JP2000056521A - Double-sided image forming method and its device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance productivity by quickly achieving double-sided image formation. SOLUTION: A first transfer belt 8 is placed opposite to photoconductor drums 6 (Y, M, C) and a second transfer belt 24 is placed downstream from the first transfer belt 8. After a first image on the photoconductor drums 6 has been transferred onto the first transfer belt 8, the second transfer belt 24 is brought into contact with the first transfer belt 8 to transfer the first image onto the second transfer belt 24. The belts are brought out of contact and the first image is held on the second transfer belt 24. Transfer paper is fed onto the first transfer belt 8 and a second image on the photoconductor drums 6 is transferred onto its surface. The transfer paper is passed with its back in contact with the top of the second transfer belt 24 to transfer the first image on the second transfer belt 24 onto the back of the transfer paper.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double-sided image forming method for forming images on the front and back surfaces of transfer paper, and a double-sided image forming apparatus applicable to an electrostatic copying machine, a laser printer, and the like.

[0002]

2. Description of the Related Art JP-A-63-180969 discloses that
An image forming unit having a photoreceptor drum is arranged around a transfer belt (transfer and transfer belt) so that an image on one side of an image to be double-sided copied becomes a mirror image when transferred onto the transfer belt. Formed on the photoreceptor drum, the image on the photoreceptor drum is transferred onto a transfer belt, transfer paper is superimposed on the transfer image, and the image on the other side of the image to be double-sided copied is It is formed on a photosensitive drum as a normal transfer type image, and at the same time as this image is transferred to a transfer paper on a transfer belt, a double-sided copy is created by transferring the image on the transfer belt to the back of the transfer paper. An embodiment of a double-sided copy creation method and an apparatus (full color image forming apparatus) using the method is disclosed. The transfer belt is wound around a pair of rollers arranged at intervals in the transfer direction of the transfer paper, that is, an upstream roller and a downstream roller.

[0003]

However, the above-mentioned conventional method and apparatus for making a double-sided copy have the following problems. (1) The image to be transferred onto the back side of the transfer paper, which has been transferred onto the transfer belt, moves upward on the downstream side in accordance with the rotation of the transfer belt, winds a roller on the downstream side, and then moves on the downstream side in the upstream direction. After moving to the upper upstream end by winding the upstream roller, the leading end position of the transfer roller will be adjusted to the position of the leading end of the transfer paper fed from the paper feed unit in a timely manner. Transported to As described above, the transfer paper cannot be fed until the leading end of the image to be transferred to the back surface of the transfer paper, which has been transferred onto the transfer belt, moves to the vicinity of the upper upstream end of the transfer belt. The time loss is large, so that it is not possible to quickly perform double-sided image formation, resulting in low productivity. This problem increases as the distance between the roller on the upstream side and the roller on the downstream side of the transfer belt increases. Therefore, it is difficult to apply this problem particularly to a full-color image forming apparatus using four image carriers. (2) When the above-described invention is applied to a full-color image forming apparatus, a color image is formed by sequentially stacking color toners on a transfer belt and then transferred to the back surface of the transfer paper. Are stacked, the color of the image is different on the front and back of the transfer paper, and the image of the same color on the front and back of the transfer paper may not be obtained. (3) Since the distance that the unfixed toner moves on both sides of the transfer paper, that is, the time required to move the transfer paper, is relatively long, there is a possibility that the image may be distorted during the conveyance to the fixing device.

The present invention has been made based on the above-mentioned facts, and an object of the present invention is to provide a novel double-sided image forming method and apparatus capable of rapidly performing double-sided image formation and thus having high productivity. That is.

Another object of the present invention is to provide a new color image forming apparatus which can obtain an image of the same color on the front and back of the transfer paper without any difference in the color of the image on the front and back of the transfer paper. To provide a double-sided image forming method and apparatus.

Still another object of the present invention is to reduce the distance traveled in a state where unfixed toner is present on both sides of the transfer paper, and hence the time, so as to prevent image collapse at the time of conveyance to the fixing device. And a novel double-sided image forming method and apparatus.

Other objects and features of the present invention will become apparent from the following description of embodiments of a double-sided image forming method and apparatus constructed in accordance with the present invention with reference to the accompanying drawings.

