JPH1138687A - Both-side image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To record an image on the both surfaces of a recording material in which the productivity per one sheet of the recording material is identical to the productivity when the image is recorded on one surface and the difference of an image quality between the both surfaces is eliminated while effectively evading the jam and the wrinkle of the recording material and image irregularity when the recording material rushes into a fixing means. SOLUTION: This device is provided with a secondary intermediate transfer means 8 secondarily transferring primary transfer images T1 and T2 carried on first and second intermediate transfer belts 2 and 4 with respect to the both surfaces of a recording material 5 in the area where the belts 2 and 4 are brought into contact with each other or they are close to each other and a fixing means 11 fixing the images T1 and T2 transferred on the both surfaces of the material 5. Then, the angles of θ1 and θ2 formed by the belts 2 and 4 arranged and bent at an almost identical position on the downstream side of the transfer means 8 and the carrying direction of the material 5 to the fixing means 11 from the transfer means 8 are respectively set to be <=90 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrophotographic copying machine,
The present invention relates to an image forming apparatus such as a printer, and more particularly to an improvement of a double-sided image forming apparatus capable of forming a double-sided image.

[0002]

2. Description of the Related Art As a conventional double-sided image forming apparatus capable of forming a double-sided image, a first image formed on a latent image carrier such as a photoreceptor is transferred and fixed to a first surface of a sheet, and then the sheet is fixed. Is reversed, and the sheet is fed again, and subsequently, the second image formed on the latent image carrier is transferred and fixed to the second surface of the sheet. However, in this method, since the image forming unit passes the paper twice, the productivity per sheet becomes slower than half of that for single-sided recording, and the paper curls during the first fixing. There are various problems such as poor transfer at the second transfer and fixing, paper wrinkling, the occurrence of jams in the conveyance path, and noise when the paper is reversed and re-fed.

As a double-sided image forming apparatus which solves such a problem, the present applicant has firstly formed first and second image forming sections each including a photosensitive member and an intermediate transfer belt corresponding to both sides of a sheet. The first and second images are secondarily transferred between the intermediate transfer belts on both sides of a sheet after the respective images on the photoreceptor are firstly transferred to the intermediate transfer belt (Japanese Patent Application No. Hei 8 (1996) -108).
-108449). According to this method, double-sided recording can be performed only by passing the sheet once through the image forming unit, so that it is possible to improve the productivity while solving the above problem.

[0004]

In the above-mentioned double-sided image forming apparatus, there is no means for controlling the attitude of the sheet holding the unfixed image on both sides between the secondary transfer section and the fixing device, and the image forming apparatus is provided on the sheet. The paper is attracted to the charged intermediate transfer belt, etc. due to the charged toner, and the paper posture becomes unstable, and jams, paper wrinkles, and image disturbances due to defective entry of the fixing device are likely to occur. Issues.

SUMMARY OF THE INVENTION The present invention has been made to solve the above technical problems, and it is possible to effectively prevent the occurrence of jamming, wrinkling, and image disturbance of a recording material when the fixing means enters, and to improve the quality of the recording material per sheet. Productivity is the same as when recording on one side,
An object of the present invention is to provide a double-sided image forming apparatus capable of performing double-sided recording with no image quality difference between both sides.

[0006]

That is, a first embodiment of the double-sided image forming apparatus according to the present invention is as shown in FIG.
A first image carrier 1 on which a first image T1 is carried;
A first intermediate transfer belt 2 disposed opposite to the image carrier 1,
A first intermediate primary transfer means 6 for primarily transferring the first image T1 on the first image carrier 1 to the first intermediate transfer belt 2, a second image carrier 3 carrying the second image T2, A second intermediate transfer belt 4 opposed to the second image carrier 3 and a second intermediate primary transfer for primary transferring the second image T2 on the second image carrier 3 to the second intermediate transfer belt 4 In a region where the means 7 and the first intermediate transfer belt 2 and the second intermediate transfer belt 4 are in contact with or close to each other, the primary transfer images T1 and T2 on the intermediate transfer belts 2 and 4 are An intermediate secondary transfer unit 8 for secondary transfer, and an image T transferred to both surfaces of the recording material 5
1, fixing means 11 for fixing T2. The feature of the first embodiment is that the first and second intermediate transfer belts 2 and 4 are bent and arranged at substantially the same position on the downstream side of the intermediate secondary transfer means 8. The angles θ1 and θ2 between the first and second intermediate transfer belts 2 and 4 on the downstream side of the means 8 and the recording material conveyance direction from the intermediate secondary transfer means 8 to the fixing means 11 are respectively 90 degrees or less. In a mode in which the second intermediate transfer belts 2 and 4 are bent at different positions downstream of the intermediate secondary transfer unit 8, the first and second intermediate transfer belts downstream of the intermediate secondary transfer unit 8 are arranged. Intermediate transfer belt 2 or 4 located closer to fixing means 11 among 2, 4
And the angle .theta.1 or .theta.2 between the intermediate secondary transfer means 8 and the fixing means 11 with respect to the recording material conveyance direction is set to 90 degrees or less. FIG. 1 illustrates an example in which the first and second intermediate transfer belts 2 and 4 are bent at substantially the same position on the downstream side of the intermediate secondary transfer means 8.

In such a technical means, the intermediate secondary transfer means 8 may perform the transfer to both sides of the recording material 5 one by one in a continuous manner, but the simplification of the transfer device and the image disturbance may be avoided. From the viewpoint of avoiding the problem reliably, it is preferable to simultaneously transfer the recording material 5 to both surfaces. Here, as a mode for simultaneously transferring the recording material 5 to both surfaces,
For example, in a type in which the first image T1 and the second image T2 are formed by an electrophotographic method, the first and second images T1 and T2 carried on the first intermediate transfer belt 2 and the second intermediate transfer belt 4 are It is necessary that the polarities are opposite to each other in the secondary transfer area. At this time, the first and second images T1 and T2 may be originally made of the opposite polarity material, or
Using the same polarity material, providing polarity reversing means at appropriate places,
The polarity of one image may be reversed.

[0008] In the intermediate secondary transfer means 8, as a mode for simultaneously transferring images to both surfaces of the recording material 5, for example, the first
A pair of transfer members are provided with the intermediate transfer belt 2 and the second intermediate transfer belt 4 interposed therebetween, and a transfer bias is applied to one of the transfer members and the other transfer member is grounded. A pair of transfer members is provided with the transfer belt 2 and the second intermediate transfer belt 4 interposed therebetween, and transfer biases having different polarities are applied to these transfer members. At this time, as a method of applying a bias to the transfer member, a transfer bias may be directly applied to the transfer member. However, in order to apply a uniform transfer bias to the entire transfer member, a contact roll or the like having a uniform surface may be used. It is preferable that the intermediate member is disposed in contact with the transfer member, and a transfer bias is applied through the intermediate member.

Further, in the intermediate secondary transfer means 8, as a mode for continuously transferring both surfaces of the recording material 5 one by one, for example, the transfer is performed on the first surface and the second surface of the recording material 5, respectively. Of the recording material 5 on the first surface and the second surface of the recording material 5 by these transfer members. One in which transfer is performed sequentially and continuously is exemplified. At this time, a method similar to the method described above can be employed for applying a transfer bias to the transfer member.

Further, the intermediate secondary transfer means 8 normally performs suction holding and secondary transfer of the recording material 5, but from the viewpoint of more reliably holding the recording material 5,
Before the next transfer area, an adsorbing means for adsorbing the recording material 5 to either the first intermediate transfer belt 2 or the second intermediate transfer belt 4 may be provided.

