JP4074749B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, or a printer. More specifically, the present invention relates to an image forming apparatus that applies a transfer bias to a transfer member that is configured to be able to contact with and separate from the surface of an image carrier. An electrophotographic image forming apparatus for transferring a toner image formed on the surface of the image carrier onto a transfer material conveyed toward a transfer portion between the carrier and the carrier.
[0002]
[Prior art]
Conventionally, an image carrier such as a photosensitive drum, a photoreceptor belt, or an intermediate transfer belt has been used as this type of image forming apparatus, and a toner image formed on the image carrier is transferred to paper or OHP by a transfer unit. An image forming apparatus that transfers images onto a transfer material such as a sheet is known.
[0003]
For example, in the “image forming apparatus” disclosed in Japanese Patent Laid-Open No. 11-231667, a toner image formed on the photosensitive drum is transferred to the intermediate transfer by a primary transfer bias roller which is a primary transfer member of the transfer unit. Primary transfer is performed on the 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 that is a secondary transfer member, and at the transfer portion where the intermediate transfer belt and the secondary transfer bias roller are in contact with each other, The toner image primarily transferred onto the intermediate transfer belt is electrically attracted and secondarily transferred onto the transfer material conveyed toward the transfer portion.
[0004]
By the way, the transfer member is usually configured so as to be able to come into contact with and separate from the surface of the image carrier by contact and separation means. This is because the transfer member always contacts the surface of the image carrier to prevent the transfer member and the image carrier from being deformed over time, or a plurality of toner images are continuously formed 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.
In particular, in an intermediate transfer type image forming apparatus that collectively transfers a plurality of color toner images that are sequentially superimposed and transferred onto the intermediate transfer belt by the secondary transfer bias roller, when forming a color image of two or more colors. The contact between the intermediate transfer belt and the secondary transfer bias roller is essential.
[0005]
Also, the contact and separation between the intermediate transfer belt and the secondary transfer bias roller is performed by arranging a plurality of photosensitive drums along the intermediate transfer belt, and for each color toner image formed on each photosensitive drum. In a tandem type image forming apparatus that performs primary transfer by superimposing the intermediate transfer belt on the intermediate transfer belt and then secondary-transferring the primary transferred toner image at a nip between the intermediate transfer belt and a secondary transfer bias roller. Is also essential.
[0006]
[Problems to be solved by the invention]
However, as described above, in the image forming apparatus configured to contact and separate the transfer member with respect to the surface of the image carrier, when the transfer member contacts and separates from the surface of the moving image carrier. The image carrier may vibrate instantaneously in the moving direction. This is considered to be due to the force (inertial force, frictional force, etc.) that prevents the movement of the image carrier due to the contact between the surface of the image carrier and the contact / separation member. It is done.
[0007]
In particular, when the image carrier is constituted by a belt-like member as in the above-described intermediate transfer belt, an image carrier comprising this belt-like member (hereinafter referred to as “image carrier belt”). The vibration in the moving direction at the time of contact with the contact member becomes significant. That is, this type of belt-like member has a certain degree of slack even in a stretched state. Therefore, when the contact member comes into contact with the image carrier belt, the belt portion on the downstream side in the moving direction from the contact portion of the image carrier belt with respect to the contact member is abruptly tensioned. Accordingly, the progress of the belt portion on the upstream side in the moving direction from the contact portion of the image carrier belt is temporarily stopped. Such tension and stop of 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, the vibration in the moving direction at the time of contact of the image carrier belt with the contact member is larger than that of a drum-like image carrier having relatively high rigidity.
[0008]
For this reason, in this type of conventional image forming apparatus, for example, as shown in FIG. 6A, the intermediate transfer belt 501 is in contact with or separated from the intermediate transfer belt 501. Due to the vibration of the transfer belt 501, the charged toner T, which is a part of the toner image carried on the intermediate transfer belt 501, is scattered around the transfer portion A where the intermediate transfer belt 5012 secondary transfer bias roller 605 contacts and separates. There was something to do.
Then, the charged toner T scattered around the transfer portion A falls on a transfer paper guide plate 601 for guiding the transfer paper P conveyed toward the transfer portion A by the registration roller 610.
[0009]
For this reason, in this type of conventional image forming apparatus, as shown in FIG. 6B, when the transfer paper P is conveyed along the transfer paper guide plate 601 by the registration roller 610, the transfer paper P is transferred. The charged toner T falling on the paper guide plate 601 may be scraped up by the leading edge of the transfer paper P and adhere to the image transfer surface of the transfer paper P. Further, the adhesion of the charged toner T to the image transfer surface of the transfer paper P sometimes deteriorates the image quality of the toner image that is secondarily transferred to the image transfer surface.
