JP2002182507A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that freely forms a multi-color image of high image quality on the surface or back or both the sides of a transfer material without providing a transfer-material inverting means. SOLUTION: The apparatus has a first intermediate transfer belt 19, and a transfer roller 20a which transfers a toner image on a photoreceptor 9 to the surface of the first intermediate transfer belt 23. The apparatus also has a second intermediate transfer belt 23, and a transfer roller 23a which transfers a toner image on the first intermediate transfer belt to the surface of a transfer material being carried by the second intermediate transfer belt or to the surface of the intermediate transfer belt. The apparatus further has a transfer charger 23e which transfers the toner image on the second intermediate transfer belt to the back of the transfer paper being carried by the second intermediate transfer belt, and a fixing device 28 which fixes the toner image on the transfer material by passing the transfer material between fixing rollers 280a and 280b arranged in a pair. Herein, the fixing rollers 280a and 280b are made of a material having small surface roughness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile, and a printer, and more particularly, to an intermediate transfer member capable of transferring a toner image on an image carrier, and the image carrier. The present invention relates to an image forming apparatus provided with a transfer unit for transferring an upper toner image onto an intermediate transfer member.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus using such an intermediate transfer member, for example, toner images of different colors formed sequentially on an image carrier are successively transferred onto the intermediate transfer member and superposed. 2. Description of the Related Art A color image forming apparatus that collectively transfers images from an intermediate transfer member onto a transfer material such as paper after the alignment is known.

[0003]

When an image is formed on both surfaces of a transfer material in an image forming apparatus provided with the above-mentioned intermediate transfer member, the transfer material once discharged outside the apparatus is set again in a manual feed tray or a paper feed cassette. Or a method of attaching a reverse / double-sided tray as an option. However, the method of setting the transfer material on the manual feed tray or the like again has a problem that the operability is poor and the top and bottom of the image are easily mistaken. In addition, the method using the reversing / double-sided tray is costly. In particular, when forming a full-color image, the amount of toner on the transfer material increases, and the transfer material easily curls. It is easy to cause troubles such as jams. Further, if these methods are used in a full-color image forming apparatus, the use of oil in the fixing device may cause the supply of oil contained in the transfer material once passing through the fixing device, and the risk of adverse effects on the intermediate transfer member. Is high.

An image forming apparatus provided with an intermediate transfer member for forming a multicolor image on both surfaces of a transfer material without using a reversing means has conventionally been known as an image carrier and an intermediate transfer member. A multi-color toner image is formed in such a manner that the two toner images are transferred to a transfer material conveyed between an image carrier and an intermediate transfer member. However, in this type of image forming apparatus, a non-contact developing method using a one-component developer is used to superimpose a toner image on an image carrier, so that the reproducibility of a halftone image is poor. There is a defect that the quality is inferior.

The present invention has been made in view of the above problems, and has as its object to provide a high-quality multicolor image on the front surface, the back surface, or both surfaces of a transfer material without providing a reversing means for the transfer material. To provide an image forming apparatus that can freely form the image.

[0006]

In order to achieve the above object, according to the present invention, a first intermediate transfer member capable of transferring a toner image on an image carrier and a toner on the image carrier are provided. An image forming apparatus comprising: a first transfer unit configured to transfer an image onto a first intermediate transfer body, wherein the first transfer unit is configured to transfer a transfer material,
A second intermediate transfer member capable of transferring the toner image on the first intermediate transfer member, and a surface of a transfer material conveyed by the second intermediate transfer member on the first intermediate transfer member, or a second intermediate transfer member. A second transfer means for transferring the toner image on the intermediate transfer member, and a third transfer means for transferring the toner image on the second intermediate transfer member to the back surface of the transfer material being conveyed by the second intermediate transfer member. And a fixing device for fixing the toner image on the transfer material by passing the transfer material between the pair of first and second rollers, wherein the first roller and the second roller of the fixing device are provided. The surface portion of the roller is made of a material having a small surface roughness.

