JPH10133431A - Both-side image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce irregularities in image, the wrinkles, curling and jamming of paper sheet, etc., caused by a disturbed rushing attitude of a recording material into a fixing means, and to prevent a failure in transfer, by applying a transfer bias consisting of an AC voltage to an intermediate secondary transfer means, transferring the image on an intermediate transfer body to the recording material side and eliminating an electric charge for holding the image on the intermediate transfer body slide. SOLUTION: A first image T1 on a photoreceptor drum 11 is transferred onto an intermediate transfer belt 20 a first transfer corotron 12. Continuously, the paper P is carried to between an attracting roll 14 and an attracting corotron 15 and attracted onto the intermediate transfer body belt 20. Similarly, a second image T2 is transferred onto the front surface of the paper P by the first transfer corotron 12. After that, the paper P is carried up to a paper ejecting end and the AC voltage is applied to both of a pair of second transfer corotrons 13a and 13b, so that the first image T1 on the belt 20 is transferred to the rear surface of the paper P and simultaneously the paper P is peeled from the belt 20, to simultaneously fix both surfaces of the paper P by a fixing unit 17.

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, for example, a first image formed on a photoreceptor as an image carrier is transferred and fixed to a first side of a sheet.
In general, the sheet is reversed and re-fed, and subsequently, the second image formed on the photoconductor is transferred and fixed on the second surface of the sheet. However, in this method, the paper is curled during the first fixing because the image forming section is passed twice, and a transfer failure, paper wrinkles at the time of the second transfer and fixing, and a jam in the transport path occur. There are various technical problems, such as that the paper is easy to make, and noise is easily generated when the paper is reversed and re-fed. In addition, there is also a technical problem that the conveyance path becomes longer for reversing the sheet and re-feeding the sheet, thereby lowering the productivity compared with the one-sided recording.

As a prior art for solving such a technical problem, for example, as shown in FIG.
And a first transfer device 1 for transferring the toner image T1 (first image) or T2 (second image) on the photosensitive drum 101 to the intermediate transfer belt 102 or paper P.
03, disposed at the sheet discharge end of the intermediate transfer belt 102,
The toner image T1 or T2 on the intermediate transfer belt 102 is
An apparatus having a second transfer device 104 for transferring the image to a printer (for example, JP-A-1-209470) is already known. The recording operation in this apparatus will be briefly described. First, a first image T1 is formed on the photosensitive drum 101,
Is transferred onto the intermediate transfer belt 102 by the transfer device 103. Subsequently, a second image T2 is formed on the photosensitive drum 101, and the sheet P is transferred to the photosensitive drum 101 and the intermediate transfer belt 102.
And the first transfer unit 103 transfers the second
The image T2 is transferred. After that, the first image T1 on the intermediate transfer belt 102 is transferred onto the sheet P by the second transfer unit 104, the sheet P is separated from the intermediate transfer belt 102, and fixed by the fixing unit 106.

[0004]

However, in such a conventional double-sided image forming apparatus, the second transfer unit 104 is simply disposed at the discharge end of the sheet P of the intermediate transfer belt 102, and the intermediate transfer belt 102 The transfer property of the image from the intermediate transfer belt 102 to the paper P is mainly considered, and the peelability of the paper P is hardly considered. Therefore, there is a technical problem that it is difficult to control the paper posture between the fixing devices 106, and image disturbance, paper wrinkles, curls, jams, and the like due to the disturbance of the paper entering posture into the fixing devices 106 are likely to occur.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned technical problems, and it is possible to avoid disturbance of the recording material entering the fixing means while maintaining good image transferability.
Accordingly, an object of the present invention is to provide a double-sided image forming apparatus capable of obtaining a good double-sided image with less image disturbance, paper wrinkle, curl, jam, and the like. Furthermore, in addition to the above technical issues,
Another object of the present invention is to provide a double-sided image forming apparatus capable of performing double-sided printing with the same productivity as that of single-sided printing.

[0006]

That is, according to one aspect of the present invention for solving the above technical problem, as shown in FIG. 1A, a first image T1 and a second image T2 are formed and carried. In a double-sided image forming apparatus including at least one image carrier 1 and an intermediate transfer member 2 disposed opposite to the image carrier 1, any one of the first image T1 and the second image T2 on the image carrier 1 A direct transfer unit 4 for directly transferring one of them to one side of the recording material 3, a first image T1 and a second image T2 on the image carrier 1.
And an intermediate primary transfer means 5 for transferring one of the two to the intermediate transfer body 2, and a transfer bias provided at the discharge end of the recording material 3 of the intermediate transfer body 2 and applied with a transfer bias composed of an AC voltage. And an intermediate secondary transfer means 6 for transferring the first image T1 or the second image T2 transferred to the other side of the recording material 3.

Another embodiment of the present invention which solves the above technical problem is an image carrier 1 as shown in FIG.
It has an intermediate transfer member 2, a direct transfer unit 4, an intermediate primary transfer unit 5, and an intermediate secondary transfer unit 6. However, unlike the above-described embodiment, the intermediate secondary transfer unit 6 is composed of a DC superimposed AC voltage. It is characterized by applying a transfer bias.

[0008] Still another embodiment of the present invention for solving the above technical problem is, as shown in FIG. 1A, an image carrier 1, an intermediate transfer member 2, a direct transfer device 4, an intermediate primary transfer device. 5 and an intermediate secondary transfer means 6, but the intermediate secondary transfer means 6 is different from the above-described embodiment in that a transfer bias composed of a DC voltage equal to or higher than the DC voltage of the transfer bias of the intermediate primary transfer means 5 is used. In addition, a separating unit 7 is provided behind the intermediate secondary transfer unit 6 for forcibly separating the recording material 3 attached to the intermediate transfer body 2.

Furthermore, in one aspect of the present invention which solves the technical problem relating to productivity in addition to the technical problem described above, a first image T1 is formed and carried as shown in FIG. A first image carrier 1a, a second image carrier 1b on which a second image T2 is formed and carried, and a first image carrier 1a
In the double-sided image forming apparatus provided with the intermediate transfer member 2 on which the image T2 is disposed facing each other, the first image carrier 1a
Direct transfer means 4 for transferring one of the image T1 and the second image T2 on the second image carrier 1b to one side of the recording material 3,
First image T1 on first image carrier 1a and second image carrier 1
b of the second image T2 on the intermediate transfer body 2
And a first transfer means provided at the discharge end of the recording material 3 of the intermediate transfer body 2 and transferred to the intermediate transfer body 2 by applying a transfer bias composed of an AC voltage.
An intermediate secondary transfer means 6 for transferring the image T1 or the second image T2 to another one side of the recording material 3 is provided. As another mode, the intermediate secondary transfer means 6 for applying a transfer bias composed of a DC superimposed AC voltage is used, or the DC voltage of the transfer bias of the intermediate primary transfer means 5 is used as the intermediate secondary transfer means 6. And a separating unit 7 for forcibly separating the recording material 3 adhered onto the intermediate transfer body 2 behind the intermediate secondary transfer unit 6. Is also good.

