JP2000338796A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image forming device by which transfer material can be surely separated at a curvature at a separation part without utilizing any auxiliary separating means such as a separating claw impairing durability of the image carrier or a destaticizing charger disturbing a transfer toner image even when the radius of curvature of an image carrying surface of an image carrier at the separation part is difficult to be made small. SOLUTION: In this device, a periphery surface of a secondary transfer roll 8 formed in the radius Rb of curvature is smaller than radius Ra of curvature of the image carrying surface of an intermediate transfer drum 5D is brought into press contact with the image carrying surface of the intermediate transfer drum 5D to elastically deform the surface of an elastic body layer 5a of the intermediate transfer drum 5D to be made along the periphery surface of the secondary transfer roll 8. Thus, the direction of movement (a) of the transfer paper P is changed to the direction being rapidly away from the image carrier surface along the periphery surface of the separating roll 13 when the transfer paper P is passed through a nip part between the secondary transfer roll 8 and the intermediate transfer drum 5D, thus the transfer paper P is separated at the curvature by the small radius of curvature at the nip part and the strength of the transfer paper P.

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, a facsimile, and a printer.
A transfer material that transfers a toner image carried on an image bearing surface of an image carrier such as a photoconductor drum or an intermediate transfer drum onto a transfer material such as an OHP sheet or copy paper, and then moves with the image bearing surface of the image carrier. The present invention relates to an image forming apparatus provided with a separating means for separating the image forming apparatus from the image bearing surface.

[0002]

2. Description of the Related Art In this type of image forming apparatus, generally,
A toner image formed by a well-known electrophotographic image forming process is carried on an image bearing surface of an image carrier such as a photoconductor or an intermediate transfer body formed in a drum shape or a belt shape. Then, a transfer material such as an OHP sheet or copy paper is fed to a transfer portion between a transfer unit such as a transfer charger or a transfer roller to which a predetermined transfer bias is applied and the image carrier. The transfer unit transfers the toner image onto the transfer material. The transfer material onto which the toner image has been transferred is separated from the image bearing surface of the image bearing member, and after the toner image is fixed by the fixing unit, is discharged outside the apparatus by a discharge roller or the like as a discharge unit. .

As an image forming apparatus for forming a full-color image on the transfer material, there is a method in which the transfer material is held on a transfer material carrier such as a transfer drum and is placed on a photosensitive member as an image carrier. The formed yellow, magenta, cyan, and black toner images are sequentially superimposed on the transfer material by the transfer unit and transferred, and then the transfer material is separated from the transfer material carrier by the separation unit. And fixing the full-color toner image transferred onto the transfer material by the fixing means. The image (toner image) of each color of yellow, magenta, cyan, and black formed on the photosensitive member as the latent image carrier was not directly transferred to the transfer material, but was once formed in a drum shape or a belt shape. While the primary transfer is performed while sequentially superimposing on the image carrying surface of the intermediate transfer body as the image carrying body, the transfer material is fed to a transfer portion between the image carrying surface of the intermediate transfer body and the transfer means, After the full-color toner image primary-transferred onto the image bearing surface of the intermediate transfer member by the transfer means is secondarily transferred (collectively transferred) onto the transfer material, the image bearing surface of the intermediate transfer member is separated by the separation means. And fixing the full-color toner image secondarily transferred onto the transfer material by a fixing unit. Etc. are known. In the latter image forming apparatus, there is no need to hold the transfer material on the transfer material carrier as in the former, and therefore, small-size paper (for example, government-made postcard), thick paper (for example, 200 g / m ² paper), envelopes, and the like are used. An image can be formed (printed) on a transfer material, which has the advantage of increasing the versatility of the transfer material.

The transfer material onto which the toner image has been transferred by the transfer means at the transfer portion is easily electrostatically attracted to the image bearing surface of the image bearing member. There is a high possibility that the sheet is wound around the image bearing surface without being separated from the image bearing surface of the carrier. For this reason, in this type of image forming apparatus, usually, a separating unit is disposed downstream of the transfer portion to forcibly separate the transfer material from the image bearing surface of the image bearing member. One type of the transfer material separation method is to reduce the radius of curvature of the image bearing surface of the image carrier at the separation site on the downstream side of the transfer site, and to reduce the waist of the transfer material moving with the image carrier surface of the image carrier. Utilizing strength,
A method for separating the transfer material by curvature is known. Also,
As separation means for assisting the curvature separation of the transfer material,
Auxiliary separation means such as a separation claw having a sharp claw portion that abuts on the image bearing surface of the image bearing member and a charge elimination charger for removing a charge for electrostatically attracting the transfer material to the image bearing surface of the image bearing member are known. Have been.

[0005]

However, in this type of image forming apparatus, for example, due to the layout of the image forming unit and the transfer path of the transfer material, the image bearing surface of the image bearing member at the above-mentioned separation portion is considered. It is difficult to reduce the radius of curvature of the transfer material, and it may not be possible to reliably separate the transfer material at the separation site. In such a case, in order to separate the transfer material from the image bearing surface of the image bearing member, it is necessary to provide an auxiliary separating unit such as the above-described separating claw or static elimination charger. However, when the nail separation is used as the auxiliary separation means, the sharp nail portion of the separation claw comes into contact with the image bearing surface of the image carrier, so that the rubbing trace caused by the nail portion on the image bearing surface of the image carrier. And the durability of the image carrier deteriorates. In addition, when a static elimination charger is used as the auxiliary separating unit, the charge on the image bearing surface of the image bearing member is removed, so that the electrostatic attraction of the transfer material to the image bearing surface at the separation site is weakened. While the separation of the transfer material is facilitated, the electrostatic attraction of the toner image transferred to the transfer material at the transfer portion to the transfer material side is also weakened, so that the toner image transferred to the transfer material is disturbed. There was a problem that was likely to occur.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has as its object to reduce the size of the image carrier even when it is difficult to reduce the radius of curvature of the image carrier surface of the image carrier at the separation site. It is an object of the present invention to provide an image forming apparatus capable of reliably separating a transfer material at a separation portion without using auxiliary separation means such as a separation claw that impairs body durability or a static elimination charger that disturbs a transferred toner image. .

