JPH10133430A - Both-side image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the damage of an intermediate transfer body and image carriers caused by a failure in transfer and leakage, further, to suppress the difference in image quality between both surfaces of a recording material as small as possible, and moreover, to enable both-face recording with the same productivity as that of one-face recording. SOLUTION: This device is provided with a first image carrier 1a on which a first image T1 is formed/carried, a second image carrier 1b on which a second image T2 is formed/carried and the intermediate transfer body 2 across which these first and second image carriers 1a and 1b are arranged to face each other. In such a case, the device is further provided with a direct transfer means 6 for transferring one of the first image T1 on the first image carrier 1a and the second image T2 on the second image carrier 1b to one surface of the recording material 3, an intermediate primary transfer means 7 for transferring the other of the first and second toner images T1 and T2 to the intermediate transfer body 2 on a transfer condition coefficient from that of the direct transfer means 6 and an intermediate secondary transfer means 8 for transferring the first toner image T1 or the second toner image T2 after being transferred onto the intermediate transfer body 2, to the other surface of the recording material 3.

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. 9, a toner image T1 (first image) or a toner image T1 (first image) on the photosensitive drum 101 is constituted by a photosensitive drum 101 and an intermediate transfer belt 102. First transfer device 10 for transferring T2 (second image) to intermediate transfer belt 102 or paper P
3. An apparatus including a second transfer unit 104 disposed at the sheet discharge end of the intermediate transfer belt 102 and transferring the toner image T1 or T2 on the intermediate transfer belt 102 to the sheet P (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 first transfer unit 103 transfers the first image T1 from the photosensitive drum 101 to the intermediate transfer belt 102. And the transfer of the second image T2 from the photosensitive drum 101 to the sheet P, the transfer failure / intermediate transfer belt / photosensitive drum due to a transfer failure due to the resistance difference between the photosensitive drum 101 and the intermediate transfer belt 102 due to the presence or absence of the sheet and the leak. There is a technical problem that damage to the surface is likely to occur. Further, the first image T1 is transferred from the photosensitive drum 101 to the intermediate transfer belt 102 and then transferred to the sheet P, whereas the second image T2 is transferred directly from the photosensitive drum 101 to the sheet P. There is also a technical problem that a difference in image quality between both sides of the paper P occurs under the same transfer condition in the image forming apparatus 103.

The present invention has been made to solve the above technical problems, and a first problem to be solved is that there is no damage to the intermediate transfer member / image carrier due to poor transfer or leakage.
Moreover, the present invention provides a double-sided image forming apparatus capable of suppressing a difference in image quality between both sides of a recording material. Furthermore, the second
The 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, in addition to the above-mentioned problems.

[0006]

That is, in order to achieve the first object, the present invention provides a method in which a first image T1 and a second image T2 are formed and carried as shown in FIG. In a two-sided image forming apparatus including an image carrier 1 and an intermediate transfer body 2 disposed to face the image carrier 1, either one of the first image T1 and the second image T2 on the image carrier 1 The intermediate transfer member is directly transferred to one surface of the recording material 3 and the other one of the first image T1 and the second image T2 on the image carrier 1 is transferred under a transfer condition different from the condition for direct transfer to the recording material 3. 2 and a second transfer means 5 for transferring the first image T1 or the second image T2 transferred onto the intermediate transfer body 2 to another side of the recording material 3. It is characterized by the following.

In order to attain the second object, the present invention relates to a first image carrier 1a on which a first image T1 is formed and carried, as shown in FIG. In a double-sided image forming apparatus including a second image carrier 1b on which T2 is formed and carried, and an intermediate transfer body 2 on which the first image T1 and the second image T2 are arranged to face each other, the first image carrier 1a Direct transfer means 6 for transferring one of the upper first image T1 and the second image T2 on the second image carrier 1b to one side of the recording material 3
And the other of the first image T1 on the first image carrier 1a and the second image T2 on the second image carrier 1b is transferred to the intermediate transfer member 2 under transfer conditions different from those of the direct transfer means 6. An intermediate primary transfer unit 7;
An intermediate secondary transfer means 8 for transferring the image T1 or the second image T2 to another one side of the recording material 3 is provided.

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.