Here, as a cause of scattering of the charged toner on the image carrier, the vibration of the image carrier at the time of contacting and separating the transfer member with respect to the image carrier is cited. There is a high possibility that the image carrier is also generated by vibration or centrifugal force during rotation.
[0010]
The present invention has been made in view of the above problems, and the object of the present invention is to scatter the toner image on the image carrier onto the transfer material when the transfer member is transferred onto the transfer material. An object of the present invention is to provide an image forming apparatus capable of preventing contamination of the image transfer surface of the transfer material by charged toner.
[0011]
[Means for Solving the Problems]
  In order to achieve the above object, the invention of claim 1 comprises an image carrier that carries and moves a toner image formed of charged toner on the surface thereof, and is configured to be able to contact and separate from the surface of the image carrier. A transfer material applied to the transfer member, a transfer bias applying means for applying a transfer bias opposite to the polarity of the charged toner to the transfer member, and a transfer material toward the transfer portion between the transfer member and the image carrier. A transfer material conveying means for conveying, and transferring the transfer member by applying a transfer bias to the transfer member by the transfer bias applying means in a state where the transfer member is in contact with the surface of the image carrier. In an image forming apparatus for transferring a toner image formed on the surface of the image carrier onto a transfer material to be transferred, the transfer member is separated from the surface of the image carrier with respect to the transfer member. Same as above transfer bias It has a voltage applying means for applying a sexual voltageThe voltage application means applies a voltage having the same polarity as the transfer bias to the transfer member when the toner image formed on the surface of the image carrier passes through the transfer portion. In addition, when the toner image formed on the surface of the image carrier does not pass through the transfer portion, a voltage having the same polarity as the transfer bias is not applied to the transfer member. ConfiguredIt is characterized by that.
[0012]
  In this image forming apparatus, the voltage application means applies a voltage having the same polarity as the transfer bias to the transfer member in a state where the transfer member is separated from the surface of the image carrier. As a result, the transfer member is charged to a potential having the same polarity as the transfer bias, and the charged toner scattered around the transfer portion 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. Thus, 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 It is less likely that the image quality of the toner image transferred to the surface is degraded.
In the image forming apparatus, the transfer bias is applied to the transfer member when the toner image formed on the surface of the image carrier by the voltage applying unit passes through the transfer unit. Is applied with a voltage of the same polarity. As a result, in a state where no toner image is formed on the surface of the image carrier, that is, in a state where the toner scattering does not occur, voltage is not applied to the transfer member, and unnecessary power consumption is eliminated. Will come to be.
[0013]
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the image carrier is primarily transferred from the latent image carrier on which the toner image is formed by primary transfer means. Thereafter, the toner image is an intermediate transfer member that is secondarily transferred onto the transfer material by a secondary transfer unit.
[0014]
In this image forming apparatus, after superimposing a plurality of color toner images on the intermediate transfer member and performing primary transfer, the superimposed plurality of color toner images are secondarily transferred onto the transfer material by the secondary transfer unit. By transferring, a color image can be formed on the transfer material. When such a multi-color toner image is formed, there are many toner images carried on the intermediate transfer member, and the electric power of the intermediate transfer member of the toner image superimposed on the intermediate transfer member is obtained. The effective holding force also becomes weaker as the toner image on the surface layer superimposed last. For this reason, in such an image forming apparatus, the amount of charged toner scattered from the intermediate transfer member to the periphery of the transfer unit is large, and the charged toner scattered to the periphery of the transfer unit guides the transfer material. The drop on the transfer paper guide plate also becomes intense. In the image forming apparatus of the present invention, the charged toner scattered around the transfer portion can be forcibly adhered to the transfer member of the secondary transfer unit. Therefore, in this image forming apparatus, it is possible to obtain a color image with little contamination by the charged toner scattered around the transfer portion.
[0015]
According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the absolute value of the surface potential of the intermediate transfer member before the toner image is secondarily transferred onto the intermediate transfer member is set to 500 V or more. It is characterized by that.
