JP2007256592A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus free from grainy discharge dust and a so-called worm hole (toner more strongly adheres to a photoreceptor and/or agglutinates), that means, that partial deficiency of toner of a toner image. <P>SOLUTION: The image forming apparatus 150 has a transfer device where a mechanical nip is formed by bringing an intermediate transfer body into contact with an image carrier on which a toner image is put, and which comprises a main electrode which is arranged toward the inside of the mechanical nip on the back side of the intermediate transfer body and to which bias for transferring an electrified toner image is applied, and reverse polarity bias electrodes which are arranged on the upstream side and the downstream side of the main electrode in the moving direction of the intermediate transfer body inside the mechanical nip on the back side of the intermediate transfer body and to which bias having a reverse polarity to the bias applied to the main electrode is applied. In the image forming apparatus 150, the intermediate transfer body 10 is set so that its micro hardness on a side where the toner image is put is ≤75, it has electric field dependency of resistance in a thickness direction, and it does not have the electric field dependency of the resistance in a surface direction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrophotographic color image forming apparatus using an intermediate transfer member such as a color analog / digital PPC or a color laser printer.

Today, in electrophotographic apparatuses, there are an increasing number of color copiers and color printers in response to market demands.
A color electrophotographic apparatus is provided with a developing device of a plurality of colors around one photosensitive member, and a toner is attached to the developing device to form a composite toner image on the photosensitive member, and the toner image is transferred. A so-called revolver type that records a color image on a sheet, and a plurality of photoconductors arranged side by side are each provided with a developing device, and a single color toner image is formed on each photoconductor, and the single color toner images are sequentially formed. There is a so-called tandem type that transfers and records a composite color image on a sheet.
Comparing the revolver type and the tandem type, the former has only one photoconductor, so that there is an advantage that the size can be reduced relatively and the cost can be reduced. Times) Since full-color images are formed by repeating image formation, there is a drawback that speeding up image formation is limited, while the latter has the disadvantage of increasing the size and cost, but speeding up image formation There is an advantage that can be realized.

Recently, however, tandem-type devices have been attracting attention because full-color and monochrome-like speeds are desired.
The tandem type electrophotographic apparatus includes a direct transfer system in which images on each photoconductor are sequentially transferred to a sheet conveyed by a sheet conveying belt by a transfer device, and an image on each photoconductor by a primary transfer device. There is an indirect transfer type in which images are sequentially transferred to an intermediate transfer member and then transferred onto a sheet by a secondary transfer device.
Comparing the direct transfer type and the indirect transfer type, the former requires that a paper feeding device is arranged upstream of the tandem image forming apparatus in which the photoconductors are arranged, and a fixing device is arranged downstream. , There is a drawback of increasing the size. On the other hand, since the latter can set the secondary transfer position relatively freely, the paper feeding device and the fixing device can be arranged so as to overlap the tandem type image forming device, and the size can be reduced. There are advantages.
In the former, since the fixing device is disposed close to the tandem image forming apparatus so as not to increase the size, the fixing device cannot be disposed with a sufficient margin that the sheet can be bent. There is a drawback that the fixing device affects the image formation on the rear end side due to an impact when the leading edge of the toner enters the fixing device or a difference in sheet conveyance speed when passing through the fixing device. On the other hand, in the latter case, since the fixing device can be arranged with a sufficient margin that the sheet can bend, the fixing device can hardly affect the image formation.
For these reasons, attention has recently been paid to the indirect transfer type among tandem type electrophotographic apparatuses.
In this type of color electrophotographic apparatus, the transfer residual toner remaining on the photoconductor after the primary transfer is removed by a photoconductor cleaning device to clean the surface of the photoconductor to prepare for another image formation. Further, the transfer residual toner remaining on the intermediate transfer member after the secondary transfer is removed by an intermediate transfer member cleaning device to clean the surface of the intermediate transfer member to prepare for another image transfer.

