JPH112936A - Electrophotographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the nipping width of a transfer nipping part small, while keeping high transfer efficiency by pressing a photoreceptor belt on an intermediate transfer body, in a state where the photoreceptor belt is linearly held, between a tension roller and a cleaning roller, through the use of a transfer roller. SOLUTION: The transfer roller 23 presses the photoreceptor belt 1 on an intermediate transfer body belt 19 from the rear surface of the belt 1, in the transfer nipping part in a position facing an intermediate transfer body belt supporting/carrying roller 20. In other words, the transfer roller 23 presses the photoreceptor belt 1 on the intermediate transfer body belt 19, in the state where the belt 1 is linearly kept, between the tension roller 3 and the cleaning roller 4. Therefore, even if the transfer nipping part, becomes small because the pressing force of the transfer roller 23 is directly exerted on the intermediate transfer body belt 19 through the belt 1, the belts 1 and 19 come into uniform contact with each other. Consequently, the flocculation of toner between the belts 1 and 19 can be prevented to eliminate a failure in transfer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus such as an electronic copying machine, a laser beam printer, and a facsimile.

[0002]

2. Description of the Related Art In recent years, a color electrophotographic apparatus uses a plurality of developing devices of different colors to sequentially develop a plurality of color images on a belt-shaped photosensitive member, and transfers a toner image on the photosensitive member to an intermediate transfer member. And then collectively transfer to transfer paper (hereinafter referred to as “paper”).

In this type of apparatus, each color is developed,
Since the developed images are sequentially superimposed, it must be ensured that development of a certain color is not performed by a developing unit of another color during development of a certain color. As one of the methods, there is a method in which only the developing roller of the developing device of a required color is rotated, and the developing rollers of the remaining developing devices are not rotated. Further, there is a method in which only a developing roller of a necessary developing device is rotated to bring only the developing device close to the photoreceptor belt, and to keep other developing devices away from the photoreceptor belt.

FIG. 3 is a sectional view showing a main part of a conventional electrophotographic apparatus using the latter technique. Since the illustrated color image electrophotographic apparatus uses a non-magnetic one-component developing method, the developing roller of the developing device is configured to be able to contact and separate from the photosensitive belt.

Hereinafter, the structure of a photosensitive belt in a conventional electrophotographic apparatus will be described with reference to FIG.

An endless photoreceptor belt 1 has a belt driving roller 2 connected to a driving motor (not shown) at a position where an electrostatic latent image is formed, and a developing device contacts the belt driving roller 2 with the belt driving roller 2. The tension roller 3 forming a horizontal surface to be formed and the cleaning roller 4 corresponding to the photoconductor cleaning member 9 for scraping residual toner on the photoreceptor belt 1 are band-tuned so as to form a horizontal surface. The rollers 2, 3, 4 rotate around in the direction of arrow A.

[0007] The tension roller 3 is rotatably mounted on a holding member 36 about the center of rotation of the cleaning roller 4 as a swing center. The transfer roller 23 is rotatably attached to the holding member 36 between the tension roller 3 and the cleaning roller 4. An elastic spring 43 is hung on the holding member 36,
The tension roller 3 applies a predetermined elasticity to the photosensitive belt 1 by the elasticity of the spring 43.

An intermediate transfer belt (intermediate transfer member) 19 is provided corresponding to the photosensitive belt 1 and is rotated by an intermediate transfer belt support roller 20. A part of the outer periphery of the intermediate transfer belt 19 is in contact with a part of the outer periphery of the photoreceptor belt 1 to form a transfer nip portion. The toner image formed on the photoreceptor belt 1 is The image is transferred to the intermediate transfer body belt 19 at the section.

The transfer roller 23 is disposed near the tension roller 3 in the transfer nip portion, that is, on the upstream side in the rotation direction of the photosensitive belt 1, and presses this against the intermediate transfer belt 19. Therefore, as shown in the figure, the photoreceptor belt 1 is deformed by the transfer roller 23 between the tension roller 3 and the cleaning roller 4 along the shape of the intermediate transfer member belt supporting / conveying roller 20, whereby the intermediate transfer member belt is deformed. A large nip width is formed between the nip 19 and the nip.

