JP2007199636A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printer of a sending side primary transfer nip type capable of reducing the occurrence of toner dirt on a recording paper sheet P while suppressing disturbance of superposed images in the second and succeeding recording paper sheet P in continuous printing out. <P>SOLUTION: The printer is provided with: photoreceptors 2K, Y, M, C arranged along an area from a winding position around a drive roller 18 up to a position right before entering into a winding position around a driven stretched roller 17, and abutted on respective belt positions in the area to form a primary transfer nips; and a secondary transfer roller 20 abutted on the winding position of an intermediate transfer belt 16 around a drive roller 18 from the top surface side of the belt 15 to form a secondary transfer nip. A belt cleaning device is arranged so as to clean belt portions in the area from the winding position around the drive roller 18 up to the position right before entering into an abutting position on the photoreceptor 2K for K. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a copying machine, a printer, a facsimile machine, etc., in which toner images individually formed on a plurality of image carriers are primary-transferred on an intermediate transfer belt that is endlessly moved and then secondary-transferred to a recording member. The present invention relates to an image forming apparatus.

  In this type of image forming apparatus, the intermediate transfer belt is stretched endlessly by the rotational driving of the driving roller while being stretched by a driving roller or a driven stretching roller. A plurality of image bearing members such as a photosensitive member are brought into contact with the front surface of the intermediate transfer belt to form a plurality of primary transfer nips, while a secondary transfer contact member such as a secondary transfer roller. Is brought into contact with the front surface of the intermediate transfer belt to form a secondary transfer nip. The toner image formed on the surface of each image carrier is primarily transferred by being superimposed on the intermediate transfer belt at each primary transfer nip. Then, a superposed image such as a multicolor toner image obtained on the intermediate transfer belt by this superimposing primary transfer is caused to enter the secondary transfer nip as the belt moves. A recording member such as recording paper is fed into the secondary transfer nip so as to be synchronized with the superimposed image on the intermediate transfer belt in the nip. Then, in the secondary transfer nip, the superimposed image on the intermediate transfer belt is collectively transferred to the surface of the recording member.

  In such a configuration, a method of forming a plurality of primary transfer nips by bringing a plurality of image carriers into contact with the tension side moving portions of the intermediate transfer belt (hereinafter referred to as a tension side primary transfer nip method) is adopted. It is common. Specifically, in the intermediate transfer belt, a portion in the vicinity of the portion around the drive roller that is on the upstream side in the belt movement direction is directed toward the drive roller by receiving the winding force of the drive roller. It becomes the tension side movement part pulled by. On the other hand, a portion in the vicinity of the portion where the driving roller is hung and further downstream in the belt moving direction than the hung portion is a feeding side moving portion which moves while receiving the feeding force of the driving roller. In order to make the intermediate transfer belt run stably, it is advantageous to form the primary transfer nip by bringing each image carrier into contact with the tension side moving portion. Therefore, the tension side primary transfer nip system is adopted. There are many.

  However, due to layout restrictions and the like, a method of forming a plurality of primary transfer nips by bringing a plurality of image carriers into contact with the feed side moving portions of the intermediate transfer belt (hereinafter referred to as a feed side primary transfer nip method). ) May be desired. In such a feed-side primary transfer nip system, a secondary transfer abutment member such as a secondary transfer roller is brought into contact with a place where the intermediate transfer belt is driven with respect to a driven stretch roller to form a secondary transfer nip. And Then, when the recording member is sandwiched in the secondary transfer nip, the nip pressure is rapidly increased, thereby rapidly decreasing the belt moving speed in the secondary transfer nip for a moment. Then, a sudden decrease in the belt moving speed in the secondary transfer nip is reflected in each primary transfer nip. In the continuous printout mode in which images are continuously formed on a plurality of recording members, if such a belt moving speed is suddenly reduced at each primary transfer nip, the intermediate transfer belt is transferred from each image carrier. The superimposed image in the middle of being overlaid is disturbed. For this reason, in the continuous printout mode, the superimposed images of the second and subsequent recording members are likely to be disturbed.

  Patent Document 1 describes an image forming apparatus that can suppress such a disturbance of a superimposed image that is likely to occur when the feed-side primary transfer nip method is employed. In this image forming apparatus, a secondary transfer roller, which is a secondary transfer contact member, is brought into contact with a portion where the intermediate transfer belt is wound around a driving roller to form a secondary transfer nip. Then, the intermediate transfer belt separated from the driving roller immediately after passing through the secondary transfer nip is passed through a plurality of primary transfer nips before entering the tension position with respect to the tension roller. In such a configuration, even if the recording member is sandwiched in the secondary transfer nip and the nip pressure is increased, the intermediate transfer belt in the secondary transfer nip is favorably moved by the rotation of the driving roller that is driven to rotate. Accordingly, it is possible to suppress a rapid decrease in the belt moving speed in the secondary transfer nip when the recording member is sandwiched in the secondary transfer nip, and to suppress disturbance of the superimposed image on the second and subsequent recording members. .

JP 2002-189327 A

  However, in this image forming apparatus, there is a possibility that the recording member may be contaminated with toner due to the mixture of the secondary transfer residual toner in the secondary transfer nip. Specifically, in this image forming apparatus, a cleaning blade as a belt cleaning member is brought into contact with a portion where the intermediate transfer belt is wound around the driving roller and further downstream of the secondary transfer nip in the belt moving direction. I am letting. This cleaning blade cleans the secondary transfer residual toner adhering to the belt surface immediately after passing through the secondary transfer nip. However, in this configuration, the cleaning position, which is the contact position between the cleaning blade and the intermediate transfer belt, is very close to the secondary transfer nip, so the secondary transfer residual toner scraped off by the cleaning blade is transferred to the secondary transfer nip. It becomes easy to mix in the nip. This mixing may cause toner contamination on the recording member. In particular, in a layout in which the cleaning position is vertically above the secondary transfer nip, the belt surface from the cleaning position to the secondary transfer nip exit has a downward slope along the curved surface of the drive roller. Then, since the secondary transfer residual toner that contacts the tip of the cleaning blade falls by gravity toward the secondary transfer nip along the downward slope of the belt surface, toner contamination of the recording member is likely to occur.

  The present invention has been made in view of the above background, and an object thereof is to provide the following image forming apparatus. That is, the image forming apparatus of the feed side primary transfer nip system can reduce the occurrence of toner contamination on the recording member while suppressing the disturbance of the superimposed image on the second and subsequent recording members during continuous printout. .