[0008]

According to one aspect of the present invention, a first transfer belt is provided so as to face an image carrier, and a second transfer belt is provided downstream of the first transfer belt. After transferring the first image formed on the image carrier to the rotating first transfer belt, the first transfer belt is rotated while the second transfer belt is rotated. The first image on the first transfer belt is transferred onto the second transfer belt by contacting the second transfer belt, and then the contact of the second transfer belt is released and the rotation is stopped to stop the first transfer belt. After holding the first image on the second transfer belt and feeding the transfer paper onto the first transfer belt to transfer the second image formed on the image carrier to the surface thereof The sheet is carried out toward the second transfer belt, and then the second transfer belt is synchronized with the movement of the transfer paper. By rotating the transfer paper in the reverse direction, the transfer paper conveyed from the first transfer belt is moved while the back surface thereof is aligned with and contacts the first image on the second transfer belt. At least transferring the first image held on the second transfer belt to the back surface of the transfer paper.

According to another aspect of the present invention, a first transfer belt is provided so as to face the image carrier, and a second transfer belt is provided downstream of the first transfer belt. After transferring the first image formed on the image carrier to the rotating first transfer belt, the second transfer belt is rotated and brought into contact with the first transfer belt while being rotated. Transferring the first image on the first transfer belt onto the second transfer belt, then releasing the contact of the second transfer belt and stopping the rotation, and After the first image is held, a transfer paper is fed onto the first transfer belt to transfer the second image formed on the image carrier to the surface thereof, and then the second transfer is performed. The second transfer belt is rotated backward in time with the movement of the transfer paper. With this, the transfer paper conveyed from the first transfer belt is moved while aligning and contacting the back surface of the transfer paper with the first image on the second transfer belt, and is then transferred to the fixing device. In the fixing device, the second image transferred to the surface of the transfer paper is fixed on the surface of the transfer paper, and the first image held on the second transfer belt is transferred to the transfer paper. A double-sided image forming method, wherein the image is fixed on the back surface of the sheet simultaneously with the transfer.

According to still another aspect of the present invention, there is provided a first transfer belt having an upper surface extending along a transfer path of a transfer sheet, wherein the first transfer belt has the upper surface opposed to the image carrier. A first image to be transferred to the back surface of the transfer paper formed on the image carrier, on the upper surface of the first transfer belt, and a front surface of the transfer paper formed on the image carrier A first transfer unit for transferring a second image to be transferred to the surface of the transfer paper fed onto the first transfer belt, and a first transfer unit downstream of the first transfer belt. A second transfer belt having an upper surface positioned as a part of the transport path so that a back surface of the transfer paper disposed and unloaded from the first transfer belt can move while contacting; A driving unit for rotating the second transfer belt forward and backward, and connecting the second transfer belt to the first transfer belt. Moving means for selectively positioning the contact position and the non-contact position to be moved, and the second transfer belt positioned at the contact position in a forwardly rotated state on the first transfer belt. A second transfer unit for transferring the transferred first image; and a second transfer unit in which the back surface of the transfer paper on which the second image is transferred on the front surface is positioned at the non-contact position and rotated in the reverse direction. To transfer the first image to the back side of the transfer paper when the upper surface of the transfer belt is aligned with the first image transferred to the second transfer belt and moved while being in contact therewith. And a third transfer means.

In the present invention, the first image to be transferred onto the back side of the transfer paper, which has been transferred onto the first transfer belt, is transferred to the second transfer belt disposed downstream of the first transfer belt. Since the image is once transferred onto the belt, the transfer of the transfer paper to the first transfer belt can be started immediately before or during the transfer of the first image onto the second transfer belt. As a result, the time loss is greatly reduced, and the productivity is improved. Further, when the present invention is applied to a full-color copying machine, the first image to be transferred to the back side of the transfer paper is, for example, cyan, magenta, yellow, and black toners of respective colors are stacked on the first transfer belt in this order. When the first image is transferred onto the second transfer belt, the stacking order is reversed. However, when the first image transferred on the second transfer belt is transferred to the back surface of the transfer paper, the first image is stacked again and returned to the original stacking order. As a result, an image having the same color can be obtained on the front and back of the transfer paper without any difference in the color of the image on the front and back of the transfer paper, so that an excellent color image is guaranteed. Still further, the transfer with the unfixed toner present on both sides of the transfer sheet is performed at least after the transfer sheet reaches the upper surface of the second transfer belt, and therefore, the transfer sheet relatively moves between the transfer sheet and the fixing device. Since it is only for a short distance (relatively short time), it is possible to reliably prevent image collapse during transport until reaching the fixing device.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a so-called tandem digital full-color printer will be described in more detail with reference to FIGS. In FIGS. 1 and 2, substantially the same parts are indicated by the same reference numerals.