In such technical means, the image carrier 1, the first image carrier 1a, and the second image carrier 1b are:
Any form (drum-shaped, belt-shaped, or a combination thereof) that can carry the target image, such as a monochrome image or a color image, may be used. Alternatively, a plurality of color component images may be carried on one image carrier 1, 1a, 1b, or a plurality of image carriers 1, 1a, 1b may be provided for each color component image. It may be. As for the image forming method for the image carriers 1, 1a, 1b, various methods such as an electrophotographic method, an electrostatic transfer method, and an ink jet method can be adopted. The intermediate transfer member 2 may be a belt-shaped or drum-shaped intermediate transfer member as long as it can temporarily hold the images T1 and T2 from the image carrier 1, the first image carrier 1a, and the second image carrier 1b. Any form is acceptable.

The direct transfer means 4 and the intermediate primary transfer means 5 include images T1, T2 on the image carriers 1, 1a, 1b.
Is transferred onto the recording material 3 or the intermediate transfer member 2, various devices using corona discharge (Corotron,
Bias roll, etc.).
Further, in the type having the first image carrier 1a and the second image carrier 1b, the direct transfer unit 4 and the intermediate primary transfer unit 5 are usually provided separately and independently. In a type in which the image carrier 1 on which the image T1 and the second image T2 are formed and carried is common, it is preferable to share the direct transfer unit 4 and the intermediate primary transfer unit 5 from the viewpoint of reducing the number of parts. . Further, the transfer conditions of the direct transfer unit 4 and the intermediate primary transfer unit 5 may be the same, but since the transfer target is different from the recording material 3 and the intermediate transfer body 2, the optimum transfer condition for each transfer target is different. It is preferable to set.

Further, as the intermediate secondary transfer means 6, any device (corotron, bias roll, etc.) utilizing corona discharge can be used as long as it transfers the image (T1 or T2) on the intermediate transfer member 2 to the recording material 3. Etc.) can be selected as appropriate. Furthermore, the number of devices does not necessarily have to be a single device. For example, if the intermediate transfer member 2 is of a type formed of a thin film such as a belt, a pair of devices is provided with the intermediate transfer member 2 interposed therebetween. No problem.

When the intermediate secondary transfer means 6 applies a transfer bias comprising a DC superimposed AC voltage, the recording material 3 is separated from the intermediate transfer member 2 by appropriately adjusting the DC voltage component. Although it is possible to ensure the removability, from the viewpoint of more surely maintaining the releasability of the recording material 3, the intermediate transfer member 2 is located behind the intermediate secondary transfer unit 6.
It is preferable to provide a peeling means 7 for forcibly peeling off the recording material 3 attached on the recording material 3.

The peeling means 7 includes the intermediate transfer member 2
Any material may be used, as long as the recording material 3 adhered thereon is forcibly peeled, regardless of electrical or mechanical. However, from the viewpoint of minimizing damage to the intermediate transfer body 2 and the recording material 3, an electric means is used. It is preferable to use them.

Next, the operation of the above technical means will be described. First, in the embodiment shown in FIG. 1A, the intermediate primary transfer means 5 transfers the first image T1 (or the second image T2) formed and supported on the image carrier 1 to the intermediate transfer body 2. On the other hand, the direct transfer unit 4 directly transfers the second image T2 (or the first image T1) formed and carried on the image carrier 1 to one surface of the recording material 3. Further, the intermediate secondary transfer means 6 transfers the first image T1 (or the second image T2) on the intermediate transfer member 2 to another one side of the recording material 3. Thus, the first image T1 and the second image T2 are transferred to both surfaces of the recording material 3. At this time, in a mode in which the intermediate secondary transfer means 6 applies a transfer bias consisting of an AC voltage, the intermediate secondary transfer means 6 generates an AC transfer electric field, for example, the first image T1 on the intermediate transfer body 2. Is transferred to the recording material 3 side, and the charge for image holding on the intermediate transfer body 2 side is removed, so that the intermediate transfer body 2
Is peeled off from the recording material 3. Details will be described in an embodiment described later. Further, in the mode in which the intermediate secondary transfer means 6 applies a transfer bias composed of a DC superimposed AC voltage, the intermediate secondary transfer means 6 generates a DC superimposed AC transfer electric field,
For example, the first DC voltage component on the intermediate transfer member 2
At the same time as transferring the image T1 to the recording material 3 side, the charge for image holding on the intermediate transfer body 2 side is reduced mainly by an AC voltage component, and the electrostatic attraction force between the recording material 3 and the intermediate transfer body 2 is reduced. Weaken. Further, in a mode in which the intermediate secondary transfer means 6 applies a transfer bias composed of a DC voltage equal to or higher than the DC voltage of the transfer bias of the intermediate primary transfer means 5, the intermediate secondary transfer means 6 uses the image of the intermediate transfer body 2. A DC transfer electric field having a holding force or more is generated to transfer, for example, the first image T1 on the intermediate transfer body 2 to the recording material 3 side. Then, the recording material 3 on the intermediate transfer body 2
Is peeled off by the peeling means 7.

In the embodiment shown in FIG. 1B,
The intermediate primary transfer unit 5 transfers, for example, the first image T1 formed on and supported by the first image carrier 1a (or the second image T2 supported and formed on the second image carrier 1b) to the intermediate transfer body 2. The direct transfer unit 4 transfers the second image T2 formed on the second image carrier 1b (or the first image T1 formed and carried on the first image carrier 1a) to the recording material 3. The image is directly transferred to one side, and further, the intermediate secondary transfer means 6 transfers the first image T1 (or the second image T2) on the intermediate transfer body 2 to another side of the recording material 3. Thus, the first image T1 and the second image T2 are transferred to both surfaces of the recording material 3. At this time, the intermediate secondary transfer means 6 performs the same operation as that of the embodiment shown in FIG. 1A, and simultaneously performs the transfer operation process of the first image T1 and the second image T2 to both surfaces of the recording material 3. Therefore, double-sided recording is performed at approximately the same level as single-sided recording.

[0017]

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. 2 shows a schematic configuration of a two-sided image forming apparatus according to a first embodiment of the present invention. In FIG. 1, a double-sided image forming apparatus includes an image forming unit 10 (photosensitive drum 1) on which a first image (first toner image) and a second image (second toner image) are formed.
1, a first transfer corotron 12 and other electrophotographic devices (not shown) (including a charging device, an exposure device, a developing device, a cleaning device, etc.) and an intermediate portion where the first transfer portion of the image forming unit 10 is opposed to the device. And a transfer belt 20.