In order to achieve the above object, an invention according to claim 1 is directed to an endless intermediate transfer belt that is stretched by a tension roller and a drive roller, and is endlessly moved by rotational driving of the drive roller, Of all the regions in the circumferential direction, they are arranged along the region from passing through the hanging position with respect to the driving roller to immediately before entering the hanging position with respect to the stretching roller disposed next to the driving roller. However, a plurality of image carriers each abutting on a belt portion in the region to form a primary transfer nip, toner image forming means for forming a toner image on these image carriers, and the driving roller in the intermediate transfer belt A secondary transfer abutting member that forms a secondary transfer nip by abutting from the belt front surface side on a portion around the belt, and is attached to the front surface of the intermediate transfer belt A belt cleaning member for cleaning residual transfer residual toner, and a toner image formed on the surface of each image carrier is superposed on the intermediate transfer belt at each primary transfer nip to perform primary transfer, In the image forming apparatus that performs secondary transfer to the recording member in the secondary transfer nip, the entire area in the circumferential direction of the intermediate transfer belt passes through the position where the intermediate roller is wound, and then the drive roller The belt cleaning member is disposed so as to clean the belt portion in the region immediately before entering the contact position with the most upstream image carrier that is the most upstream image carrier in the belt moving direction. It is characterized by that.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the most upstream image carrier is bitten inside the belt loop so that the stretched portion of the intermediate transfer belt is pushed toward the belt loop inside. It is characterized by being disposed.
According to a third aspect of the present invention, in the image forming apparatus of the second aspect, as the plurality of image carriers, a Y image carrier for carrying a yellow toner image and a magenta toner image for carrying a magenta toner image. An M image carrier, a C image carrier for carrying a cyan toner image, and a K image carrier for carrying a black toner image, and the intermediate transfer belt is connected to the Y image carrier, Contacting / separating means for contacting and separating the M image carrier and the C image carrier is provided.
According to a fourth aspect of the present invention, in the image forming apparatus of the third aspect, the K image carrier is disposed as the most upstream image carrier, and the K image carrier among the plurality of image carriers. Or the amount of biting into the belt loop inside the K image carrier is made larger than that of other image carriers.
According to a fifth aspect of the present invention, in the image forming apparatus according to the first aspect, the drive roller having a larger diameter than other tension rollers that stretch the intermediate transfer belt is used. Is.
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the second to fifth aspects, the winding angle of the intermediate transfer belt with respect to the drive roller is greater than 180 [°]. It is.
According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, each of the plurality of image carriers is cylindrical or columnar, and is provided on the back surface of the intermediate transfer belt. A cleaning backing member is provided for sandwiching the intermediate transfer belt between the belt cleaning member and abutting portions between the back surface of the intermediate transfer belt and the cleaning backing member. A virtual common tangent line that touches both the peripheral surface and the peripheral surface of the drive roller, and a peripheral surface of the drive roller, and a peripheral surface of the tension roller adjacent to the drive roller on the downstream side in the belt movement direction. The layout is positioned between the virtual common tangent and the virtual common tangent.
According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, after passing through a position where the intermediate transfer belt is wound around the driving roller in the entire area in the circumferential direction, The region immediately before entering the contact position with the belt cleaning member has an ascending gradient from the contact position toward the wrapping position.
According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, the plurality of primary transfer rollers individually corresponding to the plurality of image carriers are respectively associated with the primary corresponding to the plurality of primary transfer rollers. It is characterized in that it is brought into contact with the back surface of the belt portion in the vicinity of the transfer nip and on the downstream side in the belt movement direction from the outlet of the primary transfer nip.
According to a tenth aspect of the present invention, in the image forming apparatus according to the ninth aspect, as the plurality of primary transfer rollers, roller peripheral surfaces each made of a metal material are used.

In these inventions, a plurality of image carriers are held at belt positions in an area from passing through the position where the drive roller is hung up to just before entering the position where the hanger is placed next to the drive roller. By bringing the bodies into contact with each other, the primary transfer nip is formed by the feed-side primary transfer nip method. Then, the secondary transfer contact member is brought into contact with the portion of the intermediate transfer belt that is wound around the driving roller to form the secondary transfer nip, whereby the recording member is sandwiched in the secondary transfer nip and the nip pressure is increased. Also, the intermediate transfer belt in the secondary transfer nip is favorably moved by the rotation of the drive roller that is driven to rotate. Therefore, it is possible to suppress a rapid decrease in the belt moving speed in the secondary transfer nip when the recording member is sandwiched in the secondary transfer nip, and to suppress the disturbance of the superimposed image on the second and subsequent recording members. .
Further, in these inventions, the belt cleaning member is brought into contact with the belt portion in the region from after passing through the position where the drive roller is hung up to just before entering the contact position with the most upstream image carrier. Yes. In such a configuration, the cleaning position at which the belt and the belt cleaning member come into contact with each other, and the secondary position, as compared with the image forming apparatus described in Patent Document 1 in which the belt cleaning member is brought into contact with the driving roller of the intermediate transfer belt. The distance from the transfer nip is increased to prevent the secondary transfer residual toner from being mixed into the secondary transfer nip. As a result, it is possible to reduce the occurrence of toner contamination on the recording member due to the mixing of the secondary transfer residual toner into the secondary transfer nip.

Hereinafter, as an image forming apparatus to which the present invention is applied, an embodiment of an electrophotographic printer (hereinafter simply referred to as a printer) will be described.
First, the basic configuration of the printer will be described. FIG. 1 is a schematic configuration diagram showing the printer. In this figure, the printer includes four toner image forming units for forming toner images of black, yellow, magenta, cyan, and black (hereinafter referred to as K, Y, M, and C). Each of these toner image forming units is composed of a process unit and a developing device. Taking a K toner image forming unit for forming a K toner image as an example, this is composed of a K process unit 1K and a K developing device 5K as shown in FIG.

  The process unit 1K for K includes a drum-shaped photosensitive member 2K as an image carrier, a drum cleaning device 3K, a static eliminator (not shown), a charging device 4K, and the like. These are casings serving as a common support. keeping. The unit is integrally attached to and detached from the printer main body.

  The photosensitive member 2K is rotationally driven at a linear speed of 150 [mm / sec] in the clockwise direction in the drawing by a driving unit (not shown). The charging device 4K applies a charging bias in which a DC bias is superimposed on an AC bias to a charging roller facing the photoconductor 2K, and the surface of the photoconductor 2K is, for example, −500 [V] by discharging from the charging roller. Charge uniformly. The uniformly charged surface of the photosensitive member 2K is exposed and scanned by the laser beam L and carries an electrostatic latent image for K. The electrostatic latent image for K is developed into a Y toner image by a developing device 5K using K toner (not shown). Then, primary transfer is performed on an intermediate transfer belt 16 described later.

  The drum cleaning device 3K removes transfer residual toner adhering to the surface of the photoreceptor 2K after the primary transfer process. Further, a static elimination device (not shown) neutralizes residual charges on the photoreceptor 2K after cleaning. By this charge removal, the surface of the photoreceptor 2K is initialized and prepared for the next image formation. Similarly, in the process units (1Y, M, C) of other colors, a (Y, M, C) toner image is formed on the photoreceptor (2Y, M, C), and the Y toner on the intermediate transfer belt 16 is formed. The image is primary-transferred superimposed on the image. A four-color superimposed toner image (hereinafter referred to as a four-color toner image) is formed on the intermediate transfer belt 16 by the primary transfer of the superposition.

  The developing device 5K includes a vertically long hopper 6K that stores K toner (not shown) and a developing unit 7K. In the hopper 6K, an agitator 8K that is rotationally driven by a driving means (not shown), an agitation paddle 9K that is rotationally driven by a driving means (not shown) vertically below, and a rotational drive that is driven by a driving means (not shown) in the vertical direction thereof. A toner supply roller 10K to be used is disposed. The K toner in the hopper 6K moves toward the toner supply roller 10K by its own weight while being stirred by the rotational drive of the agitator 8K and the stirring paddle 9K. The toner supply roller 10K has a metal cored bar and a roller portion made of foamed resin or the like coated on the surface of the metal core roller 10K, while adhering K toner in the hopper portion 6K to the surface of the roller portion. Rotate.