[0007]

According to a first aspect of the present invention, a toner image carried on an image bearing surface of an image bearing member is moved together with the image bearing surface of the image bearing member. In an image forming apparatus provided with a transfer unit for transferring to a transfer material, the transfer unit includes a transfer member having a pressure contact surface formed with a radius of curvature smaller than a radius of curvature of an image bearing surface of the image bearing member; And a pressing force applying means for applying a pressing force for pressing the pressing surface of the member to the image bearing surface to the transfer member, wherein the image bearing surface of the image bearing member is pressed against the pressing surface of the transfer member. Thus, it has elasticity to elastically deform along the pressing surface.

In this image forming apparatus, the press-contact surface of the transfer member is pressed against the image-bearing surface of the image carrier with the press-contact force applied by the press-contact force applying means, so that the image-bearing member is pressed. The image bearing surface of the image bearing member is elastically deformed so as to be along a pressure contact surface having a smaller radius of curvature than the curvature radius of the image bearing surface. As a result, the radius of curvature of the nip formed by the pressing surface of the transfer member and the image bearing surface of the image bearing member is smaller than the radius of curvature of the image bearing surface of the image bearing member. Therefore, in this image forming apparatus, when the transfer material passes through the nip portion formed by the pressure contact surface of the transfer member and the image bearing surface of the image carrier, the moving direction of the transfer material is The direction is changed in a direction along the surface, that is, in a direction rapidly moving away from the image bearing surface of the image bearing member. As a result, even when it is difficult to reduce the radius of curvature of the image bearing surface of the image carrier at the separation site, auxiliary separating means such as a separation claw that impairs the durability of the image carrier and a static elimination charger that disturbs the transferred toner image are used. Without the use, the small radius of curvature of the nip and the stiffness of the transfer material ensure that the transfer material is separated from the image bearing surface of the image carrier after the toner image is transferred. The image carrier may be a photoconductor carrying a primary transfer image or an intermediate transfer body carrying a secondary transfer image.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the hardness of the pressing surface of the transfer member is set higher than the hardness of the image bearing surface of the image bearing member. Is what you do.

In this image forming apparatus, the pressure contact surface formed to have a smaller radius of curvature than the curvature radius of the image bearing surface by the pressure contact of the pressure contact surface of the transfer member with the image bearing surface of the image bearing member. The image bearing surface is elastically deformed without being deformed by the elasticity of the image bearing surface, so that the image bearing surface surely follows the press contact surface. Thereby, when the transfer material passes through the nip formed by the pressing surface and the image bearing surface,
The direction of movement of the transfer material is reliably changed along the pressure contact surface in a direction away from the image bearing surface, so that the transfer material is more reliably separated from the image bearing surface of the image carrier by curvature. .

According to a third aspect of the present invention, in the image forming apparatus of the first or second aspect, the image bearing member is provided between the pressure contact surface of the transfer member and a facing surface of a facing member disposed facing the transfer member. When the pressure contact surface of the transfer member presses against the image bearing surface of the image carrier, the opposing surface of the opposing member moves the image bearing surface along the pressure contact surface. It is characterized by having elasticity or shape to deform.

In this image forming apparatus, the image carrier formed of a belt-like member moves between the press-contact surface of the transfer member and the opposing surface of the opposing member disposed opposite to the transfer member. The image bearing surface of the image carrier, which is sandwiched between the pressure contact surface of the transfer member and the opposing surface of the opposing member, is elastically deformed along the pressure contact surface of the transfer member. As a result, when the transfer material passes through the nip portion formed by the pressure contact surface and the image bearing surface, the direction of movement of the transfer material rapidly moves away from the image bearing surface along the pressure contact surface. The transfer material is surely separated from the image bearing surface of the image bearing member by a curvature.

According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the transfer member includes a rotatable transfer roller, and the pressing force applying means includes a backup member that presses against the transfer roller. It is characterized by becoming.

In this image forming apparatus, the peripheral surface of the transfer roller as the pressure contact surface of the transfer member is pressed against the image bearing surface of the image carrier by the pressure contact of the backup member as the pressure contacting means. Accordingly, the image bearing surface of the image bearing member is elastically deformed along the peripheral surface of the transfer roller, so that the transfer roller does not bend even when the diameter of the transfer roller is reduced. Therefore, in the image forming apparatus, the transfer material can be separated in curvature by using a transfer roller having a smaller radius of curvature, so that the nip formed by the peripheral surface of the transfer roller and the image bearing surface of the image bearing member is formed. The curvature of the portion can be made smaller, and even a thin (weak) transfer material that is relatively difficult to separate the curvature can be surely separated from the image bearing surface of the image carrier by the curvature.

According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the resistance value of the pressure contact surface of the transfer member is:
It is characterized in that the resistance is set higher than the resistance value of the image bearing surface of the image bearing member.

In this image forming apparatus, since the resistance value of the pressing surface of the transfer member is set higher than the resistance value of the image bearing surface of the image carrier, the transfer material is used as the image of the image carrier. The force of sticking to the carrying surface by electrostatic force is weakened.
This facilitates the separation of the curvature of the transfer material at the nip formed by the pressing surface of the transfer member and the image bearing surface of the image carrier.

According to a sixth aspect of the present invention, there is provided the image forming apparatus according to any one of the first to fifth aspects, further comprising a cleaning member for removing the deposit attached to the press contact surface of the transfer member. .

In this image forming apparatus, the cleaning member removes deposits adhered to the pressing surface of the transfer member. As a result, the back surface of the transfer material (the surface facing the pressure contact surface of the transfer member) is not contaminated by the adhered matter adhered to the pressure contact surface, so that the toner image is printed on both the front and back surfaces of the transfer material. Image deterioration such as when copying is prevented.