[0016]
As described above, as a method for increasing the electrical holding force of the intermediate transfer body of the toner image superimposed on the intermediate transfer body, before the toner image is secondarily transferred onto the intermediate transfer body, It is known to set the absolute value of the surface potential of the intermediate transfer member to 500 V or more. As a result, the laminated toner composed of a plurality of color toner images carried on the intermediate transfer member is not easily collapsed, and a high-quality image with little toner dust generation can be obtained. However, when the absolute value of the surface potential of the intermediate transfer member is set to 500 V or more in this way, toner scattering tends to occur 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 air flow 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 adhered to the transfer member of the secondary transfer unit. It becomes like this. Therefore, in this image forming apparatus, it is possible to obtain a high quality image with less toner dust and less contamination by the scattered toner.
[0019]
  Claims4The invention of claim 1,Two-wayIs3In the image forming apparatus, image processing means for forming a toner image image-processed by a dither method is provided on the surface of the image carrier.
[0020]
In this image forming apparatus, a toner image image-processed by the dither method is formed on the surface of the image carrier. As is well known, the toner image that has been image-processed by the dither method is an image having a good gradation property of pseudo halftone. Therefore, in this image forming apparatus, it is possible to obtain a high quality image with good gradation and less contamination by the scattered toner.
[0021]
  Claims5The invention of claim 1, 2,ThreeIs4The image forming apparatus includes a cleaning unit that removes toner adhering to the transfer member.
[0022]
In this image forming apparatus, the toner attached to the transfer member is removed by the cleaning unit. As a result, when the toner image formed on the image carrier by the transfer member is transferred onto the transfer material at the transfer portion, the back surface of the transfer material is contaminated by the toner adhering to the transfer member. It will be resolved.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which the present invention is applied to an electrophotographic color copying machine (hereinafter referred to as a color copying machine) which is 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. The color copying machine includes a color image reading device (hereinafter referred to as a color scanner) 1, a color image recording device (hereinafter referred to as a color printer) 2, a paper feed bank 3, and the like.
[0024]
The color scanner 1 forms an image of the document 4 on the contact glass 121 on the color sensor 125 via the illumination lamp 122, the mirror groups 123a, 123b, 123c, and the lens 124. Then, the color image information of the document 4 is read for each color separation light of, for example, Red, Green, and Blue (hereinafter, referred to as R, G, and B, respectively) and converted into an electrical image signal. The color sensor 125 of this example is composed of R, G, B color separation means and a photoelectric conversion element such as a CCD, and photoelectrically converts three color images of the original 4 color-separated by the color separation means. Reading simultaneously with the element. Then, based on the intensity levels of the color separation image signals of R, G, and B obtained by the color scanner 1, color conversion processing is performed by an image processing unit (not shown), and Black (hereinafter referred to as Bk), Cyan ( Hereinafter, color image data of C), Magenta (hereinafter referred to as M), and Yellow (hereinafter referred to as Y) are obtained.
[0025]
The operation of the color scanner 1 for obtaining the Bk, C, M, and Y color image data is as follows. In response to a scanner start signal that takes the operation and timing of the color printer 2 to be described later, the optical system including the illumination lamp 122 and the mirror groups 123a, 123b, 123c scans the document 4 in the left direction of the arrow, and once. The color image data of four colors is obtained by the scanning. By storing and extracting this in a memory (not shown), color image data of four colors is sequentially obtained. Each time, the color printer 2 sequentially visualizes the images and superimposes them to form a final four-color full-color image.
[0026]
The color printer 2 includes a photosensitive drum 200 as an image carrier, a writing optical unit 220, a revolver developing unit 230, an intermediate transfer unit 500, a secondary transfer unit 600, a fixing device 270, and the like. The photosensitive drum 200 rotates counterclockwise as indicated by an arrow, and around the photosensitive drum 201, a static elimination lamp 202, a charger 203, a potential sensor 204, and a selected developing unit of the revolver developing unit 230. A development density pattern detector 205, an intermediate transfer unit 500, a secondary transfer unit 600, and the like are arranged.
[0027]
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 light emission drive control unit (not shown), a polygon mirror 222 and its rotation motor 223, an f / θ lens 224, a reflection mirror 225, and the like.
[0028]
The revolver developing unit 230 includes a Bk developing unit 231K, a C developing unit 231C, an M developing unit 231M, and a Y developing unit 231Y, and a revolver rotation driving unit described below that rotates each developing unit in the counterclockwise direction indicated by an arrow. It is configured. 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 has a predetermined potential with respect to the metal base layer of the photosensitive drum 200. Is biased to.
