JP2002214941A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of preventing the soiling of the image-transfer surface of transfer-paper by electrified toner scattered to the periphery of a transfer part when a toner image on an image carrier is transferred the transfer-paper by a transfer member. SOLUTION: This device is constituted so that voltage having the same polarity as transfer bias is applied to a secondary transfer bias roller 605 by a voltage applying means 803. Thus, the roller 605 is electrified to have the same polarity as the transfer bias, and the electrified toner T scattered to the periphery of the transfer part A is forcibly stuck to the electrified roller 605 and the dropping of the electrified toner T onto a transfer paper guide plate 601 is reduced. Therefore, the electrified toner T is prevented from sticking to the image-transfer surface of the transfer-paper P when the paper P is carried along the plate 601 and the quality of the toner image transferred to the image- transfer surface is maintained.

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 bias is applied to a transfer member configured to be able to freely contact and separate from the surface of the image carrier, and the image is transferred onto a transfer material conveyed toward a transfer section between the transfer member and the image carrier. This is an electrophotographic image forming apparatus that transfers a toner image formed on the surface of a carrier.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus of this type, an image carrier such as a photosensitive drum, a photosensitive belt, or an intermediate transfer belt is used, and a toner image formed on the image carrier is transferred. There is known an image forming apparatus which transfers an image to a transfer material such as a sheet or an OHP sheet by means to form an image.

For example, in an "image forming apparatus" disclosed in JP-A-11-231667, a toner image formed on the photosensitive drum is transferred by a primary transfer bias roller which is a primary transfer member of the transfer means. The primary transfer is performed on the intermediate transfer belt. Then, a transfer bias having a polarity opposite to the charging polarity of the toner image is applied to a secondary transfer bias roller serving as a secondary transfer member, and a transfer unit where the intermediate transfer belt and the secondary transfer bias roller contact each other,
The toner image primary-transferred onto the intermediate transfer belt is electrically attracted to the transfer material conveyed toward the transfer unit, and is secondary-transferred.

Incidentally, the transfer member is usually constructed so as to be able to freely contact and separate from the surface of the image carrier by means of the contact and separation means. This prevents the transfer member or the image carrier from being deformed over time due to the transfer member being constantly in contact with the surface of the image carrier, or continuously transferring a plurality of toner images on the image carrier. This is to prevent contact between the toner image on the image carrier and the transfer member when an image is formed on the image carrier. In particular, by superimposing one by one on the intermediate transfer belt,
In an image forming apparatus of an intermediate transfer system in which toner images of a plurality of colors transferred next are collectively transferred by the secondary transfer bias roller, the intermediate transfer belt and the secondary transfer bias roller are used when forming a color image of two or more colors. Is required.

[0005] Further, the contact and separation between the intermediate transfer belt and the secondary transfer bias roller can be performed by disposing a plurality of photosensitive drums along the intermediate transfer belt and forming the respective colors formed on the respective photosensitive drums. After the toner image is superimposed on the intermediate transfer belt and primary-transferred, the primary-transferred toner image is transferred by a nip between the intermediate transfer belt and a secondary transfer bias roller.
This is also essential in a tandem-type image forming apparatus for performing the next transfer.

[0006]

However, as described above, in an image forming apparatus having a structure in which the transfer member comes into contact with and separates from the surface of the image carrier, the transfer member is moved relative to the surface of the moving image carrier. When the transfer member comes and goes, the image carrier may vibrate instantaneously in the moving direction. This is thought to be due to the fact that the contact between the surface of the image carrier and the contact / separation member applies a force (inertial force, frictional force, etc.) in a direction that prevents the image carrier from moving. Can be

In particular, like the above-mentioned intermediate transfer belt,
When the image carrier is formed of a belt-shaped member, a moving direction of the image carrier formed of the belt-shaped member (hereinafter, referred to as an “image carrier belt”) when the image carrier is in contact with the contact member. Vibration becomes remarkable. That is, this kind of belt-like member has some slack even in a stretched state. For this reason, when the contact member comes into contact with the image carrier belt, a belt portion on the downstream side in the movement direction from the contact portion of the image carrier belt with the contact member is suddenly tensioned. As a result, the advance of the belt portion on the upstream side in the movement direction of the contact portion of the image carrier belt is temporarily stopped. The tension and the stop of the movement of the image carrier belt are repeated until the moving speed of the image carrier belt at the contact portion is stabilized. As a result,
Vibration in the moving direction of the image carrier belt in contact with the contact member is larger than that of a drum-shaped image carrier having relatively high rigidity.

For this reason, in this type of conventional image forming apparatus, for example, as shown in FIG. 6A, when the secondary transfer bias roller 605 comes into contact with or separates from the intermediate transfer belt 501, Due to the vibration of the intermediate transfer belt 501, a part of the charged toner T of the toner image carried on the intermediate transfer belt
Transfer section A where the secondary transfer bias roller 605 comes into contact with or separates
Could be scattered around. Then, the transfer portion A
Charged toner T scattered around the periphery of the registration roller 61
0, the sheet P falls onto a transfer sheet guide plate 601 for guiding the transfer sheet P conveyed toward the transfer section A.

