JP4927431B2 - Transfer device and image forming apparatus - Google Patents

Description

  The present invention relates to a transfer device provided in an image forming apparatus using an electrophotographic process, and an image forming apparatus such as a copying machine, a facsimile, a printer, a plotter, or a composite machine including the transfer device. The present invention relates to a transfer device using an intermediate transfer member, and a color image forming apparatus including the transfer device.

  In an electrophotographic image forming apparatus such as a copying machine, a printer, a plotter, a facsimile, or a composite machine of these, a photosensitive member as an image carrier is charged by a charging unit, and an original image or image information is transferred to the charged photosensitive member. An electrostatic latent image is formed by irradiating a modulated light beam according to this, and the electrostatic latent image is developed with the toner of the developing means to be visualized, and the developed image is transferred directly or via an intermediate transfer member. The image is transferred to a transfer material such as paper, and the image transferred to the transfer material is fixed by a fixing unit to obtain an image. In the case of forming a color image, the above-described charging, latent image formation, development, and transfer processes are performed for a plurality of colors, and a plurality of colors are superimposed to form a color image.

  As an example of a color image forming apparatus, a plurality of image forming units including a photoconductor, a charging unit, a developing unit, a cleaning unit, and the like are arranged in parallel along a belt-shaped intermediate transfer body (hereinafter referred to as an intermediate transfer belt). Each image forming unit forms an image of each color of yellow, magenta, cyan, and black, and sequentially superimposes the images of each color of yellow, magenta, cyan, and black formed by each image forming unit on the intermediate transfer belt. The color image is formed by superimposing the four colors on the intermediate transfer belt, and the color image is transferred from the intermediate transfer belt to a transfer material such as transfer paper in a lump and fixed by a fixing means to form a color image. A so-called tandem type color image forming apparatus is known.

In such an image forming apparatus, generally, the image carrier of each single-color image forming unit is disposed in contact with the tension side of the intermediate transfer belt, but the image carrier is in contact with the slack side of the intermediate transfer belt. In the conventional image forming apparatus of this type, the peripheral speed of the intermediate transfer belt and the peripheral speed of the image carrier are generally set to the same speed. When the image carrier is placed in contact with the slack side of the belt, a relatively large force is applied to the intermediate transfer belt with a relatively large force in order to stabilize the contact between the intermediate transfer belt and the image carrier. It was necessary to provide a tension roll. For this reason, the tension structure of the intermediate transfer belt is complicated and enlarged, and as a result, it is difficult to reduce the size of the image forming apparatus. Further, since a relatively large tension is applied to the intermediate transfer belt, when the image forming apparatus does not operate for a long period of time (the intermediate transfer belt is not driven), the intermediate transfer belt creeps and adversely affects subsequent image formation. There is also a problem. In view of this, a color image forming apparatus has been proposed in which such problems can be solved and miniaturization can be achieved, and creep is unlikely to occur in the intermediate transfer belt (see Patent Document 1).

In this image forming apparatus, when the image carrier is disposed in contact with the slack side of the intermediate transfer belt and the primary transfer region is used on the slack side of the intermediate transfer belt, the peripheral speed of the image carrier is set to the intermediate transfer belt. It is set to be faster than the peripheral speed and faster as the distance from the drive roller. More specifically, when the image carrier of each single color image forming unit is disposed in contact with the slack side of the intermediate transfer belt, the speed of the intermediate transfer belt is Vt, and the peripheral speed of each image carrier is set. When Vdi,
Vt <Vdi
And the peripheral speed Vdi of each image carrier increases as the distance from the driving roller increases, so that the image carrier of each monochromatic image forming means is placed in contact with the slack side of the intermediate transfer belt. However, the contact state between the intermediate transfer belt and the image carrier is stabilized.

