees or more.

  According to the present invention, the peripheral surface of the drive roller is anodized and the largest bias voltage is applied to the secondary transfer roller when the intermediate transfer belt is started by the bias voltage applying means. The electrostatic attraction force is increased, the slip between the intermediate transfer belt and the driving roller is suppressed, and the intermediate transfer belt can reach the transferable speed in a short time.

1 is a schematic configuration diagram of a copying machine to which an image forming apparatus according to an embodiment of the present invention is applied. 1 is a detailed view of a secondary transfer unit of a copying machine to which an image forming apparatus according to an embodiment of the present invention is applied. It is a graph which shows the relationship between the alumite film thickness of a drive roller, and electrostatic attraction force. (A)-(d) is an experimental result which shows the relationship of the motor torque according to alumite film thickness, (e) is a graph which shows the experimental result. 6 is a graph showing the relationship between tension and grip force of an intermediate transfer belt. It is a graph which shows the relationship between the bias voltage of a drive roller, and electrostatic attraction force. 1 is a schematic configuration diagram of a control unit of a copying machine to which an image forming apparatus according to an embodiment of the present invention is applied. It is a flowchart which shows control operation. (A) is a graph showing the color misregistration amount when the bias voltage adjustment of the present invention is performed, and (b) is a graph showing the color misregistration amount when the bias voltage adjustment is not performed.

  Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings. In the following drawings, the scale of each member is appropriately changed in order to make each member a recognizable size. In the following description, a full-color copying machine P using electrophotography will be described as an example of the image forming apparatus of the present invention.

  FIG. 1 is a schematic configuration diagram of a copying machine P. The copying machine P is arranged in order from the top to the bottom, an operation display part a, an image reading part b, a discharge part c, a toner cartridge storage part d, and an image forming part e. In addition, a paper part f is provided, and a paper transport part g is provided from the paper part f located at the lower part to the discharge part d located at the upper part. Although not shown in FIG. 1, the copying machine P is also provided with a control unit h for driving and controlling the copying machine P main body shown in FIG.

  The operation display unit a is composed of a touch panel, and is configured to display predetermined information such as operation guidance for the user, and is configured to be able to input predetermined information such as the number of printed sheets.

  The image reading unit b is configured to irradiate an image of a document with light and to receive the reflected light so that the document image can be read as image data. A light receiving sensor that receives light and converts it into image data is provided.

  The discharge section c is configured such that a sheet (not shown) corresponding to the transfer material of the present invention on which predetermined contents are printed is discharged through the sheet transport section g. The bottom surface of the discharge part c is inclined, and is designed so that one end side can be aligned and stacked when a plurality of sheets are discharged.

  The toner cartridge storage portion d can store a black (BK) toner cartridge d1, a yellow (Y) toner cartridge d2, a cyan (C) toner cartridge d3, and a magenta (M) toner cartridge d4. It is configured. Each cartridge d1 to d4 is configured to be able to supply toner to an image forming unit e2 of an image forming unit e described later.

  The image forming unit e includes a laser scanning unit e1, an image forming unit e2, an intermediate transfer belt unit e3, a cleaning unit e4, a secondary transfer unit e5, and a fixing unit e6.

  The laser scanning unit e1 is rotationally driven by a light beam generator that generates laser light and a polygon motor that deflects the light beam emitted from the light beam generator, as in the known laser scanning unit. It includes a polygon mirror and an fθ lens that forms an image of a light beam deflected by the polygon mirror on a photosensitive drum (to be described later) of the image forming unit e2.

  The image forming unit e2 includes four photosensitive drums 1a to 1d provided at predetermined intervals along the conveyance direction of the intermediate transfer belt unit e3. These photosensitive drums 1a to 1d correspond to the image carrier of the present invention, and are provided corresponding to each color (BK, Y, C, M). Each of the photosensitive drums 1a to 1d is provided with a charger, a developing device, a static eliminator, a cleaner, and the like, as in the known photosensitive drum, and the laser scanning unit e1 is provided on the charged drum peripheral surface. The electrostatic latent image is generated using the toner, and the toner image is formed by the toner supplied from the toner cartridge storage portion d.