Referring first to FIG. 1, four image forming units 4C, 4M, 4Y and 4 for cyan, magenta, yellow and black are provided in a main body 2 of a full-color printer.
B are arranged in a line along the transfer path of the transfer paper extending substantially horizontally. Image forming units 4C, 4M, 4Y
And 4B are provided with corresponding photosensitive drums 6C, 6M, 6Y and 6B as image carriers. An endless first transfer belt 8 is disposed below the photosensitive drums 6C, 6M, 6Y, and 6B so as to face them. The first transfer belt 8 has an upper surface extending along a transfer path of the transfer paper.
C, 6M, 6Y and 6B. The first transfer belt 8 is wound around an upstream roller 10 arranged on the upstream side of the transfer path of the transfer paper and a downstream roller 12 arranged at a downstream distance from the upstream roller 10. ing. The downstream roller 12 is composed of a driving roller driven by an electric motor (not shown), and the upstream roller 10 is composed of a driven roller. The first transfer belt 8 is formed of a dielectric material such as ETFE (ethylene tetrafluoroethylene copolymer). In connection with the first transfer belt 8, a not-shown charging device, a cleaner, and the like, which are not shown, are provided. First transfer belt 8
Above the photosensitive drums 6C, 6M, 6Y, and 6B, image forming elements such as a main charger, a developing unit, and a cleaner are disposed. On the lower side of the photosensitive drums 6C, 6M, 6Y, and 6B across the upper moving portion of the first transfer belt 8, transfer chargers 14C, 14M, 14Y, which are transfer corona dischargers, are provided, respectively. 14B is provided. Transfer charger 14C, 14
M, 14Y and 14B constitute a first transfer unit.

Image forming units 4C, 4M, 4Y and 4
Above B, an image exposure unit 16 is provided. The main body 2 of the full-color printer is connected to an external device such as a microcomputer, for example. Then, the image data input from the external device is decomposed into color image data representing the densities of the respective color components of cyan, magenta, yellow and black.
6 given. The image exposure section 16 outputs a laser beam corresponding to image data given from a laser light source. The laser beams output in accordance with the image data are respectively passed through photoreceptor drums 6C, 6M,
Irradiation is performed on the surfaces of 6Y and 6B, and exposure corresponding to each color is performed.

The first transfer belt 8 in the transfer path of the transfer paper
On the more upstream side, the paper feed tray 18, the paper feed roller 20,
The registration roller pairs 22 are arranged in the above order toward the downstream. A second transfer belt 24, a fixing device 27 including an upper fixing roller 25 and a lower fixing roller 26, and a discharge roller pair 28 are provided downstream of the first transfer belt 8 in the transfer path of the transfer paper. Are arranged downstream in the above order. The upper fixing roller 25 and the lower fixing roller 26, which are disposed so as to be in pressure contact with each other, are each composed of a heating roller, and a heater composed of, for example, a halogen lamp is disposed inside each. The second transfer belt 24 is wound around an upper roller 30 and a lower roller 32 which are spaced apart in the vertical direction. The second transfer belt 24 is formed of a material having a dielectric property such as ETFE, for example. The upper roller 30 and the lower roller 32 are rotatably supported via frames 30a and 32a, respectively, between frame members 34 arranged at an interval in the front-rear direction (front and back directions in FIG. 1). I have. The shaft 30a and the shaft 32a are fixed to the upper roller 30 and the lower roller 32 so that they can rotate integrally therewith. Although not shown, the shaft 32a of the lower roller 32 is rotatably supported on the main body 2 via a bearing, and is an electric motor serving as a driving unit for rotating the second transfer belt 24 forward and backward. It is connected to the motor M.
Thereby, the lower roller 32 constitutes a driving roller,
The upper roller 30 constitutes a driven roller. The upper roller 30 is a roller 12 on the downstream side of the first transfer belt 8.
And a fixing device 27, and has an upper surface positioned as a part of a transfer path of the transfer sheet. This upper surface is defined by a part of an arc-shaped surface wound around the upper roller 30.

