JP2008281689A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a recording sheet from being contaminated due to discharged toner by effectively collecting the discharged toner on an intermediate transfer body in any image forming mode. <P>SOLUTION: The image forming apparatus is provided with: a plurality of image carriers 4 which carry toner images of predetermined colors different from each other; a rotatable intermediate transfer body 30 faces the plurality of image carriers 4 respectively via primary transfer areas 15 and to which the toner images are transferred from the image carriers 4 in the primary transfer areas 15; and a control part 70 which switches an image forming mode between a monochrome mode for forming an image composed of one color toner image, and a multi-color mode for forming an image by superposing a plurality of color toner images, and controls to collect toner on the intermediate transfer body 30 by the plurality of image carriers 4 by bringing the plurality of image carries 4 into contact with the intermediate transfer body 30 for a predetermined time when starting to drive and rotate the intermediate transfer body 30 in image forming operation in the monochrome mode. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus and an image forming method, and in particular, to an image forming apparatus such as a copier, a printer, a facsimile, or a multifunction machine having these functions combined, and these image forming apparatuses. The present invention relates to a method of forming an image using the same.

  A so-called tandem image forming apparatus has been proposed as an electrophotographic color image forming apparatus. The tandem image forming apparatus has a configuration in which four photoconductors corresponding to the respective colors of yellow (Y), magenta (M), cyan (C), and black (K) are arranged around the intermediate transfer member. ing. When printing in full-color mode using a tandem image forming apparatus, image formation is performed with the four photoconductors in contact with the intermediate transfer member, and each color toner image formed on each photoconductor is intermediate. The image is sequentially transferred (primary transfer) to the transfer body, and is superimposed on the intermediate transfer body. On the other hand, when printing in the monochrome mode, only the black photosensitive member is placed in contact with the intermediate transfer member, and image formation is performed with the three photosensitive members other than black spaced apart from the intermediate transfer member. Are transferred (primary transfer) to the intermediate transfer member. When the toner image transferred to the intermediate transfer member is conveyed to the nip portion (secondary transfer region) between the intermediate transfer member and the secondary transfer member by the rotation of the intermediate transfer member, the sheet passes through the secondary transfer region, etc. (Secondary transfer). Toner remaining on the intermediate transfer member without being transferred to the recording sheet in the secondary transfer region is removed from the surface of the intermediate transfer member by a cleaning device provided downstream of the secondary transfer region in the rotation direction of the intermediate transfer member. Is done.

  Patent Document 1 discloses a cleaning device for an intermediate transfer member.

  As shown in FIG. 9, the cleaning device of Patent Document 1 includes a cleaning brush 142 disposed in contact with the intermediate transfer belt 130 and a charging disposed in contact with the intermediate transfer belt 130 on the upstream side of the cleaning brush 142. A brush 174, a collection roller 177 disposed in contact with the cleaning brush 142, and a scraper 178 provided in contact with the collection roller 177 are provided. A power source 184 is connected to the scraper 178, and the charging brush 174 is grounded. When the power supply 184 is turned on, a current supplied from the power supply 184 to the scraper 178 flows through the collection roller 177, the cleaning brush 142, and the intermediate transfer belt 130 to the charging brush 174. When the current on the charging brush 174 flows and the toner on the intermediate transfer belt 130 passes through the contact portion with the charging brush 174 by the rotation of the belt 130, the polarity of most of the toner particles is negative ( The toner charged in the negative polarity with the regular charging polarity of the toner is conveyed further downstream by the rotation of the intermediate transfer belt 130, and the cleaning brush having a high potential at the contact portion between the belt 130 and the cleaning brush 142. It is electrostatically attracted to 142 and removed from the outer peripheral surface of the belt 130.