Further, with respect to the layout of the intermediate transfer belts 2, 4, the intermediate transfer belts 2, 4 are bent at substantially the same position on the downstream side of the intermediate secondary transfer means 8, for example. The intermediate transfer belts 2 and 4 are wound around the pair of roll-shaped transfer members themselves, or the bridge members of the intermediate transfer belts 2 and 4 are arranged at substantially the same position on the downstream side of the intermediate secondary transfer means 8. Means to do. On the other hand, a mode in which the intermediate transfer belts 2 and 4 are bent and arranged at different positions on the downstream side of the intermediate secondary transfer unit 8 is, for example, one of the intermediate transfer belts 2 or 4 and the middle 2
On the downstream side of the next transfer means 8, another intermediate transfer belt 4 or 2
Or a bridging member for each of the intermediate transfer belts 2 and 4 at a different position downstream of the intermediate secondary transfer means 8.

Further, as shown in FIG. 2, a second embodiment of the double-sided image forming apparatus according to the present invention comprises a first image carrier 1, a first intermediate transfer belt 2, and a first intermediate 1 similar to those shown in FIG. In addition to the next transfer means 6, the second image carrier 3, the second intermediate transfer belt 4, and the second intermediate primary transfer means 7, the first intermediate transfer belt 2
In a region where the recording material 5 is in contact with or in proximity to the second intermediate transfer belt 4, the recording material 5 is suction-held at a position corresponding to the second image T2 on the second intermediate transfer belt 4, and the first intermediate transfer of the recording material 5 is performed. A first intermediate secondary transfer means 9 for secondary-transferring the primary transfer image T1 on the first intermediate transfer belt 2 to one side facing the belt 2, and a first intermediate secondary transfer means 9; The recording material 5 sucked and held by the second intermediate transfer belt 4 has a second surface on one side facing the second intermediate transfer belt 4.
A second intermediate secondary transfer unit 10 for secondarily transferring the primary transfer image T2 on the intermediate transfer belt 4; and a fixing unit 11 for fixing the images T1 and T2 transferred to both surfaces of the recording material 5; (2) The angle θ2 between the second intermediate transfer belt 4 bent and arranged on the downstream side of the intermediate secondary transfer unit 10 and the recording material transport direction from the second intermediate secondary transfer unit 10 to the fixing unit 11 is set to 90 degrees or less. It is characterized by the following.

Further, as shown in FIG. 3, a third embodiment of the double-sided image forming apparatus according to the present invention has the same components (first image carrier 1, first intermediate transfer belt 2, 1 middle 1
A second transfer means 6, a second image carrier 3, a second intermediate transfer belt 4, a second intermediate primary transfer means 7, an intermediate secondary transfer means 8, and a fixing means 11). The feature of the third embodiment is that the first and second intermediate transfer belts 2 and 4 are bent at substantially the same position on the downstream side of the intermediate secondary transfer means 8. The peeling claws 12a and 12b are provided in contact with or close to the first and second intermediate transfer belts 2 and 4 which are bent and arranged on the downstream side of the transfer means 8, respectively, and the first and second intermediate transfer belts 2 and 4 are provided. In a mode in which the first and second intermediate transfer belts 2 and 4 on the downstream side of the intermediate secondary transfer means 8 are bent and arranged at different positions on the downstream side of the intermediate secondary transfer means 8, the fixing means 11 is provided. In other words, the peeling claw 12a or 12b is provided in contact with or close to the intermediate transfer belt 2 or 4 located. FIG. 3 illustrates an example in which the first and second intermediate transfer belts 2 and 4 are bent at substantially the same position on the downstream side of the intermediate secondary transfer means 8.

Further, as shown in FIG. 4, the fourth embodiment of the double-sided image forming apparatus according to the present invention has the same components (the first image carrier 1, the first intermediate transfer belt 2, A first intermediate primary transfer means 6, a second image carrier 3, a second intermediate transfer belt 4, a second intermediate primary transfer means 7, a first intermediate secondary transfer means 9, a second intermediate secondary transfer means 10, Fixing means 11), and a peeling claw 12 is provided in contact with or close to the second intermediate transfer belt 4 bent and arranged downstream of the second intermediate secondary transfer means 10.

In the embodiments of FIGS. 1 to 4,
The layout of the image carriers 1 and 3 and the intermediate transfer belts 2 and 4 of the present invention may be appropriately selected. However, if the importance of stabilizing the attitude of the recording material 5 entering the fixing unit 11 is emphasized, the recording material 5 A portion corresponding to the secondary transfer area is disposed in the substantially vertical direction in the conveyance path of the recording medium, and a fixing unit 11 on which an unfixed image on both surfaces of the recording material 5 is fixed below the secondary transfer area.
Is preferably provided. Here, as the fixing means 11, a fixing means for fixing unfixed images on both sides of the recording material 5 at the same time is used, but the fixing means is not limited to this. For example, an unfixed image on one side of the recording material 5 is assumed first. After the attachment, the image on both sides of the recording material 5 for permanent fixing may be appropriately selected. Although FIGS. 1 to 4 illustrate a vertical type in which the transport direction of the recording material 5 is substantially vertical, the present invention is not limited to this. Needless to say, a horizontal type in which the direction is substantially horizontal is also included.

In FIG. 1 to FIG. 4, as a mode for forming a color image, the first intermediate transfer belt 2 and the second
Since the intermediate transfer belt 4 is an intermediate transfer belt that carries color images T1 and T2 in which image components of a plurality of colors are multiplex-transferred, in order to form the color images T1 and T2 without disturbing the intermediate transfer belts 2, When the image on the intermediate transfer belt 4 passes through the secondary transfer area without being transferred onto the recording material 5, the two intermediate transfer belts 2 and 4 are separated from each other. At the time of transfer, it is necessary to provide a contacting / separating means in which the two intermediate transfer belts 2 and 4 are in contact with or close to each other. Further, as a mode for forming a color image in a short time, the first image carrier 1 and the second image carrier 3 are composed of a plurality of color component image carrier groups each carrying a plurality of color image components. The first intermediate transfer belt 2 and the second intermediate transfer belt 4 transfer and hold image components from a plurality of color component image carrier groups of the first image carrier 1 and the second image carrier 3. No.

Next, the operation of the above technical means will be described. First, in the embodiment shown in FIG. 1, the first intermediate primary transfer means 6 primarily transfers the first image T1 on the first image carrier 1 to the first intermediate transfer belt 2 and the second intermediate primary transfer. The means 7 primarily transfers the second image T2 on the second image carrier 3 to the second intermediate transfer belt 4. Thereafter, the intermediate secondary transfer means 8
In the area where the first intermediate transfer belt 2 and the second intermediate transfer belt 4 are in contact with or close to each other, the primary transfer images T 1,
T2 is secondarily transferred. Then, the fixing unit 11 is connected to the recording material 5.
The first and second images T1 and T2 on both sides are fixed. The first and second bends arranged at substantially the same position on the downstream side of the intermediate secondary transfer means 8
By setting the angles θ1 and θ2 between the intermediate transfer belts 2 and 4 and the recording material conveyance direction from the intermediate secondary transfer unit 8 to the fixing unit 11 to 90 degrees or less, the angle at the exit of the intermediate secondary transfer unit 8 is reduced. The posture of the recording material 5 can be stabilized, and the electric force acting between the intermediate transfer belts 2 and 4 and the recording material 5 can be eliminated, so that the conveyance of the recording material 5 to the fixing unit 11 can be performed stably. it can.