  That is, since the peripheral speed of the image carrier is higher than the peripheral speed of the intermediate transfer belt, when the apparatus operates (when the intermediate transfer belt and the image carrier are driven to rotate), the intermediate transfer belt and the image carrier are Since the tension that reduces the slack of the intermediate transfer belt acts on the intermediate transfer belt by the rotation of the image carrier at the contact portion with the body, the image carrier of each single color image forming unit is placed on the slack side of the intermediate transfer belt. In spite of the contact arrangement, it is possible to stabilize the contact state between the intermediate transfer belt and the image carrier without necessarily providing a tension roll or the like that is conventionally required. Therefore, the tension structure of the intermediate transfer belt can be simplified and the size can be reduced, and as a result, the image forming apparatus can be reduced in size. In addition, since it is not always necessary to provide a tension roll or the like that is conventionally required, when the image forming apparatus does not operate for a long period of time (the intermediate transfer belt and the image carrier are not driven), the intermediate transfer belt has a very large tension. As a result, creep deformation of the intermediate transfer belt does not occur, and the subsequent image formation is not adversely affected.

JP 2002-268325 A

  In the prior art color image forming apparatus, the primary transfer means is constituted by a transfer blade. However, when the primary transfer means is constituted by a transfer blade, if the primary transfer pressure at which the transfer blade comes into contact with the image carrier via the intermediate transfer belt is large, the running stability of the intermediate transfer belt is disturbed.

Here, as a factor disturbing the running stability of the intermediate transfer belt,
(1) Paper passing state in the secondary transfer area,
(2) Contact pressure of the belt cleaning member,
(3) Primary transfer pressure,
Although the drive roller of the intermediate transfer belt has both the support roller in the secondary transfer region and the roller facing the belt cleaning member, both of the above problems (1) and (2) are eliminated. be able to.
However, when a transfer blade is used as the primary transfer member, if the contact pressure (primary transfer pressure) is large, the running stability of the intermediate transfer belt may be disturbed. If the running stability of the intermediate transfer belt is disturbed, it may cause image quality deterioration such as occurrence of color misregistration.

  The present invention has been made in view of the above circumstances, and provides a transfer device capable of improving the running stability of the intermediate transfer belt by reducing the primary transfer pressure at which the primary transfer member contacts the image carrier. The purpose is to provide. Another object of the present invention is to provide an image forming apparatus that includes the transfer device and can improve the image quality by preventing the occurrence of color misregistration.

In order to achieve the above object, the present invention employs the following technical means.
The first means of the present invention includes an endless belt-shaped intermediate transfer member that is arranged to face a plurality of image carriers arranged side by side and is stretched by a plurality of rollers, and the intermediate transfer to the image carrier. and a primary transfer member that is placed through the body, one of said plurality of rollers is a driving roller for driving the intermediate transfer body, the ability to configure the secondary transfer region In the transfer device having the function of the opposing portion of the cleaning unit that is in contact with the intermediate transfer member, the primary transfer member is a metal roller, and the image carrier is supported with respect to the image carrier. The intermediate transfer member is arranged to be offset from the contact position between the intermediate transfer member and the intermediate transfer member on the downstream side in the transport direction of the intermediate transfer member.

According to a second means of the present invention, in the transfer device of the first means, the intermediate transfer member is an intermediate transfer belt using a resin film.
The third aspect of the present invention, in the transfer apparatus of the first or second means, said offset, you characterized in that it is a 6 to 10 mm.

According to a fourth means of the present invention, in the transfer device of any one of the first to third means, the primary transfer pressure of the primary transfer member is 12 N / m or less, respectively.
The fifth means of the present invention is characterized in that in the transfer device of any one of the first to third means, at least two biases to be applied to the primary transfer member are shared. .

According to a sixth means of the present invention, in the transfer device of any one of the first to fifth means, the primary transfer pressure is set to be smaller in the primary transfer area arranged near the secondary transfer area. Features.
According to a seventh aspect of the present invention, in the transfer device according to any one of the first to sixth means, the transfer device includes a secondary transfer member disposed to face the drive roller via the intermediate transfer body. It shall be the feature.

According to an eighth means of the present invention, in the transfer device of any one of the first to seventh means, a tension roller that applies tension to the intermediate transfer member separately from the drive roller in the plurality of rollers. It is characterized by having.
According to a ninth means of the present invention, in the transfer device of the eighth means, the plurality of image carriers and the primary transfer member are downstream of the driving roller in the transport direction of the intermediate transfer member, and A contact with the intermediate transfer member at a position upstream of the tension roller.
According to a tenth means of the present invention, in the transfer device of the eighth or ninth means, the intermediate transfer member is located downstream of the drive roller and upstream of the tension roller and downstream of the tension roller. It is stretched so as to extend in the horizontal direction in the region upstream of the drive roller .
The eleventh means of the present invention is that the “plurality of image carriers arranged side by side” and the “primary image formed by superimposing images formed on the image carriers arranged opposite to the plurality of image carriers” In the image forming apparatus, comprising: an intermediate transfer body to be transferred; and a transfer device having a means for secondary transfer of an image transferred onto the intermediate transfer body and secondarily transferred onto the transfer material. As described above, a transfer device of any one of the first to tenth means is provided.