  In the developing unit 7K of the developing device 5K, a developing roller 11K that rotates while contacting the photoreceptor 2K and the toner supply roller 10K, and a thinning blade 12K that contacts the tip of the developing roller 11K are disposed. Yes. The K toner adhered to the toner supply roller 10K in the hopper 6K is supplied to the surface of the development roller 11K at a contact portion between the development roller 11K to which a development bias is applied by a power source (not shown) and the toner supply roller 10K. . When the supplied K toner passes through the contact position between the roller and the thinning blade 12K as the developing roller 11K rotates, the layer thickness on the roller surface is regulated. Then, the K toner after the layer thickness regulation adheres to the electrostatic latent image for K on the surface of the photosensitive member 2K in the developing region which is a contact portion between the developing roller 11K and the photosensitive member 2K. By this adhesion, the electrostatic latent image for K is developed into a K toner image.

  The K toner image forming unit has been described with reference to FIG. 2, but the Y, M, and C toner images are also formed on the surfaces of the photoreceptors 2Y, M, and C by the same process in the Y, M, and C toner image forming units. Is formed.

  In FIG. 1 described above, an optical writing unit 70 is disposed above the four toner image forming units. The optical writing unit 70, which is a latent image writing means, optically scans the photoreceptors 2K, Y, M, and C in the process units 1K, Y, M, and C with laser light L emitted from a laser diode based on image information. To do. By this optical scanning, electrostatic latent images for K, Y, M, and C are formed on the photoreceptors 2K, Y, M, and C. The optical writing unit 70 is a photosensitive member that passes through a plurality of optical lenses and mirrors while polarizing a laser beam (L) emitted from a light source in a main scanning direction by a polygon mirror that is rotationally driven by a polygon motor (not shown). Is irradiated. Instead of the optical writing unit 70 having such a configuration, a unit that performs optical writing by light irradiation from an LED array may be employed.

  Below the four toner image forming portions, a transfer unit 15 is provided that moves the endless intermediate transfer belt 16 endlessly in the counterclockwise direction in the drawing. In addition to the intermediate transfer belt 16, the transfer unit 15 serving as transfer means includes a driving roller 17, a driven roller 18, four primary transfer rollers 19K, Y, M, and C, a secondary transfer roller 20, a belt cleaning device 21, and a cleaning device. A backup roller 22 is provided.

  The intermediate transfer belt 16 is stretched between a drive roller 18 and a driven stretch roller 17 disposed inside the loop. Then, it is moved endlessly in the same direction by the rotational force of the driving roller 18 that is driven to rotate counterclockwise in the figure by a driving means (not shown).

  The four photosensitive members 2K, 2Y, 2M, and 2C are stretch rollers adjacent to the drive roller 18 after passing through a position where the intermediate transfer belt 16 is wound around the drive roller 18 in the entire circumferential direction. They are lined up along the region before entering the hung position on the driven tension roller 17. The primary transfer nips for K, Y, M, and C are formed in contact with the above-described regions. That is, this printer employs a feed-side primary transfer nip system. The intermediate transfer belt 16 passes through the position where the intermediate transfer belt 16 is wound around the driving roller 18 and then enters each primary transfer nip in the order of K, Y, M, and C.

  Inside the loop of the intermediate transfer belt 16, in addition to the driven tension roller 17 and the drive roller 18, four primary transfer rollers 19K, Y, M, and C and a cleaning backing roller 22 are also arranged. A primary transfer bias is applied to the primary transfer rollers 19K, Y, M, and C sandwiching the intermediate transfer belt 16 between the photoreceptors 2K, Y, M, and C by a power source (not shown). As a result, a transfer electric field is formed between the electrostatic latent images on the photoreceptors 2K, Y, M, and C and the primary transfer rollers 19K, Y, M, and C. Instead of the primary transfer rollers 19K, Y, M, and C, a transfer charger, a transfer brush, or the like may be employed.

  When the K toner formed on the surface of the photoconductor 2K of the K process unit 1K enters the K primary transfer nip as the photoconductor 2K rotates, the photoconductor is exposed to light due to the transfer electric field and the nip pressure. Primary transfer is performed on the intermediate transfer belt 16 from the body 2K. The intermediate transfer belt 16 on which the K toner image has been primarily transferred in this way passes through the primary transfer nips for Y, M, and C sequentially along with the endless movement thereof, so that the photoreceptors 2Y, M, and The Y, M, and C toner images on C are primary-transferred sequentially superimposed on the K toner image. A four-color toner image is formed on the intermediate transfer belt 16 by the primary transfer of superposition.

  The transfer unit 15 also has a secondary transfer roller 20 disposed outside the loop of the intermediate transfer belt 16. The secondary transfer roller 20 as a secondary transfer abutting member abuts from the belt front surface side at a place where the intermediate transfer belt 16 is wound around the driving roller 18 to form a secondary transfer nip. A secondary transfer bias is applied to the secondary transfer roller 20 by a transfer bias power source (not shown). By this application, a secondary transfer electric field is formed between the secondary transfer roller 20 and the drive roller 18 connected to the ground.

  In this printer, the secondary transfer roller 20 as a secondary transfer contact member is brought into contact with the driving roller 18 on the intermediate transfer belt 16 so as to form the secondary transfer nip. It has become. That is, even when the recording paper P is sandwiched in the secondary transfer nip and the nip pressure is increased, the intermediate transfer belt 16 in the secondary transfer nip is favorably moved by the rotation of the driving roller 18 that is driven to rotate. Therefore, the superimposed image on the second and subsequent recording sheets P during continuous printout is suppressed while suppressing a rapid decrease in the belt moving speed in the secondary transfer nip when the recording sheet P is sandwiched in the secondary transfer nip. Disturbance can be suppressed.

  The reason why the feed side primary transfer nip method is adopted in this printer is as follows. That is, the intermediate transfer belt 16 needs to be stretched by at least two stretching rollers. The number of belts may be any number as long as it is two or more, but the example in which only two stretching rollers are used can stretch the intermediate transfer belt 16 with the simplest configuration. Therefore, in this printer, only two of the driving roller 18 and the driven stretching roller 17 are used as the stretching roller. In order to suppress the disturbance of the superimposed image on the second and subsequent recording sheets P, in this printer, as described above, the secondary transfer roller 20 is applied to the place where the intermediate transfer belt 16 is wound around the drive roller 18. A secondary transfer nip is formed by contact. Further, as shown in the drawing, the intermediate transfer belt 16 is stretched in a horizontally long posture extending substantially in the horizontal direction. In such a configuration, as shown in the figure, the four photoconductors are brought into contact with the upper tension surface (feeding side movement location) of the belt, or are brought into contact with the lower tension surface (belt side movement location) of the belt. Any of the configurations can be employed. However, in the latter configuration, four process units 1K, Y, M, and C are disposed below the intermediate transfer belt 16, so that the process unit can be attached and detached from above the printer with the upper cover 50 opened. Disappear. Therefore, in this printer, the four photosensitive members are brought into contact with the feeding side moving portion that becomes the upper tension surface of the belt, so that the process unit can be attached and detached from above the printer. For this reason, the feed side primary transfer nip system is adopted.

  Below the transfer unit 15, a paper feed cassette 30 that stores a plurality of recording papers P in a stack of paper sheets is slidably attached to the printer housing. In the paper feed cassette 30, a paper feed roller 30a is brought into contact with the top recording paper P of the paper bundle, and the recording paper is rotated by rotating it in a counterclockwise direction in the drawing at a predetermined timing. P is sent out toward the paper feed path 31.

