JP2007171784A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that prevents a transfer-abnormality image, such as an image with partial deficiency and a void image, principally due to excessive pressing of a nip part while maintaining less scattering during transfer, high efficiency, and a high transfer rate, and to provide an image forming apparatus that applies a bias having the same polarity with toner for transfer scattering prevention and reversing prevention to the entrance side/exit side of a transfer nip part while surely securing a necessary mechanical transfer nip and preventing a leak between a plurality of bias application electrodes provided in the transfer nip. <P>SOLUTION: The image forming apparatus 150 is configured such that a primary transfer nip during primary transfer operation abuts in a state the same nip width is formed irrelevantly to whether there is contact pressure of a bias applying means 5 on a primary transfer member 10. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a bias applying device in primary transfer of a color image forming apparatus using an intermediate transfer belt in electrophotography, electrostatic recording, electrostatic printing, and the like. The present invention also relates to an image forming apparatus such as a printer, a fax machine, and a copying machine.

2. Description of the Related Art Today, electrophotographic apparatuses are increasing in color, such as color copiers and color printers, according 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 one photoconductor, so there is an advantage that it can be reduced in size and cost, but it is possible to reduce the cost several times (usually four times) using one photoconductor. Since full-color images are formed by repeating image formation, there is a drawback in that there is a limit to speeding up the image formation, and the latter has the disadvantage of increasing the size and cost, but speeding up the image formation There are advantages that are possible.
Recently, however, tandem-type cameras 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, the latter has the advantage that the secondary transfer position can be set relatively freely, and the paper feeding device and the fixing device can be arranged so as to overlap with the tandem type image forming device, and the size can be reduced.
In the former case, when the fixing device is arranged close to the tandem type image forming apparatus so as not to increase the size, the sheet conveyance speed when the impact or the like when the leading edge of the sheet enters the fixing device passes through the fixing device. The difference or the like propagates to the rear end side of the sheet at the secondary transfer position, so that the fixing device affects the image formation on the rear end side. On the other hand, in the latter case, the fixing device can be arranged at a position corresponding to the length of the sheet from the secondary transfer position, so that the fixing device does not affect the secondary transfer image formation. For these reasons, an indirect transfer type tandem electrophotographic apparatus has recently attracted attention.
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, indirect transfer tandem-type electrophotographic devices have little transfer dust and high transfer efficiency while maintaining high-efficiency transfer rates. It was a problem that could not be prevented.

In the intermediate transfer body system, the color toner images are sequentially transferred onto the intermediate transfer body. In the process of transferring the second and subsequent colors to the intermediate transfer system, a “reverse transfer” phenomenon may occur in which the toner in the previous process returns from the intermediate transfer member to the photosensitive member. This phenomenon is usually improved by lowering the transfer bias. However, if the transfer bias is lowered too much, the transfer rate of the color toner during transfer becomes insufficient and “transfer residual” increases. Therefore, the transfer bias is adjusted in consideration of the trade-off relationship between the “reverse transfer” reduction condition and the “transfer residual” reduction condition.
However, the proper transfer bias condition range is not uniform, and the proper bias condition range is shifted due to the influence of fluctuations in the potential of the transfer belt and the photoconductor, which causes variations in transfer performance.
The cause of “reverse transfer” is an electrostatic induction phenomenon or discharge in or near the primary transfer nip region. The direct cause is that the ions generated by the discharge move and the toner accepts the ions to change the charge amount. When this discharge occurs, the image quality also deteriorates.
On the other hand, it was effective to perform transfer by applying a sufficient transfer electric field and further reduce excessive discharge. Furthermore, in order to reduce both transfer residue and reverse transfer, it is effective to provide bias applying means at the entrance and exit of the transfer nip and to apply an electric field with a bias having the same polarity as the toner polarity to the intermediate transfer member.
However, in a machine where the photosensitive drum has a small diameter of Φ30 mm or less and the primary transfer nip is narrow, it is difficult to design densely arranged electrodes having different potentials in a narrow place due to layout constraints. It was. In addition, if the resistance between adjacent electrodes is kept high and is not substantially insulated, a large amount of current flows between the electrodes, and the power supply capacity must be increased, which is disadvantageous in terms of power supply specifications.

Further, most of the current intermediate transfer belts are electronic conductive resistors in which carbon or the like is kneaded and dispersed in a polymer material, and the resistance has an electric field dependency. When such an intermediate transfer belt is used, the resistance is low in the primary transfer electric field action region, but the resistance increases when the action electric field intensity decreases after leaving the primary transfer nip. The transfer bias charge remaining in the intermediate transfer belt easily disappears due to movement in the belt when the resistance is low.However, in the case of the above-described belt, the remaining charge is increased because the resistance increases as it leaves the primary transfer nip. It tends to increase, and air discharge may occur when the gap between the photosensitive member and the belt is widened when the intermediate transfer belt is peeled off. Due to the occurrence of this discharge, polar ions different from the normal charging polarity of the toner are generated and moved to the toner forming the image. There is a problem in that the toner is irregularly moved and the amount of dust in the image increases. The solid image also has a problem in that the toner Q / M on the surface layer is changed to lower the transfer rate.
Therefore, when using a belt having a high resistance when the applied electric field strength is weak, it is required to reduce the primary discharge outlet discharge. For example, Patent Document 1 discloses that an electrode is placed on the downstream side considerably away from the nip.
However, this method has a problem that a large amount of electric charge tends to remain in a belt having a large capacitance and high electric field dependency.
There are two possible reasons for this. First, even when a counter bias is applied to the exit peeling location as in Patent Document 2, no electric field is applied to an intermediate transfer belt having high resistance voltage dependency. At the same time, the resistance becomes high, and it becomes difficult for the electric charge to move to a place where the electric potential becomes lower due to static elimination, and the electric potential of the belt does not decrease, and the residual electric charge is difficult to decrease. In this case, since static elimination is performed at the outlet of the mechanical nip, it is considered that the static elimination time in the belt moving direction is insufficient.
Second, the residual charge remaining in the medium resistance member is still left inside the belt even after the residual charge on the belt surface is neutralized. In this case as well, a shortage of static elimination time in the belt moving direction can be considered, but a shortage of static elimination time in the belt thickness direction can also be considered. Here, since the static elimination is performed at the exit end of the mechanical nip, in addition to the shortage of static elimination time, the resistance to the low potential side in the belt thickness direction is high due to the belt being separated or the belt thickness. There is also a possibility of insufficient static elimination time.
In view of the above, there has been a demand for starting the charge removal before the residual charge obtained by the belt in the nip comes out from the primary transfer, so that there is no shortage of charge removal, and image abnormalities are not caused thereby.

