JP3733270B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus of an intermediate transfer system and a development simultaneous cleaning system.
[0002]
[Prior art]
In recent years, color needs have been increasing in image forming apparatuses such as copying machines and laser beam printers. As a color image forming method, the electrophotographic method is said to be the most excellent in terms of image forming speed and the like.
[0003]
In electrophotographic image forming apparatuses, miniaturization, high functionality, and colorization have been promoted, but on the other hand, there are increasing demands for improved reliability, system deployment, maintenance-free, and friendly to people and the environment. Various image forming apparatuses have been proposed to meet these requirements.
[0004]
Recently, the intermediate transfer method is becoming the mainstream among these image forming apparatuses. This method has advantages such as not selecting a transfer material and excellent color registration (low color shift). Furthermore, in order to increase the speed of color image output, a plurality of (for example, four) photosensitive drums (photosensitive members) are stacked, and a toner image is sequentially transferred onto the intermediate transfer member. There has been proposed an image forming apparatus that collectively transfers toner images onto a transfer material.
[0005]
Further, in order to cope with ecology, a method of reducing the amount of toner to be discarded by collecting and reusing the transfer residual toner, for example, a method that eliminates cleaning means such as a simultaneous development cleaning method (hereinafter referred to as “cleanerless”). ) Have been put into practical use, and there is an advantage that the image forming apparatus itself can be miniaturized by adopting such a system.
[0006]
In the case of adopting the above-described cleanerless system, it can be satisfactorily achieved by using the spherical toner produced in the polymerization method. The reason why the spherical toner produced by the polymerization method can achieve the toner-reusing process by the cleaner-less process or the simultaneous development cleaning will be described below, focusing on the adhesion force between the toner and the photosensitive drum.
[0007]
When the toner adheres to the photosensitive drum due to a developing bias or a latent image potential in the developing process, there are a mirror force and a van der Waals force as main forces acting on the toner in contact with the surface of the photosensitive drum. The mirror power greatly depends on the charge amount and its distance. The surface of the pulverized toner produced by conventional pulverization has irregularities, and the convex portions are intensively charged by frictional charging. On the other hand, since the surface of the polymerized toner produced by the polymerization method has a spherical shape or a shape close to a spherical shape, the surface is uniformly charged.
[0008]
In the pulverized toner, since the convex portions are in contact with each other and a lot of electric charges exist in a very close region, the mirror power increases. However, when it is spherical like a polymerized toner, the contact state is almost point-like, and the amount of charge in the adjacent area is small, and the mirror power is smaller than the pulverized toner, so the van der Waals force is more recent. It becomes very large when the area is affected and touches on a flat surface.
[0009]
Further, when pulverized toner is used, many toners are in contact with the above-mentioned convex portions, and in this case, the van der Waals force becomes very large. On the other hand, since the surface shape of the polymerized toner is spherical, the toner comes into contact at almost points. Therefore, the van der Waals force is also smaller for the polymerized toner.
[0010]
For the above reasons, in the case of a nearly spherical polymerized toner, the reflection force on the photosensitive drum, van der Waals force, that is, the adhesion force is reduced, transfer residual toner in transfer is small, and the toner collecting effect at the time of simultaneous development cleaning Becomes larger, and cleaner-free and simultaneous development cleaning becomes possible.
[0011]
FIG. 3 shows an example of an image forming apparatus using the intermediate transfer method and the development simultaneous cleaning method.
[0012]
The image forming apparatus shown in the figure includes four image forming units UM (magenta), UC (cyan), UY (yellow), and UBk (black) that form toner images of four different colors. An intermediate transfer belt 31 is disposed so as to pass through these image forming units.
[0013]
These four image forming units have the same configuration, and hereinafter, the configuration of the cyan image forming unit UC will be described as a representative.
[0014]
The image forming unit UC has a cylindrical electrophotographic photosensitive member (photosensitive drum) 11 whose surface layer is made of OPC (organic optical semiconductor), for example, as an image carrier, and the photosensitive drum 11 rotates in the direction of arrow a. Driven. A primary charger 12 is installed in contact with the photosensitive drum 11. An exposure unit 13 exposes the surface of the photosensitive drum 11 to the primary charger 12 on the downstream side in the rotation direction of the photosensitive drum 11. Reference numeral 14 denotes a developing unit, which is installed on the further downstream side of the exposure position of the photosensitive drum 11 so as to be adjacent to the photosensitive drum 11. A toner hopper (toner supply unit) 15 supplies a necessary amount of toner to the developing unit 14 via the toner buffer 16 as needed.