For this reason, in a conventional image forming apparatus of this type, as shown in FIG.
When the transfer paper P is transported along the transfer paper guide plate 601, the charged toner T falling on the transfer paper guide plate 601 is scraped up by the leading end of the transfer paper P. Therefore, the toner may adhere to the image transfer surface of the transfer paper P. Then, due to the adhesion of the charged toner T to the image transfer surface of the transfer paper P, the image quality of the toner image secondarily transferred to the image transfer surface may be reduced. Here, the vibration of the image carrier when the transfer member comes into contact with or separates from the image carrier is cited as a cause of the scattering of the charged toner on the image carrier. There is a high possibility that the image bearing member is also generated due to vibration during rotation of the image carrier, centrifugal force, or the like.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for transferring a toner image on an image carrier onto a transfer material by a transfer member. It is an object of the present invention to provide an image forming apparatus capable of preventing contamination of an image transfer surface of the transfer material by charged toner scattered in the image forming apparatus.

[0011]

In order to achieve the above object, the present invention is directed to an image bearing member which moves while carrying a toner image formed by a charged toner on a surface thereof, A transfer member that is configured to be able to contact and separate from the surface, a transfer bias applying unit that applies a transfer bias having a polarity opposite to the polarity of the charged toner to the transfer member, and a transfer bias between the transfer member and the image carrier. Transfer material conveying means for conveying the transfer material toward the transfer portion, wherein a transfer bias is applied to the transfer member by the transfer bias applying means while the transfer member is in contact with the surface of the image carrier. An image forming apparatus that transfers a toner image formed on the surface of the image carrier onto a transfer material conveyed toward the transfer unit, wherein the transfer member is separated from the surface of the image carrier. In the state, the transfer member And it is characterized in that it has a voltage applying means for applying a voltage of the transfer bias having the same polarity against.

In this image forming apparatus, a voltage having the same polarity as the transfer bias is applied to the transfer member by the voltage applying means while the transfer member is separated from the surface of the image carrier. Is done. Thereby, the transfer member is charged to a potential having the same polarity as the transfer bias,
The charged toner scattered around the transfer section as described above adheres to the charged transfer member. That is, the charged toner scattered around the transfer portion is forcibly attached to the transfer member. Therefore, in this image forming apparatus, the charged toner scattered around the transfer portion is less likely to fall on the transfer paper guide plate for guiding the transfer material. Thereby, when the transfer material is conveyed along the transfer paper guide plate, the charged toner falling on the transfer paper guide plate adheres to the image transfer surface of the transfer material, and the image transfer Deterioration of the image quality of the toner image transferred to the surface is reduced.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the image bearing member transfers the toner image from the latent image bearing member on which the toner image is formed by a primary transfer unit. After the transfer, the toner image is an intermediate transfer member that is secondarily transferred onto the transfer material by a secondary transfer unit.

In this image forming apparatus, a plurality of color toner images are superimposed on the intermediate transfer member and primary-transferred, and then the superposed plurality of color toner images are transferred to the transfer material by the secondary transfer means. By performing the secondary transfer, a color image can be formed on the transfer material. When such a plurality of color toner images are formed, the toner image carried on the intermediate transfer member is large, and the electric power of the toner image of the toner image superimposed on the intermediate transfer member is large. Also, the final holding power becomes weaker as the toner image on the surface layer is overlaid last. Therefore, in such an image forming apparatus, the amount of the charged toner scattered from the intermediate transfer member to the periphery of the transfer portion is large, and the charged toner scattered to the periphery of the transfer portion is used to guide the transfer material. Also falls sharply onto the transfer paper guide plate. In the image forming apparatus of the present invention, the charged toner scattered around the transfer section can be forcibly attached to the transfer member of the secondary transfer unit. Therefore,
In this image forming apparatus, a color image with less contamination by the charged toner scattered around the transfer portion can be obtained.

According to a third aspect of the present invention, in the image forming apparatus of the second aspect, the absolute value of the surface potential of the intermediate transfer member before the secondary transfer of the toner image onto the intermediate transfer member is 50%.
It is characterized by being set to 0 V or more.

As a method for increasing the electrical holding force of the toner image superimposed on the intermediate transfer member as described above, the toner image is secondarily transferred onto the intermediate transfer member. The absolute value of the surface potential of the intermediate transfer member was 500 V
It is known to set above. This makes it difficult for the laminated toner composed of the toner images of a plurality of colors carried on the intermediate transfer member to collapse, and to obtain a high-quality image with less generation of toner dust. However, when the absolute value of the surface potential of the intermediate transfer member is set to 500 V or more, toner scattering easily occurs when the intermediate transfer member rotates. This is considered to be caused by the fact that the laminated toner carried on the intermediate transfer member acts as a fin when the intermediate transfer member rotates, and an airflow is generated around the intermediate transfer member. In the image forming apparatus of the present invention, the charged toner scattered by setting the absolute value of the surface potential of the intermediate transfer member to 500 V or more can be forcibly attached to the transfer member of the secondary transfer unit. Become like
Therefore, in this image forming apparatus, it is possible to obtain a high-quality image in which the generation of toner dust is small and the contamination by the scattered toner is small.

