JP2003248376A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent image staining caused by the soiling of an externally laying roller installed on the downstream side of the secondary transfer part of an intermediate transfer belt. <P>SOLUTION: A varistor and a diode or a resistor are connected to the externally laying roller. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer.

[0002]

2. Description of the Related Art FIG. 4 shows a schematic structure of a conventional image forming apparatus. The image forming apparatus shown in the figure is an electrophotographic four-color full-color laser beam printer having four image forming units and an intermediate transfer belt.

An image forming apparatus as shown in the figure uses a primary transfer section to transfer the toner images formed on a plurality of photosensitive drums.
Images are sequentially formed on the intermediate transfer member, and the full-color image superimposed on the intermediate transfer member is collectively transferred onto the recording material by the secondary transfer unit.

In the image forming apparatus described above, the recording material P passing through the secondary transfer portion T2 may be wound around the intermediate transfer belt 1 to cause a conveyance jam. 2000-1373
There is an 86 publication.

According to Japanese Patent Laid-Open No. 2000-137386, the pressing member 1d is pressed from the outside of the intermediate transfer belt 1 on the downstream side of the secondary transfer portion T102 to bend the intermediate transfer belt 1 inward. As a result, in the separation portion A of the recording material P, the winding amount of the intermediate transfer belt 1 around the outer peripheral surface of the secondary transfer opposing roller 1b can be increased, so that the curvature of the intermediate transfer belt 1 has a secondary transfer opposing roller 1b.
The curvature is almost the same as that of b, and good separation of the recording material P can be realized.

[0006]

However, according to the above-mentioned image forming apparatus, the toner not transferred onto the recording material at the secondary transfer portion adheres to the pressure member 1d, and the pressure member 1d is formed.
If it accumulates on the recording material d, the toner may fall on the recording material passing vertically below the pressure member 1d and stain the recording material. In order to solve this problem, the intermediate transfer member cleaning device 18 is provided on the intermediate transfer belt 1, on the downstream side of the secondary transfer portion T2,
It is also possible to arrange it on the upstream side of the pressure member 1d,
In the case of such a configuration, if there is no rigid member facing the intermediate transfer member cleaning member 18, a large pressing force cannot be applied and complete cleaning cannot be performed.
However, the additional provision of the rigid member facing the intermediate transfer member cleaning member 18 causes a cost increase.

Further, in another structure disclosed in Japanese Patent Laid-Open No. 2000-137386, an opposing roller is provided at an opposing position of the pressing member sandwiching the intermediate transfer belt 1, and the pressing member and the opposing roller are arranged. The secondary transfer residual toner on the intermediate transfer belt is transferred to the pressing member by forming an electric field between the secondary transfer residual toner and the cleaning unit provided in contact with the pressing member to recover the secondary transfer residual toner. There is also a method of recovering the dust and removing the stain on the pressure member, but such a configuration requires a counter roller and a power source for forming an electric field, which also causes a large increase in cost.

The present invention has been made in view of the above circumstances, and when an intermediate transfer belt is used, the recording material can be prevented from being soiled with a structure that achieves good separation of the recording material while suppressing cost. It is an object of the present invention to provide an image forming apparatus designed to achieve the above.

[0009]

According to the invention for achieving the above object, a plurality of image forming units are arranged along the running direction of an endless intermediate transfer belt which is wound around a plurality of rollers. The toner images formed on the image carriers of the image forming units are sequentially primary-transferred onto the intermediate transfer belt at a primary transfer portion between the image carrier and the intermediate transfer belt, and then, In an image forming apparatus for collectively secondary-transferring a plurality of toner images on an intermediate transfer belt onto a recording material by applying a bias to a secondary transfer member at a secondary transfer portion, the intermediate transfer belt is One of the plurality of rollers that are stretched over is a secondary transfer facing roller that faces the secondary transfer member, and the secondary transfer facing roller and its downstream side along the running direction of the intermediate transfer belt. Last Law in A pressure member that bends the intermediate transfer belt inward with respect to the outer common tangent line connecting the and, and has a recording material conveyance path vertically below the pressure member; After the toner image is transferred onto the recording material, a toner recovery means for recovering the toner remaining on the intermediate transfer belt is provided, and the pressure member is on the downstream side of the secondary transfer portion on the intermediate transfer belt and the toner. In the image forming apparatus located on the upstream side of the collecting means, the impedance of the pressing member is controlled. Further, the impedance of the transfer charging means may be controlled by connecting the transfer charging means to a non-linear element.

Further, the non-linear element may be a varistor, a Zener diode or a resistor.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment> FIG. 1 shows an example of an image forming apparatus according to the present invention. The image forming apparatus shown in FIG.
FIG. 1 is an electrophotographic four-color full-color laser beam printer having four image forming units and an intermediate transfer belt (intermediate transfer member). FIG. 1 is a vertical cross-sectional view showing the schematic configuration thereof.