Here, the first and second intermediate transfer belts 2 and 4 downstream of the intermediate secondary transfer means 8 and the intermediate secondary transfer means 8
From the recording material conveyance direction from the fixing unit 11 to the fixing means 11
The electric force acting between the intermediate transfer belts 2 and 4 and the recording material 5 under the condition that 1, θ2 exceeds 90 degrees will be briefly described with reference to FIGS. 5 and 6. FIGS. 5 and 6 show a case where the transfer bias Vt is applied to one transfer member 8a of the intermediate secondary transfer means 8 and the other transfer member 8b is grounded in an apparatus for simultaneously transferring images to both surfaces of the recording material 5. And a state on the downstream side of the intermediate secondary transfer means 8 when transfer biases Vt (-) and Vt (+) having different polarities are applied to the pair of transfer members 8a and 8b, respectively. In both cases, the first image T1 of negative polarity is transferred to the first intermediate transfer belt 2 side of the recording material 5 and the second image T2 of positive polarity is transferred to the second intermediate transfer belt 4 side by the intermediate secondary transfer means 8. You.

As shown in FIG. 5, a negative transfer bias Vt is applied to the transfer member 8a on the first intermediate transfer belt 2 side of the intermediate secondary transfer means 8, and the transfer member 8b on the second intermediate transfer belt 4 side is applied. Is grounded, the first intermediate transfer belt 2 on the downstream side of the intermediate secondary transfer means 8 is negatively charged, while the voltage on the second intermediate transfer belt 4 is substantially 0V. At this time, since the angles θ1 and θ2 between the first and second intermediate transfer belts 2 and 4 and the recording material conveyance direction from the intermediate secondary transfer means 8 to the fixing means 11 exceed 90 degrees, the recording material When the first intermediate transfer belt 2 side is higher than the other surface as the image density of No. 5, the charge 13 on the first intermediate transfer belt 2 and the first
Due to the repulsive force with the image T1, the recording material 5 moves to the second intermediate transfer belt 4 side. Conversely, when the image density of the recording material 5 is higher at the second intermediate transfer belt 4 side than at the other surface, the second image T2 is formed.
Receives attraction force from both the first and second intermediate transfer belts 2 and 4.

As shown in FIG. 6, a negative transfer bias Vt (-) is applied to the transfer member 8a of the intermediate secondary transfer means 8 on the first intermediate transfer belt 2 side, and the second intermediate transfer belt 4
When the positive transfer bias Vt (+) is applied to the transfer member 8b on the side, the first and second intermediate transfer belts 2 and 4 are connected to the first and second images T1 and T2 on the recording material 5, respectively. The first and second images T1 and T2 are compared with the case where the transfer bias Vt is applied to one of the transfer members 8a of the intermediate secondary transfer means 8 and the other transfer member 8b is grounded, because they are charged to the opposite polarity. Although the repelling force from the electric charges 13 and 14 of the first and second intermediate transfer belts 2 and 4 makes it difficult to be attracted slightly, however, it is attracted depending on the balance of the image density on both sides of the recording material 5.

In the embodiment shown in FIG. 1, each of the intermediate transfer belts 2 and 4 is bent at substantially the same position on the downstream side of the intermediate secondary transfer means 8. Are bent at different positions on the downstream side of the intermediate secondary transfer means 8, the angle θ1 or θ2 of the intermediate transfer belt 2 or 4 near the fixing means 11 is set to 90 degrees or less. The posture of the recording material 5 at the exit of the intermediate secondary transfer means 8 can be stabilized, and the electric force acting between the intermediate transfer belt 2 or 4 and the recording material 5 can be eliminated. 5 The transfer can be performed stably.

In the embodiment shown in FIG. 2, a first image primary transfer step and a second image primary transfer step similar to those described above are performed. Thereafter, the first intermediate secondary transfer means 9
In a region where the first intermediate transfer belt 2 and the second intermediate transfer belt 4 are in contact with or close to each other, the recording material 5 is suction-held at a position corresponding to the second image T2 on the second intermediate transfer belt 4, and The primary transfer image T1 on the first intermediate transfer belt 2 is secondarily transferred to one side of the recording material 5 facing the first intermediate transfer belt 2 (first image secondary transfer step). Next, a second intermediate secondary transfer means 10 provided at a stage subsequent to the first intermediate secondary transfer means 9 faces the second intermediate transfer belt 4 of the recording material 5 sucked and held by the second intermediate transfer belt 4. The primary transfer image T2 on the second intermediate transfer belt 4 is secondary-transferred to the one side (second image secondary transfer step). Then, the fixing unit 11 fixes the first and second images T1 and T2 on both surfaces of the recording material 5. The second intermediate transfer belt 4 and the second intermediate secondary transfer unit 10 that are bent and arranged on the downstream side of the second intermediate secondary transfer unit 10
From the recording material conveyance direction from the fixing unit 11 to the fixing means 11
By setting 2 to 90 degrees or less, the second intermediate secondary transfer means 1
The position of the recording material 5 at the exit 0 can be stabilized, and the electric force acting between the intermediate transfer belts 2 and 4 and the recording material 5 can be eliminated, and the conveyance of the recording material 5 to the fixing means 11 can be stabilized. Can be done.

Further, in the embodiment shown in FIG.
Peeling claws 12a, 12b provided on the downstream side of the next transfer means 8
Is to peel off the recording material 5 on the intermediate transfer belts 2 and 4 when the recording material 5 causes a peeling failure at the exit of the intermediate secondary transfer means 8 or to transfer the recording material 5 to the intermediate transfer belts 2 and 4 Prevents adsorption. In FIG. 3, the intermediate transfer belts 2 and 4 are bent at substantially the same position on the downstream side of the intermediate secondary transfer means 8. In a mode in which the separation claw 12a or 12b is bent only at the intermediate transfer belt 2 or 4 near the fixing unit 11, the separation claw 12a or 12b is used for recording. The peeling failure of the material 5 or the re-adsorption is prevented.

Further, in the embodiment shown in FIG. 4, the peeling claw 1 provided on the downstream side of the second intermediate secondary transfer means 10 is provided.
2 is for peeling off the recording material 5 on the intermediate transfer belts 2 and 4 when the recording material 5 causes a peeling failure at the exit of the second intermediate secondary transfer means 10 or for transferring the recording material 5 to the second intermediate transfer belt. 4 to prevent re-adsorption.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. First Embodiment FIG. 7 shows a schematic configuration of a two-sided image forming apparatus according to a first embodiment of the present invention. In FIG. 1, the two-sided image forming apparatus includes a first image forming unit 20a that forms a first image on a first surface of a sheet P, and a second image forming unit that forms a second image on a second surface of the sheet P. 20b, a double-sided image forming unit and 20a,
Fixing device 50 for fixing an image on paper P passing through 20b
And

In this embodiment, each image forming unit 20
Reference numerals a and 20b denote photosensitive drums 21a and 21b and a charging roll 22 for charging the surfaces of the photosensitive drums 21a and 21b.
a, 22b and an exposure device 23 for writing electrostatic latent images for the first and second images on the charged photosensitive drums 21a, 21b.
a, 23b and developing units 24a, 2 for visualizing the electrostatic latent images written on the photosensitive drums 21a, 21b with toner.
4b, intermediate transfer belts 25a and 25b arranged in contact with photosensitive drums 21a and 21b, and photosensitive drums 21a and 2b.
1 for primary transfer of the toner images T1 and T2 (for example, normal images in the present embodiment) on the intermediate transfer belts 25a and 25b.
Next transfer rolls 26a, 26b and photosensitive drums 21a, 2
Cleaners 27a and 27b for removing the residual toner on
And A polarity reversal corotron 28 is disposed downstream of the photosensitive drum 21b of the second image forming unit 20b at the developing position.