As mentioned above, as a factor disturbing the running stability of the intermediate transfer belt,
(1) Paper passing state in the secondary transfer area,
(2) Contact pressure of the belt cleaning member,
(3) Primary transfer pressure,
In the transfer apparatus of the present invention, the driving roller of the intermediate transfer belt has both the opposing roller in the secondary transfer region and the roller facing the belt cleaning member, so that the above (1), (2 ) Can be solved together. In the present invention, the primary transfer member is offset from the image carrier in the transport direction of the intermediate transfer member, whereby the primary transfer member is offset from the image carrier facing position. Since the primary transfer pressure is reduced, the above problem (3) can be solved.

In the transfer device of the present invention, the primary transfer member is a metal roller, so that the cost can be reduced as compared with the conventional foam roller or rubber roller.
In the present invention, the pre-discharge in front of the primary transfer region can be prevented by setting the offset direction of the primary transfer member to the downstream side in the conveyance direction of the intermediate transfer belt. If a discharge occurs between the image carrier and the intermediate transfer belt before the primary transfer starts, the image is disturbed and the image quality deteriorates. By applying a primary transfer bias from the downstream side of the intermediate transfer belt. This can be prevented.

If the primary transfer pressure is set to a high pressure, the running performance of the intermediate transfer belt is disturbed as described above. Therefore, in the present invention, the intermediate transfer belt running stability can be ensured by setting the primary transfer pressure to 12 N / m or less.
Further, in the present invention, by sharing one part or all of the primary transfer bias, the power source can be shared, and the cost of the entire image forming apparatus can be reduced.

  In an image forming apparatus that uses the primary transfer member on the belt loose side, the influence of the primary transfer pressure on the belt running performance increases as the position is closer to the secondary transfer region, that is, the upstream side near the drive unit. On the other hand, as the primary transfer region becomes downstream, the transferability decreases. Therefore, in order to secure the transferability at the downstream position, it is necessary to improve the primary transfer bias or the primary transfer pressure. Therefore, in the present invention, the primary transfer pressure is set to be lower for the primary transfer member disposed near the drive unit, that is, the upstream side in the conveyance direction of the intermediate transfer belt, and set to be higher for the downstream side. Transferability can be ensured while reducing adverse effects on belt running stability due to the pressure of the next transfer.

  Since the image forming apparatus of the present invention includes the transfer device having the above-described configuration and effects, a high-quality image (single color, multicolor, full color image) having good transferability and no color shift can be formed. Can do.

  Hereinafter, the configuration, operation, and operation of the present invention will be described in detail based on the illustrated embodiments.

  FIG. 1 shows a schematic configuration example of the entire image forming apparatus. Reference numerals 1Y, 1M, 1C, and 1Bk in the figure are cylindrical photosensitive drums having a diameter of 24 mm arranged along the intermediate transfer belt 50 of the transfer device 5, and a peripheral speed of 140 mm / mm in the direction of the arrow in the figure. Rotating at s. Roller-shaped chargers 2Y, 2M, 2C, and 2Bk as charging means are pressed against the surfaces of the photosensitive drums 1Y, 1M, 1C, and 1Bk, and are rotated by the rotation of the photosensitive drums 1Y, 1M, 1C, and 1Bk. The photosensitive drums 1Y, 1M, 1C, and 1Bk are uniformly rotated by a high-voltage power supply (not shown) and a bias in which an alternating current (AC) is superimposed on the DC is applied to the photosensitive drums 1Y, 1M, 1C, and 1Bk. It is charged to 500V.

