JP2019128491A - Image forming apparatus - Google Patents

Abstract

To form, in an image forming apparatus having a second image forming unit provided in an upper part in the gravity direction of a first image forming unit, images on the same surface of a recording material with the first image forming unit and second image forming unit, while preventing rubbing of the images compared with a case where the image forming apparatus forms an image from a lower part in the gravity direction with the second image forming unit.SOLUTION: An image forming apparatus comprises: a first image forming unit that forms images on one face of a recording medium; an inversion unit that inverts the recording material on the one face of which the images are formed by the first image forming unit and conveys the recording material to the first image forming unit; and a second image forming unit that is provided in an upper part in the gravity direction of the first image forming unit, conveys the recording material inverted by the inversion unit and passing through the first image forming unit such that the one face is directed upward in the gravity direction, and forms an image on the one face from an upper part in the gravity direction.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus.

  As a conventional technique, Patent Document 1 discloses a composite printer apparatus in which a monochrome printer apparatus and a color printer apparatus are arranged so as to overlap each other in the direction of gravity.

Japanese Patent Application Laid-Open No. 10-198106

For example, in an image forming apparatus provided with a second image forming unit that forms an image such as a spot color, in addition to the first image forming unit that forms an image of YMCK color, for example, the first area is reduced. There is a case where the second image forming unit is provided above the gravity direction of the image forming unit.
In the case where the second image forming unit is provided above the first image forming unit in the direction of gravity, the second image forming unit is directed to the direction of gravity in the second image forming unit in view of suppressing rubbing and the like of the image forming surface of the recording material. May be directed upwards. However, when the image forming surface is directed upward in the direction of gravity in the second image forming unit, the first image forming unit and the second image forming unit may be used depending on the configuration and arrangement of the first image forming unit and the second image forming unit. Therefore, it may be difficult to form an image on the same surface of the recording material.

  According to the present invention, in an image forming apparatus in which a second image forming unit is provided above the first image forming unit in the direction of gravity, the image is rubbed compared to when an image is formed from the lower side in the direction of gravity in the second image forming unit. An object of the present invention is to form an image on the same surface of the recording material by the first image forming unit and the second image forming unit.

According to the first aspect of the present invention, there is provided a first image forming portion for forming an image on one side of a recording material, and the front and back of the recording material on which an image is formed on the one side by the first image forming portion. A reversing unit for feeding to the first image forming unit, and a recording material which is provided above the direction of gravity of the first image forming unit, and which has been turned over by the reversing unit and passed through the first image forming unit The image forming apparatus includes a second image forming unit that conveys one surface facing upward in the direction of gravity and forms an image on the one surface from above in the direction of gravity.
In the invention according to claim 2, when the first image forming unit does not form an image on the recording material by the second image forming unit, the first image forming unit forms an image on the one surface of the recording material, and then the reversing unit 2. The image forming apparatus according to claim 1, wherein the recording material is discharged without passing through.
The invention according to claim 3 is characterized in that the first image forming unit conveys the recording material to the second image forming unit without going through the reversing unit when an image is not formed on the recording material. The image forming apparatus according to claim 1.
According to a fourth aspect of the present invention, the first image forming unit heats a toner image forming unit that forms a toner image on the one surface of the recording material, and a toner image formed by the toner image forming unit. A fixing unit that fixes the recording material, and the fixing unit reduces the fixing strength of the toner image when the recording material after passing through the reversing unit passes, as compared with that before passing through the reversing unit. The image forming apparatus according to claim 1, wherein:
According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the fixing unit does not perform a fixing process when the recording material that has passed through the reversing unit passes. .
According to a sixth aspect of the present invention, the first image forming unit includes a first toner image forming unit that forms a toner image on the one surface of the recording material, and a toner image formed by the first toner image forming unit. A first fixing unit that heats and fixes the recording material onto the recording material, and the second image forming unit includes a second toner image forming unit that forms a toner image on the one surface of the recording material from above in the direction of gravity. A second fixing unit that heats and fixes the toner image formed by the second toner image forming unit to the recording material, and the first fixing unit passes the recording material after passing through the reversing unit. The image forming apparatus according to claim 1, wherein the recording material is heated at the time of printing.
According to a seventh aspect of the present invention, the first image forming unit rotates with the recording material interposed between the image holding unit that holds the toner image and faces the one surface of the recording material, and the image holding unit. An image transfer unit that transfers the toner image held on the image holding unit to the one surface of the recording material, a power source that applies a transfer voltage to the image holding unit or the image transfer unit, and the image transfer unit. A fixing unit that fixes the toner image transferred by the recording material to the recording material, and the power source is configured to determine the absolute value of the transfer voltage when the recording material passes through the reversing unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is lowered as compared to that before passing.
The invention according to claim 8 is the image forming apparatus according to claim 7, wherein the power supply does not apply the transfer voltage when the recording material after passing through the reversing unit passes. .
According to a ninth aspect of the present invention, the first image forming unit includes a first toner image forming unit that forms a toner image on the one surface of the recording material, and a toner image formed by the first toner image forming unit. A first fixing unit that heats and fixes the recording material onto the recording material, and the second image forming unit includes a second toner image forming unit that forms a toner image on the one surface of the recording material from above in the direction of gravity. A second fixing unit that heats and fixes the toner image formed by the second toner image forming unit to the recording material, and the second image forming unit, when not forming an image on the recording material, The image forming apparatus according to claim 1, wherein the recording material on which the image is formed in the first image forming unit is received and heated in the second fixing unit.
The invention according to claim 10 is characterized in that the first image forming unit conveys the recording material to the second image forming unit without going through the reversing unit. It is.
According to an eleventh aspect of the present invention, the first image forming unit reverses the recording material on which the toner image is formed by the first toner image forming unit and the toner image is fixed by the first fixing unit by the reversing unit. 10. The image forming apparatus according to claim 9, wherein the sheet is conveyed to the second image forming unit.
The invention according to claim 12 is characterized in that the first image forming unit conveys the recording material reversed in the reversing unit to the second image forming unit after heating again in the first fixing unit. The image forming apparatus according to claim 11.