In this embodiment, each of the intermediate transfer belts 25a and 25b is wound around an appropriate number of holding rolls (one is a driving roll and the other is a driven roll), and is synchronized with the photosensitive drums 21a and 21b. It is designed to rotate. Further, holding rolls arranged corresponding to areas where the respective intermediate transfer belts 25a and 25b are in contact with or in proximity to each other are configured as secondary transfer rolls 40a and 40b. Further, the fixing device 5 is connected to the secondary transfer rolls 40a and 40b.
0 and the secondary transfer rolls 40a, 40
b, the intermediate transfer belts 25a, 25 bent downstream of
The holding rolls are arranged so that the angles θ1 (between AB) and θ2 (between A and C) with respect to 5b are each 90 degrees or less, and the angles θ1 and θ2 are set to, for example, 80 degrees, respectively. . The intermediate transfer belts 25a and 25b are made of a resin such as polyimide, acrylic, vinyl chloride, polyester, polycarbonate, polyethylene terephthalate (PET) or various rubbers containing an appropriate amount of an antistatic agent such as carbon black, and have a volume resistance. Rate is 10 ⁹ to 10 ¹⁴ Ω · cm
And the thickness is, for example, 0.08 mm
Is set to Reference numerals 30a and 30b denote belt cleaners for removing residual toner on the intermediate transfer belts 25a and 25b.

Although the secondary transfer rolls 40a and 40b can be transferred by using both conductive ones, the first and second intermediate transfer belts 25a and 40b can be used for transfer to small-sized paper.
When 25b is in direct contact, the secondary transfer rolls 40a, 40a
b, an excessive current flows between them, so that a sufficient transfer electric field cannot be formed and transfer failure occurs, or the intermediate transfer belt 25
Since a and 25b are easily damaged, it is preferable to use at least a conductive roll coated with a semiconductive or insulating material.

In this embodiment, the secondary transfer roll 40
For both a and 40b, a metal shaft coated with EPDM rubber dispersed with carbon black and having a volume resistivity of 10 ⁶ Ω · cm is used.
A transfer bias 41 was applied to the shaft a, and the shaft of the secondary transfer roll 40b was grounded. In addition, as the coating material, a material obtained by dispersing conductive particles (such as carbon black or aluminum) or an ion conductive agent (such as LiClO ₄ ) in polyurethane rubber or silicon rubber can be used.
The volume resistivity is preferably set to 10 ⁵ to 10 ⁹ Ω · cm.

Further, in the present embodiment, the toner T
1, T2 uses a negatively charged toner, and primary transfer rolls 26a,
DC current +10 μA and −10 μA are respectively applied to 26b, and DC current +400 μ
A, DC voltage +500 V was applied to the grid. First,
The outer diameters of the second photosensitive drums 21a and 21b and the circumferential lengths of the first and second intermediate transfer belts 25a and 25b were the same.
The distance from the secondary transfer position to the fixing device 50 was shorter than the minimum sheet length, and the rotation speed of the fixing roll was equal to or slightly lower than the speed of the intermediate transfer belts 25a and 25b. Also,
The fixing device 50 has the same shape of the upper and lower fixing rolls so that the fixing nip is linear, and a heater is disposed inside each of them. In FIG. 7, reference numeral 31 denotes a paper tray, and 32 denotes a transport roll for transporting the paper P.

Next, an image forming process of the double-sided image forming apparatus according to the present embodiment will be described. First photosensitive drum 2
The first toner image T1 formed on 1a is transferred by a primary transfer roll 26a onto a first intermediate transfer belt 25a moving at substantially the same speed as the first photosensitive drum 21a. Similarly, after inverting the polarity of the second toner image T2 formed on the second photosensitive drum 21b by applying a voltage to the polarity inversion corotron 28 at the same timing as on the first photosensitive drum 21a,
The second intermediate transfer belt 25b is driven by the primary transfer roll 26b.
Transfer to the top. Then, the sheet P is conveyed from the sheet tray 31 to the secondary transfer rolls 40a and 40b at the same time, and the toner image T on the intermediate transfer belts 25a and 25b is transferred.
After simultaneously transferring T1 and T2 onto the paper P, both sides are simultaneously fixed by the fixing device 50.

In the case of single-sided recording, for example, by applying a bias having a polarity opposite to that of a normal transfer bias to the primary transfer roll 26a or 26b on which no recording is performed, it is possible to prevent back surface contamination. In addition, a method of switching the developing bias or a method of separating the photosensitive drums 21a and 21b from the intermediate transfer belts 25a and 25b may be used.

As described above, the photosensitive drums 21a, 21b
From the toner images T1 and T1 on the intermediate transfer belts 25a and 25b.
T2 is transferred respectively, the paper P is transported between the secondary transfer rolls 40a, 40b, the images on the intermediate transfer belts 25a, 25b are simultaneously transferred to both sides of the paper P, and are transported to the fixing device 50 as they are to simultaneously fix both sides. By doing so, a double-sided image without image disturbance could be obtained at the same recording speed as for one side per sheet.

The paper transport direction A from the secondary transfer rolls 40a and 40b to the fixing device 50 and the secondary transfer roll 40
a, the intermediate transfer belt 2 bent at the downstream side of 40b
Angles θ1 (between AB) and θ2 (A−
C) is 90 degrees or less, electrical disturbance during paper transport from the secondary transfer section to the fixing device 50 can be eliminated, the paper posture can be stabilized, and the fixing device 50 can be fixed.
Can be brought close to the secondary transfer unit, and it is possible to reduce incomplete entry into the fixing unit 50, jams, paper wrinkles, and the like without providing a special sheet attitude control unit between the secondary transfer unit and the fixing unit 50. Was.

In the present embodiment, the transfer device 2
Although a bias roll is used for 6a, 26b, and 40a, a corotron may be used. Further, in this embodiment, the polarity of the toner image T2 is reversed on the photosensitive drum 21b by using the toner having the same charging polarity.
b may be reversed, or toners having different charging polarities may be used. In the present embodiment, a transfer bias is applied to one secondary transfer roll 40a and the other secondary transfer roll 40b is grounded. However, transfer biases having different polarities are applied to both the secondary transfer rolls 40a and 40b. It may be applied. Such design modification items can be appropriately adopted in the following embodiments.

Second Embodiment FIG. 8 shows a schematic configuration of a two-sided image forming apparatus according to a second embodiment of the present invention. In the figure, the basic configuration of this double-sided image forming apparatus is substantially the same as that of the first embodiment,
Unlike the first embodiment, each intermediate transfer belt 25a, 25
A first secondary transfer unit including a secondary transfer roll 44b and a backup roll 45a is provided corresponding to the area where b contacts or approaches, and at the subsequent stage of the first secondary transfer unit,
This is provided with a second secondary transfer section including a secondary transfer corotron 49 and a backup roll 45b. Then, the secondary transfer roll 44b and the secondary transfer corotron 49
Are applied with predetermined biases 55 and 56. The tension member 5 is provided upstream of the secondary transfer roll 44b.
2 were provided. Note that components similar to those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and detailed description thereof will be omitted. In this embodiment, devices around the photosensitive drums 21a and 21b (devices for charging, exposing, developing, and cleaning) are omitted. The same applies to the following embodiments.