According to a second aspect of the present invention, a first intermediate transfer member capable of transferring a toner image on an image carrier and a first intermediate transfer member transferring the toner image on the image carrier onto the first intermediate transfer member are provided. A second intermediate transfer member capable of transferring a transfer material and transferring a toner image on the first intermediate transfer member, and a second intermediate transfer member capable of transferring the toner image on the first intermediate transfer member to a second intermediate transfer member. The second surface to be transferred onto the surface of the transfer material being conveyed by the transfer body or onto the second intermediate transfer body
Transfer means, a third transfer means for transferring the toner image on the second intermediate transfer body to the back surface of the transfer material being conveyed by the second intermediate transfer body, a pair of first rollers and a second transfer means. And a fixing device for fixing the toner image on the transfer material by passing the transfer material between the first and second rollers. The first roller and the second roller of the fixing device are the same component. It is assumed that.

According to a third aspect of the present invention, in the image forming apparatus of the first or second aspect, a cleaning unit for cleaning the surface of the second intermediate transfer member is provided.

In the first and second aspects of the present invention, when an image is formed only on the surface of the transfer material, a toner image corresponding to the normal image of the desired image is formed on the image carrier. This toner image is transferred to the first intermediate transfer member by the first transfer means, and the toner image on the first intermediate transfer member is transferred by the second intermediate transfer member by the second transfer means. It is transferred to the surface of the material. When an image is formed only on the back surface of the transfer material, a toner image corresponding to a mirror image of the desired image is formed on the image carrier. This toner image is transferred to the first intermediate transfer member by the first transfer unit, and further transferred onto the second intermediate transfer member by the second transfer unit. Then, the toner image on the second intermediate transfer member is transferred by a third transfer unit onto a transfer material being conveyed by the second intermediate transfer member. Further, when images are formed on both surfaces of the transfer material, a toner image corresponding to a mirror image of the desired image for the back surface formed on the image carrier is transferred by the second transfer means via the first intermediate transfer member. The image is transferred onto the second intermediate transfer member. Then, the toner image corresponding to the normal image of the desired front surface image formed on the image carrier is transferred to the first intermediate transfer member by the first transfer unit. The first intermediate transfer member and the second
The toner images transferred to the intermediate transfer member are respectively transferred to the front surface and the back surface of the transfer material conveyed by the second intermediate transfer member by the second transfer unit and the third transfer unit. In particular, in the first aspect of the present invention, the first fixing device includes:
Even if a multicolor toner image is formed on both surfaces of the transfer material with a low softening temperature toner by forming the surface portions of the roller and the second roller with a material having a small surface roughness, Can be prevented from occurring. In particular, in the invention of claim 2, since the first roller and the second roller of the fixing device are the same parts, both rollers can be shared.

A single-color toner image may be transferred to the first intermediate transfer member and the second intermediate transfer member, or a multi-color toner image may be superimposed and transferred in multiple layers. .

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a color copying apparatus as an image forming apparatus will be described below. FIG. 1 is a schematic configuration diagram of the entire color copying apparatus according to the present embodiment, and FIG. 2 is a schematic configuration diagram of main parts of the entire copying apparatus. First, an outline of a color image reading device (hereinafter, referred to as “color scanner”) 1 and a color image recording device (hereinafter, referred to as “color printer”) 2 constituting the color copying apparatus will be described with reference to FIG.

The color scanner 1 forms an image of an original 3 on a color sensor 7 via an illumination lamp 4, a mirror group 5, and a lens 6, and outputs color image information of the original.
For example, blue (hereinafter, referred to as B), green (Gr)
een (hereinafter G), red (Red, hereinafter R)
Is read for each color separation light and is converted into an electric image signal. The B, G, and R obtained by the color scanner 1
A color conversion process is performed by an image processing unit (not shown) based on the color separation image signal intensity level of black (hereinafter, referred to as black).
Bk), cyan (Cyan, hereinafter C), magenta (Magenta, hereinafter M), yellow (Yello
w, hereafter referred to as Y).

In the color printer 2, the writing optical unit 8 converts the color image data from the color scanner 1 into an optical signal, performs optical writing corresponding to the original image, and performs photowriting on the photosensitive member 9 as an image carrier. To form an electrostatic latent image. The photoconductor 9 rotates counterclockwise as indicated by an arrow, and around the photoconductor cleaning unit (including a pre-cleaning static eliminator) 10 and a static elimination lamp 1
1, charging device 12, potential sensor 13, Bk developing device 14,
C developing unit 15, M developing unit 16, Y developing unit 17, optical sensor 18 for detecting a development density pattern, first intermediate transfer belt 19 as a first intermediate transfer body, and first transfer as a first transfer unit A first intermediate transfer belt unit having a bias roller 20a and the like are arranged.