Further, in Patent Document 3, at least a part of the intermediate transfer member is disposed so as to be adjacent to the image holding surface in the transfer zone, and forms a transfer nip, a front transfer zone, and a rear transfer zone; A first bias voltage potential is applied to the intermediate transfer member in the pre-transfer zone, arranged adjacent to the pre-transfer zone, to minimize the transfer electric field and from the image holding surface to the pre-transfer zone. A means for preventing toner particles from being transferred to the intermediate transfer member; and a second bias voltage potential applied to the intermediate transfer member in the transfer nip, disposed adjacent to the transfer nip, from the image holding surface From the image holding surface to the substrate, comprising means for generating a high transfer electric field for attracting toner particles to the intermediate transfer member in the transfer nip Apparatus for transferring electrostatic toner particles, was disclosed. As a result, an intermediate transfer member having a backing substrate that is electrically conductive and resistant in the lateral direction can be realized.
Further, in Patent Document 4, a primary bias having a polarity opposite to that of the toner image of the first image carrier is provided on the back surface of the intermediate transfer member facing the first image carrier that carries the developed toner image. An image forming apparatus having a plurality of stages of primary transfer processes for transferring the toner image from the carrier to the intermediate transfer member by applying the transfer device, wherein the primary bias is a constant current. Was disclosed. As a result, it was possible to provide a transfer device that can prevent image density deficiency due to a decrease in transfer rate, density unevenness due to abnormal discharge due to excessive primary transfer current, and the like.
Patent Document 5 discloses an image carrier, toner image forming means for forming a toner image on the image carrier, a belt-shaped intermediate transfer member supported by a plurality of support members, and an image on the image carrier. In the image forming apparatus, the image forming apparatus includes: a primary transfer unit that transfers the toner image to the intermediate transfer member; and a secondary transfer unit that transfers the toner image on the intermediate transfer member to a transfer material. Of these, a transfer member that presses the support member closest to the primary transfer portion closest to the primary transfer portion where the image carrier and the intermediate transfer member face each other toward the surface of the image carrier. 2 is provided so as to be able to take a possible position and a separated position separated from the intermediate transfer body, and is located on the upstream side and the downstream side in the intermediate transfer body moving direction of the support member closest to the primary transfer portion. Two fixedly arranged support members are connected to the primary transfer. The intermediate transfer member that is stretched by the fixed support member when the closest support member is located at the separation position is provided so as to be separated from the image carrier, and the primary transfer portion closest to the primary transfer unit. An image forming apparatus comprising: a support member driving unit that moves the support member between the transferable position and the separation position; and a control unit that controls the support member driving unit. It was disclosed. As a result, an image forming apparatus capable of contacting and separating the intermediate transfer belt with respect to the photosensitive drum at a predetermined timing with a simpler structure as compared with the conventional structure in which the two support rollers are moved is provided. We were able to.

JP 2003-057963 A Japanese Patent No. 3346063 Japanese Patent Laid-Open No. 5-273787 JP 2003-057995 A JP 2002-108113 A

However, with the above means, there is little transfer dust, and while maintaining a high efficiency transfer rate, it is possible to prevent abnormal transfer images caused mainly by excessive pressurization of the transfer nip such as worm-eating images and hollow images. It was a problem.
Therefore, the present invention has been made in view of the above problems, and the problem is that the transfer nip portion such as a worm-eating image and a hollow image is pressed while maintaining a high efficiency transfer rate with less transfer dust. An object of the present invention is to provide an image forming apparatus that prevents an abnormal transfer image caused mainly by excess.
In addition, the necessary mechanical transfer nip is ensured, and leakage between the bias application electrodes provided in the transfer nip is prevented, preventing transfer dust and reverse transfer at the entrance and exit sides of the transfer nip. It is an object of the present invention to provide an image forming apparatus that applies a bias having the same polarity as the toner polarity.
Furthermore, in the primary transfer nip, after applying a normal transfer bias, when the intermediate transfer member still keeps the mechanical nip with the photosensitive member, a neutralization electric field is applied to complete the appropriate neutralization, and then from the nip. An object of the present invention is to provide an image forming apparatus that applies each bias of a bias application station so as to be peeled off.

The features of the present invention, which is a means for solving the above problems, are listed below.
In the present invention, a drum-shaped image carrier having a radius R [mm] that is rotated by forming a toner image on the surface thereof, and a primary transfer nip width W _T1 (viewed from the image carrier side) in contact with the image carrier. N1) [mm] and a contact angle θ _T1 (N1) [°] forming a nip and rotating in the same direction to transfer the toner image from the image carrier, and a belt-like primary transfer member, On the back surface of the primary transfer member, a primary transfer bias applying member that applies toner and a different polarity bias through a contact energization location at a position in the nip between the upstream end and the downstream end of the transfer nip, In an electrophotographic image forming apparatus using a primary transfer body having a primary transfer correction bias applying member that applies a bias having the same polarity as that of toner in the front or rear primary transfer nip, Primary transcription There wherein regardless of whether a touch contact pressure of the primary transcript of the bias applying means, an image forming apparatus, characterized in that is configured to abut in a state capable of forming the same nip width. Here, the primary transfer member and the intermediate transfer member are the same, and the back surface of the primary transfer member is a non-transfer surface and the surface opposite to the image carrier.
Further, according to the present invention, the relationship between the primary transfer nip width W _T1 (N1) and the rotation direction nip width W _T1 (0) of the transfer member and the photosensitive member in a state in which no bias load is applied to the primary transfer member. ,
W _T1 (0) ≧ 0.9 × W _T1 (N1)
It is characterized by being.
Here, the primary transfer nip width W _T1 (N1) and the state where there is no contact load on the primary transfer body of the bias applying means are the same as the position of the belt drive means on the belt during the primary transfer operation. It is in a state of being in contact with the image carrier while maintaining the same.
Furthermore, in the present invention, the relationship between the contact angle θ _T1 (N1) and the contact angle θ _T1 (0) without the bias application means contact load is
θ _T1 (0) ≧ 0.9 × θ _T1 (N1)
It is characterized by being.
Further, the present invention relates to the maximum distance (upstream L _IN (N1), downstream L _OUT (N1)) from the rotation center of the image carrier to the surface of the primary transfer member during the primary transfer operation and the drum-like image carrier. The maximum difference (L _IN (N1) -R and L _OUT (N1) -R) between the radii R is 0.2 mm or less. Here, the surface of the primary transfer body is the transfer surface and the surface side where the bias applying means is in contact with the back surface.

The present invention is an image forming apparatus comprising a primary transfer bias applying member during a primary transfer operation and a primary transfer nip forming roller that rotates to a distant position. Here, the primary transfer nip forming roller is a backup roller that guides the movement of the primary transfer body so that the primary transfer body on the belt is partially wound around the peripheral surface of the drum-shaped image carrier.
The present invention is characterized in that there is a means for switching the position of the rotating primary transfer nip forming roller, and the primary transfer body can be automatically or manually switched to a position where the primary transfer nip is not formed during non-primary transfer or when stopped. To do.
Further, the present invention separates the means for applying a bias at the primary transfer nip from the belt-like primary transfer body when the rotating primary transfer nip forming roller is switched to a position where the transfer nip is not formed during non-primary transfer. It is characterized by.
The present invention is characterized in that a bias having the same polarity as the bias application polarity on the transfer nip outlet side is applied to the rotating primary transfer nip forming roller during primary transfer.

