JP3796041B2 - 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 printer, and a fax machine, and more particularly to an image forming apparatus using an intermediate transfer member.
[0002]
[Prior art]
Conventionally, as an electrophotographic image forming apparatus using an intermediate transfer member, a toner image formed on a photosensitive member as an image carrier is transferred to the intermediate transfer member, and the toner image on the intermediate transfer member is transferred to transfer paper. What is transferred to a transfer material such as (recording paper) is known. In this apparatus, after a toner image charged on a predetermined polarity formed on an image carrier is transferred to an intermediate transfer member using electrostatic force, the toner image on the intermediate transfer member is transferred using electrostatic force. Transfer onto the transfer material.
The image forming apparatus using the above intermediate transfer member can superimpose the toner image formed on the image bearing member on the intermediate transfer member, so that it is widely used in a color image forming apparatus for forming a color image on a transfer material. It has been. In this color image forming apparatus, toner images of respective colors sequentially formed on an image carrier are transferred onto an intermediate transfer member, and then the superimposed toner images are collectively transferred onto a transfer material using electrostatic force. Transcript. In such a color image forming apparatus, in order to sequentially form toner images on the image carrier on the intermediate transfer member, the following transfer bias (transfer electric field) is controlled in the primary transfer step. .
For example, in JP-A-4-318578, the volume resistivity is 10 as an intermediate transfer member.⁸-10¹²In the primary transfer process in which the toner image is transferred from the image carrier to the intermediate transfer member, the transfer bias is stepped up each time the toner images of the respective colors are superimposed.
In Japanese Patent Publication No. 7-86714, in order to prevent transfer failure in toner overlap transfer in a primary transfer process in which a toner image is transferred from an image carrier to an intermediate transfer member, at the time of primary transfer of the final toner image, Control is performed to apply a transfer bias larger than that at the time of the primary transfer of the immediately preceding color toner image.
[0003]
[Problems to be solved by the invention]
However, the volume resistivity of the intermediate transfer member is 10⁸-10¹⁴When a medium resistance material or an insulator made of about Ωcm is used, if the transfer bias at the time of primary transfer is increased as described in Japanese Patent Laid-Open No. 4-318578 and Japanese Patent Publication No. 7-86714, In some cases, the burden of secondary transfer from the next intermediate transfer member to the transfer material is increased. In other words, when an intermediate transfer member formed of a medium resistance material or an insulator is used, if primary transfer is performed by applying a transfer bias having a polarity opposite to the toner charging polarity to the transfer member of the primary transfer unit, The toner charge amount of the toner image transferred onto the transfer body, that is, the potential of the toner image increases. The superposed toner image with the increased potential has a large electrostatic force that tends to adhere to the intermediate transfer member. Therefore, in order to perform sufficient transfer at the secondary transfer portion that transfers the superposed toner image to the transfer material. As the charge amount of the toner on the intermediate transfer member is increased, a larger secondary transfer potential is required, and the burden on the secondary transfer portion is increased. Therefore, when considering the burden on the entire image forming apparatus using the intermediate transfer member, a transfer potential that suppresses the potential increase of the toner image on the intermediate transfer member as much as possible while maintaining sufficient transfer efficiency in the primary transfer unit. Control is desirable.
In particular, when performing a transfer operation for transferring a non-overlapping toner image that does not overlap the toner image already transferred onto the intermediate transfer member in the primary transfer unit, the non-overlapping toner image is transferred with a transfer bias larger than necessary. Since the toner image is transferred, it is necessary to suppress a burden on the secondary transfer portion due to the potential increase of the toner image.
The problem that the burden on the secondary transfer unit becomes large is not only a color image forming apparatus that superimposes a plurality of color toner images, but also a plurality of toner images that are superimposed and transferred onto an intermediate transfer member, Any toner image formed on the intermediate transfer member can be transferred to the transfer material at once.
[0004]
The present invention has been made under the above background. The purpose of the present invention is to transfer the intermediate transfer member on the intermediate transfer member at the primary transfer portion even when an intermediate transfer member formed of a medium resistance material or an insulator is used. When transferring a non-overlapping toner image that does not overlap with the toner image being applied, the increase in the potential of the toner image on the intermediate transfer member is suppressed and the burden on the secondary transfer unit is reduced while maintaining sufficient transfer efficiency. It is an object of the present invention to provide an image forming apparatus.
