JP2007010920A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of forming a high quality image without disturbing unfixed images on both sides of a recording medium. <P>SOLUTION: The image forming apparatus holds a first image from a first image forming unit 60 onto a first image carrier belt 21 and holds a second image from a second image forming unit 61 onto a second image carrier belt 31. The image forming apparatus comprises a first transfer station and a second transfer station including a first transfer means 46 and a second transfer means 47 respectively for transferring the first image and the second image to the first side and second side, respectively, of a recording medium P. The image forming apparatus also comprises a recording medium transfer means 50 including: a recording medium conveyance path 43A for supplying and conveying the recording medium P between the first and second transfer stations; and a conveyance belt 51 for conveying the recording medium P to a heat fixing device 63, which fixes the images on both sides of the recording medium P exited from the second image carrier unit 30. In the image forming apparatus, the recording medium transfer means 50 has a conveying part that is longer than the maximum image. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus including a fixing device that transfers a toner image formed on a photoreceptor to a recording material such as transfer paper and fixes the transferred toner image.

In electrophotographic image forming apparatuses such as copiers, printers, and facsimile machines, as a method for recording images on both front and back sides of transfer paper (recording body), transfer paper that has received image transfer and fixing on one side in the image forming unit In general, a method is used in which toner is transferred to another surface of a transfer sheet and fixed when the sheet is reversed without being discharged and fed to the image forming unit again (see, for example, Patent Documents 1 to 3). ).
However, in the above conventional double-sided recording method, curling occurs on the transfer paper when the transfer direction of the transfer paper is switched or once the transfer paper is heated and pressurized through the fixing device, thus ensuring transport reliability. Have many issues.
As a method for solving such a problem, for example, in Patent Document 1, after a toner image is transferred and formed on both sides of a transfer sheet, unfixed toner images formed on both sides by a single fixing operation are collectively displayed. A configuration for fixing is disclosed.
Specifically, the first image formed on the photoconductor is transferred to the transfer belt by the first transfer unit, and then the second image formed on the photoconductor is transferred to one side of the transfer paper by the first transfer unit. Transcript to. Thereafter, the first image on the transfer belt is transferred to the other side of the transfer paper by the second transfer means, whereby the image is transferred to both sides of the transfer paper, and then passed through the fixing device and fixed.
However, in the method of Patent Document 1, since the leading edge of the transfer paper carrying an unfixed image on both sides is unloaded from the transfer belt until the leading edge of the transfer paper is unloaded. The toner image is disturbed.
On the other hand, in Patent Document 2, a toner image is transferred to both sides of a transfer paper, and then the transfer paper is transported to a fixing device. A spur is installed in the transport path to prevent the unfixed toner image from being disturbed. ing.
However, in this case, the spur that conveys the transfer paper carrying the unfixed toner image to the fixing device becomes soiled with toner over time, and the spur toner moves to the transfer paper, resulting in degradation of image quality. I will let you. In addition, if the vertical conveyance is adopted for the purpose of downsizing, the result is that the conveyance quality is further deteriorated due to the strength of the recording medium.
JP-A-1-209470 Japanese Patent Laid-Open No. 10-142869

However, in a conventional image forming apparatus having a configuration in which an image is sequentially transferred onto each side of a transfer sheet and then conveyed to a fixing device to fix the unfixed images on both sides at once, the unfixed images on both sides are transferred. The image could not be conveyed to the fixing unit without being disturbed or causing image deterioration.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of forming a high-quality image without disturbing unfixed images on both sides by transporting a recording medium in close contact with a transport unit to a fixing nip of the fixing apparatus. It is to provide.

In order to solve the above-described problems, the invention described in claim 1 includes a first image carrying unit for carrying a first image from the first image forming unit on a first image carrying belt, and a second image forming unit. A second image carrying unit for carrying the second image on the second image carrying belt, and a first transfer means for transferring the first image carried by the first image carrying unit to the first surface of the recording medium. A first transfer station including: a second transfer station including a second transfer means for transferring the first image carried by the second image carrying unit onto a second surface of the recording medium; and A recording medium conveyance path for supplying and conveying the recording medium between the second transfer stations, and a conveyance belt for conveying the recording medium to the heat fixing device for fixing the images on both sides of the recording medium that has exited the second image carrier unit. Record transfer An image forming apparatus comprising means, wherein the length of conveyance of said recording medium conveying means is a maximum image length or more.
According to a second aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the conveying belt of the recording medium conveying unit is configured in an endless belt shape.
According to a third aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the conveying belt of the recording medium conveying means is a heat-resistant belt.
According to a fourth aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the conveying belt made of the recording material transport means is made of polyimide.

According to a fifth aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein a volume resistance value of the conveying belt of the recording material transporting unit is 10 ⁶ to 10 ¹² Ωcm.
According to a sixth aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the thickness of the conveying belt of the recording medium conveying means is 50 to 600 [mu].
According to a seventh aspect of the present invention, there is provided a paper feeding device capable of supplying the recording medium from substantially the same paper supply surface as the recording medium conveyance path upstream of the recording medium conveyance direction in the recording medium conveyance path. An image forming apparatus according to claim 1.
According to an eighth aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the recording material conveyance path is substantially the same surface from the paper feeding surface of the paper feeding unit to the fixing nip.
According to a ninth aspect of the present invention, in the first transfer station and the second transfer station, the first intermediate transfer belt and the second intermediate transfer belt are not in contact with each other, and the transfer is arranged in each transfer station. The image forming apparatus according to claim 1, wherein a transfer roller to which a bias can be applied is adopted as a transfer unit provided upstream in the recording material conveyance direction.

  According to the present invention, in order to obtain a high-quality print, the recording medium conveying means has the length of the conveying section that is equal to or greater than the maximum image length, so both sides of the recording medium that has exited the second image carrier unit. Therefore, it is possible to provide an image forming apparatus capable of obtaining high image quality without disturbing the image because the image is not put into the fixing nip until the transfer of both sides is completed and the image is not separated from the conveying belt to the fixing unit. .