In the present embodiment, in the present embodiment, a toner of a developing device (not shown) uses a negative toner, and a positive toner image (first image) is formed on the surface of the photosensitive drum 11 by a well-known electrophotographic process. ) T1 or a mirror image toner image (second image) T2 is formed.
Further, the first transfer corotron 12 of the image forming unit 10 transfers the first image T1 on the photosensitive drum 11 to the intermediate transfer belt 20, and transfers the second image T2 on the photosensitive drum 11 to one side of the paper P. The first transfer corotron 12 is applied with, for example, a DC current of +200 μA.

Further, in this embodiment, the intermediate transfer belt 20 is stretched between a driving roll 21 and a driven roll (tension roll for tension adjustment) 22, and the first transfer corotron is connected to the intermediate transfer belt 20. It is arranged on the back side. The intermediate transfer belt 20 has a volume resistivity of 10% by containing an appropriate amount of an antistatic agent such as carbon black into a resin such as polyimide, acrylic, vinyl chloride, polyester, or polycarbonate or various rubbers.
^It is formed to have a thickness of ⁹ to 10 ¹³ Ω · cm, and its thickness is set to, for example, 0.1 mm.

Further, a pair of second transfer corotrons 13a and 13b are arranged opposite to the sheet discharge end of the intermediate transfer belt 20 behind the first transfer portion with the intermediate transfer belt 20 interposed therebetween. The first image T1 is transferred to the other side of the sheet P. In particular, in the present embodiment, an AC voltage (for example, 7 kV _pp / 600 in the present embodiment) is applied to the second transfer corotron pair 13a, 13b.
Hz) is applied.

In front of the transfer portion of the intermediate transfer belt 20, a suction roll 14 is disposed with the intermediate transfer belt 20 interposed therebetween.
And an adsorbing corotron 15 for adsorbing the sheet P to the intermediate transfer belt 20. In the present embodiment, a direct current of +300 μA is applied to the suction corotron 15 to make the suction roll 14 conductive and ground. A fixing unit 17 fixes an unfixed toner image on the separated sheet P.

Next, an image forming process of the double-sided image forming apparatus according to the present embodiment will be described. First, the first image T1 formed on the photosensitive drum 11 is transferred by the first transfer corotron 12 onto the intermediate transfer belt 20 moving at substantially the same speed as the photosensitive drum 11. Subsequently, the intermediate transfer belt 2
The sheet P is conveyed between the suction roll 14 and the suction corotron 15 in synchronization with the rotation of 0, and is suctioned onto the intermediate transfer belt 20. Similarly, a second image image T2 is formed on the photosensitive drum 11 in synchronization with the rotation of the intermediate transfer belt 20, and is transferred onto the second surface (upper surface) of the sheet P by the first transfer corotron 12. Thereafter, the sheet P is transported to the sheet discharge end of the intermediate transfer belt 20, and the second transfer corotron pair 13a, 13b
To the intermediate transfer belt 2
At the same time as the first image T1 on the sheet 0 is transferred to the first surface (lower surface) of the sheet P, the sheet P is peeled off from the intermediate transfer belt 20 and both sides of the sheet P are simultaneously fixed by the fixing device 17.

Here, the second transfer corotron pair 13a, 1
The transfer principle using the AC voltage 3b will be described with reference to FIG. By applying a positive voltage to the first transfer corotron 12, the first image (first toner image) T 1 is transferred to the intermediate transfer belt 2.
Transfer to 0. The toner T1 of negative polarity is held on the front side of the intermediate transfer belt 20, and the positive charge e ⁺ (the + symbol is added to the thin line 中 in the figure) is held on the back side. By applying a positive voltage to the suction corotron 15, the sheet P is suctioned to the intermediate transfer belt 20. At this time, since the suction roll 14 is grounded, the negative charge e ⁻ (a thin line ○ is indicated by a minus sign in the drawing) is held on the back side of the paper P, while the positive charge is held on the back side of the intermediate transfer belt 20. . By applying a positive voltage to the first transfer corotron 12, the second image (second toner image) T2 is transferred onto the paper P. A negative toner T2 is held on the upper side of the sheet P, and a positive charge is held on the back side of the intermediate transfer belt 20. By applying an AC voltage to the second transfer corotron pair 13a, 13b, the charge on the back side of the intermediate transfer belt 20 is eliminated. Since the first toner image T1 on the lower side of the sheet P is sandwiched between the sheet P and the intermediate transfer belt 20, the toner charge amount does not change much. Since the upper side of the paper P is directly exposed to the alternating electric field in a state where the negative polarity toner T1 is present on the back side of the paper P, positive charges are generated on the front and back sides of the paper P such that the charges are balanced. The first toner image T1 on the intermediate transfer belt 20 is transferred onto the sheet P by the
The paper P can be peeled from zero.

FIG. 4 shows a second transfer corotron pair 13a, 13
4 shows the relationship between the AC voltage applied to b and the transfer efficiency. According to the figure, the transfer efficiency is 8 when the AC voltage applied to the second transfer corotron pair 13a, 13b is in the range of 4 to 10 kV _PP.
It is understood that sufficient transferability and peelability exceeding 5% are obtained.

As described above, the second transfer corotron pair 13
By applying an AC voltage to a and 13b, the first toner image T1 on the intermediate transfer belt 20 can be reliably transferred to the first surface of the sheet P without separately providing a peeling device such as a peeling corotron. Transfer the paper P to the intermediate transfer belt 20
, And a good double-sided image without transfer failure or image disturbance was obtained.

In this embodiment, a corotron is used for the first transfer device 12, the second transfer device 13b, and the suction device 15, but a bias roll may be used. The second transfer corotron pair 13a, 13b may be a combination of a corotron to which an AC voltage is applied and a grounded counter electrode. In this case, from the viewpoint of reducing the number of components, it is preferable that the tension roll 22 of the intermediate transfer belt 20 be electrically grounded and used as a counter electrode.

Further, in the present embodiment, from the viewpoint of further reducing the image quality difference between the first image T1 and the second image T2 on both sides of the sheet P, the transfer condition of the first transfer corotron 12 is set to the first condition. It is preferable to set differently when transferring the image T1 and when transferring the second image T2. Hereinafter, a method of setting the transfer conditions will be described. FIG. 5 shows a state in which a photosensitive drum (indicated as a photosensitive member in the figure) 11 is transferred to a sheet P,
Relationship between DC current value applied to first transfer corotron 12 and transfer efficiency when toner images (first image and second image) are respectively transferred from 1 to intermediate transfer belt (indicated as an intermediate transfer body in the figure) 20 Is shown. Here, the lower limit of the transfer efficiency is 80 in the transfer of the second image T2 from the photosensitive drum 11 to the sheet P.
%, And about 90% is required for the transfer of the first image T1 from the photosensitive drum 11 to the intermediate transfer belt 20. The transfer current value satisfying the above condition is +150 to +2 in the transfer of the first image T1.
50 μA, +200 to +400 μ for the second image T2 transfer
It was about A. Also, about +3 at the time of transferring the first image T1.
An image quality defect due to leakage occurred at 00 μA or more. From the above results, for example, the first transfer corotron 12 has +200 μA at the time of the transfer of the first image T1 and +30 at the time of the transfer of the second image T2.
0 μA was applied.