  A registration roller pair 32 is disposed near the end of the paper feed path 31. The registration roller pair 32 stops the rotation of both rollers as soon as the recording paper P delivered from the paper feed cassette 30 is sandwiched between the rollers. Then, rotation driving is resumed at a timing at which the sandwiched recording paper P can be synchronized with the four-color toner image on the intermediate transfer belt 16 in the above-described secondary transfer nip, and the recording paper P serving as a recording member is moved to the secondary transfer nip. Send out toward.

  The four-color toner image on the intermediate transfer belt 16 brought into close contact with the recording paper P at the secondary transfer nip is secondarily transferred onto the recording paper P under the influence of the secondary transfer electric field and the nip pressure. Combined with the white color of P, a full color toner image is obtained. The recording paper P having the full-color toner image formed on the surface in this manner is separated from the secondary transfer roller 20 and the intermediate transfer belt 16 by the curvature when passing through the secondary transfer nip. Then, the toner is fed into a fixing device 34 described later via a post-transfer conveyance path 33.

  The transfer residual toner that has not been transferred to the recording paper P adheres to the intermediate transfer belt 16 after passing through the secondary transfer nip. This is cleaned from the belt surface by a belt cleaning device 21 in contact with the front surface of the intermediate transfer belt 16. The cleaning backing roller 22 disposed inside the loop of the intermediate transfer belt 16 backs up the cleaning of the belt from the inside of the loop by sandwiching the intermediate transfer belt 16 with the belt cleaning device 21.

  The driving roller 18 has an elastic surface layer made of polyurethane rubber having a thickness of about 0.3 to 1 [mm] on the surface of a cylindrical or columnar roller portion. Due to the elastic deformation of the elastic surface layer, the intermediate transfer belt 16 is brought into close contact with the roller portion of the driving roller 18 to suppress belt slip on the driving roller 18. If the adhesion between the driving roller 18 and the intermediate transfer belt 16 can be sufficiently ensured, the elastic surface layer is made thinner (for example, about 0.05 to 0.1 mm), and the elastic surface layer due to temperature fluctuations is reduced. You may make it suppress the change of the diameter of the drive roller resulting from the fluctuation | variation in thickness, and the change of a belt moving speed by extension.

  As the intermediate transfer belt 16, a conductive material such as PVDF (vinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), TPE (thermoplastic elastomer) or the like is used. A resin film-like endless belt in which a conductive material is dispersed can be used. In the present embodiment, the intermediate transfer belt 16 is an endless belt having a single layer structure in which carbon black is added to PC and having a thickness of 140 [μm].

As the intermediate transfer belt 16, a belt having a volume resistivity in the range of 10 ⁸ to 10 ¹² [Ωcm] and a surface resistivity in the range of 10 ⁹ to 10 ¹² [Ω / □] is used. desirable. When the volume resistivity and surface resistivity of the intermediate transfer belt 16 exceed the upper limits of the above-described ranges, the belt is well charged and passes through the transfer nip within the formation range of the four primary transfer nips K to C. Charge up every time. In order to reduce the variation in electric field strength between the primary transfer nips due to the charge-up, individual primary transfer biases are applied to the primary transfer rollers 19K, Y, M, and C, respectively. The necessity arises, or it becomes necessary to provide a plurality of static elimination means, which causes an increase in cost. Further, when the volume resistivity and the surface resistivity are below the lower limits of the above ranges, the transfer current from the primary transfer rollers 19K, Y, M, and C flows not only in the belt thickness direction but also in the belt circumferential direction, This causes toner scattering in each primary transfer nip.

  The electrical resistance of the intermediate transfer belt 16 can be measured as follows. That is, a probe (inner electrode diameter 50 mm, ring electrode inner diameter 60 mm: JIS-K6911 compliant) is connected to a digital ultra-high resistance microammeter (manufactured by Advantest: R8340A), and 1000 V (surface resistivity) on the front and back of the intermediate transfer belt 16 Voltage of 500V) is applied. Then, the current value of the ammeter can be read under the conditions of discharge = 5 [sec], charge = 10 [sec], 22 ° C. and 55% RH, and the resistance value can be obtained based on the read result and the applied voltage. is there.

The secondary transfer roller 20 is obtained by coating the surface of a roller core made of metal such as stainless steel with an elastic surface layer made of an elastic material such as conductive urethane. This elastic surface layer has a resistance value adjusted to a range of 10 ⁶ to 10 ¹⁰ [Ω] by dispersion of the conductive material. If the resistance value of the elastic surface layer exceeds the upper limit of the above range, the secondary transfer current becomes difficult to flow between the secondary transfer roller 20 and the drive roller 18, so that a secondary for obtaining the required secondary transfer property is obtained. The transfer bias becomes a considerably high voltage, which causes an increase in power supply and running cost. Also, by applying a high voltage secondary transfer bias, discharge is caused at the secondary transfer nip exit or entrance gap, and white spot missing due to the discharge occurs on the halftone image. This is remarkable in a low-temperature and low-humidity environment (for example, 10 ° C. and 15% RH). On the other hand, if the resistance value falls below the lower limit of the above-described range, it is difficult to achieve both secondary transfer properties of a multi-color image portion (for example, a three-color superimposed image) and a single-color image portion existing on the same image. This is because the secondary transfer roller 20 has a resistance value that is too low, so that a secondary transfer current sufficient to transfer a monochrome image portion at a relatively low voltage flows, but a monochrome image is required to transfer a multicolor image portion. This is because a voltage value higher than the optimum voltage is required for the portion, and if the voltage is set to a voltage at which the multi-color image portion can be transferred, the transfer current becomes excessive in the single-color image and the secondary transfer efficiency is significantly reduced.

The electrical resistance of the secondary transfer roller 20 can be measured as follows. That is, the secondary transfer roller 20 is rotatably supported by a conductive metal plate, and a load of 4.9 [N] on one side (total of 9.8 N on both sides) is applied to both ends of the roller shaft. Then, the resistance value is obtained based on the value of the current that flows when a voltage of 1000 [V] is applied between the metal core and the metal plate in an environment of 22 ° C. and 55% RH. In the present embodiment, the secondary transfer roller 20 is a roller whose resistance value of the surface elastic layer is adjusted to 10 ^7.8 [Ω].

  The four primary transfer rollers 19K, Y, M, and C have the same configuration as the secondary transfer roller 20.

  The fixing device 34 forms a fixing nip by a fixing roller 34a containing a heat source such as a halogen lamp (not shown) and a pressure roller 34b that rotates while contacting the fixing roller 34a with a predetermined pressure. The recording paper P fed into the fixing device 34 is sandwiched between the fixing nips such that the unfixed toner image carrying surface is brought into close contact with the fixing roller 34a. Then, the toner in the toner image is softened by the influence of heating and pressurization, and the full color image is fixed.

  In this printer, the type information of the recording paper P accommodated in the paper feed cassette 30 is received and stored by an input operation to a numeric keypad or the like. Then, the process speed (the linear speed of the belt or the photoconductor) is changed according to the type information. For example, if the type of recording paper P is thick paper with a continuous weight of about 110 [Kg], the process linear speed is set to half the speed of plain paper, and the recording paper P passes through the fixing nip within 2 times of the plain paper. To. Thereby, the toner image can be reliably fixed even on the thick paper.