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The configuration and operation of the embodiment according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic central sectional view showing an internal configuration of an image forming apparatus to which the present invention is applied. FIG. 2 is a schematic view showing the vicinity of the recording material transport means. FIG. 3 is a schematic diagram showing a simplified arrangement of the image carrier belt in FIG.
In the image forming apparatus main body 6 shown in FIG. 1, a first image carrier 21 is provided with a first image carrier belt 21 that moves endlessly in the direction of the arrow at the upper part of the recording material conveyance path 43A extending in a substantially horizontal direction. A second image carrier unit 30 provided with a second image carrier belt 31 that moves the body unit 20 endlessly in the direction of the arrow is provided below.
Four first image forming units 60Y, 60C, 60M, and 60K are arranged adjacent to the upper tension surface of the first image carrier belt 21, and four tilted tension surfaces of the second image carrier belt 31 have four. The second image forming units 61Y, 61C, 61M and 61K are arranged adjacent to each other.
Y, C, M, and K attached to the numbers of the first and second image forming units 20 and 30 correspond to the colors of the toner to be handled, Y is yellow, C is cyan, M is magenta, K means black.
Y, C, M, and K are attached to the first and second image forming units 20 and 30 and the photosensitive member 1 that rotates together with the first image carrying belt 21 and the second image carrying belt 31 has the same meaning. ing. The photoreceptors 1Y to 1K are arranged at the same interval, and at least at the time of image formation, are in contact with a part of the stretched portion between the first and second image carrying belts 21 and 31, respectively.
The operation / display unit 9 provided on the upper surface of the image forming apparatus 6 includes a keyboard and the like. By inputting conditions for image formation using the keyboard and the like, the state of the apparatus and the like are displayed on the display unit, and information exchange between the operator and the image forming apparatus is facilitated. Reference numeral 7 denotes a document reading device, and 8 denotes a paper feeding device that can be additionally installed.
The waste toner storage unit 49 provided in the image forming apparatus 6 is connected to the cleaning device 2 of the image forming units 60 and 61 and the cleaning devices 20A and 30A of the image carrying belt. Collect and store foreign material.
Since the cleaning device (2, 20A, 30A) does not include a large-capacity waste toner storage unit, each cleaning device can be reduced in size, and the waste toner disposal operability is also good.
A full sensor (not shown) is used to issue a warning such as toner disposal in the waste toner storage unit or container replacement. In the electrical / control device 48 provided in the image forming apparatus 6, various power supplies, control boards, and the like are protected and housed in a sheet metal frame.
The surface of each photoconductor is subjected to a discharging operation of residual potential by the discharging device Q (FIGS. 4 and 5) to prepare for the next image forming / transferring step. The removed foreign matters such as toner and paper dust are sent to the collection unit 49 by the collection unit 2c.

As shown in FIG. 2, the recording medium P that has passed through the second transfer station is extended to the fixing nip N in the heat fixing device 63 provided downstream in the conveyance direction of the recording medium P on the extension of the recording medium conveyance path 43A. In addition, a recording medium transporting means 50 is provided for transporting while maintaining a flat state.
1 and 2, the recording medium transport means 50 is provided to prevent deterioration of the image transferred to the recording medium P before the fixing process, and supports rollers 52 that support a conveyor belt 51 that moves endlessly in the direction of the arrow. 53, 54, 55, and 56. Since the recording body P can be conveyed to the fixing device 63 in a stacked state without being separated from the second image carrier 31, image deterioration before the fixing process can be prevented.
Outside the conveying belt 51, a cleaning device 50 </ b> A is opposed to the roller 55, an adsorption charger 57 is arranged to adsorb the recording medium P to be opposed to the roller 56, and a static elimination / separation charger 58 is opposed to the roller 54. ing.
The functions of the conveying belt supporting rollers 52 to 56 described above will be described. 52 is a receiving roller, 53 is a supporting roller, 54 is a separation / charger facing roller, 55 is a cleaning backing roller, and 56 is a driven roller.
In order to eliminate the guide plate between the fixing nip N and the recording material transporting means 50, the recording material transporting means 50 is brought close to the fixing device 63. For this purpose, the conveying belt 51 of the recording material transport means 50 is a heat-resistant belt. As a result, since it is not affected by heat from fixing, it is possible to have a configuration in which the recording medium transport means 50 is brought close to the fixing device 63, and a configuration in which a guide plate is unnecessary is possible.

The conveyance belt 51 that moves together with the recording medium P in contact with the unfixed toner image is negatively charged by the suction charger 57 with the same polarity as the toner. The conveyance belt 51 of the recording medium transporting unit 50 has a resistance value, and an electric charge is applied to the conveyance belt 51, whereby the recording medium P can be electrically held and can be conveyed in close contact with the conveyance belt 51.
A polyimide belt can be adopted as the transport belt 51. The surface is provided with a releasability from the toner and has a chargeable resistance value. Further, the thickness of the conveying belt 51 of the recording material transporting unit 50 can be set to 50 to 600 μm, so that a belt configuration can be obtained. The traveling speed of the conveying belt 51 is matched with the traveling speed of the recording material P in the heat fixing device 63.
A fixing device 63 having a heating unit and including a heating roller 63a and a pressure roller 63b is provided on the downstream side of the recording medium transporting unit 50 in the recording medium conveyance direction. A type having a heater inside the roller, a belt fixing device that runs a heated belt, a fixing device that employs induction heating as a heating method, and the like can be employed.

In this embodiment, the belt is run, and heaters H1 and H2 are arranged as heating elements on the belt conveyance roller. In order to make the color tone and glossiness of the images on both sides of the recording medium the same, the material, hardness, surface properties, etc. of the fixing roller and fixing belt are made equal in the vertical direction.
A cooling roller pair 62 having a cooling function is provided in the conveyance path after fixing in order to cool the recording medium after fixing and stabilize the unstable toner state at an early stage. A heat pipe structure roller having a heat radiating portion can be employed.
The cooled recording medium is discharged and stacked on a discharge stack portion 59 provided on the left side of the image forming apparatus 6 by a discharge roller pair 64. The discharge stacking unit 59 employs a mechanism in which a receiving member 59a is moved up and down in accordance with a stack level by an elevator mechanism (not shown) so that a large amount of sheets can be stacked.
Note that it is also possible to transport the sheet toward another post-processing apparatus through the sheet discharge stack unit 59. As another post-processing apparatus, an apparatus for bookbinding such as punching, cutting, folding, and binding can be cited.
The toner cartridges 66Y, 66C, 66M, and 66K for each color in which unused toner is stored are detachably stored in the space 65. Toner is supplied to each developing device as necessary by a toner conveying means (not shown).