  However, in the technique of Patent Document 1, the toner that is not negatively charged at the contact portion between the intermediate transfer belt 130 and the charging brush 174 and electrostatically adsorbed to the brush fibers of the brush 174, or the brush fibers of the charging brush 174 The toner and the like mechanically entangled with each other are accumulated in the charging brush 174. The toner accumulated in the charging brush 174 is caused by the vibration of the brush fibers of the brush 174 that are pulled by the belt 130 when the belt 130 starts to rotate during the next image forming operation. In some cases, the ink is discharged from the inside of the brush 174 to the outer peripheral surface of the belt 130.

  Since the discharged toner is toner accumulated in the charging brush 174, the discharged toner contains a lot of toner having a very small charge amount and toner charged to positive polarity (polarity opposite to the normal charging polarity). On the other hand, an electric field is formed in the nip portion (primary transfer region) between the intermediate transfer belt and the photoconductor to move the negatively charged toner from the photoconductor to the belt by the transfer bias applied to the primary transfer roller. Yes. For this reason, when the discharged toner is conveyed to the primary transfer region by the rotation of the belt, a part of the discharged toner moves from the belt to the photoconductor, contrary to the negatively charged toner.

When an image is formed in a full color mode using a tandem image forming apparatus, the four photosensitive members are arranged in contact with the intermediate transfer belt, and therefore, the discharged toner is discharged before reaching the secondary transfer area. Pass through the primary transfer area. In each primary transfer region where the electric field is formed, a part of the discharged toner is collected on the photoconductor. Therefore, most of the discharged toner is collected by the four photoconductors, and the discharged toner can be prevented from being conveyed to the secondary transfer region and adhering to the recording sheet.
JP 2004-310060 A

  However, when an image is formed in the monochrome mode using the tandem image forming apparatus, only one photosensitive member (photosensitive member corresponding to black) is in contact with the intermediate transfer belt. Only one primary transfer area passes through before reaching the next transfer area. Therefore, most of the discharged toner is conveyed to the secondary transfer region by the belt, and adheres to the recording sheet during the secondary transfer, which may cause the recording sheet to become dirty.

  Therefore, an object of the present invention is to effectively collect the discharged toner on the intermediate transfer member regardless of the image forming mode and prevent the recording sheet from being contaminated by the discharged toner.

In order to solve the above problems, an image forming apparatus according to the present invention provides:
A plurality of image carriers that carry toner images of predetermined colors different from each other;
A rotatable intermediate transfer member that faces the plurality of image carriers with a primary transfer region interposed therebetween, and in which the toner image is transferred from the image carrier in the primary transfer region;
The image formation mode is switched between a single color mode for forming an image composed of only one color toner image and a multi-color mode for forming an image formed by superimposing a plurality of color toner images. When the rotation of the intermediate transfer member is started during operation, the plurality of image carriers are brought into contact with the intermediate transfer member for a predetermined time, and the toner recovery is performed such that the toner on the intermediate transfer member is recovered by the plurality of image carriers. And a control unit that controls to perform the operation.

  In this specification, “image forming operation” refers not only to the operation of forming a toner image on an image carrier or intermediate transfer member, but also to a series of operations performed during printing, A pre-processing sequence and a post-processing sequence performed before and after the toner image forming operation are included.

An image forming method according to the present invention includes:
Using an image forming apparatus comprising a plurality of image carriers that carry toner images of predetermined colors different from each other and a rotatable intermediate transfer member that faces each of the plurality of image carriers with a primary transfer region interposed therebetween. An image forming method in which an image is formed by switching between a single color mode for forming an image composed of only one color toner image and a multi-color mode for forming an image formed by superimposing a plurality of color toner images. ,
When starting rotation of the intermediate transfer member during image formation in the monochrome mode, a toner recovery operation is performed to recover the toner on the intermediate transfer member with a plurality of the image carriers,
The toner collecting operation is
Bringing two or more image carriers into contact with the intermediate transfer member for a predetermined time;
The toner on the intermediate transfer member is electrostatically transferred from the intermediate transfer member to the image carrier in a plurality of primary transfer regions formed between the two or more image carriers and the intermediate transfer member. Forming an electric field to be moved;
A step of separating an image carrier other than the image carrier on which image formation is performed among the two or more image carriers from the intermediate transfer member.