  The recording paper P discharged from the fixing device 34 passes through the post-fixing conveyance path 35 and then reaches the branch point between the paper discharge path 36 and the pre-reversal conveyance path 41. On the side of the post-fixing conveyance path 35, a switching claw 42 that is rotationally driven around a rotation shaft 42a is disposed. By the rotation, the vicinity of the end of the post-fixing conveyance path 35 is closed. Or open. At the timing when the recording paper P is sent out from the fixing device 34, the switching claw 42 stops at the rotational position indicated by the solid line in the drawing, and the vicinity of the end of the post-fixing conveyance path 35 is opened. Therefore, the recording paper P enters the paper discharge path 36 from the conveyance path 35 after fixing, and is sandwiched between the rollers of the paper discharge roller pair 37.

  When the single-sided print mode is set by an input operation to an operation unit including a numeric keypad (not shown) or a control signal sent from a personal computer (not shown), the recording sandwiched between the paper discharge roller pair 37 is set. The paper P is discharged out of the machine as it is. Then, it is stacked on the stack portion that is the upper surface of the upper cover 50 of the housing.

  On the other hand, when the duplex printing mode is set, the trailing edge of the recording paper P conveyed through the paper discharge path 36 while the front end is sandwiched between the paper discharge roller pair 37 passes through the post-fixing conveyance path 35. The switching claw 42 is rotated to the position of the one-dot chain line in the drawing, and the vicinity of the end of the post-fixing conveyance path 35 is closed. At substantially the same time, the paper discharge roller pair 37 starts to rotate in the reverse direction. Then, the recording paper P is conveyed while the rear end side is directed to the top, and enters the pre-reversal conveyance path 41.

  FIG. 1 shows the printer from the front side. The front side in the direction perpendicular to the drawing is the front side of the printer, and the back side is the rear side. In the drawing, the right side of the printer is the right side and the left side is the left side. The right end portion of the printer is a reversing unit 40 that can be opened and closed with respect to the housing body by rotating about a rotating shaft 40a. When the paper discharge roller pair 37 rotates in the reverse direction, the recording paper P enters the pre-reversal conveyance path 41 of the reversing unit 40 and is conveyed from the upper side to the lower side in the vertical direction. Then, after passing between the rollers of the pair of reverse conveying rollers 43, it enters the reverse conveying path 44 that is curved in a semicircular shape. Furthermore, while the upper and lower surfaces are reversed as the sheet is conveyed along the curved shape, the traveling direction from the upper side in the vertical direction to the lower side is also reversed, and conveyed from the lower side in the vertical direction toward the upper side. Is done. Thereafter, the toner enters the secondary transfer nip again through the above-described paper feed path 31. Then, after the full color image is collectively transferred to the other surface, the post-transfer conveyance path 33, the fixing device 34, the post-fixation conveyance path 35, the paper discharge path 36, and the paper discharge roller pair 37 are sequentially passed. And discharged outside the machine.

  The reversing unit 40 described above has an external cover 45 and a rocking body 46. Specifically, the external cover 45 of the reversing unit 40 is supported so as to rotate about a rotation shaft 40a provided in the housing of the printer main body. By this rotation, the outer cover 45 opens and closes with respect to the housing together with the swinging body 46 held therein. As shown by the dotted line in the figure, when the outer cover 45 is opened together with the swinging body 46 therein, the paper feed path 31 formed between the reversing unit 40 and the printer body side, the secondary transfer nip, and after the transfer. The conveyance path 33, the fixing nip, the post-fixing conveyance path 35, and the paper discharge path 36 are vertically divided into two and exposed to the outside. Thereby, jammed paper in the paper feed path 31, the secondary transfer nip, the post-transfer conveyance path 33, the fixing nip, the post-fixation conveyance path 35, and the paper discharge path 36 can be easily removed.

  The swing body 46 is supported by the external cover 45 so as to rotate about a swing shaft (not shown) provided in the external cover 45 in a state where the external cover 45 is opened. When the swinging body 46 is opened with respect to the external cover 45 by this rotation, the pre-reversal transport path 41 and the reverse transport path 44 are vertically divided into two and exposed to the outside. As a result, the jammed paper in the pre-reversal conveyance path 41 and the reversal conveyance path 44 can be easily removed.

  The upper cover 50 of the printer housing is supported so as to be rotatable about a rotation shaft 51 as indicated by an arrow in the drawing, and is rotated counterclockwise in the drawing to Opened. Then, the upper opening of the housing is greatly exposed to the outside. Thereby, the optical writing unit 71 is exposed. Then, by removing the optical writing unit 71, the four process units 1K, Y, M, and C are exposed and can be attached and detached.

  FIG. 3 is an enlarged configuration diagram showing a transfer unit 15 in a conventional feed side primary transfer nip type printer together with four photoconductors 2K, Y, M, and C. In the conventional printer, as shown in the figure, the cleaning blade 21a of the belt cleaning device 21 is brought into contact with a region downstream of the secondary transfer nip at the position where the intermediate transfer belt 16 is wound around the driving roller 18 in the belt moving direction. I was letting. However, in such a configuration, the cleaning position where the cleaning blade 21a and the intermediate transfer belt 16 abut is very close to the secondary transfer nip, so that the secondary transfer residual toner scraped off by the cleaning blade 21a is transferred to the secondary transfer nip. It becomes easy to mix in the nip. This mixing may cause toner contamination on the recording paper P. In particular, in the illustrated configuration in which the cleaning position is located vertically above the secondary transfer nip, the belt surface from the cleaning position to the secondary transfer nip exit descends along the curved surface of the drive roller 18 as shown in FIG. It becomes a gradient. Then, as indicated by an arrow A in the figure, the secondary transfer residual toner T in contact with the tip of the cleaning blade 21a falls down toward the secondary transfer nip along the downward gradient of the belt surface, so that the recording paper P Toner contamination is likely to occur.

Next, a characteristic configuration of the printer according to the embodiment will be described.
FIG. 5 is an enlarged configuration diagram showing the transfer unit 15 of the printer according to the present embodiment together with the four photoconductors 2K, Y, M, and C. As shown in the figure, in this printer, after passing through a position where the intermediate transfer belt 16 is circumferentially wound around the driving roller 18, the intermediate transfer belt 16 is positioned on the most upstream side in the belt moving direction with respect to the driving roller 18. The cleaning blade 21a is brought into contact with the area before entering the contact position with the K photoconductor 2K which is the most upstream image carrier. In such a configuration, the secondary transfer residual toner secondary transfer is performed by increasing the distance between the cleaning position where the intermediate transfer belt 16 and the cleaning blade 21a abut and the secondary transfer nip as compared with the conventional configuration shown in FIG. Reduces entry into the nip. As a result, it is possible to reduce the occurrence of toner contamination on the recording paper P due to the mixing of the secondary transfer residual toner into the secondary transfer nip.

  As the driving roller 18, a roller portion having a peripheral surface of a roller portion coated with an elastic layer having a thickness of 0.05 to 0.1 [mm] is used. Further, as the cleaning backing roller 22, a roller part made of a metal member having a diameter of 8 to 10 [mm] is used.

  In the present invention, the tension roller refers to a belt winding around the roller circumferential surface in a state in which all the front surface abutting members (for example, photoconductors) that abut on the front surface of the intermediate transfer belt 16 are removed. The rollers are arranged so that the angle is 90 [°] or more. Therefore, the four primary transfer rollers 19K, Y, M, and C and the secondary transfer backing roller 22 are in contact with the back surface of the intermediate transfer belt 16, but are not tension rollers that stretch the intermediate transfer belt 16. .