In particular, in the present embodiment, the angle θ2 () formed between the sheet conveying direction A from the second secondary transfer section to the fixing device 50 and the intermediate transfer belt 25b bent and arranged downstream of the backup roll 45b. (Between A and C) is 90 degrees or less.
Set to 0 degrees.

In this embodiment, the toner T
1, T2 uses a negatively charged toner, and primary transfer rolls 26a,
DC currents +20 μA and −20 μA are respectively applied to 26b.
A DC voltage of +3 kV was applied to the next transfer roll 44 b, and a DC current of +300 μA was applied to the secondary transfer corotron 49 by superimposing an AC voltage of 8 kV _PP / 600 Hz. The backup rolls 45a and 45b were grounded. Further, the secondary transfer roll 44b and the backup rolls 45a and 45b are formed by coating a metal shaft with EPDM rubber dispersed with carbon black and having a volume resistivity of 10 ⁶ Ω · cm. C) 30 degrees, 7 respectively
0 degrees.

Next, an image forming process of the double-sided image forming apparatus according to the present embodiment will be described. Similarly to the first embodiment, the first and second photosensitive drums 21a and 21b
The first and second toner images T1 and T2 are transferred onto the intermediate transfer belts 25a and 25b. The sheet P is conveyed to the secondary transfer section, and first, the first toner image T1 is transferred between the secondary transfer roll 44b and the backup roll 45a, which is the first secondary transfer section, and then the second toner image is transferred to the second secondary transfer section. After the second toner image T2 is continuously transferred onto the sheet P between a certain secondary transfer corotron 49 and the backup roll 45b, both sides are simultaneously fixed by the fixing device 50. In the secondary transfer section, the first toner image T1 is formed by an electric field between the secondary transfer roll 44b and the backup roll 45a.
Since the second toner image T2 is transferred to both sides of the sheet P by the electric field between the secondary transfer corotron 49 and the backup roll 45b, the transfer is performed to both sides of the sheet P without changing the polarities of the first and second toner images T1, T2. be able to. Further, by adsorbing the sheet P to the second intermediate transfer belt 25b at the time of the first secondary transfer, accurate transfer can be performed while preventing the occurrence of image disorder.

As described above, the photosensitive drums 21a and 21b
From the toner images T1 and T1 on the intermediate transfer belts 25a and 25b.
T2 is transferred, the sheet P is conveyed between the intermediate transfer belts 25a and 25b, and the image on the intermediate transfer belts 25a and 25b is transferred to the secondary transfer roll 44b or the secondary transfer corotron 49 and the electric field between the backup rolls 45a and 45b. , The image is continuously transferred to both sides of the paper P, and the fixing device 5
By transferring to 0 and fixing both sides simultaneously, it is possible to obtain a double-sided image without disturbing images, fine lines, and wrinkles without changing the polarity of each toner image at the same recording speed as one side per sheet. Was completed.

The angle .theta.2 (between A and C) formed between the paper transport direction A from the second secondary transfer portion to the fixing device 50 and the intermediate transfer belt 25b bent and arranged downstream of the backup roll 45b is set. By setting the angle to 90 degrees or less, it is possible to eliminate the electric disturbance during the sheet conveyance from the second secondary transfer portion to the fixing device 50, stabilize the sheet posture, and perform the secondary transfer of the fixing device 50. As a result, it is possible to reduce poor entry into the fixing device, jams, paper wrinkles, and the like without providing a special sheet attitude control unit between the secondary transfer portion and the fixing device 50.

Third Embodiment FIG. 9 shows a schematic structure of a double-sided image forming apparatus according to a third embodiment of the present invention. In the figure, the basic configuration of the double-sided image forming apparatus is substantially the same as that of the first embodiment. However, unlike the first embodiment, the paper transport path is vertical, and the intermediate transfer belts 25a and 25b are in contact or close proximity. A fixing device 50 is provided below the next transfer portion, and a polarity reversal corotron 28 is arranged to face the second photosensitive drum 21b. Further, the paper transport direction A from the secondary transfer rolls 40a, 40b to the fixing device 50 and the secondary transfer rolls 40a, 40
0b, the intermediate transfer belt 25a bent and arranged on the downstream side
Angle θ1 (between AB) and θ2 (between AC) with 25b
Are set at 90 degrees or less, and the angles θ1 and θ2 are set to 80 degrees, for example.

In this embodiment, the toners T1 and T2 are made of negatively charged toner. DC current +10 μA and −10 μA are respectively applied to the primary transfer rolls 26a and 26b, DC current +300 μA is applied to the polarity inversion corotron 28, and the grid voltage is applied. +500 V and DC voltages -1 kV and +1 kV were applied to the secondary transfer rolls 40a and 40b, respectively. In addition, carbon black is dispersed in EPDM rubber on a metal shaft on the secondary transfer rolls 40a and 40b, and the volume resistivity is 10 ⁶
What covered what was made into ohm * cm was used.

Next, an image forming process of the double-sided image forming apparatus according to the present embodiment will be described. First photosensitive drum 2
The first toner image T1 formed on 1a is transferred onto the first intermediate transfer belt 25a by the primary transfer roll 26a. Similarly, the second toner image T formed on the second photosensitive drum 21b at the same timing as the first photosensitive drum 21a
2 is inverted by applying a voltage to the polarity inversion corotron 28, and is transferred onto the second intermediate transfer belt 25b by the primary transfer roll 26b. The sheet P is conveyed between the secondary transfer rolls 40a and 40b at the same time, and the toner images T1 and T2 on the intermediate transfer belts 25a and 25b are transferred to the sheet P.
After the images are simultaneously transferred onto both sides, the image is fixed on both sides simultaneously by the fixing device 50.

As described above, the photosensitive drums 21a, 21b
From the toner images T1 and T1 on the intermediate transfer belts 25a and 25b.
T2 is transferred respectively, the sheet P is conveyed between the intermediate transfer belts 25a and 25b, and the images on the intermediate transfer belts 25a and 25b are simultaneously transferred to both sides of the sheet P by the electric field between the secondary transfer rolls 40a and 40b, respectively. Then, the sheet was conveyed perpendicularly to the fixing device 50 and simultaneously fixed on both sides, so that a double-sided image without image disturbance could be obtained at the same recording speed as one side per sheet.

The paper transport direction A from the secondary transfer rolls 40a and 40b to the fixing device 50 and the secondary transfer roll 40
a, the intermediate transfer belt 2 bent at the downstream side of 40b
Angles θ1 (between AB) and θ2 (A−
By setting each of the angles C to 90 degrees or less, it is possible to eliminate the electric disturbance during the conveyance of the sheet from the secondary transfer section to the fixing device 50, stabilize the sheet posture, and fix the fixing device 50.
Can be brought close to the secondary transfer section, and it is possible to reduce poor entry into the fixing apparatus, jams, paper wrinkles, and the like without providing any special paper attitude control means between the secondary transfer section and the fixing apparatus 50. . In particular, in the present embodiment, by vertically transporting the paper, the posture of the paper P after passing through the second transfer unit is further stabilized, and the posture of the paper when the fixing device 50 enters is stabilized. Disturbance and occurrence of paper wrinkles can be prevented.

