JP2002062744A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out transferring of an image to both sides of paper, without making the constitution or the control of a transfer complicated and to prevent disturbances in a transferred image on the paper. SOLUTION: In the apparatus, a first side image is transferred from a photoreceptor 1 to an intermediate transfer belt 10 (A). A second side image is formed on the photoreceptor 1 and charging polarity of the first side image is reversed by a charging charger 17, while being carried by a belt 10 (B). The first side image and the second side image are simultaneously transferred to a paper by a transfer roll 21 (C), and images on both sides are fixed by fixing means 18 and 30 on a belt 10 (D).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image forming apparatus capable of forming an image on both sides of a recording medium.

[0002]

2. Description of the Related Art Some image forming apparatuses such as copiers, printers, and facsimile machines are configured so that images can be formed on both sides of a recording medium (hereinafter referred to as paper).
In a conventional image forming apparatus capable of recording on both sides, an image (a visible image) on one side formed on an image carrier is transferred and fixed on a sheet, and the sheet is reversed by a reversing path or the like and fed again. In general, a two-pass system in which an image (visible image) on the other side is transferred and fixed on the back side of the sheet is used.

In the case of double-sided recording by this method, there are many problems in securing the reliability of paper conveyance due to switching of the paper conveyance direction and paper curl due to fixing of a single-sided image.
In addition, there is a problem that image defects occur due to defective transfer to curled paper.

As a system for solving these problems, a one-pass system in which a toner image is transferred to both sides of a sheet using a first image carrier and a second image carrier, and then fixed once. Stuff has been proposed.

FIG. 7 is a schematic diagram showing a process in an example of a conventional one-sided double-sided transfer. In the development and primary transfer process (A), the toner image (−charge) formed on the photoconductor 1 (first image carrier) is transferred to the first transfer unit 21.
(+ Voltage application), the intermediate transfer belt 10 (second
Image carrier). In the secondary development (second surface development) step (a), a toner image (−charge) serving as the second surface is formed on the photoconductor 1, and the first surface image is transferred to the belt 1.
It is carried around 0 and goes around once. Further, paper is fed in time with these images.

In the secondary transfer step (c), the photosensitive member 1 is applied to the second surface of the sheet by the action of the first transfer means 21 (+ voltage application).
The upper toner image (-charge) is transferred. At this time, the paper is superimposed on the first surface toner image on the belt 10.
In the third transfer step (d), the second transfer means 22 is turned on.
(+ Voltage application), and the toner image on the first surface (−charge) on the belt 10 is transferred to the first surface of the sheet. Then, the sheet is transported to a fixing device (not shown), and the belt is cleaned.

As described above, in the example shown in FIG. 7, the transfer step is performed three times, and the last transfer is performed by charging the toner from the side on which the toner is transferred (the second side of the sheet) to the first on the belt 10. The surface toner image is transferred to paper. Therefore, due to the influence of the charge, problems such as disturbance of the toner image transferred to the second surface (the right side surface in the drawing) of which the upper surface is opened and electrostatic offset at the time of fixing due to charge-up of the transfer paper occur. .

In view of the above, there has been proposed a device in which an image can be transferred to both sides of a sheet by a transfer means disposed on the first side of the sheet. For example, Japanese Patent No. 2906538 (Japanese Unexamined Patent Application Publication No. Hei 3-253881) discloses a first type formed on a photoreceptor.
The image is transferred to the transfer belt by the first transfer means, and then the polarity of the second image formed on the photoreceptor is reversed on the photoreceptor before the transfer step, and if the polarities of the first image and the second image are different. It is disclosed that the first image and the second image are simultaneously transferred to both sides of a sheet by one transfer means.

Japanese Patent Application Laid-Open No. 2000-105513 discloses that the polarity of a first image and the polarity of a second image are made different by using two developing devices each containing a developer having a different polarity.
Further, it is disclosed that the first image and the second image are simultaneously transferred to both sides of a sheet by configuring the polarity of the transfer voltage to be switchable.

[0010]

FIG. 8 shows the structure of the above-mentioned Japanese Patent Laid-Open Publication No.
FIG. 3 is a schematic diagram illustrating a double-side transfer process in the apparatus described in Japanese Patent No. 253881. In the development and the primary transfer step (A), the toner image (-charge) formed on the photoreceptor 1 is formed.
Is transferred to the intermediate transfer belt 10 by the operation of the transfer unit 21 (+ voltage application). In the secondary development step (a),
The polarity of the toner image (−charge) formed on the photoconductor 1 is inverted (+ charged) by charging from the corona charger 6. Then, in the secondary transfer step (c), the voltage applied from the transfer means 21 is switched to the opposite polarity (-), and the first image and the second image are simultaneously transferred to both sides of the sheet. Thereafter, in the transport step (d), the sheet is transported to the fixing device, and the belt is cleaned.