As described above, the transfer conditions of the first transfer corotron 12 are controlled to appropriate transfer current values for the case where the transfer is performed from the photosensitive drum 11 to the sheet P and the case where the transfer condition is from the photosensitive drum 11 to the intermediate transfer belt 20, respectively. In addition, it was possible to obtain a good double-sided image having no image defects due to transfer failure or leak and having a small difference in image quality.

Embodiment 2 FIG. 6 shows a schematic configuration of Embodiment 2 of a double-sided image forming apparatus to which the present invention is applied. In the figure, the basic configuration of the two-sided image forming apparatus is substantially the same as that of the first embodiment, but, unlike the first embodiment, one second transfer corotron 13 is provided at a position facing the tension roll 22 of the intermediate transfer belt 20.
And a separation corotron 16 provided behind the separation corotron. 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 is omitted here.

In the present embodiment, in particular, the second transfer corotron 13 has a DC superimposed AC voltage (in the present embodiment, an AC voltage of 8 kV _PP / 600 Hz and a DC voltage of +1 kV).
V) is applied. Further, a negative toner is used as the toner for forming the first image T1 and the second image T2. The first transfer corotron 12 has a DC current of +200 μA, the peeling corotron 16 has an AC voltage of 7 kV _PP / 600 Hz, and the adsorbing corotron 15 has an AC voltage of 7 kV _PP / 600 Hz. Applied a DC current of +250 μA.
The suction roll 14 and the tension roll 22 are conductive and grounded.

Next, an image forming process of the double-sided image forming apparatus according to the present embodiment will be described. First, similarly to Embodiment 1, the first image T formed on the photosensitive drum 11
1 is transferred by the first transfer corotron 12 onto the intermediate transfer belt 20 moving at substantially the same speed as the photosensitive drum 11. Subsequently, the paper P is transported between the suction roll 14 and the suction corotron 15 in synchronization with the rotation of the intermediate transfer belt 20, and is suctioned onto the intermediate transfer belt 20. Similarly, a second image T2 is formed on the photosensitive drum 11 in synchronization with the rotation of the intermediate transfer belt 20, and the first transfer corotron 12 forms the sheet P.
Is transferred to the second surface (upper surface). Thereafter, the sheet P is conveyed to the sheet discharge end of the intermediate transfer belt 20, and the first image T1 on the intermediate transfer belt 20 is applied to the first surface of the sheet P by applying a DC superimposed AC voltage to the second transfer corotron 13. (Lower surface), and subsequently, peeling corotron 16
The sheet P is separated from the intermediate transfer belt 20 by applying an AC voltage to the sheet P, and the fixing device 17 simultaneously fixes both sides of the sheet P.

As described above, by applying a DC superimposed AC voltage to the second transfer corotron 13, the intermediate transfer belt 2
0 to the paper P without fail, and the paper P
The paper P can be stably peeled off from the intermediate transfer belt 20 by weakening the attraction force between the belt and the intermediate transfer belt 20 and providing the peeling corotron 16 in opposition to the tension roll 22 as a counter electrode. And a good double-sided image without image disturbance was obtained.

In this embodiment, a corotron is used for the first transfer device 12 and the suction device 15, but a bias roll may be used. Further, in the present embodiment, the driven roll (tension roll) 22 functions as a counter electrode of the second transfer corotron 13, but the counter electrode of the second transfer corotron 13 may be separately provided instead of the driven roll 22. Good. Further, the second transfer corotron 13 is a corotron pair as in the first embodiment (13a, 1 in FIG. 2).
3b). At this time, a positive DC voltage (having the same polarity as the first transfer corotron 12) is applied to the outer corotron of the intermediate transfer belt 20, and a negative DC voltage is applied to the inner corotron, superimposed on the AC voltage. I just need. Further, an AC voltage of DC superposition may be applied to the peeling corotron 16. Further, instead of the peeling corotron 16, a peeling claw may be arranged at a non-image portion of the paper P, or both may be used together.

Embodiment 3 The basic structure of a double-sided image forming apparatus according to the present embodiment is substantially the same as that of Embodiment 2, but is different from Embodiment 2.
A DC voltage higher than the DC voltage of the first transfer corotron 12 is applied to the second transfer corotron 13. In the configuration of the present embodiment, the current value applied to the first transfer corotron 12 when the first image T1 is transferred from the photosensitive drum 11 onto the intermediate transfer belt 20 and the transfer from the intermediate transfer belt 20 to the paper P are performed. FIG. 7 shows the relationship with the current value applied to the second transfer corotron 13 at this time. In FIG. 7, the horizontal axis Cin indicates the input image density, and the vertical axis Dout indicates the output density. This figure shows how the relationship between the image area ratio and the density changes with respect to the current value applied to the second transfer corotron 13 when the current value applied to the first transfer corotron 12 is +300 μA. According to the figure, when the current value applied to the second transfer corotron 13 is equal to or more than the current value (= + 300 μA) applied to the first transfer corotron 12, the density is equal to the density when the image is directly transferred from the photosensitive drum 11 to the paper P. Is obtained. This figure shows the case where the current value applied to the first transfer corotron 12 is +300 μA. However, even if this current value was changed, this relationship did not change. As described above, it has been found that when a DC voltage is applied to the second transfer corotron 12, it is necessary to apply a current value equal to or higher than the current value applied to the first transfer corotron.

In this embodiment, the first image T
1. A negatively charged toner is used as the toner for forming the second image T2, and an AC voltage of 7 kV _PP / 60 is applied to the peeling corotron 16.
A DC current of +20 μA was superimposed on 0 Hz, and a DC current of +300 μA was applied to the adsorption corotron 15. The suction roll 14 and the tension roll 22 are conductive and grounded.