[0005]
[Means for Solving the Problems]
  In order to achieve the above object, the invention of claim 1 is different from each other in that a transfer electric field is formed between an image carrier and an intermediate transfer member by a transfer member to which a transfer bias is applied, and the image is formed on the image carrier. A primary transfer unit that sequentially transfers a plurality of color toner images to the intermediate transfer member; and a secondary transfer unit that collectively transfers the toner images formed on the intermediate transfer member to a transfer material.A toner image of a specific color among a plurality of second and subsequent toner images formed on the image carrier is a non-overlapping toner image that does not overlap a toner image already transferred onto the intermediate transfer member. Transferred to the transcriptIn an image forming apparatus, a single color toner imageButIntermediate transfer memberDuring the primary transfer of the first color toner image transferredThe transfer bias is T [V], the initial potential of the intermediate transfer member is Vo [V], and the potential of the background on the intermediate transfer member immediately before transferring the non-overlapping toner image is Vlast [V]. TheAfter the second colorWhen performing a transfer operation for transferring a non-overlapping toner image from the image carrier to the intermediate transfer member,Tns = T + (Vlast-Vo)Transfer bias T satisfying ns Apply [V]Control means for controlling is provided.
[0006]
  The image forming apparatus according to claim 1 is formed on the image carrier.After the second colorAmong the toner images, a toner image of a specific color is transferred to the intermediate transfer member as a non-overlapping toner image that does not overlap the toner image already transferred onto the intermediate transfer member. Then, the non-overlapping toner image which is the toner image of the specific color is removed from the image carrier.During ~When performing the transfer operation to transfer to the intermediary transfer body, NonTransfer bias when transferring superimposed toner imagesAs, Satisfying the above predetermined formulaApply transfer biasBy controlling with the control means,NonOverlapping toner images with sufficient transfer efficiencyDuring ~This enables transfer to the background portion of the intermediate transfer member, and suppresses the increase in the potential of the toner image on the intermediate transfer member as compared with the conventional case where the transfer bias is increased each time the primary transfer is repeated. be able to.
[0007]
  According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the non-overlapping toner image is black.colorA toner image,TheImmediately before transferring the black toner imagethe aboveWhen the potential of the background portion on the intermediate transfer member is Vlast [V]TheTransfer the black toner image from the image carrier to the intermediate transfer member.When performing the transfer operation,Tbk = T + (Vlast−Vo) is satisfiedTransfer bias T bk Apply [V]It is characterized by controlling as follows.
[0008]
In the image forming apparatus according to the second aspect, the transfer bias is applied when the black toner image, which is a non-overlapping toner image, is primarily transferred onto the intermediate transfer member on which the toner image of a color other than black has already been transferred. By controlling so as to satisfy the predetermined formula, the black toner image can be transferred to the background portion of the intermediate transfer member with sufficient transfer efficiency, and the potential of the toner image on the intermediate transfer member is increased. Suppress.
[0009]
  According to a third aspect of the present invention, in the image forming apparatus of the first aspect, the first color toner image transferred to the intermediate transfer member is a black toner image, and the second color toner image is the non-overlapping toner image. ,TheWhen the potential of the background portion on the intermediate transfer body immediately before transferring the second color toner image is Vlast '[V].TheTransfer the second color toner image from the image carrier to the intermediate transfer member.When performing the transfer operation,T2 = T + (Vlast'-Vo) is satisfiedTransfer bias T 2 Apply [V]It is characterized by controlling as follows.
[0010]
In the image forming apparatus according to claim 3, when the toner image of the second color other than black, which is a non-overlapping toner image, is primarily transferred onto the intermediate transfer body on which the black toner image has already been transferred, By controlling the transfer bias so as to satisfy the predetermined formula, the toner image of the second color can be transferred to the background portion of the intermediate transfer member with sufficient transfer efficiency, and the toner on the intermediate transfer member can be transferred. Suppresses potential rise in image.
[0011]
  According to a fourth aspect of the invention, the transfer order of the black toner image can be changed.2An image forming apparatus, wherein the transfer bias Tb is based on the transfer order of the black toner image.k ofIt is characterized by performing control.
[0012]
  In this image forming apparatus, even when the transfer order of the black toner image is changed, the transfer bias Tb is based on the transfer order of the black toner image.k ofBy performing the control, when the non-overlapping toner image (black toner image or toner image of the second color other than black) is primarily transferred, the non-overlapping toner image is sufficiently transferred with sufficient transfer efficiency. The toner image can be transferred to a portion, and the potential increase of the toner image on the intermediate transfer member is suppressed.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment in which the present invention is applied to an electrophotographic color copying machine (hereinafter referred to as “color copying machine”) as an image forming apparatus will be described below.