When the toner image of each color formed on the photosensitive belt is transferred onto the intermediate transfer belt 19, the nip width is increased between the photosensitive belt 1 and the intermediate transfer belt 19. This is for maintaining uniform contact and improving transfer efficiency.

[0011]

However, when such a large nip width is formed, pressure is applied to the toner image by the electrostatic attraction force between the photosensitive belt and the intermediate transfer member, and toner aggregation is promoted. On the contrary, the transfer efficiency may be deteriorated. That is, a large nip width has a trade-off relationship with the cause of transfer failure.

In a configuration in which the photoreceptor belt is suspended and supported by a plurality of rollers, the photoreceptor belt itself is an endless belt formed by bonding both ends of a cloth in terms of cost. There is an error in the circumference at each point in the axial direction. For this reason, the photoreceptor belt is wavy where the belt winding angle with respect to the roller is large. In the above-described conventional example, the winding angle of the belt in the belt driving roller portion is maximized in order to improve driving reliability and save space.

The undulation occurs in the charging area and the developing area.
As a result, the surface potential of the photosensitive belt varies,
An image defect occurs due to variation in the state of development contact between the photosensitive belt and the developing roller.

It is an object of the present invention to provide an electrophotographic apparatus capable of reducing the nip width of a transfer nip formed between a photosensitive belt and an intermediate transfer member while maintaining good transfer efficiency. And

Another object of the present invention is to provide an electrophotographic apparatus capable of preventing an image defect caused by a wavy photosensitive belt.

[0016]

In order to solve this problem, an electrophotographic apparatus according to the present invention comprises a first roller, a second roller, and a third roller which are provided rotatably, respectively. An endless photoreceptor belt having an electrostatic latent image formed on the outer peripheral surface and being rotated around while being tuned and supported by the first, second and third rollers, and an electrostatic latent image formed on the photoreceptor belt A plurality of developing units that supply toner between the first roller and the second roller to develop an electrostatic latent image and form toner images of different colors on the photosensitive belt; An intermediate transfer member that transfers the formed toner image between the second roller and the third roller and collectively transfers the toner image to transfer paper is provided between the second roller and the third roller. And the photosensitive belt between the second roller and the third roller is straightened. A transfer roller that forms a transfer nip by pressing it against the intermediate transfer body while maintaining the transfer state, thereby maintaining good transfer efficiency while keeping the photosensitive belt and the intermediate transfer body together. The nip width of the formed transfer nip can be reduced.

In this electrophotographic apparatus, the transfer roller can be constituted by a member whose outer periphery has elasticity.

Further, the electrophotographic apparatus of the present invention comprises a first roller, a second roller, and a third roller which are provided rotatably, and a band adjustment by the first, second, and third rollers. An endless photoreceptor belt that is supported and rotated around and an electrostatic latent image is formed on the outer peripheral surface, and the electrostatic latent image formed on the photoreceptor belt is moved between the first roller and the second roller. A plurality of developing units that supply toner at the same time to develop the electrostatic latent image and form toner images of different colors on the photosensitive belt,
An intermediate transfer member for transferring a toner image formed on the photoreceptor belt between a second roller and a third roller and transferring the toner image to a transfer sheet; a second roller and a third roller; And a transfer roller that presses the photoreceptor belt against the intermediate transfer member to form a transfer nip.
The rigidity of the first roller is higher than the rigidity of the second and third rollers. This causes the photosensitive belt to undulate at the transfer nip. Can be prevented from being caused by image defects.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a first roller and a second roller which are rotatably provided, respectively.
And an endless photoreceptor belt on which an electrostatic latent image is formed on the outer peripheral surface while being tuned and supported by the first, second and third rollers, and a photosensitive belt. A first roller and a second roller on the electrostatic latent image formed on the body belt;
Develops the electrostatic latent image by supplying toner between the rollers,
A plurality of developing units for forming toner images of different colors on the photoreceptor belt; and the toner images formed on the photoreceptor belt are transferred between the second roller and the third roller and transferred. An intermediate transfer member that transfers images onto paper collectively, and is provided between the second roller and the third roller, while the photosensitive belt between the second roller and the third roller is held in a linear state. This is an electrophotographic apparatus having a transfer roller that forms a transfer nip by pressing this against an intermediate transfer member, and a uniform contact pressure is ensured between the photoreceptor belt and the intermediate transfer member. The nip width of the transfer nip formed by the photoreceptor belt and the intermediate transfer member can be reduced while maintaining high transfer efficiency.