In the configuration of the present embodiment, the toner cartridge is common to the image forming units 60 and 61 arranged above and below, but can be separated. The toner cartridge 66K for black toner that is highly consumed can be set to have a particularly large capacity. The storage space 65 is on the back side when viewed from the operation direction on the top surface of the image forming apparatus 6, and a plane portion is secured on the near side of the top surface of the image forming apparatus 6, so that it can be used as a work table.
The operation / display unit 9 provided on the upper surface of the image forming apparatus 6 is provided with a keyboard and the like. The conditions for image formation can be input, and the state of the apparatus is displayed on the display unit. Information exchange with the image forming apparatus 6 is facilitated.
The waste toner container 49 provided in the image forming apparatus 6 is connected to the image forming unit cleaning device 2 (FIGS. 4 and 5), the image bearing belt cleaning devices 20A and 30A, and the conveying belt 51 cleaning device 50A. Collects and stores foreign particles such as waste toner and paper dust all at once.
Since the cleaning devices (2, 20A, 20B, and 50A) do not include a large-capacity waste toner storage unit, each cleaning device can be reduced in size, and the waste toner disposal operability is good.
A full sensor (not shown) can be used to issue a warning such as toner disposal in the waste toner container 49 or container replacement. In the electrical / control device 48 provided in the image forming apparatus 6, various power supplies, control boards, and the like are protected and housed in a sheet metal frame.
The inside of the image forming apparatus 6 becomes hot due to heat from the heat fixing device 63 or heat generated from the electrical device. However, as a countermeasure against this, a fan F is provided to prevent deterioration of the function due to heat of the internal members.
The fan F is coupled to the heat radiating portion of the cooling roller pair 62 to ensure the cooling effect of the cooling roller pair 62. Reference numeral 7 denotes a document reading device, and 8 denotes a paper feeding device that can be additionally installed.
As described above, the photoconductors 1Y to 1K are arranged at the same interval, and at least at the time of image formation, are in contact with a part of the stretched portion between the image bearing belts 21 and 31, respectively. This contacting surface is called an image receiving surface, and the positional relationship is shown in a schematic diagram showing the arrangement of the image carrier belt in FIG.

In FIG. 3, the positional relationship between the first image carrier belt 21 and the second image carrier belt 31 is as shown in the drawing with the recording material conveyance path 43A interposed therebetween. )) Can be secured large. In other words, since the conveyance surface of the recording medium conveyance path 43A and the sheet supply surface from the sheet supply device are configured to be substantially the same level, the sheet supply device is increased to increase the height of the sheet supply device. can do.
As described above, the first image forming unit 60 (Y, C, M, K) is placed on the upper stretched surface of the first image carrier belt 21 of the first image carrier unit 20 and the second image carrier belt 31. The second image forming unit (Y, C, M, K) of the second image carrier unit 30 is disposed on the inclined tension surface.

FIG. 4 is an enlarged view showing a configuration of a first image forming unit which is one main part for image formation. In the first image carrier unit 20, although the color of the toner to be handled is different, the configurations of the first image forming units 60Y, 60C, 60M, and 60K are the same, so the configuration of the first image forming unit 60 will be described as a representative. To do.
In FIG. 4, the cylindrical photosensitive member 1 is rotatably supported so as to rotate in the direction of the arrow by a drive source (not shown) during the operation of the image forming apparatus 6 (FIG. 1). Around the photosensitive member 1, an image forming member such as a scorotron charger 3, an exposure device 4, a developing device 5, a cleaning device 2 and a photostatic device Q, which are charging means according to an electrostatic photographic process, a potential sensor S1, an image A sensor S2 is provided.
The photoreceptor 1 is formed by forming an organic photosensitive layer (OPC), which is a photoconductive substance, on an aluminum cylinder surface having a diameter of about 30 to 120 mm, for example. A photoconductor on which an amorphous silicon (a-Si) layer is formed can also be used.
A belt-like photoreceptor can also be employed. The cleaning device 2 includes a cleaning brush 2a, a cleaning blade 2b, and a recovery member 2c, and removes and recovers foreign matters such as toner remaining on the surface of the photoreceptor.
The exposure device 4 scans light corresponding to image data for each color on the surface of each photosensitive member 1 that has been uniformly charged by the charging unit 3 to form an electrostatic latent image. The exposure apparatus 4 in the illustrated example is an exposure apparatus that includes an LED (light emitting diode) array and an imaging element as light emitting elements.
However, it is also possible to employ a laser scanning type exposure apparatus that uses a laser light source, a polygon mirror, or the like and uses a beam of light modulated in accordance with image data to be formed. As the charging means, in addition to the scorotron charger 3, a type that contacts the surface of the photoreceptor 1, for example, a charging roller can be employed.

The development in the present embodiment is a development system that employs a two-component developer composed of toner and carrier. The electrostatic latent image for each color formed on the surface of each photoconductor 1 by a laser beam with respect to the negatively charged photoconductor 1 is made of toner of a predetermined color having the same polarity (negative polarity) as the photoconductor 1 and the charging polarity. Developed to become a visible image. So-called reversal development is performed.
When each color toner of yellow (Y), cyan (C), magenta (M), and black (K) is consumed by the developing device that handles each color, the consumption amount is detected by the magnetic-permeable toner detecting means 5e. . As a result, as shown in FIG. 1, toner of each color is supplied to each developing device 5 from a toner cartridge 66 provided in the toner cartridge housing portion 65 inside the image forming apparatus 6 by a supply unit (not shown).
As this supply means, a system using a known MONO pump can be adopted. According to this method, there are few restrictions on the installation location of the toner cartridge, which is advantageous for space allocation in the image forming apparatus. Further, since the toner can be replenished in a timely manner, it is not necessary to provide a large toner storage space in the developing device 5, and the developing device 5 can be downsized.
The developing device 5 is provided with screws 5c and 5d for stirring and conveying the toner and the carrier. When the developing device 5 is mounted on the image forming apparatus 6, one end of the toner replenishing means is connected to a part of the screw 5d.
The toner is supplied to the developing roller 5a that rotates in the direction of the arrow by the screw 5c, and the thickness of the toner layer on the surface of the developing roller 5a is restricted to a predetermined thickness by the blade 5b.
The developing roller 5a is a cylinder made of stainless steel or aluminum, and is supported by the frame of the developing device 5 so as to be rotatable and a distance from the photoreceptor 1 is properly secured, and a predetermined magnetic force line is formed inside. A magnet (not shown) is provided.
The potential sensor S1 and the image sensor S2 detect whether or not the surface potential after exposure on the surface of the photoconductor and the density of the toner adhering to the surface of the photoconductor after the development process are appropriate. Information is sent to control means (not shown) for setting and controlling image forming conditions.