  Further, as the driven tension roller 17, a roller having the same diameter as that of the driving roller 18 is used. In such a configuration, the belt winding angle with respect to the driven tension roller 17 (the line segment connecting the belt winding start point on the roller circumferential surface and the roller center, and the line segment connecting the belt winding end point on the roller circumferential surface and the roller center) The angle formed is 180 [°]. Further, the belt winding angle with respect to the drive roller 18 is also 180 [°].

Next, printers according to the respective examples in which a more characteristic configuration is added to the printer according to the embodiment will be described.
[First embodiment]
FIG. 6 is an enlarged configuration diagram showing the transfer unit 15 of the printer according to the first embodiment together with the four photoconductors 2K, 2Y, 2M, and 2C. As shown in the figure, in this printer, the photosensitive member 2K for K, which is the most upstream image carrier, is pushed so that the extended portion of the driving roller 18 and the driven tension roller 17 on the intermediate transfer belt 16 is pushed inward of the belt loop. Is inserted into the belt loop. By encroaching in this way, the winding angle of the intermediate transfer belt 16 with respect to the drive roller 18 is increased as compared with the case of not encroaching. That is, in this printer, the winding angle of the belt around the driving roller 18 is larger than 180 [°] in the printer according to the embodiment. As a result, the adhesion between the driving roller 18 and the intermediate transfer belt 16 is enhanced, and belt slip on the driving roller 18 that is likely to occur due to the cleaning blade 21a being brought into contact with the belt moving side movement portion is prevented. Can be suppressed.

  Each roller disposed inside the loop of the intermediate transfer belt 16 includes a belt unit front plate (not illustrated) disposed on one end side in the width direction of the intermediate transfer belt, and a belt unit (not illustrated) disposed on the other end side. It is arranged between the rear side plate. Two moving brackets 151 are arranged between the belt unit front side plate and the belt unit rear side plate so as to be arranged at a predetermined distance in the belt width direction. Of the four primary transfer rollers 19K, Y, M, and C, three for Y, M, and C are rotatably supported by moving brackets 151 at the rotational axes at both ends in the axial direction. The two swing brackets 151 are supported by the belt unit front side plate and the belt unit rear side plate so as to be movable in the vertical direction. The printer is provided with a moving means (not shown) for moving the two swing brackets 151 in the vertical direction.

  In this printer, the combination of the moving means, the two swing brackets 151, the belt unit front side plate, and the belt unit rear side plate functions as a contact / separation means. Then, by this contact / separation means, the intermediate transfer belt 16 is made into a Y photoconductor 2Y as a Y image carrier, an M photoconductor 2M as an M image carrier, and a C photoconductor as a C image carrier. 2C. Specifically, in the figure, a state is shown in which these two swing brackets 151 have been moved to the upper limit point within the vertical movement range. In this state, the three primary transfer rollers 19Y, 19M, and 19C for Y, M, and C are a little with the stretched portion between the driving roller 18 and the driven stretching roller 17 on the intermediate transfer belt 16 facing upward. Push up. By this push-up, the intermediate transfer belt 16 contacts the Y, M, and C photoconductors 2Y, 2M, and 2C, and a primary transfer nip is formed. On the other hand, as shown in FIG. 7, when the swing bracket 151 is moved to the lower limit within the movable range in the vertical direction, the primary transfer rollers 19Y, 19M, 19Y for Y, M, and C are used. C does not push up the intermediate transfer belt 16. Then, the intermediate transfer belt 16 is separated from the Y, M, and C photoconductors 2Y, 2M, and 2C. As a result, the primary transfer nips for Y, M, and C are not formed.

  In this printer, the intermediate transfer belt 16 is stretched between a monochrome mode for forming a monochrome image composed of only K toner images and a multicolor mode for forming a multicolor image by superposing two or more toner images. It is supposed to be different. Specifically, in the multicolor mode, as shown in FIG. 6, the moving bracket 151 is moved to the upper limit point, and the intermediate transfer belt 16 is attached to all of the four photoconductors 2K, Y, M, and C. The printing operation is performed in the contact state. On the other hand, in the monochrome mode, as shown in FIG. 7, the moving bracket is moved to the lower limit point, and the intermediate transfer belt 16 is separated from the Y, M, and C photoconductors 2Y, 2M, and 2C. Perform printing operation with. As a result, regardless of the monochrome mode, the Y, M, and C photoconductors 2Y, 2M, and 2C that are not necessary for monochrome image formation are brought into contact with the intermediate transfer belt 16 so that the photoconductors and the intermediate transfer belt 16 are in contact with each other. Consumption can be avoided.

  In this printer, as described above, the K photoconductor 2K as the K image carrier is disposed as the most upstream image carrier, and only the photoconductor 2K out of the four photoconductors bites into the belt loop. It is This is for the reason explained below. That is, in the present printer, the intermediate transfer belt 16 is changed to the Y, M, and C photoconductors 2Y, M, and C by changing the tension posture of the intermediate transfer belt 16 by the movement of the moving bracket 151 as described above. Is close to and away from. In such a configuration, it is assumed that these three photoconductors 2Y, 2M, and 2C are also arranged so as to bite inside the belt loop. As a result, the intermediate transfer belt 16 cannot be brought into contact with or separated from the Y, M, and C photoconductors 2Y, M, and C unless the moving range of the moving bracket 151 in the vertical direction is significantly increased. From the range in which the tension of the intermediate transfer belt 16 can be changed, it is difficult to move the moving bracket 151 up and down within a considerably large range. Accordingly, it is difficult to bring the intermediate transfer belt 16 into and out of contact with the Y, M, and C photoconductors 2Y, M, and C. In contrast, in this printer, the Y, M, and C photoconductors 2Y, 2M, and 2C are arranged so as not to bite into the belt loop, and the belt is used in both the monochrome mode and the multicolor mode. Only the photosensitive member 2K for K which contacts is bitten. In such a configuration, the intermediate transfer belt 16 is easily brought into and out of contact with the Y, M, and C photoconductors 2Y, M, and C while increasing the winding angle of the belt with respect to the drive roller 18, and in the monochrome mode. It is possible to avoid unnecessary consumption of the photosensitive member and the belt.

  FIG. 8 is a schematic diagram for explaining a virtual common tangent in the transfer unit 15. In the drawing, the illustration of the intermediate transfer belt is omitted for convenience. In the figure, a two-dot chain line indicated by reference numeral L1 is a virtual common tangent line that contacts both the peripheral surface of the K photoconductor and the peripheral surface of the drive roller 18 as the most upstream image carrier. A two-dot chain line indicated by reference numeral L2 contacts both the peripheral surface of the drive roller 18 and the peripheral surface of the driven stretch roller 17 that is a stretch roller adjacent to the drive roller on the downstream side in the belt movement direction. Virtual common tangent.