Next, an image forming process of the double-sided image forming apparatus according to the present embodiment will be described. As in the second embodiment, the first image T1 formed on the photosensitive drum 11 is transferred by the first transfer corotron 12 onto the intermediate transfer belt 20 moving at substantially the same speed as the photosensitive drum 11. Subsequently, the paper P is transported between the suction roll 14 and the suction corotron 15 in synchronization with the rotation of the intermediate transfer belt 20, and is suctioned onto the intermediate transfer belt 20. Similarly, the second image T2 is transferred to the photosensitive drum 1 in synchronization with the rotation of the intermediate transfer belt 20.
1 and transferred onto the second surface (upper surface) of the paper P by the first transfer corotron 12. Thereafter, the sheet P is conveyed to the sheet discharge end of the intermediate transfer belt 20, and a first level T1 on the intermediate transfer belt 20 is applied to the first image T1 on the intermediate transfer belt 20 by applying a predetermined level of DC voltage to the second transfer corotron 13. Transfer to the surface (lower surface), followed by release corotron 16
The paper P is peeled off from the intermediate transfer belt 20 by applying an AC voltage superimposed on the paper P, and the fixing device 17 simultaneously fixes both sides of the paper P.

As described above, by applying a DC voltage higher than that applied to the first transfer corotron 12 to the second transfer corotron 13, the image transfer from the intermediate transfer belt 20 to the sheet P is performed reliably, and By providing the sheet 16 in opposition to the tension roll 22 as the counter electrode, the sheet P could be stably peeled off from the intermediate transfer belt 20, and a good double-sided image without transfer failure or image disturbance could be obtained. .

In this embodiment, a corotron is used for the first transfer device 12, but a bias roll may be used. In this case, the effective current value of the second transfer corotron 13 may be set to be larger than that of the first transfer roll. Further, under the condition satisfying the above relationship, constant voltage control can be performed.

Embodiment 4 FIG. 8 shows a schematic configuration of Embodiment 4 of a double-sided image forming apparatus to which the present invention is applied. In FIG. 1, a two-sided image forming apparatus includes a first image forming unit 10a (photosensitive drum 11a, first transfer roll 12a, and other electrophotographic devices (charging device, exposure device, developing device) not shown) on which a first image is formed. , Cleaning devices, etc.)
A second image forming unit 10b (including a photosensitive drum 11b, a second transfer roll 12b, and other electrophotographic devices (not shown) such as a charging device, an exposure device, a developing device, and a cleaning device) on which a second image is formed; An intermediate transfer belt 20 is provided with transfer portions of the first image forming unit 10a and the second image forming unit 10b facing each other.

In this embodiment, the first image forming unit 1
0a is a device for transferring the first image T1 on the photosensitive drum 11a to the intermediate transfer belt 20, while the second transfer roll 12b of the second image forming unit 10b is a device for transferring the first image T1 on the photosensitive drum 11b. This is a device for directly transferring the two images T2 to a sheet. In particular, in the present embodiment, the first transfer roll 12a and the second transfer roll 12b are elastic rolls coated with urethane foam, silicone rubber, or the like.
The volume resistivity is formed to be 10 ⁶ to 10 ¹⁰ Ω · cm, and a load of, for example, 10 to 50 gf / cm is applied from both ends by a compression coil spring (not shown).
Further, a transfer corotron 13 for secondary transfer is provided at a paper discharge end behind the second transfer portion of the intermediate transfer belt 20,
The first image T1 on the intermediate transfer belt 20 is transferred to another side of the sheet P. Note that a corotron may be used as the transfer device instead of the transfer roll.

In the present embodiment, a portion of the intermediate transfer belt 20 opposite to a sheet suction portion on the way from the transfer portion of the first image forming portion 10a to the transfer portion of the second image forming portion 10b is suctioned. A roll 14 and a suction bias roll 18 are provided.
To be electrostatically attracted. Reference numeral 31 denotes a paper tray, and 32 denotes a transport (for example, a vacuum transport) for vertically transporting the paper P in the paper tray 31 to a paper suction portion of the intermediate transfer belt 20.
Reference numerals 16 and 17 are a peeling corotron and a fixing device, respectively.

Further, in the present embodiment, the same intermediate transfer belt 20 as that in the first embodiment is used, and the intermediate transfer belt 20 is hung between a driving roll 21 and a driven roll (tension roll for tension adjustment) 22. The first transfer roll 12a and the second transfer roll 12b are provided on the back side of the intermediate transfer belt 20, respectively. In the present embodiment, the outer diameters of the photosensitive drums 11a and 11b and the drive roll 21 of the intermediate transfer belt 20 are the same, and the photosensitive drums 11a and 11b are driven by the same drive source.

Further, a toner of a developing device (not shown) of each of the image forming units 10a and 10b uses a negative toner, and a positive toner image (first image) is formed on the surface of the photosensitive drum 11a by a well-known electrophotographic process. ) T1 is such that a toner image (second image) T2 of a mirror image is formed on the surface of the photosensitive drum 11b.

In particular, in the present embodiment, the first image T1,
Negatively charged toner is used as the toner for forming the second image T2, DC current +10 μA is applied to the first transfer roll 12a and the second transfer roll 12b, and the transfer corotron 13 for the secondary transfer is used.
, A DC voltage of +7 kV (effective current ≧ + 10 μA), a peeling corotron 16 with an AC voltage of 7 kV _PP / 600 Hz superimposed with a DC current of +20 μA, and a suction roller 18 with a DC current of +20 μA. The suction roll 14 and the tension roll 22 are conductive and grounded.

Next, an image forming process of the double-sided image forming apparatus according to the present embodiment will be described. First, the first image T1 formed on the first photosensitive drum 11a is transferred onto the intermediate transfer belt 20 moving at substantially the same speed as the first photosensitive drum 11a by the first transfer roll 12a. The sheet P is conveyed to the sheet attracting portion of the intermediate transfer belt 20 via the transport 32 in a timely manner, and the sheet P is attracted onto the intermediate transfer belt 20 by the attracting bias roll 18. Subsequently, the second image T2 is transferred to the second photosensitive drum 11b in synchronization with the rotation of the intermediate transfer belt 20.
And the second transfer roll 12b forms
Transfer to the surface (upper surface). Thereafter, the intermediate transfer belt 20
The first image T1 on the intermediate transfer belt 20 is transferred to the first surface (lower surface) of the sheet P by conveying the sheet P to the sheet discharge end of the sheet P and applying a predetermined level of DC voltage to the transfer corotron 13 for secondary transfer. After the sheet P is peeled off from the intermediate transfer belt 20 by the peeling corotron 16, the fixing device 17
To fix both sides of the sheet P at the same time.

As described above, by applying to the transfer corotron 13 for the secondary transfer a DC voltage at which the effective current is equal to or greater than the current applied to the second transfer roll 12b, the image from the intermediate transfer belt 20 to the sheet P is transferred. By performing transfer reliably and providing the peeling corotron 16 in opposition to the tension roll 22 as a counter electrode, the paper P can be peeled off from the intermediate transfer belt 20 stably, and a good transfer without defective transfer or image disturbance can be obtained. A double-sided image could be obtained with the same productivity per sheet as in single-sided printing. In the present embodiment, the outer diameters of the drive rolls 21 of the photosensitive drums 11a and 11b and the intermediate transfer belt 20 are set to be the same, and the photosensitive drums 11a and 11b and the intermediate transfer belt 20 are driven by the same drive source. A difference in speed is unlikely to occur, and images on both the front and back sides of the sheet P can be accurately positioned.