According to a fourth aspect of the present invention, in the image forming apparatus of the first, second or third aspect, the voltage applying means is arranged so that the toner image formed on the surface of the image carrier passes through the transfer section. In this state, a voltage having the same polarity as the transfer bias is applied to the transfer member.

In the image forming apparatus, when the toner image formed on the surface of the image bearing member is passing through the transfer portion by the voltage applying means, the transfer member is transferred to the transfer member. A voltage having the same polarity as the bias is applied. Accordingly, in a state where the toner image is not formed on the surface of the image carrier, that is, in a state where the toner does not scatter, no voltage is applied to the transfer member, and unnecessary power consumption is eliminated. Will be done.

Further, the invention of claim 5 is based on claims 1, 2,
The image forming apparatus of (3) or (4) is characterized in that it has an image processing means for forming a toner image subjected to image processing by the dither method on the surface of the image carrier.

In this image forming apparatus, a toner image subjected to image processing by the dither method is formed on the surface of the image carrier. As is well known, the toner image subjected to image processing by the dither method becomes a pseudo halftone image with good gradation. Therefore, in this image forming apparatus,
It is possible to obtain a high-quality image with good gradation and little contamination by the scattered toner.

The invention according to claim 6 is based on claims 1, 2,
The image forming apparatus according to any one of 3, 4, and 5, further comprising a cleaning unit for removing the toner attached to the transfer member.

In this image forming apparatus, the toner adhered to the transfer member is removed by the cleaning means. Accordingly, when the toner image formed on the image carrier by the transfer member is transferred onto the transfer material in the transfer portion, contamination of the back surface of the transfer material due to the toner attached to the transfer member is prevented. Will be resolved.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electrophotographic color copying machine (hereinafter, referred to as a color copying machine) as an image forming apparatus will be described. First, the schematic configuration and operation of the color copying machine according to the present embodiment will be described with reference to FIG. This color copier includes a color image reading device (hereinafter, referred to as a color scanner) 1,
Color image recording device (hereinafter referred to as color printer)
2, a paper feed bank 3 and the like.

The color scanner 1 converts the image of the document 4 on the contact glass 121 into an illumination lamp 122, mirror groups 123a, 123b, 123c, and a lens 124.
And form an image on the color sensor 125 via. Then, the color image information of the document 4 is stored in, for example, Red, Green.
The image data is read for each of n, Blue (hereinafter, R, G, B) color separation lights and converted into an electric image signal. The color sensor 125 of this example is composed of R, G, and B color separation means and a photoelectric conversion element such as a CCD, and photoelectrically converts a three-color image of the document 4 separated by the color separation means. Reading by the element at the same time. Then, based on the intensity levels of the R, G, B color separation image signals obtained by the color scanner 1, a color conversion process is performed by an image processing unit (not shown), and Black (hereinafter, referred to as Bk), Cyan
(Hereinafter, referred to as C), Magenta (hereinafter, referred to as M), and Yellow (hereinafter, referred to as Y) color image data are obtained.

The operation of the color scanner 1 for obtaining the Bk, C, M, and Y color image data is as follows. Upon receiving a scanner start signal that is timed with the operation of the color printer 2 described later, an optical system including an illumination lamp 122 and mirror groups 123a, 123b, 123c scans the document 4 in the left direction of the arrow, and performs once. To obtain four color image data. This is stored in a memory (not shown) and pulled out, thereby sequentially obtaining four color image data. Then, each time the color printer 2 sequentially visualizes and superimposes the images to form a final four-color full-color image.

The color printer 2 includes a photosensitive drum 200 as an image carrier, a writing optical unit 220,
Revolver developing unit 230, intermediate transfer unit 50
0, a secondary transfer unit 600, a fixing device 270, and the like. The photosensitive drum 200 rotates in the counterclockwise direction indicated by an arrow, and the photosensitive drum cleaning device 2 surrounds the photosensitive drum 200.
01, static elimination lamp 202, charger 203, potential sensor 2
04, a selected developing unit of the revolver developing unit 230, a developing density pattern detector 205, an intermediate transfer unit 500, a secondary transfer unit 600, and the like.

The writing optical unit 220
Converts the color image data from the color scanner 1 into an optical signal, performs optical writing corresponding to the image of the document 4, and forms an electrostatic latent image on the photosensitive drum 200. The writing optical unit 220 includes a semiconductor laser 221 as a light source, a laser emission drive control unit (not shown), a polygon mirror 222 and a rotation motor 223, an f / θ lens 224, a reflection mirror 225, and the like.

The revolver developing unit 230
Is composed of a Bk developing unit 231K, a C developing unit 231C, an M developing unit 231M, a Y developing unit 231Y, and a revolver rotation drive unit which rotates each developing unit in a counterclockwise direction indicated by an arrow. A developing bias in which an AC voltage Vac is superimposed on a negative DC voltage Vdc is applied to each developing sleeve by a developing bias power supply (not shown), and the developing sleeve is set at a predetermined potential with respect to the metal base layer of the photosensitive drum 200. Biased.