However, in such an image forming apparatus, the occurrence of discharge dust and insect bites has been a problem. Therefore, an application has been filed for improving the quality of a transfer image in which the electric field width is narrowed so that the toner is not discharged. Specifically, the transfer electric field is applied in a mechanically close state and the transfer electric field is removed, or the electrode that shields the transfer electric field is arranged downstream and upstream. It has been filed to consolidate. Patent Document 1 discloses that an electric field is narrowed by applying a bias film or a blade to the center of the nip.
In order to realize this, it is necessary that the adjacent electrodes are sufficiently insulated in a medium such as an intermediate transfer member. On the other hand, it is essential that the resistance is small in the transfer electric field application direction. For the latter, an intermediate transfer material having a high electric field dependency is currently commercially available.
However, in the above system, there is a concern about electrode wear. Since the electrical connection must be stable even if worn, it is necessary here to raise the bite. For this reason, the pressure between the blade and the intermediate transfer member tends to be excessive. After passing under three blades, the aggregating action becomes more intense, and there is a possibility that a phenomenon of “worm biting” occurs in which the toner has a strong adhesion force or agglomerates. Therefore, as a countermeasure against this, it is first considered to use a surface elastic belt for the intermediate transfer member.
However, the resistance of such an elastic belt tends to fluctuate when the amount of deformation is large. This becomes noticeable when dispersing carbon black or the like without carefully considering the internal electrical characteristics, and the low resistance part of the elastic part is connected like a chain, creating a conduction path with an unrelated place. . As a result, there is a problem in that the withstand voltage is lowered by the high voltage applied in the transfer, and a large current flows in an unexpected path. Further, when the resistance on the belt surface is lowered, there is a problem that the transfer dust is remarkably increased.

In addition, when a transfer bias is applied with a narrow width at the nip formed between the image carrier and the intermediate transfer member, air breakdown discharge is less likely to occur due to close contact, and toner charging is less likely to occur. Furthermore, since static elimination is applied downstream from the nip inlet, it is possible to prevent the (+) high voltage of the main electrode from leaking to the nip inlet. Further, even at the nip outlet, when the contact state is resolved and separation starts, the static elimination of the belt is completed, so that peeling discharge is less likely to occur.
However, such a method has a problem that the electric field dependence of the resistance must be appropriately limited. When the resistance is excessively reduced, a leak between different polarity bias electrodes occurs, resulting in a problem that an effective value of the transfer electric field cannot be obtained.

JP 2001-183918 A

  Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus that does not cause graininess, discharge dust, and insect bite.

The features of the present invention, which is a means for solving the above problems, are listed below.
In the present invention, an intermediate transfer member is brought into contact with an image carrier on which a toner image is placed to form a mechanical nip, and is arranged on the back side of the intermediate transfer member toward the inside of the mechanical nip. A main electrode to which a bias for transferring a charged toner image is applied, and a main electrode disposed on the back side of the intermediate transfer member, on the inner side of the mechanical nip and upstream and downstream of the main electrode in the moving direction of the intermediate transfer member. In the image forming apparatus having a transfer device including a reverse polarity bias electrode to which a bias having a polarity opposite to the applied bias is applied, the intermediate transfer member has a micro hardness of 75 degrees or less on the side on which the toner image is placed. The image forming apparatus has an electric field dependency of resistance in a thickness direction and no electric field dependency of resistance in a surface direction.
According to the present invention, when the intermediate transfer member is biased to the surface with a bias of 10 to 1000 V, the resistance variation of the surface resistance is 1 / of the resistance variation with a bias of 10 to 1000 V in the thickness direction of the intermediate transfer member. 100 or less.
The present invention is characterized in that the intermediate transfer member is made of a material including an electronic conductive filler in an elastic layer and an inner layer in which the thickness of single bubbles in the thickness direction of the intermediate transfer member is 500 μm or less.

  According to the present invention, it has become possible to provide an image forming apparatus that does not cause graininess, discharge dust, and insect bite.