According to the first aspect of the present invention, in the image forming apparatus in which the second image forming unit is provided above the gravity direction of the first image forming unit, the second image forming unit forms an image from below the gravity direction. The first image forming unit and the second image forming unit can form an image on the same surface of the recording material while suppressing image rubbing compared to the above.
According to the second aspect of the present invention, the recording material conveyance path can be shortened as compared with the case where the second image forming unit does not form an image on the recording material, as compared with the case where the second image forming unit passes the reversing unit.
According to the third aspect of the present invention, the recording material conveyance path can be shortened as compared with the case where the first image forming unit does not form an image on the recording material, as compared with the case of passing through the reversing unit.
According to the fourth aspect of the invention, the fluctuation of the image formed in the first image forming unit is suppressed as compared with the case where the fixing strength of the toner image is not reduced compared to the case where the recording material passes the reversing unit. can do.
According to the fifth aspect of the present invention, the fluctuation of the image formed in the first image forming portion is further enhanced as compared with the case where the fixing strength of the toner image is not reduced as compared with the case where the recording material passes the reversing portion. It can be suppressed.
According to the sixth aspect of the present invention, the fixability of the image formed in the second image forming unit can be improved as compared with the case where the recording material after passing the reversing unit in the first fixing unit is not heated. .
According to the seventh aspect of the present invention, the change in the behavior of the recording material can be suppressed as compared with the case where the absolute value of the transfer voltage is not lowered as compared with the case before the recording material passes through the reversal portion.
According to the eighth aspect of the invention, the change in the behavior of the recording material can be further suppressed as compared with the case where the transfer voltage is applied when the recording material after passing through the reversing portion passes.
According to the invention of claim 9, when the second image forming unit does not form an image on the recording material, the image formed by the first image forming unit is compared to the case where the recording material is not heated by the second fixing unit. The fixability of the
According to the tenth aspect of the present invention, the conveyance path of the recording material can be shortened as compared to the case where the recording material is conveyed to the second image forming unit via the reversing unit.
According to the eleventh aspect of the present invention, it is possible to improve the fixability of the image in the second fixing unit as compared with the case where the recording material is conveyed to the second image forming unit without going through the reversing unit.
According to the twelfth aspect of the present invention, more heat can be applied to the recording material as compared to the case where the recording material inverted in the reversing unit is not heated again in the first fixing unit.

FIG. 1 is a diagram showing an entire configuration of an image forming apparatus to which a first embodiment is applied. (A)-(b) is a figure for demonstrating arrangement | positioning with the photoreceptor drum and transfer roll in a 2nd image formation part. FIG. 8 is a diagram showing an entire configuration of an image forming apparatus to which a second embodiment is applied.

First Embodiment
FIG. 1 is a diagram showing an entire configuration of an image forming apparatus 1 to which the first embodiment is applied. The image forming apparatus 1 shown in FIG. 1 uses yellow (Y), magenta (M), cyan (C), and black (K) (hereinafter, these colors are referred to as normal colors) on a sheet as an example of a recording material. A first image forming unit 100 that forms an image of the first image forming unit. Further, the image forming apparatus 1 is superposed on the first image forming unit 100 in the direction of gravity (upper side in FIG. 1), and has a special color image different from the normal color on the sheet conveyed from the first image forming unit 100. A second image forming unit 200 for forming the image.

The image forming apparatus 1 according to the present embodiment can form an image of normal color, that is, yellow, magenta, cyan and black, and can also form an image in which an image of a special color is further superimposed on an image of normal color. It has become.
Further, in this example, the second image forming unit 200 is detachably provided to the first image forming unit 100. When the second image forming unit 200 is removed from the first image forming unit 100, the first image forming unit 100 may be used alone as a color printer for forming yellow, magenta, cyan and black images. it can.

The first image forming unit 100 is a so-called tandem type color printer. The first image forming unit 100 includes a first image forming unit 10 which forms an image on a sheet in correspondence with image data. Further, in the first image forming unit 100, an image is formed by the paper supply unit 31 that supplies paper to the first image forming unit 10 and the first image forming unit 10 or the second image forming unit 20 described later. A sheet discharge unit 32 from which sheets are discharged, and a sheet stacking unit 33 on which sheets discharged from the sheet discharge unit 32 are stacked are provided. The paper discharge unit 32 feeds the paper to the paper stacking unit 33 by rotating in a predetermined first direction (the direction of arrow D in FIG. 1), and also in a second direction (in FIG. 1) opposite to the first direction. By rotating in a direction opposite to the arrow D), there is provided a discharge roll 32a for feeding a sheet to a sheet reversing path R2 described later. Further, the first image forming unit 100 includes a toner cartridge 35 corresponding to each color of yellow, magenta, cyan, and black and supplying toner of each color to the first image forming unit 10.
Furthermore, the first image forming unit 100 includes a control unit 50 that controls the overall operation of the image forming apparatus 1.

  Further, the first image forming unit 100 is provided with a first paper transport path R1 for transporting paper from the paper supply unit 31 through the first image forming unit 10 toward the paper discharge unit 32. Further, the first image forming unit 100 is provided with a paper reversing path R2 that reverses the front and back of the paper on which the image is formed by the first image forming unit 10 and conveys the paper to the first image forming unit 10 again. It is done. Furthermore, the first image forming unit 100 is connected to the first sheet conveyance path R1 on the downstream side of the first fixing device 16 described later, and the sheet having passed the first image forming unit 10 is the second image forming unit A paper delivery path R3 for delivering to 200 is provided.

The first sheet conveyance path R <b> 1 is formed to extend in the direction of gravity from the sheet supply unit 31 toward the first image forming unit 10 and then extend in the horizontal direction toward the sheet discharge unit 32. Further, the sheet delivery path R3 extends upward in the direction of gravity from the connecting portion with the first sheet transport path R1 toward the second image forming unit 200.
Although details will be described later, in the image forming apparatus 1 according to the present embodiment, the first image forming unit 100 is used when a normal color image and a special color image are formed on one side of a sheet in an overlapping manner. Then, the paper on which the normal color image is formed on one side is reversed by the paper reversing path R2, and then conveyed to the second image forming unit 200 via the paper delivery path R3. Further, in the present embodiment, the sheet reversing path R2 and the discharge roll 32a constitute a reversing portion.

The first image forming unit 10 includes four photosensitive drums 11 corresponding to yellow, magenta, cyan and black colors and arranged in parallel in the horizontal direction, and four primary drums arranged corresponding to the respective photosensitive drums 11. A transfer roll 12, an intermediate transfer belt 13 to which a toner image formed on each photosensitive drum 11 is sequentially transferred, and a toner image forming portion to which a toner image primarily transferred to the intermediate transfer belt 13 is secondarily transferred to a sheet Alternatively, the image forming apparatus includes a secondary transfer roll 14 as an example of a first toner image forming unit and a backup roll 15 disposed to face the secondary transfer roll 14 with the intermediate transfer belt 13 interposed therebetween.
In addition, the first image forming unit 10 includes a fixing unit that fixes the second-transferred toner image on a sheet or a first fixing device 16 as an example of a first fixing unit.