In this embodiment, a DC voltage of a predetermined level is applied to the transfer corotron 13 for the secondary transfer. However, as in the first and second embodiments, for example, an AC voltage or DC superposition is applied. An AC voltage may be applied.

Further, in this embodiment, from the viewpoint of reducing the difference in image quality between the first image T1 and the second image T2 on both sides of the sheet, the transfer conditions of the first transfer roll 12a and the second transfer roll 12b are considered. Is preferably set differently when the first image T1 is transferred and when the second image T2 is transferred. Hereinafter, a method of setting the transfer conditions will be described. FIG. 9 shows a state in which a first photosensitive drum (indicated as a first photosensitive body in the figure) 11a is transferred to a sheet P.
And a second photosensitive drum (indicated as a second photosensitive body in the figure) 11b
DC current values applied to the first transfer roll 12a and the second transfer roll 12b when the toner images (first image and second image) are respectively transferred to the intermediate transfer belt (shown as an intermediate transfer body) 20 from The relationship with the transfer efficiency is shown. here,
The lower limit of the transfer efficiency is 80% for the transfer of the second image T2 from the second photosensitive drum 11b to the paper P, and 90% for the transfer of the first image T1 from the first photosensitive drum 11a to the intermediate transfer belt 20.
Need a degree. The transfer current value satisfying the above condition is the first
The transfer was about +3 to +9 μA in the transfer of the image T1 and about +5 to +14 μA in the transfer of the second image T2. Also, the second image T2
At about +18 μA or more during transfer, image quality defects due to leakage occurred. From the above results, for example, DC current +5 μA for the first transfer roll 12a and +10 μA for the second transfer roll 12b
μA was applied.

In the embodiment in which the first transfer roll 12a and the second transfer roll 12b are controlled at a constant voltage, the transfer conditions may be set as follows. FIG. 10 shows a first photosensitive drum (indicated as a first photosensitive member in the figure) 11a to the paper P, and a second photosensitive drum (indicated as a second photosensitive member in the figure) 11b with an intermediate transfer belt (intermediate transfer member in the figure). 2 shows the relationship between the DC voltage applied to the first transfer roll 12a and the second transfer roll 12b and the transfer efficiency when the toner images (first image and second image) are respectively transferred to the transfer roller 20. Here, the lower limit of the transfer efficiency is about 80% for the transfer of the second image T2 from the second photosensitive drum 11b to the paper P, and about 90% for the transfer of the first image T1 from the first photosensitive drum 11a to the intermediate transfer belt 20. It is. The transfer voltage value satisfying the above conditions is +0.6 to +1.15 kV in the first image T1 transfer, and the second image T2
In the transfer, it was about +1.2 to +1.8 kV. Also, a leak occurred at about +2.0 kV or more during the transfer of the second image T2. From the above results, for example, the first transfer roll 12
DC voltage +0.8 kV was applied to a, and +1.5 kV was applied to the second transfer roll 12b.

As described above, the transfer conditions of the first transfer roll 12a and the second transfer roll 12b are changed to the first photosensitive drum 11a.
The transfer current value and the transfer voltage value are appropriately controlled in the case where the transfer current value and the transfer voltage value are respectively adjusted in a case where the image is transferred from the second photosensitive drum 11b to the intermediate transfer belt 20. A good two-sided image with a small difference was obtained with the same productivity per sheet as in one-sided printing.

Embodiment 5 FIG. 11 shows a schematic configuration of Embodiment 5 of a double-sided image forming apparatus for forming a color image to which the present invention is applied. In FIG. 1, the basic configuration of the double-sided image forming apparatus is the first color image forming apparatus.
An image forming unit 10 for forming an image T1 and a second image T2;
The image forming section 10 includes an intermediate transfer drum 50 in which a transfer portion is arranged to face the transfer portion. In the present embodiment,
The image forming unit 10 includes a photosensitive drum 11 and a latent image forming device (for example, a charging device or an exposure device) that forms an electrostatic latent image for each color component on the photosensitive drum 11.
And a rotary developing device 19 for developing an electrostatic latent image for each color component formed on the photosensitive drum 11 with a corresponding color toner.
And each color formed on the photosensitive drum 11 (in the present embodiment, Y (yellow), M (magenta), C (cyan),
A first transfer corotron 12 for sequentially transferring the first image T1 and the second image T2 (K (black)) to the intermediate transfer drum 50 or the sheet P; and a cleaning device for removing residual toner on the photosensitive drum 11. I have.

In the present embodiment, a paper suction device including a suction roll 14 and a suction bias roll 18 is provided on the intermediate transfer drum 50 on the upstream side of the transfer portion of the first transfer corotron 12. The second transfer corotron pair 13a, 13b is provided downstream of the transfer portion with the intermediate transfer drum 50 interposed therebetween. In particular, in the present embodiment, the second transfer corotron pair 13a, 13b
Is applied with an AC voltage.

In particular, in this embodiment, a negatively charged toner is used as the toner for forming the first image T 1 and the second image T 2, and the direct current +300 is applied to the first transfer corotron 12.
μA, an AC voltage of 8 kV _PP / 600 Hz was applied to the second transfer corotron pair 13a, 13b, and a DC current of +300 μA was applied to the attraction bias roll 18. The suction roll 14 was made conductive and grounded.

Next, an image forming process of the color duplex image forming apparatus according to the present embodiment will be described. First, first
A first color (Y, M, C, K) image T is transferred from the photosensitive drum 11 to the intermediate transfer drum 50 by the transfer corotron 12.
1 is sequentially transferred one color at a time in one rotation of the intermediate transfer drum 50, and the sheet P is conveyed to the sheet suction portion at the timing when the multiple-transferred first color images T1 reach the sheet suction portion. The toner is attracted onto the intermediate transfer drum 50 by the attracting bias roll 18. Subsequently, the intermediate transfer drum 5
0 formed on the photosensitive drum 11 in synchronization with the rotation of
Are sequentially transferred to the second surface (upper surface) of the sheet P by the first transfer corotron 12. Thereafter, the first image T1 on the intermediate transfer drum 50 is transferred to the first surface (lower surface) of the sheet P by applying an AC voltage to both the second transfer corotron pair 13a, 13b, and at the same time, the sheet P is transferred to the intermediate transfer drum. The sheet P is peeled off from the sheet 50 and both sides of the sheet P are simultaneously fixed by the fixing unit 17. Reference numeral 51 denotes a peeling claw which is pressed against the intermediate transfer drum 50 at the same time as an AC voltage is applied to the second transfer corotron pair 13a, 13b, and forcibly peels off a portion corresponding to the non-image portion at the end of the sheet P. Yes, it assists in the stripping action of the second transfer corotron pair 13a, 13b.