As the toner, a spherical or irregular toner obtained by a conventionally known method is used. The volume average particle diameter is 20 μm or less, preferably 10 μm or less and 4 μm or more. A carrier obtained by a conventionally known method is also used. As the particle size of the carrier, the volume average particle size is about 25 μm to 60 μm.
The average circularity of the toner used is 0.90 to 0.99. In particular, in order to obtain a high image quality, toner spheronization is required. Since the toner spheronization has a small contact area with the transfer paper, it greatly affects the transfer paper transfer and requires improvement.
It is important that the toner has a specific shape and shape distribution. With an irregularly shaped toner having an average circularity of less than 0.90 and separated from a sphere, satisfactory transferability and high image quality without dust cannot be obtained.
Further, when the average circularity exceeds 0.99, in a system employing blade cleaning or the like, a cleaning failure occurs on the photosensitive member or the transfer belt, causing stain on the image.
The shape factor SF-1 of the toner to be used can be set to 120 to 180, and the shape factor SF-2 can be set to 120 to 190. Further, Dv / Dn of the toner to be used can be set to 1.05 to 1.30.
In the present invention, the toner used has a Dv (volume average particle diameter) / Dn (number average particle diameter) of 1.05 to 1.30. Here, Dv is a volume average particle diameter (μm), and Dn is a number average particle diameter (μm).
When Dv / Dn is smaller than 1.05, the two-component developer is used as a one-component developer because the toner is fused to the surface of the carrier during a long period of stirring in the developing device, and the charging ability of the carrier is lowered. In this case, filming of the toner on the developing roller or fusing of the toner to a member such as a blade for thinning the toner is easily generated. The same applies when Dv / Dn is greater than 1.30.
Further, when Dv / Dn is smaller than 1.05, it is preferable from the viewpoint of stabilizing the behavior of the toner and making the charge amount uniform. However, it is difficult to separate the functions depending on the toner particle diameter, such as developing the fine line portion with small size particles, while developing the solid image mainly with large size particles.

FIG. 5 is an enlarged view showing a configuration of a second image forming unit which is the other main part for image formation. The second image forming units 61Y to 61K used in the second image carrier unit 30 will be described as a second image forming unit 61 as a representative with reference to FIG.
The second image forming unit 61 shown in FIG. 5 has the same constituent members as the first image forming unit 60, but the rotational direction of the photosensitive member 1 is different from that of FIG. However, they are symmetrical to each other with respect to the y-axis passing through the rotation axis 1a of the photosensitive member 1 indicated by an arrow in the drawing.
This shape is an important matter although it is related to the arrangement of image forming members provided around the photoreceptor 1. In other words, the first image forming units 60Y to 60K can be combined with a coupling unit with the image forming apparatus 6, for example, a coupling unit with a driving unit, an electrical connection unit, a toner supply unit, and a toner discharge unit. The second image forming units 61Y to 61K can be compatible.
Therefore, it is not necessary to manufacture the developing device, the cleaning device, and the parts individually for the first image forming unit 20 and the second image forming unit 30, and the efficiency in manufacturing parts and managing parts is high. Cost reduction can be achieved.
The first condition that can be used in the first image carrier unit 20 and the second image carrier unit 30 in an axisymmetric form with the first and second image forming units 20 and 30 as the center of the y-axis is photosensitive That is, a peripheral surface in which no member for image formation is provided around the body 1 is secured.
That is, a wide range in which the image carrying belt can come into contact is secured, and the second condition is that the arrangement angle of the first image carrying belt 21 and the second image carrying belt 31 is appropriate. .

The first condition and the second condition will be described with reference to FIGS. 4 or 5, the image bearing belt 21 or 31 can be installed between the arrows A1 and A2. That is, the A1 side is the developing device 5, and the A2 side is that the image carrying belt can be installed in a range where the belt does not contact the cleaning device 2.
The inclusion of the second image bearing belt 31 in FIG. 4 shows an image bearing belt in which an image forming unit symmetrical with respect to the y axis including the rotation axis 1 a of the photoreceptor 1 can be arranged.
The image forming unit 60 is used as the image forming unit 61 by vertically inverting the axis orthogonal to the y axis.
In this case, there is an influence of earth gravity, and at least in the developing device 5, conditions such as toner agitation and toner replenishment to the developing roller 5a are different and must be optimized, and it becomes impossible to share parts. .
As shown in FIG. 3, as the positional relationship between the image receiving surface of the first image carrying belt 21 and the image receiving surface of the second image carrying belt 31, the angle α between the two image receiving surfaces exceeds 180 degrees and is preferably 270 degrees. Is between 210 degrees and 255 degrees.
At this time, as the image forming unit, the first image carrying belt 21 may have the form shown in FIG. 4, and the second image carrying belt 31 may have the form shown in FIG. That is, it is possible to avoid an image forming unit that makes it impossible to share parts as described above.
Further, as shown in FIG. 3, since the recording material conveyance path 43A can be secured almost horizontally and linearly above the second image forming unit 61, the conveyance and reliability of the recording material are excellent, and the entire image forming apparatus. The unity becomes good.
In particular, the first image carrying belt 21 is stretched horizontally and flatly, and the second image carrying belt 31 is stretched long and inclined in the vertical direction, so that the recording medium conveyance path 43A is the boundary. The space in the height direction of the second image bearing belt 31 is increased below, but a sheet feeding device having a height substantially the same as the height occupied by the second image bearing belt 31 can be installed side by side.
As a result, a paper feeding device capable of storing a large amount of paper can be installed, and the paper feeding surface on the upper surface of the paper feeding device and the recording material conveyance path can be made substantially the same height, thereby ensuring the paper feeding / conveying reliability. .