The apparatus disclosed in Japanese Patent Application Laid-Open No. 2000-105513 has two developing devices each containing a developer having a different polarity. The polarity of the voltage applied to the transfer roller provided inside the loop of the belt is switchable. When transferring the first image (+ charge) from the photoconductor onto the intermediate transfer belt (primary transfer), a negative transfer voltage is applied to the transfer roller. Next, the transfer voltage applied to the transfer roller is switched to a positive polarity, and the first image (+ charge) is transferred to the first surface of the sheet, and at the same time, the second image (−charge) is transferred from the photoconductor to the second surface of the sheet. (Secondary transfer).

However, in the above publications, although the charging polarity of the toner image is made different, it is necessary to switch the polarity of the transfer voltage between the primary transfer and the secondary transfer. The significance of the control has diminished,
In addition, there is a problem that the configuration and control for switching the transfer voltage are complicated.

The present invention solves the above-mentioned problems in the conventional image forming apparatus, and transfers an image to both sides of a sheet without complicating the structure and control of the transfer. It is an object to provide an image forming apparatus that does not disturb.

[0014]

According to the present invention, a first image formed on an image carrier is transferred to an intermediate transfer member, and a second image is formed on the image carrier. And
In an image forming apparatus for simultaneously transferring the first and second images to both sides of a recording medium and transporting the recording medium to a fixing step by an intermediate transfer member, a first image formed on the image carrier is formed.
Is transferred to the intermediate transfer member, and then the first image is transferred onto the intermediate transfer member.
The first image and the second image are simultaneously transferred to both sides of a recording medium by reversing the charging polarity of the image.

Further, in order to solve the above-mentioned problem, the present invention proposes that the charging polarity of the first image is reversed to a reverse polarity by using a non-contact type charging means. Further, in order to solve the above-mentioned problem, the present invention provides an image forming method according to the present invention, wherein the second image position on the intermediate transfer member is normal with respect to the first image having the inverted charging polarity. It is proposed to form a second image and simultaneously transfer the first image and the second image to both sides of the recording medium.

In order to solve the above-mentioned problem, the present invention provides a method for simultaneously transferring an image to both sides of a recording medium, comprising: inverting a charge polarity of a first image on the intermediate transfer member; It is proposed that the first image and the second image are simultaneously transferred under the condition that the image is transferred from the image carrier to the recording medium.

Further, in order to solve the above-mentioned problem, the present invention provides a transfer means for applying a transfer electric field from a side of the intermediate transfer body opposite to a side carrying the first image, and the transfer means applies the first electric field. It is proposed to simultaneously transfer the image and the second image to both sides of the recording medium.

Further, in order to solve the above-mentioned problems, the present invention proposes that the transfer means is a transfer means for transferring a first image from the image carrier to an intermediate transfer body. Further, in order to solve the above-mentioned problem, the present invention proposes fixing images on both surfaces of the recording medium on the intermediate transfer body after the transfer of the first image and the second image to the recording medium is completed. I do.

According to another aspect of the present invention, an image formed on only one side of a recording medium is directly transferred to the recording medium, and the recording medium is transferred to the recording medium. It is proposed that the sheet be conveyed to the fixing step by the intermediate transfer member.

Further, in order to solve the above-mentioned problems, the present invention proposes fixing an image on a recording medium on the intermediate transfer member after the transfer of the image to the recording medium is completed. In order to solve the above-mentioned problem, the present invention provides an image forming apparatus, wherein the image carrier is an organic photoconductor, the image carrier is negatively charged, and a latent image obtained by exposing the image carrier to a negative developer. It is suggested that the reversal development be carried out.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional configuration diagram schematically illustrating a printer as an example of an image forming apparatus to which the present invention is applied.

In the printer shown in FIG. 1, a photosensitive drum 1 as a first image carrier is disposed substantially at the center of the apparatus. A cleaning device 2 is provided around the photosensitive drum 1.
A charge removing device 3, a charging device 4, and a developing device 5 are provided. An exposure device 7 is provided above the photoconductor drum 1, and a laser beam L emitted from the exposure device 7 is applied to the photoconductor 1 at a writing position between the charging device 4 and the developing device 5.

Below the photosensitive drum 1, a belt unit 20 is provided. The belt unit 20 is centered on the intermediate transfer belt 10 as a second image carrier,
The photoconductor 1 is provided so that a part thereof is in contact with the intermediate transfer belt 10. The intermediate transfer belt 10 has rollers 11,
It is stretched around 12, 13 and is supported so that it can run counterclockwise in the figure. The intermediate transfer belt 10 has heat resistance and has a resistance value that allows transfer of toner.

Inside the loop of the intermediate transfer belt 10,
Backing rollers 14, 15, cooling units 16, 16, fixing roller 18, transfer unit 21, and the like are provided. The fixing roller 18 has a built-in heat source such as a heater and fixes the toner image transferred onto the first surface of the sheet onto the sheet. The transfer unit 21 is provided at a position facing the photoconductor 1 with the belt 10 interposed therebetween, and transfers the toner image formed on the photoconductor 1 from the intermediate transfer belt 10 or from the intermediate transfer belt 10 to a sheet (the first surface of the sheet). And the toner image formed on the photoreceptor 1 is directly transferred onto a sheet (the second surface of the sheet).