As described above, the second transfer corotron pair 13
a, 13b by applying an AC voltage to the intermediate transfer belt 2 without providing a device such as a peeling corotron.
0 can be reliably transferred to the first surface of the sheet P, and the sheet P can be stably peeled off from the intermediate transfer belt 20. I got it.

In this embodiment, the intermediate transfer drum 50
Was used, but the intermediate transfer belt 20 may be used.
The transfer device may be a method as in the second and third embodiments.

Embodiment 6 FIG. 12 shows a schematic configuration of Embodiment 6 of a double-sided image forming apparatus for forming a color image to which the present invention is applied. In the figure, the basic configuration of the two-sided image forming apparatus is similar to that of the fourth embodiment, in that the first image forming unit 10a and the second image forming unit 1
0b, but the configuration of the first image forming unit 10a and the second image forming unit 10b is different from that of the second embodiment. Note that components similar to those of the second embodiment are denoted by the same reference numerals as those of the fourth embodiment, and a detailed description thereof will be omitted. In the present embodiment, the first image forming unit 10a is arranged such that Y (yellow),
M (magenta), C (cyan), and K (black) in this order, four photosensitive drums 11a (specifically, 11
a (Y), 11a (M), 11a (C), 11a
(K)) are arranged in parallel. On the other hand, the second image forming unit 10b includes four photosensitive drums 11b for each of K, Y, M, and C color components from the upstream side above the intermediate transfer belt 20.
(Specifically, 11b (K), 11b (Y), 11b
(M), 11b (C)) are arranged in parallel, and an electrostatic latent image for each color component is formed around each of the photosensitive drums 11a, 11b, and is developed with a corresponding color toner. An external toner image forming device (for example, a charging device, an exposing device, and a developing device) and toner images of respective colors formed on the four photosensitive drums 11a and 11b arranged corresponding to the transfer portions of the four photosensitive drums 11a and 11b And second transfer rolls 12a (specifically, 12a (Y), 12a (Y),
12a (M), 12a (C), 12a (K)), 12b
(Specifically, 12b (K), 12b (Y), 12b
(M), 12b (C)) and the respective photosensitive drums 11a, 11b.
b) and a cleaning device (not shown) for removing the residual toner on b. Note that the same reference numerals as in the fourth embodiment denote the same reference numerals as in the fourth embodiment, and a detailed description thereof will be omitted.

In particular, in the present embodiment, negatively charged toner is used as the toner for forming the first image T1 and the second image T2, and the first transfer roll 12a and the second transfer roll 12b
DC current +12 μA, and a transfer corotron 13 for secondary transfer has an AC voltage of 8 kV _PP / 600 Hz and a DC voltage +
A 1.5 kV superimposed was applied to the peeling corotron 16 at an AC voltage of 7 kV _PP / 600 Hz and a DC current of +20 μA.
A DC current of +20 μA was applied to the suction bias roll 18. The suction roll 14 was made conductive and grounded.

Accordingly, in the present embodiment, the first images formed on the respective photosensitive drums 11a (Y, M, C, K) groups by the first transfer rolls 12a (Y, M, C, K), respectively. After the multiple transfer of T1 onto the intermediate transfer belt 20, the sheet P is conveyed in a timely manner and is attracted onto the intermediate transfer belt 20. Subsequently, in synchronization with the rotation of the intermediate transfer belt 20, the second images T2 formed on the respective photosensitive drums 11b (Y, M, C, K) are transferred to the second transfer rolls 12b.
Multiple transfer is performed on the second surface (upper surface) of the paper P by (Y, M, C, K). Thereafter, the sheet P is conveyed to the end of the intermediate transfer belt 20, and the first image T 1 on the intermediate transfer belt 20 is transferred to the sheet P by applying a voltage in which an alternating current and a direct current are superimposed on the transfer corotron 13 for secondary transfer. Then, the sheet P is peeled off from the intermediate transfer belt 20 by the peeling corotron 16, and both sides of the sheet P are simultaneously fixed by the fixing device 17.

As described above, by applying a DC superimposed AC voltage to the transfer corotron 13 for the secondary transfer, the image transfer from the intermediate transfer belt 20 to the sheet P is reliably performed, and the sheet P and the intermediate transfer The paper P can be stably peeled off from the intermediate transfer belt 20 by weakening the attraction force between the belts 20 and providing the peeling corotron 16 in opposition to the tension roll 22 as a counter electrode, resulting in poor transfer and image disturbance. A good double-sided image without defects was obtained with the same productivity per sheet as in the case of single-sided. In this embodiment, a transfer device for secondary transfer is used as in the first embodiment,
Of course, a method such as the method 3 may be used.

Embodiment 7 FIG. 13 shows a schematic configuration of Embodiment 7 of a double-sided image forming apparatus to which the present invention is applied. The basic configuration of the double-sided image forming apparatus according to the figure is substantially the same as that of the first embodiment, but is different from the first embodiment. For example, the intermediate transfer belt 20 is connected to a driving roll 21 and two driven rolls 22 and 23. Over to
The conveyance of the sheet from the intermediate transfer belt 20 to the fixing device 17 is performed vertically. The same reference numerals as in the first embodiment denote the same reference numerals as in the first embodiment, and a detailed description thereof will be omitted. According to the present embodiment, in addition to the same operation as in the first embodiment, by making the paper conveyance path vertical, the posture of entering the fixing device 20 can be further stabilized, and image disorder and paper wrinkles can be reduced. It can be reliably prevented.

[0062]

As described above, according to the present invention,
By applying a transfer bias consisting of an AC voltage to the intermediate secondary transfer means, transferring the image on the intermediate transfer body to the recording material side, and removing the charge for holding the image on the intermediate transfer body side, the intermediate transfer body Since the recording material is separated from the recording medium, it is necessary to stabilize the posture of the recording material entering the fixing unit while maintaining good transferability of the image from the intermediate transfer body to the recording material without using a separation device. Can be. For this reason, it is possible to reduce the occurrence of image disturbance, paper wrinkles, curls, jams, and the like due to the disturbance of the posture of the recording material entering the fixing unit, and to always obtain a stable double-sided image without transfer failure or image disturbance. Can be.