[0029]
In the standby state of the copying machine main body, the revolver developing unit 230 has the Bk developing device 231K set 30 degrees before the developing position, and when the copying operation is started, the color scanner 1 starts the Bk color image from a predetermined timing. Data reading is started, optical writing by laser light and electrostatic latent image formation are started based on this color image data (hereinafter, an electrostatic latent image based on Bk image data is referred to as a Bk latent image. The same). Before the leading edge of the electrostatic latent image reaches the Bk developing position to enable development from the leading edge of the Bk electrostatic latent image, the Bk developing device 231K is moved to the developing position and the Bk developing sleeve starts rotating. Then, the Bk electrostatic latent image is developed with Bk toner. Thereafter, the development operation of the Bk electrostatic latent image area is continued. When the trailing edge of the electrostatic latent image passes the Bk development position, the revolver development is performed until the next color developing device immediately reaches the development position. The unit 230 rotates. This is completed at least before the leading edge of the electrostatic latent image by the next image data arrives.
[0030]
As shown in FIG. 2, the intermediate transfer unit 500 includes an intermediate transfer belt 501 that is an intermediate transfer member stretched around a plurality of rollers. Around the intermediate transfer belt 501, a secondary transfer bias roller 605 that is a secondary transfer charge applying unit of the secondary transfer unit 600, a belt cleaning blade 504 that is an intermediate transfer member cleaning unit, and a lubricant for a lubricant application unit. A lubricant application brush 505 or the like that is an application member is disposed so as to face each other.
[0031]
A position detection 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 provision of position detection marks so as to avoid the passing area of the belt cleaning blade 504, which may be difficult to arrange. A position detection mark is provided on the inner peripheral surface side of the intermediate transfer belt 501. An optical sensor 514 serving as a mark detection sensor is provided at a position between the primary transfer bias roller 507 and the drive roller 508 where the intermediate transfer belt 501 is bridged.
[0032]
The intermediate transfer belt 501 includes a primary transfer bias roller 507 serving as a primary transfer charge applying unit, a belt driving roller 508, a belt tension roller 509, a secondary transfer counter roller 510, a cleaning counter roller 511, and a feedback current detection roller 512. It is stretched around. Each roller is formed of a conductive material, and each roller other than the primary transfer bias roller 507 is grounded. The primary transfer bias roller 507 is applied with a transfer bias controlled to a predetermined current or voltage according to the number of superimposed toner images by a primary transfer power source 801 controlled at a constant current or voltage. ing.
[0033]
The intermediate transfer belt 501 is driven in the arrow direction by a belt driving roller 508 that is driven to rotate in the arrow direction by a drive motor (not shown). The intermediate transfer belt 501 is a semiconductor or an insulator and has a single layer or a multilayer structure. Further, the intermediate transfer belt is set to be larger than the maximum sheet passing size in order to superimpose the toner images formed on the photosensitive drum 200.
[0034]
A secondary transfer bias roller 605 serving as a secondary transfer unit is in contact with the surface of the intermediate transfer belt 501 at a portion stretched around the secondary transfer counter roller 510 by a contact / separation mechanism as a contact / separation unit described later. It is configured to be separable. The secondary transfer bias roller 605 is disposed so as to sandwich the recording paper P between the portion of the intermediate transfer belt 501 stretched around the secondary transfer counter roller 510 and is subjected to constant current control. A transfer bias having a predetermined current is applied by the transfer power source 802.
[0035]
The registration roller 610 feeds the transfer sheet P, which is a transfer material, between the secondary transfer bias roller 605 and the intermediate transfer belt 501 stretched around the secondary transfer counter roller 510 at a predetermined timing. The secondary transfer bias roller 605 is in contact with a cleaning blade 608 as a cleaning unit. The cleaning blade 608 is for removing the adhering matter adhering to the surface of the secondary transfer bias roller 605 for cleaning.
[0036]
In the color copying machine having such a configuration, when an 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 is placed on the photosensitive drum 200. Image formation, C toner image formation, M toner image formation, and Y toner image formation are performed. The intermediate transfer belt 501 is rotated clockwise by the belt driving roller 508 as indicated by an arrow. As the intermediate transfer belt 501 rotates, the primary transfer of the Bk toner image, the C toner image, the M toner image, and the Y toner image is performed by the transfer bias by the voltage applied to the primary transfer bias roller 507. Finally, the respective toner images are formed on the intermediate transfer belt 501 in the order of Bk, C, M, and Y.