As shown in FIG. 1, a first image carrier belt 21 as an image carrier is supported by a plurality of rollers 23, 24, 25, 26 (two), 27, 28, 29 and travels in the direction of an arrow. Provided below the photoreceptors 1Y, 1C, 1M, and 1K in the first image forming units 60Y to 60K.
The first image carrying belt 21 is endless, and is stretched and arranged so that a part of each photoconductor after the developing process comes into contact. In addition, a primary transfer roller 22 is provided on the inner peripheral portion of the first image carrying belt 21 so as to face each of the photoreceptors 1Y, 1C, 1M, and 1K.
A cleaning device 20 </ b> A is provided on the outer periphery of the first image carrying belt 21 at a position facing the roller 23. The cleaning device 20A is provided to wipe off unnecessary toner remaining on the surface of the image bearing belt 21 and foreign matters such as paper dust. The members related to the first image carrier belt 21 are integrally configured as the first image carrier unit 20 and can be attached to and detached from the image forming apparatus 6.
The second image carrier belt 31 as an image carrier is supported by a plurality of rollers 33, 34, 35, 36 (two), 37, 38 (two) and travels in the direction of the arrow, and the second image It is provided in contact with the photoreceptors 1Y, 1C, 1M, and 1K in the forming units 61Y to 61K.
The second image bearing belt 31 is endless, and is stretched and arranged so that a part of each photoconductor after the developing process comes into contact. A primary transfer roller 32 is provided on the inner peripheral portion of the second image bearing belt 31 so as to face the photoreceptors 1Y, 1C, 1M, and 1K.
The second image bearing belt 31 is endless and extends to the introduction end of the recording medium transport means 50. The recording medium transporting unit 50 extends to the nip portion N of the fixing device 63 and keeps the planar state up to the fixing nip in the fixing device 63 provided downstream of the recording body P in the transport direction of the recording body P. It also has a transport function to transport.
This is intended to send the unfixed images on both sides from the transfer unit to the fixing unit without disturbing them. The length X (distance from the second transfer station described later to the nip of the fixing unit) of the conveying unit is ensured to be equal to or longer than the maximum print image length. The photoconductors are stretched and arranged so that a part of each photoconductor after the development process comes into contact.

As described above, the second image carrier belt 31 includes a conveyance unit having a distance X from the second transfer unit 47 to the fixing nip equal to or greater than the maximum image length. As a result, the distance from the fixing nip to the second transfer means 47 is set to the maximum image length, so that switching can be performed before the leading edge of the recording body after transfer enters the fixing nip.
A primary transfer roller 32 is provided on the inner peripheral portion of the second image bearing belt 31 so as to face the photoreceptors 1Y, 1C, 1M, and 1K. On the outer periphery of the second image carrying belt 31, a cleaning device 30 </ b> A is provided at a position facing the cooling roller 62 and the roller 33 for cooling the second image carrying belt 31 heated by the fixing device 63.
The cleaning device 30 </ b> A wipes off unnecessary toner remaining on the surface of the second image carrying belt 31 and foreign matters such as paper dust. The cooling roller 62 uses a heat pipe. The members related to the second image carrier belt 31 are integrally configured as the second image carrier unit 30 and can be attached to and detached from the image forming apparatus 6.

Next, the configuration and material of the image bearing belt will be described. The image carrying belts 21 and 31 are belts having, for example, a resin film or rubber having a base thickness of 50 to 600 μm as a base. This belt has a resistance value capable of electrostatically transferring the toner image carried by each photoreceptor 1 to the belt surface by a bias applied to the primary transfer rollers 22 and 32.
In one embodiment, such an image bearing belt is obtained by dispersing carbon in polyimide and adjusting its volume resistance to about 10 ⁶ to 10 ¹² Ωcm. Belt detent ribs for stabilizing the running of the belt are provided on one side or both ends of the belt.
The image bearing belt 31 is provided with a PFA coating layer on the surface thereof in order to obtain toner releasability. As described above, polyimide is used as the material of the second image carrier belt 31. Since polyimide is a heat-resistant material, it can be applied to a fixing device.
A first image carrying belt 21 as an image carrier that is supported by a plurality of rollers 23, 24, 25, 26 (two), 27, 28, 29 and runs in the direction of the arrow is a first image forming unit 60Y. It is provided below the photoreceptors 1Y, 1C, 1M, and 1K at ˜60K.

To describe the other functions of the first image bearing belt supporting rollers 23 to 29, 23 is a belt supporting roller (backing of the cleaning device), 24 is a driving roller, 25 is a driven roller, and 26 is an image receiving surface maintaining roller. (Two), 27 is a tension roller, 28 is a transfer counter roller, and 29 is a bending roller.
The image bearing belt 21 is endless, and is stretched and arranged so that a part of each photoconductor after the developing process comes into contact. In addition, a primary transfer roller 22 is provided on the inner peripheral portion of the first image carrying belt 21 so as to face each of the photoreceptors 1Y, 1C, 1M, and 1K.
A cleaning device 20 </ b> A is provided on the outer periphery of the first image carrying belt 21 at a position facing the roller 23.
The cleaning device 20 </ b> A wipes off unnecessary toner remaining on the surface of the image bearing belt 21 and foreign matters such as paper dust. The members related to the image carrier belt 21 are integrally configured as the first image carrier unit 20 and can be attached to and detached from the image forming apparatus 6.
A second image carrier belt 31 as an image carrier that is supported by a plurality of rollers 33, 34, 35, 36 (two), 37, 38 and runs in the direction of the arrow is a second image forming unit 61 </ b> Y to 61 </ b> K. In contact with the photoreceptors 1Y, 1C, 1M, and 1K.
The functions of the second image bearing belt supporting rollers 33 to 38 are described below. 33 is a cleaning backing roller, 34 is a driving / transfer facing roller, 35 is a driven roller, 36 is an image receiving surface maintaining roller (two), 37 is a tension roller, and 38 is a transfer counter roller.
The image carrying belt 31 is endless and is stretched and arranged so that a part of each photoconductor after the developing process comes into contact. A primary transfer roller 32 is provided on the inner peripheral portion of the image bearing belt 31 so as to face the photoreceptors 1Y, 1C, 1M, and 1K. A cleaning device 30 </ b> A is provided on the outer periphery of the second image carrying belt 31 at a position facing the roller 33.
The cleaning device 30 </ b> A wipes away unnecessary toner remaining on the surface of the image bearing belt 31 and foreign matters such as paper dust. The members related to the image carrier belt 31 are integrally configured as the second image carrier unit 30 and can be attached to and detached from the image forming apparatus 6.