[0015]
Reference numeral 21 denotes an intermediate transfer belt as an intermediate transfer member. The intermediate transfer belt 21 is stretched by a drive roller 22, a support roller 23, and a backup roller 24, and is rotationally driven in the direction of arrow R21 by the rotation of the drive roller 22 in the direction of arrow 22 while contacting the photosensitive drum 11. The intermediate transfer belt 21 is sandwiched between the transfer blade 25, and thereby, a primary transfer nip portion (primary transfer portion) N between the photosensitive drum 11 and the intermediate transfer belt 21.₁ Is formed. Reference numeral 26 denotes a secondary transfer roller, which is installed against the backup roller 24, and has a secondary transfer nip portion (secondary transfer portion) N between the intermediate transfer belt 21 and the secondary transfer roller.₂ Is forming.
[0016]
Reference numeral 31 denotes a paper feed cassette that stores the transfer material P, and reference numeral 32 denotes a secondary transfer nip portion N that transfers the transfer material P fed and conveyed by a feeding and conveying means (not shown).₂ It is a registration roller to be supplied to. A fixing device 41 is arranged in the vicinity of the driving roller 22 of the intermediate transfer belt 21. Reference numeral 51 denotes an intermediate transfer member cleaner.
[0017]
Reference numeral 17 denotes a pre-exposure (static elimination) lamp, which is disposed between the transfer blade 25 and the primary charger 12.
[0018]
The operation of the image forming apparatus configured as described above will be described using an image forming unit UC for forming a cyan toner image. The operation of other image forming units is the same.
[0019]
The photosensitive drum 11 is rotationally driven in the direction of arrow R11, and after the surface is uniformly negatively charged by the primary charger 12, it is exposed by the exposure device 13 and corresponds to a color separation image obtained by color separation of the input document. An electrostatic latent image is formed. The developing device 14 performs reversal development using negatively charged toner, and forms a toner image corresponding to the electrostatic latent image on the surface of the photosensitive drum 11. The toner image formed on the surface of the photosensitive drum 11 is primarily transferred by the transfer blade 25 onto the intermediate transfer belt 21 rotating at the same speed as the photosensitive drum 11.
[0020]
The above operation is performed in each image forming unit, and the toner images formed on the respective photosensitive drums 11 are sequentially sequentially transferred to the intermediate transfer belt 21 in a multiple transfer manner. In the case of the full color mode, the image is transferred to the intermediate transfer belt 21 in the order of M (magenta), C (cyan), Y (yellow), and Bk (black). Necessary color toners are sequentially transferred onto the intermediate transfer belt 21 in the same process as described above. The multiple transferred composite toner image is secondarily transferred by the secondary transfer roller 26 to the transfer material P supplied by the registration roller 32 or the like. The transfer material P onto which the toner image has been secondarily transferred is heated and pressurized by the fixing device 41 to fix the toner image on the surface.
[0021]
On the other hand, after the primary transfer of the toner image, the potential of the photosensitive drum 11 is uniformly adjusted by the pre-exposure lamp 17, and the primary transfer residual toner remaining on the surface is recharged by the primary charger 12, and then the developing unit 14. In the developing operation, the toner is collected in the developing device and used again for image formation. In addition, the secondary transfer residual toner adhering to the surface of the intermediate transfer belt 31 that has finished the secondary transfer onto the transfer material P is removed and collected by the intermediate transfer body cleaner 51 having the cleaning blade 51a. .
[0022]
[Problems to be solved by the invention]
In the image forming apparatus having the above-described configuration, that is, an image forming apparatus having a plurality of image forming units using a cleaner-less system that collects transfer residual toner on the photosensitive drum 11 by the developing device 14 and adopting an intermediate transfer method. When the cleaning blade type intermediate transfer member cleaner 51 is used, an excessive load is applied to the intermediate transfer belt 21, and there is a problem that the torque for driving the intermediate transfer belt 21 is increased. When this torque is increased, the image of the intermediate transfer belt 21 becomes unstable, or the intermediate transfer belt 21 is shifted to one side in the main scanning direction (the width direction of the intermediate transfer belt), resulting in a disordered registration. There arises a problem that the image forming apparatus cannot be used due to the failure or the driving of the intermediate transfer belt 21 is stopped.