The invention according to claim 2 of the present invention provides:
The invention according to claim 1, wherein the transfer roller is an electrophotographic apparatus in which the outer periphery is formed of a member having elasticity, and the pressure applied to the toner image in the transfer nip portion is further reduced, so that the toner image is damaged. And transfer of higher quality becomes possible.

According to a third aspect of the present invention, the first roller and the second roller are provided rotatably.
And an endless photoreceptor belt on which an electrostatic latent image is formed on the outer peripheral surface while being tuned and supported by the first, second and third rollers, and a photosensitive belt. A first roller and a second roller on the electrostatic latent image formed on the body belt;
Develops the electrostatic latent image by supplying toner between the rollers,
A plurality of developing units for forming toner images of different colors on the photoreceptor belt, and the toner images formed on the photoreceptor belt are transferred between the second roller and the third roller and transferred. An intermediate transfer member that transfers the image onto paper at once, and a transfer roller that is provided between the second roller and the third roller and that presses the photosensitive belt against the intermediate transfer member to form a transfer nip portion; An electrophotographic apparatus in which the rigidity of the first roller is higher than the rigidity of the second and third rollers,
Since the undulation of the photoreceptor belt is generated at the transfer nip portion, an effect of preventing an image defect due to the undulation of the photoreceptor belt can be prevented.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. In these drawings, the same members are denoted by the same reference numerals, and duplicate description is omitted.

(Embodiment 1) FIG. 1 is a sectional view showing an electrophotographic apparatus according to an embodiment of the present invention, and FIG. 2 is a sectional view showing a main part of FIG.

An endless photoreceptor belt 1 on which a photosensitive receiving layer such as an organic photoconductor (OPC) is applied in the form of a thin film has a drive motor (not shown) where an electrostatic latent image is formed.
And a belt driving roller (first roller) 2 connected to the developing device 7B, 7Y, 7
A tension roller (second roller) 3 that forms a horizontal surface with which the M and C contact, and a cleaning roller (third roller) 4 that corresponds to the photoconductor cleaning 9 that scrapes residual toner on the photoconductor belt 1. The three rollers are tuned and supported so as to form a horizontal plane. The photoreceptor belt 1 is moved by an arrow A by these rollers 2, 3, and 4.
Is rotated in the direction.

The tension roller 3 is movably held by a holding member 36 about the center of rotation of the cleaning roller 4 as a swing center. A rigid metal transfer roller 23, which is located between the tension roller 3 and the cleaning roller 4, is rotatably attached to the holding member 36.

The holding member 36 has a spring 43 which is elastic.
The tension roller 3 applies a predetermined tension in a substantially horizontal direction of the photosensitive belt 1 by the elastic force of the spring 43. And the photoreceptor belt 1
When the photosensitive belt 1 is pushed down by the contact of the developing rollers 44 of the developing units 7B, 7Y, 7M, 7C located above the tensioner 3, the tension roller 3 is displaced and the tension of the photosensitive belt 1 increases. Is absorbed, and a change in the circumference is prevented.

Above the photoreceptor belt 1, black (B), yellow (Y), magenta (M), and cyan are arranged along the outer peripheral surface in the rotation direction downstream of a portion where an electrostatic latent image to be described later is formed. Developing devices 7B, 7Y, 7M, and 7C for storing the developers, that is, the toners, of the respective colors of (C) are provided. A laser beam generator 6 for forming an electrostatic latent image on the photosensitive belt 1 at the position of the belt driving roller 2 is provided beside the developing units 7B, 7Y, 7M, 7C. Further, a photoreceptor cleaning device 9, a static eliminator 10, and a charger 5 are provided below the photoreceptor belt 1.