Next, the configuration and material of the image bearing belt will be described. The image carrying belts 21 and 31 are belts having, for example, a resin film or rubber having a base thickness of 50 to 600 μm as a base. This belt has a resistance value capable of electrostatically transferring the toner image carried by each photoreceptor 1 to the belt surface by a bias applied to the primary transfer rollers 22 and 32.
In one embodiment, such an image bearing belt is obtained by dispersing carbon in polyimide and adjusting its volume resistance to about 10 ⁶ to 10 ¹² Ωcm. Belt detent ribs for stabilizing the running of the belt are provided on one side or both ends of the belt.
The image bearing belt 31 is provided with a PFA coating layer on the surface thereof in order to obtain toner releasability. The material of the second image bearing belt 31 can be polyimide as described above. Since polyimide is a heat-resistant material, it can be applied to a fixing device.
The configuration of the primary transfer roller will be described. As one embodiment, the primary transfer rollers 22 and 32 are formed by coating a metal roller, which is a core metal, with a conductive rubber material, and a bias is applied to the core metal part from a power source (not shown). The In the conductive rubber material, carbon is dispersed in urethane rubber, and the resistance is adjusted to a volume resistance of about 10 ⁵ Ωcm.
Monochrome recording using only black toner is also possible. In such a case, there are photosensitive members that are not used. Therefore, not only the unused photoreceptors 1Y, 1C, 1M or the developing device 5 are operated, but also a mechanism for keeping these unused photoreceptors and the image carrying belt 21 or 31 in a non-contact state is provided.

In the present embodiment, an internal frame (not shown) that supports the roller 26 and the primary transfer roller 22 is provided. The inner frame is supported so as to be rotatable around a certain point, and is rotated in a direction away from the photoreceptor 1.
As a result, only the photosensitive member 1K comes into contact with the image carrier belt 21 or 31, and an image forming process is executed, so that a monochrome image using black toner can be created. This is advantageous in terms of improving the life of the photoreceptor 1.
Further, a first secondary transfer roller 46 is provided in the vicinity of the support roller 28 on the outer periphery of the first image carrying belt 21. The secondary transfer roller 46 is formed by coating a conductive rubber on the surface of a metal roller that is a core metal. A bias is applied to the mandrel from a power source (not shown). Carbon is dispersed in the rubber, and the volume resistance is adjusted to about 10 ⁷ Ωcm.
The first image carrying belt 21 is carried by applying a bias to the first secondary transfer roller 46 while passing a sheet (recording body P) between the first image carrying belt 21 and the secondary transfer roller 46. The toner image is transferred to the recording material P.
A transfer charger 47 serving as a second secondary transfer unit is provided on the outer periphery of the second image bearing belt 31 and in the vicinity of the support roller 34. The transfer charger 47 is a known type, and a thin wire of tungsten or gold is used as a discharge electrode, held by a casing (not shown), and a transfer current is applied to the discharge electrode from a power source (not shown).
By applying a transfer current while passing the recording medium P between the image bearing belt 31 and the transfer charger 47, an image formed by toner carried by the second image bearing belt 31 is transferred to the recording medium P. The polarity of the transfer current applied to the transfer roller 46 and the transfer charger 47 is a positive polarity opposite to the polarity of the toner.
Further, on the right side of the image forming apparatus 6, a paper feeding device 40 that accommodates a recording medium is provided. A paper feed device (tray) 40a storing a large number of recording media in a plurality of stages, for example, an upper stage, and three stages of paper feed cassettes 40b, 40c, and 40d below each are pulled out to the front side (operation surface side) perpendicular to the paper surface. It is arranged to be possible.
Among the recording media P stored in the paper feed tray 40a and the paper feed cassettes 40b, 40c, and 40d, the uppermost recording material (paper) P is selectively selected by the corresponding paper feeding / separating means 41A to 41D. Are reliably fed to the recording medium conveyance paths 43B and 43A by a plurality of conveyance roller pairs 42B.

A pair of registration rollers 45 are provided in the recording medium conveyance path 43A in order to take a feeding timing for sending the recording medium P to the secondary transfer position. Further, a jogger 44 for setting the position perpendicular to the conveyance direction of the recording medium to a normal position is provided in the recording medium conveyance path 43A.
The jogger 44 includes a guide member (not shown) that moves from both sides toward the end of the recording body P with respect to the conveyance direction of the recording body P, and the guide member moves the recording body P from both sides of the running paper. The recording material P is aligned with a predetermined position by pressing for a moment.
The recording material P is conveyed from the registration roller pair 45 toward a transfer area which is a first transfer station including the first image carrying belt 21 and the secondary transfer roller 46. Thereafter, the sheet is conveyed toward a transfer area which is a second transfer station including the second image carrying belt 31 and the transfer charger 47.
A recording medium can be supplied to the recording medium conveyance path 43C having the conveyance roller pair 42C from another sheet feeding device 8 that can be installed upstream in the conveyance direction. The uppermost recording medium of the paper feed tray 40a is fed, and the upper paper feed surface of the paper feed tray 40a is arranged so as to be conveyed substantially horizontally without being bent thereafter. Therefore, even thick recording media and highly rigid paperboard can be reliably fed.
In addition, it is advantageous to employ air feeding composed of a vacuum mechanism so that the sheet feeding tray 40a can reliably feed even when recording bodies having various characteristics are stored. Although not shown, a sensor for detecting the recording medium P is provided at a key point of the recording medium conveyance path and serves as a trigger for various signals based on the presence of the recording medium P.

A sheet feeding device 40a capable of supplying the recording medium P from substantially the same sheet feeding and supply surface as the recording medium conveyance path 43A is provided upstream of the recording medium conveyance path 43A in the conveyance direction of the recording medium P.
As a result, a straight recording medium conveyance path is formed, and a highly rigid recording medium P can be supplied and conveyed, and an image forming apparatus that can widely cope with the types and characteristics of the recording medium P can be provided. In this case, the recording material conveyance path 43A is substantially on the same plane from the paper feeding surface of the paper feeding unit to the fixing nip.
The paper (recording member) P is conveyed from the registration roller pair 45 toward a transfer area which is a first transfer station including the first image carrying belt 21 and the secondary transfer roller 46. Thereafter, the sheet is conveyed toward a transfer area which is a second transfer station including the second image carrying belt 31 and the transfer charger 47.
A fixing device 63 having a heating unit is provided on the downstream side in the sheet conveying direction of the recording medium conveying unit 43A. As the fixing device 63, a type having a heater inside the roller, a belt fixing device for running a heated belt, a fixing device adopting induction heating as a heating method, or the like can be adopted.
An operation during single-sided recording in which a full-color image is formed on one side of a sheet (recording body) P in the above configuration will be described. There are basically two types of single-sided recording methods that can be selected.
One of the two types is a method of directly transferring an image carried on the first image carrying belt 21 to one side of the recording medium P. The other method is a method in which the image carried on the second image carrying belt 31 is directly transferred to one side of the recording medium P.