According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the transfer member faces the transfer member at a separated position where the pressure contact surface of the transfer member is separated from the image bearing surface of the image carrier. However, when the transfer material passes between the image bearing surface of the image carrier and the pressure contact surface of the transfer member, the transfer material is located at a pressure contact position where the pressure contact surface of the transfer member presses against the image bearing surface. It has a transfer member contacting / separating means for facing the transfer member.

In this image forming apparatus, the transfer member contacting / separating means is used to move the image carrier in accordance with the timing at which the transfer material passes between the image bearing surface of the image carrier and the pressure contact surface of the transfer member. The press contact surface of the transfer member is brought into contact with and separated from the image bearing surface. Thus, only when the transfer material is separated from the image bearing surface of the image bearing member, the pressure contact surface of the transfer member comes into pressure contact with the image bearing surface of the image bearing member. Dirt due to powder and the like is minimized. Here, the timing at which the transfer material passes between the image bearing surface of the image bearing member and the pressure contact surface of the transfer member is defined by a nip portion between the image bearing surface of the image bearing member and the pressure contact surface of the transfer member. At the timing when the leading end of the transfer material is clamped and at least the curvature separation of the transfer material is started, the image bearing surface is moved until the rear end of the transfer material passes through the nip portion. It is not necessary that the pressure contact surface of the transfer member keeps pressing.

According to an eighth aspect of the present invention, in the apparatus according to the first to seventh aspects, a transfer material passing through a nip portion formed by a pressing surface of the transfer means and an image bearing surface of the image bearing member is provided. On the other hand, an air blowing means for blowing air from the downstream side to the upstream side in the moving direction of the transfer material is provided.

In this image forming apparatus, when the transfer material passes through a nip portion formed by the pressing surface of the transfer means and the image bearing surface of the image carrier, the air blowing means applies the transfer material to the transfer material. Air is blown toward the leading end from the downstream side in the moving direction of the transfer material to the upstream side. Thereby, the air blowing means blows the transfer material, which is curvature-separated by the nip portion between the image bearing surface of the image bearing member and the pressing surface of the transfer member, and the image bearing surface of the image bearing member. The air enters and the separation state between the image bearing surface of the image bearing member and the transfer material is maintained, so that the transfer material can be reliably separated from the image bearing surface. Here, the air blown to the leading end of the transfer material by the air blowing means enters the space between the transfer material and the image bearing surface of the image carrier to form an air film, and the transfer once the curvature is separated. The pressure is set to a relatively weak pressure that can maintain the separated state between the image bearing surface of the image bearing member and the transfer material so that the material is not attracted to the image bearing surface of the image bearing member again by the electrostatic force. This prevents the toner image transferred onto the transfer material from being disturbed by the blowing of the air.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a full-color copying machine (hereinafter simply referred to as "copier") as an image forming apparatus will be described below. First, a schematic configuration of the copying machine according to the present embodiment will be described. As shown in FIG. 1, around a photosensitive drum 1 as a latent image carrier, a charging roller 2 as a charging unit, an optical writing unit 3 as a data writing device, a developing unit 4 as a developing unit, an intermediate unit An intermediate transfer drum 5D as an image carrier of the transfer means, a photosensitive drum cleaning unit 6 as a cleaning means for the photosensitive drum 1, and the like are provided. Around the intermediate transfer drum 5D, an intermediate transfer drum cleaning unit 7 as a cleaning unit for the intermediate transfer drum 5D, and a secondary unit as a transfer unit for transferring a toner image to a transfer paper P as a recording medium. A transfer roller 8 and the like are provided.

In FIG. 1, the photosensitive drum 1 is driven to rotate in a direction indicated by an arrow at a constant speed during copying by a driving means such as a motor (not shown). Then, after the surface of the photosensitive drum 1 is uniformly charged in the dark by the charging roller 2,
The optical writing unit 3 irradiates the surface with writing light based on image data to form an image. As a result, an electrostatic latent image corresponding to the image data is formed on the surface of the photosensitive drum 1.
The image data is a desired full-color image, yellow,
Single-color image data separated into magenta, cyan, and black color information. On the surface of the photosensitive drum 1, each electrostatic latent image corresponding to the image data of each of these colors is provided at a predetermined timing. Are formed sequentially.

The electrostatic latent image of each color formed on the surface of the photosensitive drum 1 is visualized sequentially by the developing unit 4 for each color. The developing unit 4 includes a yellow developing unit 4Y, a magenta developing unit 4M, a cyan developing unit 4C, and a black developing unit 4K in which toners of yellow, magenta, cyan, and black are individually stored. Each developing unit 4
Y, 4M, 4C, and 4K sequentially visualize the electrostatic latent images of each color formed on the surface of the photosensitive drum 1 with toner of each color at respective development sites facing the photosensitive drum 1, Yellow, magenta, cyan, and black toner images are sequentially formed on the surface of the photosensitive drum 1.

The toner images of the respective colors of yellow, magenta, cyan, and black sequentially formed on the photosensitive drum 1 in this manner are transferred onto the intermediate transfer drum 5D, which is driven to rotate at the same speed as the photosensitive drum 1. Are sequentially superimposed and primary transferred. Thereby, a color image in which toner images of yellow, magenta, cyan, and black are superimposed,
It is formed on the intermediate transfer drum 5D. During this time, the transfer paper P stored in the paper feed cassette 9 is fed by a paper feed roller 10 as a paper feed unit, a transport roller 11, and a registration roller 1.
2, the sheet is conveyed to a secondary transfer portion between the intermediate transfer drum 5D and the secondary transfer roller 8. Then, at this secondary transfer portion, the color image formed on the intermediate transfer drum 5D is collectively transferred onto the transfer paper P by the secondary transfer roller 8. The transfer paper P on which the color images are collectively transferred in this manner is separated from the image bearing surface of the intermediate transfer drum 5D by the secondary transfer roller 8 also serving as a separating unit and the air nozzle 14 serving as an air blowing unit, and the transfer belt 1
5, the sheet is conveyed toward a fixing unit 16 as a fixing device. After the fixing unit 16 fixes the color image on the transfer sheet P, the transfer sheet P is discharged onto a discharge tray 17.