Fourth Embodiment FIG. 10 shows a schematic configuration of a four-sided image forming apparatus according to a fourth embodiment of the present invention. In the figure, the basic configuration of the double-sided image forming apparatus is substantially the same as that of the first embodiment, but is different from the first embodiment, and the first and second intermediate transfer belts 25a,
Secondary transfer rolls 40a and 40b are provided at a secondary transfer portion in contact with or close to the secondary transfer roll 25b, and tension rolls 51 are provided on both sides of the secondary transfer roll 40b on the intermediate transfer belt 25b side.
a, 51b. In the present embodiment, in particular, the tension rolls 51a and 51b function as holding rolls for holding the intermediate transfer belt 25b in a state of being bridged (tension state), and are disposed substantially along the transport direction of the paper P. The surface of the secondary transfer roll 40b is arranged on substantially the track of the intermediate transfer belt 25b stretched between the tension rolls 51a and 51b.

The angle .theta.2 (A-A) formed between the paper transport direction A from the secondary transfer section to the fixing device 50 and the intermediate transfer belt 25b bent and arranged downstream of the tension roll 51b.
C)) is set to 90 degrees or less.
The angle θ2 is set to, for example, 70 degrees.

In the present embodiment, the secondary transfer roll 40
For both a and 40b, a metal shaft coated with EPDM rubber dispersed with carbon black and having a volume resistivity of 10 ⁶ Ω · cm is used.
A transfer bias 41 was applied to the shaft a, and the shaft of the secondary transfer roll 40b was grounded. The secondary transfer roll 40a had a rubber hardness of 70 degrees (Asuka C), and the secondary transfer roll 40b had a rubber hardness of 30 degrees (Asuka C). 2
In order to use the secondary transfer roll 40a as a tension roll and prevent slippage of the intermediate transfer belt 25a, the rubber hardness (Asuka C) of the secondary transfer roll 40a should be 50 degrees or more, preferably 70 degrees or more. desirable. It is desirable that the secondary transfer roll 40b has a rubber hardness (Asuka C) of 50 degrees or less, preferably 40 degrees or less in order to secure a transfer nip and prevent an increase in nip pressure. Further, metal rolls were used for the tension rolls 51a and 51b.

Further, in the present embodiment, the toner T
1, T2 uses a negatively charged toner, and primary transfer rolls 26a,
DC current +10 μA and −10 μA are respectively applied to 26b, and DC current +400 μ
A, DC voltage +500 V was applied to the grid.

Next, an image forming process of the double-sided image forming apparatus according to the present embodiment will be described. First photosensitive drum 2
The first toner image T1 formed on 1a is transferred by a primary transfer roll 26a onto a first intermediate transfer belt 25a moving at substantially the same speed as the first photosensitive drum 21a. Similarly,
At the same timing as on the first photosensitive drum 21a, the second toner image T2 formed on the second photosensitive drum 21b is inverted by applying a voltage to the polarity inversion corotron 28, and then the second toner image T2 is transferred by the primary transfer roll 26b. The image is transferred onto the intermediate transfer belt 25b. Then, adjust the timing to the paper tray 3
1 is transported between the secondary transfer rolls 40a and 40b, and the toner images T1 and T1 on the intermediate transfer belts 25a and 25b are conveyed.
After the transfer of T2 onto the sheet P at the same time, both sides are simultaneously fixed by the fixing device 50. As described above, the photosensitive drums 21a and 21a
1b to the toner image T on the intermediate transfer belts 25a and 25b.
1 and T2, respectively, and the sheet P is transported between the secondary transfer rolls 40a and 40b. The images on the intermediate transfer belts 25a and 25b are simultaneously transferred onto both sides of the sheet P. By performing the simultaneous fixing on both sides, a double-sided image without image disturbance could be obtained at the same recording speed as that for one side per sheet.

Further, the secondary transfer section is connected to a secondary transfer roll 40a.
Is also used as a tension roll as a high hardness rubber roll, and the secondary transfer roll 40b is a low hardness rubber roll and the tension rolls 51a and 51b are disposed on both sides thereof, so that a sufficient transfer nip width is maintained, By increasing the pressure, it was possible to prevent the thin line from being hollowed out and the paper from being wrinkled. Further, since the tension of each of the intermediate transfer belts 25a and 25b can be sufficiently maintained, the slip of the belt can be prevented. In the present embodiment, the tension members 51a, 5
Although a roll is used for 1b, a metal plate or the like can be appropriately used as long as it can hold the tension of the intermediate transfer belt and does not hinder rotation. Also, the secondary transfer roll 40
The angle .theta.2 (between A and C) formed between the paper transport direction A from the a and 40b to the fixing device 50 and the intermediate transfer belt 25b bent and arranged on the downstream side of the tension roll 51b should be 90 degrees or less. And from the secondary transfer section to the fixing device 50
In this case, the electrical disturbance during the transport of the paper sheet can be eliminated, the paper posture can be stabilized, and the fixing device 50 can be brought close to the secondary transfer portion. Thus, poor entry into the fixing device 50, jam, paper wrinkles, and the like can be reduced without providing the fixing device 50.

In the case of this embodiment, even when both-sided simultaneous transfer is performed in the secondary transfer section (secondary transfer rolls 40a and 40b), the transfer from the secondary transfer section to the tension roll 51b is performed. Is the intermediate transfer belt 25b
Is transported while being sucked and held by the secondary transfer roll 4 and the paper transport direction A from the secondary transfer section to the fixing device 50.
The angle θ1 (between A and B) between the intermediate transfer belt 25a and the intermediate transfer belt 25a that is bent downstream of Oa does not necessarily need to be 90 degrees or less.

Fifth Embodiment FIG. 11 shows a schematic configuration of a double-sided image forming apparatus according to a fifth embodiment of the present invention. In the figure, the basic configuration of the two-sided image forming apparatus is substantially the same as that of the first embodiment, but is different from the first embodiment, and the first photosensitive drum group 21a (specifically, 21aY , 21a
M, 21aC, 21aK), the second photosensitive drum group 21b
(Specifically, 21bY, 21bM, 21bC, 21b
K) and the corresponding primary transfer rolls 26a, 26
b (specifically, 26aY, 26aM, 26aC, 26a
K, 26bY, 26bM, 26bC, 26bK), and as a bias application method for the secondary transfer roll 40a, a contact roll 48 is provided in contact with the secondary transfer roll 40a, and the secondary transfer is performed via the contact roll 48. The bias is applied to the roll 40a.

Further, tension rolls 51a and 51b are arranged on both sides of the secondary transfer roll 40a. In particular, in the present embodiment, the tension rolls 51a and 51b function as holding rolls that hold the intermediate transfer belt 25a in a state of being bridged (tension state), and are disposed substantially along the transport direction of the paper P. These tension rolls 51a,
The surface of the secondary transfer roll 40a is arranged on a substantially orbit of the intermediate transfer belt 25a stretched between the belts 51b. Furthermore, the peeling claw 61 is brought into contact with or close to the tension roll 51b and the secondary transfer roll 40b on the downstream side of the paper transport path with respect to the rolls 51b and 40b.
a and 61b were respectively arranged.