FIG. 1 is a schematic configuration diagram of an image forming unit which is a main part of the color copying machine according to the present embodiment. In addition to the image forming unit shown in FIG. 1, this color copying machine is composed of a color image reading unit (not shown) (hereinafter referred to as a color scanner), a paper feeding unit, and a control unit as a control means for controlling them. Yes.
[0014]
The color scanner reads color image information of a document for each color separation light of, for example, red, green, and blue (hereinafter referred to as “R”, “G”, and “B”, respectively) and converts them into electrical image signals. To do. Then, based on the color separation image signal intensity levels of R, G, and B obtained by this color scanner, color conversion processing is performed by an image processing unit (not shown) to obtain black, cyan, magenta, yellow (hereinafter, “ Bk ”,“ C ”,“ M ”, and“ Y ”) are obtained.
[0015]
1 includes a photosensitive drum 100 as an image carrier, a charging charger 200 as a charging unit, a photosensitive member cleaning device 300 including a cleaning blade and a fur brush, a writing optical unit (not shown) as an exposure unit, and development. A revolver developing unit 400 as a means, an intermediate transfer unit 500, a secondary transfer unit 600 as a secondary transfer means, a fixing unit using a fixing roller pair 701, and the like.
[0016]
The photosensitive drum 100 rotates counterclockwise as indicated by an arrow in the figure, and around the charging charger 200, the photosensitive member cleaning device 300, the selected developing device of the revolver developing unit 400, and the intermediate transfer unit. An intermediate transfer belt 501 as an intermediate transfer member 500 is disposed.
[0017]
Further, the writing optical unit converts the color image data from the color scanner into an optical signal, and applies the laser beam L corresponding to the image of the document on the surface of the photosensitive drum 100 uniformly charged by the charging charger 200. Irradiation is performed to perform optical writing, and an electrostatic latent image is formed on the photosensitive drum 100. This writing optical unit can be composed of, for example, a semiconductor laser as a light source, a laser light emission drive control unit, a polygon mirror and its rotation motor, an f / θ lens, a reflection mirror, and the like.
[0018]
The revolver developing unit 400 includes a Bk developing unit 401 that uses Bk toner, a C developing unit 402 that uses C toner, an M developing unit 403 that uses M toner, a Y developing unit 404 that uses Y toner, and the entire unit. The developing revolver driving unit is rotated clockwise. Each of the developing devices 401 to 404 installed in the revolver developing unit 400 is developed as a developer carrying member that rotates by bringing the ears of the developer into contact with the surface of the photosensitive drum 100 in order to develop the electrostatic latent image. The sleeve includes a developer paddle that rotates to draw up and stir the developer, and a developing sleeve driving unit that rotates the developing sleeve clockwise as indicated by an arrow.
[0019]
In this embodiment, the toner in each of the developing devices 401 to 404 is negatively charged by stirring with the ferrite carrier, and each developing sleeve has a negative DC voltage by a developing bias power source as a developing bias applying unit (not shown). A developing bias voltage in which an AC voltage Vac (AC component) is superimposed on Vdc (DC component) is applied, and each developing sleeve is biased to a predetermined potential with respect to the metal substrate layer of the photosensitive drum 100.
[0020]
In the standby state of the color copying machine main body, the revolver developing unit 400 is stopped at the home position where the Bk developing unit 401 is located at the developing position, and when the copy start key is pressed, the color scanner 1 starts the Bk color from a predetermined timing. Reading of image data is started, and light writing by laser light L, that is, formation of an electrostatic latent image, is started based on the color image data (hereinafter, an electrostatic latent image based on Bk image data is referred to as “Bk electrostatic latent image” C). The same applies to M, Y).
[0021]
Before the leading edge of the electrostatic latent image reaches the Bk development position so that development is possible from the leading edge of the Bk electrostatic latent image, the Bk developing sleeve is started to rotate, and the Bk electrostatic latent image is cleaned with Bk toner. develop. Thereafter, the development operation of the Bk electrostatic latent image area is continued. When the rear end portion of the Bk electrostatic latent image passes the Bk development position, the developer of the next color comes to the development position immediately. The revolver developing unit 400 rotates. This is completed at least before the leading edge of the electrostatic latent image based on the next image data reaches the developing position.