On the other hand, the residual toner remaining on the photosensitive drum 1 without being primarily transferred to the intermediate transfer drum 5D of the toner image of each color formed on the photosensitive drum 1 is removed by the photosensitive drum cleaning unit 6. It is removed and collected from the photosensitive drum 1. Further, the residual toner remaining on the intermediate transfer drum 5D without being secondary-transferred onto the transfer paper P of the toner image primarily transferred on the intermediate transfer drum 5D is removed and collected by the intermediate transfer drum cleaning unit 7. . Thereafter, the residual potential of the surface of the photosensitive drum 1 is removed by the charge removing lamp 18 to prepare for the next image formation.

Next, a separating operation for separating the transfer paper P after the secondary transfer, which is a characteristic part of the copying machine according to the present embodiment, from the image bearing surface of the intermediate transfer drum 5D will be described. The transfer paper P on which the toner image has been transferred by the secondary transfer roller 8 at the secondary transfer portion is the intermediate transfer drum 5D.
Is likely to be electrostatically attracted to and wrapped around the image bearing surface. Therefore, in this type of copying machine, it is necessary to dispose a separating means at a separating portion on the downstream side of the secondary transfer portion and to forcibly separate the transfer paper P from the image bearing surface of the intermediate transfer drum 5D. . As a means for separating the transfer paper P, the radius of curvature of the image bearing surface of the intermediate transfer body at the separation site is reduced, and the transfer paper P is moved by using the rigidity of the transfer paper P moving with the image bearing surface. A method of separating the paper P by curvature can be considered. Further, as separation means for assisting the curvature separation of the transfer paper P, a separation claw having a sharp claw portion abutting on the image bearing surface of the image carrier, or a transfer material being statically attached to the image bearing surface of the image carrier. It is conceivable to use an auxiliary separating means such as a charge removing charger for removing charges to be electroadsorbed.

However, when an intermediate transfer body as an image carrier on which a color image is formed is formed in a drum shape as in the copying machine according to the present embodiment, the layout and transfer of the image forming unit are performed. Due to the transport path of the paper P,
It is difficult to reduce the radius of curvature of the image bearing surface of the intermediate transfer drum 5D at the separation site, and it is impossible to reliably separate the transfer paper P at the separation site. Therefore, in this copying machine, in order to separate the transfer paper P from the image bearing surface of the intermediate transfer drum 5D, it is usually necessary to provide auxiliary separation means such as the above-described separation claw and a charge removing charger. However, when the nail separation is used as the auxiliary separation means, the sharp nail portion of the separation nail abuts on the image carrying surface of the intermediate transfer member 5, so that the image carrying surface has a rubbing trace caused by the nail portion. The durability of the intermediate transfer drum 5D deteriorates.
Further, when a charge removing charger is used as the auxiliary separating means, the charge on the image bearing surface of the intermediate transfer drum 5D is removed, so that the electrostatic attraction of the transfer paper P to the image bearing surface at the separation portion is weakened. Although the separation of the transfer paper P is facilitated, the electrostatic attraction of the toner image transferred to the transfer paper P at the transfer portion on the transfer paper P side is also weakened. Disorder is likely to occur in the applied toner image.

Therefore, in the copying machine according to the present embodiment, as shown in FIG. 2, as the separating means, a pressure contact formed at a radius of curvature Rb smaller than the radius of curvature Ra of the image bearing surface of the intermediate transfer drum 5D. A secondary transfer roller 8 having a surface (a peripheral surface in this example) is used. Then, a pressing force is applied to the secondary transfer roller 8 by a pressing force applying means 19 such as a coil spring or a plate spring, so that the pressing surface of the secondary transfer roller 8 is pressed against the image bearing surface of the intermediate transfer drum 5D. It is constituted so that. Further, the image bearing surface of the intermediate fourth transfer drum 5D is configured to have an elasticity to be elastically deformed along the pressure contact surface when the pressure contact surface of the secondary transfer roller 8 is pressed. In the copying machine shown in FIG. 2, an elastic layer 5a made of rubber, hard sponge, or the like having an image bearing surface formed on the outer surface of the intermediate transfer drum 5D is provided. Is pressed by the pressure contact surface of the secondary transfer roller 8 so as to be elastically deformed along the pressure contact surface.

In this copying machine, the peripheral surface of the secondary transfer roller 8 is pressed against the image bearing surface of the intermediate transfer drum 5D by the pressing force applied by the pressing force applying means 19, so that the intermediate transfer is performed. The image bearing surface of the intermediate transfer drum 5D (the surface of the elastic layer 5a) extends along the peripheral surface of the secondary transfer roller 8 formed with a radius of curvature Rb smaller than the radius of curvature Ra of the image bearing surface of the drum 5D. Elastically deform. As a result, the radius of curvature of the nip formed by the peripheral surface of the secondary transfer roller 8 and the image bearing surface of the intermediate transfer drum 5D becomes smaller than the radius of curvature Ra of the image bearing surface of the intermediate transfer drum 5D. Become. Accordingly, in this copying machine, as shown in FIG. 2, the transfer paper P passes through the nip formed by the peripheral surface of the secondary transfer roller 8 and the image bearing surface of the intermediate transfer drum 5D, as shown in FIG. The moving direction a of the transfer paper P is a direction along the peripheral surface of the secondary transfer roller 8, that is, the intermediate transfer drum 5.
The direction is changed to a direction that is sharply separated from the image bearing surface of D. As a result, as described above, even when it is difficult to reduce the radius of curvature Ra of the image bearing surface of the intermediate transfer drum 5D at the separation site, the separation claw that impairs the durability of the intermediate transfer drum 5D or the secondary transfer is performed. Due to the small radius of curvature of the nip and the stiffness of the transfer paper P, the transfer paper P is transferred to the intermediate transfer drum 5D at the secondary transfer portion without using an auxiliary separating means such as a static elimination charger that disturbs the toner image. The curvature can be surely separated from the surface.