Each of the image forming units is a photosensitive drum 11a, 11b corresponding to a toner of each color of yellow, magenta, cyan and black as an image carrier.
It has 11c and 11d. The transfer belt 1 as an intermediate transfer member is in contact with each of the above-described photosensitive drums 11a to 11d to form a respective primary transfer portion (primary transfer nip portion) T1.

The resistance of the intermediate transfer belt 1 preferably has a volume resistivity of 10 ⁸ to 10 ¹⁵ Ω · cm, and is made of urethane resin, fluorine resin, nylon resin, polyimide resin, silicone rubber, or the like. It is possible to use an elastic material such as hydrin rubber, or a material in which carbon or conductive powder is dispersed to adjust the resistance.

If the resistance value of the intermediate transfer belt 1 is increased, it is possible to suppress the lateral scattering of the toner image at the time of transfer. Therefore, in this embodiment, the volume resistivity is 10 ^13.
Ω · cm was used.

The intermediate transfer belt 1 includes a driving roller 1a, a secondary transfer counter roller 1b, and a supporting roller 1c which are contained therein.
It is wound around a roller of a book. The belt pressure roller (rotating body) 1d arranged outside the intermediate transfer belt 1 applies tension to the intermediate transfer belt 1 by pressing the intermediate transfer belt 1 so as to bend the intermediate transfer belt 1 inward. Although the tension depends on the material of the intermediate transfer belt 1, the elongation is 1
It is desirable that the intermediate transfer belt 1 is set so that the intermediate transfer belt 1 is not fractured or permanently deformed. It is set to apply a load. The belt pressure roller 1d is located downstream of the secondary transfer portion T2 on the intermediate transfer belt and upstream of the intermediate transfer belt cleaning device described later.

In each primary transfer section, the primary transfer rollers 15a, 15b, 15c and 15d are connected to the photosensitive drum 11a.
The intermediate transfer belt 1 is sandwiched between 11b, 11c, and 11d to form a primary transfer portion T1. Each of the primary transfer rollers is formed by covering the outer peripheral surface of the core metal with an elastic material having a medium resistance (actual resistance when applying 1 kV is 10 ⁶ to 10 ¹⁰ Ω) to form a roller shape. In this embodiment, transfer is performed on each primary transfer roller by controlling a constant current of 10 μA.

The secondary transfer roller 3 is formed by coating the outer peripheral surface of a core metal with an EPDM foam layer having a medium resistance value, and is arranged at a position facing the secondary transfer counter roller 1b. The intermediate transfer belt 1 is provided between the transfer opposite roller 1b and
A secondary transfer portion (secondary transfer nip portion) T2 is formed between the intermediate transfer belt 1 and the intermediate transfer belt 1. The recording material P such as paper is nipped and conveyed at the secondary transfer portion. The current control of the secondary transfer roller is generally controlled to be variable depending on the type of recording material and the environment, but in this embodiment, when the image is formed on the plain paper in the normal environment, the control is 20 μA.

The operation of the image forming apparatus as a whole will be described below with the addition of a description of the configuration as appropriate.

The photosensitive drum 11a is a driving means (not shown).
1 is rotated counterclockwise in FIG. 1, uniformly charged by the primary charger 12a, and modulated by the image information signal sent from the host computer.
An electrostatic latent image is formed on the surface by the laser light from a. At this time, the intensity of the laser light and the irradiation spot diameter are appropriately set according to the resolution of the image forming apparatus and the desired image density, and the electrostatic latent image on the photosensitive drum 11a is a portion irradiated with the laser light ( Bright part) potential VL is about -100V
In addition, the potential VD of the non-irradiated portion (dark portion) is held at about -700 V charged by the primary charger 12a.

The electrostatic latent image reaches the portion facing the developing device 14a by the rotation of the photosensitive drum 11a, and the toner charged to the same polarity (in this embodiment, negative polarity) is applied to the bright portion of the electrostatic latent image. It is attached and developed as a toner image. In four-color full-color image formation, toner images are similarly formed by the photosensitive drums 11a to 11d corresponding to the respective colors, the primary charging devices 12a to 12d, the scanners 13a to 13d, and the developing devices 14a to 14d. Are sequentially primary-transferred onto the intermediate transfer belt 1 at each primary transfer portion T1 and are combined so as to overlap on the intermediate transfer belt 1. In each primary transfer portion T1, a toner image is formed by an electric field formed in the primary transfer portion T1 by a voltage (+100 to +1000 V) having a polarity opposite to that of the toner applied to the conductive rollers 15a to 15d in contact with the back surface of the intermediate transfer belt 1. Is primarily transcribed. The intermediate transfer belt 1 is the photosensitive drum 11d.
The toner images of four colors are carried on the intermediate transfer belt 1 at a stage when the primary transfer portion T1 of FIG. On the other hand, the photosensitive drum 11 that has completed the primary transfer of the toner image
The surfaces of a to 11d are cleaned by the cleaning devices 16a to 16d, respectively, and then prepared for the next image forming step.