  The best mode for carrying out the present invention will be described below with reference to the drawings. Note that it is easy for a person skilled in the art to make other embodiments by changing or correcting the present invention within the scope of the claims, and these changes and modifications are included in the scope of the claims. The following description is an example of the best mode of the present invention, and does not limit the scope of the claims.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an embodiment of the present invention, which is a tandem type indirect transfer type image forming apparatus. In the figure, reference numeral 150 is a copying machine body, 200 is a paper feed table on which it is placed, 300 is a scanner mounted on the copying machine body 150, and 400 is an automatic document feeder (ADF) mounted on the scanner.
The copying machine main body 150 is provided with an endless belt-shaped intermediate transfer member 10 in the center. The intermediate transfer member 10 is a single-layer belt made from a single-layer polyimide material.
As shown in FIG. 1, in the illustrated example, it is wound around three support rollers 14, 15, 16 and can be rotated and conveyed clockwise in the figure.
In this illustrated example, an intermediate transfer body cleaning device 17 that removes residual toner remaining on the intermediate transfer body 10 after image transfer is provided to the left of the second support roller 15.
Further, on the intermediate transfer member 10 stretched between the first support roller 14 and the second support roller 15, four image forming units 18 of black, cyan, magenta, and yellow are arranged along the conveyance direction. The tandem image forming apparatus 20 is arranged side by side.
An exposure device 21 is further provided on the tandem image forming apparatus 20 as shown in FIG.

On the other hand, a secondary transfer device 22 is provided on the side opposite to the tandem image forming apparatus 20 with the intermediate transfer body 10 interposed therebetween. In the illustrated example, the secondary transfer device 22 is configured by spanning a secondary transfer belt 24, which is an endless belt, between two rollers 23, and is pressed against the third support roller 16 via the intermediate transfer body 10. The image on the intermediate transfer body 10 is transferred to a sheet.
A fixing device 25 for fixing the transfer image on the sheet is provided beside the secondary transfer device 22. The fixing device 25 is configured by pressing a pressure roller 27 against a fixing belt 26 that is an endless belt. The secondary transfer device 22 described above is also provided with a sheet transport function for transporting the image-transferred sheet to the fixing device 25. Of course, a non-contact charger may be arranged as the secondary transfer device 22, and in such a case, it is difficult to provide this sheet conveyance function together.
In the illustrated example, under such a secondary transfer device 22 and a fixing device 25, a sheet reversing device 28 for reversing the sheet so as to record images on both sides of the sheet in parallel with the tandem image forming device 20 described above. Is provided.

When making a copy using this color copying machine, the document is set on the document table 30 of the automatic document feeder 400. Alternatively, the automatic document feeder 400 is opened, a document is set on the contact glass 32 of the scanner 300, and the automatic document feeder 400 is closed and pressed by it. When a start switch (not shown) is pressed, when a document is set on the automatic document feeder 400, the document is transported and moved onto the contact glass 32, and then the document is set on the other contact glass 32. Immediately drives the scanner 300 and travels through the first traveling body 33 and the second traveling body 34. Then, the first traveling body 33 emits light from the light source and further reflects the reflected light from the document surface toward the second traveling body 34, and is reflected by the mirror of the second traveling body 34 and passes through the imaging lens 35. The document is placed in the reading sensor 36 and the original content is read.
When a start switch (not shown) is pressed, one of the support rollers 14, 15 and 16 is rotationally driven by a drive motor (not shown), the other two support rollers are driven to rotate, and the intermediate transfer body 10 is rotated and conveyed. To do. At the same time, the individual image forming means 18 rotates the photoconductor 40 to form black, yellow, magenta, and cyan monochrome images on each photoconductor 40. Then, along with the conveyance of the intermediate transfer member 10, the single color images are sequentially transferred to form a composite color image on the intermediate transfer member 10.