  FIG. 9 is an enlarged schematic view showing the cleaning position in the transfer unit 15 and its surroundings in an enlarged manner. Also in the figure, the illustration of the intermediate transfer belt is omitted for convenience. In addition, in the drawing, for the sake of convenience, the circumferential surface of the cleaning backing roller 22 as a cleaning backing member is partially thickened, but the thickened portion is in contact with the intermediate transfer belt in the cleaning backing roller 22. It is a tangent. In this printer, as shown in the drawing, the contact portion is provided with a virtual common tangent L1 that is in contact with both the peripheral surface of the driving roller 18 and the peripheral surface of the photosensitive member for K (not shown) that is the most upstream image carrier. The layout is located between the peripheral surface of the roller 18 and the virtual common tangent L2 that contacts both the peripheral surface of the driven stretch roller 17 (not shown). This is for the reason explained below. In other words, if the cleaning backing roller 22 is arranged so as to bite toward the outside of the belt loop, the K photoconductor is bitten toward the inside of the belt loop to increase the belt winding angle with respect to the driving roller 18. Despite being, you can no longer make it bigger. Further, when the cleaning blade 21a is disposed so that the belt extending portion between the K photoconductor and the driving row 18 is further intruded toward the inner side of the belt loop, the surface of the belt moves toward the moving side of the belt. Excess pressure is applied by friction with the cleaning blade 21a that does not move. And it becomes easy to cause the slip of the belt on the driving roller 18 by applying an excessive pressure to the feeding side moving portion. By positioning the contact portion of the cleaning backing roller 22 with the intermediate transfer belt between the virtual common tangent L1 and the virtual common tangent L2, the K photoconductor is bitten inward of the belt loop. While increasing the belt winding angle with respect to the driving roller 18, it is possible to suppress the occurrence of belt slip due to excessive pressure applied by contact with the cleaning blade 21 a at the belt moving side movement position.

  In the present printer, as shown in FIG. 6, the entire area in the circumferential direction of the intermediate transfer belt 16 passes through the position where the intermediate transfer belt 16 is wound around the driving roller 18, and then the cleaning position which is in contact with the cleaning blade 21a. The region up to just before entering the position has an upward gradient from the cleaning position toward the wrapping position. In such a configuration, it is possible to avoid a situation in which the secondary transfer residual toner scraped off from the belt by the cleaning blade 21a is gravity dropped from the belt surface to the secondary transfer nip due to the downward gradient of the belt surface.

  In this printer, as the primary transfer rollers 19K, Y, M, and C for K, Y, M, and C, metal rollers whose roller peripheral surfaces are made of a metal material are used.

  FIG. 10 is an enlarged configuration diagram showing the transfer unit 15 in a modified apparatus of the printer. In this modified apparatus, a primary transfer bias is applied to the back surface of the intermediate transfer belt 16 by an indirect application method. In the indirect application method, as shown in the figure, primary transfer rollers 19K, Y, M, and C individually corresponding to the photoreceptors 2K, Y, M, and C are respectively disposed in the vicinity of the corresponding primary transfer nips. In addition, it is a method of contacting the back surface of the belt portion on the downstream side in the belt moving direction from the outlet of the primary transfer nip. In such an indirect application method, the center-to-center distance connecting the center of the photoconductor and the center of the primary transfer roller corresponding thereto is the sum of the radius of the photoconductor, the radius of the primary transfer roller, and the thickness of the intermediate transfer belt 16. Larger than the value. By adopting the indirect application method, the transfer dust at the nip entrance is generated even if the primary transfer rollers 19K, Y, M, and C use metal rollers that are cheaper than those coated with rubber on the surface. Can be difficult. Further, the length of the primary transfer nip can be increased and the primary transfer performance can be improved as compared with the direct application method in which the primary transfer roller is brought into contact with the belt portion on the back side of the primary transfer nip.

[Second Embodiment]
FIG. 11 is an enlarged configuration diagram showing the transfer unit 15 in the printer according to the second embodiment. In this printer, a driving roller 18 having a diameter larger than that of a driven stretching roller 17 that is another stretching roller that stretches the intermediate transfer belt 16 is used. In such a configuration, as shown in the figure, even if the K photoconductor 2K, which is the most upstream image carrier, is not disposed in the belt loop, it is 180 [° with respect to the drive roller 18. ], The intermediate transfer belt can be wound at a larger winding angle than the above, and belt slip on the driving roller 18 can be suppressed.

  As described above, in the printer according to the first embodiment, the K photoconductor, which is the most upstream image carrier, is bitten into the belt loop so that the extended portion of the intermediate transfer belt 16 is pushed toward the belt loop. It is arranged. In this configuration, for the reasons described above, the adhesion between the driving roller 18 and the intermediate transfer belt 16 is improved, and the driving roller 18 that is likely to be generated by bringing the cleaning blade 21a into contact with the moving side movement portion of the belt. Belt slip on the top can be suppressed.

  In the printer according to the first embodiment, as a plurality of image carriers, a Y photoreceptor 2Y as a Y image carrier for carrying a yellow toner image and a magenta toner image are carried. An M photoconductor 2M as an M image carrier, a C photoconductor 2C as a C image carrier for carrying a cyan toner image, and a K image carrier K as a black image. And a photosensitive member 2K. Further, contact / separation means for contacting / separating the intermediate transfer belt 16 with the Y, M, C photoconductors 2Y, M, C is provided. In this configuration, for the reasons described above, the intermediate transfer belt 16 is separated from the Y, M, and C photoconductors 2Y, 2M, and 2C in the monochrome print mode, so that the photoconductor and the intermediate transfer belt 16 are wasted. It can be avoided.

  In the printer according to the first embodiment, the K photoconductor 2K is disposed as the most upstream image carrier, and only the K photoconductor 2K out of the four photoconductors bites into the belt loop. It is In such a configuration, the intermediate transfer belt 16 is easily brought into and out of contact with the photoreceptors 2Y, M, and C for Y, M, and C while increasing the belt winding angle with respect to the drive roller 18 for the reason described above. Thus, it is possible to avoid wasteful consumption of the photoreceptors and belts in the monochrome mode.

  In the printer according to the second embodiment, the driving roller 18 is larger in diameter than the driven tension roller 17 that is another tension roller that stretches the intermediate transfer belt 16. In such a configuration, for the reasons described above, the intermediate transfer belt has a winding angle greater than 180 [deg.] With respect to the drive roller 18 without having to arrange the most upstream image carrier toward the inner side of the belt loop. To prevent the belt from slipping on the driving roller 18.

  Further, in the printers according to the first and second embodiments, the winding angle of the intermediate transfer belt 16 with respect to the driving roller 18 is larger than 180 [°], so that it is 180 [°] or less. As compared with this, the slip of the belt on the driving roller 18 can be suppressed.

  Further, in the printer according to the first embodiment, each of the plurality of photosensitive members uses a cylindrical one. Further, a cleaning backing roller 22 is provided as a cleaning backing member that sandwiches the intermediate transfer belt 16 between the intermediate transfer belt 16 and a cleaning blade 21a as a belt cleaning member while being in contact with the back surface of the intermediate transfer belt 16. Then, a virtual common tangent line in which the contact portion between the back surface of the intermediate transfer belt 16 and the cleaning backing roller 22 is in contact with both the peripheral surface of the K photoconductor 2K and the peripheral surface of the driving roller 18 as the most upstream image carrier. Positioned between L1 and the virtual common tangent L2 that contacts both the peripheral surface of the drive roller 18 and the peripheral surface of the driven stretch roller 17 that is a stretch roller adjacent to the drive roller on the downstream side in the belt movement direction. It has a layout to let you. In such a configuration, for the reasons described above, the K photoconductor is bitten inward of the belt loop to increase the belt winding angle with respect to the driving roller 18, and the belt is brought into contact with the cleaning blade 21a at the moving side of the belt. It is possible to suppress the occurrence of belt slip due to excessive pressure applied by.