The charger 5 includes a charging wire 11 made of a tungsten wire or the like, a shield plate 12 made of a metal plate, and a grid plate 13. And the charging wire 1
When a high voltage is applied to the photosensitive belt 1, the charged wire 11 causes a corona discharge, and the photosensitive belt 1
Are uniformly charged. Reference numeral 14 denotes a laser beam of image data emitted from the laser beam generator 6. In this embodiment of the laser printer, the laser beam 14 is
Controlled by a signal from a host computer (not shown), a plurality of electrostatic latent images are formed on the photoreceptor belt 1 respectively corresponding to specific components among a plurality of predetermined color components.

The developing units 7B, 7Y, 7M and 7C for the respective colors are
The developing units 7B, 7Y, 7M, and 7C are arranged in a predetermined storage section provided in the apparatus main body at equal intervals and detachably in a horizontal row (horizontal direction). Except for the same configuration.

When developing an electrostatic latent image of a predetermined color corresponding to each of the developing units 7B, 7Y, 7M, and 7C, the developing units 7B, 7Y, 7M, and 7C abut on the photosensitive belt 1. Contact cams 15B, 15Y, 15M, and 15C are provided, and when the contact cams 15B, 15Y, 15M, and 15C do not push down the developing devices 7B, 7Y, 7M, and 7C in the direction of the photoreceptor belt 1, they are removed. Separation springs 16B, 16Y, 16M, and 16C are provided to separate from the standby position. The contact cams 15B, 15Y, 15M, and 15C are provided on the developing device removable cover 17 on the upper surface of the apparatus main body.
The developing unit detachable cover 17 is supported by a fixed developing unit detachable cover shaft 18 so as to be freely opened and closed.

The intermediate transfer member unit 8 includes an intermediate transfer member belt (intermediate transfer member) 19 made of a conductive resin or the like, and three intermediate transfer member belt supporting / conveying rollers 20 on which the intermediate transfer member belt 19 is adjusted. , 21 and 22. The intermediate transfer member may be a drum-shaped member other than the belt-shaped member as in the present embodiment. In order to transfer the toner image on the photoconductor belt 1 onto the intermediate transfer belt 19, an intermediate transfer roller 23 is disposed opposite the photoconductor belt 1 with the intermediate transfer belt 19 interposed therebetween.

The intermediate transfer belt 19 whose surface peripheral length is set to be equal to the surface peripheral length of the photoreceptor belt 1 has a part of its outer periphery at the position of the intermediate transfer belt support and transport roller 20. And a transfer nip portion is formed in contact with a part of the outer periphery of the transfer nip. Then, the toner image formed on the photosensitive belt 1 is transferred to the intermediate transfer belt 19 at the transfer nip portion.

The transfer roller 23 forms the transfer nip and presses the photosensitive belt 1 against the intermediate transfer belt 19.

As shown in detail in FIG. 2, the transfer roller 23 transfers the photosensitive belt 1 to the intermediate transfer belt 19 from the back surface thereof at a transfer nip portion opposite to the intermediate transfer belt support roller 20. Pressing. That is, the transfer roller 23 presses the photosensitive belt 1 between the tension roller 3 and the cleaning roller 4 against the intermediate transfer belt 19 while maintaining the photosensitive belt 1 in a linear state.

Accordingly, the pressing force of the transfer roller 23 directly acts on the intermediate transfer belt 19 via the photoreceptor belt 1, so that even if the transfer nip portion becomes small, the photoreceptor belt 1 and the intermediate transfer Is contacted uniformly.
As a result, the pressure of the toner image due to the electrostatic attraction force between the photoreceptor belt 1 and the intermediate transfer belt 19 is reduced, so that toner aggregation is prevented and transfer failure is prevented.

In the first embodiment, the material of the transfer roller 23 is made of metal. However, the outer periphery of the transfer roller 23 is made of an elastic member such as urethane rubber having a rubber hardness of 45 degrees or less or foamed sponge. May be. According to this, since the pressure applied to the toner image at the transfer nip portion is further reduced, damage to the toner image is reduced, and higher quality transfer can be performed.

In order to scrape off the residual toner on the intermediate transfer belt 19, an intermediate transfer belt cleaning device 24 is installed near the intermediate transfer belt support roller 21. The intermediate transfer body belt cleaning device 24 is separated from the intermediate transfer body belt 19 while a synthetic image is formed on the intermediate transfer body belt 19, and comes into contact with the intermediate transfer body belt 19 only when it is used for cleaning.