When the copying machine main body is in a standby state, the revolver developing unit 230 moves the Bk developing device 231K to the 30
When the copy operation is started, reading of the Bk color image data is started from the color scanner 1 at a predetermined timing. Image formation starts (hereinafter, an electrostatic latent image based on Bk image data is converted to Bk image data).
It is called a latent image. The same applies to C, M, and Y). Before the front end of the electrostatic latent image reaches the Bk developing position, the Bk developing unit 231K is moved to the developing position and the rotation of the Bk developing sleeve is started before the front end of the electrostatic latent image reaches the Bk developing position so that development can be performed from the front end of the Bk electrostatic latent image. And B
The k electrostatic latent image is developed with Bk toner. And after that Bk
The developing operation of the electrostatic latent image area is continued, but when the trailing end of the electrostatic latent image passes the Bk developing position, the revolver developing unit 230 is immediately moved until the developing device for the next color comes to the developing position.
Rotates. This is completed at least before the leading end of the electrostatic latent image based on the next image data arrives.

As shown in FIG. 2, the intermediate transfer unit 500 includes an intermediate transfer belt 501 which is an intermediate transfer member stretched over a plurality of rollers. Around the intermediate transfer belt 501, the second transfer unit 600
Secondary transfer bias roller 60 as a secondary transfer charge applying means
5, a belt cleaning blade 504 serving as an intermediate transfer body cleaning unit, a lubricant applying brush 505 serving as a lubricant applying member of a lubricant applying unit, and the like are disposed so as to face each other.

Further, a position detecting mark is provided on the outer peripheral surface or the inner peripheral surface of the intermediate transfer belt 501. However, on the outer peripheral surface side of the intermediate transfer belt 501, it is necessary to devise a method of providing a position detection mark so as to avoid the pass area of the belt cleaning blade 504, and it may be difficult to arrange the mark. A position detection mark is provided on the inner peripheral surface side of the intermediate transfer belt 501. An optical sensor 514 as a mark detecting sensor is provided with an intermediate transfer belt 501.
Are provided between the primary transfer bias roller 507 and the drive roller 508, which are bridged.

The intermediate transfer belt 501 includes a primary transfer bias applying roller 507, a belt driving roller 508, a belt tension roller 509, and a primary transfer charge applying means.
Secondary transfer opposed roller 510, cleaning opposed roller 5
11 and a feedback current detection roller 512. Each roller is formed of a conductive material, and each roller other than the primary transfer bias roller 507 is grounded. A transfer bias controlled to a predetermined magnitude of current or voltage in accordance with the number of superimposed toner images is applied to the primary transfer bias roller 507 by a primary transfer power supply 801 controlled by a constant current or a constant voltage. ing.

The intermediate transfer belt 501 is driven in the direction of the arrow by a belt drive roller 508 that is driven to rotate in the direction of the arrow by a drive motor (not shown). The intermediate transfer belt 501 is made of a semiconductor or an insulator and has a single-layer or multilayer structure. Further, the intermediate transfer belt is set to be larger than the maximum paper-passable size in order to overlap the toner images formed on the photosensitive drum 200.

A secondary transfer bias roller 605 serving as a secondary transfer means is a contact / separation mechanism as a contact / separation means to be described later with respect to the surface of the intermediate transfer belt 501 at a portion stretched by the secondary transfer opposing roller 510. , So as to be able to come and go. The secondary transfer bias roller 605 is a part of the intermediate transfer belt 50 that is stretched around the secondary transfer facing roller 510.
1 is provided so as to sandwich the recording paper P therebetween.
A transfer bias of a predetermined current is applied by a secondary transfer power supply 802 controlled by a constant current.

The registration roller 610 feeds the transfer paper P as a transfer material at a predetermined timing between the secondary transfer bias roller 605 and the intermediate transfer belt 501 stretched over the secondary transfer opposing roller 510. A cleaning blade 608, which is a cleaning unit, is in contact with the secondary transfer bias roller 605. The cleaning blade 608 is for removing the adhered matter attached to the surface of the secondary transfer bias roller 605 for cleaning.

In a color copying machine having such a configuration,
When the image forming cycle is started, the photosensitive drum 200
Is rotated in a counterclockwise direction indicated by an arrow by a drive motor (not shown), and Bk toner image formation, C toner image formation, M toner image formation, and Y toner image formation are performed on the photosensitive drum 200. The intermediate transfer belt 501 is rotated clockwise by an arrow by a belt driving roller 508.
The Bk toner image, the C toner image, the M toner image, and the Y toner are transferred by a transfer bias caused by a voltage applied to the primary transfer bias roller 507 with the rotation of the intermediate transfer belt 501.
The primary transfer of the toner image is performed, and finally Bk, C, M,
The toner images are formed on the intermediate transfer belt 501 in the order of Y so as to overlap each other.