Each of the above-mentioned developing devices includes a developing sleeve (14a, 15a, 16a, 17a) which rotates by bringing a spike of the developer into contact with the surface of the photoreceptor 9 to develop an electrostatic latent image; Developing paddle (14b, 15b, 16b, 17b) rotating for pumping and stirring, and toner concentration sensor for developer (14c, 15c, 16c, 17c)
It is composed of

In FIG. 2, a first intermediate transfer belt 19
Are the drive roller 21, the first transfer bias roller 20a,
And is driven by the driven roller groups 20b and 20c, and is driven and controlled by a drive motor (not shown) as described later. Further, there is provided a separation mechanism (not shown) for driving the first intermediate transfer belt 19 so as to be able to separate and contact the photoconductor 9.

A belt cleaning unit 22 is provided at a predetermined position facing the surface of the first intermediate transfer belt 19. This unit 22 includes the brush roller 2
2a, a rubber blade 22b, a mechanism 22c for contacting and separating from the belt, and the like. The timing of the contact / separation operation of the belt cleaning unit 22 is such that the belt cleaning unit 22 is separated from the belt surface from the start of printing until the end of the belt transfer at the rear end of the Y (final color) image, At the timing, the cleaning is performed by bringing the belt surface into contact with the contact / separation mechanism 22c.

Also, a second intermediate transfer member as a second intermediate transfer member capable of transferring a toner image on the first intermediate transfer belt 19 is opposed to a portion of the first intermediate transfer belt 19 wound around the drive roller 21. A second transfer belt including an intermediate transfer belt 23 and a second transfer bias roller 23a as a second transfer unit;
Is provided. The second intermediate transfer belt 23 opposes the transfer paper 24 to the drive roller 21 of the first intermediate transfer belt 19 by a plurality of support rollers such as a second transfer bias roller 23a, a drive roller 23b, and driven rollers 23c and d. From the fixing unit 2 described later
It is stretched so that it can be directly transported up to 8. By stretching in this manner, when an image is formed on the back surface (the lower surface in the figure) of the transfer paper 24, the back surface of the transfer paper 24 comes into contact with the second intermediate transfer belt 23 on which the toner image is transferred. However, the toner image on the back surface of the transfer paper 24 may be disturbed because the transfer paper having the toner image transferred to the back surface is directly guided to the fixing device without contacting other conveying members. It is established without.

The second intermediate transfer belt 23 has a second
Each roller is disposed such that a tension portion between the transfer bias roller 23a and the driven roller 23d is pressed against the drive roller 21 via the first intermediate transfer belt 19. As described above, since the stretched portion of the second intermediate transfer belt 23 is configured to be softly pressed against the drive roller 21 via the first intermediate transfer belt 19, the transfer roller is connected via the first intermediate transfer belt 19. As compared with a case where the drive roller 21 is pressed against the drive roller 21 with a high pressing force, the occurrence of a missing portion in the character portion can be prevented. Further, the transfer paper is linearly conveyed at the pressure contact position of the second intermediate transfer belt 23, and the magnitude relationship between the electrical resistances of the first intermediate transfer belt 19 and the second intermediate transfer belt 23 is defined as described later. Since the effect of adsorbing the paper 24 to the second intermediate transfer belt 23 is obtained, the separability of the transfer paper from the first intermediate transfer belt 19 is improved, and a static elimination needle or the like that assists the separation of the transfer paper as in the related art There is no need to provide a separation assisting means.

The toner image on the second intermediate transfer belt 23 is transferred to the back surface of the transfer paper 24 so that the toner image on the second intermediate transfer belt 23 is opposed from above to a portion wound around the driven roller 23b of the second intermediate transfer belt 23 on the fixing device side described later. A transfer charger 23e is provided as a third transfer unit for transferring the image to the printer. By transferring the toner image to the back surface of the transfer paper 24 immediately before the fixing device in this manner, the toner on the back surface of the transfer paper 24 once transferred, for example, when the transfer is performed in the middle of the second intermediate transfer belt 23, The image is not disturbed by the second intermediate transfer belt 23. Further, a belt cleaning unit 23f using a cleaning blade is provided on a portion of the second intermediate transfer belt 23 that is wound around the driven roller 23c.