[0022]
The intermediate transfer unit 500 includes an intermediate transfer belt 501 as an intermediate transfer member stretched around a plurality of rollers. Around the intermediate transfer belt 501 are a secondary transfer belt 601 as a transfer material carrier of the secondary transfer unit 600, a secondary transfer bias roller 605 as a secondary transfer charge applying unit, and an intermediate transfer member cleaning unit. A belt cleaning blade 504, a lubricant application brush 505 as a lubricant application means, and the like are arranged to face each other.
[0023]
The intermediate transfer belt 501 is stretched around a primary transfer bias roller 507, a belt driving roller 508, a belt tension roller 509, a secondary transfer counter roller 510, a cleaning counter roller 511, and a ground roller 512 as primary transfer charge applying means. It is built. Each roller is formed of a conductive material, and each roller other than the primary transfer bias roller 507 is grounded.
[0024]
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 with a constant current or voltage. Has been. The intermediate transfer belt 501 is driven in the direction of the arrow by a belt driving roller 508 that is driven to rotate in the direction of the arrow by a drive motor (not shown).
[0025]
The intermediate transfer belt 501 has a single-layer or multi-layer structure made of a semiconductor or insulator material.
[0026]
In a transfer portion (hereinafter referred to as “primary transfer portion”) that transfers the toner image on the photosensitive drum 100 to the intermediate transfer belt 501, the intermediate transfer belt 501 is moved to the photosensitive drum by the primary transfer bias roller 507 and the earth roller 512. A nip portion having a predetermined width is formed between the photosensitive drum 100 and the intermediate transfer belt 501 by stretching so as to press against the 100 side. Further, a belt neutralizing brush 513 that is grounded is brought into contact with the inner peripheral surface of the intermediate transfer belt 501 at the nip as a primary transfer unit neutralizing unit.
[0027]
Further, as shown in FIG. 2, the nip width Wn of the primary transfer portion and the distance L from the downstream end of the nip portion in the belt moving direction to the contact position of the belt neutralizing brush 513 are such that predetermined transfer conditions can be obtained. Set to.
[0028]
The lubricant application brush 505 polishes zinc stearate 506 as a lubricant formed in a plate shape, and applies the polished fine particles to the intermediate transfer belt 501. The lubricant application brush 505 is also configured to be adjacent to the intermediate transfer belt 501 and is controlled to contact the intermediate transfer belt 501 at a predetermined timing.
[0029]
  The secondary transfer unit 600 includes a secondary transfer belt 601 stretched between three support rollers 602, 603, and 604, and the stretched portion between the support rollers 602 and 603 of the intermediate transfer belt 501 is the 2 It can be pressed against the next transfer facing roller 510. One of the three support rollers 602, 603, and 604 is a drive roller that is rotationally driven by a drive unit (not shown), and the secondary transfer belt 601 is driven by the drive roller in a direction indicated by an arrow in the drawing..
[0030]
The secondary transfer bias roller 605 is a secondary transfer unit, and is disposed so as to sandwich the intermediate transfer belt 501, the transfer paper, and the secondary transfer belt 601 between the secondary transfer counter roller 510 and a constant current. A transfer bias having a predetermined current is applied by a secondary transfer power source 802 to be controlled. Further, the support roller 602 and the secondary transfer bias roller are set so that the secondary transfer belt 601 and the secondary transfer bias roller 605 can take a position where they are pressed against and separate from the secondary transfer counter roller 510. A separation mechanism (not shown) for driving 605 in the direction of the arrow is provided. The secondary transfer belt 601 in the separated position is indicated by a two-dot chain line in FIG.
[0031]
A member denoted by reference numeral 650 in FIG. 1 is a pair of registration rollers, and is interposed between the intermediate transfer belt 501 and the secondary transfer belt 601 sandwiched between the secondary transfer bias roller 605 and the secondary transfer counter roller 510. Then, the transfer paper P as a transfer material is fed in at a predetermined timing.
[0032]
A portion of the secondary transfer belt 601 that is wound around the support roller 603 on the opposite side of the fixing roller is opposed to a transfer sheet neutralization charger 606 as a transfer material neutralization unit and a belt neutralization charger 607 as a transfer material carrier neutralization unit. is doing. Further, a cleaning blade 608 as a transfer material carrier cleaning means is in contact with a portion of the secondary transfer belt 601 that is wound around a lower support roller 604 in the drawing.