A fixing device 30, a belt cleaning device 25, and a charging unit 17 are provided on the outer peripheral portion of the intermediate transfer belt 10.
Has been deployed. The charging means 17 is provided for the intermediate transfer belt 1.
This is for inverting the polarity of the toner transferred to 0.

The fixing device 30 has a fixing roller 19 having a built-in heat source such as a heater, and fixes the toner image transferred onto the second surface of the sheet onto the sheet. The fixing device 30 is rotatably supported about a fulcrum 30a. Then, the belt 10 is rotated by a mechanism (not shown) as indicated by an arrow G, and is configured to be able to press against and separate from the fixing roller 18 with the belt 10 (and paper) therebetween.

The cleaning device 25 for the intermediate transfer belt 10 has a cleaning roller 25a and a blade 2 inside.
5b, a toner conveying means 25c, etc., and has a function of wiping off unnecessary toner remaining on the surface of the intermediate transfer belt 10. The toner accumulated in the cleaning device 25 is
The toner is conveyed to a collection container (not shown) by the toner conveying unit 25c. The cleaning device 25 includes a rotation fulcrum 25d.
Is configured to be rotatable around an arrow H as shown by an arrow H.
By rotating the entire cleaning device 25 by a mechanism (not shown), the cleaning roller 25 a can be moved toward and away from the intermediate transfer belt 10.

In this embodiment, a photosensitive drum (first image carrier) 1, a cleaning device 2, a static eliminator 3, a charging device 4, a developing device 5 and the like are integrally incorporated into a unit to form a unit.
The process cartridge is configured so that it can be replaced at the end of its life.

A paper feed cassette 2 is provided at a lower portion of the apparatus main body.
6 are provided. The paper cassette 26 is configured to be able to be pulled out to the right in the drawing. Transfer paper P as a recording material is stored in the cassette 26. Cassette 26
A paper feed roller 27 is provided at an upper position on the front side (right side in the drawing) in the paper feed direction. A registration roller pair 28 is provided on the right side of the photosensitive drum 1. A guide member 29 for guiding a sheet from the sheet feeding roller 27 to the registration roller 28 is provided. Above the cassette 26, an electrical unit E1 and a control device E2 are arranged. On the right side of the apparatus, a manual paper feed device 35 is provided, and a paper feed roller 36 for sending out the paper P set on the paper setting table 37 is provided.

In FIG. 1, a switching claw 42 is provided on the left side of the belt unit 20. This switching claw 42
Is configured to be swingable about a fulcrum 43, and switches the conveyance direction of the sheet sent from the belt unit 20 to a sheet discharge stack section 40 provided on the upper surface of the apparatus main body or a sheet discharge tray 44 on the side of the apparatus. When the switching claw 42 is at the position shown in the figure, the sheet is sent to the sheet discharge stack unit 40, and when the switching claw 42 is switched in the direction of arrow J, the sheet is sent to the sheet discharge tray 44.

A transport roller pair 33 for transporting a sheet is disposed above the switching claw 42. Further, a paper discharge roller pair 34 for discharging the paper to the paper discharge stack unit 40 is disposed further above. Transport roller pair 33
And between the paper discharge roller pair 34 are guided by guide members 31a and 31b. On the other hand, a paper discharge roller pair 32 for discharging paper to the paper discharge tray 44 is disposed on the left side of the switching claw 42.

An image forming operation in the printer having the above-described configuration will be described. First, an operation for obtaining images on both sides of a sheet will be described. When images are obtained on both sides of a sheet, an image to be formed first is called a first side image, an image to be formed later is called a second side image, and a sheet side on which the first side image is transferred is a first side of the sheet. The sheet surface on which the second-side image is transferred is referred to as a sheet second side.

The image forming apparatus of this embodiment is a so-called printer, and a signal for writing is sent from a host machine (not shown), for example, a computer. The exposure device 7 is driven based on the received image signal, and light from a laser light source (not shown) of the exposure device is scanned by a polygon mirror 7a that is rotationally driven by a motor.
The light is irradiated onto the photosensitive drum 1 uniformly charged by the charging device 4 via the mirror 7b, the fθ lens 7c, etc., and a latent image corresponding to the written information is formed on the photosensitive member 1.

The electrostatic latent image on the photoreceptor 1 is developed by the developing device 5, and a visible image with toner is formed and held on the surface of the photoreceptor. The toner image on the photoreceptor 1 is transferred to the surface of the intermediate transfer belt 10 running in synchronization with the photoreceptor 1 by transfer means 21 on the back side of the intermediate transfer belt 10 as a second image carrier.

The surface of the photoreceptor 1 is cleaned of remaining toner by the cleaning device 2 and is discharged by the discharging device 3 to prepare for the next image forming cycle. Intermediate transfer belt 10
Carries the toner image transferred to the front surface (the image transferred to the first surface of the sheet) and runs counterclockwise in the figure. At this time, the fixing device 30 and the cleaning device 25 are controlled so as to keep the non-operating state (the interruption of the electric input or the separation from the intermediate transfer belt 10) so that the toner image is not disturbed.