[0037]
For example, the Bk toner image formation is performed as follows. In FIG. 2, a charging charger 203 uniformly charges the surface of the photosensitive drum 200 to a predetermined potential with a negative charge by corona discharge. The timing is determined based on the belt mark detection signal, and raster exposure with laser light is performed based on the Bk color image signal by a writing optical unit (not shown). When this raster image is exposed, the charge proportional to the exposure light amount disappears in the exposed portion of the surface of the photosensitive drum 200 that is initially uniformly charged, and a Bk electrostatic latent image is formed. When the negatively charged Bk toner on the developing roller of the Bk developing device 231K comes into contact with this Bk electrostatic latent image, the toner does not adhere to the remaining portion of the photosensitive drum 200, and the charge is not charged. The toner is attracted to the nonexposed portion, that is, the exposed portion, and a Bk toner image similar to the electrostatic latent image is formed.
[0038]
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 that is driven to rotate at a constant speed in contact with the photosensitive drum 200. Some untransferred residual toner remaining on the surface of the photoreceptor drum 200 after the primary transfer is cleaned by the photoreceptor cleaning device 201 in preparation for reuse of the photoreceptor drum 200. On the photosensitive drum 200 side, the process proceeds to the Y image forming process after the Bk image forming process, and reading of the Y image data by the color scanner starts at a predetermined timing, and the photosensitive drum is written by laser beam writing with the Y image data. A Y electrostatic latent image is formed on the surface of 200.
[0039]
Then, after the rear end portion of the previous Bk electrostatic latent image passes and before the front end portion of the T electrostatic latent image reaches, the revolver developing unit 230 is rotated, and the Y developing device 231Y develops. The Y electrostatic latent image is developed with Y toner. Thereafter, the development of the Y electrostatic latent image area is continued. When the trailing edge of the Y electrostatic latent image passes, the revolver developing unit is rotated in the same manner as in the case of the previous Bk developing machine 231K, and the next The C developing machine 231C is moved to the developing position. This is also completed before the leading edge of the next C electrostatic latent image reaches the developing position. Note that the C and M image forming steps are the same as the Bk and Y steps described above because the color image data reading, electrostatic latent image forming, and developing operations are the same as those described above.
[0040]
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 on the intermediate transfer belt 501 and primarily transferred. As a result, a toner image having a maximum of four colors 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 is waiting at the nip of the registration roller 610.
[0041]
When the leading edge of the toner image on the intermediate transfer belt 501 reaches the secondary transfer portion where the nip is formed by the intermediate transfer belt 501 stretched around the secondary transfer counter roller 510 and the secondary transfer bias roller 605. Then, the registration roller 610 is driven so that the leading edge of the transfer paper P coincides with the leading edge 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 image are transferred. Resist alignment is performed.
[0042]
In this way, when the transfer paper P passes through the secondary transfer portion, the four-color superimposed toner image on the intermediate transfer belt 501 is transferred by the transfer bias applied by the secondary transfer power source 802 to the secondary transfer bias roller 605. Are collectively transferred (secondary transfer) onto the transfer paper P. After the transfer paper P is conveyed along the transfer paper guide plate 601 and passed through a portion facing the transfer paper neutralization charger 606 composed of a static elimination needle disposed on the downstream side of the secondary transfer portion, the transfer paper P is discharged. Then, it is sent toward the fixing device 270 by the belt conveying devices 210 and 211 (see FIG. 1). Then, after the toner image is melted and fixed at the nip portions of the fixing rollers 271 and 272 of the fixing device 270, the transfer paper P is sent out of the apparatus main body by the discharge roller 212 and stacked face up on a copy tray (not shown). The
[0043]
On the other hand, the surface of the photosensitive drum 200 after the belt transfer is cleaned by the photosensitive member cleaning device 201 and is uniformly discharged by the discharging lamp 202. Further, residual toner remaining on the surface of the intermediate transfer belt 501 after the toner image is secondarily transferred to the transfer paper P is cleaned by the belt cleaning blade 504. The belt cleaning blade 504 is configured to be brought into contact with and separated from the surface of the intermediate transfer belt 501 at a predetermined timing by a cleaning member separating and contacting mechanism (not shown). A toner seal member 503 that contacts and separates from the surface of the intermediate transfer belt 501 is provided on the upstream side of the belt cleaning blade 504 in the moving direction of the intermediate transfer belt 501. The toner seal member 503 receives the falling toner dropped from the belt cleaning blade 504 when cleaning the residual toner, and prevents the falling toner from scattering on the transfer path of the transfer paper P. The toner seal member 503 is brought into contact with and separated from the surface of the intermediate transfer belt 501 together with the belt cleaning blade 504 by the cleaning member separating and contacting mechanism.