In the present embodiment, from the configuration of the image forming apparatus 6, when the image carried on the first image carrying belt 21 is directly transferred to one side of the recording material P, the image is formed on the upper surface of the recording material P. When the image carried on the second image carrying belt 31 is directly transferred to one side of the recording material P, the image is formed on the lower surface of the recording material P.
When the data to be recorded is a plurality of pages, it is convenient to control the image forming order so that the pages are aligned on the paper discharge stack unit 59. An explanation will be given of a method in which an image is carried on the first image carrying belt 21 and then transferred to a sheet so that the image order is recorded in order from the image data of the last page and the page order is aligned.
When the image forming apparatus 6 is operated, the photoreceptors 1Y, 1C, 1M, and 1K in the first image carrying belt 21 and the first image forming units 60Y to 60K rotate. At the same time, the second image carrier belt 31 rotates. However, the photoreceptors 1Y, 1C, 1M, and 1K in the second image forming units 61Y to 61K are separated from the second image carrier belt 31 and are not rotated. Is done.
First, image formation by the image forming unit 60Y is started. Light corresponding to image data for yellow emitted from the LED is uniformly charged by the charging device 3 by the operation of the exposure device 4 (see FIGS. 4 and 5) composed of an LED (light emitting diode) array and an imaging element. The surface of the photoreceptor 1Y is irradiated to form an electrostatic latent image.
This electrostatic latent image is developed with yellow toner by the developing roller 5a, becomes a visible image, and is electrostatically applied on the first image carrying belt 21 that moves in synchronization with the photoreceptor 1Y by the transfer action of the primary transfer roller 22. Primary transfer. Such latent image formation, development, and primary transfer operations are sequentially performed in the same manner on the photoconductors 1C, 1M, and 1K.
As a result, yellow, cyan, magenta, and black toner images are carried on the first image carrying belt 21 as sequentially overlapping full-color toner images, and are moved in the direction of the arrow together with the first image carrying belt 21. .
At the same time, the recording material P used for recording is fed from one of the paper feed trays 40a or the paper feed cassettes 40b to 40d in the paper feed device 40 by one of the paper feed / separation means 41A to 41D for feeding and transported. It is conveyed to the recording material conveyance path 43C by the roller pairs 42B and 42C.

Before the leading edge of the recording body P is not picked up by the registration roller pair 45, the jogger 44 operates to push both sides of the recording body P from both lateral directions with respect to the sheet conveyance direction. Lateral alignment is achieved.
The registration roller pair 45 is stationary, and the leading end of the recording medium P is stationary while entering the nip of the registration roller pair 45, but the position with the image on the first image carrier belt 21 is normal. At the same time, the registration roller pair 45 rotates to convey the recording material P to the transfer area.
The full-color toner image on the first image carrying belt 21 is transferred to the upper surface of the recording material P conveyed in synchronization with the first image carrying belt 21 by receiving a transfer action by the secondary transfer roller 46. The bias applied to the secondary transfer roller 46 has a positive polarity opposite to the charging polarity of the toner.
Thereafter, the surface of the first image carrying belt 21 is cleaned by the belt cleaning device 20A. Further, foreign matters such as toner remaining on the surfaces of the photoreceptors 1Y, 1C, 1M, and 1K in the first image forming units 60Y to 60K that have finished the primary transfer are removed from the cleaning brush 2a of the cleaning device 2 (FIGS. 4 and 5). Then, it is removed from the surface of each photoconductor by the cleaning blade 2b.
The surface of each photoconductor is subjected to a discharging operation of residual potential by the discharging device Q (FIGS. 4 and 5) to prepare for the next image forming / transferring step. Sensors S1 and S2 (FIGS. 4 and 5) indicate whether or not the surface potential of the photosensitive member surface after exposure and the concentration of toner attached to the photosensitive member surface after the development process are appropriate. It detects and sends information to a control means (not shown) for setting and controlling image forming conditions as appropriate.

The recording medium (paper) P onto which the toner image that has been superposed and carried on the image carrying belt 21 is transferred is transferred toward the fixing device 63 by the conveying belt of the fixing device 63. The surface of the conveyance belt 51 is charged in advance by the adsorption charger 57 of the recording medium P so that the recording medium P can be reliably transferred together with the conveyance belt 51.
The static elimination / separation charger 58 operates so that the recording material P is separated from the conveyance belt 51 and is reliably sent to the heat fixing device 63. The toners of the respective colors superimposed on the recording medium P are subjected to a fixing action by the heat of the fixing device 63, and are melted and mixed to form a color image completely.
Until the fixed toner is completely fixed on the recording medium P, the image is lost or distorted by rubbing against the guide member or the like of the conveyance path. In order to prevent this problem, the cooling roller pair 62 as a cooling unit is operated to cool the toner and the recording material P.
Thereafter, the paper is discharged to the paper discharge stack 59 by the paper discharge roller 64 with the image surface facing upward. In the paper discharge stack unit 59, the image forming order is programmed so that the recorded matter of young pages is sequentially stacked and stacked. As a result, the page order is aligned.
Since the paper discharge stack unit 59 descends as the number of discharged recording materials increases, the sheets can be stacked in an orderly and reliable manner, and the page order is not disturbed. Instead of directly stacking the recorded recording material P on the discharge stacking unit 59, it is possible to carry out a punching process or to transport it to a post-processing device such as a sorter, a collator, a binding device or a folding device.
In another method of forming an image on one side of the recording medium P, the image formation is not performed in the first image forming units 60Y to 60K, and the image data of the young pages is sequentially formed for page alignment. Although the formation is different, the details are omitted because it is basically the same as the one-side recording process described above.

Next, the operation during double-sided recording in which images are formed on both sides of the recording medium P will be described. When a start signal is input to the image forming apparatus 6, the first image carrying belt 21 displays an image for each color sequentially formed by the first image forming units 60 </ b> Y, 60 </ b> C, 60 </ b> M, and 60 </ b> K described in the single-side recording operation. The primary transfer is performed sequentially.
In almost parallel to the step of carrying as the first image, the images for each color sequentially formed by the second image forming units 61Y, 61C, 61M, 61K are sequentially primary-transferred to the second image carrying belt 31, The step of carrying as a second image is performed.
With the configuration shown in FIG. 1, in order for the first image and the second image to coincide with each other at the front end in the transport direction of the recording medium P, the second image is delayed from the start of the formation of the first image. The formation of is started. Further, since the recording medium P is stopped and retransmitted by the registration roller pair 45, the recording medium P is fed in consideration of the time, and the surface roughness of the recording medium front and back is measured between the rollers 42A by the measuring devices 67 and 68, and Further, the jogger 44 is used for alignment.
The registration roller pair 45 takes the timing to convey the recording material P to a first transfer station constituted by a transfer roller 46 as a first secondary transfer means and a first image carrying belt 21. A transfer current having a positive polarity is applied to the transfer roller 46, and the image is transferred from the first image carrying belt 21 to one side (upper surface in the drawing) of the recording medium P.