When the intermediate transfer belt 10 travels to a predetermined position, a toner image to be transferred to another surface (second surface) of the sheet starts to be formed on the photosensitive member 1 in the above-described process, and is selected. Paper feeding is started from the fed paper feeding device (the cassette 26 or the manual feed tray 35). When the paper feed roller 27 or 36 rotates in the direction of the arrow, the paper P in the paper feed cassette 26 or at the top of the paper feed table 37 is pulled out, and is conveyed to the registration roller pair 28.

The intermediate transfer belt 10 travels in synchronization with the photosensitive member 1, and the toner image (first surface image) previously transferred onto the intermediate transfer belt 10 makes one turn to rotate the belt 10 and the photosensitive member 1.
Are conveyed toward the position where they contact. At this time, the polarity of the toner image carried on the belt 10 is reversed by the action of the charging means 17 provided before the roller 12.

The registration roller pair 28 ensures that the positions of the toner image (second-side image) on the sheet and the photoconductor 1 and the toner image (first-side image) on the belt 10 are regular.
The sheet is sent out at a proper timing by the pair of registration rollers 28. The sheet is sent to a transfer position where the photoconductor 1 and the belt 10 are in contact with each other, and the toner images (the first-side image and the second-side image) are simultaneously transferred onto both sides of the sheet by the transfer unit 21.

The sheet on which the toner images are transferred on both sides is sent to the fixing area by the running of the belt 10. Here, the fixing device 30 is rotated so that the fixing roller 19 is pressed against the fixing roller 18 with the belt 10 interposed therebetween.
Image on paper in cooperation with printer and fixing roller 18 (both sides)
Are fixed at once. After the transfer of the toner image, the sheet is fixed in a state where the sheet and the intermediate transfer belt 10 are overlapped without being separated from the intermediate transfer belt 10, so that the toner image is not disturbed and the occurrence of image blur is prevented.

The sheet after fixing is separated from the intermediate transfer belt 10 by a roller 11 at a curvature, and the conveying direction is switched by a branching claw 42. Is discharged.

When the paper is discharged to the paper discharge stack 40 on the upper surface of the apparatus, the second surface of the double-sided image, that is, the surface directly transferred from the photoreceptor to the paper, becomes the lower surface and the paper discharge stack 40 In order to align the pages, the image of the second page is created first, the toner image is held on the intermediate transfer belt 10, the image of the first page is created later, and the What is necessary is just to transfer directly from the surface of the body 1 to paper. Therefore, when the paper is discharged to the discharge stack unit 40 in the page order, the first-side image is the image of the second page, and the second-side image is the image of the first page. The same applies to the images on the third and subsequent pages. If there are images on even pages, the images on the even pages are formed first and transferred and held on the intermediate transfer belt 10,
An odd-numbered page immediately before the even-numbered page is created later, and is directly transferred from the surface of the photoconductor 1 to a sheet.

On the other hand, when the paper is discharged to the paper discharge tray 44 on the side of the apparatus, the second surface of the double-sided image, that is, the surface directly transferred from the photoconductor to the paper is the upper surface and is discharged to the paper discharge tray 44. Is placed. Therefore, in this case, the pages are not stacked in the page order. The user can specify whether to discharge the sheet to the discharge stack unit 40 or to discharge the sheet to the discharge tray 44.

However, it is also possible to stack sheets on the sheet discharge tray 44 in the order of pages. In this case, on the contrary, the first side image is set as the first page image and the second side image is set as the opposite side. 2
The image of the page. The same applies to the images of the third and subsequent pages. If an image is present on an odd page, the image of the odd page is formed first, transferred and held on the intermediate transfer belt 10, and the even page next to the odd page is formed. May be created later.

Normally, a reverse image (mirror image) is formed on the photoreceptor 1 and a normal image is obtained by directly transferring the image on a sheet. However, the image transferred on the intermediate transfer belt 10 is When the image is transferred onto the photoconductor 1, if it is formed into a mirror image on the photoconductor 1, the image becomes a mirror image when transferring the paper. Therefore, in the present embodiment, the image (first-side image) transferred from the intermediate transfer belt 10 to the sheet is formed as a normal image on the surface of the photoconductor 1, and
The toner image (second surface image) directly transferred from the photoconductor 1 to the paper is exposed so as to be a mirror image on the photoconductor surface.

The image forming order for page alignment as described above can be realized by a known technique for storing image data in a memory, and the exposure for switching between normal and reverse images can be realized by a known image processing technique.

After the image is transferred from the photosensitive member 1 and the intermediate transfer belt 10 to the sheet, the cleaning device 25 separated from the intermediate transfer belt 10
Cleaning device 25 so that 5a contacts belt 10
Is rotated to transfer the residual toner transferred to the sheet to the surface of the cleaning roller 25a, and scraped off by the blade 25b. The scraped toner is collected in a storage unit (not shown) by the toner conveying unit 25c.