[0033]
The transfer paper neutralization charger 606 neutralizes the charge held on the transfer paper P so that the transfer paper can be satisfactorily separated from the secondary transfer belt 601 with the strength of the transfer paper itself. . The belt neutralization charger 607 neutralizes charges remaining on the secondary transfer belt 601. Further, the cleaning blade 608 is for removing the adhering matter adhering to the surface of the secondary transfer belt 601 for cleaning.
[0034]
In the color copying machine configured as described above, when an image forming cycle is started, the photosensitive drum 100 is first rotated counterclockwise as indicated by an arrow, and the intermediate transfer belt 501 is rotated clockwise as indicated by an arrow. As the intermediate transfer belt 501 rotates, Bk toner image formation, C toner image formation, M toner image formation, and Y toner image formation are performed, and finally, on the intermediate transfer belt 501 in the order of Bk, C, M, and Y. A toner image is formed in an overlapping manner.
[0035]
For example, Bk toner image formation is performed as follows. The charging charger 200 uniformly charges the photosensitive drum 100 with a negative charge to a predetermined potential by corona discharge. Then, 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 photosensitive drum 100 that is initially uniformly charged, and a Bk electrostatic latent image is formed. When the negatively charged Bk toner on the Bk developing sleeve comes into contact with this Bk electrostatic latent image, the toner does not adhere to the remaining portion of the photosensitive drum 100, and the portion without charge, that is, the exposure. The Bk toner is attracted to the part, and a Bk toner image similar to the electrostatic latent image is formed. The Bk toner image formed on the photosensitive drum 100 is transferred to the surface of the intermediate transfer belt 501 that is driven at a constant speed in contact with the photosensitive drum 100. Hereinafter, the transfer of the toner image from the photosensitive drum 100 to the intermediate transfer belt 501 is referred to as “primary transfer”.
[0036]
Some untransferred residual toner remaining on the surface of the photoreceptor drum 100 after the primary transfer is cleaned by the photoreceptor cleaning device 300 in preparation for reuse of the photoreceptor drum 100.
[0037]
On the photosensitive drum 100 side, the process proceeds to the C image forming process after the Bk image forming process, and reading of C image data by a color scanner starts at a predetermined timing, and C electrostatic latent image formation is performed by laser beam writing using the C image data. I do. Then, after the rear end portion of the previous Bk electrostatic latent image passes and before the front end portion of the C electrostatic latent image reaches, the revolver developing unit is rotated, and the C developing device 402 is moved to the developing position. The C electrostatic latent image is developed with C toner. Thereafter, development of the C electrostatic latent image area is continued, but when the rear end of the C electrostatic latent image passes, the revolver developing unit is rotated in the same manner as in the case of the Bk developing unit 401, and the next The M developing device M is moved to the developing position. This is also completed before the leading edge of the next M electrostatic latent image reaches the developing position.
The image forming process for M and Y is not described because the operations of reading color image data, forming an electrostatic latent image, and developing are the same as those of the above-described BK and C processes.
[0038]
Bk, C, M, and Y toner images sequentially formed on the photosensitive drum 100 are sequentially transferred to the intermediate transfer belt 501 after being aligned on the same surface. As a result, a toner image in which a maximum of four colors are superimposed is formed on the intermediate transfer belt 501. The superimposed toner images on the intermediate transfer belt 501 are collectively transferred onto transfer paper in the next secondary transfer process.
[0039]
At the time when the image forming operation is started, the transfer sheet P is fed from a sheet feeding unit such as a transfer sheet cassette (not shown) or a manual feed tray, and waits at a nip of a registration roller pair 650 (not shown). When the leading edge of the toner image on the intermediate transfer belt 501 approaches the secondary transfer portion where the nip is formed by the secondary transfer counter roller 510 and the secondary transfer bias roller, the leading edge of the transfer paper P is just the toner image. The registration roller pair 650 is driven so as to coincide with the leading edge of the toner, and registration of the transfer paper P and the toner image is performed. Then, the transfer paper P is superimposed on the toner image on the intermediate transfer belt 501 and passes through the secondary transfer portion. At this time, the four-color superimposed toner image on the intermediate transfer belt 501 is collectively transferred onto the transfer paper P by the transfer bias formed by the transfer bias applied to the secondary transfer bias roller. When passing through a portion facing the transfer sheet neutralization charger 606 disposed downstream of the secondary transfer portion in the secondary transfer belt moving direction, the transfer sheet P is neutralized, peeled off from the intermediate transfer belt 501, and fixed to the fixing roller. Sent to pair 701. The toner image is melted and fixed at the nip portion of the fixing roller pair 701, sent out of the apparatus main body by a pair of discharge rollers (not shown), and stacked face up on a copy tray (not shown) to obtain a full color copy.