For example, the formation of the Bk toner image is performed as follows. In FIG. 2, the charging charger 203 includes:
The surface of the photosensitive drum 200 is uniformly charged to a predetermined potential with a negative charge by corona discharge. The timing is determined based on the belt mark detection signal, and a writing optical unit (not shown) performs raster exposure using laser light based on the Bk color image signal. When this raster image is exposed, in the exposed portion of the surface of the photosensitive drum 200 that is initially uniformly charged, the charge proportional to the amount of exposure light disappears, and a Bk electrostatic latent image is formed. In this Bk electrostatic latent image,
The negatively charged Bk on the developing roller of the Bk developing device 231K
Due to the contact of the toner, the toner does not adhere to the portion of the photosensitive drum 200 where the charge remains, and the toner is attracted to the portion having no charge, that is, the exposed portion, and Bk similar to the electrostatic latent image is obtained. A toner image is formed.

The Bk toner image formed on the photosensitive drum 200 in this manner is primarily transferred onto the surface of the intermediate transfer belt 501 which is rotating at a constant speed while being in contact with the photosensitive drum 200. The photosensitive drum 20 after this primary transfer
A small amount of untransferred residual toner remaining on the surface of
The photoconductor drum 200 is cleaned by the photoconductor cleaning device 201 in preparation for reuse. This photosensitive drum 200
On the side, the process proceeds to the Y image forming process after the Bk image forming process, and the reading of the Y image data by the color scanner starts at a predetermined timing.
An electrostatic latent image is formed.

After the trailing end of the previous Bk electrostatic latent image has passed and before the leading end of the T electrostatic latent image has reached, the rotating operation of the revolver developing unit 230 is performed, and the Y developing machine 231Y is set at the development position, and the Y electrostatic latent image is developed with the Y toner. Thereafter, the development of the Y electrostatic latent image area is continued, but when the rear end of the Y electrostatic latent image passes, the revolver developing unit rotates as in the case of the Bk developing machine 231K, and the next operation is performed. Is moved to the developing position. This is also completed before the leading end of the next C electrostatic latent image reaches the developing position. In the image forming processes of C and M, the operations of reading the color image data, forming the electrostatic latent image, and developing are the same as those in the processes of Bk and Y described above, and thus the description is omitted.

The Bk, Y, C, and M toner images sequentially formed on the photosensitive drum 200 in this way are sequentially aligned on the same surface of the intermediate transfer belt 501 and are primarily transferred. As a result, a toner image in which a maximum of four colors are superimposed on the intermediate transfer belt 501 is formed. on the other hand,
At the time when the image forming operation is started, the transfer paper P is fed from a paper feed unit such as a transfer paper cassette or a manual feed tray, and stands by at the nip of the registration roller 610.

The front end of the toner image on the intermediate transfer belt 501 is applied to a secondary transfer portion where a nip is formed by the intermediate transfer belt 501 stretched around the secondary transfer opposing roller 510 and the secondary transfer bias roller 605. When the transfer paper P is approaching, the registration roller 610 is driven so that the front end of the transfer paper P coincides with the front end of the toner image, and the transfer paper P is conveyed along the transfer paper guide plate 601, and the transfer paper P and the toner are transferred. Registration with the image is performed.

As described above, when the transfer paper P passes through the secondary transfer section, four colors on the intermediate transfer belt 501 are generated by the transfer bias by the voltage applied to the secondary transfer bias roller 605 by the secondary transfer power supply 802. The superimposed toner image is collectively transferred (secondarily transferred) onto the transfer paper P. The transfer paper P is conveyed along the transfer paper guide plate 601 and is discharged by passing through a portion facing a transfer paper discharging charger 606 formed of a discharging needle disposed downstream of the secondary transfer unit. Is sent to the fixing device 270 by the belt conveying devices 210 and 211 (see FIG. 1). Then, the transfer paper P is transferred to the fixing rollers 271 and 272 of the fixing device 270.
After the toner image is fused and fixed at the nip portion, the toner image is sent out of the apparatus main body by the discharge roller 212 and is stacked face up on a copy tray (not shown).

On the other hand, the photosensitive drum 2 after the belt transfer
The surface of the cleaning member 201 is cleaned by the photoconductor cleaning device 201, and is uniformly discharged by the discharging lamp 202. Further, the residual toner remaining on the surface of the intermediate transfer belt 501 after the secondary transfer of the toner image onto the transfer paper P is cleaned by the belt cleaning blade 504. The belt cleaning blade 504 is configured to be brought into and out of contact with the surface of the intermediate transfer belt 501 at a predetermined timing by a cleaning member separation / contact mechanism (not shown). On the upstream side of the belt cleaning blade 504 in the moving direction of the intermediate transfer belt 501, a toner seal member 503 that comes into contact with and separates from the surface of the intermediate transfer belt 501 is provided. The toner seal member 503 receives the dropped toner dropped from the belt cleaning blade 504 during the cleaning of the residual toner, and prevents the dropped toner from scattering on the transfer path of the transfer paper P. The toner seal member 503 is brought into and out of contact with the surface of the intermediate transfer belt 501 together with the belt cleaning blade 504 by the cleaning member separation / contact mechanism.

The lubricant 506 shaved off by the lubricant application brush 505 is applied to the surface of the intermediate transfer belt 501 from which the residual toner has been removed.
The lubricant 506 is made of, for example, a solid such as zinc stearate, and is provided so as to be in contact with the lubricant applying brush 505. Also, the intermediate transfer belt 501
Remaining on the surface of the intermediate transfer belt 501
The toner is removed by the charge removing bias applied by the belt charge removing brush 502 in contact with the surface of the sheet. Here, the lubricant applying brush 505 and the belt neutralizing brush 502
Are brought into contact with and separated from the surface of the intermediate transfer belt 501 at a predetermined timing by respective contact / separation mechanisms (not shown).