Each photosensitive drum 11 is rotationally driven in a predetermined direction (the direction of arrow A in FIG. 1) by a driving unit (not shown).
Further, around each photosensitive drum 11, a charging device that charges the surface of the photosensitive drum 11, and an exposure that forms an electrostatic latent image by exposing the surface of the photosensitive drum 11 charged by the charging device. A device, a developing device for developing and visualizing an electrostatic latent image formed on the photosensitive drum 11 with toners of respective colors, a cleaner for removing toner remaining on the photosensitive drum 11 after primary transfer, and the like are arranged in this order (Not shown).

Each primary transfer roll 12 is disposed opposite to the corresponding photosensitive drum 11 via the intermediate transfer belt 13. These primary transfer rolls 12 primarily transfer the toner image formed on the corresponding photosensitive drum 11 onto the intermediate transfer belt 13.
The intermediate transfer belt 13 is rotatably passed around by a primary transfer roll 12 and a plurality of support rolls (not shown). The intermediate transfer belt 13 is rotationally driven in the arrow B direction by a drive roll (not shown) of the plurality of support rolls.

  The secondary transfer roll 14 is provided to face the intermediate transfer belt 13 and is pressed against the backup roll 15 via the intermediate transfer belt 13. The secondary transfer roll 14 forms a secondary transfer portion Ta with the backup roll 15. Then, in the secondary transfer portion Ta, a transfer voltage is applied to the secondary transfer roll 14 or the backup roll 15 by a power supply (not shown), and the secondary transfer roll 14 is on the intermediate transfer belt 13 in the secondary transfer portion Ta. The toner images of the respective colors primary-transferred sequentially on the sheet are secondarily transferred (collective transfer) onto the sheet. In this example, the secondary transfer roll 14 secondarily transfers the toner image from the left side in the drawing to the paper supplied from the paper supply unit 31 and transported through the first paper transport path R1. In the present embodiment, the intermediate transfer belt 13 and the backup roll 15 constitute an image holding unit, and the secondary transfer roll 14 constitutes an image transfer unit.

The first fixing device 16 includes, for example, a heating member having a heat source such as a halogen lamp, a resistance heating element, and an induction heating coil, and a pressure member forming a pressure portion Na between the heating members. By passing the sheet to the portion Na, the toner image is fixed to the sheet by heat and pressure.
Although details will be described later, the first fixing device 16 of the present embodiment can change the fixing strength based on the control by the control unit 50. Here, the fixing strength is the magnitude of heat or pressure supplied to the sheet on which the toner image is formed. The first fixing device 16 has, for example, a heating temperature by the heat source of the heating member, a pressure between the heating member and the pressure member in the pressure unit Na, a length in the conveyance direction of the pressure unit Na, and the pressure unit Na. The fixing strength can be changed by changing the conveyance speed or the like of the passing paper.
In the present embodiment, the sheet on which the toner image is fixed by the first fixing device 16 is conveyed upward in the gravitational direction with the image forming surface facing the left side in the drawing.

  The second image forming unit 200 is a so-called direct transfer single-color printer that forms an image of a spot color on a sheet. Here, the special color is a color different from the normal color. For example, a special color, that is, a color that is difficult to realize from yellow, magenta, cyan, and black toners can be mentioned. Specific examples of such features include white, transparent colors, light cyan, light magenta, orange, violet, green, etc., as well as metallic colors such as gold and silver colored with metal pigments. It is not limited to

The second image forming unit 200 includes a second image forming unit 20 that forms an image on the paper conveyed from the first image forming unit 100 from above in the direction of gravity corresponding to the image data.
The second image forming unit 200 also includes a toner cartridge 36 that supplies toner to the second image forming unit 20. In this example, the toner cartridge 36 is provided at a position shifted in the horizontal direction with respect to the second image forming unit 20. More specifically, the toner cartridge 36 is provided at a position shifted from the second image forming unit 20 in a direction away from a second fixing device 26 described later. Thereby, in the image forming apparatus 1 of the present embodiment, the direction of gravity of the second image forming unit 200 is compared with the case where the toner cartridge 36 and the second image forming unit 20 are disposed overlapping each other in the direction of gravity. The dimensions can be reduced. Further, compared with the case where the toner cartridge 36 is provided at a position close to the second fixing device 26, toner deterioration due to heat from the second fixing device 26 is suppressed.

  In addition, the second image forming unit 200 is configured to convey a sheet received from the sheet delivery path R3 of the first image forming unit 100 to the sheet stacking unit 33 through the second image forming unit 20. Is provided. The second sheet conveyance path R4 receives the sheet from the sheet delivery path of the first image forming unit 100 and conveys the sheet from the lower side to the upper side in the direction of gravity, and the second image from the upper end in the direction of gravity in the upstream portion R4a A downstream portion R4b that extends in the horizontal direction through the forming portion 20 and conveys the paper toward the paper stacking portion 33;

  In the second image forming unit 200 of the present embodiment, the second image forming unit 20 is provided in the downstream portion R4b in the second paper transport path R4. In the downstream portion R4b of the second paper transport path R4, the paper is transported so that the image forming surface on which an image is formed by the second image forming unit 20 faces upward in the direction of gravity. Then, the second image forming unit 20 forms an image on the sheet from above in the direction of gravity.

In the present embodiment, the second image forming unit 20 forms an image from the upper side in the direction of gravity in the downstream portion R4b of the second sheet conveyance path R4. The length of the upstream portion R4a extending in the direction of gravity can be shortened as compared with the case where the image is formed in the horizontal direction. Thereby, compared with the case where the 2nd image formation part 20 forms an image from a horizontal direction in upstream part R4a, the dimension of the gravity direction of the 2nd image formation unit 200 and the image forming apparatus 1 whole can be made small. .
When the second image forming unit 20 is configured to form an image from the upper side in the gravity direction, the horizontal direction of the second image forming unit 200 is compared with the case where the second image forming unit 20 forms an image from the horizontal direction. Directional dimensions may increase. However, since the second image forming unit 200 has a smaller number of components as compared to the first image forming unit 100, the horizontal dimension is less likely to be larger than that of the first image forming unit 100. Therefore, even when the second image forming unit 20 is configured to form an image from above in the direction of gravity, the increase in the horizontal dimension of the entire image forming apparatus 1 is suppressed.