  Subsequently, the photosensitive drums 1Y, 1M, 1C, and 1Bk are exposed to light L corresponding to image information by an exposure unit 3 that is a latent image forming unit, and an electrostatic latent image is formed. This exposure step is performed by the exposure means 3 comprising a laser beam scanner using, for example, a laser diode, an optical deflector, and a scanning imaging optical system. In addition, a light emitting diode (LED) array and an imaging element array are provided. You may carry out with the line-shaped optical writing apparatus etc. which combined.

The developing means of the present embodiment is a one-component contact developing device, and is provided with a yellow developing device 4Y, a magenta developing device 4M, a cyan developing device 4C, a black developing device corresponding to each of the photosensitive drums 1Y, 1M, 1C, 1Bk. The developing unit 4Bk is composed of four developing units, and the electrostatic latent images on the photosensitive drums 1Y, 1M, 1C, and 1Bk are visualized as toner images by a predetermined developing bias supplied from a high voltage power source (not shown). To do.
The photoconductor cleaning units 6Y, 6M, 6C, and 6Bk clean the transfer residual toner on the surface of each photoconductor drum. Reference numeral 61 denotes a blade provided in each of the photoconductor cleaning units 6Y, 6M, 6C, and 6Bk.

  The four photosensitive drums 1Y, 1M, 1C, and 1Bk are arranged in parallel along the intermediate transfer belt 50 of the transfer device 5, and yellow (Y), magenta (M), and cyan (C ) And black (Bk) in this order, and a visible image of each color is sequentially superimposed and transferred onto the intermediate transfer belt 50 to form a full-color image.

  The intermediate transfer belt 50 is stretched by a driving roller (having functions of a secondary transfer counter roller and a cleaning counter roller) 51, primary transfer rollers 53Y, 53M, 53C, 53Bk, and a tension roller 52. The drive roller 51 is rotated by a drive motor (not shown) so as to be rotated in the direction of the arrow in the figure. As belt tension, 15 N / m on one side is pressed by a spring (not shown) via bearings on both sides of the rotating shaft of the tension roller 52 that rotates in a driven manner.

  In the present embodiment, the driving roller 51 is made of a surface layer made of polyurethane rubber (thickness: 0.3 to 1 mm). However, a roller in which a thin layer coating (thickness 0.05 to 0.1 mm) is applied to a metal roller has a small diameter change due to temperature, and is more preferable for use as a driving roller.

  As the primary transfer member, a conductive blade, a conductive sponge roller, a metal roller, or the like can be used. In this embodiment, primary transfer rollers 53Y, 53M, 53C, and 53Bk made of stainless steel (SUS) having a diameter of 8 mm are used. Using. The primary transfer rollers 53Y, 53M, 53C, and 53Bk are offset from the photosensitive drums 1Y, 1M, 1C, and 1Bk arranged opposite to each other by 6 to 10 mm on the downstream side in the conveyance direction of the intermediate transfer belt 50. In this embodiment, the primary transfer rollers 53Y, 53M, 53C, and 53Bk are disposed in pressure contact with the intermediate transfer belt 50 by a spring or the like at a position 8 mm downstream, and are driven to rotate with respect to the conveyance of the intermediate transfer belt 50. The arrangement positions of the primary transfer rollers 53Y, 53M, 53C, 53Bk in the height direction will be described later.

  A predetermined transfer bias +500 to +800 V is commonly applied to the photosensitive drums 1Y, 1M, 1C, and 1Bk by a single high-voltage power source (not shown) to the primary transfer rollers 53Y, 53M, 53C, and 53Bk. Then, a transfer electric field is formed through the toner image to transfer the toner images on the photosensitive drums 1Y, 1M, 1C, and 1Bk to the intermediate transfer belt 50.

Reference numeral 55 in FIG. 1 denotes an intermediate transfer belt cleaning unit, which performs cleaning by scraping off transfer residual toner on the intermediate transfer belt 50 with a blade 55a.
Each roller that stretches the intermediate transfer belt 50 is supported from both sides of the intermediate transfer belt 50 via bearings by an intermediate transfer belt unit side plate (not shown) of the transfer device 5.

  Materials used for the intermediate transfer belt 50 include PVDF (polyvinylidene fluoride), ETEF (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), TPE (thermoplastic elastomer), and carbon black. An endless belt made of a resin film in which a conductive material such as the above is dispersed can be used. As an example, in this example, a resin film having a single layer structure in which carbon black is added to PC (polycarbonate) and having a thickness adjusted to 140 μm was used.