  The intermediate transfer belt unit e3 has an endless intermediate transfer belt 2 made of a laminated belt formed by laminating an elastic layer on a synthetic resin belt base. One side (left side in FIG. 1) of the intermediate transfer belt 2 is opposed to a part of the conveyance unit g provided in the longitudinal direction on one end side of the main body of the copying machine P, and the other side (right side in FIG. 1). ) Is provided substantially horizontally so as to be positioned on the other end side of the main body of the copying machine P. That is, the intermediate transfer belt 2 is configured such that one side is stretched around a drive roller 3 connected to a drive source (not shown) and the other side is stretched around a tension roller 4. The drive roller 3 is one of the constituent elements that characterize the present invention, and will be described in detail later with reference to FIG.

Primary transfer rollers 5a to 5d are respectively provided at positions of the intermediate transfer belt 2 facing the photosensitive drums 1a to 1d with the intermediate transfer belt 2 interposed therebetween. The primary transfer rollers 5a to 5d are configured to be able to rotate in accordance with the movement of the intermediate transfer belt 2, and are configured to be able to deal with the cancellation of three colors or the cancellation of four colors. In the case of canceling three colors or canceling four colors, the corresponding transfer rollers 5a to 5d are separated from the intermediate transfer belt 2, and the tension applied to the intermediate transfer belt 2 changes.
In addition to the driving roller 3 and the tension roller 4, the intermediate transfer belt 2 is supported by a conversion roller that changes the moving direction of the belt. Although only one conversion roller is shown in FIG. 1, as shown in FIG. 2 described later, it is provided as necessary.

  The cleaning unit e4 is provided on the tension roller 4 side, and is configured to remove the toner remaining on the intermediate transfer belt 2 using a blade and to discharge the removed toner into a waste toner bottle (not shown). .

  As shown in FIG. 2, the secondary transfer unit e5 is composed of the above-described drive roller 3, the secondary transfer roller 6 and the conversion roller 7 that are disposed so as to face the drive roller 3 and sandwich the intermediate transfer belt 2 therebetween. It is configured.

  The drive roller 3 is a metal roller made of an aluminum alloy, and the peripheral surface of the roller is anodized, that is, anodized. As shown in FIG. 3, it is experimentally understood that the electrostatic attracting force to the intermediate transfer belt 2 can be obtained when a bias voltage is applied, as shown in FIG. However, it has also been found that the electrostatic attraction force does not significantly increase even when the layer thickness increases. Moreover, since the manufacturing cost increases as the layer thickness increases, it can be said that a preferable layer thickness is 1.0 to 10.0 μm. The drive roller 3 is a metal roller, so it has excellent durability, and since it is made of an aluminum alloy, it can be manufactured at a low cost. Further, the roller peripheral surface is an alumite-treated layer with a high electrical resistance. Since it is formed, it can be excellent in electrostatic attraction force.

  The fact that the alumite film thickness is preferably 1.0 to 10.0 μm is supported by the experimental results shown in FIGS. Each of the four setting conditions shown in FIGS. 4A to 4D includes an intermediate transfer belt winding angle of 180 degrees with respect to the drive roller, an intermediate transfer belt tension 20N, a secondary transfer roller pressing force 20N, When the transfer bias of the secondary transfer roller is from the top of the table, the positive bias current is 10, 20, 30 μA, the reverse bias voltage (500 V), and the motor torque of the driving roller is measured immediately before slipping, and the alumite film thickness is 0. 6, 1.3, 8.2, and 0.0 (no anodized layer) μm, and FIG. 4E shows the relationship between the current value of the secondary transfer bias and the torque. It is a graph. In particular, as is apparent from FIG. 4 (e), there is no significant difference in the motor torque value between 1.3 μm and 8.2 μm of the alumite film thickness. It is confirmed that the range of 10.0 μm is preferable.

  The secondary transfer roller 6 is connected to a bias voltage adjustment unit (see “e7” to be described later) that can change a bias voltage value or a current value.

  As described above, the secondary transfer roller 6 faces the drive roller 3 and is disposed with the intermediate transfer belt 2 interposed therebetween. Moreover, the secondary transfer roller 6 is always provided to press the drive roller 3. Therefore, when the intermediate transfer belt 2 is moved (rotated) by the driving roller 3, the secondary transfer roller 6 can be rotated along with the movement. When the sheet is conveyed through the conveying unit g, the secondary transfer roller 6 can be rotated with the sheet interposed between the intermediate transfer belt 2 and the sheet is fixed to the fixing unit. It can be conveyed to the e6 side.