In the present invention, if a transfer bias consisting of a DC superimposed AC voltage is applied to the intermediate secondary transfer means, an image on the intermediate transfer body is transferred mainly to the recording material by a DC voltage component. At the same time, the charge for holding the image on the intermediate transfer body side is reduced mainly by the AC voltage component, and the electrostatic attraction force between the recording material and the intermediate transfer body can be reduced. For this reason, by optimizing the DC voltage component of the transfer bias, or by using an auxiliary peeling device, it is possible to improve the transferability of the image from the intermediate transfer body to the recording material while maintaining good transferability of the image to the fixing means. Of the recording material can be stabilized, thereby reducing the occurrence of image disturbance, paper wrinkles, curls, jams, etc. due to the disturbance of the recording material entering the fixing means, and resulting in poor transfer and image disturbance. Thus, a good double-sided image free of the like can always be stably obtained.

Further, in the present invention, a transfer bias consisting of a DC voltage higher than the DC voltage applied to the intermediate primary transfer means is applied to the intermediate secondary transfer means, and a peeling means is provided behind the intermediate secondary transfer means. By doing so, the transferability of the image from the intermediate transfer body to the recording material is kept good by the intermediate secondary transfer means, while the peelability of the recording material from the intermediate transfer body is kept good by the peeling means, It is possible to stabilize the posture of the recording material entering the fixing unit. For this reason, image disturbance, paper wrinkles, curl,
The occurrence of jams and the like can be reduced, and a good double-sided image free from transfer failure and image disorder can always be stably obtained.

In particular, in the present invention, if the image carrier for forming and carrying the first image and the second image is separately provided, and the transfer operations of the first image and the second image are performed in parallel, the single-sided image can be obtained. A good double-sided recorded image can be obtained at the same recording speed as at the time.

[Brief description of the drawings]

FIGS. 1A and 1B are schematic structural views showing a double-sided image forming apparatus according to the present invention.

FIG. 2 is a schematic configuration diagram illustrating a double-sided image forming apparatus according to the first embodiment;

FIG. 3 is an explanatory diagram showing a transfer principle of a second transfer corotron pair according to the first embodiment.

FIG. 4 is a graph showing a relationship between an AC voltage applied to a second transfer corotron pair and transfer efficiency according to the first embodiment.

FIG. 5 is a graph showing a relationship between a transfer current value and a transfer efficiency of the first transfer corotron according to the first embodiment.

FIG. 6 is a schematic configuration diagram illustrating a double-sided image forming apparatus according to a second embodiment.

FIG. 7 illustrates a second example of the duplex image forming apparatus according to the third embodiment.
FIG. 7 is a graph showing a change in image density using a transfer current value of a transfer corotron as a parameter.

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

FIG. 9 is a graph showing a relationship between transfer current values and transfer efficiency of a first transfer roll and a second transfer roll according to a fourth embodiment.

FIG. 10 shows a first transfer roll and a second transfer roll according to a fourth embodiment.
FIG. 4 is a graph showing a relationship between a transfer voltage value and a transfer efficiency in a mode in which a transfer roll is controlled at a constant voltage.

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

FIG. 12 is a schematic configuration diagram of a double-sided image forming apparatus according to a sixth embodiment.

FIG. 13 is a schematic configuration diagram of a double-sided image forming apparatus according to a seventh embodiment.

FIG. 14 is an explanatory diagram illustrating an example of a conventional double-sided image forming apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image carrier, 1a ... 1st image carrier, 1b ... 2nd image carrier, 2 ... Intermediate transfer body, 3 ... Recording material, 4 ... Direct transfer means,
5: Intermediate primary transfer means, 6: Intermediate secondary transfer means, 7: Peeling means, 10: Image forming unit, 10a: First image forming unit,
10b: second image forming unit, 11: photosensitive drum, 11a ...
1st photosensitive drum, 11b ... 2nd photosensitive drum, 12 ... 1st
Transfer corotron, 12a: first transfer roll, 12b: second transfer roll, 13: second transfer corotron (transfer corotron for secondary transfer), 13a, 13b: second transfer corotron pair, 20: intermediate transfer belt, 50 ... intermediate transfer drum, P ... paper, T1 ... first image, T2 ... second image

Claims (5)

[Claims] At least one image carrier (1) on which a first image (T1) and a second image (T2) are formed and supported, and an intermediate transfer body (1) arranged to face the image carrier (1) 2), the first image (T1) and the second image (T1) on the image carrier (1).
2) a direct transfer means (4) for directly transferring either one of them to one side of the recording material (3); and a first image (T1) and a second image (T) on the image carrier (1).
An intermediate primary transfer means (5) for transferring one of the other of the two to the intermediate transfer member (2); and a transfer bias provided at a discharge end of the recording material (3) of the intermediate transfer member (2) and comprising an AC voltage. Is applied to the first image (T1) or the second image (T1) transferred on the intermediate transfer body (2).
A two-sided image forming apparatus comprising: an intermediate secondary transfer means (6) for transferring an image (T2) to another side of a recording material (3). 2. At least one image carrier (1) on which a first image (T1) and a second image (T2) are formed and supported, and an intermediate transfer member (1) arranged to face the image carrier (1) 2), the first image (T1) and the second image (T1) on the image carrier (1).
2) a direct transfer means (4) for directly transferring either one of them to one side of the recording material (3); and a first image (T1) and a second image (T) on the image carrier (1).
An intermediate primary transfer means (5) for transferring one of the other to the intermediate transfer body (2), and a recording medium (3) provided at a discharge end of the intermediate transfer body (2) and comprising a DC superimposed AC voltage. First image (T1) transferred on intermediate transfer body (2) by applying transfer bias
Alternatively, an intermediate secondary transfer means (6) for transferring the second image (T2) to another side of the recording material (3) is provided. 3. A peeling means (7) for forcibly peeling off a recording material (3) attached on an intermediate transfer body (2) behind an intermediate secondary transfer means (6). And a double-sided image forming apparatus. 4. An at least one image carrier (1) on which a first image (T1) and a second image (T2) are formed and supported, and an intermediate transfer member (1) arranged to face the image carrier (1). 2), the first image (T1) and the second image (T1) on the image carrier (1).
2) a direct transfer means (4) for directly transferring either one of them to one side of the recording material (3); and a first image (T1) and a second image (T) on the image carrier (1).
An intermediate primary transfer means (5) for transferring one of the other to the intermediate transfer body (2); and an intermediate primary transfer means (5) provided at a discharge end of the recording material (3) of the intermediate transfer body (2). A) the first image (T1) or the second image (T2) transferred onto the intermediate transfer member (2) by applying a transfer bias consisting of a DC voltage equal to or higher than the transfer bias DC voltage of the recording material (3); An intermediate secondary transfer means (6) for transferring to another surface of the recording medium, and a recording material (3) provided behind the intermediate secondary transfer means (6) and adhered on the intermediate transfer body (2). A double-sided image forming apparatus, comprising: 5. A device according to claim 1, wherein a first image carrier (1a) on which a first image (T1) is formed and carried, and a second image (T2) is formed and carried. A double-sided image forming apparatus, wherein the second image carrier (1b) is provided separately.