The first intermediate transfer belt 19 has a thickness of about 150 μm and a specific surface resistivity of 1 × 10 ⁷ to 1 × 10 ^{12 in} which carbon is dispersed in a resin material (for example, polycarbonate or fluorine resin). Ω, a resin sheet having a volume resistivity of 1 × 10 ⁸ to 1 × 10 ¹⁴ Ωcm can be used. The upper limit of the resistivity is set so that the charges do not remain more than necessary, so that there is no need for a discharging means for removing the remaining charges. The lower limit of the resistivity is set so that a predetermined transfer electric field is formed without the transfer charge flowing into the surrounding ground member. Also,
A material in which the surface resistivity of the resin sheet is larger than the volume resistivity is selected, thereby making it difficult for dielectric breakdown to occur.

The above resin sheet has less elongation than rubber material, and is suitable for superposition of multicolor toner images requiring high-precision alignment. Regulatory measures are needed.
FIG. 3 shows a typical deviation control means, in which a deviation control member 19a made of a rubber material is attached to an inner widthwise end of the first intermediate transfer belt 19, and a roller 20b for supporting the belt 19 is provided. Are regulated at the axial end.

The second intermediate transfer belt 23 has a thickness t = 0.5-0.5 as shown in the sectional view of FIG.
A surface coat of a base rubber 230 such as urethane or chloroprene rubber having a thickness of 0.6 mm and a fluorine coat 231 having a thickness δ of 10 to 30 μm can be used. Since a belt using such a rubber material has a larger elongation than a resin sheet, it is suitable when it is not necessary to superimpose a plurality of toner images with high accuracy. In the case of rubber material, FIG.
As shown in (b), the belt 23 can be made to protrude from the end of the row 23b, and the belt can be regulated using the elasticity of the belt 23, so that there is no need to provide any special deviation regulating means. Further, in the case of the rubber material, the margin for slip during the rotation drive is large. In addition, this belt 23
The surface specific resistivity of the base rubber is 1 × 10 ⁷ to 1 × 10
^{About 12} Ω, surface resistivity on fluorine coat is 1 ×
It is 10 ⁸ to 1 × 10 ¹³ Ω. By using a belt having such a resistivity, as in the case of the first intermediate transfer belt 19, there is an advantage that the transfer charge can be reduced and the cost can be reduced due to the elimination of the charge removing means.

When a plurality of toner images are successively superimposed on the second intermediate transfer belt 23 with high precision alignment, it is preferable to use a resin sheet having a small elongation like the first intermediate transfer belt. In this case, there is also an advantage that the surface releasability of the second intermediate transfer belt 23 is prevented from being deteriorated, and the life can be extended. Further, in order to satisfactorily separate the transfer paper from the first intermediate transfer belt 19, it is preferable that the electric resistance of the second intermediate transfer belt 23 be larger than that of the first intermediate transfer belt 19.

At a position where the transfer paper separated from the second intermediate transfer unit is conveyed, a fixing device 28 having a pair of upper and lower fixing rollers 280a and 280b is provided as shown in an enlarged view of FIG. ing. A layer (for example, an RTV silicone rubber layer) of a material having high releasability and a small surface roughness is formed on the core of each of the fixing rollers 280a and 280b, and heaters 281a and 281b are provided inside the core. have. Since the surface portion is made of a material having high releasability and having a small surface roughness and excellent smoothness, an image formed by a color toner having a low softening temperature on transfer paper to improve color reproducibility is obtained. Even if the fixing roller 280 is formed,
A good color toner image can be fixed on both sides of the transfer paper without offsetting the toner to a and b. The surface roughness of the fixing rollers 280a and 280b is preferably 4 μm or less, and more preferably about 2 μm, in terms of JIS 10-point average Rz.

Further, around the upper and lower fixing rollers 280a and 280b, cleaning members 282a and 282b, oil supply members 283a and 283b, peeling claws 284a and 284b, and a temperature detecting member 28 are provided.
5a, b, over-temperature rise prevention members 286a, b and the like are provided. In the fixing device 28 of the present embodiment, the upper and lower fixing rollers 280a and 280b are made of the same component, and various members provided around each roller are used in common to reduce the cost.