[0040]
On the other hand, the surface of the photoconductor belt 100 after the primary transfer is cleaned by the photoconductor cleaning device 300 and is uniformly discharged by a discharge lamp (not shown).
Further, the toner remaining on the surface of the intermediate transfer belt 501 after the toner image is transferred to the transfer paper P is cleaned by a belt cleaning blade 504 pressed against the intermediate transfer belt 501 by a contact / separation mechanism (not shown).
[0041]
Here, in the case of repeat copying, the operation of the color scanner and the image formation on the photosensitive drum 100 are performed for the first color of the second sheet at a predetermined timing following the fourth color (Y) image forming process of the first sheet. The process proceeds to the image forming process (Bk). Further, the intermediate transfer belt 501 has a second Bk toner in the area 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. The image is transferred to the belt. After that, the operation is the same as the first sheet.
[0042]
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 developer of the revolver developing unit 400 is in the developing operation state until the predetermined number of sheets is completed, and the belt cleaning blade 504 is pressed against the intermediate transfer belt 501. Copy operation is performed continuously.
[0043]
Next, in the color copying machine having the above configuration, Bk toner does not overlap with other toners for primary transfer bias control when performing a transfer operation in which a certain toner does not overlap with other toners. A case will be described as an example.
[0044]
When the transfer operation is executed, the C toner, M toner, and Y toner may be formed on the intermediate transfer belt 501, but the Bk toner is not formed on the other toner. Therefore, the primary transfer bias control in this embodiment is performed as follows. As shown in the flowchart of the copy mode in FIG. 3A, after the copy operation is started and the scanning of the original is finished (step 1), a Bk toner image which is an image of a toner color component which is not formed on the intermediate transfer belt is transferred. In the primary transfer process of transferring to the 501, the primary transfer power source 508 is set by the control unit so that the primary transfer bias Vbk [V] applied to the primary transfer bias roller 507 becomes a value represented by the following formula 1. Control (steps 2 and 3). Here, the transfer bias necessary for transferring the monochrome toner image to the intermediate transfer belt 501 with sufficient efficiency is T [V], the initial potential of the intermediate transfer belt 501 is Vo [V], and the Bk transfer process is performed. The background potential on the immediately preceding intermediate transfer belt is Vlast [V].
On the other hand, if the toner color component image is not overlaid, transfer is performed under conventional primary transfer bias conditions (step 4).
[Expression 1]
Tbk = T + (Vlast-Vo)
[0045]
Further, even when the control for changing the image forming order is performed, the primary transfer bias is set to the transfer bias expressed by the above formula 1 in the transfer process in which the Bk toner image is always transferred.
[0046]
Further, when the order of image formation is such that the Bk toner image is transferred to the first color, if the background potential of the intermediate transfer belt 501 immediately before the transfer process of the second color toner image is Vlast ′ [V]. In the control unit, the primary transfer power supply 508 is set so that the primary transfer bias T2 [V] applied to the primary transfer bias roller 507 when transferring the second color toner image becomes a value represented by the following formula 2. To control.
[Expression 2]
T2 = T + (Vlast'-Vo)
[0047]
Similar primary transfer bias control is also performed in the printer mode of FIG. For example, the control unit determines the image overlay state based on image information sent from an external computer or the like. In the primary transfer step of transferring the Bk toner image, which is an image of the toner color component that is not overlapped, to the intermediate transfer belt 501, the primary transfer bias Vbk [V] applied to the primary transfer bias roller 507 is the above formula. The primary transfer power source 508 is controlled by the control unit so as to be a value indicated by 1 (steps 1 and 2). On the other hand, if the toner color component image is not overlaid, the image is transferred under conventional primary transfer bias conditions (step 3).
[0048]
As described above, according to the present embodiment, the toner transfer of the toner image primarily transferred onto the intermediate transfer belt 501 while maintaining a sufficient transfer efficiency during the transfer of the Bk toner image by the primary transfer bias control. The increase in the amount can be suppressed as much as possible and the burden on the secondary transfer portion can be reduced.
[0049]
【Example】
Next, a more specific example of the color copying machine according to the above embodiment will be described.