Next, one recording material P such as paper is taken out from the paper feeding means (not shown) and inserted into the secondary transfer portion T2.
At this time, a voltage (+1 to +6 kV) having a polarity opposite to that of the toner is applied to the secondary transfer roller 3, so that the toner images of four colors are collectively secondary-transferred from the intermediate transfer belt 1 onto the recording material P. Transcribed.

The intermediate transfer belt 1 is a belt pressure roller 1.
Since the amount of winding of the intermediate transfer belt 1 around the outer peripheral surface of the secondary transfer opposing roller 1b can be increased in the separating portion A of the recording material P by the action of d, the curvature of the intermediate transfer belt 1 has a secondary transfer opposing roller. The curvature is almost the same as that of 1b, and good separation of the recording material P can be realized. If the diameter of the secondary transfer counter roller 1b is 30 mm or less, it is possible to handle a thin recording material P as well. When the thickness is preferably 25 mm or less, good separation can be ensured even with a paper having a basis weight of 60 g / m ² , and the reliability of the image forming apparatus can be improved.

The recording material P carrying the unfixed toner image after passing through the secondary transfer portion T2 reaches the fixing device 17 and is heated.
It is pressed and fixed as a permanent image. On the other hand, the surface of the intermediate transfer belt 1 that has finished transferring the toner image to the recording material P is removed by the intermediate transfer body cleaning device 18. The intermediate transfer member cleaning device 18 uses a cleaning blade made of urethane rubber as the intermediate transfer belt 1.
The secondary transfer residual toner adhering to the surface of the intermediate transfer belt 1 (the toner remaining on the surface of the intermediate transfer belt 1 without being secondarily transferred to the recording material P at the time of secondary transfer) is scraped by bringing it into contact with the surface. This is collected as waste toner in a waste toner box. The intermediate transfer member cleaning device 1
8, the support roller 1c is arranged to face each other, so that a pressing force sufficient to scrape off the toner can be applied without separately providing the facing member of the intermediate transfer member cleaning device 18. Further, since the cleaning is performed by scraping off the toner with the blade member, the intermediate transfer member cleaning device 18 does not need a bias applying unit or the like, and a simple structure with reduced cost can be obtained.

In the above image forming apparatus, the belt pressure roller 1d is located on the downstream side of the secondary transfer portion T2 on the intermediate transfer belt 1 and at the intermediate transfer member cleaning device 18.
Since it is located on the upstream side of, the toner comes in contact with the secondary transfer residual toner due to the arrangement. When the secondary transfer residual toner accumulates on the belt pressure roller 1d, the recording material conveyance path is vertically below the belt pressure roller 1d, and therefore the toner attached to the belt pressure roller 1d is recorded. The recording material may become dirty due to falling onto the material.

This is because the charged secondary transfer residual toner adheres to and accumulates on the belt pressure roller 1d by an electrostatic mirroring force. When this accumulated amount increased to some extent, it dropped from the belt pressure roller 1d and soiled the recording material. When the current flowing through the belt pressure roller 1d was measured with an ammeter, a current of about 5 μA was flowing. In other words, by the primary transfer, about 4
A current of 0 μA, which is supplied from the outside by secondary transfer, is about 2
The current of 0 μA was not completely canceled and remained on the back surface of the intermediate transfer belt, and this charged electric charge was removed by the belt pressure roller 1d. It was found that the secondary transfer residual toner adheres to the belt pressure roller 1d due to this static elimination current.

Therefore, a high voltage varistor 20 having a varistor voltage of 3 kV was connected to the belt pressure roller 1d to regulate the current flowing through the belt pressure roller 1d.

With such a structure, it is possible to reduce the adhered amount to about 1/3 of the conventional one. Specifically, A
When 7% of the image is formed on 4 size paper, when about 30,000 sheets of image are formed so far, dirt is attached on the paper, but by using the above configuration, 10
Up to ten thousand sheets, stains no longer adhere to the paper.

The current flowing through the belt pressure roller 1d and the amount of toner attached depend on the resistance of the intermediate transfer belt, the configuration of the secondary transfer portion, the type of recording material, the environment in which the apparatus is used, etc. It is needless to say that the present invention is not limited to such a configuration, and the same effects can be obtained according to the present invention even when various factors as described above are touched.