  In the printer according to the first embodiment, the entire area of the intermediate transfer belt 16 in the circumferential direction passes through the position where the intermediate transfer belt 16 is wound around the drive roller 18 and then reaches the cleaning position which is the contact position with the cleaning blade 21a. The area up to just before entering is an upward gradient from the cleaning position toward the hanging position. In such a configuration, it is possible to avoid a situation in which the secondary transfer residual toner scraped off from the belt by the cleaning blade 21a is gravity dropped from the belt surface to the secondary transfer nip due to the downward gradient of the belt surface.

  In the modified apparatus of the printer according to the first embodiment, a plurality of primary transfer rollers 19K, Y, M, and C individually corresponding to the plurality of photoconductors 2K, Y, M, and C are provided respectively. An indirect application method is employed in which the belt is brought into contact with the back surface of the belt portion in the vicinity of the corresponding primary transfer nip and on the downstream side in the belt movement direction from the outlet of the primary transfer nip. In such a configuration, the length of the primary transfer nip is increased compared to the direct application method in which the primary transfer rollers 19K, Y, M, and C are brought into contact with the belt portion on the back side of the primary transfer nip. Performance can be improved. Further, even when a metal roller that is cheaper than the surface of the primary transfer roller 19K, Y, M, or C coated with rubber or the like is used, transfer dust at the nip entrance can be made difficult to occur.

  Further, in the modified apparatus of the printer according to the first embodiment, the plurality of primary transfer rollers 19K, Y, M, and C each have a roller peripheral surface made of a metal material. The cost can be reduced as compared with the case of using a material coated with the like.

1 is a schematic configuration diagram illustrating a printer according to an embodiment. FIG. 3 is an enlarged configuration diagram illustrating a process unit for K in the printer. FIG. 6 is an enlarged configuration diagram showing a transfer unit in a conventional feed-side primary transfer nip type printer together with four photoconductors. FIG. 6 is an enlarged schematic view showing a cleaning position and its surroundings in a transfer unit of a conventional feed side primary transfer nip type printer. FIG. 3 is an enlarged configuration diagram illustrating a transfer unit of the printer according to the embodiment together with four photosensitive members. FIG. 3 is an enlarged configuration diagram illustrating a transfer unit of the printer according to the first embodiment together with four photosensitive members. FIG. 3 is an enlarged configuration diagram partially showing the transfer unit in a state where a moving bracket is moved to a lower limit point. The schematic diagram for demonstrating the virtual common tangent in the transfer unit. FIG. 3 is an enlarged schematic diagram showing an enlarged view of a cleaning position and its periphery in the transfer unit. FIG. 7 is an enlarged configuration diagram illustrating a transfer unit in a modified apparatus of the printer according to the first embodiment together with four photosensitive members. FIG. 9 is an enlarged configuration diagram illustrating a transfer unit in a printer according to a second embodiment together with four photoconductors.

Explanation of symbols

1K, Y, M, C: Process unit (part of toner image forming means)
2K, Y, M, C: photoconductor (image carrier)
5K, Y, M, C: developing device (part of toner image forming means)
16: Intermediate transfer belt 17: Driven stretch roller (stretch roller)
18: Drive roller 19K, Y, M, C: Primary transfer roller 20: Secondary transfer roller (secondary transfer contact member)
21: Belt cleaning device 21a: Cleaning blade (cleaning member)
70: Optical writing unit (part of toner image forming means)
P: Recording paper (recording member)

Claims (10)

An endless intermediate transfer belt that is endlessly moved by rotation of the driving roller while being stretched by a stretching roller and a driving roller;
Of the entire area in the circumferential direction of the intermediate transfer belt, the area from passing through the position where the intermediate roller is wound to the position immediately before entering the position where the roller is disposed next to the driving roller A plurality of image carriers that form a primary transfer nip in contact with the belt portion in the region while being arranged along the line,
Toner image forming means for forming a toner image on these image carriers;
A secondary transfer abutting member that forms a secondary transfer nip by abutting from the front surface side of the belt on the intermediate transfer belt with respect to the driving roller;
A belt cleaning member for cleaning secondary transfer residual toner adhering to the front surface of the intermediate transfer belt,
The toner image formed on the surface of each image carrier is primarily transferred onto each intermediate transfer belt by superimposing on each intermediate transfer nip, and then secondarily transferred to a recording member in the secondary transfer nip. In the image forming apparatus,
Of the entire area in the circumferential direction of the intermediate transfer belt, the most upstream image, which is an image carrier located on the most upstream side in the belt moving direction with respect to the driving roller after passing through the winding position with respect to the driving roller. An image forming apparatus, wherein the belt cleaning member is disposed so as to clean a belt portion in an area immediately before entering a contact position with a carrier. The image forming apparatus according to claim 1.
An image forming apparatus characterized in that the most upstream image carrier is disposed inside the belt loop so as to push the extended portion of the intermediate transfer belt toward the inside of the belt loop. The image forming apparatus according to claim 2.
As the plurality of image carriers, a Y image carrier for carrying a yellow toner image, an M image carrier for carrying a magenta toner image, and a C image carrier for carrying a cyan toner image And a K image carrier for carrying a black toner image, and contact / separation means for bringing the intermediate transfer belt into contact with and separating from the Y image carrier, M image carrier and C image carrier. An image forming apparatus provided. The image forming apparatus according to claim 3.
The K image carrier is arranged as the most upstream image carrier, and only the K image carrier among the plurality of image carriers is bitten inside the belt loop, or in the K image carrier. An image forming apparatus characterized in that the amount of biting into the belt loop is larger than that of other image carriers. The image forming apparatus according to claim 1.
An image forming apparatus using a driving roller having a larger diameter than other stretching rollers that stretch the intermediate transfer belt. The image forming apparatus according to any one of claims 2 to 5,
An image forming apparatus, wherein a winding angle of the intermediate transfer belt with respect to the driving roller is set to be larger than 180 [°]. The image forming apparatus according to claim 1,
As the plurality of image carriers, cylindrical or columnar ones are used, and a cleaning backing member is provided that sandwiches the intermediate transfer belt with the belt cleaning member while contacting the back surface of the intermediate transfer belt, A contact portion between the back surface of the intermediate transfer belt and the cleaning backing member, a virtual common tangent line that contacts both the peripheral surface of the most upstream image carrier and the peripheral surface of the drive roller, and the periphery of the drive roller. An image forming apparatus characterized in that the layout is located between a surface and a virtual common tangent line that is in contact with both of the peripheral surfaces of adjacent stretching rollers on the downstream side in the belt movement direction with respect to the driving roller. The image forming apparatus according to claim 1,
Of the entire region in the circumferential direction of the intermediate transfer belt, the region from the contact position to the point immediately before entering the contact position with the belt cleaning member after passing through the contact position with the drive roller is applied from the contact position. An image forming apparatus having an ascending gradient toward a position. The image forming apparatus according to claim 1,
A plurality of primary transfer rollers individually corresponding to the plurality of image carriers are respectively arranged in the vicinity of the corresponding primary transfer nip and on the downstream side in the belt movement direction from the outlet of the primary transfer nip. An image forming apparatus, wherein the image forming apparatus is in contact with the back surface of the image forming apparatus. The image forming apparatus according to claim 9.
An image forming apparatus, wherein each of the plurality of primary transfer rollers has a roller peripheral surface made of a metal material.

Images