The recording material P having an image on one side in this way is continuously sent to the second transfer station having the transfer charger 47 as the second secondary transfer means by the conveying action of the transfer roller 46. Then, by applying a positive polarity transfer current to the transfer charger 47, the full-color second image previously carried on the second image carrying belt 31 is collectively transferred to the lower surface of the recording medium P.
The recording material P having the full color toner image transferred on both sides in this way is transported to the fixing device 63 by the transport belt 51. The suction charger 57 charges the surface of the transport belt 51 with the same negative polarity as the polarity of the toner. The unfixed toner on the lower surface of the recording body is prevented from moving to the conveyance belt 51.
An alternating current is applied to the charge removal / separation charger 58, and the recording material P is separated from the transport belt 51 and transferred to the heat fixing device 63. The toner images on both sides of the recording medium P are subjected to fixing processing by heat of the heat fixing device 63, and are melted and mixed. The recording material P subsequently passes through the cooling roller 65 and is discharged onto the paper discharge stack portion 59 by the paper discharge roller 64.
When double-sided recording is performed on a recording medium of a plurality of pages, the image forming order is controlled so that an image of a young page becomes the bottom surface and is stacked on the paper discharge stack unit 59. Then, when it is taken out from there and the top and bottom surfaces are reversed, the recorded matter is one page in order from the top, the second page is the second page, the second page is the third page, and the back is the fourth page.
Such control of image forming sequence and control such as increasing the power input to the fixing device compared to single-sided recording are executed by a control means (not shown). As for the single-sided recording and the double-sided recording operation, an example in which full-color recording is executed has been described, but monochrome recording using only black toner is also possible.

According to the present invention, registration aligning means (lateral registration correction jogger 44, registration roller 45) for the recording medium P is provided in a flat recording medium conveyance path 43A constructed upstream from the first transfer station. Make the image on the recording medium. Accordingly, it is possible to provide an image forming apparatus capable of obtaining a good image without skewing of the recording material P, leading edge registration, and lateral displacement.
In the first transfer station and the second transfer station, the first intermediate transfer belt 21 and the second intermediate transfer belt 31 are not in contact with each other, and the upstream of the transfer means arranged in each transfer station in the recording material transport direction. A transfer roller 46 to which a bias can be applied is adopted as the deployed transfer means.
As a result, the transfer means 46 and 47 are provided at the first and second stations, respectively, and the transfer roller 46 is employed at the first station, so that the recording medium P can be reliably conveyed, and the recording medium P at the transfer station can be transported. It is possible to provide a one-pass double-sided image forming apparatus that realizes reliable image transfer onto the recording material P that is reliably conveyed and does not cause image distortion.

1 is a schematic central sectional view showing an internal configuration of an image forming apparatus to which the present invention is applied. It is the schematic which takes out and shows the recording-material conveyance means vicinity. FIG. 2 is a simplified diagram showing an arrangement of image carrier belts in FIG. 1. It is an enlarged view showing a configuration of a first image forming unit which is one main part for image formation. It is an enlarged view showing a configuration of a second image forming unit which is the other main part for image formation.

Explanation of symbols

6 Image Forming Device 20 First Image Carrying Unit 20A Cleaning Device 21 First Image Carrying Belt 22 Primary Transfer Roller 30 Second Image Carrying Unit 30A Cleaning Device 31 Second Image Carrying Belt 40a Paper Feeding Device 42A Conveying Means (Recording Material Conveying) Road)
43A Recording medium conveyance path 44 Registration alignment means (lateral registration correction jogger)
45 Conveying means (registration roller, recording material conveying path)
46 First transfer means (first transfer charger)
47 Second transfer means (second transfer charger)
50 Recorder transfer means (conveyance means)
50a Conveyor belt cleaning device 51 Conveyor belt 60 First image forming unit (60Y, C, M, K)
61 Second image forming unit (61Y, C, M, K)
62 Cooling means 63 Fixing device 65 Cooling means (cooling roller)
L Length of the conveyance part of the recording medium transporting means (conveying means) P Recording medium (paper)

Claims (9)

  A first image carrying unit for carrying the first image from the first image forming unit on the first image carrying belt, and a second image carrying unit for carrying the second image from the second image forming unit on the second image carrying belt. A first transfer station including first transfer means for transferring the first image carried by the first image carrying unit to a first surface of a recording medium; and the second image carrying unit carrying the first transfer station. A second transfer station including a second transfer means for transferring the first image onto the second surface of the recording medium, and a recording medium conveyance for supplying and conveying the recording medium between the first and second transfer stations. In the image forming apparatus, further comprising: a recording body transporting unit having a path and a transport belt that transports the image on both sides of the recording body exiting the second image carrier unit to a heat fixing device. Image forming apparatus, wherein the length of the conveying section of not less than the maximum image length.   The image forming apparatus according to claim 1, wherein the conveyance belt of the recording medium transfer unit is configured as an endless belt.   The image forming apparatus according to claim 1, wherein the conveyance belt is a heat-resistant belt.   The image forming apparatus according to claim 1, wherein the material of the conveying belt is polyimide. 5. The image forming apparatus according to claim 1, wherein the conveyance belt has a volume resistance value of 10 ⁶ to 10 ¹² Ωcm.   The image forming apparatus according to claim 1, wherein the conveyance belt has a thickness of 50 to 600 μm.   7. A sheet feeding device capable of supplying the recording medium from a substantially same sheet feeding and supply surface as the recording medium conveyance path upstream of the recording medium conveyance direction in the recording medium conveyance path. The image forming apparatus according to any one of the above.   The image forming apparatus according to claim 1, wherein the recording material conveyance path is substantially the same surface from a paper feeding surface to a fixing nip of the paper feeding device.   In the first transfer station and the second transfer station, the first intermediate transfer belt and the second intermediate transfer belt are not in contact with each other, and upstream of the transfer means arranged in each transfer station in the recording material conveyance direction. 2. The image forming apparatus according to claim 1, wherein a transfer roller to which a bias can be applied is adopted as the arranged transfer means.

Images