  The second image forming unit 20 forms a transfer portion Tb between the photosensitive drum 21 and the photosensitive drum 21 and transfers a toner image formed on the photosensitive drum 21 onto a sheet of paper. A transfer roll 22 as an example, and a second fixing device 26 as an example of a second fixing unit that fixes the transferred toner image on a sheet.

The photosensitive drum 21 is rotationally driven in a predetermined direction (the direction of the arrow C in FIGS. 1 and 2) by a driving unit (not shown).
Further, around the photosensitive drum 21, a charging device that charges the surface of the photosensitive drum 21, an exposure device that exposes the surface of the photosensitive drum 21 charged by the charging device to form an electrostatic latent image, and a photosensitive A developing device for exposing the electrostatic latent image formed on the body drum 21 with toner to form an electrostatic latent image, a cleaner for removing toner remaining on the photosensitive drum 21 after transfer, and the like are arranged in this order (Not shown).

As described above, in the second image forming unit 20, the transfer unit Tb is transported so that the image forming surface of the sheet faces upward in the direction of gravity. Then, the second image forming unit 20 forms an image from above in the direction of gravity on the paper conveyed from the first image forming unit 100 in the transfer unit Tb.
FIGS. 2A and 2B are diagrams for explaining the arrangement of the photosensitive drum 21 and the transfer roll 22 in the second image forming unit 20, and the arrangement of the photosensitive drum 21 and the transfer roll 22. It is a figure showing an example.

When the transfer portion Tb is formed by the rotating photosensitive drum 21 and the transfer roll 22 as in the present embodiment, an image is formed from above in the direction of gravity in the transfer portion Tb. It means that 21 is arranged above the direction of gravity as compared with the transfer roll 22. More specifically, it means that the rotation center 21 a of the photosensitive drum 21 is positioned above the rotation center 22 a of the transfer roll 22 in the direction of gravity.
Therefore, in the case where an image is formed from above in the direction of gravity at the transfer portion Tb, for example, as shown in FIG. 2A, the entire photosensitive drum 21 is positioned above the direction of gravity than the transfer roll 22. In addition, as shown in FIG. 2B, a form in which the positions of the photosensitive drum 21 and the transfer roll 22 in the gravitational direction partially overlap is also included.

  Further, in the present embodiment, “the image forming surface of the sheet faces upward in the gravity direction” means that the direction in which the image forming surface faces in the transfer portion Tb (perpendicular to the image forming surface in the transfer portion Tb) is at least It means that it has a component directed upward.

  Returning to FIG. 1, in the second image forming unit 20 of the present embodiment, the entire photosensitive drum 21 is positioned above the transfer roll 22 in the direction of gravity, as in the example shown in FIG. ing.

  The second fixing device 26 further includes a heating member having a heat source such as a halogen lamp, a resistance heating element, and an induction heating coil, and a pressing member forming a pressing portion Nb between the heating member and the heating member. By passing the sheet to the pressure unit Nb, the toner image is fixed to the sheet by heat and pressure.

  Note that the second image forming unit 200 does not have a stacking unit for stacking sheets. Although the details will be described later, the sheet on which the image of the spot color is formed by the second image forming unit 20 is conveyed along the downstream portion 4b of the second sheet conveyance path R4 and provided in the first image forming unit 100. The sheet is stacked on the sheet stacking unit 33. Accordingly, for example, the configuration of the image forming apparatus 1 can be simplified as compared with a case where a stacking unit for stacking sheets is provided in each of the first image forming unit 100 and the second image forming unit 200.

Subsequently, an image forming operation performed in the image forming apparatus 1 of the present embodiment will be described. The image forming operation described below is executed under the control of the control unit 50.
First, in the image forming apparatus 1, after a normal color image is formed on one surface of a sheet by the first image forming unit 100 (first image forming unit 10), one of the sheets on which the normal color image is formed. The operation in the case where the image of the spot color is superimposed and formed by the second image forming unit 200 (second image forming unit 20) on the surface of the image forming apparatus 100 will be described.

In the image forming apparatus 1, image data received from a PC (not shown) is subjected to image processing by the control unit 50, and the first image forming unit 10 and the second image forming unit 200 of the first image forming unit 100. To the second image forming unit 20.
In the first image forming unit 10 of the first image forming unit 100, each photosensitive drum 11 corresponding to each color of the normal color is charged to a predetermined potential by the charging device while rotating in the direction of arrow A, It is exposed by the exposure device which emits light based on the image data supplied from the unit 50. Thus, electrostatic latent images relating to the respective color images are formed on the respective photosensitive drums 11. Then, the electrostatic latent images formed on the photosensitive drums 11 are developed by the developing device, and toner images of respective colors of yellow, magenta, cyan and black are formed on the respective photosensitive drums 11.

The toner images of the respective colors formed on the respective photosensitive drums 11 are multi-transferred onto the intermediate transfer belt 13 moving in the direction of the arrow B by using the respective primary transfer rolls 12.
In addition, the sheet is conveyed from the sheet supply unit 31 to the secondary transfer unit Ta via the first sheet conveyance path R1 in accordance with the timing at which the toner image multiplex-transferred onto the intermediate transfer belt 13 reaches the secondary transfer roll 14. Is done. The normal color toner image on the intermediate transfer belt 13 is collectively transferred onto one surface of the sheet by the secondary transfer roll 14 in the secondary transfer portion Ta.

  Thereafter, the sheet on which the toner image of the normal color is formed is separated from the intermediate transfer belt 13 and conveyed upward along the first sheet conveyance path R1 in the direction of gravity to reach the first fixing device 16. The toner image of the normal color on the paper conveyed to the first fixing device 16 is fixed on the paper by the fixing processing by heat and pressure by the first fixing device 16.

  The sheet on which the toner image of the normal color is fixed is conveyed along the first sheet conveyance path R1 and reaches the sheet discharge unit 32. In the paper discharge unit 32, a part of the paper is discharged from the paper discharge unit 32 toward the paper stacking unit 33 by rotating the discharge roll 32 a in the first direction (arrow D direction). Subsequently, the discharge roll 32a is rotated in the second direction (the direction opposite to the arrow D), whereby the sheet is sent out to the sheet reversing path R2.

  Then, the sheet is conveyed along the sheet reversing path R2, so that the front and back are reversed, and the secondary transfer unit Ta of the first image forming unit 10 and the image forming surface are directed to the right side in the drawing again. Pass the pressure part Na. The paper that has passed through the secondary transfer portion Ta and the pressurizing portion Na is conveyed upward in the direction of gravity, and is delivered to the second image forming unit 200 via the paper delivery path R3.