[0044]
The lubricant 506 scraped 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 in this way. The lubricant 506 is made of, for example, a solid body such as zinc stearate, and is disposed so as to come into contact with the lubricant application brush 505. Further, the residual charge remaining on the surface of the intermediate transfer belt 501 is removed by a neutralizing bias applied by the belt neutralizing brush 502 in contact with the surface of the intermediate transfer belt 501. Here, the lubricant application 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 and separation mechanisms (not shown).
[0045]
Here, at the time of repeat copy, the operation of the color scanner and the image formation on the photosensitive drum 200 are performed at a predetermined timing following the first color (M) image formation process of the first sheet and the first color of the second sheet. The process proceeds to the image forming process (Bk). Further, the intermediate transfer belt 501 has a second Bk toner image on the surface cleaned by the belt cleaning blade 504 on the surface following the batch transfer process of the first four-color superimposed toner image to the transfer paper. Make primary transfer. After that, the operation is the same as the first sheet. The above is a copy mode for obtaining a four-color full-color copy. 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, only the predetermined color developing machine of the revolver developing unit 230 is set in the developing operation state until the predetermined number of sheets is completed, and the belt cleaning blade 504 is kept in contact with the intermediate transfer belt 501. The copy operation is performed in the state.
[0046]
The above is a copy mode for obtaining a four-color full-color copy. 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. Further, in the single color copy mode, only the predetermined color developer of the revolver developing unit 230 is set in the developing operation state until the predetermined number of copies are completed, and the belt cleaning blade 504 is brought into contact with the intermediate transfer belt 501. The copy operation is performed in the left state.
[0047]
By the way, the belt cleaning blade 504 and the secondary transfer bias roller 605 are configured to be able to contact and separate from the intermediate transfer belt 501 by a contact and separation mechanism as the contact and separation means. In this type of copying machine, as shown in FIG. 6A, when the secondary transfer bias roller 605 contacts and separates from the intermediate transfer belt 501, the intermediate transfer belt 501 vibrates in the moving direction. As a result, a part of the charged toner T in the toner image carried on the intermediate transfer belt 501 may fall on the transfer paper guide plate 601.
Therefore, in this type of conventional image forming apparatus, as shown in FIG. 6B, when the transfer paper P is conveyed along the transfer paper guide plate 601 by the registration roller 610, The charged toner T falling on the transfer paper guide plate 601 is sometimes scraped up by the leading end of the transfer paper P and adheres to the image transfer surface of the transfer paper P. Further, the adhesion of the charged toner T to the image transfer surface of the transfer paper P sometimes deteriorates the image quality of the toner image that is secondarily transferred to the image transfer surface.
[0048]
Therefore, in the color copying machine according to the present embodiment, for example, as shown in FIG. 3, a voltage application unit 803 applies a voltage having the same polarity as the transfer bias to the secondary transfer bias roller 605. And
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 charged on 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.
[0049]
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 that guides the transfer paper P. Thus, 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.
[0050]
The timing at which the voltage application means 803 applies a voltage having the same polarity as the transfer bias to the secondary transfer bias roller 605 is as shown in FIG. The secondary transfer bias roller 605 before and after the toner images of the respective colors primarily transferred onto the intermediate transfer belt 501 as the image carrier are secondarily transferred onto the transfer paper P are formed on the intermediate transfer belt 501. The state is separated from the surface. The separation distance G between the secondary transfer bias roller 605 and the intermediate transfer belt 501 at the time of separation is about 1 mm.
[0051]
Further, here, a voltage of +1.4 KV is applied to the secondary transfer bias roller 605 by the voltage applying means 803 while the intermediate transfer belt 501 is rotating. Further, the transfer bias applied to the secondary transfer bias roller 605 by the secondary transfer power source 802 was set to +2 KV. The timing at which the voltage having the same polarity as the transfer bias is applied to the secondary transfer bias roller 605 is not limited to that shown in FIG. 4. For example, the intermediate transfer belt 501 is stopped. Also good.