  According to the present invention, when the rotation of the intermediate transfer member is started during the image forming operation in the single color mode, the plurality of image carriers are arranged so as to contact the intermediate transfer member for a predetermined time. The discharged toner on the intermediate transfer member discharged from the charging member of the cleaning device with the start of the rotation drive passes through the primary transfer region between the intermediate transfer member and the image carrier a plurality of times. Therefore, the discharged toner on the intermediate transfer member can be effectively collected by the image carrier in a plurality of primary transfer areas, and the discharged toner can be prevented from adhering to a recording sheet such as paper in the secondary transfer area.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings. In the following description, terms indicating a specific direction (for example, “up”, “down”, “left”, “right”, and other terms including them, “clockwise direction”, “counterclockwise” ”) Is used to facilitate understanding of the invention with reference to the drawings, and the present invention should not be construed as being limited by the meaning of these terms. Further, in the image forming apparatus and the developing apparatus described below, the same reference numerals are used for the same or similar components.

[1. Image forming apparatus]
FIG. 1 shows a schematic configuration of an image forming apparatus 2 according to an embodiment of the present invention. The image forming apparatus 2 is an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multi-function machine having a combination of these functions. Currently, various types of electrophotographic image forming apparatuses have been proposed. The illustrated image forming apparatus is a so-called tandem color image forming apparatus.

  The image forming apparatus 2 includes an image reading unit 20 for reading a document image and a printing unit 22 for printing the read image.

  The image reading unit 20 separates and reads the original image into three colors of red (R), green (G), and blue (B) by a known mechanism, and also reads red (R), green (G), and blue ( It is configured to create the image data of B). In the figure, reference numeral 24 denotes a display unit for displaying various information relating to printing, and reference numeral 25 denotes a panel operation unit for performing a print start operation and various setting operations relating to printing. .

The print unit 22 includes an endless intermediate transfer belt 30 (corresponding to an intermediate transfer member in claims). A material having an electrical resistance of 1 × 10 ⁶ Ω / □ or more and 1 × 10 ¹³ Ω / □ or less is preferably used for the intermediate transfer belt 30. Specific examples of materials used for the belt 30 include, for example, , Polycarbonate, polyphenylene sulfide and the like. Further, as the intermediate transfer belt 30, a belt having a thickness of, for example, 50 μm or more and 150 μm or less is preferably used.

  The intermediate transfer belt 30 is wound around a plurality of rollers 32, 33 and 34. A roller 32 on the right side of the drawing is a drive roller that is drivingly connected to a motor (not shown), and the driving roller 32 connected to the motor rotates based on the driving of the motor to rotate the belt 30 and another roller 33 in contact with the belt 30. , 34 rotate counterclockwise in the figure.

  As the driving roller 32, one having an outer diameter of, for example, 12 mm or more and 30 mm or less is preferably used, whereby the size of the apparatus can be reduced. At least the surface of the driving roller 32 is made of a material having a large friction coefficient such as rubber or urethane, whereby the frictional force with the intermediate transfer belt 30 is increased, and the driving force is transmitted to the intermediate transfer belt 30 satisfactorily. it can.

  In addition, the intermediate transfer belt 30 is given a predetermined tension by a plurality of rollers 32, 33, and 34 in order to ensure a sufficient frictional force between the driving roller 32 and the intermediate transfer belt 30. The magnitude of tension applied to the intermediate transfer belt 30 is preferably 15N or more and 50N or less, for example.