  The drive torque D that can be transmitted to the intermediate transfer belt 2 by the drive roller 3 can be expressed by the following equation. In the following equation, T1 is the tension by the tension roller 4 of the intermediate transfer belt 2 indicated by an arrow in FIG. 2, and T2 is the pressing force of the secondary transfer roller 6 indicated by the arrow T2 in FIG. It corresponds.

  FIG. 5 shows the relationship between the tension of the intermediate transfer belt 2 and the grip force with which the driving roller 3 holds the intermediate transfer belt 2 in a state where no bias voltage is applied to the secondary transfer roller 6. It can be seen that the grip force between the driving roller 3 and the intermediate transfer belt 2 is substantially proportional to the tension of the intermediate transfer belt 2.

  FIG. 6 shows the relationship between the bias voltage for the secondary transfer roller 6 and the grip force of the drive roller 3 due to electrostatic attraction of the intermediate transfer belt 2. When the tension of the intermediate transfer bell 2 was set to 17N and 25N, the blip force at which the driving roller 3 held the intermediate transfer belt 2 was measured by changing the bias voltage for the secondary transfer roller 6 respectively. The graph is obtained by excluding the assumed value of the grip force between the driving roller 3 and the intermediate transfer belt 2 due to each tension of the intermediate transfer belt 2. As is apparent from this figure, whether the tension of the intermediate transfer belt 2 is 17N (indicated by a broken line) or 25N (indicated by a solid line), the grip force due to the electrostatic adsorption force increases as the bias voltage increases. I understand that. The electrostatic attraction force is substantially the same at the time of the positive bias voltage and at the time of the reverse bias voltage. If the bias voltage value is increased, the electrostatic attracting force can be increased. However, since there is a concern that a bias voltage value exceeding the necessary electrostatic attracting force may affect the print quality, FIG. As shown in the figure, about 2000V is sufficient. The secondary transfer bias at the time of image formation performs constant current control, but the voltage is about 1500 V, and the grip force due to the electrostatic attraction force is slightly less than 0.3 N · m. It can be seen that when the bias voltage is 2000 V, a grip force by an electrostatic attraction force exceeding 0.4 N · m can be obtained.

  Naturally, the slip of the intermediate transfer belt 2 with respect to the drive roller 3 can be reduced if the winding angle of the intermediate transfer belt 2 with respect to the drive roller 3 (see θ in the above equation and θ in FIG. 2) is increased. In the present invention, it is proved that the angle can be reduced to 130 degrees because the electrostatic attraction force is increased by subjecting the surface of the drive roller 3 to alumite treatment. In this way, the winding angle of the intermediate transfer belt 2 with respect to the drive roller 3 can be reduced, so that the winding angle of the intermediate transfer belt 2 can be reduced, and the secondary transfer roller 6 is connected to the drive roller 3 and the intermediate transfer. It is also possible to effectively suppress the generation of a dust image at the transfer nip portion by arranging an offset upstream of the winding start position of the belt 2.

  The fixing unit e6 is provided in a part of the transport unit g on the downstream side of the secondary transfer unit e5, and a pair of sheets arranged so as to sandwich the paper transporting the transport unit g. It is composed of rollers. The toner image on the sheet transferred by the secondary transfer unit e5 by being pressed and heated by the pair of rollers can be fixed on the sheet.

  The paper section f is composed of a paper feed tray f1 provided so as to be openable and closable with respect to the apparatus main body, and a paper cassette f2 provided so as to be drawable with respect to the apparatus main body. The sheet is fed one by one from the sheet feeding tray f1 to the sheet conveying unit g via a pickup roller. Further, the sheet cassette f2 is also configured to be able to supply sheets one by one to the sheet transport unit g via a pickup roller.

  The paper transport part g is provided from the paper part f located at the lower part to the discharge part d located at the upper part, and is composed of a plurality of transport rollers and a guide plate. The paper transport unit g is configured to transport the paper supplied from the paper unit f one by one toward the discharge unit c.