On the other hand, when a start switch (not shown) is pressed, one of the paper feed rollers 42 of the paper feed table 200 is selectively rotated, and the sheet is fed out from one of the paper feed cassettes 44 provided in multiple stages in the paper bank 43, so Are separated one by one into the paper feed path 46, transported by the transport roller 47, guided to the paper feed path 48 in the copying machine main body 150, and abutted against the registration roller 49 to stop. Alternatively, the sheet feed roller 50 is rotated to feed out the sheets on the manual feed tray 51, separated one by one by the separation roller 52, put into the manual feed path 53, and abutted against the registration roller 49 and stopped.
Then, the registration roller 49 is rotated in synchronization with the composite color image on the intermediate transfer body 10, the sheet is fed between the intermediate transfer body 10 and the secondary transfer device 22, and transferred by the secondary transfer device 22. A color image is recorded on the sheet.

The image-transferred sheet is conveyed by the secondary transfer device 22 and sent to the fixing device 25. The fixing device 25 applies heat and pressure to fix the transferred image. Are discharged and stacked on the discharge tray 57. Alternatively, it is switched by the switching claw 55 and put into the sheet reversing device 28, where it is reversed and guided again to the transfer position, and the image is recorded also on the back surface, and then discharged onto the discharge tray 57 by the discharge roller 56.
On the other hand, the intermediate transfer member 10 after the image transfer is removed by the intermediate transfer member cleaning device 17 to remove the toner remaining on the intermediate transfer member 10 after the image transfer, so that the tandem image forming device 20 prepares for the image formation again.

The toner is mixed with a charge control agent (CCA) and a colorant in a resin such as polyester, polyol, and styrene acrylic, and by adding a substance such as silica and titanium oxide around the resin, its charging characteristics and fluidity. Is increasing. The particle size of the additive is usually in the range of 0.1 to 1.5 μm. Examples of the colorant include carbon black, phthalocyanine blue, quinacridone, and carmine. The charging polarity is negative charging in the illustrated example.
As the toner, a toner obtained by externally adding the above kind of additive to a base toner in which wax or the like is dispersed and mixed can be used. Further, the toner is not limited to those prepared by a pulverization method, but toners prepared by a polymerization method or the like can be used. In general, a toner prepared by a polymerization method, a heating method, or the like can be formed with a shape factor of 90% or more, and the coverage of the additive depending on the shape is extremely high.

In the present invention, when a plurality of electrodes are brought close to each other on the inner surface and reverse polarity biases are applied to each other, not only the resistance on the back surface is kept high enough, but also the material in the belt is transmitted to the bias of the adjacent electrode. The countermeasure is taken in consideration of the disadvantages of the elastic belt.
As for the electronic conductivity used here, the square root of the applied electric field is proportional to the current in the case of a normal thin belt. Further, the potential of the photosensitive member is (−), and the (−) charge flows at the same time as the intermediate transfer member contacts the photosensitive member. This means that when the stress inside the belt is considered, a large resistance fluctuation occurs in a state where pressure is applied to the material.

FIG. 2 is a view showing a narrow electric field applying device.
The intermediate transfer body 10 is made by centrifugal molding of polyimide as a polymer material, and has a foam layer on the surface. In FIG. 2, a single layer of polyimide is shown, but an appropriate amount of carbon black is dispersed and adjusted to an appropriate resistance. A crystalline belt having orientation such as PC (polycarbonate) may be used by being foamed.
A carbon black dispersed polyimide belt was taken up as the belt. The volume resistance of this belt has a large voltage dependency. When the applied voltage is changed from 25V to 250V, ρv decreases by the third power. Belts in which the conductivity of the middle resistance region is expressed by dispersing the conductive agent show similar tendencies, although with varying degrees.