The intermediate transfer belt 10 having passed through the cleaning area is cooled by the operation of the cooling means 16 and 17. Various heat radiation systems can be adopted as the cooling units 16 and 17. In the method of circulating air, the toner image held on the surface of the intermediate transfer belt 10 is not disturbed.
It is convenient to allow air to flow after transfer to a recording medium (paper). A cooling means using a heat pipe, which takes heat by directly contacting the inner surface of the loop of the intermediate transfer belt 10, can also be adopted.

Next, the operation for obtaining an image on one side of a sheet will be described. To get an image on one side of the paper,
The step of transferring the toner to the intermediate transfer belt 10 can be omitted, and the toner image formed on the surface of the photoconductor 1 is directly transferred to paper. In the case of a single-sided image, the toner image on the photoreceptor 1 is a mirror image, and becomes a normal image when transferred to a sheet.

In FIG. 1, the sheet P is sent between the photosensitive member 1 and the intermediate transfer belt 10 in synchronization with the toner image formed on the photosensitive member 1 so as to be aligned with the toner image.
1 transfers the toner from the photoreceptor 1 onto the paper.

The sheet on which the toner image has been transferred moves together with the intermediate transfer belt 10, and the toner is fixed. afterwards,
The sheet is separated from the intermediate transfer belt 10 and placed on the sheet discharge stack section 40 or the sheet discharge tray 44 according to the direction of the switching claw. When the paper is discharged to the paper discharge stack unit 40, even if the originals of several pages are processed in order from one page, when the paper is taken out from the paper discharge stack unit 40, the printed matter is in page order.

FIG. 2 is a schematic view conceptually showing an image forming process at the time of double-sided recording in the present embodiment. However, FIG. 2 shows a second embodiment in which the fixing device is arranged downstream of the intermediate transfer belt 10 (downstream in the sheet conveyance direction). Also, the intermediate transfer belt 10 is illustrated in a vertically arranged state in the space of the drawing.

In FIG. 2, the image forming process at the time of double-sided recording is shown in FIG.
Development and primary transfer (transfer to belt 10), (a) secondary development (second side development), (c) secondary transfer (double-side transfer to paper), (d) fixing, and belt cleaning They are shown separately. For convenience, in FIG. 2, the photoconductor 1 and the intermediate transfer belt 10 are illustrated as being separated from each other,
The photoconductor 1 and the intermediate transfer belt 10 are provided in contact with each other.

In FIG. 2A, the photosensitive member 1 is charged (-) by the charging means 4, and the developing device 5 (-) charges the electrostatic latent image formed by the writing light L from the exposure device.
A state is shown in which charged toner (indicated by black circles in the figure) is applied, and the toner is primarily transferred to the intermediate transfer belt 10 by the operation of the transfer unit 21 (+ voltage is applied).

In FIG. 2A, a toner image (-charge) on the second surface is formed on the photosensitive member 1 and the toner image (first surface image) carried on the intermediate transfer belt 10 is conveyed. During the conveyance, the polarity of the toner image carried on the belt 10 is inverted to the positive polarity by the charging of the charging means 17. Further, the sheet P is transferred to the registration roller 28 at a timing so that the position of the sheet P becomes regular.
Is transmitted.

In FIG. 2C, the operation of the transfer means 21 (+
By applying a voltage, the front and back sides of the paper (first side, second side)
3 shows a state in which the toner image is transferred (secondary transfer) at a time to the (surface). The toner (+ charge) on the intermediate transfer belt 10 is electrostatically repelled by the transfer roller 21 to which the + voltage is applied and is transferred to the paper, and the toner (−charge) is electrostatically transferred from the photoconductor 1 to the paper. Is transferred by suction to
The toner is simultaneously transferred to both sides of the paper.

FIG. 2D shows a state in which the sheet is conveyed to the fixing area while the sheet is attracted to the intermediate transfer belt 10, and the toner images are fixed on both sides of the sheet. Further, the belt cleaning device 25 is pressed against the belt 10 to remove residual toner on the belt 10.

As described above, according to the present invention, the polarity of the toner (primarily transferred) carried on the second image carrier on the second image carrier (intermediate transfer belt 10) is determined by the non-contact charging means ( Since the polarity is switched by the charging charger 17), simultaneous transfer (secondary transfer) of the toner image to both sides of the paper is possible by one transfer means (21), and transfer is performed by primary transfer and secondary transfer. There is no need to change the polarity of the applied voltage of the means, and the configuration of switching the applied voltage polarity of the transfer means is unnecessary, which is excellent in cost. Further, since the charge is not applied from the open surface of the sheet to which the toner is transferred, disturbance of the toner image transferred to the upper surface (second surface) of the sheet and electrostatic offset at the time of fixing due to charge-up of the transfer sheet are caused. Is prevented.

When an image is obtained only on one side of a sheet,
The toner image formed on the photoconductor 1 may be directly transferred to a sheet, and the toner (−charge) on the photoconductor 1 is suction-transferred by the transfer roller 21 to which + voltage is applied. Further, the charging polarity of the photoconductor and the charging polarity of the toner in the above description are merely examples, and the polarity may be opposite to that of the present embodiment.