In the embodiment of FIG. 1A, the first transfer means 4 and the second transfer means 5 are usually provided separately, but a part of them is shared. But it doesn't hurt. For example, the intermediate transfer member 2
By providing a polarity inversion means for inverting the polarity of the first image T1 (or the second image T2) transferred above,
The recording material 3 is arranged on the intermediate transfer body 2 on which the first image T1 (or the second image T2) is formed, and the recording material 3 is
When transferring the second image T2 (or the first image T1) onto
The first image T1 on the intermediate transfer body 2 by the first transfer means 4
(Or the second image T2) can be simultaneously transferred to the other side of the recording material 3. At this time, the polarity reversing means and the first transfer means 4 function as the second transfer means 5.

In the embodiment shown in FIG. 1B,
The location of the direct transfer means 6 may be a portion facing the intermediate transfer member 2 or a portion not facing the intermediate transfer member 2, but from the viewpoint of making the device configuration compact. In this case, it is preferable to directly dispose the transfer means 6 at a portion facing the intermediate transfer member 2. Here, the intermediate secondary transfer means 8 is usually provided separately from the direct transfer means 6 and the intermediate primary transfer means 7, but a portion may be shared. For example, if a polarity reversing unit for reversing the polarity of the first image T1 (or the second image T2) transferred onto the intermediate transfer body 2 by the intermediate primary transfer unit 7 is provided, the first image T1 (or the second image T2) is provided. When the recording material 3 is disposed on the intermediate transfer body 2 on which the image T2) is formed, and the second image T2 (or the first image T1) is transferred onto the recording material 3 by the direct transfer means 6, the direct transfer is performed. By means 6, the first image T1 (or the second image T2) on the intermediate transfer body 2 can be simultaneously transferred onto the other side of the recording material 3.
At this time, the polarity reversing unit and the direct transfer unit 6 function as the intermediate secondary transfer unit 8.

Further, as an example of setting the first transfer means 4 or the intermediate primary transfer means 7, the applied current or the applied voltage for the transfer condition to the intermediate transfer member 2 is smaller than that for the direct transfer to the recording material 3. The setting is used.

From the viewpoint of minimizing the difference in image quality between the first and second images T1 and T2 transferred to both sides of the recording material 3, the first image T
1. It is preferable to set the transfer conditions of the transfer units 4, 5 or 6 to 8 so that the final transfer efficiency of the second image T2 is substantially the same.

Next, the operation of the above technical means will be described. First, in the embodiment shown in FIG. 1A, the first transfer means 4 transfers the first image T1 (or the second image T2) formed and carried on the image carrier 1 to the intermediate transfer body 2. On the other hand, the second image T2 (or the first image T1) formed and carried on the image carrier 1 is directly transferred to one side of the recording material 3. Further, the second transfer means 5 is configured to control the first image T1 on the intermediate transfer body 2.
(Or the second image T2) is transferred to the other 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 the first transfer unit 4, since the transfer condition to the recording material 3 and the transfer condition to the intermediate transfer body 2 are different, each transfer condition is applied to the transfer target (the recording material 3 or the intermediate transfer body 2). By setting them together, the degree of transfer from the image carrier 1 can be favorably maintained for each transfer target.

In the embodiment shown in FIG. 1B,
For example, the intermediate primary transfer means 7 transfers the first image T1 (or the second image T2) formed and carried on the first image carrier 1a to the intermediate transfer body 2, and the direct transfer means 6 The second image T2 (or the first image T1) formed and carried on the two-image carrier 1b is directly transferred to one side of the recording material 3, and the intermediate secondary transfer means 8 further comprises The one image T1 (or the second image T2) is transferred to the other side of the recording material 3. Thereby, the first image T1 and the second image T2 are formed on both sides of the recording material 3.
Is transferred. At this time, since the process of transferring the first image T1 and the second image T2 to both sides of the recording material 3 is performed in parallel, double-sided recording is performed at approximately the same level as single-sided recording.

[0015]

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 this embodiment, 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 the intermediate transfer belt 20. This is a device for transferring to one side of the paper P. On the other hand, a second transfer corotron 13 is provided behind the first transfer portion of the intermediate transfer belt 20, so that the first image T1 on the intermediate transfer belt 20 is transferred to another side of the sheet P. I have. In addition, the intermediate transfer belt 2 is located in front of the transfer portion of the intermediate transfer belt 20.
A suction roll 14 and a suction corotron 15 are provided with the sheet P interposed therebetween, and the sheet P is sucked to the intermediate transfer belt 20. Reference numeral 16 is provided on the rear side of the second transfer corotron 13,
Reference numeral 17 denotes a fixing unit for fixing an unfixed toner image on the separated sheet P. In this embodiment, a corotron is used as the transfer device, but a bias roll may be used.