The color printer 2 includes a transfer paper 2
Feed roller 2 for feeding paper 4 at a predetermined timing
5. A registration roller 26 is provided. Further, as a control means for controlling the image forming process, for example, CP
A system control plate (not shown) comprising U, ROM, RAM, and I / O interfaces is provided. The system control plate includes an operation unit having a mode selection button as an image mode selection unit for selecting an image mode, and a belt drive motor. In addition, various driving devices such as a solenoid and a developing sleeve motor in the belt contacting / separating mechanism and various detecting devices are connected.

The transfer paper cassettes 30, 31, 32,
Reference numeral 33 stores transfer papers of various sizes, which are fed and conveyed in the direction of the registration rollers 26 from the storage cassette of the size paper designated by the operation panel (not shown) at a certain timing. Reference numeral 34 denotes a manual paper feed tray for OHP paper or thick paper.

Next, the toner image forming process and the transfer process in the color image forming apparatus having the above-described configuration are described by Bk,
The case of forming C, M, and Y will be described (however, the order of forming toner images is not limited to this). When the copy operation is started, reading of Bk image data starts at a predetermined timing by the color scanner 1, and
Based on this image data, optical writing with a laser beam on the photoreceptor 9 uniformly charged by the charger 12 and formation of a latent image start (hereinafter, an electrostatic latent image based on Bk image data is referred to as a Bk latent image). C, M, and Y are referred to as a C latent image, an M latent image, and a Y latent image, respectively). Before the front end of the latent image reaches the developing position of the Bk developing device 14 so that development is possible from the front end of the Bk latent image, the rotation of the developing sleeve 14a is started, and the Bk latent image is charged with negatively charged Bk toner. develop. Thereafter, the developing operation of the Bk latent image area is continued, and the rear end of the latent image is
At the point of time when it has passed the k developing position, the developing operation is brought into an inoperative state.
This is completed at least before the leading end of the C latent image based on the next C image data arrives.

Then, the Bk toner image formed on the photosensitive member 9 is transferred onto the surface of the first intermediate transfer belt 19 driven at the same speed as the photosensitive member 9 (hereinafter, toner from the photosensitive member 9 to the intermediate transfer belt). Image transfer is referred to as "belt transfer." This belt transfer is performed by the first transfer bias roller 20a in a state where the photoconductor 9 and the first intermediate transfer belt 19 are in contact with each other.
Is applied by applying a predetermined bias voltage (positive voltage in this example).

Here, on the photoconductor 9 side, after the Bk process, C
In the process, reading of C image data by the color scanner 1 starts at a predetermined timing, and a C latent image is formed by writing a laser beam based on the image data. C
The developing device 15 starts rotating the developing sleeve 15a with respect to the developing position after the rear end of the previous Bk latent image has passed and before the leading end of the C latent image has arrived, so that the C latent image is Develop with toner. Thereafter, the development of the C latent image area is continued, and when the trailing end of the latent image has passed, the development is disabled as in the case of the Bk developing device. This is also completed before the leading end of the next M latent image arrives. In each of the steps M and Y, the operations of reading image data, forming a latent image, and developing are performed in the same manner as the steps Bk and C described above.

As described above, the first intermediate transfer belt 19 includes
The Bk, C, M, and Y toner images sequentially formed on the photoconductor 9 are sequentially aligned and transferred to the same surface, and a four-color superimposed toner image is formed. Thereafter, the four-color superimposed toner image on the first intermediate transfer belt 19 is applied to the second transfer bias roller 23a in a state where the first intermediate transfer belt 19 is in contact with the transfer paper 24 or the second intermediate transfer belt 23. By applying a bias voltage (positive voltage in this example), the image is collectively transferred onto the surface of the transfer paper 24 or the second intermediate transfer belt 23. Here, when the four-color superimposed toner image is transferred onto the second intermediate transfer belt 23 at a time, the toner image on the second intermediate transfer belt 23 is further transferred by positive transfer discharge by the transfer charger 23e. The image is transferred to the back surface of the paper 24.

Here, it is possible to make the first intermediate transfer belt 19 and the second intermediate transfer belt 23 have medium resistance as described above, thereby eliminating the need for the charge removing means. It is necessary to perform the self-static elimination by dropping the supporting roller to the ground.