FIG. 3 is a schematic diagram conceptually showing an image forming process at the time of double-sided recording in the third embodiment in which the configuration of the fixing device is different. In the space of the drawing, the intermediate transfer belt 1
0 is shown in the state arranged in the vertical direction.

In the embodiment of FIG. 3, the fixing device 30 (the fixing device disposed outside the belt loop of the intermediate transfer belt 10) in the embodiment of FIG. 1 is a non-contact type fixing device. The fixing device 30B is of a type that does not come into contact with the conveyed paper, and fixes a toner image by emitting light from an infrared lamp, a xenon lamp, or the like. Since the fixing device 30B is a non-contact type, the fixing device 30B does not need to be rotatable and is fixedly provided. Except for this, it is the same as the embodiment of FIG.

The embodiment of FIG. 3 (and the embodiment of FIG. 1)
Is different from the embodiment of FIG. 2 in that the fixing device 30B (or 3
2) except that (0) is provided on the intermediate transfer belt portion.
The operation of the image forming process is the same as that described in FIG.

Also in the case of the configuration shown in FIG. 3 or FIG. 1, as in the case of FIG. 2, the second image carrier (intermediate transfer belt 10)
Since the polarity of the toner carried (primarily transferred) on the second image carrier is switched by a non-contact charging means (charging charger 17), one transfer means (21)
This allows simultaneous transfer (secondary transfer) of toner images to both sides of the paper, and eliminates the need to change the polarity of the voltage applied to the transfer unit between the primary transfer and the secondary transfer. Because it is unnecessary, it is excellent in cost.
Further, since the charge is not applied from the open surface of the sheet to which the toner is transferred, disturbance of the toner image transferred to the upper surface (second surface) of the sheet and electrostatic offset at the time of fixing due to charge-up of the transfer sheet are caused. Is prevented.

In the case of the embodiment of FIG. 3, similarly to the embodiment of FIG. 1, after the toner image is transferred, the sheet is fixed in a state where the sheet and the intermediate transfer belt 10 are overlapped without being separated from the intermediate transfer belt 10. Thus, the toner image is not disturbed, and the occurrence of image blur is prevented. In the case of the embodiment shown in FIG. 3, the fixing device 30c is of a non-contact type that does not come in contact with or separate from the belt 10, so that the configuration and control can be simplified.

FIG. 4 is a sectional view showing a schematic configuration of a fourth embodiment in which the belt units 20 are arranged in the vertical direction. This embodiment uses an intermediate transfer belt 10 as a second image carrier.
This is a vertical conveyance method in which the paper is conveyed in the upward direction. The fixing device 30 has the same form as the embodiment of FIG. The embodiment of FIG. 4 is the same as the embodiment of FIG. 1 except that the belt unit 20 is arranged in the vertical direction, and its operation is the same as that of the embodiment of FIG. Omitted.

Next, an embodiment in which the present invention is applied to a color image forming apparatus will be described. 5 and 6 show examples of the configuration of the color image forming apparatus. The embodiment shown in FIG. 5 includes a revolver type developing device 5R, and the embodiment shown in FIG. 6 includes a tandem type developing device 5T on one side of the photoreceptor belt 1B. Further, in the embodiment shown in FIGS. 5 and 6, the intermediate transfer belt 10 is configured to be able to contact and separate from the photosensitive drum 1. The other configuration is the same as that of the monochromatic embodiment of FIG. 4, and only different portions will be described.

In FIG. 5, a revolver type developing device 5R
Has four developing devices 5a to 5d, and is driven to rotate counterclockwise in the figure as shown by arrows, and can switch each developing device to the developing position. Four developing devices 5a-
d stores each color toner that enables full color development. For example, the developing device 5a is yellow,
b stores magenta toner, the developing unit 5c stores cyan toner, and the developing unit 5d stores black toner. In the case of monochrome printing, the developing device 5d containing the black toner is moved to the developing position, and the same image forming operation as in the above-described embodiment is performed.

The operation for forming a full-color image will be described. The photosensitive drum 1 and the intermediate transfer belt 10
In a state in which is separated, first, optical information to be developed with yellow toner is written from the exposure device 7 on the surface of the charged photoconductor 1. The yellow toner is applied to the electrostatic latent image from the yellow developing device 5a moved to the developing position and developed. Similarly, a magenta image is formed on the surface of the photoconductor 1 and is superimposed on the yellow image. In addition, a cyan image is formed and superimposed on the previous image on the photoreceptor. Finally, an image using the black toner is superimposed, and four color images are formed and carried on the surface of the photoconductor. In forming four color images, the photosensitive drum 1 rotates four times.

When four color images are formed on the surface of the photoreceptor, the intermediate transfer belt 10 contacts the photoreceptor drum 1 and
The photoreceptor 1 is transferred onto the transfer paper fed by the registration roller 28 in a timely manner by the action of the first transfer means 21.
The upper color image is transferred.