Further, as the resistance of the intermediate transfer belt 50, a volume resistivity of 10 ⁸ to 10 ¹¹ Ω · cm and a surface resistivity of 10 ⁸ to 10 ¹¹ Ω / □ in an environment of 22 ° C. and 55% RH (both manufactured by Mitsubishi Chemical Corporation) Measurement with HirestaUP MCP-HT450, thickness 140 μm, applied voltage 500 V, applied time 10 seconds) are desirable. When the volume resistivity and surface resistivity of the intermediate transfer belt 50 exceed the above-described ranges, the intermediate transfer belt 50 is charged. Therefore, the set voltage value of the primary transfer bias is set higher as it goes downstream in the image forming order. Therefore, it is difficult to use a single power supply for the primary transfer unit. This is because the discharge potential generated in the transfer process, the transfer material peeling process, etc. increases the charged potential on the surface of the intermediate transfer belt 50 and makes self-discharge difficult. It is necessary to provide it. Also, if the volume resistivity and surface resistivity are below the above ranges, the charging potential decays faster, which is advantageous for static elimination by self-discharge. However, since the current during transfer flows in the surface direction, the toner splatters. Will occur. Therefore, the volume resistivity and the surface resistivity of the intermediate transfer belt 50 in this embodiment must be within the above ranges.

A reference numeral 54 in FIG. 1 denotes a secondary transfer roller disposed to face the driving roller 51 with the intermediate transfer belt 50 in the secondary transfer region. The secondary transfer roller 54 is configured by covering a metal core such as SUS with an elastic body such as urethane adjusted to a resistance value of 10 ⁶ to 10 ¹⁰ Ω with a conductive material. Here, if the resistance value of the secondary transfer roller 54 exceeds the above range, it becomes difficult for the current to flow. Therefore, in order to obtain the required transfer property, a higher voltage must be applied, which increases the power supply cost. Invite. In addition, since it is necessary to apply a high voltage, discharge occurs in the gap before and after the transfer nip portion, and white spots are lost on the halftone image due to the discharge. This is remarkable in a low temperature and low humidity environment (for example, 10 ° C., 15% RH). On the contrary, when the resistance value of the secondary transfer roller 54 falls below the above range, a plurality of color image portions (for example, three-color superimposed images of Y, M, and C) and a single color image portion (for example, black) existing on the same image. The transferability with other characters cannot be compatible. This is because the resistance value of the secondary transfer roller 54 is low, so that a sufficient current flows to transfer a single color image portion with a relatively low voltage. This is because a voltage value higher than the optimum voltage is required for the portion, and setting a voltage capable of transferring a plurality of color image portions results in excessive transfer current in a monochromatic image, resulting in a reduction in transfer efficiency.

  The resistance value of the secondary transfer roller 54 is measured by installing the secondary transfer roller 54 on a conductive metal plate and 4.9 N / m on one side on both ends of the core metal (total of 9.8 N / m on both sides). It calculated from the value of the electric current which flows when the voltage of 1 kV is applied between a metal core and the said metal plate in the state which applied this load.

  A sheet feeding cassette 7 on which a transfer material P such as transfer paper is loaded is disposed at the lower part of the image forming apparatus. The transfer material P is fed one by one by a sheet feeding / conveying roller 8 and a separation roller 9, and a registration roller. 10, the toner image leading edge on the surface of the intermediate transfer belt 50 is fed in time to reach the secondary transfer position, and a predetermined transfer bias is applied to the secondary transfer roller 54 by a high voltage power source (not shown). The toner image on the transfer belt 50 is transferred to the transfer material P. The transfer material P to which the toner image has been transferred is separated from the intermediate transfer belt 50 by the curvature of the driving roller 51 that also serves as a secondary transfer counter roller and the rigidity of the transfer material itself, and is conveyed to the fixing unit 11 and transferred to the transfer material P. The transferred toner image is fixed by a pair of fixing rollers (a heating roller 11a and a pressure roller 11b) of the fixing unit 11, and then discharged to a paper discharge unit (not shown).