  Although not shown in FIG. 1, the control unit h is provided in the copying machine P. As shown in FIG. 7, the control unit h has a CPU 102 that performs overall drive control of the copier P main body using a system program stored in the ROM 100 and working data stored in the RAM 101. ing. The CPU 102 stores the image reading unit b described above via the bus line, an image data storage unit b1 that stores data read by the image reading unit b, and data stored in the image data storage unit b1. An image data processing unit b2 that generates and develops development data, an image forming unit e that includes a bias voltage adjusting unit e7 that adjusts the bias voltage and current of the secondary transfer unit e5, a paper transport unit g, and an operation display unit a. It is connected. The bias voltage adjusting unit e7 corresponds to the bias voltage applying unit of the present invention. Note that the CPU 102 is also provided with a communication control unit for communicating with these devices when the copying machine P has a FAX function or can be connected to an external information device.

  The bias voltage adjusting unit e7 uses a bias voltage Va (hereinafter referred to as “start-up bias voltage Va”) that is used when the intermediate transfer belt 2 is rotated (started to reach the transferable speed from the stop time). The bias voltage Vb used when transferring the toner image onto the paper (hereinafter referred to as “transfer bias voltage Vb”), and after the intermediate transfer belt is started to rotate (after reaching the transferable speed), the transfer material The bias voltage Vc can be changed to a bias voltage Vc used when not transferred to the image (hereinafter referred to as “non-transfer bias voltage Vc”). These bias voltages are determined so that Va ≧ Vb> Vc. The relationship between the start bias voltage Va and the transfer bias voltage Vb may be Va> Vb. In the present invention, the bias voltage Vb at the time of transfer is sequentially reduced from the bias voltage Va at the time of startup, including the case of the bias voltage Va at the time of start ≧ the bias voltage Vb at the time of transfer.

  Hereinafter, the control operation will be described with reference to the flowchart of FIG. Assume that a power switch (not shown) of the copying machine P is turned on (step 100 affirmation (hereinafter, step is “S”, affirmation is “Y”, and negation is “N”)). Then, the type of color printing or monochrome printing is selected via the operation display unit a, and predetermined information such as the number of printed sheets is input.

  When the start button of the operation display unit a is pressed (S102Y), although omitted in the flowchart of FIG. 8, the image of the document set in the image reading unit b is read, and the read data is image data. The image data stored in the storage unit b1 and then stored is processed by the image data processing unit b2 for the laser scanning unit e1.

  When the reading of the document is completed, the driving roller 3 starts to be driven, and the rotation of the intermediate transfer belt 2 is started. At the same time, the moving speed of the intermediate transfer belt 2 reaches a stable speed. The bias voltage applied to the secondary transfer roller 6 is the startup bias voltage Va (S104). By applying the start-up bias voltage Va, the electrostatic attracting force between the driving roller 3 and the intermediate transfer belt 2 is increased, and the intermediate transfer belt 2 can be rotated while suppressing slippage from the start of driving of the driving roller 3. it can. The start-up bias voltage Va is continuously applied for a predetermined time (S106Y). Therefore, the intermediate transfer belt 2 can be brought to the stable speed in a short time by increasing the electrostatic attraction force until the intermediate transfer belt 2 reaches the stable speed and suppressing the slip.

  The predetermined time will be described with reference to FIGS. 9A and 9B. FIG. 9A shows the present invention, in which the driving bias voltage Va is applied from the start of driving of the driving roller 3. In this case, the color misregistration state is shown, and the color misregistration hardly occurs. FIG. 6B shows a color misregistration state when the start-up bias voltage Va is not applied in the comparative example of the present invention. In the range indicated by a in this figure, a large color misregistration occurs, that is, a large color misregistration occurs after the driving of the driving roller 3 is started until the moving speed of the intermediate transfer belt 2 becomes constant. The state which has arisen is shown. FIG. 2B shows a state in which a large color shift occurs from the start of the movement of the intermediate transfer belt 2 to 200 mm. Therefore, the predetermined time is determined based on the time until the moving speed of the intermediate transfer belt 2 becomes constant.