In this embodiment, the intermediate transfer belt 2
The first transfer corotron 0 is disposed between a driving roll 21 and a driven roll (tension roll for tension adjustment) 22. The first transfer corotron is disposed on the back side of the intermediate transfer belt 20. The intermediate transfer belt 20 is prepared by adding an appropriate amount of an antistatic agent such as carbon black to a resin such as polyimide, acrylic, vinyl chloride, polyester, or polycarbonate or various rubbers, and has a volume resistivity of 10 ⁹ to 1.
0 ¹³ Omega formed such that · cm, the thickness is set to 0.1mm for example.

In the present embodiment, a toner of a developing device (not shown) uses a negative polarity toner, and a positive toner image (first image) T1 or a mirror image is formed on the surface of the photosensitive drum 11 by a well-known electrophotographic process. Toner image (second image) T2
Is formed.

In particular, in the present embodiment, the transfer conditions of the first transfer corotron 12 are determined when the first image T1 is transferred and when the second image T2 is transferred.
It is set differently for the transfer. Hereinafter, a method of setting the transfer conditions will be described. FIG. 3 shows toner images (first and second images) from a photosensitive drum (indicated as a photoreceptor in the figure) 11 to paper P and from the photosensitive drum 11 to an intermediate transfer belt (indicated as an intermediate transfer body in the figure) 20. Shows the relationship between the DC current value applied to the first transfer corotron 12 and the transfer efficiency in the case where each is transferred. Here, the lower limit of the transfer efficiency is required to be about 80% for the transfer of the second image T2 from the photosensitive drum 11 to the paper P, and about 90% 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 +250 μm in the first image T1 transfer.
A, about +200 to +400 μA in the transfer of the second image T2. Also, about +300 μm at the time of transferring the first image T1.
Above A, image quality defects due to leakage occurred.

From the above results, the first transfer corotron 12 has +200 μA during the transfer of the first image T1, +300 μA during the transfer of the second image T2, and +20 μA during the transfer of the second image T2.
0 μA, AC voltage of 7 kV _PP /
A DC current of +20 μA was superimposed on 600 Hz, and a DC current of +300 μA was applied to the adsorption corotron 15. The suction roll 14 and the driven roll (tension roll) 22 are electrically conductive and grounded. Further, the first image T on the intermediate transfer belt 20 is transferred by the second transfer corotron 13.
In order to satisfactorily transfer 1 to the paper P, it is preferable that the current value applied to the second transfer corotron 13 be equal to or larger than the current value applied to the first transfer corotron 12.

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 conveyed to the sheet discharge end of the intermediate transfer belt 20, and the first image T1 on the intermediate transfer belt 20 is transferred to the first surface (lower surface) of the sheet P by the second transfer corotron 13, and the separation corotron The sheet P is separated from the intermediate transfer belt 20 by 16, and both sides of the sheet P are fixed simultaneously by the fixing device 17.

As described above, by controlling the transfer conditions of the first transfer corotron 12 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 is performed 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.

Second Embodiment FIG. 4 shows a schematic configuration of a two-sided image forming apparatus according to a second embodiment of the present invention. 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 section 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).
A transfer corotron 13 for secondary transfer is provided on the rear side of the second transfer portion of the intermediate transfer belt 20 so that the first image T1 on the intermediate transfer belt 20 is transferred to another one side of the sheet P. Has become. Note that a corotron may be used as the transfer device instead of the transfer roll.

Further, in the present embodiment, a portion of the intermediate transfer belt 20 opposite to the 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 denote a peeling corotron and a fixing device similar to those of the first embodiment, 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.

A negative toner is used as a toner of a developing device (not shown) of each of the image forming units 10a and 10b, 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.