  In the second image forming unit 200, the paper delivered from the first image forming unit 100 is transported along the second paper transport path R4. Specifically, the sheet is conveyed upward in the direction of gravity along the upstream portion R4a of the second sheet conveyance path R4 while the image forming surface on which the toner image of the normal color is formed is directed to the right in the figure. Subsequently, the sheet changes its traveling direction along the downstream portion R4b of the second sheet conveyance path R4, is horizontally conveyed in the left direction in the drawing while the image forming surface is directed upward in the gravity direction, and reaches the transfer portion Tb. Do.

  Further, in the second image forming unit 20 of the second image forming unit 200, the photosensitive drum 21 is charged to a predetermined potential by the charging device while rotating in the direction of arrow C, and the image supplied from the control unit 50 It is exposed by an exposure device that emits light based on data. Thereby, an electrostatic latent image relating to the image of the special color is formed on the photosensitive drum 21. The electrostatic latent image formed on the photosensitive drum 21 is developed by a developing device, and a special color toner image is formed on the photosensitive drum 21.

Then, the special color toner image formed on the photosensitive drum 21 is electrostatically applied from above in the gravitational direction by the transfer roll 22 to the image forming surface facing upward in the gravitational direction of the paper conveyed to the transfer unit Tb. Transcribed.
Thereafter, the sheet onto which the toner image of the special color is transferred is peeled off from the surface of the photosensitive drum 21, and the image forming surface is directed upward in the direction of gravity along the downstream portion R4b of the second sheet conveyance path R4. The sheet is conveyed to the fixing device 26.

  As described above, in the second image forming unit 200 of the present embodiment, in the second sheet conveyance path R4 (downstream portion R4b) between the transfer portion Tb and the pressing portion Nb of the second fixing device 26, the sheet is While the image forming surface is directed upward in the direction of gravity. Thus, for example, unlike the case where the sheet is conveyed with the image forming surface directed downward in the direction of gravity, the unfixed toner image transferred to the sheet at the transfer portion Tb is transferred to the second sheet conveyance path R4 (downstream portion R4b Contact with a guide or the like provided below the direction of gravity) is suppressed. Then, the disturbance of the image, the contamination of the sheet, and the like caused by the contact of the unfixed toner image with the guide and the like are suppressed.

The toner image on the paper transported to the second fixing device 26 is fixed on the paper by the fixing processing by heat and pressure by the second fixing device 26. Then, the sheet on which the fixed image of the normal color and the special color is formed is conveyed along the second sheet conveyance path R4 with the image forming surface directed upward in the direction of gravity, and provided in the first image forming unit 100. The paper is discharged to the paper stacking unit 33.
In this way, the image forming process is repeatedly executed for the number of printed sheets.

  When a superimposed image of a normal color image and a special color image is formed on one side of the sheet in this way, the first fixing device 16 of the first image forming unit 100 and the second image forming unit 200 are connected. The fixing process is performed by both the fixing device 26. Electric power is required to generate the heat necessary for the fixing process in the first fixing device 16 and the second fixing device 26. When the peaks where the power for generating the heat necessary for the fixing process becomes large overlap between the first fixing device 16 and the second fixing device 26, the power burden on the image forming apparatus 1 tends to be large. Therefore, in the present embodiment, the peak of electric power that generates heat in the first fixing device 16 and the peak of electric power that generates heat in the second fixing device 26 can be shifted based on control by the control unit 50. preferable.

  Here, as described above, in the image forming apparatus 1 according to the present embodiment, when the normal color image and the special color image are formed on one side of the sheet so as to overlap each other, the first image forming unit 10 performs the process. The sheet on which the normal color toner image is fixed and the front and back sides are reversed in the sheet reversing path R2 passes through the secondary transfer portion Ta and the pressure unit Na of the first image forming unit 10 again.

  When the paper whose front and back are reversed passes through the secondary transfer portion Ta again, the absolute value of the transfer voltage applied to the secondary transfer portion Ta by the power source can be reduced based on the control by the control unit 50. preferable. In other words, the absolute value of the transfer voltage applied to the secondary transfer portion Ta when the paper with the front and back reversed passes through the secondary transfer portion Ta is the same as when the normal color toner image is transferred to the paper. Is preferably lower than the absolute value of the transfer voltage applied to the secondary transfer portion Ta.

The absolute value of the transfer voltage applied to the secondary transfer portion Ta when the paper with the front and back reversed again passes through the secondary transfer portion Ta is the secondary value when the normal color toner image is transferred to the paper. When the transfer voltage is equal to or greater than the absolute value of the transfer voltage applied to the transfer portion Ta, the sheet is likely to be charged when passing through the secondary transfer portion Ta. In this case, when the sheet is separated from the intermediate transfer belt 13 or the like, a discharge tends to occur through the sheet, and this discharge may cause a change in the behavior of the sheet.
On the other hand, by reducing the absolute value of the transfer voltage applied to the secondary transfer portion Ta when the sheet whose front and back is reversed passes the secondary transfer portion Ta again, the behavior change of the sheet due to discharge or the like It can be suppressed.
Furthermore, it is more preferable not to apply a transfer voltage to the secondary transfer portion Ta when the paper whose front and back are reversed passes through the secondary transfer portion Ta again. Thereby, the change in the behavior of the paper due to the discharge can be further suppressed. When the transfer voltage is not applied to the secondary transfer portion Ta, the sheet may be transported by rotating the secondary transfer roll 14 or the intermediate transfer belt 13 or the like.

  Further, when the paper whose front and back are reversed passes through the pressure unit Na again, it is preferable to reduce the fixing strength of the first fixing device 16 to the paper based on the control by the control unit 50. In other words, the heat or pressure applied to the sheet by the first fixing device 16 when the sheet with the front and back reversed again passes through the pressurization unit Na is used to fix the normal color toner image on the sheet. The heat or pressure applied to the sheet by the first fixing device 16 is preferably smaller.

As a method for reducing the fixing strength of the first fixing device 16 on the paper, for example, the heating temperature by the heat source of the heating member is lowered, or the pressure between the heating member and the pressure member in the pressure unit Na is reduced. And shortening the transport direction length of the pressing unit Na and increasing the transport speed of the sheet passing through the pressing unit Na.
When the paper whose front and back sides are reversed passes through the pressure unit Na again, the image of the normal color after being fixed on the paper is heated or pressed again by reducing the fixing strength of the first fixing device 16 to the paper. It is possible to suppress fluctuations in the image due to being performed. The fluctuation of the image may include, for example, an increase in gloss (glossy) of an image of a normal color after being fixed on a sheet.