The photoconductor 40 and the intermediate transfer belt 10 form a mechanical nip Nm from the suspension rollers 123 and 124 and rotate in the same direction.
The transfer blade 100, the exit blade 101, and the entrance blade 102 are each formed into a plate shape of 0.5 mm to 3.0 mm, and the direction in which the polymer flows in the belt rotation direction so that the mechanical deterioration is minimized. To be molded. As the material, a conductive ion agent dispersion type or a kneading dispersion type of an electronic conductive agent is generally used. In the present invention, a conductive ion agent dispersed type is adopted. This is formed after quantitatively mixing Na and Li ion agents as conductive ion agents. This resistance has little voltage dependency and pressure dependency and is preferable for the use of the present invention. However, an electronic conductive agent kneading dispersion type may be selected in consideration of resistance variation due to the environment. In this case, carbon powder (making structure), titanium oxide powder, etc. are selected as the electronic conductive agent, and urethane resin, silicon resin, fluororesin, CR (chloroprene / neoprene synthetic rubber), EPDM (ethylene / propylene rubber), hydrin rubber It may be kneaded into rubber materials such as. These materials are adjusted to have a resistance of about 1 × 10 ⁶ to 1 × 10 ¹³ Ωcm, preferably about 1 × 10 ⁷ to 1 × 10 ¹⁰ Ωcm. These molded products have almost the same order of surface resistivity as that of one. Although not shown, these may be a two-layer type. The important point is that the connection between the terminal and the contact portion with the intermediate transfer body 10 and the resistance of the contact portion are in the middle resistance region.

As for the arrangement position of these blades 100, 101, 102, the transfer blade 100 is generally slightly downstream from the approximate center of Nm. Based on the position of the transfer blade 100, the position up to the exit blade 101 is divided into an exit width Nex obtained on the belt and an entrance width Nin projected up to the position of the entrance blade 102 on the belt. The sum of Nin and Nex as a whole becomes the effective bias application width Ne of the transfer electric field.
Here, an insulating material 105 is installed between the entrance and exit electrodes. This is made of a thin general insulating resin sheet.

A power source for supplying a bias to each blade 100, 101, 102 is supplied with a bias source 110 for the transfer blade 100, a bias source 111 for the other blade 101, and a bias source 112 for the blade 102. Although not shown, a constant voltage or a constant current can be controlled by a CPU or the like.
These blades 100, 101, 102 are supported by a support holder 106. The blades 100, 101, and 102 are designed in consideration of bending and not being too close to each other. If the blade comes into contact due to deflection or the like, a large electric leakage occurs between these components, and damage to the power source or a predetermined bias cannot be applied. Of course, when such a leak occurs, the substantial transfer bias from the photoconductor 40 to the intermediate transfer body 10 is reduced, and the image quality may be deteriorated. Therefore, it is necessary to design and manufacture with high accuracy.

FIG. 3 shows an example in which a general elastic belt is used as the intermediate transfer member 10. Here, a foamed urethane layer having a thickness of about 500 μm is provided. The belt is made by appropriately dispersing carbon black. Here, in general, when the elastic layer is subjected to pressure or subjected to a reaction force of toner aggregation, the thickness slightly changes and a shearing force acts inside. Although this is not large, a conductive route may occur. In that case, the pressure resistance of the portion where the pressure is applied decreases, and the resistance decreases at once. Such changes are likely to occur where the surface deformation is large.
When this portion swells, a low resistance region such as P low is formed as shown in FIG. 3, and a conductive path W is formed at a portion having the same pressure. Since this is a leakage current portion that can be generated inside the belt, there is no influence on the outside of the belt, and the required current flows, but no current flows on the photosensitive member 40 side, specifically, between two applied voltages. Therefore, transferability is deteriorated.
In the intermediate transfer member 10, the surface elastic layer and the inner resin layer may be applied by a carbon black conductive agent. At this time, the conductive path W passes through the interface. Since this interface is connected for one round of the belt, it is easy to create abnormal charging inside the machine.

FIG. 4 is a view showing an elastic belt for a narrow electric field applying device. There is a difference in the layer structure of the belt from FIG. This belt is an elastic belt and needs to have a micro surface hardness of 75 degrees or less in order to transfer even a pulverized toner similar to a conventional toner. Thereby, a worm-eaten image can be reduced.
FIG. 5 is an example of a defective belt. Since the belt has an originally low surface resistance, it cannot prevent graininess, discharge dust, and insect bites.