Between the frame 34 and the main body 2, the second transfer belt 24 is selected between a contact position where the second transfer belt 24 contacts the first transfer belt 8 and a non-contact position where the second transfer belt 24 does not contact the first transfer belt 8. Solenoid 36 which is a moving means for positioning
Are arranged. Between the frame 34 and the main body 2,
A tension coil spring 38 for returning the second transfer belt 24 to the non-contact position is provided, and biases the frame body 34 to rotate counterclockwise around the axis 32a. The counterclockwise rotation of the frame body 34 is disposed on the main body 2 and regulated by a stopper 39. When the frame body 34 is rotated clockwise in FIG. 1 by the urging of the solenoid 36 and positioned at the contact position, a part of the arc-shaped surface of the second transfer belt 24 wound around the upper roller 30 But,
The first transfer belt 8 is brought into contact (pressure contact) with a part of the arc-shaped surface of the first transfer belt 8 wound around the roller 12 on the downstream side of the first transfer belt 8. By deenergizing the solenoid 36,
The frame body 34 is turned counterclockwise in FIG. 1 by the tension coil spring 38 and is positioned at the non-contact position.

The upper roller 30 is connected to a positive voltage power supply, and is configured to apply a positive voltage. This electrical connection 40 constitutes the second transfer means. Above the upper roller 30, a transfer charger 42 composed of a transfer corona discharger is disposed at a distance from the upper roller 30. The transfer charger 42 constitutes a third transfer unit.

When the printer operation for forming images on both sides of the transfer paper is started, the image forming units 4C, 4M, 4M
The Y and 4B photosensitive drums 6C, 6M, 6Y and 6B are rotated, and the first transfer belt 8 is rotated in the counterclockwise direction in FIG. In the image exposure section 16, laser beams corresponding to image data input from an external device are applied to the photosensitive drums 6C and 6C.
M, 6Y and 6B are irradiated, and the toner image of each color component is
The first image to be transferred to the back surface of the transfer paper is formed at a predetermined timing. Photoconductor drums 6C, 6M, 6
The toner images of the respective colors formed on Y and 6B are transferred to the transfer chargers 14C, 14M, as the first transfer belt 8 rotates.
By 14Y and 14B, the image is transferred to the same position on the first transfer belt 8 in the form of being stacked in the order of cyan, magenta, yellow and black. In this embodiment, each color toner image is charged to a negative electrode,
A positive high voltage is applied to each of the transfer chargers 14C, 14M, 14Y and 14B.

The second transfer belt 24 is rotated at a predetermined timing by the rotation of the electric motor M. Then, by urging the solenoid 36, the second transfer belt 24 is rotated clockwise about the shaft 32a, and is positioned at the contact position as described above.
When the second transfer belt 24 is positioned at the contact position,
The second transfer belt 24 is brought into contact with the first transfer belt 8 at the position of the roller 30 above the second transfer belt 24 and the roller 12 downstream of the first transfer belt 8. At this contact portion, the peripheral speed of the second transfer belt 24 is specified to be the same as the peripheral speed of the first transfer belt 8.
When the first image transferred to the first transfer belt 8 reaches the contact portion with the second transfer belt 24, a positive voltage is applied to the roller 30 on the upper side of the second transfer belt 24. The first image composed of the negatively charged toner image is transferred onto the second transfer belt 24. Note that the timing at which the second transfer belt 24 is brought into contact with the first transfer belt 8 is at least before the leading end of the first image transferred onto the first transfer belt 8 passes through the contact portion. Is controlled. When the length of the first image (the length in the moving direction of the first transfer belt 8) is relatively long, the leading end of the first image is moved from the first transfer belt to the second transfer belt 24. During the transfer, the rear end of the first image may be transferred onto the first transfer belt by the transfer charger 14B (black toner image).