Furthermore, from the viewpoint of suppressing image fluctuation due to the image of the normal color after being fixed to the paper being heated or pressed again, when the paper whose front and back is reversed passes the pressing part Na again More preferably, the fixing process by the first fixing device 16 is not performed.
In the description of the present embodiment, “no fixing process” means a case where power is not supplied to the heating source of the fixing device (the first fixing device 16 and the second fixing device 26). The case where the heating member or the pressure member is rotated without supplying electric power to transport the paper in the fixing device includes the case where “the fixing process is not performed”.

On the other hand, when it is necessary to apply more heat to the paper, the first fixing is performed based on the control by the control unit 50 when the paper whose front and back are reversed passes through the pressure unit Na again. It is preferable to supply electric power to the heating source of the device 16 to apply heat to the paper again.
For example, when more heat needs to be applied to the paper, for example, when it is desired to increase the gloss (gloss) of a special color image formed by the second image forming unit 20 or when the basis weight of the paper is large. Etc.

  Compared with the case where heat is not applied by the first fixing device 16 by applying heat to the paper by the first fixing device 16 when the paper with the front and back reversed again passes through the pressure unit Na. The temperature of the sheet conveyed to the image forming unit 200 can be raised. Thereby, the gloss (gloss) of the special color image formed by the second image forming unit 20 of the second image forming unit 200 can be increased. Further, even when the basis weight of the sheet is high, the occurrence of the fixing failure can be suppressed for the image of the special color formed by the second image forming unit 20 of the second image forming unit 200.

Subsequently, only the normal color image is formed on one side of the sheet by the first image forming unit 100 (first image forming unit 10), and the second image forming unit 200 (second image forming unit 20) has a special color. The operation when no image is formed will be described.
In the first image forming unit 10 of the first image forming unit 100, the image forming operation is performed as in the above-described example, and the toner image of the normal color is collectively transferred onto one side of the sheet in the secondary transfer unit Ta. . Thereafter, the sheet to which the toner image of the normal color has been transferred is conveyed to the first fixing device 16 and subjected to fixing processing by heat and pressure by the first fixing device 16 and fixed on the sheet.

The sheet on which the toner image of the normal color is fixed is conveyed along the first sheet conveyance path R1, and the sheet stacking unit 33 is disposed via the sheet discharge unit 32 with the image forming surface facing downward in the direction of gravity. Discharged into In this way, the image forming process is repeatedly executed for the number of printed sheets.
In the image forming apparatus 1 according to the present embodiment, when only a normal color image is formed on a sheet and no special color image is formed, the sheet is directly discharged to the sheet stacking unit 33 without passing through the sheet reversing path R2. As a result, compared to the case where the sheet is discharged through the sheet reversing path R2, the sheet conveyance path can be shortened, and the productivity can be improved.

  On the other hand, as described above, the fixability of the toner image on the sheet may be different depending on the type of the sheet, the image density, and the like. When an image is formed on a sheet having a large basis weight, or when the image density is high, the fixability of the toner image on the sheet tends to be low. In such a case, it is preferable to apply more heat and pressure to the paper in order to improve the fixability of the toner image on the paper. Also, when increasing the gloss (gloss) of an image formed on a sheet, it is preferable to apply more heat and pressure to the sheet.

  In the image forming apparatus 1 according to the present embodiment, when it is necessary to apply more heat to the sheet, after the fixing process is performed by the first fixing device 16 based on the control by the control unit 50. The sheet of paper is conveyed to the second image forming unit 200. Then, the second fixing device 26 of the second image forming unit 200 performs the fixing process by heat and pressure again. Thereby, for example, even when an image is formed on a sheet having a large basis weight or when the image density is high, the occurrence of fixing failure is suppressed as compared with the case where the second fixing device 26 does not perform the fixing process again. be able to. Further, the gloss (gloss) of the image can be increased as compared with the case where the second fixing device 26 does not perform the fixing process again.

In the case where the sheet after the fixing process is performed by the first fixing device 16 is conveyed to the second image forming unit 200, the sheet is directly conveyed to the second image forming unit 200 without passing through the sheet reversing path R2. Alternatively, the sheet may be conveyed to the second image forming unit 200 after reversing the front and back sides in the sheet reversing path R2.
When the sheet is directly transported to the second image forming unit 200 without passing through the sheet reversing path R2, the sheet transporting path can be shortened as compared with the case where the sheet is transported through the sheet reversing path R2, and the productivity is improved. It can be done. In this case, in the second sheet conveyance path R4 (downstream portion R4b) of the second image forming unit 200, the sheet is conveyed with the image forming surface on which the normal color image is formed facing downward in the direction of gravity. Is done. However, since the normal color image is once subjected to the fixing process in the first fixing device 16 of the first image forming unit 100, problems such as rubbing of the image hardly occur.

On the other hand, when the sheet is conveyed to the second image forming unit 200 after reversing the front and back through the sheet reversing path R2, a normal color image is formed on the second fixing device 26 of the second image forming unit 200. Then, the image forming surface is conveyed in a state of being directed upward in the direction of gravity. In this case, the heat is easily transmitted to the image forming surface of the sheet in the second fixing device 26. Thereby, the occurrence of fixing failure can be further suppressed, or the gloss (glossy) of the image can be further enhanced.
When the sheet is reversed in the sheet reversing path R2, the sheet passes through the pressing unit Na of the first image forming unit 100 before being transported to the second image forming unit 200. In this case, the sheet may be subjected to a fixing process by supplying power to the heat source of the first fixing device 16 before being conveyed to the second image forming unit 200. As a result, the fixing process of the first fixing device 16 is performed twice, the fixing process of the second fixing device 26 is performed once, and the fixing process is performed three times. More heat can be given.

Subsequently, the first image forming unit 100 (first image forming unit 10) does not form a normal color image, and the second image forming unit 200 (second image forming unit 20) forms one surface of the sheet. The operation when only the spot color image is formed will be described.
In the first image forming unit 100, the paper is transported from the paper supply unit 31 along the first paper transport path R1, and is delivered to the second image forming unit 200 via the paper delivery path R3. At this time, for example, the sheet may be conveyed by rotating the secondary transfer roll 14 of the first image forming unit 100 or the heating member or the pressing member of the first fixing device 16.