Further, in the present embodiment, a roller-shaped member which is driven to rotate with respect to the intermediate transfer belt is used as the pressing member. However, by adopting the roller shape, the pressure applied to the intermediate transfer belt is made constant. Has the advantage of reducing the damage given to the intermediate transfer belt,
By being driven to rotate with respect to the intermediate transfer belt, there is an advantage that wear between the intermediate transfer belt and the intermediate transfer belt is suppressed to be small.

According to the first embodiment, even if a good recording material separating property is achieved by the pressing member 1d, even if the recording material conveying path is provided vertically below the pressing member 1d, the pressing member 1d can be used. It is possible to prevent the recording material from being contaminated due to the toner drop, and it is not necessary to additionally dispose a rigid member facing the intermediate transfer member cleaning member 18, so that the cost can be suppressed.

<Second Embodiment> FIG. 2 shows a schematic view of an image forming apparatus according to the second embodiment. In the second embodiment, the diode 21 is connected to the pressing member instead of the varistor 20. The intermediate transfer belt used had a deposition resistivity of 10 ¹⁰ Ωcm. This is because the currents of the primary transfer and the secondary transfer can be suppressed, and the cost can be reduced by reducing the capacity of the high voltage transformer. The other basic configuration is similar to that of the first embodiment.

Even in the above-described structure, the secondary transfer residual toner on the pressing member 1d can be prevented from adhering, and the pressing member 1d can achieve good recording material separability, but can also be applied. Even when the recording material conveying path is provided vertically below the pressure member 1d, it is possible to prevent the recording material from being contaminated due to toner falling from the pressure member 1d, and to add a rigid member facing the intermediate transfer member cleaning member 18. Since it is not necessary to dispose it, the cost can be reduced.

Further, as shown in FIG. 3, the same effect was obtained when a resistor 22 of 50 MΩ was connected instead of the diode.

[0035]

As described above, according to the present invention,
While ensuring good separation of the recording material from the intermediate transfer belt, even when the recording material conveying path is vertically below the belt pressing member, toner is transferred from the pressing member onto the recording material conveying path. Since the recording material is not dropped, the recording material can be prevented from being soiled, and the intermediate transfer member cleaning member 18 can be prevented.
Since it is not necessary to additionally dispose a rigid body member facing to, it is possible to reduce the cost.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an image forming apparatus according to a first embodiment.

FIG. 2 is a schematic diagram showing an image forming apparatus according to a second embodiment.

FIG. 3 is a schematic diagram showing another image forming apparatus according to the second embodiment.

FIG. 4 is a vertical cross-sectional view showing a schematic configuration of a conventional image forming apparatus.

[Explanation of symbols]

1 Intermediate Transfer Belt 1a Driving Roller 1b Secondary Transfer Opposing Roller 1c Supporting Roller 1d Pressing Member (Rotating Member, Belt Pressing Roller) 3 Secondary Transfer Rollers 11a, 11b, 11c, 11d Image Carrier (Photosensitive Drum) 18 Intermediate Transfer member cleaning device 20 Varistor 21 Diode 22 Resistance A Separation part P Recording material T1 Primary transfer part T2 Secondary transfer part

Claims (3)

[Claims] 1. A toner image formed on an image carrier of each of the image forming units, in which a plurality of image forming units are arranged along a running direction of an endless intermediate transfer belt which is stretched over a plurality of rollers. Are sequentially primary-transferred onto the intermediate transfer belt at a primary transfer portion between the image carrier and the intermediate transfer belt, and then a plurality of toner images on the intermediate transfer belt are transferred to the secondary transfer portion. In the image forming apparatus that collectively performs the secondary transfer on the recording material by applying a bias to the secondary transfer member, one of the plurality of rollers around which the intermediate transfer belt is wound is A secondary transfer facing roller that faces the next transfer member, wherein a secondary transfer facing roller along the running direction of the intermediate transfer belt and an outer common tangent line connecting the roller closest to the secondary transfer facing roller to the secondary transfer facing roller Than the common tangent The intermediate transfer belt is provided with a pressing member that bends inward, and a recording material conveyance path is provided vertically below the pressing member. After the toner image is transferred to the recording material, the intermediate transfer belt is transferred onto the intermediate transfer belt. In the image forming apparatus, wherein the pressing member is located downstream of the secondary transfer portion on the intermediate transfer belt and upstream of the toner collecting means. An image forming apparatus characterized by controlling the impedance of a pressure member. 2. The image forming apparatus according to claim 1, wherein the impedance of the transfer charging unit is controlled by connecting the transfer charging unit to a non-linear element. 3. The non-linear element is a varistor, a Zener diode or a resistor.
Or the image forming apparatus according to 2.