An intermediate transfer belt having a thickness of 0.15 mm, a width of 368 mm, and an inner peripheral length of 565 mm was used as the intermediate transfer belt 501, and the moving speed of the intermediate transfer belt 501 was set to 200 mm / sec. The intermediate transfer belt 501 was made of ETFE (ethylene-tetrafluoroethylene copolymer).
[0050]
Further, a nickel-plated metal roller was used as the primary transfer bias roller 507, a metal roller was used as the earth roller 512, and a metal roller or a conductive resin roller was used as the other rollers.
[0051]
For example, in the order of image formation in which Bk toner is first transferred to the primary transfer bias roller 507, the first color Bk toner image is 1.2 kV and the second color toner image On the other hand, a DC transfer bias was applied, such as 1.2 kV, 1.3 kV for the third color toner image, and 1.4 kV for the fourth color toner image. Further, for example, in the case of an image forming order in which a Bk toner image is transferred to the fourth color, 1.2 kV for the first color toner image, 1.3 kV for the second color toner image, and the third color A DC transfer bias of 1.4 kV was applied to the toner image and 1.2 kV was applied to the Bk toner image of the fourth color.
[0052]
Further, the nib width Wn of the primary transfer portion shown in FIG. 2 was set to 15 mm, and the distance L from the downstream end of the nib portion in the belt moving direction to the support position of the belt neutralizing brush 513 was set to 7 mm. Moreover, as the belt static elimination brush 513, the electroconductive thing by which the carbon containing resin fiber was planted was used.
[0053]
Further, as the secondary transfer bias roller 605, a roller having a surface layer made of conductive sponge or conductive rubber and a core layer made of metal or conductive resin is used, and constant current control is performed on this roller at 10 to 20 μA. The applied transfer bias was applied. The secondary transfer belt 601 is made of PVDF (polyvinylidene fluoride) and has a thickness of 100 μm and a volume resistivity of 10¹³A belt material of Ωcm was used.
[0054]
The transfer paper neutralization charger 606 uses a discharger to which only an AC voltage or an AC + DC voltage is applied by a power supply (not shown), and the belt neutralization charger 607 also has a discharger to which only an AC voltage or an AC + DC voltage is applied by a power supply (not shown). Was used. Further, the cleaning blade 608 is brought into contact with the portion of the secondary transfer belt 601 that is wound around the support roller 604 in a counter manner.
[0055]
In the above embodiment, the example in which the photosensitive drum 100 is used as the image carrier has been described. However, the present invention can also be applied to an image carrier having another shape. For example, the present invention can also be applied to a photoreceptor belt that is stretched between two rollers and moves endlessly.
[0056]
In the above-described embodiment, an example in which the intermediate transfer belt 501 is used as the intermediate transfer member has been described. However, the present invention can also be applied to a member using an intermediate transfer member having another shape. Further, the electrical characteristics (volume resistivity, surface resistivity, etc.), thickness, structure (single layer, two layers,...), Material, material, etc. of the intermediate transfer belt 501 are appropriate depending on the imaging conditions. Various things can be selected and employed.
[0057]
In the above-described embodiment, an example in which the primary transfer bias roller is used as the primary transfer charge applying unit has been described. However, the present invention can be applied to a configuration using primary transfer charge applying units having other shapes. be able to. Further, the primary transfer charge may be applied in the nip of the primary transfer portion as long as it is downstream of the neutralization position by the primary transfer non-static means such as the static elimination brush in the intermediate transfer belt moving direction.
[0058]
Further, in the above embodiment, the values of the primary transfer bias voltage and current applied to the primary transfer charge applying means such as the primary transfer bias roller 507 are not limited to the above examples, and various values are available. A suitable value can be set according to image forming conditions.
[0059]
In the above-described embodiment, an example in which the secondary transfer bias roller is used as the secondary transfer charge applying unit has been described. However, in the present invention, a member having another shape such as a blade or a brush is used instead of the roller. It can also be applied to things.
[0060]
In the above-described embodiment, the case where the photosensitive drum 100 has a negative charging potential and a developing device employing a reversal developing method using a two-component developer has been described. The present invention is not limited to the charging potential of the body drum 100, and can be similarly applied to those using a one-component developer and those using a regular development system.
[0061]
【The invention's effect】
According to the first, second, third, and fourth aspects of the invention, the toner that has already been transferred onto the intermediate transfer member at the primary transfer portion even when an intermediate transfer member formed of a medium resistance material or an insulator is used. When transferring a non-overlapping toner image that does not overlap the image, while maintaining sufficient transfer efficiency, the transfer bias is increased on each intermediate transfer member as compared with the conventional case where the transfer bias is increased for each primary transfer. This is advantageous in that the increase in the potential of the toner image can be suppressed and the burden on the secondary transfer portion can be reduced.