In the present invention, at least one of a primary transfer bias applying member having the same polarity voltage as the toner and a primary transfer correction bias applying member having the same polarity voltage as that of the toner is in sliding contact with the back surface of the primary transfer body during the primary transfer. The image forming apparatus is a rotating member.
In addition, the present invention provides a non-primary transfer fulcrum for each operation of the primary transfer bias applying member for the same polarity voltage as the toner, the primary transfer correction bias applying member for the toner and the different polarity voltage, and the primary transfer nip forming roller. Sometimes it moves to a position away from the photosensitive member, and the bias applying means and the primary transfer member are brought into a non-contact state.

According to the present invention, by the means for solving the above-described problems, a transfer abnormal image mainly caused by excessive pressurization of the transfer nip portion such as a worm-eating image and a hollow image is maintained while maintaining a high transfer rate with a small transfer dust. It has become possible to provide an image forming apparatus that prevents this.
In addition, the necessary mechanical transfer nip is ensured, and leakage between the bias application electrodes provided in the transfer nip is prevented, preventing transfer dust and reverse transfer at the entrance and exit sides of the transfer nip. Therefore, it is possible to provide an image forming apparatus that applies a bias having the same polarity as the toner polarity.
Furthermore, in the primary transfer nip, after applying a normal transfer bias, when the intermediate transfer member still keeps the mechanical nip with the photosensitive member, a neutralization electric field is applied to complete the appropriate neutralization, and then from the nip. It has become possible to provide an image forming apparatus that applies each bias of a bias application station so as to be peeled off.

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.

According to the present invention, a plurality of bias applying means can be reliably brought into contact with the intermediate transfer belt in the primary transfer nip without leaking each other with a weak contact pressure.
In addition, at a position where the gap between the primary transfer member and the photosensitive member is kept zero or minute, the desired primary transfer member can be neutralized by applying a bias having the same polarity as the toner and a low applied voltage. Furthermore, a suitable primary transfer nip can be reliably formed with a simple configuration. The gap is preferably 200 μm, and the applied voltage is preferably 1 kV or less in absolute value.
Further, according to the present invention, it is possible to prevent strong contamination such as local distortion deformation such as indentation due to contact between the primary transfer member and the photosensitive member, and toner fixation. Furthermore, it is possible to prevent strong contamination such as local distortion deformation such as indentation due to contact between the primary transfer body and the bias applying means, and foreign matter fixation.
In the present invention, the charge imparted to the primary transfer member by applying the primary transfer bias is discharged not only before leaving the photosensitive member but also after leaving, with the same bias power source, thereby suppressing the superimposed primary transfer bias voltage of the color image. In addition, it is possible to prevent the discharge in the vicinity of the upstream of the primary transfer nip entrance upstream of the color to be subjected to the primary transfer next. In addition, the primary transfer bias applying means can be simplified, space-saving, and cost can be reduced. Furthermore, the contact / separation mechanism between the primary transfer body and the primary transfer bias applying means can be simplified and the cost can be reduced.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a view showing a color image forming apparatus of a tandem type indirect transfer system according to an embodiment of the present invention. 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 preferably non-stretching to prevent the expansion and contraction of the image. In this embodiment, the intermediate transfer member 10 is a single-layer belt made of a single-layer polyimide material.
Examples of the resin applied to the intermediate transfer member (intermediate transfer belt) include known thermoplastic resins, thermoplastic elastomers, thermosetting resins, and the like in addition to PI (polyimide). Vinyldenide), ETFE (ethylene-tetrafluoroethylene copolymer), PC (polycarbonate), polyester resin, polyamide resin, polyurethane resin, polyether resin, polyvinyl resin, and the like. It is made of a mixed / synthetic material in which an electric resistance is adjusted by dispersing a conductive material in the resin, and its volume resistivity is in a range of 10 ^{7 to} 10 ¹³ Ω · cm under a 1 kV application condition of a bias voltage level given at the time of primary transfer. In addition, a thin layer of 50 to 200 μm and a layer that is easily bent is preferable.
Examples of the conductive material for adjusting the resistance of the intermediate transfer member include carbon, metal powder such as aluminum and nickel, metal oxide such as titanium oxide, quaternary ammonium salt-containing polymethyl methacrylate, polyvinylaniline, and polyvinylpyrrole. One kind or two or more kinds of conductive polymer compounds such as polydiacetylene, polyethyleneimine, boron-containing polymer compound and polypyrrole can be used.

The intermediate transfer member is wound around the three support rollers 14, 15, and 16 so that the intermediate transfer member can be rotated and conveyed clockwise in the drawing. 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.
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 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, a sheet reversing device for reversing the sheet so as to record images on both sides of the sheet is provided below the secondary transfer device 22 and the fixing device 25 in parallel with the tandem image forming device 20. .

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 the 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. At that time, the scanner 300 is immediately driven to travel 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, and then the switching roller 55 is used to switch the discharge roller. The paper is discharged at 56 and stacked on the paper 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 an 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 body 10 after the image transfer is removed by the intermediate transfer body cleaning device 17 to remove residual toner remaining on the intermediate transfer body 10 after the image transfer, so that the tandem image forming apparatus 20 can prepare for another image formation.
Here, a conductive rubber roller is used as the registration roller 49, and a bias is applied. The surface is a conductive NBR rubber having a diameter of Φ18 and a thickness of 1 mm. The electric resistance is about 10 ⁹ Ω · cm in terms of the volume resistance of the rubber material, and a voltage of about −850 V is applied to the toner transfer side (front side). Although a voltage of about +200 V is applied to the back side of the paper, it may be grounded especially when there is little need to consider paper dust transfer on the back side. Further, a DC bias is applied as the applied voltage, but this may be an AC voltage having a DC offset component. The AC superimposed DC bias can uniformly charge the paper surface. The paper surface after passing through the registration roller 49 is slightly negatively charged. Therefore, in the transfer from the intermediate transfer body 10 to the sheet, care should be taken because the transfer conditions may change compared to the case where no voltage is applied to the registration roller 49.

FIG. 2 is a diagram illustrating a tandem image forming apparatus. In the tandem image forming apparatus 20, the individual image forming means 18 includes, for example, a charging device 60, a developing device 61, a primary transfer device 62, and a photoconductor cleaning around a drum-shaped photoconductor 40 as shown in FIG. The apparatus 63, the static elimination apparatus 64, etc. are provided. In the illustrated example, the photosensitive member 40 has a drum shape in which a photosensitive organic photosensitive material is applied to a base tube made of aluminum or the like to form a photosensitive layer. However, the photosensitive member 40 may have an endless belt shape.
Although not shown in the drawing, at least the photosensitive member 40 is provided, and a process cartridge is formed by all or a part of the parts constituting the image forming unit 18 so that it can be attached to and detached from the copier body 150 at once, thereby improving maintenance. You may do it. Of the portions constituting the image forming unit 18, the charging device 60 is formed in a roller shape in the illustrated example, and charges the photosensitive member 40 by applying a voltage in contact with the photosensitive member 40.
The developing device 61 may use a one-component developer. However, in the illustrated example, a two-component developer composed of a magnetic carrier and a nonmagnetic toner is used. Then, the agitation unit 66 that conveys the two-component developer while stirring and adheres to the developing sleeve 65, and the developing unit 67 that transfers the toner of the two-component developer attached to the developing sleeve 65 to the photoreceptor 40. The stirring unit 66 is positioned lower than the developing unit 67.
The stirring unit 66 is provided with two parallel screws 68. The two screws 68 are partitioned by a partition plate 69 except for both ends. A toner concentration sensor 71 is attached to the developing case 70.