  In the image forming apparatus according to the present exemplary embodiment, the monochrome mode for forming an image of any one of yellow (Y), magenta (M), cyan (C), and black (Bk), yellow (Y), magenta ( M), Cyan (C), Black (Bk) Two-color mode in which images of two colors are overlapped, Yellow (Y), Magenta (M), Cyan (C), Black (Bk) It has a three-color mode in which images of three colors are superimposed and a full-color mode in which the above-described four-color superimposed images are formed, and these modes can be specified and executed by an operation unit (not shown). is there.

Further, in this embodiment, the process speed at the time of fixing is changed depending on the type of the transfer material P. Specifically, when a transfer material having a basis weight of 110 g / m ² or more is used, the process speed is set to half speed, and the transfer material is a normal process in the fixing nip formed by the fixing roller pair of the fixing unit 11. The toner image can be secured by passing through twice the speed.

  In the image forming apparatus configured as described above, the primary transfer pressure is made variable by changing the height-direction positions of the primary transfer members (primary transfer rollers) 53Y, 53M, 53C, and 53Bk. A color image pattern was printed while changing the transfer pressure stepwise, and evaluation was performed by visual image confirmation. As an example of the fifth means described above, the primary transfer rollers 53Y, 53M, 53C, and 53Bk were made to have the same height, and the pressure was changed while the primary transfer pressure was set almost uniformly. As shown in FIG. 1, a good image was obtained when the primary transfer pressure was 12 N / m or less, more preferably 10 N / m or less.

  Next, as an example of the seventh means, when the primary transfer pressure by each primary transfer member (primary transfer roller) 53Y, 53M, 53C, 53Bk is set non-uniformly and image confirmation is performed in the same manner, As shown in Table 2 below, a good image was obtained by setting the primary transfer pressure smaller for the primary transfer member disposed near the secondary transfer region on the upstream side in the conveyance direction of the intermediate transfer belt. .

  As described above based on the embodiments, in the transfer device 5 of the present invention, the driving roller 51 of the intermediate transfer belt 50 has a configuration in which the opposing roller in the secondary transfer region and the roller facing the belt cleaning member are combined. Accordingly, the influence of the sheet passing state in the secondary transfer region, the contact pressure of the belt cleaning blade 55a, and the like is small, and the running stability of the intermediate transfer belt 50 can be ensured. In the present invention, the primary transfer members (primary transfer rollers) 53Y, 53M, 53C, and 53Bk are offset from the photosensitive drums 1Y, 1M, 1C, and 1Bk in the conveyance direction of the intermediate transfer belt 50. As a result, the primary transfer rollers 53Y, 53M, 53C, and 53Bk are offset from the positions facing the photosensitive drums 1Y, 1M, 1C, and 1Bk, and the primary transfer pressure is reduced. Disturbance in running stability of the intermediate transfer belt 50 due to pressure can also be prevented.

In the transfer device 5 of the present invention, the primary transfer rollers 53Y, 53M, 53C, and 53Bk are made of metal rollers, so that the cost can be reduced as compared with the conventional foaming rollers and rubber rollers.
In the present invention, the pre-discharge in front of the primary transfer region can be prevented by setting the offset direction of the primary transfer rollers 53Y, 53M, 53C, and 53Bk to the downstream side in the transport direction of the intermediate transfer belt 50. If a discharge occurs between the photosensitive member and the intermediate transfer belt before the primary transfer starts, the image is disturbed and the image quality deteriorates. However, by applying a primary transfer bias from the downstream side of the intermediate transfer belt 50. This can be prevented.

If the primary transfer pressure is set to a high pressure, the running performance of the intermediate transfer belt 50 is disturbed as described above. Therefore, in the present invention, the running stability of the intermediate transfer belt 50 can be ensured by setting the primary transfer pressure to 12 N / m or less, more preferably 10 N / m or less.
Further, in the present invention, by sharing a part or all of the primary transfer bias applied to the primary transfer rollers 53Y, 53M, 53C, and 53Bk, the power source can be shared, and the cost of the entire image forming apparatus is reduced. can do.