[0062]
In particular, according to the second and fourth aspects of the invention, when the black toner image, which is a non-overlapping toner image, is primarily transferred onto the intermediate transfer member on which the toner image of a color other than black has already been transferred, There is an effect that the burden on the secondary transfer portion can be reduced by suppressing the potential increase of the color toner image on the intermediate transfer member while maintaining sufficient transfer efficiency.
[0063]
In particular, according to the third and fourth aspects of the invention, the second-color toner image of a color other than black, which is a non-overlapping toner image, is primarily transferred onto the intermediate transfer body on which the black toner image has already been transferred. In some cases, there is an effect that the burden on the secondary transfer portion can be reduced by suppressing the potential increase of the toner image on the intermediate transfer member while maintaining sufficient transfer efficiency.
[0064]
In particular, according to the fourth aspect of the present invention, even when the transfer order of the black toner image is changed, the non-overlapping toner image (black toner image or second color toner image other than black) is first-ordered. When transferring, the non-overlapping toner image can be transferred to the intermediate transfer member with sufficient transfer efficiency, and the increase in the potential of the toner image on the intermediate transfer member is suppressed to reduce the burden on the secondary transfer portion. There is an effect that can be.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a color copying machine according to an embodiment.
FIG. 2 is an enlarged view of a primary transfer portion of the color copying machine.
FIG. 3A is a flowchart of a copy mode of the color copier.
(B) is a flowchart of a printer mode of the color copying machine.
[Explanation of symbols]
100 Photosensitive drum
500 Intermediate transfer unit
501 Intermediate transfer belt
503 Belt Charger Charger
504 Belt cleaning blade
507 Primary transfer bias roller
508 Belt drive roller
508a Drive motor
509 Belt tension roller
510 Secondary transfer counter roller
511 Cleaning counter roller
512 Belt neutralization roller
513 Belt static elimination brush
601 Secondary transfer belt
605 Secondary transfer bias roller
801 Primary transfer power supply
802 Secondary transfer power supply
804 Power supply for static elimination

Claims (4)

A transfer electric field is formed between the image carrier and the intermediate transfer member by a transfer member to which a transfer bias is applied, and a plurality of different color toner images formed on the image carrier are sequentially transferred to the intermediate transfer member. A plurality of toner images of the second and subsequent colors formed on the image carrier, comprising: a primary transfer unit; and a secondary transfer unit that collectively transfers a toner image formed on the intermediate transfer member onto a transfer material. In the image forming apparatus in which a toner image of a specific color is transferred to the intermediate transfer member as a non-overlapping toner image that does not overlap the toner image already transferred onto the intermediate transfer member,
The toner image of the first color on which the single color toner image is transferred onto the intermediate transfer member is T [V] at the time of primary transfer, the initial potential of the intermediate transfer member is Vo [V], and the non-overlapping toner When the potential of the background portion on the intermediate transfer body immediately before transferring the image is Vlast [V],
When performing a transfer operation for transferring the non-overlapping toner image from the image carrier to the intermediate transfer member,
Tns = T + (Vlast-Vo)
An image forming apparatus comprising control means for controlling to apply a transfer bias Tns [V] satisfying the above. The image forming apparatus according to claim 1.
The non-overlapping toner image is a black toner image;
A transfer operation of transferring the black toner image from the image carrier to the intermediate transfer member when the potential of the background portion on the intermediate transfer member immediately before the transfer of the black toner image is Vlast [V]. At runtime
Tbk = T + (Vlast-Vo)
The image forming apparatus is controlled to apply a transfer bias Tbk [V] satisfying the above. The image forming apparatus according to claim 1.
The first color toner image transferred to the intermediate transfer member is a black toner image, the second color toner image is the non-overlapping toner image,
Transfer the second color toner image from the image carrier to the intermediate transfer member when the potential of the background portion on the intermediate transfer member immediately before transferring the second color toner image is Vlast '[V]. When performing the transfer operation,
T2 = T + (Vlast'-Vo)
The image forming apparatus is controlled to apply a transfer bias T2 [V] satisfying the above. The image forming apparatus according to claim 2, wherein the transfer order of the black toner image can be changed.
An image forming apparatus, wherein the transfer bias Tb k is controlled based on a transfer order of the black toner image.

Images