Here, at the time of the repeat copy, the operation of the color scanner and the image formation on the photosensitive drum 200 are as follows.
After the fourth sheet (M) image forming step of the first sheet, the process proceeds to the second sheet first color (Bk) image forming step at a predetermined timing. Further, after the batch transfer process of the first four-color superimposed toner image onto the transfer paper, the second Bk toner image is formed on the surface of the intermediate transfer belt 501 by the belt cleaning blade 504. The primary transfer is performed. Thereafter, the operation is the same as that of the first sheet.
The above is the copy mode for obtaining a four-color full-color copy. However, in the three-color copy mode and the two-color copy mode, the same operation as described above is performed for the designated color and the number of times. In the case of the single color copy mode,
Until the predetermined number of sheets is completed, the revolver developing unit 2
The copying operation is performed with only the 30 color developing machines in the developing operation state and the belt cleaning blade 504 kept in contact with the intermediate transfer belt 501.

The above is the copy mode for obtaining a four-color full-color copy. However, in the three-color copy mode and the two-color copy mode, the same operation as described above is performed for the designated color and the number of times. Become. In the case of the single-color copy mode, only the developing unit of the predetermined color of the revolver developing unit 230 is in the developing operation state until the predetermined number of copies is completed, and the belt cleaning blade 504 is brought into contact with the intermediate transfer belt 501. The copy operation is performed in the state in which the copy operation is performed.

Incidentally, the belt cleaning blade 504 and the secondary transfer bias roller 605 are configured to be able to freely contact and separate from the intermediate transfer belt 501 by the contact and separation mechanism as the contact and separation means. In this type of copying machine, as shown in FIG. 6A, a secondary transfer bias roller 605 is attached to the intermediate transfer belt 501.
When the intermediate transfer belt 501 comes and goes, the intermediate transfer belt 501 vibrates in the movement direction, and a part of the charged toner T of the toner image carried on the intermediate transfer belt 501 is transferred onto the transfer paper guide plate 601. There was a fall. For this reason, in this type of conventional image forming apparatus, as shown in FIG.
When the transfer paper P is conveyed along the transfer paper guide plate 601 by the registration rollers 610, the charged toner T falling on the transfer paper guide plate 601 is moved by the leading end of the transfer paper P. In some cases, the transfer paper P was scraped up and adhered to the image transfer surface of the transfer paper P. Then, due to the adhesion of the charged toner T to the image transfer surface of the transfer paper P, the image quality of the toner image secondarily transferred to the image transfer surface may be reduced.

Therefore, in the color copying machine according to the present embodiment, for example, as shown in FIG.
03, a voltage having the same polarity as that of the transfer bias is applied to the secondary transfer bias roller 605. As a result, the secondary transfer bias roller 605 is charged to a potential having the same polarity as the transfer bias, and the charged toner scattered around the transfer portion A as described above is applied to the charged secondary transfer bias roller 605. Adhere to. That is, the charged toner T scattered around the transfer portion A is forcibly attached to the secondary transfer bias roller 605.

Therefore, in this color copying machine, the charged toner T scattered around the transfer portion A is less likely to fall on the transfer paper guide plate 601 for guiding the transfer paper P. As a result, when the transfer paper P is transported along the transfer paper guide plate 601, the charged toner T falling on the transfer paper guide plate 601 adheres to the image transfer surface of the transfer paper P. Thus, the image quality of the toner image transferred to the image transfer surface is less likely to deteriorate.

The timing at which the voltage applying means 803 applies a voltage having the same polarity as the transfer bias to the secondary transfer bias roller 605 is, for example, as shown in FIG. The secondary transfer bias roller 605 turns on the intermediate transfer belt 605 before and after the toner image of each color primarily transferred onto the intermediate transfer belt 501 as an image carrier is secondarily transferred onto the transfer paper P. It is assumed that the belt is separated from the surface of the belt 501. At this time, the separation distance G between the secondary transfer bias roller 605 and the intermediate transfer belt 501 is about 1 mm.

Here, the intermediate transfer belt 501 is used.
Is rotating, the voltage applying means 803 applies +1.4 K to the secondary transfer bias roller 605.
A voltage of V is applied. Further, the transfer bias applied to the secondary transfer bias roller 605 by the secondary transfer power source 802 was +2 KV. The timing at which a voltage having the same polarity as that of the transfer bias is applied to the secondary transfer bias roller 605 is not limited to the timing shown in FIG. 4. For example, when the intermediate transfer belt 501 is stopped. Is also good.