Here, the hardness of the peripheral surface of the secondary transfer roller 8 is preferably set higher than the hardness of the image bearing surface of the intermediate transfer drum 5D. That is, if the hardness of the peripheral surface of the secondary transfer roller 8 is set higher than the hardness of the image bearing surface of the intermediate transfer drum 5D,
By pressing the peripheral surface of the secondary transfer roller 8 against the image bearing surface of D, the peripheral surface of the secondary transfer roller 8 formed with a radius of curvature Rb smaller than the radius of curvature Ra of the image bearing surface is moved to the image bearing surface. The image bearing surface is elastically deformed so as to reliably follow the peripheral surface of the secondary transfer roller 8 without being deformed by the elasticity of the secondary transfer roller 8. Accordingly, when the transfer paper P passes through the nip formed by the peripheral surface of the secondary transfer roller 8 and the image bearing surface of the intermediate transfer drum 5D, the moving direction a of the transfer paper P is changed to the secondary transfer. The transfer paper P is surely changed along the peripheral surface of the roller 8 so as to be sharply separated from the image bearing surface of the intermediate transfer drum 5D, and the curvature of the transfer paper P can be more reliably separated from the image bearing surface of the intermediate transfer drum 5D. Become like

FIG. 3 shows a schematic configuration of another copying machine according to the present embodiment. In FIG. 3, components having the same functions as those of the components in the copying machine shown in FIG. 1 are denoted by the same reference numerals as those in FIG. Omitted. The intermediate transfer body of the copying machine shown in FIG. 3 has a structure in which a press-contact surface (peripheral surface) of the secondary transfer roller 8 and an opposing surface (peripheral surface) of an opposing roller 20 disposed opposite to the secondary transfer roller 8 And an intermediate transfer belt 5B made of a belt-like member that moves.

In FIG. 3, four photosensitive drums 1Y, 1 on which toner images of yellow, magenta, cyan, and black are individually formed around the intermediate transfer belt 5B.
M, 1C and 1K are provided. Around each of the photosensitive drums 1Y, 1M, 1C, 1K, image forming means for each color for individually forming a toner image of each color is provided. On each of the photoconductor drums 1Y, 1M, 1C, and 1K, an electrostatic latent image of each color of yellow, magenta, cyan, and black is formed in accordance with image data of each color, and a yellow developing unit 4Y and a magenta developing unit 4M are formed. The electrostatic latent image is visualized by a developing unit 4 including a cyan developing unit 4C and a black developing unit 4K. Then, each photosensitive drum 1Y, 1
The yellow, magenta, cyan, and black toner images formed on M, 1C, and 1K are transferred onto the intermediate transfer belt 5B, which is driven to rotate at the same speed as the photosensitive drums.
The primary transfer rollers 21Y, 21M, 21C, and 21K sequentially superimpose and perform primary transfer. This allows
A color image in which toner images of yellow, magenta, cyan, and black are superimposed is formed on the intermediate transfer belt 5B. During this time, the transfer paper P accommodated in the paper feed cassette 9 is moved between the intermediate transfer belt 5B and the secondary transfer roller 8 by the paper feed roller 10, the transport roller 11, and the registration roller 12 as paper feed means. It is transported to the secondary transfer site. Then, at this secondary transfer portion, the color image formed on the intermediate transfer belt 5B is collectively transferred onto the transfer paper P by the secondary transfer roller 8. The transfer paper P on which the color images are collectively transferred in this way is image-bearing on the intermediate transfer belt 5B by the secondary transfer roller 8 serving also as the secondary transfer means and the separation means and the air nozzle 14 serving as an air blowing means. Conveyor belt 1
5, the sheet is conveyed toward a fixing unit 16 as a fixing device. After the fixing unit 16 fixes the color image on the transfer sheet P, the transfer sheet P is discharged onto a discharge tray 17.

On the other hand, the residual toner remaining on the photosensitive drums 1Y, 1M, 1C and 1K without being primary-transferred to the intermediate transfer belt 5B is transferred to the photosensitive drum cleaning unit 6
From the photosensitive drums 1Y, 1M, 1C and 1K. Further, residual toner remaining on the intermediate transfer belt 5B without being secondarily transferred to the transfer paper P is removed and collected by the intermediate transfer drum cleaning unit 7. After that, the surface of each photoconductor drum 1Y, 1M, 1C, 1K
The residual potential is removed by the charge removing lamp 18 to prepare for the next image formation.

Next, a separating operation by the secondary transfer roller 8 for separating the transfer paper P after the secondary transfer, which is a characteristic part of the copying machine, from the image bearing surface of the intermediate transfer belt 5B will be described. Even when an intermediate transfer body as an image carrier on which a color image is formed is formed in a belt shape as in this copying machine, due to the layout of the image forming unit and the transport path of the transfer paper P, It is difficult to reduce the radius of curvature of the image bearing surface of the intermediate transfer belt 5B at the separation site, and it may not be possible to reliably separate the transfer paper P at the separation site.

Therefore, in this copying machine, as shown in FIG. 3, the intermediate transfer belt 5B is provided between the pressure contact surface of the secondary transfer roller 8 and the opposing roller 20 disposed opposite to the secondary transfer roller 8. The second transfer roller 8 is configured to move between the second transfer roller 8 and the second transfer roller 8.
When the pressure contact surface of the intermediate transfer belt 5B is pressed against the image bearing surface of the intermediate transfer belt 5B, the image bearing surface of the intermediate transfer belt 5B is allowed to deform along the pressure contact surface of the secondary transfer roller 8. I do. That is, in this copying machine, as shown in FIG. 4, an elastic layer 20a made of rubber, hard sponge, or the like is provided on the outer circumference of
When the opposing surface is pressed by the pressure contact surface of the secondary transfer roller 8, it is elastically deformed along the pressure contact surface.