On the other hand, the developing portion 67 is provided with a developing sleeve 65 facing the photoreceptor 40 through the opening of the developing case 70, and a magnet 72 is fixedly provided in the developing sleeve 65. Further, a doctor blade 73 is provided with the tip approaching the developing sleeve 65. In the illustrated example, the distance at the closest portion between the doctor blade 73 and the developing sleeve 65 is set to 500 μm.
Then, the two-component developer is conveyed and circulated while being stirred by the two screws 68 and supplied to the developing sleeve 65. The developer supplied to the developing sleeve 65 is drawn up and held by the magnet 72 to form a magnetic brush on the developing sleeve 65. The magnetic brush is trimmed to an appropriate amount by the doctor blade 73 as the developing sleeve 65 rotates. The developer that has been cut off is returned to the stirring unit 66.

On the other hand, of the developer on the developing sleeve 65, the toner is transferred to the photoreceptor 40 by the developing bias voltage applied to the developing sleeve 65, and the electrostatic latent image on the photoreceptor 40 is visualized. After the visualization, the developer remaining on the developing sleeve 65 leaves the developing sleeve 65 and returns to the stirring unit 66 where there is no magnetic force of the magnet 72. When the toner concentration in the stirring unit 66 becomes light by this repetition, it is detected by the toner concentration sensor 71 and the stirring unit 66 is replenished with toner.
In the illustrated example, the linear velocity of the photosensitive member 40 is 200 mm / s, and the linear velocity of the developing sleeve 65 is 240 mm / s. The developing process is performed with the diameter of the photoconductor 40 being 50 mm and the diameter of the developing sleeve 65 being 18 mm. The toner charge amount on the developing sleeve 65 is in the range of −10 to −30 μC / g. The development gap GP, which is the gap between the photoconductor 40 and the development sleeve 65, can be set in the range of 0.8 mm to 0.4 mm in the related art, and the development efficiency can be improved by reducing the value.
The thickness of the photoreceptor 40 is 30 μm, the beam spot diameter of the optical system is 50 × 60 μm, and the light quantity is 0.47 mW. Further, the developing process is performed with the charging (pre-exposure) potential V ₀ of the photoreceptor 40 being −700 V, the post-exposure potential _VL being −120 V, and the developing bias voltage being −470 V, that is, the developing potential 350 V.

Next, the primary transfer device 62 is formed in a roller shape and is pressed against the photoconductor 40 with the intermediate transfer body 10 interposed therebetween. Separately, it is not limited to a roller shape, and may be a brush or a non-contact corona charger.
The photoconductor cleaning device 63 is provided with a cleaning blade 75 made of polyurethane rubber, for example, with its tip pressed against the photoconductor 40, and the outer periphery of the photoconductor cleaning device 63 contacts the photoconductor 40 and rotates the conductive fur brush 76 in the direction of the arrow. Prepare freely. Further, a metal electric field roller 77 for applying a bias to the fur brush 76 is rotatably provided in the direction of the arrow, and the tip of the scraper 78 is pressed against the electric field roller 77. Further, a collection screw 79 for collecting the removed toner is provided.
Then, residual toner on the photoconductor 40 is removed by a fur brush 76 that rotates in the counter direction with respect to the photoconductor 40. The toner adhering to the fur brush 76 is removed by applying a bias by the electric field roller 77 that contacts the fur brush 76 and rotates in the counter direction. The electric field roller 77 is cleaned by a scraper 78. The toner collected by the photoconductor cleaning device 63 is brought to one side of the photoconductor cleaning device 63 by a collection screw 79, and returned to the developing device 61 by a toner recycling device 80, which will be described in detail, for reuse.

The static eliminator 64 is a lamp, for example, and initializes the surface potential of the photoreceptor 40 by irradiating light.
Then, along with the rotation of the photosensitive member 40, the surface of the photosensitive member 40 is first uniformly charged by the charging device 60, and then the writing light L from the exposure device 21 is irradiated from the exposure device 21 according to the reading content of the scanner 300. As a result, an electrostatic latent image is formed on the photoreceptor 40.
Thereafter, toner is attached by the developing device 61 to visualize the electrostatic latent image, and the visible image is transferred onto the intermediate transfer member 10 by the primary transfer device 62. The surface of the photoconductor 40 after the image transfer is cleaned by removing residual toner with the photoconductor cleaning device 63, and is neutralized with the static eliminator 64 to prepare for another image formation.

FIG. 3 is an enlarged view of a main part of the color copying machine shown in FIG. In FIG. 3, each image forming unit 18 of the tandem image forming apparatus 20, each photoconductor 40 of the image forming unit 18, each developing device 61, each photoconductor cleaning device 63, and each photoconductor 40 of each image forming unit 18. After the respective symbols of the respective primary transfer devices 62 provided to face each other, BK is added for black, Y for yellow, M for magenta, and C for cyan. .
3 is a conductive roller provided in contact with the base layer side of the intermediate transfer body 10 between the primary transfer devices 62, although not shown. The conductive roller 74 prevents a bias applied by each primary transfer device 62 at the time of transfer from flowing into the adjacent image forming means 18 through the intermediate resistance base layer.

Next, the toner recycling apparatus 80 will be described. The recovery screw 79 of the photoconductor cleaning device 63 is provided with a roller portion 82 having a pin 81 at one end. Then, one side of the belt-like collected toner conveying member 83 of the toner recycling device 80 is hung on the roller portion 82, and a pin 81 is inserted into the long hole 84 of the collected toner conveying member 83. The outer periphery of the collected toner conveying member 83 is provided with blades 85 at regular intervals, and the other side is hung on the roller portion 87 of the rotating shaft 86.
The collected toner conveying member 83 is put in the conveying path case 88 together with the rotating shaft 86. The conveyance path case 88 is formed integrally with the cartridge case 89, and one of the above-described two screws 68 of the developing device 61 is placed at the end of the developing device 61 side.
Then, the driving force is transmitted from the outside to rotate the collection screw 79, and the collection toner conveying member 83 is rotated and conveyed, and the toner collected by the photoconductor cleaning device 63 is conveyed to the developing device 61 through the conveyance path case 88. Then, the screw 68 is rotated into the developing device 61. Thereafter, as described above, the two screws 68 are conveyed and circulated while stirring together with the developer already in the developing device 61, supplied to the developing sleeve 65, and cut off by the doctor blade 73, and then the photosensitive member 40. And the latent image on the photoreceptor 40 is developed.