In the second image forming unit 20 of the second image forming unit 200, an image forming operation is performed in the same manner as in the above-described example, and a special color toner image is transferred onto one surface of the sheet from above in the gravity direction in the transfer unit Tb. The Thereafter, the sheet to which the special color toner image has been transferred is conveyed to the second fixing device 26, and subjected to fixing processing by heat and pressure by the second fixing device 26, and is fixed on the sheet.
Then, the sheet on which the special color toner image is fixed is conveyed along the second sheet conveyance path R4 with the image forming surface directed upward in the direction of gravity, and is discharged to the sheet stacking unit 33. In this way, the image forming process is repeatedly executed for the number of printed sheets.

  Further, in the image forming apparatus 1 of the present embodiment, when only the image of the spot color is formed on the sheet by the second image forming unit 200 (second image forming unit), the sheet is conveyed to the second image forming unit 200. The sheet may be preheated by the first fixing device 16 of the first image forming unit 100 before printing. Accordingly, the temperature of the sheet conveyed to the second image forming unit 200 can be raised compared to the case where the sheet is not heated in advance by the first fixing device 16, and the special color formed by the second image forming unit 200 can be increased. Fixability of the toner image to the sheet can be improved.

Subsequently, an image of a normal color is formed on one side of the sheet by the first image forming unit 100 (first image forming unit 10), and then the second image forming unit 200 (second image forming unit 20). The operation when a special color image is formed on the other side of the paper will be described.
In the first image forming unit 10 of the first image forming unit 100, the image forming operation is performed as in the above-described example, and the toner image of the normal color is collectively transferred onto one side of the sheet in the secondary transfer unit Ta. . Thereafter, the sheet on which the toner image of the normal color has been transferred is conveyed to the first fixing device 16, and is fixed on one surface of the sheet by receiving a fixing process using heat and pressure by the first fixing device 16.

The sheet on which the normal color image is fixed on one side by the first fixing device 16 does not pass through the sheet reversing path R2, in other words, is not reversed inside and out, and passes through the sheet delivery path R3 to form a second image. It is transported to the unit 200.
In the second image forming unit 200, the sheet is in a state in which one surface on which a normal color image is formed is directed downward in the gravity direction and the other surface on which no image is formed is directed upward in the gravity direction. Is conveyed to the second image forming unit 20.

In the second image forming unit 20 of the second image forming unit 200, an image forming operation is performed in the same manner as in the above-described example, and a special color toner image is transferred onto the other surface of the sheet from above in the gravity direction in the transfer unit Tb. The Thereafter, the sheet on which the special color toner image has been transferred is conveyed to the second fixing device 26, and is subjected to a fixing process by heat and pressure by the second fixing device 26 and fixed on the other surface of the sheet.
Then, the sheet on which the special color toner image is fixed is conveyed along the second sheet conveyance path R4 and is discharged to the sheet stacking unit 33. In this way, the image forming process is repeatedly executed for the number of printed sheets.

Second Embodiment
Next, a second embodiment of the present invention will be described. The same reference numerals are used for the same configuration as that of the first embodiment, and the detailed description thereof is omitted here. FIG. 3 is a view showing the overall configuration of the image forming apparatus 1 to which the second embodiment is applied.
Similar to the first embodiment, the image forming apparatus 1 according to the second embodiment includes a first image forming unit 100 that forms an image of a normal color on a sheet, and the first image forming unit 100 above the gravitational direction. And a second image forming unit 200 that forms an image of a spot color on a sheet stacked and conveyed from the first image forming unit 100.

  The first image forming unit 100 is a so-called rotary color printer. The first image forming unit 10 of the first image forming unit 100 includes a photosensitive drum 11, a rotary developing device 17, an intermediate transfer belt 13 to which a toner image formed on the photosensitive drum 11 is transferred, A secondary transfer roll 14 that secondary-transfers the toner image primarily transferred onto the intermediate transfer belt 13 to a sheet; and a backup roll 15 that is disposed opposite to the secondary transfer roll 14 with the intermediate transfer belt 13 interposed therebetween. ing. In addition, the first image forming unit 10 includes a first fixing device 16 that fixes the second-transferred toner image on a sheet.

As shown in FIG. 3, the first image forming unit 100 according to the second embodiment includes the first image forming unit 10 from the paper supply unit 31 as in the first image forming unit 100 according to the first embodiment. A first sheet conveyance path R1 for conveying the sheet through the sheet discharge unit 32; a sheet inversion path R2 for conveying the sheet whose front and back sides are inverted again to the first image forming unit 10; and a first image forming unit 10 And a sheet delivery path R3 for delivering the sheet having passed through to the second image forming unit 200.
In the first image forming unit 100 of the second embodiment, the first sheet conveyance path R1 is formed in an S-shape.

  In the first image forming unit 100 of the second embodiment, the first fixing device 16 is in a horizontal direction with respect to the secondary transfer portion Ta formed between the secondary transfer roll 14 and the backup roll 15. They are arranged side by side. Thus, for example, the size in the gravity direction of the first image forming unit 100 can be reduced as compared with the case where the first fixing device 16 is disposed above the secondary transfer portion Ta in the gravity direction.

  The second image forming unit 200 forms images of two different types of special colors (first special color and second special color) on the paper conveyed from the first image forming unit 100. As shown in FIG. 3, the second image forming unit 20 corresponds to the two photosensitive drums 21 arranged in parallel in the horizontal direction corresponding to the first special color and the second special color, and to the respective photosensitive drums 21. And two transfer rolls 22 arranged in the same manner. The second image forming unit 20 also includes a second fixing device 26 for fixing the image of the spot color on the sheet.

  In the image forming apparatus 1 of the second embodiment, when an image of a normal color and an image of a spot color are formed on one side of a sheet, the first image of the first image forming unit 100 is the same as in the first embodiment. The sheet on which the normal color image is formed on one surface in the forming unit 10 is reversed to the front and back via the sheet reversing path R <b> 2 and then conveyed to the second image forming unit 200. Then, in the second image forming unit 200, a special color image is formed on the one surface of the sheet received from the first image forming unit 100 from above in the direction of gravity by the second image forming unit 20.

  As described above, when the image forming apparatus 1 includes the first image forming unit 10 and the second image forming unit 20 provided above the first image forming unit 10 in the gravity direction, the second image forming is performed. In the section 20, an image is formed from the upper side in the gravity direction with respect to the sheet conveyed with the image forming surface upward in the gravity direction. Accordingly, for example, the size of the image forming apparatus 1 in the gravitational direction can be reduced as compared with the case where the second image forming unit 20 forms an image from the horizontal direction.