Thus, in this copying machine, the intermediate transfer belt 5B moves between the pressure contact surface of the secondary transfer roller 8 and the opposing surface of the opposing roller 20 disposed opposite to the secondary transfer roller 8. As a result, the image bearing surface of the intermediate transfer belt 5 </ b> B, which is sandwiched between the pressure contact surface of the secondary transfer roller 8 and the opposing surface of the opposing roller 20, is larger than the curvature radius Rc of the opposing surface of the opposing roller 20. The secondary transfer roller 8 is elastically deformed along the peripheral surface of the secondary transfer roller 8 having a small radius of curvature Rb. As a result, the transfer paper P passes through the nip formed by the pressure contact surface of the secondary transfer roller 8 and the image bearing surface of the intermediate transfer belt 5B.
Is changed in the direction along the peripheral surface of the secondary transfer roller 8, that is, in the direction abruptly away from the image bearing surface of the intermediate transfer belt 5B. Accordingly, as described above, even when it is difficult to reduce the radius of curvature of the image carrying surface of the intermediate transfer belt 5B at the separation site, the separation claw or the secondary transferred toner that impairs the durability of the intermediate transfer belt 5B By using the small radius of curvature of the nip portion and the stiffness of the transfer paper P, the transfer paper P is separated from the image bearing surface of the intermediate transfer belt 5B at the separation portion without using an auxiliary separation means such as a charge removing charger that disturbs the image. The curvature can be surely separated.

Here, the hardness of the peripheral surface of the secondary transfer roller 8 is preferably set higher than the hardness of the opposing surface of the opposing roller 20. That is, if the hardness of the peripheral surface of the secondary transfer roller 8 is set to be higher than the hardness of the opposing surface of the opposing roller 20, the peripheral surface of the secondary transfer roller 8 is pressed against the image bearing surface of the intermediate transfer belt 5B. The peripheral surface of the secondary transfer roller 8 is not deformed by the elasticity of the opposing surface of the opposing roller 20, and the image bearing surface of the intermediate transfer belt surely follows the peripheral surface of the secondary transfer roller 8. It becomes elastically deformed.

On the other hand, as described above, the pressing surface of the secondary transfer roller 8 is moved to the intermediate transfer drum 5D (or the intermediate transfer belt 5).
The pressing force applying means for applying the pressing force for pressing against the image bearing surface to the secondary transfer roller 8 in FIG. 5B is a backup as a backup member for pressing against the secondary transfer roller 8 as shown in FIG. It is desirable to use the roller 21. That is, in this image forming apparatus, the peripheral surface of the secondary transfer roller 8 is pressed against the backup roller 21 as the pressing force applying means, and the image bearing surface of the intermediate transfer drum 5D (or the intermediate transfer belt 5B) is pressed. Is pressed, the image bearing surface is elastically deformed along the peripheral surface of the secondary transfer roller 8, so that even when the diameter of the secondary transfer roller 8 is reduced, Does not bend. Therefore, in the image forming apparatus, the transfer paper P is formed using the secondary transfer roller 8 having a smaller radius of curvature.
Of the secondary transfer roller 8
And the intermediate transfer drum 5D (or the intermediate transfer belt 5).
The intermediate transfer drum 5D (or the intermediate transfer belt 5) can be used even with thin (weak) transfer paper P, in which the curvature of the nip formed by the image bearing surface B) can be made smaller and the curvature separation is relatively difficult.
The curvature can be surely separated from the image carrying surface of B).

The resistance value of the pressure contact surface of the secondary transfer roller 8 is determined by the intermediate transfer drum 5D or the intermediate transfer belt 5.
It is preferable that the resistance is set higher than the resistance value of the image bearing surface of B. That is, since the resistance value of the pressing surface of the secondary transfer roller 8 is set higher than the resistance value of the image bearing surface of the intermediate transfer drum 5D or the intermediate transfer belt 5B, the transfer paper P is transferred The force of applying the electrostatic force to the drum 5D or the image bearing surface of the intermediate transfer belt 5B is weakened. This facilitates the separation of the curvature of the transfer paper P at the nip formed by the pressing surface of the secondary transfer roller 8 and the image bearing surface of the intermediate transfer drum 5D or the intermediate transfer belt 5B.

On the other hand, as shown in FIG. 5, a cleaning blade 23 as a cleaning member for removing foreign matter adhering to the peripheral surface of the secondary transfer roller 8 contacts the peripheral surface of the backup roller 21. Are located. The cleaning blade 23 removes the adhering matter adhering to the peripheral surface of the secondary transfer roller 8 via the backup roller 21 so that the back surface of the transfer paper P (the peripheral surface of the secondary transfer roller 8 The opposite surface) is no longer contaminated by the adhered matter on the peripheral surface, so that image deterioration such as when a toner image is copied on both sides of the transfer sheet P is prevented. The cleaning member may be a fur brush, or may be arranged so as to directly contact the peripheral surface of the secondary transfer roller 8.

Further, the secondary transfer roller 8 has a flat
As shown by the broken line in FIG. 6, the intermediate transfer drum 5D (or the intermediate transfer belt 5B) faces a separation position where the pressure contact surface is separated from the image bearing surface of the intermediate transfer drum 5D (or the intermediate transfer belt 5B). 2) Image bearing surface and secondary transfer roller 8
When the transfer paper P passes between the pressure contact surfaces of FIG.
As shown by a solid line, the transfer member contacting / separating means 24 causes the intermediate transfer drum 5D (or the intermediate transfer belt 5) to move toward the pressing position where the pressing surface presses against the image bearing surface.
It is preferable to be configured to be able to freely contact and separate from the image carrying surface of B). 6 includes a swing lever 25, an eccentric cam 26, and a spring 27. The secondary transfer roller 8 is rotatably connected to a swing end of a swing lever 25. Swing lever 25
Is pivotally supported on a side plate of a copying machine main body (not shown) by a support shaft 28. The eccentric cam 26 is disposed on the base end side of the swing lever 25. The spring 27
The swinging lever 25 is suspended between the base end of the swinging lever 25 and a side plate of the copying machine so that the side surface of the swinging lever 25 is elastically pressed against the cam surface (peripheral surface) of the eccentric cam 26.