[0023]
Further, in the image forming apparatus employing the intermediate transfer method, the arrangement position of the intermediate transfer body cleaner 51 is limited between the driving roller 22 and the backup roller 24. In this case, since the disposition position is close to the fixing device 41, the waste toner collected in the intermediate transfer body cleaner 51 is hardened due to the influence of radiant heat from the fixing device 41, thereby causing problems such as defective conveyance of the waste toner. May occur.
[0024]
Furthermore, by providing the intermediate transfer body cleaner 51, it is necessary to provide a waste toner collection container and a waste toner transport path for collecting waste toner, which increases the size of the entire image forming apparatus and increases costs. Cause problems.
[0025]
The present invention has been made in view of the above-described circumstances, and provides a good intermediate transfer member cleaning without applying an excessive load to the intermediate transfer member and without being affected by radiant heat from the fixing device. Further, an object of the present invention is to provide an image forming apparatus that can use all toner for image formation without generating waste toner.
[0026]
[Means for Solving the Problems]
  The present invention according to claim 1A plurality of image forming units having image carriers are arranged along the moving direction of the intermediate transfer member, and toner images formed on the image carriers by the developing means of the image forming units are used as the image carriers. And sequentially transfer the toner image on the intermediate transfer member onto the transfer material via the secondary transfer portion. In the image forming apparatus that performs secondary transfer and collects and recycles residual toner remaining on the image carrier by the developing unit, the secondary transfer unit along the moving direction of the intermediate transfer body And further upstream of the most upstream image forming unit of the plurality of image forming units,Abuttingly disposed on the intermediate transfer member;The transfer residual toner remaining on the intermediate transfer member is charged with a polarity opposite to that of the toner at the time of primary transfer.With elastic rollerA charging unit is provided, and the most upstream image forming unit is an image forming unit for forming a black toner image.
[0027]
  According to a second aspect of the present invention, in the image forming apparatus of the first aspect,The elastic roller isVolume resistivity is 10⁵-10¹³Ω · cmAbutting against the intermediate transfer member at a total pressure of 0.98 to 2.94 N (100 to 300 g).It is characterized by that.
[0028]
  The present invention according to claim 3 provides1 or 2In the image forming apparatus,Of the plurality of image forming units, the image forming unit that first primarily transfers a toner image onto the intermediate transfer member is an image forming unit that forms the black toner image.
[0037]
According to the above-described configuration, it is possible to realize good cleaning of the intermediate transfer member without applying an excessive load to the intermediate transfer member and without being affected by the radiant heat from the fixing device. In addition, it is possible to use all the toner for image formation without generating waste toner, and it becomes unnecessary to provide a special means for collecting waste toner, so that low running cost and space saving can be achieved. Can be realized.
[0038]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0039]
<Embodiment 1>
FIG. 1 shows an example of an image forming apparatus according to the present invention. The image forming apparatus shown in the figure is a four-color full-color image forming apparatus of a cleanerless type using an intermediate transfer member, and the figure is a longitudinal sectional view showing a schematic configuration thereof.
[0040]
More specifically, in the present embodiment, a plurality of image forming units are provided, and an intermediate transfer belt (intermediate transfer member) is disposed vertically through each image forming unit, and is formed by a polymerization method as described above. An image forming process method is adopted in which the toner is collected at the same time as the development by a cleanerless method using the spherical toner.
[0041]
Each image forming unit has a structure in which members for charging, exposure, development, and pre-exposure are integrated with an image carrier as a center. In the image forming apparatus shown in FIG. Black, magenta, cyan, and yellow image forming units UBk, UM, UC, and UY are arranged in order from the upstream side in the rotation direction. This order is the order when the toner image is primarily transferred onto the intermediate transfer belt 21. The configuration of each image forming unit UBk, UM, UC, UY is basically the same. Hereinafter, an example of the black image forming unit UBk that has a characteristic action in the present invention will be described.
[0042]
The image forming unit UBk has a cylindrical electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 11 as an image carrier. The photosensitive drum 11 is formed by providing a photosensitive layer of OPC (organic photoconductor) on the surface of a drum base body in which a conductive member such as aluminum is formed in a cylindrical shape. The photosensitive drum 11 is rotationally driven in the direction of arrow R11 by a driving unit (not shown). Reference numeral 12 denotes a primary charger having a primary charging roller 12a that comes into contact with the surface of the photosensitive drum 11, and uniformly charges the surface of the photosensitive drum 11 to a predetermined negative potential. Reference numeral 13 denotes an exposure unit that exposes the image portion with light information corresponding to each color separation image obtained by color-separating the input image on the surface of the photosensitive drum 11 uniformly charged by the primary charger 12. Reference numeral 14 denotes a developing device (developing means) installed further downstream than the exposure position of the photosensitive drum 11. The developing device 14 contains toner generated by a polymerization method and having a negatively charged characteristic as a developer. A toner hopper 15 supplies a necessary amount of toner to the developing device 14 as needed via the toner buffer 16.