  As shown in FIG. 1, in an image forming apparatus that uses the primary transfer rollers 53Y, 53M, 53C, and 53Bk on the loose side of the intermediate transfer belt 50, in the vicinity of the secondary transfer region, that is, on the upstream side in the transport direction of the intermediate transfer belt 50. The closer to the drive roller 51, the greater the influence of the primary transfer pressure on the belt running performance. On the other hand, as the primary transfer region becomes downstream, the transferability decreases. Therefore, in order to secure the transferability at the downstream position, it is necessary to improve the primary transfer bias or the primary transfer pressure. Therefore, in the present invention, the primary transfer pressure is set to a lower value for the primary transfer roller disposed near the drive unit, that is, the upstream side in the conveyance direction of the intermediate transfer belt 50, and set to a higher value for the downstream side. Transferability can be ensured while reducing adverse effects on belt running stability due to primary transfer pressure.

  Since the image forming apparatus of the present invention includes the transfer device 5 having the above-described configuration and effects, a high-quality image (single color) in which the running of the intermediate transfer belt 50 is stable, transferability is good, and there is no color misregistration. Multicolor, full-color images).

1 is a schematic configuration diagram of an image forming apparatus showing an embodiment of the present invention.

Explanation of symbols

1Y, 1M, 1c, 1Bk: photosensitive drum (image carrier)
2Y, 2M, 2C, 2Bk: Charger (charging means)
3: Exposure means 4Y, 4M, 4C, 4Bk: Developer (developing means)
5: Transfer device 6Y, 6M, 6C, 6Bk: Photoconductor cleaning unit 7: Paper feed cassette 8: Paper feed roller 9: Separation roller 10: Registration roller 11: Fixing means 50: Intermediate transfer belt (intermediate transfer body)
51: Driving roller 52: Tension roller 53Y, 53M, 53C, 53Bk: Primary transfer roller (primary transfer member)
54: Secondary transfer roller (secondary transfer member)
55: Intermediate transfer belt cleaning unit

Claims (11)

Is arranged to face the plurality of image carriers arranged in parallel, is placed through the endless belt-shaped intermediate transfer member is stretched by a plurality of rollers, said intermediate transfer member to said image bearing member 1 A second transfer member,
One of the plurality of rollers is a drive roller for driving the intermediate transfer member, and functions as a secondary transfer region and a function of a facing portion of the cleaning unit that contacts the intermediate transfer member. In a transfer device having a configuration that combines
The primary transfer member is a metal roller, and is offset from the contact position between the image carrier and the intermediate transfer member with respect to the image carrier and is offset downstream in the transport direction of the intermediate transfer member. A transfer apparatus characterized by being made. The transfer device according to claim 1,
The transfer apparatus, wherein the intermediate transfer member is an intermediate transfer belt using a resin film. In the transfer device according to claim 1 or 2,
The transfer apparatus , wherein the offset is 6 to 10 mm . The transfer device according to any one of claims 1 to 3,
The primary transfer pressure of the primary transfer member is 12 N / m or less, respectively . The transfer device according to any one of claims 1 to 3 ,
A transfer apparatus characterized in that at least two or more biases applied to the primary transfer member are shared . In the transfer device according to any one of claims 1 to 5 ,
A transfer apparatus, wherein a primary transfer pressure is set to be smaller in a primary transfer area disposed near a secondary transfer area . In the transfer device according to any one of claims 1 to 6,
A transfer device comprising a secondary transfer member disposed opposite to the driving roller via the intermediate transfer member . In the transfer device according to any one of claims 1 to 7,
A transfer apparatus comprising: a tension roller that applies tension to the intermediate transfer member, in addition to the drive roller, among the plurality of rollers . The transfer device according to claim 8.
The plurality of image carriers and the primary transfer member are in contact with the intermediate transfer member at positions downstream of the driving roller and upstream of the tension roller with respect to the conveyance direction of the intermediate transfer member. Characteristic transfer device . The transfer device according to claim 8 or 9,
The intermediate transfer member is stretched so as to extend horizontally in a region downstream of the drive roller and upstream of the tension roller and in a region downstream of the tension roller and upstream of the drive roller. A transfer device characterized by . A plurality of image carriers arranged side by side;
An intermediate transfer member that is arranged opposite to the plurality of image carriers and on which the images formed on the image carriers are primarily transferred and superimposed;
An image forming apparatus comprising: a transfer device having a means for secondarily transferring an image primarily transferred onto the intermediate transfer member onto the transfer material;
An image forming apparatus comprising the transfer device according to claim 1 as the transfer device.

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