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 embodiment.
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. In the description so far, the toner is prepared by a pulverization method, but a toner prepared by a polymerization method or the like can also 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.
Here, the shape factor is originally sphericity and is defined as “the surface area of a sphere having the same volume as a particle / the surface area of an actual particle * 100%”. Calculate with The definition is “circumference of circle having the same projected area as the particle / projection contour length of the actual particle * 100%”. Then, the closer the projected circle is to a perfect circle, the closer to 100%. The range of the volume average particle diameter of the toner is preferably 3 to 12 μm. In the present invention, it is possible to sufficiently cope with an image having a high resolution of 1200 dpi or more with 6 μm.

The magnetic particles (carriers) contain a magnetic material such as ferrite with a metal or resin as a core, and the surface layer is coated with a silicon resin or the like. The particle size is preferably in the range of 20 to 50 μm. The resistance is optimally a dynamic resistance in the range of 10 ^{4 to} 10 ⁶ Ω. However, the measurement method is to hold a roller (Φ20 mm; 600 rpm) containing a magnet, contact an electrode having a width of 65 mm and a length of 1 mm with a gap of 0.9 mm, and set the upper limit voltage level (high resistance silicon coating). It is a measured value when an applied voltage of 400 V is applied to the carrier and several volts is applied to the iron powder carrier.

The developing sleeve 65 has a non-magnetic rotatable sleeve shape, and a plurality of magnets 72 are disposed therein. Since the magnet 72 is fixed, a magnetic force can be applied when the developer passes through a predetermined place. In the illustrated example, the diameter of the developing sleeve 65 is φ18, and the surface is roughened so as to fall within the range of 10 to 30 μm RZ by performing a process of forming a plurality of grooves having a depth of 1 to several mm by sandblasting.
The magnet 72 has five magnetic poles of N ₁ , S ₁ , N ₂ , S ₂ , and S ₃ in the rotation direction of the developing sleeve 65 from the position of the doctor blade 73. (Toner + magnetic particles) formed by the magnet 72 is carried on the developing sleeve 65 as a developer, and the toner is mixed with the magnetic particles to obtain a specified charge amount. In the illustrated example, a range of −10 to −30 [μC / g] is preferable. The developing sleeve 65 to form a magnetic brush of the developer, in the region of the S ₁ side of the magnet 72 is disposed to face the photoreceptor 40.

In the illustrated example, as shown in FIG. 3, the cleaning device 17 is provided with two fur brushes 90 and 91 as cleaning members. The fur brushes 90 and 91 are Φ20 mm, acrylic carbon, 6.25 D / F, 100,000 pieces / inch ² , 1.0 × 10 ⁷ Ω, and are in contact with the intermediate transfer member 10 to be in the counter direction. It is provided to rotate. A bias having a different polarity is applied to each fur brush 90, 91 from a power source (not shown).
Such fur brushes 90 and 91 are provided so as to rotate in the forward direction in contact with metal rollers 92 and 93, respectively. In this example, a (−) voltage is applied from the power source 94 to the metal roller 92 on the upstream side in the rotation direction of the intermediate transfer body 10, and a (+) voltage is applied from the power source 95 to the metal roller 93 on the downstream side. The tips of the blades 96 and 97 are pressed against the metal rollers 92 and 93, respectively.
Then, along with the rotation of the intermediate transfer member 10 in the direction indicated by the arrow, the surface of the intermediate transfer member 10 is cleaned by applying a bias (−), for example, using the fur brush 90 on the upstream side. If -700V is applied to the metal roller 92, the fur brush 90 becomes -400V, and the (+) toner on the intermediate transfer member 10 is transferred to the fur brush 90 side. The removed toner is further transferred from the fur brush 90 to the metal roller 92 due to a potential difference, and scraped off by the blade 96.

Further, the toner on the intermediate transfer member 10 is removed by the fur brush 90, but a lot of toner still remains on the intermediate transfer member 10. Those toners are charged (−) by a (−) bias applied to the fur brush 90. This is considered to be charged by charge injection or discharge.
However, the toner can be removed by performing cleaning by applying a bias (+) this time using the fur brush 91 on the downstream side. The removed toner is transferred from the fur brush 91 to the metal roller 93 due to a potential difference, and scraped off by the blade 97.
The toner scraped off by the blades 96 and 97 is collected in a tank (not shown). You may make it return to the image development apparatus 61 using a toner recycling apparatus.
After the cleaning with the fur brush 91, most of the toner is removed, but a small amount of toner still remains on the intermediate transfer member 10. These toners are charged to (+) by a (+) bias applied to the fur brush 91. However, even when toner cannot be removed by the two fur brushes 90 and 91 and toner remains on the intermediate transfer member 10, it is reversely transferred to the photosensitive member 40BK at the black primary transfer position and recovered by the photosensitive member cleaning device 63BK. can do.

FIG. 4 shows a primary transfer portion in the present invention. The photoconductor 120 and the intermediate transfer belt 121 form a mechanical nip Nm from the suspension rollers 123 and 124 and rotate in the same direction.
The transfer blade 100, the outlet blade 101, and the inlet blade 102 are each made of a polymer or rubber. For example, in the former material, carbon is kneaded into a material such as urethane resin, silicon resin, or fluorine resin, and the resistance is adjusted to within 10 ^{6 to} 10 ¹³ Ω. The resistance is desirably about 10 ^{6 to} 10 ¹⁰ Ω. In the latter material, carbon is kneaded into a rubber material such as CR, EPDM, and hydrin rubber, and the resistance is adjusted to substantially the same value. At the time of molding, it is formed into a plate shape having a thickness of T0.5 to T1.5 mm, and is formed in the direction in which the polymer flows in the belt rotation direction so that the wear mechanical deterioration is minimized.
As for the arrangement position of these blades, the transfer blade 100 is generally slightly downstream from the approximate center of Nm. Based on the position of the transfer blade 100, an exit width Nex obtained by photographing the position up to the exit blade 101 on the belt and an entrance width Nin projected up to the position of the entrance blade 102 on the belt. Note that the sum of these Nin and Nex is the effective bias application width Ne of the transfer electric field as a whole. Further, Nm ≧ Ne.

Individually, each bias power source is provided with a bias source 110 for the transfer blade 100, a bias source 112 for the other blade 102, and a bias source 114 for the blade 104. Although not shown, these can be controlled by a CPU or the like.
Further, these blades are supported by a support holder 105 and are put together. During primary transfer, the intermediate transfer belt on the dimensions is used to reduce the deformation due to wear of the blade and to suppress frictional force on the intermediate transfer belt, and to suppress scratches, wear and deterioration of the intermediate transfer belt. Is preferably 0.5 mm or less, and the contact pressure exerted on the intermediate transfer belt is preferably 50 N / m or less in terms of linear pressure in the blade length direction. If the blade deflection is large and the blade interval having a different potential and polarity approaches abnormally, electric leakage occurs between these blades, causing damage to the power supply and the like.