  A secondary transfer roller 40 (corresponding to a secondary transfer member in claims) that presses the recording sheet 36 together with the belt 30 outside the belt portion supported by the drive roller 32 disposed on the right side in the drawing. Is provided. The secondary transfer roller 40 is arranged to be switchable between a position in contact with the outer peripheral surface of the belt 30 and a position separated from the outer peripheral surface of the belt 30. In a state where the secondary transfer roller 40 is in contact with the outer peripheral surface of the belt 30, the contact portion (nip portion) forms a secondary transfer region 41. As the secondary transfer roller 40, for example, an ion conductive roller is used, but an electronic conductive roller can also be used. The secondary transfer roller 40 is connected to a power source 68 as a secondary transfer bias applying device. When the power supply 68 is turned on, the secondary transfer roller 40 is applied with a polarity opposite to the normal charging polarity, specifically, for example, a positive secondary transfer bias.

  A cleaning device 64 for the intermediate transfer belt is provided outside the belt portion supported by the roller 34 arranged on the left side in the drawing. The configuration of the cleaning device 64 will be described later.

  Below the belt portion moving from the roller 34 on the left side to the roller 32 on the right side in the drawing, yellow (Y), magenta (M), cyan (C), black ( Four image forming units 3 (3Y, 3M, 3C, and 3K) that respectively create toner images of corresponding colors using the developer K) are arranged along the intermediate transfer belt 30.

  Each image forming unit 3 includes a cylindrical photosensitive member 4 as an electrostatic latent image carrier. Around the photoconductor 4, the charger 8, the exposure device 10, the developing device 18, and the primary transfer roller (corresponding to the primary transfer member in the claims) in that order along the rotation direction (clockwise direction in the drawing). 14 and a photosensitive member cleaning member 16 are disposed.

  The primary transfer roller 14 is disposed inside the endless intermediate transfer belt 30. The primary transfer roller 14 can be switched between a state where it is pressed against the photoconductor 4 via the intermediate transfer belt 30 and a state where it is separated from the photoconductor 4 by switching the arrangement of the photoconductor 4. In a state where the primary transfer roller 14 is pressed against the photoconductor 4 via the belt 30, a primary transfer region 15 is formed at the nip portion between the belt 30 and the photoconductor 4. The arrangement of the photoconductors 4 is switched when the four photoconductors 4 individually move up and down. Specifically, the vertical movement of each photoconductor 4 is performed by driving a cam mechanism (not shown) by a motor (not shown) and moving the image forming process unit including the photoconductor 4 up and down by the operation of the cam mechanism. The configuration for switching between the pressure contact state and the separation state of the photosensitive member 4 and the belt 30 is not limited to the above configuration. For example, the photosensitive member 4 is fixed at a position separated from the belt 30 and the primary transfer roller 14 is moved up and down. Thus, the belt 30 may be switched between a state in which the belt 30 is pressed against the photoconductor 4 and a state in which the belt 30 is separated from the photoconductor 4. As shown in FIG. 2, the primary transfer roller 14 is connected to a power source 64 as a primary transfer bias applying device. When the power supply 64 is turned on, a polarity opposite to the normal charging polarity of the toner (corresponding to the first polarity in the claims), specifically, for example, a positive primary transfer bias is applied to the primary transfer roller 14. The

  Returning to FIG. 1, a control unit 70 is provided above the print unit 22 to control various operations related to printing.

  The control unit 70 displays an image in which a monochrome mode (corresponding to the single-color mode in the claims) for forming an image composed of only a black toner image and four color toner images of yellow, magenta, cyan, and black are superimposed. Switching control between the full color mode to be formed (corresponding to the multi-color mode in claims) is performed.

  In the present invention, the configuration for switching the image forming mode by the control unit 70 is a single color mode for forming an image composed of only one color toner image and a multi-color for forming an image formed by superimposing a plurality of color toner images. If it is the structure switched between color modes, it will not be restricted to said structure. That is, in the present invention, the single color mode may be configured to form an image with a toner image of one color other than black, and the multicolor mode may be configured with a toner image of any two or three colors of the four colors. It is good also as a structure which forms an image.

  A paper feed cassette 44 as a paper feed device is detachably disposed below the print unit 22. The recording sheets 36 such as sheets stacked and accommodated in the sheet feeding cassette 44 are sent out one by one from the uppermost one to the conveying path 50 by the rotation of the sheet feeding roller 52 disposed in the vicinity of the sheet feeding cassette 44.