When toner images of the same polarity are formed on both the intermediate transfer belts 19 and 23, the polarity of the toner image on one of the belts is changed so that the second bias transfer roller 2
3a, it is possible to perform simultaneous transfer (one of them is a push-in transfer method), but in the case of the configuration of the color image forming apparatus of the present embodiment, the transfer paper 24 is transferred from the second intermediate transfer belt 23 from the simultaneous transfer position. Since the span to the separation position where separation is performed is long, and the belt potential at the separation position becomes approximately 0 V due to the self-static elimination effect of the belt 23, there is a high possibility that transfer failure will occur. In general, charge having a polarity opposite to that of the toner is used as the charge used for the transfer, and a so-called indentation transfer method using a charge having the same polarity as the toner has a small transfer margin. For this reason, in the present embodiment, the second
To transfer the toner image from the intermediate transfer belt 23 to the transfer paper 24, a method using a transfer charge having a polarity opposite to that of the toner using a transfer charger 23e as a third transfer unit is employed.

As shown in FIGS. 6A to 6C,
For example, when toner images of four colors are formed in the order of Bk, C, M, and Y on the first intermediate transfer belt 19, assuming that the amount of the toner image of each color is 1, the second image transferred at a transfer rate of 90%. The amount of toner image on the intermediate transfer belt 23 is 0.9 for Bk only.
Becomes When the toner image is further transferred onto the transfer paper 24, the amount of the Y toner image becomes 0.9. In other words, only the toner of the lowermost layer and the uppermost layer is left as a transfer residue, and the toner amount is reduced. Therefore, in the present embodiment, as described later, the transfer paper 2
In the case where an image is formed on both surfaces of No. 4, not only the toner of the lowermost layer but also the toner of the uppermost layer on the first intermediate transfer belt 19 are increased in advance, so that the toner amount of each color is balanced, and the transfer amount is increased. The density and color of the copy image on the front and back sides of the paper 24 can be made equal. The control of the toner amount in the toner image of each color can be easily performed by changing a known writing light amount or a developing bias voltage.

As described above, the intermediate transfer belt 19,
The transfer paper 24 on which the four-color superimposed toner image from the 23 surface has been collectively transferred to at least one of the front surface and the back surface is conveyed to a fixing device 28 and the fixing roller 2 controlled to a predetermined temperature.
80a and 80b fuse and fix the toner image to copy tray 29
To get a full color copy.

The photoreceptor 9 after the belt transfer is replaced with a photoreceptor cleaning unit 10 (a pre-cleaning static eliminator 10).
a, the brush roller 10b, and the rubber blade 10c) are used to clean the surface, and the charge is uniformly removed by the charge removing lamp 11.

At the time of repeat copying, the color scanner 1
The operation of (1) and image formation on the photoconductor 9 proceed to the second sheet Bk (first color) image step at a predetermined timing following the first sheet Y (fourth color) image step. Further, the surface of the first intermediate transfer belt 19 is cleaned by the cleaning unit 2 following the batch transfer process of the first four-color superimposed image onto transfer paper.
The second Bk toner image is belt-transferred to the area cleaned in step 2. After that, the operation is the same as that of the first sheet.

The above is the description of the copy mode for obtaining four full colors. However, in the case of the three-color copy mode and the two-color copy mode, the same operation as described above is performed for the designated color and the number of times. become. Further, in the case of the single-color copy mode, until a predetermined number of sheets are completed, the copy operation is performed with only the developing device of that color being in a developing operation (springing).

Next, an image forming operation when each image forming mode (front single color mode, back single color mode, front multicolor mode, back multicolor mode) is selected from the operation unit will be briefly described.

[Surface Single Color Mode] A normal toner image is formed on the photosensitive member 9 and the first intermediate transfer belt 19 is driven by the first bias transfer roller 23a to which a predetermined transfer voltage is applied.
Transferred to the upper side to form a mirror image toner image. Then, the mirror image toner image on the first intermediate transfer belt 19 is transferred to the surface of the transfer paper 24 sent from the registration roller 26 in a timely manner by a second bias transfer roller 23 a to which a predetermined transfer voltage is applied. To form a normal toner image. The normal toner image is fixed on the surface of the transfer paper 24 by the fixing device 28 as a final image. In this image forming mode, the second intermediate transfer belt 23 is used as a transfer conveyance belt that conveys the transfer paper 24 to the fixing device 28, and the transfer charger 23e is controlled so as to be inactive or operate as a separation charger.