Particularly, in the present embodiment, the transfer conditions of the first transfer roll 12a and the second transfer roll 12b are set differently. Hereinafter, a method of setting the transfer conditions will be described. FIG. 5 shows a first photosensitive drum (indicated as a first photosensitive member in the figure) 1
A toner image (first image, second image) is transferred from 1a to paper P and from a second photosensitive drum (shown as a second photosensitive member in the figure) 11b to an intermediate transfer belt (shown as an intermediate transfer body) 20 in the figure. The relationship between the DC current value applied to the first transfer roll 12a and the second transfer roll 12b and the transfer efficiency in the case of each transfer is shown. Here, the lower limit of the transfer efficiency is the second photosensitive drum 1
80% in the transfer of the second image T2 from
The transfer of the first image T1 from the photosensitive drum 11a to the intermediate transfer belt 20 requires about 90%. The transfer current value satisfying the above conditions is +3 to +9 μA for the first image T1 transfer,
The transfer was about +5 to +14 μA in the second image T2 transfer. At the time of transfer of the second image T2, an image quality defect due to leakage occurred at about +18 μA or more.

From the above results, the direct current +5 μA was applied to the first transfer roll 12a, and +10 μA was applied to the second transfer roll 12b.
A, DC voltage +7 is applied to the transfer corotron 13 for the secondary transfer.
kV, peeling corotron 16 has an AC voltage of 7 kV _PP / 6
A DC current of +20 μA was superimposed on 00 Hz, and a DC current of +10 μA was applied to the attraction bias roll 18. The suction roll 14 and the driven roll (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 sheet P is conveyed to the sheet discharge end of the second transfer belt, and the first image T on the intermediate transfer belt 20 is transferred by the transfer corotron 13 for the secondary transfer.
1 is transferred to the first surface (lower surface) of the sheet P, and the sheet P is separated from the intermediate transfer belt 20 by the separation corotron 16, and then both sides of the sheet P are simultaneously fixed by the fixing device 17.

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 is controlled to an appropriate value in the case where the image is transferred from the second photosensitive drum 11b to the intermediate transfer belt 20, and there is no image defect due to transfer failure or leakage, and the image quality difference is small. Simple double-sided image on paper 1
It was possible to obtain the same productivity per sheet as in single-sided printing.

In this embodiment, the photosensitive drum 11
By making the outer diameters of the drive rolls 21a and 11b and the intermediate transfer belt 20 the same and driving the same by the same drive source, a difference in speed between the photosensitive drums 11a and 11b and the intermediate transfer belt 20 hardly occurs. The positioning of the images on both sides could be performed accurately.

Embodiment 3 The basic configuration of a double-sided image forming apparatus according to this embodiment is as follows.
The second embodiment is substantially the same as the second embodiment, but differs from the second embodiment in that the first transfer roll 12a and the second transfer roll 12b are controlled at a constant voltage. FIG. 6 shows a state in which a first photosensitive drum (indicated as a first photosensitive body in the figure) 11a is transferred to a sheet
And a second photosensitive drum (indicated as a second photosensitive body in the figure) 11b
DC voltage 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 (indicated as an intermediate transfer body in the figure) 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 voltage value satisfying the above condition is the first
The transfer was about +0.6 to +1.15 kV in the image T1 transfer, and was about +1.2 to +1.8 kV in the second image T2 transfer.
Also, a leak occurred at about +2.0 kV or more during the transfer of the second image T2.

From the above results, the DC voltage +0.8 kV was applied to the first transfer roll 12a, and + DC k
1.5 kV, DC voltage +7 kV for transfer corotron 13 for secondary transfer, AC voltage 7 kV for peeling corotron 16
_A DC current of +20 μA was superimposed on _PP / 600 Hz, and a DC current of +10 μA was applied to the attraction bias roll 18. The suction roll 14 and the driven roll (tension roll) 22 are conductive and grounded.

As described above, the transfer conditions of the first transfer roll 12a and the second transfer roll 12b are changed to the second photosensitive drum 11b.
The transfer voltage is controlled to an appropriate value in the case of the transfer from the first photosensitive drum 11a to the intermediate transfer belt 20 and the transfer from the first photosensitive drum 11a to the intermediate transfer belt 20. Simple double-sided image on paper 1
It was possible to obtain the same productivity per sheet as in single-sided printing. still,
Also in the present embodiment, it is possible to change the transfer roll to corotron as a transfer device.