In this embodiment, the secondary transfer roll 4
In No. 0a, a metal shaft was coated with an insulating EPDM rubber, and the surface thereof was coated with a thin layer of a conductive EPDM rubber to have a surface resistance of 10 ⁹ Ω / cm ² , and the contact roll 48 was a metal shaft. As the secondary transfer roll 40b, a metal shaft coated with EPDM rubber dispersed with carbon black and having a volume resistivity of 10 ⁵ Ω · cm was used. Various rubbers and resins having a volume resistivity of 10 ¹¹ Ω · cm or more can be used for the insulating layer.
A material in which conductive particles such as carbon black are dispersed in dF, polyester, acrylic, or the like can be used, and the surface resistance is preferably 10 ⁸ to 10 ¹⁰ Ω / cm ² . The rubber hardness (Asuka C) for coating the secondary transfer rolls 40a and 40b was 30 degrees and 70 degrees, respectively, and metal rolls were used for the tension rolls 51a and 51b.

The toners T1 and T2 use negatively charged toner.
Next transfer rolls 26aY to 26aK, 26bY to 26bK
DC current +10 μA, -1 for each YMCK transfer
0 μA is applied to the polarity-reversed corotron 28 (specifically, 28 μA).
Y, 28M, 28C, 28K) have a DC current of + 300μ
A, the grid voltage +500 V is applied to the secondary transfer roll 40a
A DC voltage of -4 kV was applied to a contact roll 48 in contact with. The secondary transfer roll 40b was grounded.

Next, an image forming process of the double-sided image forming apparatus according to the present embodiment will be described. The first toner images T1 are successively transferred from the first photosensitive drum groups 21aY, 21aM, 21aC, 21aK to the first intermediate transfer belt 25a in the order of YMCK by the primary transfer rolls 26aY, 26aM, 26aC, 26aK. . Similarly, after the polarity of the second toner image T2 (YMCK) formed on the second photosensitive drum group 21bY, 21bM, 21bC, 21bK is inverted by the polarity inversion corotron 28, the primary transfer rolls 26bY, 26bM, The images are sequentially transferred onto the second intermediate transfer belt 25a by 26bC and 26bK. The sheet P is conveyed at the appropriate timing, and the intermediate transfer belts 25a, 25a
After the toner images T1 and T2 on 5b are simultaneously transferred onto the sheet P, both sides are fixed simultaneously by the fixing device 50.

As described above, the photosensitive drum 21a (21a
YMCK toner images T on the intermediate transfer belts 25a and 25b from the groups Y to 21aK) and 21b (21bY to 21bK).
1 and T2 are superimposed and transferred, respectively, to the intermediate transfer belts 25a and 25a.
5b, and the intermediate transfer belts 25a and 25
b is simultaneously transferred to both sides of the sheet P by the electric field between the secondary transfer rolls 40a and 40b, and is simultaneously horizontally transferred to the fixing device 50 and simultaneously fixed on both sides, so that image disturbance or thin line dropout occurs. Thus, a double-sided color image free of paper wrinkles could be obtained at the same recording speed as for one side per sheet.

The peeling claws 61a, 61a are provided at the exit of the secondary transfer section.
1b, the paper P is transferred to the intermediate transfer belt 25a,
In addition, it was possible to prevent the paper from being attracted to the fixing device 25b, and to control the posture of the paper, thereby preventing a jam due to a failure to enter the fixing device.
In this embodiment, since the sheet is conveyed from the secondary transfer section to the tension roll 51b while being held by the intermediate transfer belt 25a, the secondary transfer roll 40
It is not always necessary to provide the separation claw 61b on the intermediate transfer belt 25b bent and arranged on the downstream side b.

For example, when the peeling claw method is employed in the same embodiment as that shown in FIGS. 7 to 10, the secondary transfer is performed as shown by phantom lines in FIGS. The intermediate transfer belt 25a downstream of the rolls 40a, 40b,
The separation claw 61a is provided on the intermediate transfer belt 25b on the downstream side of the backup roll 45b, as shown by the imaginary line in FIG. 8, or the tension is provided, as shown by the imaginary line in FIG. The separation claw 61 may be provided on the intermediate transfer belt 25b on the downstream side of the roll 51b. When such a peeling claw method is adopted, the angle conditions (θ1, θ2) of the intermediate transfer belts 25a, 25b on the downstream side of the secondary transfer portion required in the respective embodiments of FIGS. There are no restrictions.

However, from the viewpoint of ensuring the stable conveyance of the sheet, the intermediate transfer belt 25 on the downstream side of the secondary transfer portion is used.
It is preferable to adopt a peeling claw method in addition to the angle conditions a and 25b.

[0063]

As described above, according to the present invention,
A first image on the first image carrier is primarily transferred to a first intermediate transfer belt, while a second image on the second image carrier is primarily transferred to a second intermediate transfer belt; Alternatively, each image on each intermediate transfer belt is secondarily transferred to both sides of the recording material while the recording material is held on either one of the intermediate transfer belts. In addition to increasing the degree of freedom in layout, it is possible to obtain a double-sided image of the same quality with no misalignment between the front and back sides at the same recording speed as one side per recording material.

In particular, according to the first to third aspects of the present invention,
By devising the layout of the intermediate transfer belt bent and arranged on the downstream side of the secondary transfer portion, it is possible to avoid a situation in which the recording material toward the fixing unit is attracted to the charged intermediate transfer belt side. It is possible to stabilize the posture of the recording material from the next transfer section to the fixing means, and accordingly, it is possible to effectively prevent the recording material from jamming, wrinkling, and image disturbance due to a defective entrance of the fixing means.

According to the invention of claims 4 to 6,
Since a peeling claw is provided at a necessary portion of the intermediate transfer belt bent and arranged on the downstream side of the secondary transfer portion, the recording material that enters from the secondary transfer portion toward the fixing unit is separated from the intermediate transfer belt even if the recording material enters the fixing portion. Even if a defect or re-adsorption is attempted, this can be reliably prevented, and the posture of the recording material from the secondary transfer unit to the fixing unit can be stabilized accordingly.

According to the seventh aspect of the present invention, a portion corresponding to the secondary transfer area in the transport path of the recording material is disposed in a substantially vertical direction, and both sides of the recording material are disposed below the secondary transfer area. Since the fixing means for fixing the unfixed image is provided, the posture of the recording material entering the fixing means can be further stabilized.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an outline of a first embodiment of a two-sided image forming apparatus according to the present invention.

FIG. 2 is an explanatory diagram illustrating an outline of a second embodiment of the duplex image forming apparatus according to the present invention.

FIG. 3 is an explanatory diagram illustrating an outline of a third aspect of the duplex image forming apparatus according to the present invention.

FIG. 4 is an explanatory diagram showing an outline of a fourth embodiment of the duplex image forming apparatus according to the present invention.

FIG. 5 is an explanatory diagram showing a state around the downstream side of a secondary transfer portion when the angle condition of the intermediate transfer belt is not satisfied in the example of the mode shown in FIG. 1;

FIG. 6 is an explanatory view showing a state around the downstream side of the secondary transfer portion when the angle condition of the intermediate transfer belt is not satisfied in another example of the embodiment of FIG. 1;

FIG. 7 is a schematic configuration diagram illustrating a double-sided image forming apparatus according to the first embodiment;

FIG. 8 is a schematic configuration diagram illustrating a double-sided image forming apparatus according to a second embodiment.

FIG. 9 is a schematic configuration diagram illustrating a double-sided image forming apparatus according to a third embodiment.

FIG. 10 is a schematic configuration diagram illustrating a double-sided image forming apparatus according to a fourth embodiment.