In this color copying machine, a plurality of color toner images are superimposed on the intermediate transfer belt 501 and primary-transferred, and then the superposed plurality of color toner images are transferred to the secondary transfer bias roller. When a color image is formed on the transfer paper P by secondary transfer to the transfer paper P by 605, a large amount of toner images are carried on the intermediate transfer belt 501, and The electrical retention of the superimposed toner image on the intermediate transfer belt 501 is also weaker as the surface toner image is superimposed last. For this reason, in such a color copying machine,
The amount of the charged toner T scattered around the transfer portion A from the intermediate transfer belt 501 is large, and the transfer paper guide plate 601 of the transfer paper P of the charged toner T scattered around the transfer portion A is provided.
Falling up also becomes intense. Accordingly, in such a color copying machine, as described above, the charged toner T scattered around the transfer portion A is transferred to the secondary transfer bias roller 6
By forcibly attaching the toner to the transfer portion 05, a color image with less contamination by the charged toner T scattered around the transfer portion A can be obtained.

Here, when the intermediate transfer belt 501 is constituted by a multi-layered endless belt having a high resistance layer, if the polarity of the charged toner is negative, the intermediate transfer belt 501 The surface potential of the intermediate transfer belt 501 before the toner image is secondarily transferred is set to −50.
It is preferable to set the voltage to 0 V or more. As a result, the electric holding force of the intermediate transfer belt 501 for the toner image superimposed on the intermediate transfer belt 501 is increased, and the stacked toner composed of the toner images of a plurality of colors carried on the intermediate transfer belt 501 is increased. Is less likely to collapse and a high quality image with less toner dust is obtained.

However, as described above, the intermediate transfer belt 5
When the absolute value of the surface potential of 01 is set to 500 V or more,
As described above, toner scattering easily occurs when the intermediate transfer belt 501 rotates. Therefore, in this color copying machine, by applying a voltage having the same polarity as the transfer bias to the secondary transfer bias roller 605 by the voltage applying means 803, the surface potential of the intermediate transfer belt 501 is controlled. Is set to 500 V or more, the scattered charged toner T can be forcibly adhered to the secondary transfer bias roller 605. As a result, it is possible to obtain a high-quality image in which generation of toner dust is small and in which contamination by the scattered toner is small.

The timing at which a voltage is applied to the secondary transfer bias roller 605 by the voltage applying means 803 is determined by the timing at which the toner image formed on the surface of the intermediate transfer belt 501 passes through the transfer section A. It may be in the state of being. Thereby, the intermediate transfer belt 50
No toner image is formed on the surface of No. 1, that is,
In a state where the toner scattering does not occur, no voltage is applied to the secondary transfer bias roller 605, and unnecessary power consumption is eliminated.

The color copying machine according to the present embodiment
An image processing unit is provided on the surface of the intermediate transfer belt 501 to form a toner image subjected to image processing by the dither method. This makes it possible to obtain a high-quality image on the surface of the intermediate transfer belt 501, in which the pseudo-halftone image-processed by the dither method has good gradation characteristics and is less contaminated by the scattered toner T.

In this color copier, as described above, the toner adhered to the peripheral surface of the secondary transfer bias roller 605 is removed by the cleaning blade 608. Accordingly, when the toner image formed on the intermediate transfer belt 501 is transferred onto the transfer material P by the transfer unit A by the secondary transfer bias roller 605, the circumference of the secondary transfer bias roller 605 is The contamination of the back surface of the transfer paper P due to the toner attached to the surface is eliminated.

In the above embodiment, the case where the image carrier is the intermediate transfer belt 501 has been described. However, the present invention is also applied to an image forming apparatus in which the image carrier is a drum-shaped intermediate transfer member. be able to. Further, the present embodiment is an example in which the present invention is applied to an image forming apparatus including the intermediate transfer unit 500. For example, a transfer material that does not include the intermediate transfer unit and is transported from the image carrier by a transfer material transport belt. The present invention can be similarly applied to an image forming apparatus having a configuration in which image data is directly transferred to an image forming apparatus. In this case, the transfer material transport belt serves as an image carrier. The deceleration means is also effective in a tandem type image forming apparatus.

FIG. 5 shows an example of the tandem type image forming apparatus. FIG. 5 shows four photosensitive drums 11BK, 11Y, 11M, and 11C for forming toner images of four different colors (black, yellow, magenta, and cyan).
1 shows a configuration example of a four-drum type color copying machine including In this four-drum type color copying machine, the primary transfer bias rollers 20BK, 20Y, 20M, and 20 as the support members closest to the primary transfer unit are provided for each photosensitive drum.
C is provided so as to take a transferable position where the intermediate transfer belt 15 is pressed toward the surface of the photosensitive drum to form a primary transfer nip and a separated position separated from the intermediate transfer belt 11. These primary transfer bias roller, two support rollers and secondary transfer bias roller 1
6, an intermediate transfer belt 15 is stretched and supported.

When the primary transfer bias roller is located at the separated position, the stretched portion of the intermediate transfer belt 15 stretched by the support roller is separated from the photosensitive drum 11 by the fixedly disposed support roller. It is provided as follows.
Further, the primary transfer bias rollers 20BK, 20Y,
20M and 20C are respectively driven by a contact / separation mechanism (not shown), and at a predetermined timing, the photosensitive drum 11B
K, 11Y, 11M, and 11C can be brought into contact with and separated from the intermediate transfer belt 15.