[Backside Single Color Mode] A toner image of a mirror image is formed on the photoreceptor 9 and the first intermediate transfer belt 19 is driven by the first bias transfer roller 23a to which a predetermined transfer voltage is applied.
The toner image is transferred to a normal toner image. Then, the normal toner image on the first intermediate transfer belt 19 is transferred onto the second intermediate transfer belt 23 by the second bias transfer roller 23a to which a predetermined transfer voltage is applied, and a mirror image toner image is formed. I do. Then, the second intermediate transfer belt 23
The upper mirror image toner image is transferred to the back surface of the transfer paper 24 sent from the registration roller 26 in a timely manner by the transfer charger 23e to which a predetermined transfer voltage is applied, to form a normal toner image. . The normal toner image is fixed on the surface of the transfer paper 24 by the fixing device 28 as a final image. In this image forming mode, the second bias transfer roller 23a is controlled so as to be inoperative or to operate with the same polarity as the toner when transferring the toner image to the back surface of the transfer paper 24.

[Surface Multicolor Mode (Example of Four-Color Full-Color)] A normal Bk toner image is formed on the photoreceptor 9 and a first bias transfer roller 23a to which a predetermined transfer voltage is applied.
Is transferred onto the first intermediate transfer belt 19 by the mirror image B.
A k toner image is formed. Then, the photoreceptor 9 and the first intermediate transfer belt 19 are driven with high precision, the C toner image is transferred to the Bk toner image while being positioned, and the M toner image,
The toner image is transferred, and a four-color full-color toner image of a mirror image is formed on the first intermediate transfer belt 19. A second bias transfer roller in which a predetermined transfer voltage is applied to the surface of the transfer paper 24 sent from the registration roller 26 at a time by applying a mirror image of the four full-color toner images on the first intermediate transfer belt 19 The image is transferred by the reference numeral 23a to form a normal full-color four-color toner image. The normal toner image is fixed on the surface of the transfer paper 24 by the fixing device 28 as a final image. In this image forming mode, the second intermediate transfer belt 23 is used as a transfer conveyance belt for conveying the transfer paper 24 to the fixing device 28, and the transfer charger 23e
Is controlled to be inactive or to operate as a separate charger.

[Backside Multicolor Mode (Example of Four-Color Full Color)] A first bias transfer roller 23a is formed by forming a mirror image of a Bk toner image on the photosensitive member 9 and applying a predetermined transfer voltage.
Is transferred onto the first intermediate transfer belt 19 by the
A k toner image is formed. Then, the photoreceptor 9 and the first intermediate transfer belt 19 are driven with high precision, the C toner image is transferred to the Bk toner image while being positioned, and the M toner image,
The toner image is transferred, and a four-color full-color toner image of a normal image is formed on the first intermediate transfer belt 19. And this first
The four full-color toner images of the normal image on the intermediate transfer belt 19 are transferred onto the second intermediate transfer belt 23 by the second bias transfer roller 23a to which a predetermined transfer voltage is applied,
A four-color mirror image of a full-color toner image is formed. Then, the four-color full-color toner image of the mirror image on the second intermediate transfer belt 23 is transferred to the back surface of the transfer paper 24 sent from the registration roller 26 in a timely manner by a transfer charger 23e to which a predetermined transfer voltage is applied. To form a four-color full-color toner image of a normal image. The four-color full-color toner image of the normal image is fixed on the surface of the transfer paper 24 by the fixing device 28 as a final image. In this image forming mode, the second bias transfer roller 23a is controlled so as to be inoperative or to operate with the same polarity as the toner when transferring the toner image to the back surface of the transfer paper 24.

When the double-sided mode for forming an image on both sides of the transfer paper 24 is selected, a single color of the front side and the back side is selected.
Regardless of multicolor, an image can be formed on both the front and back sides of the transfer paper 24 by controlling the operations in the above four modes in combination.

As described above, according to the present embodiment, the contact developing method can be employed without providing the reversing means and in comparison with the method in which a plurality of toner images are formed on the photosensitive member 9 in a superposed manner. Transfer higher quality multicolor images to transfer paper 24
Can be formed freely on the front surface, the back surface, or both surfaces.