After the first image is completely transferred from the first transfer belt 8 to the second transfer belt 24, the solenoid 3
6 is deenergized, the second transfer belt 24 moves to the shaft 32a.
Is rotated in the counterclockwise direction, and is positioned at the non-contact position as described above. At the same time, the electric motor M
Is stopped, and the rotation of the second transfer belt 24 is stopped. The first image transferred onto the second transfer belt 24 is held as it is. The transfer paper stored in the paper feed cassette 18 is fed to the registration roller pair 22 by the paper feed roller 20 at a predetermined timing.
The timing at which the transfer paper starts to be fed by the paper feed roller 20 may be the time when the first image is completely transferred to the first transfer belt 8. This transfer paper is a pair of registration rollers 22
Is transferred onto the first transfer belt 8 and is conveyed by the first transfer belt 8. On the other hand, the photosensitive drums 6C, 6
At M, 6Y, and 6B, a toner image of each color component is formed at a predetermined timing as a second image to be transferred onto the surface of the transfer paper. The toner images of the respective colors formed on the photosensitive drums 6C, 6M, 6Y and 6B are transferred to the transfer chargers 14C, 14M and 14Y as the first transfer belt 8 rotates.
And 14B, the image is transferred to the same position on the surface of the transfer paper on the first transfer belt 8 in the form of being stacked in the order of cyan, magenta, yellow and black.
The transfer paper on which the second image has been transferred to the surface is discharged from the first transfer belt 8 to the downstream side of the transport path.

The second transfer belt 24 at the non-contact position is moved by the electric motor M in time with the movement of the transfer paper.
Is rotated in the counterclockwise direction, which is the opposite direction. The back surface of the transfer paper carried out from the first transfer belt 8 is the upper surface positioned as a part of the transfer path of the transfer paper.
It passes over a part (upper part) of the arc-shaped surface wound around the upper roller 30 of the second transfer belt 24 while being aligned with and in contact with the first image on the second transfer belt 24. I do. The leading end of the first image transferred and held on the second transfer belt 24 is moved to a predetermined position on the leading end of the back surface of the transfer paper. At the same time or slightly before, a high positive voltage is applied to the transfer charger 42 located above the roller 30 above the second transfer belt 24, and the first image on the second transfer belt 24 is It is transferred to the back of the transfer paper. The transfer paper on which the second image has been transferred on the front surface and the first image has been transferred on the back surface is conveyed to a fixing device 27, and passes between the upper fixing roller 25 and the lower fixing roller 26 to form a double-sided image. Is fixed on the transfer paper, and is discharged onto a discharge tray (not shown) by the discharge roller pair 28. The above cycle is repeated, and a color image is printed on both sides of a predetermined number of transfer sheets.

When an image is formed only on one side (front side) of the transfer paper by the full-color printer shown in FIG. 1, the color image is formed on the surface of the transfer paper fed onto the first transfer belt 8 as described above. Transcribe The transfer paper on which the color image has been transferred on the surface is carried out from the first transfer belt 8,
After passing over the upper surface of the second transfer belt 24 and being fixed by the fixing device 27, the sheet is discharged onto a discharge tray (not shown) by a pair of discharge rollers 28. Immediately before the transfer paper conveyed from the first transfer belt 8 passes over the upper surface of the second transfer belt 24, the second transfer belt 24 is counterclockwise driven by the electric motor M while being positioned at the non-contact position. It is turned in the direction. As a result, the transfer paper is smoothly passed and transported. At this time, the application of the voltage to the transfer charger 42 is stopped. Since a positive voltage is applied to the upper roller 30 of the second transfer belt 24, when the transfer paper passes, the toner image transferred to the surface of the transfer paper is prevented from being disturbed.

In the full-color printer shown in FIG. 1, when the first image to be transferred on the back surface of the transfer paper is completely transferred to the first transfer belt 8, that is, the most downstream of each of the photosensitive drums When the black toner image on the photosensitive drum 6B at the position is stacked and transferred on the toner image already transferred on the first transfer belt 8,
Immediately, the feeding of the transfer paper by the paper feed roller 20 can be started. As a result, the time loss is greatly reduced as compared with the above-described conventional technology, and the productivity is improved. The first image to be transferred to the back surface of the transfer paper is such that toners of respective colors are stacked and transferred on the first transfer belt 8 in the order of cyan, magenta, yellow, and black. When the image is transferred onto the second transfer belt 24, the order of stacking is reversed in the order of black, yellow, magenta, and cyan. However, when the first image transferred on the second transfer belt 24 is transferred to the transfer paper on the back surface, the first image is re-inverted and returned to the original stacking order. As a result, an image having the same color can be obtained on the front and back of the transfer paper without any difference in the color of the image on the front and back of the transfer paper, so that an excellent color image with no difference in gloss is guaranteed. Furthermore, the movement with the unfixed toner present on both sides of the transfer paper is caused by the relatively short distance between the top of the roller 30 above the second transfer belt 24 and the fixing device 27, and therefore, Since the time is relatively short, it is possible to reliably prevent image collapse during transport until reaching the fixing device 27.