For comparison, an example of the conventional primary transfer nip of FIG. 5 will be described. Nin is a distance between the belt contact positions of the transfer blade 100 and the suspension roller 124, and Nex is a distance between the belt contact positions of the transfer blade 100 and the suspension roller 123. In this conventional example, Nm <Ne. Here, FIG. 6 shows an expected view of the surface potential of the intermediate transfer belt. Here, the transfer bias 110 applies a (+) bias in order to transfer the (−) toner. The entrance bias 112 is (−) biased to suppress the transfer of the toner.
In the conventional example, since the (+) charge on the non-image surface of the belt still remains at the separation portion of the intermediate transfer belt on the remaining exit side, the gap potential rises due to peeling and a small discharge occurs. On the other hand, in the present invention, since the exit bias 111 is added to the closely contacted belt, the neutralization is completed, and this discharge does not occur. Therefore, transfer dust and the like are improved.

FIG. 7 shows the behavior regarding the voltage of the resistance of the intermediate transfer member used in the present invention. In the figure, the resistance is low under an electric field, the resistance increases when the electric field deviates from the electric field, and the square root of the electric field is proportional to the current. In addition, even if there is electric field variability in a normal ion conductive material, there are fluctuations up to this point. This is a process advantage. However, since an intermediate transfer belt containing such an ionic conductive material generally has a large environmental fluctuation, it is necessary to change and control the use conditions depending on the environment.
Here, each of the blades 100, 101, and 102 is fixedly connected to the same support member with an insulator at regular intervals. This is useful for increasing the position accuracy. The resistance of the blade is preferably 10 ^{6 to} 10 ¹¹ Ω. These resistors are capable of supplying and supplying necessary and sufficient charges for the intermediate transfer belt and avoiding troubles caused by concentrated leaks.

Here, FIG. 8 shows an example in which negative bias applying means in the vicinity of the entrance and exit of the primary transfer nip are summarized. Here, the same bias voltage can be applied. Here, the main electrode 140 is a medium resistance member having a square cross-section bar shape. The power supply 110 is connected by an electrode (not shown). Here, the medium resistance member is the aforementioned carbon dispersion type member.
On the other hand, the integrated electrode 142 for the inlet / outlet is made of a medium resistance material and is formed into a complicated shape, but here it has a diaphragm shape indicated by 145 in the figure, and this portion is deformed. With this, an appropriate pressing force can be given.
Here, the entrance / exit electrodes are supported by an insulating support member 143 and supported by an insulating support member 141 that supports the main electrode 140. The former support material 143 is made of a general insulating resin or the like. Further, the support member 141 is made of a member that is somewhat deformed, such as rubber. When the medium resistance member is used, the energization resistance can be changed between the entrance end and the exit end of the effective electric field Ne. As a result, a stronger (-) charge is applied to the inlet and a weaker (-) charge is applied to the outlet. Moreover, the dust on the entrance side can be eliminated and the amount of discharge can be reduced at the exit.

FIG. 9 is a view showing a state in which a roller P is provided for forming the primary transfer nip of the present invention. FIG. 9 (2) shows a state during primary transfer, and FIG. 9 (3) shows a state during non-transfer.
The bias applying means has been shown as an example of a blade, but as the blade material, a known material such as a rubber blade, a metal blade, or a resin blade having electrical conductivity capable of imparting a necessary charge to the intermediate transfer member can be applied. . As another example of bias applying means, a brush, a small-diameter metal roller, or the like may be used.
As for the electrical characteristics of the intermediate transfer member, the volume resistivity is suitably 10 ^{7 to} 10 ¹³ Ω · cm, more preferably 10 ^{8 to} 10 ¹⁰ Ω · cm when a bias voltage level of 1 kV applied at the time of the primary transfer member is applied. It is. Further, the surface resistivity of the abutting surface of the bias voltage applying means, which is the surface resistivity of the back surface, is suitably 10 ^{8 to} 10 ¹² Ω / □, more preferably 10 ^{10 to} 10 ¹¹ Ω / □.
The load torque of the intermediate transfer transfer member is 1.0 Nm or less for high durability even when the load due to the frictional resistance when the bias applying unit is brought into contact or the frictional load resistance of the cleaning member becomes maximum. Preferably, in this embodiment, the contact pressure (linear pressure) of the intermediate transfer member and the bias applying unit to the friction surface is suppressed to 20 N / m or less, or the friction coefficient between the friction surfaces is 0.5 or less. At least one surface is provided with a known lubricating substance to make it slippery, so that it is 0.3 Nm or less.

FIG. 10 (1) and FIG. 10 (2) are explanatory views according to the embodiment of the present invention. In this example, the contact width between the intermediate transfer belt and the photosensitive member is not changed by the contact and separation of the bias applying means 5 and 6 with respect to the intermediate transfer belt.
In the present invention, the primary transfer nip width W _T1 (N1) when the primary transfer body of the primary transfer correction bias application member, which is a bias application unit, is brought into contact with the photoconductor is the primary transfer of the bias application unit. It is within 10% increase of the nip width W _T1 (0) in the rotational direction of the transfer member and the photosensitive member in a state where there is no contact load on the member. In the present invention, the equation can also be expressed as W _T1 (N1) ≦ 1.11 × W _T1 (0).
In the preferred nip formation state of the present invention, W _T1 (0) is sufficiently wide and 4 mm or more is preferable, and in the state of the present invention, W _T1 (N1) = W _T1 (0).
However, it is difficult to secure W _T1 (0) sufficiently wide (for example, 3.9 mm or less) because the photosensitive drum diameter is a small diameter of Φ30 mm or less, or due to the arrangement of the transfer nip forming roller shown in FIG. When the tip contact position of the bias applying means is at the entrance of the transfer nip and it is necessary to secure a distance of 4.0 mm from the bias applying means contact position to the primary transfer correction bias applying member tip contact position, The primary transfer correction bias applying member, which is a bias applying means, is brought into contact with the vicinity of the rotation direction exit of the contact nip between the transfer member and the photosensitive member in the state without contact load, and the nip width, W _T1 (N1) ≈W _T1 (0). For example, it is possible to prevent an excessive current from flowing between the tips of the two types of bias applying means (or members).
Even when the bias applying means is applied to the primary transfer body at a weak contact pressure or lower, W _T1 (N1)> W _T1 (0). For example, in the above-described embodiment, the case is 50 N / m or less or 20 N / m in terms of linear pressure. Therefore, in the present invention, the equation indicates the upper limit of W _T1 (N1).

Examples and comparative examples are shown below.
(Example)
Example 1
When W _T1 (0) = 4.0 mm and the contact pressure of the bias applying means to the primary transfer member is 5 N / m, W _T1 (N1) = 4.0 to 4.4 mm and W _T1 (0)> 0. .9 × W _T1 (N1) or 1.11 × W _T1 (0)> W _T1 (N1) ≧ W _T1 (0).

(Comparative Example 1)
When W _T1 (0) = 3.0 mm and the contact pressure of the bias applying means to the primary transfer member is 10 N / m, W _T1 (N1) = 4.0 to 4.4 mm, and 0.68 × W _T1 (N1 ) ≦ W _T1 (0) ≦ 0.75 × W _T1 (N1), or 1.47 × W _T1 (0)> W _T1 (N1) ≧ 1.33 × W _T1 (0).