In FIG. 6, the transfer member contacting / separating means 24 is synchronized with the timing at which the transfer paper P passes between the image bearing surface of the intermediate transfer drum 5 and the pressure contact surface of the secondary transfer roller 8.
Is rotated by a predetermined angle. This allows
The secondary transfer roller 8 is swung between a separated position indicated by a broken line in FIG. 6 and a press-contact position indicated by a solid line in FIG. 6 so that the secondary transfer roller 8 moves relative to the image bearing surface of the intermediate transfer drum 5. The press contact surfaces are separated from each other. As described above, in this copying machine, the pressure contact surface of the secondary transfer roller 8 is pressed against the image bearing surface of the intermediate transfer drum 5 only when the transfer paper P is separated from the image bearing surface of the intermediate transfer drum 5. Therefore, contamination of the press contact surface of the secondary transfer roller 8 with toner, paper dust, or the like can be minimized.

The copying machine according to the present embodiment has
As shown in FIG. 4 to FIG. 4, the secondary transfer roller 8 blows air to the leading end of the transfer paper P separated from the image bearing surface of the intermediate transfer drum 5D (or the intermediate transfer belt 5B). An air nozzle 14 is provided as a means. Immediately after the separation of the transfer paper P from the image bearing surface of the intermediate transfer drum 5D (or the intermediate transfer belt 5B) by the secondary transfer roller 8 is started, the air nozzle 14 is connected to the leading end of the transfer paper P. Against
The air is blown from the downstream side to the upstream side in the moving direction of the transfer paper P. Thus, the transfer paper P whose curvature is separated by the nip portion between the image bearing surface of the intermediate transfer drum 5D (or the intermediate transfer belt 5B) and the pressure contact surface of the secondary transfer roller 8, and the image bearing surface And the separation state between the image bearing surface of the intermediate transfer drum 5D (or the intermediate transfer belt 5B) and the transfer paper P is maintained,
Transfer paper P can be reliably separated from the image bearing surface. The air blown to the leading end of the transfer paper P by the air nozzle 14 is applied to the transfer paper P and the intermediate transfer drum 5D so that the toner image transferred to the transfer paper P is not disturbed by the blowing of the air. (Or an image transfer surface of the intermediate transfer belt 5B) so that an air film is formed so that the transfer paper P once separated in curvature is not attracted to the image transfer surface again by electrostatic force.
The pressure is set to be relatively weak enough to maintain the separation state between the image bearing surface and the transfer paper P.

In the copying machine shown in FIG. 3, the intermediate transfer belt 5B is stretched as an opposing member opposing the secondary transfer roller 8 for separating the transfer paper P moving with the intermediate transfer belt 5B for curvature. The opposing roller 20 which also serves as a roller to be bridged is used.
As shown in FIG. 7 (a), an elastic body layer 30a is provided on the opposing surface side of the strip-shaped opposing plate 30, and as shown in FIG. 7 (b), the strip-shaped opposing plate 31 itself is formed. A shape previously curved to a shape along the radius of curvature of the secondary transfer roller 8,
Alternatively, as shown in FIG. 7C, a plurality of transfer papers P are formed on the peripheral surface of the secondary transfer roller 8 with the intermediate transfer belt 5B interposed therebetween so that the transfer paper P is curved along the peripheral surface of the secondary transfer roller 8. The guide rollers 32 and 33 (here, two) may be arranged to face each other.

As a secondary transfer means for separating the transfer paper P by curvature, in addition to the secondary transfer roller 8 as described above, for example, as shown in FIG. A belt-shaped transfer plate 34 having a pressure contact surface having a smaller radius of curvature than the radius of curvature of the image bearing surface of the belt 5B may be used. Further, when the transfer plate 34 is used as the secondary transfer means, as shown in FIG. 9, the swing lever 25 itself of the transfer member contact / separation means 24 is moved to the transfer plate 3.
4 may be used.

[0048]

According to the first to eighth aspects of the present invention, the transfer material passes through a nip portion formed by the pressing surface of the transfer member and the image bearing surface of the image carrier, so that the transfer material The moving direction is changed to a direction along the press-contact surface of the transfer member, that is, a direction to rapidly move away from the image bearing surface of the image carrier. As a result, even when it is difficult to reduce the radius of curvature of the image bearing surface of the image carrier at the separation site, auxiliary separating means such as a separation claw that impairs the durability of the image carrier and a static elimination charger that disturbs the transferred toner image are used. An excellent effect that the transfer material can be surely separated from the image bearing surface of the image carrier after the transfer of the toner image by the small radius of curvature of the nip portion and the rigidity of the transfer material without using the nip portion. There is.

In particular, according to the second aspect of the present invention, the pressure contact surface formed with a smaller radius of curvature than the curvature radius of the image bearing surface by the pressure contact of the pressure contact surface of the transfer member with the image bearing surface of the image carrier. Is not deformed by the elasticity of the image bearing surface, and the image bearing surface is elastically deformed so as to surely follow the pressure contact surface, so that the transfer material can be more reliably moved from the image bearing surface of the image bearing member. There is an excellent effect that the curvature can be separated.

Further, according to the third aspect of the present invention, the image carrier constituted by the belt-like member is provided between the pressing surface of the transfer member and the opposing surface of the opposing member disposed opposite to the transfer member. By the movement, the image bearing surface of the image carrier, which is sandwiched between the pressure contact surface of the transfer member and the opposing surface of the opposing member, is elastically deformed along the pressure contact surface of the transfer member. As a result, when the transfer material passes through the nip portion formed by the pressure contact surface and the image bearing surface, the direction of movement of the transfer material rapidly moves away from the image bearing surface along the pressure contact surface. Therefore, there is an excellent effect that the transfer material can be surely separated from the image bearing surface of the image bearing member by a curvature.

According to the fourth aspect of the present invention, the peripheral surface of the transfer roller as the pressure contact surface of the transfer member is pressed against the image bearing surface of the image carrier by the pressure contact of the backup member as the pressure contacting means. As a result, the image bearing surface of the image bearing member is elastically deformed along the peripheral surface of the transfer roller. Accordingly, even when the diameter of the transfer roller is reduced, the transfer roller does not bend and the transfer material can be separated in curvature by using a transfer roller having a smaller radius of curvature. The curvature of the nip formed between the surface and the image bearing surface of the image carrier can be reduced,
There is an excellent effect that even a thin (weakly stiff) transfer material having a relatively difficult curvature separation can be surely separated from the image bearing surface of the image carrier by curvature.