[0052]
By the way, in this color copying machine, after superimposing a plurality of color toner images on the intermediate transfer belt 501 and performing primary transfer, the superposed multiple color toner images are transferred to the secondary transfer bias roller 605 by the secondary transfer bias roller 605. When a secondary image is transferred onto the transfer paper P and a color image is formed on the transfer paper P, a large amount of toner images are carried on the intermediate transfer belt 501 and are superimposed on the intermediate transfer belt 501. The electric holding force of the intermediate transfer belt 501 for the toner image is also weaker as the toner image on the surface layer superimposed last. For this reason, in such a color copying machine, the amount of the charged toner T scattered from the intermediate transfer belt 501 to the periphery of the transfer portion A is large, and the transfer of the charged toner T scattered to the periphery of the transfer portion A is performed. The fall of the paper P onto the transfer paper guide plate 601 also becomes intense.
Therefore, in such a color copying machine, as described above, the charged toner T scattered around the transfer portion A is forcibly adhered to the secondary transfer bias roller 605, so that A color image with little contamination by the charged toner T scattered around can be obtained.
[0053]
Here, when the intermediate transfer belt 501 is formed of a multi-layered endless belt having a high resistance layer, the toner image is formed on the intermediate transfer belt 501 when the polarity of the charged toner is negative. It is preferable that the surface potential of the intermediate transfer belt 501 before the secondary transfer is set to −500 V or more.
As a result, the electrical holding force of the intermediate transfer belt 501 for the toner image superimposed on the intermediate transfer belt 501 is increased, and a laminated toner composed of a plurality of color toner images carried on the intermediate transfer belt 501. Is less likely to collapse, and a high-quality image with less toner dusting can be obtained.
[0054]
However, when the absolute value of the surface potential of the intermediate transfer belt 501 is set to 500 V or more as described above, toner scattering is likely to occur when the intermediate transfer belt 501 rotates as described above.
Therefore, in this color copying machine, the surface potential of the intermediate transfer belt 501 is applied 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. When the absolute value of is set to 500 V or more, the charged toner T scattered can be forcibly adhered to the secondary transfer bias roller 605. As a result, it is possible to obtain a high-quality image with less toner dust and less contamination by the scattered toner.
[0055]
The voltage application unit 803 applies a voltage to the secondary transfer bias roller 605 when the toner image formed on the surface of the intermediate transfer belt 501 passes through the transfer portion A. Sometimes it is good.
As a result, in a state where no toner image is formed on the surface of the intermediate transfer belt 501, that is, in a state where toner scattering does not occur, no voltage is applied to the secondary transfer bias roller 605, which is wasteful. Power consumption will be eliminated.
[0056]
Further, the color copying machine according to the present embodiment has image processing means for forming a toner image subjected to image processing by the dither method on the surface of the intermediate transfer belt 501. As a result, a high-quality image can be obtained on the surface of the intermediate transfer belt 501 with good pseudo-halftone gradation processed by the dither method and with little contamination by the scattered toner T.
[0057]
In this color copying machine, as described above, the toner attached 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 portion A by the secondary transfer bias roller 605, the periphery of the secondary transfer bias roller 605 is increased. Contamination of the back surface of the transfer paper P due to the toner adhering to the surface is eliminated.
[0058]
In the above embodiment, the case where the image carrier is the intermediate transfer belt 501 has been described. However, the present invention can also be applied to an image forming apparatus in which the image carrier is a drum-shaped intermediate transfer member. . Furthermore, this embodiment is an example applied to an image forming apparatus provided with an intermediate transfer unit 500. For example, a transfer material that is not provided with an intermediate transfer unit and is conveyed from an image carrier by a transfer material conveyance belt. The present invention can be similarly applied to an image forming apparatus configured to perform direct transfer. In this case, the transfer material conveyance belt is an image carrier. The deceleration means is also effective in a tandem image forming apparatus.
[0059]
FIG. 5 shows an example of the tandem image forming apparatus. FIG. 5 shows a configuration of a four-drum type color copying machine including four photosensitive drums 11BK, 11Y, 11M, and 11C for forming toner images of four different colors (black, yellow, magenta, and cyan). An example is shown.
In this four-drum type color copying machine, for each photosensitive drum, primary transfer bias rollers 20BK, 20Y, 20M, and 20C as the support member closest to the primary transfer portion, and the intermediate transfer belt 15 on the surface of the photosensitive drum. It is provided so that a transferable position where the primary transfer nip is formed by pressing toward the intermediate transfer belt 11 and a separation position separated from the intermediate transfer belt 11 can be taken. An intermediate transfer belt 15 is stretched and supported by these primary transfer bias rollers, two support rollers, and a secondary transfer bias roller 16.
[0060]
The fixedly arranged support rollers are provided so that the stretched portion of the intermediate transfer belt 15 stretched by the support rollers is separated from the photosensitive drum 11 when the primary transfer bias rollers are located at the separated positions. It has been.