Embodiment 4 FIG. 7 shows a schematic configuration of Embodiment 4 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 two-sided image forming apparatus includes an image forming section 10 for forming a first image T1 and a second image T2 of a color, and an intermediate transfer drum in which a transfer portion of the image forming section 10 is arranged to face. 50. In the present embodiment, the image forming unit 10 includes a photosensitive drum 11 and the photosensitive drum 1.
A latent image forming device (eg, a charging device, an exposure device) (not shown) for forming an electrostatic latent image for each color component on
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;
Each color (in this embodiment, Y (yellow), M (magenta), C (cyan), K (color) formed on the photosensitive drum 11
A first transfer corotron 12 for sequentially transferring the (black) first image T1 and the second image T2 to the intermediate transfer drum 50 or the sheet P; and a cleaning device for removing residual toner on the photosensitive drum 11. .

In the present embodiment, a paper suction device including a suction roll 14 and a suction corotron 15 is provided on the intermediate transfer drum 50 on the upstream side of the transfer site of the first transfer corotron 12. On the downstream side of the portion, a second transfer corotron pair 13a, 13b is provided with the intermediate transfer drum 50 interposed therebetween. In particular, in the present embodiment, an AC voltage is applied to the second transfer corotron pair 13a, 13b.

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. It is adsorbed on the intermediate transfer drum 50 by the adsorption corotron 15. Subsequently, the second color (Y, M, C, K) images T2 formed on the photosensitive drum 11 in synchronization with the rotation of the intermediate transfer drum 50 are sequentially transferred by the first transfer corotron 12 to the second surface of the sheet P. (Upper surface). Thereafter, an AC voltage is applied to both the second transfer corotron pair 13a and 13b, thereby causing the first transfer
At the same time as the image T1 is transferred to the first surface (lower surface) of the sheet P, the sheet P is peeled off from the intermediate transfer drum 50, and the fixing device 17 fixes both sides of the sheet P simultaneously. 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.

Also in this embodiment, the photosensitive drum 11
By controlling the transfer conditions at the time of transferring the first image T1 from the photosensitive drum 11 to the intermediate transfer drum 50 and at the time of transferring the second image T2 from the photosensitive drum 11 to the sheet P to appropriate values,
A good double-sided color image with no image defects due to transfer failure or leak and with little difference in image quality could be obtained.

Fifth Embodiment FIG. 8 shows a schematic configuration of a double-sided image forming apparatus for forming a color image according to a fifth embodiment of the present invention. In the figure, the basic configuration of the double-sided image forming apparatus is the same as that of the second embodiment.
Similarly, the first image forming unit 10a and the second image forming unit 10
b, but the configuration of the first image forming unit 10a and the second image forming unit 10b is different from the second embodiment. Note that components similar to those of the second embodiment are denoted by the same reference numerals as those of the second 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 the order of four photosensitive drums 11a for each color component (specifically, 11a
(Y), 11a (M), 11a (C), 11a (K))
Are arranged in parallel, while the second image forming unit 10
b denotes K, Y, and K from the upstream side above the intermediate transfer belt 20.
Four photosensitive drums 11b for each color component of M and C (specifically, 11b (K), 11b (Y), 11b (M), 11b)
b (C)) are arranged in parallel.
A toner image forming device (for example, a charging device, an exposing device, a developing device) (not shown) for forming an electrostatic latent image for each color component and developing the electrostatic latent image with a corresponding color toner around 1a and 11b; Photosensitive drums 11a, 1
Four photosensitive drums 1 arranged corresponding to the transfer site 1b
First and second transfer rolls 12a (specifically, 12a (Y), 12a (M), and 12a) for sequentially transferring the respective color toner images formed on 1a and 11b to the intermediate transfer belt 20 or the sheet P.
12a (C), 12a (K)), 12b (specifically, 1
2b (K), 12b (Y), 12b (M), 12b
(C)), and a cleaning device (not shown) for removing residual toner on each of the photosensitive drums 11a and 11b. The same reference numerals as in the second embodiment denote the same reference numerals as in the second embodiment, and a detailed description thereof will be omitted.

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.

Also in this embodiment, the first image T1 is transferred from the first photosensitive drum 11a to the intermediate transfer belt 20, and the second image T1 is transferred from the second photosensitive drum 11b to the paper P.
By controlling the transfer conditions when transferring 2 to appropriate values, there is no image defect due to transfer failure or leak, and a good two-sided color image with little image quality difference is produced at the same time as one side per sheet. I was able to get by sex.