A paper cassette 25 for storing paper 26 is provided directly below the apparatus main body. And the paper 26
Are sent out one by one from a paper cassette 25 to a paper transport path 28 by a paper feed roller 27. In order to match the position of the sheet 26 with the composite image formed on the intermediate transfer belt 19, a registration roller 29 for temporarily stopping and waiting the sheet 26 is provided in pressure contact with the driven roller 30. Further, a paper transfer roller 31 for transferring the composite image formed on the intermediate transfer belt 19 to the paper 26 is provided on the paper transport path 28, and the composite image is transferred to the paper 2.
Only when the image is transferred onto the transfer belt 6, it is rotated in contact with the intermediate transfer belt 19.

In order to fix the composite image transferred to the paper 26, a fixing device 32 including a heat roller 33 having a heat source therein and a pressure roller 34 is disposed. Then, the composite image transferred by the pressure and heat is fixed on the sheet 26 by the pinching rotation between the heat roller 33 and the pressure roller 34 when passing through the fixing device 32, and a color image is formed. A paper discharge roller pair 35 is provided downstream of the fixing device 32. Then, at the rear end of the paper transport path 28,
A paper discharge tray 37 provided at the upper part of the machine body is provided, and the paper 26 is stored here.

The paper feed unit 41 constituting the paper feed path 28 has a manual feed tray 40 and a manual feed roller 42 incorporated therein.
, And paper of a size other than the paper 26 accommodated in the printer.

The operation of the electrophotographic apparatus configured as described above will be described below. In FIG. 1, first, a high voltage is applied to a charging line 11 in a charger 5 connected to a high voltage power supply to cause a corona discharge to uniformly charge the surface of the photoreceptor belt 1 to about -500V to -650V. Next, the photoreceptor belt 1 is rotated in the direction of arrow A by a driving device (not shown), and the photoreceptor belt 1 is charged uniformly.
When a laser beam 14 corresponding to a predetermined color of a plurality of color components, for example, a black (B) image, is irradiated on the surface of the photoreceptor belt 1, the irradiated portion on the photoreceptor belt 1 loses its charge and the electrostatic latent image Is formed. On the other hand, in the developing device 7B in which black toner contributing to development is stored, a DC motor (not shown) is rotated by a color selection signal from a host computer (not shown), and thus the developing device 7B is connected. When the contact cam 15B rotates by 180 degrees, the contact cam 15B comes into contact with the photosensitive belt 1 against the pressing force of the separation spring 16B. The developing device 7B that has completed the development moves from the contact position with the photoreceptor belt 1 to the standby position by the spring force of the separation spring 16B when the contact cam 15B is further rotated by 180 degrees. While the developing device 7B is developing, the other developing devices 7Y, 7M, and 7C are separated from the photosensitive belt 1.

Next, when the color of cyan (C) is selected, for example, a DC motor (not shown) is rotated in a predetermined direction, and the connected cam 15C is rotated by 180 degrees, and the developing unit 7C is rotated.
Are brought into contact with the photosensitive belt 1. Then, cyan development is started by the same operation as described above. In the case of a copying machine or a printer using four colors, such a developing operation is sequentially repeated four times, and the developing operation is performed on the intermediate transfer body belt 19.
The toner images of colors B, C, M, and Y are superimposed to form a composite image.

When a high voltage having a polarity opposite to that of the toner is applied to the paper transfer roller 31, the composite image formed in this manner is moved from the paper cassette 25 to the paper transport path 28 by the pressure.
Are collectively transferred to the sheet 26 sent along the line, and then sent to the fixing device 32. Then, the image is fixed by the heat and the sandwiching force between the heat roller 33 and the pressure roller 34 to form a color image. Paper 26 that has passed through fixing device 32
Is discharged to a paper discharge tray 37 through a paper discharge roller pair 35.

(Embodiment 2) In an electrophotographic apparatus according to Embodiment 2 of the present invention, a belt driving roller (first roller) for rotating the photosensitive belt around is a stainless steel roller having a thickness of about 2 mm. The tension roller (second roller) and the cleaning roller (third roller) are made of aluminum and have a thickness of about 1 mm.
Therefore, the rigidity of the belt driving roller is set higher than the rigidity of the tension roller and the cleaning roller. The other portions are substantially the same as the electrophotographic apparatus according to the first embodiment or the conventional electrophotographic apparatus described above.