  FIG. 6 is a diagram showing the surface hardness of the elastic belt and the transferability to the Japanese paper. The belt hardness is varied with respect to the transferability to the rippled Japanese paper (NBS Ricoh-made Japanese paper specification application paper, smoothness 5 seconds). When the belt surface hardness was 60 to 70 degrees, the transfer to the Japanese paper was good, but when the hardness was greater than 75 degrees, the transferability was poor. As a result, the micro hardness is 75 degrees or less, so that the cohesive pressure for the toner can be reduced, and image abnormality can be eliminated in the transfer of the toner image. Desirably, a micro hardness of 65 degrees or less is more effective.

  In the present invention, since the electric field dependency of resistance is high only in the thickness direction in the intermediate transfer member material, the resistance is lowered by the transfer member material between the photosensitive member 40 when a bias is applied. FIG. 7 is a diagram showing a change in resistance in the thickness direction of the elastic belt. Thereby, a transfer electric field and a static elimination electric field can be applied efficiently. Further, the resistance remains high in the surface direction, and current does not have to be leaked to the adjacent electrode side. 8 and 9 are diagrams showing a method for evaluating the charge leakage to the belt adjacent electrode. Charge leakage was evaluated by this method.

Further, in the present invention, if the resistance decrease in the thickness direction is 1/100 or less, even if a high bias voltage is applied, the current that actually flows next does not cause a problem in practice. It should be noted that it is preferably 1/1000 or less.
The measuring method is based on a measuring method based on JIS K6911. Specifically, using a resistivity meter Hiresta UP (MCP-HT450) manufactured by Mitsubishi Chemical, changing the measurement voltage in the range of 10 to 1000 V, the ratio of volume resistivity and surface resistivity of various test pieces Is 1/100 or less. The above characteristics can be created, for example, by centrifugally molding carbon in polyimide.
FIG. 10 is a diagram showing changes in ρv and ρs with respect to the applied voltage. Here, ρv is the resistance in the thickness direction, and ρs is the surface resistance. From the figure, it can be seen that the surface resistance is 1/100 or less of the resistance variation in the thickness direction.

Furthermore, according to the present invention, the electric field dependency in the thickness direction can be effectively expressed by using a material having a filler having electronic conductivity in the elastic layer and forming a large number of single bubbles in the thickness direction. FIG. 11 is a diagram showing single bubbles, and FIG. 12 is a diagram showing a method for creating single bubbles.
Here, an example of using a foaming material containing a conductive agent or conductive ions for the elastic belt will be described. Rubber or the like can also be used.
First, a base layer of the belt is formed by centrifugal molding or the like using a normal non-foaming material (see FIG. 12a). This base layer is required to have high mechanical strength and a medium resistance region (10 ⁶ to 10 ¹² Ω · cm). Further, it is made of carbon black mixed PC (polycarbonate), ETFE (ethylene-tetrafluoroethylene copolymer), PVdF (vinylidene fluoride), PI (polyimide), or the like.
Next, a conductive filler is mixed with a foam material (polyurethane or the like) and applied onto the base material layer (see FIG. 12b). Here, the foamed polyurethane is obtained by polyaddition reaction of diisocyanate and polyol, and the hard and soft characteristics can be controlled by selecting the kind of polyol, and foamed with a physical foaming agent using reaction heat or water. Foaming with CO ₂ gas generated by the addition is performed. Therefore, a method of applying the raw material components to the mold immediately after mixing is employed.
Next, the foaming process is operated. The bubble size is determined by the amount of foaming agent, the foaming temperature, and the material viscosity by adjusting the bubble generation rate based on the heat generation, presence / absence of centrifugal force and solvent volatilization rate. When the mold is rotated at a high speed in the stage where the viscosity is increased and the foaming is slowly advanced, the high density portion of each material is gradually pushed outward by centrifugal force. At this time, the bubbles extend in the thickness direction (see FIG. 12c).
In addition, about a conductive filler, if it is hydrophobic, a whirling will arise in a bubble. (See FIG. 12d). This causes a sudden drop in resistance under pressure. Therefore, hydrophilic treatment is performed on the surface of the conductive filler to increase the compatibility. Then, the conductive filler is not exposed inside the foam. As a result, even during pressurization, a conductive path through which an extra current flows is less likely to occur, resulting in a resistance with low pressure dependency.
Further, a release layer can be applied to the surface layer. This has an effect of improving the cleaning property by a blade or the like.