[0043]

As described above, according to the present invention,
When transferring the first image and the second image on the image carrier to the recording material or the intermediate transfer member, the transfer conditions are made different for each transfer object, so that the transfer for each transfer object is optimized. This makes it possible to obtain a good double-sided recorded image free from transfer defects and image defects due to leaks and capable of suppressing a difference in image quality between both sides of the recording material. In particular, in the present invention, if the image carriers for forming and carrying the first image and the second image are separately provided, and the transfer operations of the first image and the second image are performed in parallel, the same as in the single-sided case A good double-sided recorded image can be obtained at a recording speed.

[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 illustrates a first example of the two-sided image forming apparatus according to the first embodiment.
FIG. 4 is a graph showing a relationship between a transfer current value and a transfer efficiency in a transfer corotron.

FIG. 4 is a schematic configuration diagram showing a two-sided image forming apparatus according to a second embodiment.

FIG. 5 illustrates a first example of the duplex image forming apparatus according to the second embodiment.
FIG. 4 is a graph showing a relationship between transfer current values of a transfer roll and a second transfer roll and transfer efficiency.

FIG. 6 illustrates a first example of the duplex image forming apparatus according to the third embodiment.
FIG. 4 is a graph showing a relationship between transfer voltage values of a transfer roll and a second transfer roll and transfer efficiency.

FIG. 7 is a schematic configuration diagram of a two-sided image forming apparatus according to a fourth embodiment.

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

FIG. 9 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 ... 1st transfer means,
Reference numeral 5: second transfer unit, 6: direct transfer unit, 7: intermediate primary transfer unit, 8: intermediate secondary transfer unit, 10: image forming unit, 1
0a: first image forming unit, 10b: second image forming unit, 11
... Photosensitive drum, 11a ... First photosensitive drum, 11b ... Second
Photosensitive drum, 12: first transfer corotron, 12a: first
Transfer roll, 12b second transfer roll, 13 second transfer corotron (transfer corotron for secondary transfer), 20 intermediate transfer belt, 50 intermediate transfer drum, P paper, T1
... First image, T2 ... Second image

Claims (4)

[Claims] 1. A common image carrier (1) on which a first image (T1) and a second image (T2) are formed and held, and an intermediate transfer member (2) arranged to face the image carrier (1) ), The first image (T1) and the second image (T1) on the image carrier (1).
2) is transferred directly to one side of the recording material (3), and the other of the first image (T1) and the second image (T2) on the image carrier (1) is transferred to the recording material. (1) a first transfer means (4) for transferring to the intermediate transfer member (2) under transfer conditions different from the direct transfer conditions to the intermediate transfer member (2), and a first image (T1) or (T1) transferred on the intermediate transfer member (2) And a second transfer means (5) for transferring the second image (T2) to another side of the recording material (3). 2. A first image on which a first image (T1) is formed and carried.
An image carrier (1a), a second image carrier (1b) on which a second image (T2) is formed and carried, and the first image carrier (1b)
a) and an intermediate transfer member (2) in which the second image carrier (1b) is arranged to face each other, wherein the first image (T1) and the first image (T1) on the first image carrier (1a) are provided. A direct transfer means (6) for transferring one of the second images (T2) on the second image carrier (1b) to one side of the recording material (3), and a first transfer means (6) on the first image carrier (1a). An intermediate for transferring one of the one image (T1) and the other of the second image (T2) on the second image carrier (1b) to the intermediate transfer body (2) under different transfer conditions from the direct transfer means (6) A primary transfer means (7), and an intermediate secondary transfer means for transferring the first image (T1) or the second image (T2) transferred onto the intermediate transfer body (2) to another one side of the recording material (3) (8) A double-sided image forming apparatus comprising: 3. The double-sided image forming apparatus according to claim 1, wherein the first transfer unit (4) or the intermediate primary transfer unit (7) is compared with a condition for direct transfer to the recording material (3). A double-sided image forming apparatus, wherein an applied current or an applied voltage is set to be small with respect to a transfer condition to the intermediate transfer member (2). 4. The two-sided image forming apparatus according to claim 1, wherein the final transfer efficiency of the first image (T1) and the second image (T2) to both sides of the recording material (3) is substantially the same. A double-sided image forming apparatus, wherein transfer conditions of each transfer means (4, 5 or 6 to 8) are set as follows.