As described above, when the rigidity of the belt driving roller is higher than that of the other two rollers, the undulation of the photosensitive belt 1 does not occur near the belt driving roller but near the tension roller and the cleaning roller, in other words, the transfer. Generated at the nip.

Here, in the transfer nip portion, the transfer roller presses the photosensitive belt against the intermediate transfer belt in order to secure transferability, and therefore, the transfer nip is structurally less susceptible to undulation.

Therefore, undulations in the charging area and the developing area are eliminated, and image defects due to variations in the surface potential of the photosensitive belt and variations in the state of development contact between the photosensitive belt and the developing roller can be prevented.

The thickness of each roller described above is not limited to this, and can be variously set as long as the rigidity of the belt driving roller is higher than the other two rollers.

In the above description, the present invention is applied to an example in which the present invention is applied to a color laser beam printer. However, irrespective of color or monochrome, various other electrophotographic apparatuses such as an electronic copying machine and a facsimile are used. Can be similarly implemented.

[0050]

As described above, according to the present invention, the transfer roller presses the intermediate transfer member while keeping the photosensitive belt between the second roller and the third roller in a linear state. Therefore, a uniform contact pressure is secured between the two. As a result, an effective effect that the nip width of the transfer nip formed by the photoreceptor belt and the intermediate transfer body can be reduced while maintaining good transfer efficiency can be obtained.

Further, according to the present invention, since the outer periphery of the transfer roller is formed of an elastic member, the pressure applied to the toner image at the transfer nip portion is further reduced.
An advantageous effect is obtained that the damage to the toner image is further reduced and higher quality transfer is possible.

According to the present invention, by making the rigidity of the first roller higher than that of the second and third rollers, the photoreceptor belt undulates at the transfer nip portion. An effective effect of preventing image defects due to waving of the body belt can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an electrophotographic apparatus according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a main part of FIG. 1;

FIG. 3 is a sectional view showing a main part of a conventional electrophotographic apparatus.

[Explanation of symbols]

 Reference Signs List 1 photoconductor belt 2 belt drive roller (first roller) 3 tension roller (second roller) 4 cleaning roller (third roller) 7B, 7Y, 7M, 7C developing device 19 intermediate transfer belt (intermediate transfer member) ) 23 transfer roller 26 paper (transfer paper)

Claims (3)

[Claims] A first roller, a second roller, and a third roller, each of which is rotatably provided; and a band which is tuned and supported by the first, second, and third rollers, and is rotated around the outer periphery. An endless photoreceptor belt on which an electrostatic latent image is formed on a surface;
A plurality of developing units that supply toner between the first roller and the second roller to develop the electrostatic latent image and form toner images of different colors on the photoconductor belt; An intermediate transfer member that transfers the toner image formed thereon between the second roller and the third roller and collectively transfers the toner image to transfer paper; and the second roller and the third roller. And pressing the photoconductive belt between the second roller and the third roller against the intermediate transfer member while keeping the photoreceptor belt in a linear state. An electrophotographic apparatus, comprising: a transfer roller for forming an image. 2. An electrophotographic apparatus according to claim 1, wherein said transfer roller has an outer periphery made of an elastic member. 3. A first roller, a second roller, and a third roller which are rotatably provided, respectively, and are tuned and supported by the first, second, and third rollers to rotate around the outer periphery. An endless photoreceptor belt on which an electrostatic latent image is formed on a surface;
A plurality of developing units that supply toner between the first roller and the second roller to develop the electrostatic latent image and form toner images of different colors on the photoconductor belt; An intermediate transfer member that transfers the toner image formed thereon between the second roller and the third roller and collectively transfers the toner image to transfer paper; and the second roller and the third roller. And a transfer roller for pressing the photosensitive belt against the intermediate transfer member to form a transfer nip portion, wherein the first roller has a rigidity of the second and third rollers. An electrophotographic apparatus, wherein the rigidity of the roller is higher than the rigidity of the roller.