  Further, in the second image forming unit 200, the second image forming unit 20 forms an image on the sheet from above in the direction of gravity, whereby the second sheet conveyance path between the transfer unit Tb and the pressing unit Nb. In R4 (downstream portion R4b), the image forming surface of the sheet does not hang down in the direction of gravity. Therefore, the unfixed toner image transferred to the sheet at the transfer portion Tb is prevented from coming into contact with a guide or the like provided below the second sheet conveyance path R4 (downstream portion R4b) in the direction of gravity. Then, rubbing of the image and disturbance of the image caused by the unfixed toner image coming into contact with the guide and the like are suppressed.

Furthermore, in the image forming apparatus 1, after the sheet on which the image of the normal color is formed on one side by the first image forming unit 10 of the first image forming unit 100 is reversed via the sheet reversing path R2, It is conveyed to the second image forming unit 200. Then, in the second image forming unit 200, a special color image is formed on the one surface of the sheet received from the first image forming unit 100 from above in the direction of gravity by the second image forming unit 20.
Thus, even when the second image forming unit 20 adopts a configuration in which an image is formed from above in the direction of gravity in order to suppress image rubbing, the first image forming unit 10 and the second image forming unit 20 are used. Thus, an image can be formed on the same side of the sheet. That is, in the image forming apparatus 1 having the above configuration, the normal color image and the spot color image are formed on the same side (one side) of the sheet while suppressing image rubbing in the second image forming unit 20. be able to.

  In each of the above-described embodiments, the first image forming unit 10 forms an image of a normal color, that is, yellow, magenta, cyan and black, and the second image forming unit 20 forms the image of the special color. However, the present invention is not limited to this. Each of the first image forming unit 10 and the second image forming unit 20 may form a normal color image, or may form a special color image. It may form an image of a selected one or more colors.

Further, the image forming method in the first image forming unit 10 and the second image forming unit 20 is not particularly limited. Each of the first image forming unit 10 and the second image forming unit 20 may be a tandem image forming unit or an image forming unit including a rotary developing device, and uses an intermediate transfer belt. Instead, it may be a direct transfer type image forming unit for transferring an image directly from the photosensitive drum to a sheet. The first image forming unit 10 and the second image forming unit 20 may be an image forming unit that forms an image by a method other than the electrophotographic method such as an inkjet method. Furthermore, the image forming methods of the first image forming unit 10 and the second image forming unit 20 may be equal to or different from each other.
Furthermore, when an electrophotographic image forming unit is employed as the first image forming unit 10 or the second image forming unit 20, a fixing device that fixes an image on a sheet performs a fixing process using heat and pressure. In addition to the method, for example, a method such as flash fixing which performs fixing processing using light energy may be adopted.

DESCRIPTION OF SYMBOLS 1 ... image forming apparatus, 10 ... 1st image forming part, 16 ... 1st fixing device, 20 ... 2nd image forming part, 26 ... 2nd fixing device, 100 ... 1st image forming unit, 200 ... 2nd image formation unit

Claims (12)

A first image forming unit that forms an image on one surface of the recording material;
A reversing unit configured to reverse the front and back of the recording material on which the image is formed on the one surface by the first image forming unit and to send the recording material to the first image forming unit;
The recording material is provided above the first image forming unit in the gravity direction, and the recording material that has been reversed by the reversing unit and passed through the first image forming unit is arranged so that the one surface faces upward in the gravity direction. An image forming apparatus comprising: a second image forming unit that conveys and forms an image from above in the direction of gravity with respect to the one surface.   The first image forming unit forms an image on the one surface of the recording material when the second image forming unit does not form an image on the recording material, and then the recording material is not passed through the reversing unit. The image forming apparatus according to claim 1, wherein the image forming apparatus discharges the image.   The image according to claim 1, wherein the first image forming unit conveys the recording material to the second image forming unit without passing through the reversing unit, when the image is not formed on the recording material. Forming device. The first image forming unit includes a toner image forming unit that forms a toner image on the one surface of the recording material, and a fixing unit that heats and fixes the toner image formed by the toner image forming unit to the recording material. With
2. The fixing unit according to claim 1, wherein when the recording material after passing through the reversing unit passes, the fixing unit reduces the fixing strength of the toner image as compared with that before passing through the reversing unit. Image forming device.   The image forming apparatus according to claim 4, wherein the fixing unit does not perform a fixing process when the recording material after passing through the reversing unit passes. The first image forming unit heats the toner image formed by the first toner image forming unit that forms a toner image on the one surface of the recording material and the first toner image forming unit, and fixes the toner image on the recording material. A first fixing unit that
The second image forming unit heats the toner image formed by the second toner image forming unit that forms a toner image on the one surface of the recording material from above in the direction of gravity, and the second toner image forming unit. And a second fixing unit for fixing to the recording material.
The image forming apparatus according to claim 1, wherein the first fixing unit heats the recording material when the recording material after passing the reversing unit passes. The first image forming unit rotates with the recording material sandwiched between the image holding unit that holds the toner image and faces the one surface of the recording material, and holds the toner image. An image transfer portion for transferring the toner image to the one surface of the recording material, a power source for applying a transfer voltage to the image holding portion or the image transfer portion, and recording the toner image transferred by the image transfer portion A fixing unit that fixes to the material,
2. The power supply according to claim 1, wherein when the recording material after passing through the reversing portion passes, the power supply decreases the absolute value of the transfer voltage as compared with that before passing through the reversing portion. Image forming apparatus.   The image forming apparatus according to claim 7, wherein the power supply does not apply the transfer voltage when the recording material after passing through the inversion portion passes. The first image forming unit heats the toner image formed by the first toner image forming unit that forms a toner image on the one surface of the recording material and the first toner image forming unit, and fixes the toner image on the recording material. And a first fixing unit,
The second image forming unit heats the toner image formed by the second toner image forming unit that forms a toner image on the one surface of the recording material from above in the direction of gravity, and the second toner image forming unit. And a second fixing unit for fixing to the recording material.
When the second image forming unit does not form an image on a recording material, the second image forming unit receives the recording material on which the image is formed by the first image forming unit, and heats the recording material at the second fixing unit. An image forming apparatus according to claim 1.   The image forming apparatus according to claim 9, wherein the first image forming unit conveys the recording material to the second image forming unit without passing through the reversing unit.   The first image forming unit reverses the recording material on which the toner image is formed by the first toner image forming unit and the toner image is fixed by the first fixing unit by the reversing unit, and then the second image formation is performed. The image forming apparatus according to claim 9, wherein the image forming apparatus is transported to a unit.   12. The image forming apparatus according to claim 11, wherein the first image forming unit transports the recording material inverted by the reversing unit to the second image forming unit after being heated again by the first fixing unit. Image forming apparatus.

Images