The primary transfer bias rollers 20BK, 20Y, 20M, and 20C are driven by a contact / separation mechanism (not shown), and the photosensitive drums 11BK, 11Y, 11M, and 11C and the intermediate transfer belt 15 are contacted and separated at a predetermined timing. Can be made.
[0061]
In a copying machine having a plurality of photosensitive drums as in this apparatus, toner scattering from the photosensitive drums also increases. Therefore, even in such a copying machine, according to the present invention, the voltage application unit 803 applies a voltage having the same polarity as the transfer bias to the secondary transfer bias roller 605, whereby the transfer due to the toner scattering is performed. Contamination of the paper P can be reduced.
[0062]
【The invention's effect】
  Claims 1 to5According to the 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 conveyed along the transfer paper guide plate. In this case, the charged toner falling on the transfer paper guide plate may adhere to the image transfer surface of the transfer material, and the image quality of the toner image transferred to the image transfer surface may deteriorate. There is an excellent effect of decreasing.
According to the first to fifth aspects of the present invention, when no toner image is formed on the surface of the image carrier, no voltage is applied to the transfer member, and unnecessary power consumption is eliminated. There is an excellent effect of becoming.
[0063]
In particular, according to the second aspect of the present invention, since the charged toner scattered around the transfer portion can be forcibly adhered to the transfer member of the secondary transfer means, the charged toner scattered around the transfer portion is charged. There is an excellent effect that a color image with little contamination by toner can be obtained.
[0064]
In particular, according to the invention of claim 3, there is an excellent effect that it is possible to obtain a high quality image with less generation of toner dust and less contamination by the scattered toner.
[0066]
  Claims4According to this invention, there is an excellent effect that a high-quality image can be obtained with good gradation and less contamination by the scattered toner.
[0067]
  Claims5According to the invention, 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 onto the transfer material by the transfer unit. In this case, there is an excellent effect that contamination of the back surface of the transfer material due to the toner adhering 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 configuration 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 timing for applying a voltage 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 for explaining a state of toner scattering around a transfer unit in a conventional image forming apparatus.
[Explanation of symbols]
200 Photosensitive drum
203 Charger charger
220 Writing optical unit
230 Revolver development unit
500 Intermediate transfer unit
501 Intermediate transfer belt
502 Belt neutralization 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 counter roller
600 Secondary transfer unit
601 Transfer paper guide plate
605 Secondary transfer bias roller
606 Transfer paper static elimination charger
610 Registration Roller
802 Secondary transfer power supply
803 Voltage application means
A transcription part
P transfer paper
T Charging toner

Claims (5)

An image carrier that carries and moves a toner image formed by charged toner on the surface, a transfer member configured to be able to contact with and separate from the surface of the image carrier, and the polarity of the charged toner on the transfer member A transfer bias applying means for applying a transfer bias having a polarity opposite to that of the transfer material, and a transfer material conveying means for conveying the transfer material toward a transfer portion 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, the transfer bias is applied to the transfer member by the transfer bias applying means, and the image carrier is transferred onto the transfer material conveyed toward the transfer unit. In the image forming apparatus for transferring the toner image formed on the surface of
Voltage transfer means for applying a voltage having the same polarity as the transfer bias to the transfer member in a state where the transfer member is separated from the surface of the image carrier;
The voltage applying means applies a voltage having the same polarity as the transfer bias to the transfer member when the toner image formed on the surface of the image carrier passes through the transfer portion. In addition, when the toner image formed on the surface of the image carrier does not pass through the transfer portion, a voltage having the same polarity as the transfer bias is not applied to the transfer member. An image forming apparatus configured to be configured . The image forming apparatus according to claim 1.
The image carrier is primarily transferred from the latent image carrier on which the toner image is formed by a primary transfer unit, and then the toner image is secondarily transferred onto the transfer material by a secondary transfer unit. An image forming apparatus, which is an intermediate transfer member to be transferred. The image forming apparatus according to claim 2.
An image forming apparatus, wherein an absolute value of a surface potential of the intermediate transfer member before the toner image is secondarily transferred onto the intermediate transfer member is set to 500 V or more. The image forming apparatus according to claim 1, 2 or 3,
An image forming apparatus comprising image processing means for forming a toner image subjected to image processing by a dither method on the surface of the image carrier. Claims 1, 3 or the image forming apparatus 4,
An image forming apparatus comprising: a cleaning unit that removes toner adhering to the transfer member.

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