Similarly, FIG. 11 (1) and FIG. 11 (2) are explanatory diagrams according to the embodiment of the present invention.
In the present invention, the contact angle θ _T1 (N1) of the primary transfer member with respect to the photosensitive drum when the primary transfer correction bias applying member that is a bias applying means is in contact with the photosensitive member via the primary transfer member is It is within 10% increase of the contact angle θ _T1 (0) between the primary transfer member and the photosensitive drum in a state where there is no contact load on the primary transfer member of the bias applying unit. Further, the equation can be expressed as θ _T1 (N1) ≦ 1.11 × θ _T1 (0), and the contact angle is also referred to as a winding angle.
In a preferred nip formation state of the present invention, θ _T1 (0) is sufficiently large, and the photosensitive drum diameter is preferably 7.6 ° or more at Φ60 mm. This corresponds to a nip width of 4.0 mm or more. In the state of the present invention, θ _T1 (N1) = θ _T1 (0).
However, it is difficult to secure θ _T1 (0) sufficiently large (for example, 7 ° for a photosensitive drum of Φ60 mm) due to the small diameter of the photosensitive drum of Φ30 mm or less or due to the arrangement of the transfer nip forming roller illustrated in FIG. The tip contact position of the primary transfer bias applying means is at the transfer nip entrance, and the contact angle from the bias applying means contact position to the primary transfer correction bias applying member tip contact position is 7 as described above. When it is necessary to secure 6 °, the primary transfer correction bias applying member as bias applying means is brought into contact with the vicinity of the exit in the rotation direction of the contact nip between the transfer member and the photosensitive member in a state without contact load. Therefore, the contact angle is θ _T1 (N1) ≈θ _T1 (0). For example, it is possible to prevent an excessive current from flowing between the tips of the two types of bias applying means (or members).
Even when the bias applying means is applied to the primary transfer body at a weak contact pressure or less, θ _T1 (N1)> θ _T1 (0). For example, in the above-described embodiments, it is applied to the primary transfer member at 50 N / m or less or 20 N / m in terms of linear pressure. Therefore, in the present invention, the equation indicates the upper limit of θ _T1 (N1).

Examples and comparative examples are shown below.
(Example)
(Example 2)
When θ _T1 (0) = 7.6 ° and the contact pressure of the bias applying means to the primary transfer member is 5 N / m, θ _T1 (N1) = 7.6 to 8.4 ° and θ _T1 (0) > 0.9 × θ _T1 (N1), or 1.11 × θ _T1 (0)> θ _T1 (N1) ≧ θ _T1 (0).

(Comparative Example 2)
When θ _T1 (0) = 5.7 ° and the contact pressure of the bias applying means to the primary transfer member is 10 N / m, θ _T1 (N1) = 7.6 to 8.4 °, and 0.68 × θ _T1 (N1) ≦ θ _T1 (0) ≦ 0.75 × θ _T1 (N1) or 1.47 × θ _T1 (0)> θ _T1 (N1) ≧ 1.33 × θ _T1 (0).

Similarly, FIG. 12 (1) and FIG. 12 (2) are explanatory diagrams according to the embodiment of the present invention. FIG. 12A shows a state in which the bias application electrodes 5 and 6 are in contact with the intermediate transfer body 7, and FIG. 12B shows that the bias application electrodes 5 and 6 are separated from the intermediate transfer body 7. Represents a state.
When the diameter of the photosensitive drum is 60 mm, the radius R is 30 mm. In the state of (1), in the present invention, L _IN (N1) and L _OUT (N1) are both 30 mm.
On the other hand, in the state of (2), the transfer nip forming roller P plays a role of pressing the intermediate transfer member 7 against the photosensitive member side, so that the front side of the intermediate transfer member 7 at the point where the bias application electrode contacts in FIG. In some cases, the distances L _IN (N1) and L _OUT (N1) are 30 mm, but the bias application electrode is located at a position where a slight gap is generated between the photosensitive member, such as a small diameter of Φ30 mm or less. The contact position may be determined, and the gap in that case is kept to 0.2 mm or less. (1) The bias application electrode contact pressure when the gap is set to 0 mm in the state shown in FIG. / M or less.

  FIGS. 13A and 13B are explanatory diagrams according to the embodiment of the present invention. The roller P and the bias applying means 5 and 6 are integrally configured to change the distance from the photosensitive member.

In FIG. 14, the means for applying two types of bias to the intermediate transfer belt are both elastic bodies. In the example shown in FIG. 15, the tip of a thin metal plate of SUS, phosphor bronze, titanium copper, and high beryllium copper is shown in FIG. In the example in which an R-bending part is formed and the R part is brought into contact with the intermediate transfer belt, the contact pressure is made uniform and the intermediate transfer belt is prevented from being worn or damaged.
FIG. 16 shows an example in which the primary transfer bias means is a rotating roller.
FIG. 17 shows an example in which the primary transfer bias means is a rotating roller as in FIG. 16, but the roller has a very small diameter, and a backup roller is provided below to prevent uneven contact pressure due to bending deformation. Indicates.
FIG. 18 shows that when the distance between the tip portions of the two types of bias applying means is narrowed, the upstream bias applying means is adjusted so that the distance between the insulating spacer portions placed in the fixed portion is widened. An example is shown in which the bias application means on the lower and upstream sides is a counter contact.
FIG. 19 shows an example in which a roller having a very small diameter is used as a means for applying the same polarity bias as that of the downstream toner, contrary to FIG.
FIG. 20 shows an example in which the means for applying two kinds of biases is a roller having a very small diameter and a backup roller.
FIG. 15 shows that the tip of the bias applying means is a metallic thin plate of SUS, phosphor bronze, titanium copper, and high beryllium copper with an R bend as described in the explanation of FIG. 14, and the R portion is brought into contact with the intermediate transfer belt. In this example, the contact pressure is made uniform and the intermediate transfer belt is prevented from being worn or damaged.
Each of the examples in FIGS. 9 to 20 shows an example in which the bias applying means having different polarities are uniformly brought into contact with the intermediate transfer belt with a weak pressure in the primary transfer nip. In addition, the same effect can be obtained, and there are various modifications such as using a brush as a bias applying means.