[0043]
Reference numeral 21 denotes an intermediate transfer belt as an intermediate transfer member, which is stretched around three rollers. The three rollers are a drive roller 22, a support roller 23, and a muck-up roller 24. The intermediate transfer belt 21 has a volume resistivity of 10^Three -10^Four The volume resistivity is 10 as a dielectric layer on the surface of Ω · cm urethane rubber.^Four A flexible endless belt in which a PTFE layer (polytetrafluoroethylene layer) of Ω · cm or more is formed, or a flexible endless belt in which carbon black for resistance adjustment is dispersed in polyimide resin ( Volume resistivity 10^Ten-10¹⁴Ω · cm). The intermediate transfer belt 21 is rotationally driven in the arrow R21 direction as the driving roller 22 rotates in the arrow R22 direction.
[0044]
A primary transfer blade 25 is disposed inside the intermediate transfer belt 21. The primary transfer blade 25 has a base material with a volume resistivity of 10⁹ -10¹¹A portion of the surface layer that is formed of a semiconductor layer of Ω · cm and that contacts the back surface of the intermediate transfer belt 21 has a low surface roughness and a low coefficient of friction and is excellent in wear resistance, such as a fluororesin, Those composed of nylon resin or the like are suitable. The primary transfer blade 25 presses the intermediate transfer belt 21 from the back side to the surface of the photosensitive drum 11, and a primary transfer nip portion (primary transfer portion) N between the intermediate transfer belt 21 and the photosensitive drum 11.₁ Is forming.
[0045]
In each of the image forming units UBk, UM, UC, UY, the toner images of the respective colors formed on the photosensitive drum 11 are primarily transferred in the order of black, magenta, cyan, and yellow onto the intermediate transfer belt 21 by the respective transfer blades 25. And superimposed on the intermediate transfer belt 21. The toner images thus multiplex-transferred onto the intermediate transfer belt 21 are secondarily transferred onto the transfer material P all at once by the backup roller 24 and the secondary transfer roller 26. The transfer material P stored in the paper feed cassette 31 is transferred to a secondary transfer nip portion N by a feeding / conveying means (not shown), a registration roller 32, and the like.₂ It was supplied to.
[0046]
The transfer material P after the secondary transfer of the toner image is conveyed to a fixing device 41 where it is heated and pressed to fix the toner image on the surface. Thereby, a four-color full-color image is obtained.
[0047]
On the other hand, the surface of the photosensitive drum 11 after the primary transfer of the toner image is uniformly adjusted by the pre-exposure lamp 17, and the primary transfer residual toner remaining on the surface is negatively charged again by the primary charging roller 12. Thereafter, the image is collected in the developing device during the developing operation by the developing device 14 and again used for image formation.
[0048]
The charging unit 50 which is a part of the feature of the present invention is downstream of the backup roller 24 in the rotation direction of the intermediate transfer belt 21 and upstream of the black image forming unit UBk as the first image forming unit. Has been placed. The charging unit 50 removes the secondary transfer residual toner remaining on the surface of the intermediate transfer belt 21 without being transferred to the transfer material P during the secondary transfer, to the primary transfer nip portion N.₁ Thus, the toner is charged positively opposite to the polarity of the toner transferred to the intermediate transfer belt 21.
[0049]
The charging unit 50 includes a charging member 52 and a power source 53 that applies a bias to the charging member 52. The charging member 52 is constituted by an elastic roller having a three-layer structure of a low resistance sponge layer made of acrylic sponge, a resistance layer made of acrylic urethane, and a surface release layer made of a fluororesin in order from the inside. Volume resistivity is 10 for the resistive layer.^Five -10⁹ Ω · cm, surface release layer is 10¹²-10¹⁶Ω · cm, and the volume resistivity of the entire charging member is 10^Five -10¹³Ω · cm. Further, it is in contact with the intermediate transfer belt 21 with a total pressure of 0.98 to 2.94 N (100 to 300 g), and is driven in the rotation direction (arrow R21 direction) of the intermediate transfer belt 21 by a driving means (not shown). On the other hand, it is rotationally driven in the counter direction (arrow R52 direction). The contact pressure of the charging member 52 is 1/20 to 1/3 of the contact pressure required when the conventional cleaning blade is directly contacted with the intermediate transfer belt 21 for cleaning.