FIG. 2 shows another embodiment in which the present invention is applied to a full-color printer. The difference between the full-color printer shown in FIG. 2 and the full-color printer shown in FIG. 1 is that a part of the second transfer belt 24 is wound around the lower fixing roller 26. The transfer of the first image transferred to the belt 24 to transfer paper is to be performed simultaneously with fixing. Since other configurations and operations are substantially the same, only the differences will be mainly described.

The second transfer belt 24 is wound around the first fixing roller 26 on the lower side, the second roller 50 and the third roller 52. In this embodiment, as described later, the toner image on the second transfer belt 24 is melted between the upper fixing roller 25 and the lower fixing roller 26, so that the toner image is simultaneously transferred to the rear surface of the transfer paper. Since the image is fixed, the second transfer belt 2
It is necessary that the surface of No. 4 has a small degree of toner adhesion (has good releasability). Therefore, the second transfer belt 24 is preferably formed of a material having dielectric properties, for example, a polyimide belt whose surface is coated with Teflon (trade name). The second roller 50 includes the lower fixing roller 26 and the first transfer belt 8.
The third roller 52 is disposed below each of the lower fixing roller 26 and the second roller 50. Lower fixing roller 2
6, the second roller 50 and the third roller 52 are provided with a frame 5 arranged at an interval in the front-rear direction (the front and back direction in FIG. 2).
Between them, they are rotatably supported via shafts 26a, 50a and 52a, respectively. The shafts 26a, 50a and 52a are fixed to the corresponding lower fixing roller 26, the second roller 50 and the third roller 52 so as to be able to rotate integrally therewith. Although not shown, the shaft 26a of the lower fixing roller 26 is rotatably supported by the main body 2 via a bearing, and is a driving unit for rotating the second transfer belt 24 forward and backward. It is connected to the electric motor M. Therefore, the lower fixing roller 26 constitutes a driving roller, and the second roller 50 and the third roller 52 constitute driven rollers. The third roller 52 is
The second transfer belt 24 functions as a tension roller. That is, the shaft 52 of the third roller 52
a is movably supported by long holes formed in each of the frame members 54, and applies tension to the second transfer belt 24 by a compression coil spring 56 provided between each of the frame members 54 and the shaft 52a. Biased in the direction.

The upper surface of the second transfer belt 24, which is positioned as a part of the conveyance path, has at least a part of the surface wound around the lower fixing roller 26, and the lower fixing roller 26 and the second fixing roller 26. It is defined by a part of the surface extending between the rollers 50. The configuration in which the second transfer belt 24 is selectively positioned at the contact position and the non-contact position by the solenoid 36 is basically the same as that of the previous embodiment. The center is
It is defined on the shaft 26 a of the lower fixing roller 26. When the second transfer belt 14 is positioned at the contact position by the solenoid 36, a part of the surface of the second transfer belt 24 wound around the second roller 50 is located on the downstream side of the first transfer belt 8. The first transfer belt 8 wound around the roller 12 is brought into contact with a part of the surface. In this embodiment, the transfer charger 42 serving as the third transfer unit is not provided, and as will be apparent from the following description, the third transfer unit is provided with the lower fixing roller. 26 and the upper fixing roller 25.

When the printer operation for forming an image on both sides of the transfer paper is started, a first image is formed on the first transfer belt 8 in the same manner as in the previous embodiment, and the first image is formed. Is transferred and held on the second transfer belt 24. Then, the transfer paper having the second image transferred to the front surface is carried out from the first transfer belt 8, and the back surface thereof is on the upper surface of the second transfer belt 24, and the first image of the second transfer belt 24. And passed with contact.
The leading end of the first image transferred and held on the second transfer belt 24 is moved to a predetermined position on the leading end of the back surface of the transfer paper. The transfer paper having the second image transferred to the front surface is conveyed to the fixing device 27 in a state where the first image transferred onto the second transfer belt 24 is aligned with the back surface thereof, and the upper fixing roller 25 and the lower fixing roller 26. As a result, the second image transferred to the front surface of the transfer paper is fixed on the front surface of the transfer paper, and the first image on the second transfer belt 24 is transferred to the rear surface of the transfer paper and fixed at the same time. . The transfer paper having the images fixed on both sides is discharged by a discharge roller pair 28 onto a discharge tray (not shown). The above cycle is repeated, and a color image is printed on both sides of a predetermined number of transfer sheets.