According to the fifth aspect of the present invention, since the resistance value of the pressing surface of the transfer member is set higher than the resistance value of the image bearing surface of the image carrier, the transfer material can be used as the image carrier. The force of sticking to the image bearing surface by electrostatic force is weakened, and the curvature separation of the transfer material at the nip formed by the pressing surface of the transfer member and the image bearing surface of the image carrier is facilitated. effective.

According to the sixth aspect of the present invention, the cleaning member removes deposits attached to the press contact surface of the transfer member, and the back surface of the transfer material (the surface facing the press contact surface of the transfer member) is removed. Since there is no contamination by the adhered matter adhered to the pressure contact surface, there is an excellent effect that image deterioration can be prevented when a toner image is copied on both sides of the transfer material.

According to the seventh aspect of the present invention, the transfer member contacting / separating means is used by the transfer member contacting / separating means in synchronization with the timing at which the transfer material passes between the image bearing surface of the image carrier and the pressure contact surface of the transfer member. Since the pressure contact surface of the transfer member is brought into contact with and separated from the image bearing surface of the image carrier, the pressure contact surface of the transfer member is pressed against the image bearing surface of the image carrier only when separating the transfer material from the image bearing surface of the image carrier. As a result, there is an excellent effect that dirt on the press contact surface of the transfer member due to toner, paper powder, or the like can be minimized.

According to the invention of claim 8, when the transfer member starts to separate the transfer material from the image bearing surface of the image bearing member, air blowing means causes the transfer material to be moved toward the leading end of the transfer material. Air is blown from the downstream side to the upstream side in the moving direction of the transfer material. Thereby, between the transfer material having a curvature separated by a nip portion between the image bearing surface of the image bearing member and the pressing surface of the transfer member, and between the image bearing surface of the image bearing member,
The air blown from the air blowing means enters, and the separation state between the image bearing surface of the image bearing member and the transfer material is maintained, so that the transfer material can be reliably separated from the image bearing surface. Has an effect.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a copying machine according to an embodiment of the present invention.

FIG. 2 is an enlarged view of a main part showing a configuration of a transfer portion of the copying machine.

FIG. 3 is a schematic configuration diagram of another copying machine according to the embodiment of the present invention.

FIG. 4 is an enlarged view of a main part showing a configuration of a transfer portion of the other copying machine.

FIG. 5 is a schematic view of a main part for describing a backup roller for applying a pressing force to a secondary transfer roller of the copying machine.

FIG. 6 is a main part schematic diagram for explaining a transfer member contacting / separating means for bringing a secondary transfer roller into contact with / separating from an image carrier of the copying machine;

FIGS. 7A, 7B, and 7C are schematic cross-sectional views showing another configuration example of an opposing member arranged to oppose the secondary transfer roller.

FIG. 8 is a schematic sectional view showing another configuration example of a transfer member for separating a transfer material from the image bearing surface of the image bearing member by curvature.

FIG. 9 is a schematic diagram of a main part showing still another configuration example of the transfer member.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive drum 2 charging roller 3 optical writing unit 4 developing unit 5B intermediate transfer belt 5D intermediate transfer drum 5a elastic layer 8 secondary transfer roller 12 registration roller 14 air nozzle 19 pressure applying means 20 opposed roller 20a elastic layer 21 Backup roller 23 Cleaning blade 24 Transfer member contact / separation means 30, 31 Opposite plate 30a Elastic layer 32, 33 Guide roller 34 Transfer plate

Claims (8)

[Claims] An image forming apparatus comprising: a transfer unit that transfers a toner image carried on an image bearing surface of an image bearing member to a transfer material that moves together with the image bearing surface of the image bearing member; A transfer member having a pressure contact surface formed with a radius of curvature smaller than the curvature radius of the image bearing surface of the image carrier, and a pressure force for pressing the pressure contact surface of the transfer member against the image bearing surface to the transfer member. The image bearing surface of the image bearing member has an elasticity to be elastically deformed along the pressure contact surface when the pressure contact surface of the transfer member is pressed. Characteristic image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the hardness of the pressing surface of the transfer member is set higher than the hardness of the image carrying surface of the image carrier. 3. The image forming apparatus according to claim 1, wherein the image carrier moves between a press-contact surface of the transfer member and an opposing surface of an opposing member disposed to oppose the transfer member. The opposing surface of the opposing member has an elasticity or shape that deforms the image bearing surface along the pressure contact surface when the pressure contact surface of the transfer member is pressed against the image bearing surface of the image carrier. An image forming apparatus comprising: 4. The image forming apparatus according to claim 1, wherein said transfer member comprises a rotatable transfer roller, and said pressing force applying means comprises a backup member pressing against said transfer roller. Image forming apparatus. 5. The image forming apparatus according to claim 1, wherein a resistance value of a pressing surface of said transfer member is set higher than a resistance value of an image bearing surface of said image bearing member. Image forming device. 6. An image forming apparatus according to claim 1, further comprising: a cleaning member for removing an adhering substance adhering to the press contact surface of said transfer member. 7. The image forming apparatus according to claim 1, wherein the transfer member faces the transfer member at a position where a pressing surface of the transfer member is separated from an image support surface of the image carrier. When the transfer material passes between the image bearing surface of the body and the pressure contact surface of the transfer member, the transfer member faces the pressure contact position where the pressure contact surface of the transfer member presses against the image bearing surface. An image forming apparatus comprising a transfer member contacting / separating means. 8. The apparatus according to claim 1, wherein a front end portion of the transfer material passing through a nip portion formed by a pressing surface of the transfer means and an image bearing surface of the image bearing member.
An image forming apparatus comprising: an air blowing unit that blows air from a downstream side in a moving direction of the transfer material to an upstream side.