[0050]
The cleaning operation of the intermediate transfer belt 21 by the charging unit 51 having the above configuration will be described.
[0051]
Secondary transfer nip N sandwiched between the backup roller 24 and the secondary transfer roller 26₂ The secondary transfer residual toner remaining on the intermediate transfer belt 21 without being secondarily transferred from the intermediate transfer belt 21 to the transfer material P is subjected to a primary transfer nip portion N by a bias applied to the charging member 52 by the power source 53.₁ Thus, the toner is transferred to the positive polarity opposite to the polarity of the toner transferred from the photosensitive drum 11 to the intermediate transfer belt 21.
[0052]
The secondary transfer residual toner charged positively by the charging means 51 is electrostatically collected simultaneously with the primary transfer operation on the photosensitive drum 11 of the black image forming unit UBk which is the first image forming unit, and further the primary transfer is performed. After being charged negatively by the charging roller 12, it is collected in the developing unit during the developing operation by the developing unit 14, and then again used for image formation. Here, the secondary transfer residual toner remaining on the intermediate transfer belt 21 is a mixed color toner composed of four colors of yellow, magenta, cyan, and black. As reusable. Note that reusable means that no practical problem occurs even when used as black toner.
[0053]
As described above, the first embodiment has a plurality of image forming units UBk, UM, UC, and UY using a cleanerless system that collects the transfer residual toner on the photosensitive drum 11 by the developing device 14. In the image forming apparatus employing the intermediate transfer method, the secondary transfer residual toner on the intermediate transfer belt 21 is transferred to the primary transfer nip portion N on the intermediate transfer belt 21.₁ The intermediate transfer belt 21 has a charging unit 50 that is charged to a polarity opposite to the polarity of the toner transferred in step 1 and the color of the image forming unit that first forms a toner image on the intermediate transfer belt 21 is black. The intermediate transfer belt 21 can be satisfactorily cleaned without applying an excessive load to the fixing device 41 and without being affected by radiant heat from the fixing device 41, and not only the primary transfer residual toner but also the secondary transfer residual toner. Can be reused, and space saving and low running cost can be realized at the same time.
[0054]
<Embodiment 2>
The second embodiment will be described with reference to FIG.
[0055]
Also in the present embodiment, as in the first embodiment described above, the photosensitive drum 11 and four members are integrally formed by charging, exposing, developing, and pre-exposing members disposed around the photosensitive drum 11. The image forming units are arranged in the order of black, magenta, cyan, and yellow image forming units UBk, UM, UC, and UY. In addition, a spherical toner formed by a polymerization method is used as the toner, and an image is formed by a process in which a transfer residual toner on the photosensitive drum is simultaneously collected and developed by a developing device without a cleaner. Further, the toner images of the respective colors are primarily transferred onto the intermediate transfer belt 21 in a multiplexed manner, and these four color toner images are transferred to the transfer material P supplied from the registration roller 32 by the backup roller 24 and the secondary transfer roller 26. The image is transferred and fixed by the fixing device 41.
[0056]
Further, the secondary transfer nip N sandwiched between the backup roller 24 and the secondary transfer roller 26₂ The secondary transfer residual toner remaining on the intermediate transfer belt 21 without being secondarily transferred from the intermediate transfer belt 21 to the transfer material P is transferred by the charging means 50 to the primary transfer nip portion N.₁ Then, the toner is charged with a polarity opposite to that of the toner primarily transferred to the intermediate transfer belt 21 and then returned to the photosensitive drum 11 simultaneously with the primary transfer operation by the black image forming unit UBk as the first image forming unit. While being collected by the black developing device 14, it is used again for image formation.
[0057]
However, the difference from the first embodiment is that the yellow image forming unit UY as the fourth image forming unit and the secondary transfer nip N₂ The density detecting means 52 is provided opposite to the intermediate transfer belt 21. Further, the black image forming unit UBk as the first image forming unit has no black toner hopper or toner buffer, and the black developing unit 14 has a toner hopper 15 of three colors of magenta, cyan and yellow. It is connected.
[0058]
As the density detecting means 60, a light reflection type sensor (light sensor) is used, and its sensor surface 60a is parallel to the surface of the intermediate transfer belt 21 and is in the range of 1.0 to 10.0 mm from the surface of the intermediate transfer belt 21. It is arranged with a certain distance inside.