In a copying machine having a plurality of photosensitive drums as in this apparatus, toner scattering from the photosensitive drum is increased. Therefore, even in such a copying machine, according to the present invention, by applying a voltage having the same polarity as the transfer bias to the secondary transfer bias roller 605 by the voltage applying means 803, the transfer due to the toner scattering is performed. The contamination of the paper P can be reduced.

[0062]

According to the first to sixth aspects of the present invention, the charged toner scattered around the transfer portion is less likely to fall on the transfer paper guide plate for guiding the transfer material, and the transfer material is reduced. When the toner is conveyed along the transfer paper guide plate, the charged toner falling on the transfer paper guide plate adheres to the image transfer surface of the transfer material, and the toner transferred to the image transfer surface There is an excellent effect that deterioration of image quality is reduced.

In particular, according to the second aspect of the present invention, the charged toner scattered around the transfer portion can be forcibly attached to the transfer member of the secondary transfer means. There is an excellent effect that a color image with less contamination by the scattered charged toner can be obtained.

In particular, according to the third aspect of the present invention, there is an excellent effect that a high quality image can be obtained with less generation of toner dust and less contamination by the scattered toner.

According to the fourth aspect of the present invention, when no toner image is formed on the surface of the image carrier,
There is an excellent effect that no voltage is applied to the transfer member and wasteful power consumption is eliminated.

Further, according to the invention of claim 5, there is an excellent effect that a high quality image with good gradation and little contamination by the scattered toner can be obtained.

According to the invention of claim 6, since the toner attached to the transfer member is removed by the cleaning means, the toner image formed on the image carrier by the transfer member is transferred to the transfer unit. Thus, when the image is transferred onto the transfer material, there is an excellent effect that contamination of the back surface of the transfer material by toner attached to the transfer member is eliminated.

[Brief description of the drawings]

FIG. 1 is a front view showing a schematic configuration of a color copying machine according to an embodiment of the present invention.

FIG. 2 is a front view showing a schematic configuration of a main part of the color copying machine.

FIG. 3 is a schematic diagram of a main part showing a state in which a secondary transfer bias roller in a secondary transfer unit of the color copying machine is separated from an intermediate transfer belt.

FIG. 4 is a timing chart for explaining an example of a timing at which a voltage is applied to the secondary transfer bias roller by a voltage applying unit. .

FIG. 5 is a front view showing a schematic configuration of another color copying machine according to the embodiment of the present invention.

FIGS. 6A and 6B are schematic diagrams illustrating a state of toner scattering around a transfer unit in a conventional image forming apparatus.

[Explanation of symbols]

 200 Photoconductor drum 203 Charging charger 220 Writing optical unit 230 Revolver developing unit 500 Intermediate transfer unit 501 Intermediate transfer belt 502 Belt discharging brush 503 Toner seal member 504 Belt cleaning blade 505 Lubricant application brush 506 Lubricant 507 Primary transfer bias roller 508 Belt drive roller 510 Secondary transfer facing roller 600 Secondary transfer unit 601 Transfer paper guide plate 605 Secondary transfer bias roller 606 Transfer paper discharging charger 610 Registration roller 802 Secondary transfer power supply 803 Voltage applying means A Transfer unit P Transfer paper T Charging toner

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Ono 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (Reference) 2H032 AA05 BA01 BA09 BA15 BA23 BA28 BA30 CA02 CA13

Claims (6)

[Claims] An image carrier that carries a toner image formed by charged toner on the surface thereof, a transfer member that is configured to be able to contact and separate from the surface of the image carrier, A transfer bias applying unit that applies a transfer bias having a polarity opposite to the polarity of the charged toner, and a transfer material conveying unit that conveys a transfer material toward a transfer unit between the transfer member and the image carrier. In a state where the transfer member is in contact with the surface of the image carrier, a transfer bias is applied to the transfer member by the transfer bias applying unit, and the image carrier is transferred onto a transfer material conveyed toward the transfer unit. In the image forming apparatus for transferring the toner image formed on the surface of the image carrier, a voltage having the same polarity as the transfer bias is applied to the transfer member while the transfer member is separated from the surface of the image carrier. Voltage applying means An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein said image carrier is firstly transferred by a primary transfer means from a latent image carrier on which said toner image is formed, and then said toner image is transferred to said image carrier. The image is transferred onto the transfer material by the secondary transfer means.
An image forming apparatus, which is an intermediate transfer member to be next transferred. 3. The image forming apparatus according to claim 2, wherein the absolute value of the surface potential of the intermediate transfer member before the second transfer of the toner image onto the intermediate transfer member is set to 500 V or more. An image forming apparatus comprising: 4. The image forming apparatus according to claim 1, wherein the voltage applying unit is configured to output the toner image when the toner image formed on the surface of the image carrier passes through the transfer unit. An image forming apparatus configured to apply a voltage having the same polarity as the transfer bias to the transfer member. 5. An image forming apparatus according to claim 1, further comprising an image processing means for forming a toner image image-processed by a dither method on a surface of said image carrier. Image forming apparatus. 6. The image forming apparatus according to claim 1, further comprising a cleaning unit for removing the toner attached to the transfer member.