  When driving of the driving roller 3 is started and the rotation of the intermediate transfer belt 2 is started, in the case of color printing, laser light corresponding to image data is emitted from the laser scanning unit e1 to each of the photosensitive drums 1a to 1d. Irradiation forms an electrical latent image, and a toner image of each color is formed by the supplied toner. The toner images of the respective colors are sequentially superimposed and transferred onto the intermediate transfer belt 2 to synthesize a color image. Next, the color image synthesized on the intermediate transfer belt 2 is transferred to a sheet by a secondary transfer unit e5, and then subjected to a fixing process by being pressurized and heated by a fixing unit e6, whereby a sheet on which a color image is printed is obtained. It is discharged to the discharge part c. In the case of monochrome printing, only the primary transfer roller 5a of the photosensitive drum 1a is applied with a bias voltage, and the other primary transfer rollers 5b to 5d are released, that is, three colors are released, and printing is performed. During this transfer, the bias voltage is set to a transfer bias voltage Vb that is slightly smaller than the startup bias voltage Va (S108Y, S110).

  The reason why the bias voltage is set to the transfer bias voltage Vb slightly smaller than the start-up bias voltage Va at the time of transfer is that there is no concern about color misregistration because the moving speed of the intermediate transfer belt 2 is constant. In addition, if the bias voltage is low, not only can the operating cost be reduced by that amount, but if the bias voltage is low, the influence on others is small. When the starting bias voltage Va can sufficiently suppress the starting and transfer slips, the starting bias voltage Va may be lowered so that the starting bias voltage Va and the transfer bias voltage Vb are the same. it can.

  When the above-mentioned transfer is not performed (S108N), that is, when the application of the bias voltage to all the primary transfer rollers 5a to 5d is canceled and so-called four-color cancellation is performed, the intermediate transfer belt 2 Since the load is smaller than the transfer time, the bias voltage is set to the non-transfer time bias voltage Vc slightly smaller than the transfer bias voltage Vb (S112). Therefore, in this case, since the bias voltage becomes smaller, it is possible to obtain an effect such as a reduction in operation cost. In this non-transfer, no bias voltage can be applied without applying any bias voltage.

  The adjustment of the bias voltage described above is continued until the printing is finished (S114Y) and the power switch of the copying machine P is turned off (S116Y).

  In the above example, the bias voltage at the time of transfer is the same at the time of color printing and monochrome printing, but it may be changed. That is, when the printing type is monochrome, only the primary transfer roller 5a is kept in a state where a bias voltage is applied, and the load on the intermediate transfer belt 2 is smaller than that when selecting a color, so that it is smaller than when selecting a color. It can be a bias voltage.

As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the said embodiment. Various shapes, combinations, and the like of the constituent members shown in the above-described embodiments are examples, and various modifications can be made based on design requirements and the like without departing from the gist of the present invention.
In the above example, the charging state is realized by applying a bias voltage to the driving roller 3. However, the charging state can also be realized by applying a bias voltage to the intermediate transfer belt 2 facing the driving roller 3. .
Further, in the above-described example, the image forming apparatus is a copying machine, but it may be a printer, a facsimile machine, or a multifunction machine having these functions.

P: Copying machine (image forming apparatus), e: Image forming unit, e1: Laser scanning unit, e2: Development unit, e3: Intermediate transfer belt unit, e4: Cleaning unit, e5: 2 Next transfer unit, e6... Fixing unit, e7... Bias voltage adjusting unit (charge applying means), 1a to 1d... Photosensitive drum (image carrier), 2. 5a to 5d: primary transfer roller, 6: secondary transfer roller

Claims (3)

The toner image formed on the image carrier is primarily transferred to an intermediate transfer belt that is stretched around a drive roller and a tension roller, and the toner image that has been primarily transferred is opposed to the drive roller. An image forming apparatus capable of performing secondary transfer to a transfer material at a position of a secondary transfer roller provided and selecting color printing or monochrome printing ;
The drive roller has a peripheral surface anodized.
The bias voltage applied to the secondary transfer roller between the state where the intermediate transfer belt is stopped and the transferable speed is set to be higher than the bias voltage when the intermediate transfer belt is stopped or at the transferable speed. The bias voltage when the intermediate transfer belt can be transferred is higher than the bias voltage when the intermediate transfer belt is stopped , and the bias voltage during monochrome printing is set to the bias voltage during color printing. image forming apparatus characterized by Ru with a bias voltage applying means to be lower than.   The image forming apparatus according to claim 1, wherein the alumite film thickness on the peripheral surface of the drive roller is 1.0 to 10.0 μm.   The image forming apparatus according to claim 1, wherein a winding angle of the intermediate transfer belt with respect to the driving roller is 130 degrees or more.

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