The basic structure of the full-color printer shown in FIG. 2 is substantially the same as that of the full-color printer shown in FIG. 1, so that substantially the same operation and effect as described above can be obtained. The full-color printer shown in FIG. 2 is different from the full-color printer shown in FIG.
It has the advantage of not having to use.

As described above, the present invention has been described in detail based on the embodiments with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments, and furthermore, does not depart from the scope of the present invention. Various other variations or modifications are possible. For example, although the present invention has been described with reference to an embodiment in which the present invention is applied to a so-called tandem digital full-color printer, the present invention is not limited to this embodiment, but may be an analog full-color printer, a digital or analog full-color printer. The present invention can be applied to a full-color image forming apparatus such as a copying machine, a mono-color image forming apparatus that forms only a single-color image, and the like. Needless to say, the present invention can be applied to an image forming apparatus having one or more image carriers.

[0030]

According to the double-sided image forming method and apparatus of the present invention, double-sided image formation can be rapidly performed.
Therefore, productivity can be improved. Further, it is possible to reduce the distance that the unfixed toner moves on both sides of the transfer sheet, that is, the time required to move the transfer sheet, and to prevent the image from collapsing at the time of transport to reach the fixing device. When the present invention is applied to a full-color image forming apparatus, an image having the same color can be obtained on the front and back of the transfer paper without any difference in the color of the image on the front and back of the transfer paper.

[Brief description of the drawings]

FIG. 1 is a side view schematically showing a configuration of an embodiment of a two-sided image forming apparatus configured according to the present invention.

FIG. 2 is a side view schematically showing a configuration of another embodiment of a double-sided image forming apparatus configured according to the present invention.

[Explanation of symbols]

6C, 6M, 6Y, 6B Photoconductor drum (image carrier) 8 First transfer belt 10 Upstream roller 12 Downstream roller 14C, 14M, 14Y, 14B Transfer charger (first transfer unit) 24 Second Transfer belt 25 upper fixing roller 26 lower fixing roller (first roller) 27 fixing device 30 upper roller 32 lower roller 32a shaft 36 solenoid 40 second transfer means 42 transfer charger (third) Transfer means) 50 second roller 52 third roller M electric motor

Claims (6)