As the first, second and third transfer means in the above embodiment, a transfer roller and a transfer charger can be appropriately selected and used. Here, when the transfer charger is used as the second transfer means, even if it is disposed immediately below the drive roller 21 of the first intermediate transfer belt 19, unlike the case where the transfer roller is used, the second intermediate transfer belt is different. The press-contact force between the first intermediate transfer belt 19 and the first intermediate transfer belt 19 does not increase.

[0047]

According to the first and second aspects of the present invention, there is no need to provide a reversing means for the transfer material, and unlike the method in which a plurality of toner images are formed by superimposing on the image carrier,
Since a contact development method can also be adopted, a higher quality multicolor image can be formed freely on the front surface, the back surface, or both surfaces of the transfer material, and the polarity of the toner image is changed on the image carrier. There is an effect that stable transferability to both surfaces of the transfer material can be obtained without providing the polarity changing means. In particular, according to the first aspect of the present invention, the surface of the first roller and the second roller of the fixing device is made of a material having a small surface roughness, so that both surfaces of the transfer material have a low softening temperature. Even when a multicolor toner image is formed, it is possible to prevent the toner from being offset to each roller, and to form a multicolor image that is well fixed on both surfaces of the transfer material. effective. In particular, according to the second aspect of the invention, the first roller and the second roller of the fixing device can be shared, so that
There is an effect that the management of these rollers is facilitated and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a front view illustrating a schematic configuration of a color image forming apparatus according to an embodiment.

FIG. 2 is an enlarged view around a photoconductor and an intermediate transfer belt of the color image forming apparatus.

FIG. 3 is an explanatory diagram of a first intermediate transfer belt of the color image forming apparatus.

FIG. 4A is a partial cross-sectional view of a second intermediate transfer belt of the color image forming apparatus. (B) is an explanatory view of the same second intermediate transfer belt.

FIG. 5 is a front view illustrating a schematic configuration of a fixing device of the color image forming apparatus.

FIGS. 6A to 6C are explanatory diagrams of a first intermediate transfer belt, a second intermediate transfer belt, and a four-color toner image on transfer paper.

[Explanation of symbols]

 Reference Signs List 9 photoconductor 19 first intermediate transfer belt 20a first bias transfer roller 23 second intermediate transfer belt 23a second bias transfer roller 23e transfer charger 24 transfer paper 28 fixing device 280a, b fixing roller

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2H028 BA06 BB01 2H033 AA02 BA16 BA32 BA43 BA49 BB06 BB15 BB29 BB30 2H200 GA23 GA47 GA50 GB02 GB25 GB41 HA02 HA12 HB03 HB12 JA03 JA18 JB06 JB15 JB25 JB26 JC03 JC12 LBCO MA04 MB05

Claims (3)

[Claims] A first intermediate transfer member capable of transferring a toner image on an image carrier, and a first transfer means for transferring the toner image on the image carrier onto the first intermediate transfer member. An image forming apparatus comprising: a second intermediate transfer member capable of transferring a transfer material and transferring a toner image on the first intermediate transfer member; and a toner image formed on the first intermediate transfer member. A second transfer means for transferring onto the surface of the transfer material conveyed by the second intermediate transfer member or onto the second intermediate transfer member; and a second intermediate transfer of the toner image on the second intermediate transfer member A third transfer unit for transferring the image onto the back surface of the transfer material being conveyed by the body, and fixing the toner image on the transfer material by passing the transfer material between a pair of the first roller and the second roller. And a surface portion of the first roller and the second roller of the fixing device are made of a material having a small surface roughness. Image forming apparatus, characterized in that the. A first intermediate transfer member capable of transferring a toner image on the image carrier and a first transfer means for transferring the toner image on the image carrier onto the first intermediate transfer member. An image forming apparatus comprising: a second intermediate transfer member capable of transferring a transfer material and transferring a toner image on the first intermediate transfer member; and a toner image formed on the first intermediate transfer member. A second transfer means for transferring onto the surface of the transfer material conveyed by the second intermediate transfer member or onto the second intermediate transfer member; and a second intermediate transfer of the toner image on the second intermediate transfer member A third transfer unit for transferring the image onto the back surface of the transfer material being conveyed by the body, and fixing the toner image on the transfer material by passing the transfer material between a pair of the first roller and the second roller. Wherein the first roller and the second roller of the fixing device are the same part. Apparatus. 3. An image forming apparatus according to claim 1, further comprising a cleaning unit for cleaning a surface of said second intermediate transfer member.