In the case of double-sided printing, when an image on the first side is formed on the photoreceptor 1, the intermediate transfer belt 10 comes into contact with the photoreceptor drum 1 and is transferred onto the moving intermediate transfer belt 10 by the action of the transfer means 21. The first side image is transferred. First
The intermediate transfer belt 10 carrying the surface image is separated from the photoreceptor 1 at a predetermined position, stops and waits. Then, the formation of the second surface image on the photoconductor 1 is started. When a four-color image (second surface image) is formed on the photoconductor 1, the front end of the second surface image on the surface of the photoconductor 1 and the front end of the first surface image carried on the intermediate transfer belt 10 are aligned. The running of the intermediate transfer belt 10 is started so as to fit, and the intermediate transfer belt 10 is brought into contact with the photoconductor 1. The second surface image on the intermediate transfer belt 10 is conveyed toward the position where the belt 10 and the photoconductor 1 come into contact with each other by one rotation. At this time, the operation of the charging unit 17 provided before the roller 12 is performed. As a result, the polarity of the toner image carried on the belt 10 is reversed.

The registration roller pair 28 ensures that the positions of the toner image (second-side image) on the sheet and the photosensitive member 1 and the toner image (first-side image) on the belt 10 become regular.
The sheet is sent out at a proper timing by the pair of registration rollers 28. The sheet is sent to a transfer position where the photoconductor 1 and the belt 10 are in contact with each other, and the toner images (the first-side image and the second-side image) are simultaneously transferred onto both sides of the sheet by the transfer unit 21. As a result, the color image is transferred to both sides of the sheet, and the sheet is conveyed to a fixing area by the fixing device 30 while being held while being superposed on the intermediate transfer belt 10. The process after fixing is either single-sided printing or double-sided printing,
This is similar to the monochrome type embodiment.

In the embodiment shown in FIG.
B is rotatably stretched, and a tandem developing device 5T including four developing devices is arranged along an upper side thereof. Each of the developing devices 5a to 5d is configured to be individually movable to a position close to and away from the photoreceptor belt 1B, as indicated by arrows in the drawing. The four developing devices 5a to 5d store toners of respective colors that enable full-color development. For example, the developing device 5a stores yellow toner, the developing device 5b stores magenta, the developing device 5c stores cyan, and the developing device 5d stores black toner. In the case of monochrome printing, the developing device 5d containing the black toner is moved to the developing position, and the same image forming operation as in the above-described embodiment is performed.

The operation for forming a full-color image is as follows.
Basically, it is the same as the embodiment of FIG.
While rotating B four times, the four developing devices 5a to 5d are sequentially approached to the photosensitive belt 1B, and the respective color images are transferred to the photosensitive belt 1B.
A full color image is formed on B. Except that the photoreceptor is formed in a belt shape and the configuration of the developing unit 5 is different, it is the same as the embodiment of FIG. 5, and further description is omitted.

Although the present invention has been described with reference to the illustrated embodiments, the present invention is not limited to these embodiments, and various modifications are possible. For example, at the time of double-sided recording, instead of rotating the intermediate transfer belt 10 on which the first-side image has been transferred once, the belt may be reversed to convey the first-side image to a predetermined position. In this case,
Even in the case of a single-color device, it is necessary to provide a structure capable of separating the first image carrier (photoconductor 1) and the second image carrier (intermediate transfer belt 10).

Further, the first image carrier is not limited to the photosensitive drum, but may be a belt type image carrier. The charging polarity of the photoconductor / toner, the polarity of the transfer voltage, etc. are examples,
The polarity may be opposite to that of the embodiment.

Furthermore, the exposure apparatus 7 in each embodiment is of a laser type, but may be of an LED type.
Alternatively, the present invention can be implemented in an analog exposure (analog copying machine). When a normal image is obtained on a photoconductor by analog exposure, it is possible to use a mirror.

A charging means for the first image carrier;
The configuration of the developing device, the transfer unit, or the fixing device is not limited to the configuration of the above-described embodiment, and an appropriate system can be adopted. As a specific example, the transfer unit 21 may be a non-contact type charger instead of a contact type transfer roller.

Further, it goes without saying that the image forming apparatus is not limited to a printer, but may be a copying machine or a facsimile. Further, in the case of the color image forming apparatus, the order of forming the respective color images, the arrangement of the respective color developing units, and the like are not limited to the above-described embodiment.

[0078]

As described above, according to the image forming apparatus of the present invention, by inverting the charge polarity of the image transferred to the intermediate transfer member on the intermediate transfer member, the polarity of the transfer voltage can be switched. Simultaneous transfer of images to both sides of paper can be performed. Therefore, a configuration for switching the transfer voltage polarity is not required, and the cost can be reduced.

Further, the transfer is not performed in a state where the unfixed image is present on the sheet, thereby preventing the disturbance due to the disturbance of the toner image and the charge-up of the transfer sheet. According to the second aspect of the present invention, the charge polarity of the image transferred to the intermediate transfer member is inverted by using the non-contact type charging means, so that the image is not disturbed.

According to the third aspect of the present invention, the positions of the image transferred to each side of the sheet with respect to the sheet can be set to the normal positions, and an appropriate image can be simultaneously transferred to both sides of the sheet.