This is a tandem type indirect transfer type image forming apparatus. It is a figure which shows a narrow electric field application apparatus. It is the figure which showed the example using a general elastic belt. It is the figure which showed the elastic belt for narrow electric field application apparatuses. It is an example of a bad belt. It is the figure which showed the surface hardness of an elastic belt, and the transferability to a rippled Japanese paper. It is the figure which showed the change of the thickness direction resistance of an elastic belt. It is the figure which showed the charge leakage evaluation method to a belt adjacent electrode. It is the figure which showed the charge leakage evaluation method to a belt adjacent electrode. It is the figure which showed the change with respect to the applied voltage of (rho) v and (rho) s. It is the figure which showed the single bubble. It is the figure which showed the preparation method of a single bubble.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Intermediate transfer body 14 Support roller 15 Support roller 16 Support roller 17 Intermediate transfer body cleaning device 18 Image forming means 20 Tandem image forming device 21 Exposure device 22 Secondary transfer device 23 Roller 24 Secondary transfer belt 25 Fixing device 26 Fixing belt 27 Pressure roller 28 Sheet reversing device 30 Document table 32 Contact glass 33 First traveling body 34 Second traveling body 35 Imaging lens 36 Reading sensor 40 Photoconductor 42 Paper feed roller 43 Paper bank 44 Paper feed cassette 45 Separating roller 46 Paper feed Path 47 Conveying roller 48 Feeding path 49 Registration roller 50 Feeding roller 51 Manual feed tray 52 Separating roller 53 Manual feed path 55 Switching claw 56 Discharge roller 57 Discharge tray 100 Transfer blade 101 Exit blade 102 Inlet blade 105 Insulating material 106 Support Holder 110 Bias source 111 Bias source 112 Bias source 123 Suspension roller 124 Suspension roller 150 Copier main body 200 Paper feed table 300 Scanner 400 Automatic document feeder (ADF)

Claims (3)

An intermediate transfer member is brought into contact with the image carrier on which the toner image is placed to form a mechanical nip,
A main electrode to which a bias for transferring a charged toner image is applied on the back side of the intermediate transfer body and is arranged toward the inside of the mechanical nip;
On the back side of the intermediate transfer member, a bias having a polarity opposite to the bias applied to the main electrode disposed inside the mechanical nip and upstream and downstream of the main electrode in the moving direction of the intermediate transfer member was applied. A reverse polarity bias electrode;
In an image forming apparatus having a transfer device comprising:
The intermediate transfer member has a micro hardness of 75 degrees or less on the side on which the toner image is placed,
In the thickness direction, it has electric field dependency of resistance,
An image forming apparatus having no electric field dependency of resistance in a surface direction. The image forming apparatus according to claim 1.
The intermediate transfer member is
The resistance variation of the surface resistance when a bias of 10 to 1000 V is applied to the surface is 1/100 or less of the resistance variation of the bias applied to 10 to 1000 V in the thickness direction of the intermediate transfer member. Forming equipment. The image forming apparatus according to claim 2.
In the image forming apparatus, the intermediate transfer member includes an electronic conductive filler in an elastic layer,
An image forming apparatus, wherein the intermediate transfer member is made of a material having an inner layer having a thickness of single bubbles in the thickness direction of 500 μm or less.

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