1 illustrates an embodiment of the present invention and is a diagram illustrating a color image forming apparatus of a tandem type indirect transfer system. FIG. It is a figure which shows a tandem image forming apparatus. FIG. 2 is an enlarged view of a main part of the color copying machine shown in FIG. 1. It is the primary transfer part in this invention. It is the figure which showed the primary transfer nip example of the prior art example. An expected view of the surface potential of the intermediate transfer belt is shown. It is a figure which shows the behavior regarding the voltage of intermediate transfer body resistance used for this invention. It is the figure which showed the example which put together the negative polarity bias application means of primary transfer nip entrance / exit vicinity. It is a figure which shows a mode that the roller P for forming the primary transfer nip of this invention was provided. It is explanatory drawing by the Example of this invention. It is explanatory drawing by the Example of this invention. It is explanatory drawing by the Example of this invention. It is explanatory drawing by the Example of this invention. It is the figure which showed the Example (at the time of transcription | transfer) of this invention. It is the figure which showed the example of the bias application member of this invention. It is the figure which showed the Example (at the time of transcription | transfer) of this invention. It is the figure which showed the Example (at the time of transcription | transfer) of this invention. It is the figure which showed the Example (at the time of transcription | transfer) of this invention. It is the figure which showed the Example (at the time of transcription | transfer) of this invention. It is the figure which showed the Example (at the time of transcription | transfer) of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging apparatus 3 Exposure part 4 Developing apparatus 5 Bias application means (primary transfer apparatus)
6 Bias applying means (intermediate static neutralizer after primary transfer)
7 Intermediate transfer member 8 Secondary transfer device (sheet conveyance belt)
DESCRIPTION OF SYMBOLS 9 Paper feeder 10 Intermediate transfer body 11 Photoconductor cleaning apparatus 12 Intermediate transfer body cleaning apparatus 14 Support roller 15 Support roller 16 Support roller 17 Cleaning apparatus 18 Image forming means 20 Tandem image forming apparatus 21 Exposure apparatus 22 Secondary transfer apparatus 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 Feeding roller 43 Paper bank 44 Paper feed cassette 45 Separation roller 46 Paper feed path 47 Transport roller 48 Paper feed path 49 Registration roller 50 Paper feed roller 51 Manual feed tray 52 Separating roller 53 Manual paper feed path 55 Switching claw 56 Paper discharge roller 57 Paper output tray 60 Charging Device 61 Development device 62 Primary Transfer device 63 Photoconductor cleaning device 64 Static elimination device 65 Developing sleeve 66 Stirring unit 67 Developing unit 68 Screw 69 Partition plate 70 Developing case 71 Toner concentration sensor 72 Magnet 73 Doctor blade 74 Conductive roller 75 Cleaning blade 76 Fur brush 77 Electric field roller 78 Scraper 79 recovery screw 80 toner recycling device 90 fur brush 91 fur brush 92 metal roller 93 metal roller 94 power supply 95 power supply 96 blade 97 blade 100 transfer blade 101 exit blade 102 entrance blade 104 blade 105 support holder 110 transfer bias 111 exit bias 112 entrance Bias 114 Bias 120 Photoconductor 121 Intermediate transfer belt 123 Suspension roller 124 Suspension roller 140 Main pole 141 Insulating support material 42 inlet outlet integrated electrode 143 insulating support member 150 copier body 200 feeder table 300 Scanner 400 automatic document feeder (ADF)
S sheet P transfer nip forming roller L writing light L1 height difference between the primary transfer nip forming roller P and the lower part of the photosensitive drum (at the time of primary transfer)
L1 ′ Height difference between the primary transfer nip forming roller P and the lower part of the photosensitive drum (= L5 + the thickness of the intermediate transfer member 7) (during non-primary transfer)
L2 A gap between the intermediate transfer member 7 and the bias applying means 5 and 6 (at the time of non-primary transfer)
L3 Primary transfer nip forming roller P drop amount when pressure is released (non-primary transfer)
L4 Bias applying means 5 in the state shown in FIG. 13 (1) and a restoration dimension L5 in the height direction in the state shown in FIG. 13 (2) L5 A gap T between the primary transfer belt and the photosensitive drum T Tandem type image forming apparatus

Claims (10)

A drum-shaped image carrier having a radius R [mm] on which a toner image is formed and rotated;
A nip having a primary transfer nip width W _T1 (N1) [mm] and a contact angle θ _T1 (N1) [°] as viewed from the image carrier side is formed in contact with the image carrier and rotated in the same direction. A belt-like primary transfer member capable of transferring the toner image from the image carrier;
A primary transfer bias applying member for applying a toner and a different polarity bias through a contact energization point at a position between an upstream end portion and a downstream end portion of the transfer nip on the back surface of the primary transfer body;
A primary transfer correction bias applying member that applies a bias having the same polarity as the toner in the primary transfer nip in front of or behind the energized portion;
In an electrophotographic image forming apparatus using a primary transfer body having
The image forming apparatus has a configuration in which the primary transfer nip during a primary transfer operation abuts in a state where the same nip width can be formed regardless of the presence or absence of contact abutment pressure on the primary transfer body of the bias applying unit. An image forming apparatus. The image forming apparatus according to claim 1,
The image forming apparatus has a relationship between the primary transfer nip width W _T1 (N1) and the rotation direction nip width W _T1 (0) of the transfer member and the photosensitive member in a state in which no bias load is applied to the primary transfer member. ,
W _T1 (0) ≧ 0.9 × W _T1 (N1)
An image forming apparatus. The image forming apparatus according to claim 1,
In the image forming apparatus, the relationship between the contact angle θ _T1 (N1) and the contact angle θ _T1 (0) without the bias application means contact load is
θ _T1 (0) ≧ 0.9 × θ _T1 (N1)
An image forming apparatus. The image forming apparatus according to claim 1,
In the image forming apparatus, the maximum distance (upstream L _IN (N1), downstream L _OUT (N1)) from the rotation center of the image carrier to the surface of the primary transfer member during the primary transfer operation and the drum-like image carrier An image forming apparatus, wherein the maximum difference (L _IN (N1) -R and L _OUT (N1) -R) of the radius R is 0.2 mm or less. The image forming apparatus according to claim 1, wherein:
The image forming apparatus includes a primary transfer bias applying member during a primary transfer operation,
An image forming apparatus comprising: a primary transfer nip forming roller that rotates at a distant position. The image forming apparatus according to claim 5.
The image forming apparatus has a means for switching a rotating primary transfer nip forming roller position, and can automatically or manually switch the primary transfer member to a position where the primary transfer nip is not formed during non-primary transfer or when stopped. An image forming apparatus. The image forming apparatus according to claim 6.
In the image forming apparatus, when the rotating primary transfer nip forming roller is switched to a position where the transfer nip is not formed during non-primary transfer, the means for applying a bias at the primary transfer nip is separated from the belt-shaped primary transfer body. An image forming apparatus. The image forming apparatus according to claim 5.
The image forming apparatus is characterized in that a bias having the same polarity as the bias application polarity on the transfer nip outlet side is applied to a rotating primary transfer nip forming roller during primary transfer. The image forming apparatus according to any one of claims 1 to 8,
In the image forming apparatus, at least one of a primary transfer bias applying member having the same polarity voltage as that of the toner and a primary transfer correction bias applying member of the toner and the different polarity voltage is provided.
An image forming apparatus, wherein the image forming apparatus is a non-rotating member that is in sliding contact with the back surface of a primary transfer body during primary transfer. In the image forming apparatus according to any one of claims 1 to 9,
The image forming apparatus includes a primary transfer bias applying member having the same polarity voltage as that of the toner, a primary transfer correction bias applying member of the toner and the different polarity voltage, and a fulcrum portion of the operation of the primary transfer nip forming roller. Sometimes it moves away from the photoconductor,
An image forming apparatus characterized in that the bias applying means and the primary transfer member are brought into a non-contact state.

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