FIG. 11 is a schematic configuration diagram illustrating a double-sided image forming apparatus according to a fifth embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... 1st image carrier, 2 ... 1st intermediate transfer belt, 3 ... 2nd
Image carrier 4, second intermediate transfer belt 5, recording material 6,
First intermediate primary transfer means, 7... Second intermediate primary transfer means, 8
... intermediate secondary transfer means, 9 ... first intermediate secondary transfer means, 10
... Second intermediate secondary transfer means, 11 ... Fixing means, 12,12
a, 12b: peeling nail, 20a: first image forming unit, 20b
... Second image forming unit, 21a. First photosensitive drum, 21b.
Second photosensitive drum 25a First intermediate transfer belt 25b
... second intermediate transfer belt, 26a ... first primary transfer roll, 26b ... second primary transfer roll, 28 ... polarity reversal corotron, 40a, 40b ... secondary transfer roll, 44b ...
Secondary transfer roll, 45a, 45b backup roll, 50 fixing device, 51a, 51b tension roll, 61, 61a, 61b peeling claw, P paper

Claims (7)

[Claims] A first image carrier on which a first image is carried;
A first intermediate transfer belt opposed to the first image carrier, a first intermediate primary transfer unit for primarily transferring a first image on the first image carrier to the first intermediate transfer belt, A second image carrier on which the image is carried, a second intermediate transfer belt disposed opposite to the second image carrier, and a primary transfer of the second image on the second image carrier to the second intermediate transfer belt The second transfer of the primary transfer image on each intermediate transfer belt to both surfaces of the recording material in a region where the second intermediate primary transfer unit performs contact with or approaches the first intermediate transfer belt and the second intermediate transfer belt. First and second intermediate transfer belts, which are provided with an intermediate secondary transfer unit for fixing the images transferred to both surfaces of the recording material, and which are bent at substantially the same position on the downstream side of the intermediate secondary transfer unit. And the angle between the recording material conveyance direction from the intermediate secondary transfer means to the fixing means. Double-sided image forming apparatus characterized by a 90 degrees or less. 2. A first image carrier on which a first image is carried;
A first intermediate transfer belt opposed to the first image carrier, a first intermediate primary transfer unit for primarily transferring a first image on the first image carrier to the first intermediate transfer belt, A second image carrier on which the image is carried, a second intermediate transfer belt disposed opposite to the second image carrier, and a primary transfer of the second image on the second image carrier to the second intermediate transfer belt The second transfer of the primary transfer image on each intermediate transfer belt to both surfaces of the recording material in a region where the second intermediate primary transfer unit performs contact with or approaches the first intermediate transfer belt and the second intermediate transfer belt. And a fixing unit for fixing the images transferred to both surfaces of the recording material, wherein the first and second intermediate transfer belts are bent at different positions downstream of the intermediate secondary transfer unit. The intermediate transfer belt located near the fixing unit and the intermediate secondary transfer unit Double-sided image forming apparatus according to claim the angle between the recording material conveyance direction to the destination unit to be lower than or equal to 90 degrees. 3. A first image carrier on which a first image is carried;
A first intermediate transfer belt opposed to the first image carrier, a first intermediate primary transfer unit for primarily transferring a first image on the first image carrier to the first intermediate transfer belt, A second image carrier on which the image is carried, a second intermediate transfer belt disposed opposite to the second image carrier, and a primary transfer of the second image on the second image carrier to the second intermediate transfer belt The recording material is sucked and held at a position corresponding to the second image on the second intermediate transfer belt in an area where the second intermediate primary transfer means contacts or comes close to the first intermediate transfer belt and the second intermediate transfer belt. And a first intermediate secondary transfer means for secondary-transferring the primary transfer image on the first intermediate transfer belt to one side of the recording material facing the first intermediate transfer belt; and a first intermediate secondary transfer means. The second intermediate of the recording material, which is provided at the subsequent stage and is sucked and held by the second intermediate transfer belt The second intermediate secondarily transferring the primary transfer image on the second intermediate transfer belt on one side which faces the shooting belt 2
A second intermediate transfer belt, comprising: a second transfer unit; a fixing unit for fixing images transferred to both surfaces of the recording material; a second intermediate transfer belt bent and arranged downstream of the second intermediate secondary transfer unit; A double-sided image forming apparatus, wherein an angle between the recording medium conveying direction from the unit to the fixing unit is 90 degrees or less. 4. A first image carrier for carrying a first image,
A first intermediate transfer belt opposed to the first image carrier, a first intermediate primary transfer unit for primarily transferring a first image on the first image carrier to the first intermediate transfer belt, A second image carrier on which the image is carried, a second intermediate transfer belt disposed opposite to the second image carrier, and a primary transfer of the second image on the second image carrier to the second intermediate transfer belt The second transfer of the primary transfer image on each intermediate transfer belt to both surfaces of the recording material in a region where the second intermediate primary transfer unit performs contact with or approaches the first intermediate transfer belt and the second intermediate transfer belt. First and second intermediate transfer belts, which are provided with an intermediate secondary transfer unit for fixing the images transferred to both surfaces of the recording material, and which are bent at substantially the same position on the downstream side of the intermediate secondary transfer unit. A double-sided image forming apparatus, wherein a peeling claw is provided on each side. 5. A first image carrier for carrying a first image,
A first intermediate transfer belt opposed to the first image carrier, a first intermediate primary transfer unit for primarily transferring a first image on the first image carrier to the first intermediate transfer belt, A second image carrier on which the image is carried, a second intermediate transfer belt disposed opposite to the second image carrier, and a primary transfer of the second image on the second image carrier to the second intermediate transfer belt The second transfer of the primary transfer image on each intermediate transfer belt to both surfaces of the recording material in a region where the second intermediate primary transfer unit performs contact with or approaches the first intermediate transfer belt and the second intermediate transfer belt. And a fixing unit for fixing the images transferred to both surfaces of the recording material, wherein the first and second intermediate transfer belts are bent at different positions downstream of the intermediate secondary transfer unit. Contacting or approaching the intermediate transfer belt located near the fixing means. Double-sided image forming apparatus characterized in that a peeling pawl. 6. A first image carrier on which a first image is carried;
A first intermediate transfer belt opposed to the first image carrier, a first intermediate primary transfer unit for primarily transferring a first image on the first image carrier to the first intermediate transfer belt, A second image carrier on which the image is carried, a second intermediate transfer belt disposed opposite to the second image carrier, and a primary transfer of the second image on the second image carrier to the second intermediate transfer belt The recording material is sucked and held at a position corresponding to the second image on the second intermediate transfer belt in an area where the second intermediate primary transfer means contacts or comes close to the first intermediate transfer belt and the second intermediate transfer belt. And a first intermediate secondary transfer means for secondary-transferring the primary transfer image on the first intermediate transfer belt to one side of the recording material facing the first intermediate transfer belt; and a first intermediate secondary transfer means. The second intermediate of the recording material, which is provided at the subsequent stage and is sucked and held by the second intermediate transfer belt The second intermediate secondarily transferring the primary transfer image on the second intermediate transfer belt on one side which faces the shooting belt 2
A second transfer unit; and a fixing unit for fixing the image transferred to both surfaces of the recording material. The peeling claw is brought into contact with or close to a second intermediate transfer belt bent and arranged downstream of the second intermediate secondary transfer unit. And a double-sided image forming apparatus. 7. The double-sided image forming apparatus according to claim 1, wherein a portion corresponding to a secondary transfer area is arranged in a substantially vertical direction in a recording material conveyance path, and the secondary transfer area is provided. A fixing unit for fixing unfixed images on both sides of the recording material below the recording medium.