[0059]
The reason for adopting such a configuration is to stabilize the color reproducibility of black. Specifically, in the image forming apparatus shown in the first embodiment, the color distribution of the secondary transfer residual toner is naturally different depending on the image to be printed. Therefore, the secondary transfer residual toner is collected and reused. The color of black also depends on the print image. Therefore, three or more small-sized black patches having a reflection density of around 0.5 are formed on the intermediate transfer belt 21 at regular time intervals, and the density detection means 60 determines which color is magenta, cyan, or yellow. Alternatively, it is determined whether or not the amount of toner is small, and a small amount of toner is supplied from the toner hopper 15 of that color to stabilize the color of black. In addition to the toner buffer 16 for supplying toner to each color developer hopper 15 to each color toner hopper 15, an auxiliary toner buffer 16 a for supplying toner to the toner buffer 16 connected to the black developer 14. Is provided.
[0060]
Also in the second embodiment, the same effects as those of the first embodiment described above can be obtained, and more stable images can be supplied than in the first embodiment.
[0061]
In the first and second embodiments described above, the color of the toner image formed by the first image forming unit is described as black. However, the color is not limited to black in a strict sense, but is similar to this, that is, black. It may be a color. However, even in this case, it is assumed that the color of the toner image formed by the first image forming unit is darker than the color of the toner image formed by another image forming unit.
[0062]
【The invention's effect】
As described above, according to the present invention, the downstream side of the secondary transfer unit and the upstream side of the upstreammost image forming unit among the plurality of image forming units along the moving direction of the intermediate transfer member. A charging means for charging the transfer residual toner remaining on the intermediate transfer member with a polarity opposite to that of the toner at the time of primary transfer, and the most upstream image forming unit is used as an image forming unit for forming a black toner image. Therefore, it is possible to clean the intermediate transfer member without applying an excessive load to the intermediate transfer member and without being affected by the radiant heat from the fixing device, and to perform the primary transfer residual. Not only toner but also secondary transfer residual toner can be reused, and space saving and low running cost can be realized at the same time.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a schematic configuration of an image forming apparatus according to a first embodiment.
FIG. 2 is a longitudinal sectional view showing a schematic configuration of an image forming apparatus according to a second embodiment.
FIG. 3 is a longitudinal sectional view showing a schematic configuration of a conventional image forming apparatus.
[Explanation of symbols]
11 Image carrier (photosensitive drum)
14 Development means (developer)
15 Toner supply means (toner hopper)
21 Intermediate transfer body (intermediate transfer belt)
50 Charging means
52 Charging member (elastic roller)
53 Power supply
60 Concentration detection means (light sensor)
60a Sensor surface
N₁         Primary transfer part (primary transfer nip part)
N₂         Secondary transfer part (secondary transfer nip part)
P transfer material
R21 Movement direction of intermediate transfer member
UBk Uppermost stream side image forming unit (black image forming unit)
UM Image forming unit (Magenta image forming unit)
UC image forming unit (Cyan image forming unit)
UY The most downstream image forming unit (yellow image forming unit)

Claims (3)

A plurality of image forming units having image carriers are arranged along the moving direction of the intermediate transfer member, and toner images formed on the image carriers by the developing means of the image forming units are used as the image carriers. And sequentially transfer the toner image on the intermediate transfer body onto the transfer material via the secondary transfer section. In the image forming apparatus that performs secondary transfer and collects and transfers the transfer residual toner remaining on the image carrier by the developing unit.
The intermediate transfer member contacts the intermediate transfer member on the downstream side of the secondary transfer portion and further upstream of the most upstream image forming unit among the plurality of image forming units along the moving direction of the intermediate transfer member. is contact arranged, comprising a charging means having a resilient roller to charge the transfer residual toner remaining on said intermediate transfer member to the toner and opposite polarity during the primary transfer,
The most upstream image forming unit is an image forming unit that forms a black toner image.
An image forming apparatus. The elastic roller has a volume resistivity of 10 ⁵ to 10 ¹³ Ω · cm , and abuts against the intermediate transfer member at a total pressure of 0.98 to 2.94 N (100 to 300 g).
The image forming apparatus according to claim 1. Among the plurality of image forming units, the image forming unit that first primarily transfers a toner image onto the intermediate transfer member is an image forming unit that forms the black toner image.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

Images