[Claims] A first transfer belt disposed opposite to the image carrier, a second transfer belt disposed downstream of the first transfer belt, and the first transfer belt rotating; After the first image formed on the image carrier is transferred to the belt, the second transfer belt is brought into contact with the first transfer belt while rotating, so that the second transfer belt is brought into contact with the first transfer belt. Transferring one image onto the second transfer belt, then releasing the contact of the second transfer belt and stopping the rotation to hold the first image on the second transfer belt Then, a transfer paper is fed onto the first transfer belt to transfer the second image formed on the image carrier to the surface thereof, and then is carried out toward the second transfer belt, and then By rotating the second transfer belt in reverse in synchronization with the movement of the transfer paper, the first transfer belt is rotated. The transfer paper conveyed out of the transfer belt is held on the second transfer belt so that the back surface of the transfer paper moves while aligning and contacting the first image on the second transfer belt. Transferring the first image to the back side of the transfer paper. 2. A method according to claim 1, wherein a first transfer belt is provided so as to face the image carrier, a second transfer belt is provided downstream of the first transfer belt, and the first transfer belt is rotated. After the first image formed on the image carrier is transferred to the belt, the second transfer belt is brought into contact with the first transfer belt while rotating, so that the second transfer belt is brought into contact with the first transfer belt. Transferring one image onto the second transfer belt, then releasing the contact of the second transfer belt and stopping the rotation to hold the first image on the second transfer belt Then, a transfer paper is fed onto the first transfer belt to transfer the second image formed on the image carrier to the surface thereof, and then is carried out toward the second transfer belt, and then By rotating the second transfer belt in reverse in synchronization with the movement of the transfer paper, the first transfer belt is rotated. The transfer paper conveyed out of the copying belt is conveyed to a fixing device such that the back surface moves while aligning and contacting the first image on the second transfer belt, and is conveyed to a fixing device. The second image transferred to the front surface of the transfer paper is fixed to the front surface of the transfer paper, and the first image held on the second transfer belt is fixed to the back surface of the transfer paper at the same time as the transfer. And a double-sided image forming method. 3. A first transfer belt having an upper surface extending along a transfer path of a transfer sheet and having the upper surface disposed to face the image carrier, and a first transfer belt formed on the image carrier. A first image to be transferred to the back surface of the transfer paper on the upper surface of the first transfer belt, and a second image to be transferred to the front surface of the transfer paper formed on the image carrier. First transfer means for transferring to the surface of the transfer paper fed on the first transfer belt, respectively, and the first transfer means disposed downstream of the first transfer belt and A second transfer belt having an upper surface positioned as a part of the transport path so that the back surface of the transfer paper discharged from the belt can move while contacting, and rotating the second transfer belt forward and backward Driving means for moving the second transfer belt between a contact position and a non-contact position where the second transfer belt contacts the first transfer belt. Moving means for selectively positioning, and transferring the first image transferred onto the first transfer belt onto the second transfer belt positioned at the contact position in a state of being rotated forward. A second transfer means for performing
The back surface of the transfer paper on which the second image has been transferred is positioned at the non-contact position, and the upper surface of the second transfer belt, which is rotated in the reverse direction, is the first transfer image transferred to the second transfer belt. And a third transfer means for transferring the first image to the back surface of the transfer paper when the first image is moved while being aligned with and in contact with the image. Forming equipment. 4. A fixing device comprising a pair of fixing rollers, wherein the first transfer belt has an upstream roller and a downstream roller which are arranged at an interval between an upstream side and a downstream side of the transport path. And the second transfer belt is wound between an upper roller and a lower roller which are vertically spaced apart from each other, and the upper roller is the first transfer belt. The upper surface of the second transfer belt, which is disposed between the downstream roller and the fixing device and is positioned as a part of the transport path, is one of the surfaces wound around the upper roller. And the second transfer belt is further rotated by the moving means between the contact position and the non-contact position about the axis of the lower roller of the second transfer belt. Is configured to be
When the second transfer belt is positioned at the contact position by the moving unit, a part of the surface of the second transfer belt wound around the upper roller is moved to the downstream side of the first transfer belt. 4. The double-sided image forming apparatus according to claim 3, wherein a part of the surface of the first transfer belt wound around the first roller is brought into contact with the first transfer belt. 5. A fixing device comprising an upper fixing roller and a lower fixing roller, wherein the first transfer belt is provided at an interval between an upstream side and a downstream side of the transport path. The second transfer belt is wound around a first roller, a second roller, and a third roller, and the first roller is wound around the lower roller. Wherein the second roller is disposed between the lower fixing roller and the downstream roller of the first transfer belt, and the third roller is disposed on the lower fixing roller. A lower surface of the second transfer belt that is positioned below each of the roller and the second roller and that is positioned as part of the transport path and that is wound around at least the lower fixing roller. And a portion extending between the lower fixing roller and the second roller. The second transfer belt is further rotated by the moving means about the axis of the lower fixing roller between the contact position and the non-contact position. When the second transfer belt is positioned at the contact position by the moving means, a part of the surface of the second transfer belt wound around the second roller is moved to the first transfer belt. 4. The double-sided image forming apparatus according to claim 3, wherein the transfer belt is brought into contact with a part of the surface of the first transfer belt wound around the downstream roller of the transfer belt. 6. The third transfer means is defined by the upper fixing roller and the lower fixing roller, and the transfer paper having a second image transferred to a surface thereof is connected to the upper fixing roller and the lower fixing roller. The second image transferred to the surface of the transfer paper is fixed to the surface of the transfer paper when passing between the transfer roller and the fixing roller,
6. The double-sided image forming apparatus according to claim 5, wherein the first image on the second transfer belt, which is moved while being aligned with the back surface of the transfer paper, is fixed on the back surface of the transfer paper simultaneously with the transfer.