According to the structure of the fourth aspect, the first image can be transferred to the sheet under the transfer condition for transferring the second image to the sheet. According to the structure of the fifth aspect, the transfer means for applying the transfer electric field from the side opposite to the side carrying the first image of the intermediate transfer body is provided. Either can be adopted.

According to the sixth aspect, the image transfer from the image carrier to the intermediate transfer member can be performed by the transfer means for transferring the image to the paper. According to the configuration of claim 7, since the image is fixed on the intermediate transfer member after the transfer of the two-sided image is completed, it is advantageous in terms of the layout of the apparatus. Further, it is possible to prevent rubbing, image blur, discharge disturbance, and the like of the image transferred to the sheet.

According to the structure of the eighth aspect, in the case of a single-sided image, the image transfer to the intermediate transfer member and the reversal of the charging polarity are omitted, so that the productivity can be improved. According to the configuration of the ninth aspect, even in the case of a single-sided image, it is possible to prevent rubbing, image blurring, discharge disturbance, and the like of the image transferred to the sheet.

According to the tenth aspect, it is possible to perform exposure with long-wavelength light without causing light deterioration of the image carrier.
Image quality improvement and energy saving effects can also be obtained by reversal development (negative-positive development).

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram schematically illustrating a printer as an example of an image forming apparatus to which the present invention is applied.

FIG. 2 is a schematic diagram conceptually showing an image forming process at the time of double-sided recording in the present embodiment.

FIG. 3 is a schematic view conceptually showing an image forming process during double-sided recording in another embodiment.

FIG. 4 is a cross-sectional view illustrating a schematic configuration of an embodiment in which belt units are arranged in a vertical direction.

FIG. 5 is a cross-sectional view schematically showing a printer including a revolver type developing device as an example of a color image forming apparatus to which the present invention is applied.

FIG. 6 is a sectional view schematically showing a printer including a tandem developing device as an example of a color image forming apparatus to which the present invention is applied.

FIG. 7 is a schematic diagram showing an image forming process in an example of a conventional one-pass double-sided transfer.

FIG. 8 is a schematic view showing an image forming process in another example of the related art.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor drum (image carrier) 10 intermediate transfer belt 16 belt cooling unit 17 charging charger (charging unit) 18, 19 fixing roller 20 belt unit 21 transfer roller (transfer unit) 25 belt cleaning device 30 fixing device 40 paper discharge stack Department

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 2H028 BA06 BA16 BB02 BB04 BB06 2H033 AA46 BA08 BA10 BA11 BB18 BB28 BB35 BC02 2H077 GA13 GA17 2H200 GA23 GA34 GA44 GA47 GA59 GB12 GB22 GB25 HA02 HA12 HB03 HB12 JB22 J02 JA18 JC12 JC19 LB15 PA03 PA26

Claims (10)

[Claims] 1. A first image formed on an image carrier is transferred to an intermediate transfer body, a second image is formed on the image carrier, and the first and second images are recorded on a recording medium. In the image forming apparatus, the first image formed on the image carrier is transferred to the intermediate transfer body, and then transferred onto the intermediate transfer body. Wherein the charging polarity of the first image is inverted, and the first image and the second image are simultaneously transferred to both sides of a recording medium. 2. The image forming apparatus according to claim 1, wherein the charging polarity of the first image is reversed to a reverse polarity using a non-contact type charging unit. 3. A second image is formed and recorded on the image carrier such that the second image position relative to the first image on the intermediate transfer body with the charged polarity inverted is normal. The image forming apparatus according to claim 1, wherein the first image and the second image are simultaneously transferred to both surfaces of the medium. 4. The simultaneous transfer of an image to both sides of the recording medium is performed by reversing a charging polarity of a first image on the intermediate transfer body and then transferring a second image from the image carrier to a recording medium. The image forming apparatus according to claim 3, wherein the first image and the second image are simultaneously transferred under the following conditions. 5. A transfer means for applying a transfer electric field from a side of the intermediate transfer body opposite to a side carrying the first image, wherein the transfer means transfers the first image and the second image to both sides of a recording medium. The image forming apparatus according to claim 1, wherein the image is transferred simultaneously. 6. The image forming apparatus according to claim 5, wherein the transfer unit is a transfer unit that transfers a first image from the image carrier to an intermediate transfer member. 7. The image forming apparatus according to claim 1, wherein after the transfer of the first image and the second image to the recording medium is completed, the images on both surfaces of the recording medium are fixed on the intermediate transfer body. Image forming device. 8. When forming an image on only one side of a recording medium, it is necessary to directly transfer the image formed on the image carrier to a recording medium and to convey the recording medium to a fixing step by the intermediate transfer body. The image forming apparatus according to claim 1, wherein: 9. The image forming apparatus according to claim 8, wherein after the transfer of the image to the recording medium is completed, the image is fixed on the recording medium on the intermediate transfer body. 10. The image carrier is an organic photoconductor,
The image forming apparatus according to claim 1, wherein the image carrier is negatively charged, and a latent image obtained by exposing the image carrier is reversely developed with a negative developer.