  A registration roller 54 for sending the recording sheet 36 to the secondary transfer area 41 at a predetermined timing is provided in the vicinity of the paper feed roller 52. A detection sensor 55 for detecting the leading edge of the recording sheet 36 is provided in the vicinity of the registration roller 54.

  The conveyance path 50 passes from the paper feed cassette 44 through the nip portion of the registration roller pair 54, the secondary transfer region 41, the nip portion of the fixing roller pair 56, and the nip portion of the paper discharge roller pair 60 to the print unit 22. It extends to the paper discharge unit 61 provided at the top.

  An example of the image forming operation in the full color mode will be described.

  First, red (R), green (G), and blue (B) image data obtained in the image reading unit 20 is subjected to predetermined data processing in the control unit 70, and yellow (Y) and magenta (M). , Cyan (C), and black (K) image data.

  The yellow, magenta, cyan, and black image data are stored in the image memory 72 in the control unit 70, and after a predetermined image correction for correcting the misalignment, a light source (not shown) provided in the exposure apparatus 10 is used. It is converted into a drive signal for causing light emission.

  In the print unit 22, first, in each image forming unit 3, the outer peripheral surface of the photosensitive member 4 that is rotationally driven at a predetermined peripheral speed is charged by the charger 8. Next, light is projected from the exposure apparatus 10 that has received the drive signal output from the control unit 70 onto the outer peripheral surface of the charged photoconductor 4 to form an electrostatic latent image. Subsequently, the electrostatic latent image is made visible by the developer toner supplied from the developing device 18. When the toner image of each color formed on the photoconductor 4 in this way reaches the primary transfer region by the rotation of the photoconductor 4, yellow, magenta, cyan, and black are sequentially transferred from the photoconductor 4 to the intermediate transfer belt 30. Transferred (primary transfer) and overlaid.

  Untransferred toner remaining on the photosensitive member 4 without being transferred to the intermediate transfer belt 30 reaches the contact portion between the photosensitive member 4 and the cleaning member 16 and is scraped off by the cleaning member 16. It is removed from the outer peripheral surface.

  The superimposed four color toner images are conveyed to the secondary transfer region 41 by the intermediate transfer belt 30.

  On the other hand, the recording sheet 36 accommodated in the paper feed cassette 44 is sent out to the transport path 50 by the rotation of the paper feed roller 52 and is transported to the nip portion of the registration roller pair 54. The recording sheet 36 conveyed to the nip portion of the registration roller pair 54 is conveyed to the secondary transfer area 41 in accordance with the timing at which the toner image is conveyed to the secondary transfer area 41 by the intermediate transfer belt 30.

  When the recording sheet 36 is conveyed to the secondary transfer area 41, the toner image is transferred (secondary transfer) from the intermediate transfer belt 30 to the recording sheet 36. After the secondary transfer, the recording sheet 36 is conveyed to the nip portion of the fixing roller pair 56 further downstream of the secondary transfer area 41, and after the toner image is fixed by the fixing roller 56, the recording sheet 36 is discharged by the paper discharge roller 60. It is sent out to the paper section 61.

  Untransferred toner remaining on the outer peripheral surface of the intermediate transfer belt 30 without being transferred to the recording sheet 36 in the secondary transfer region 41 is removed from the intermediate transfer belt 30 by the cleaning device 64.

[2. Cleaning device]
Next, the configuration of the cleaning device 64 will be described. Here, a case where the normal charging polarity of the toner is negative will be described.

  As shown in FIG. 3, the cleaning device 64 causes the toner remaining on the outer peripheral surface of the intermediate transfer belt 30 after passing through the secondary transfer region 41 to have a normal charging polarity, that is, negative polarity (corresponding to the second polarity in the claims). A charging brush (corresponding to the charging member in claims) 74 and a cleaning brush (to claim) that scrapes the toner negatively charged by the charging brush 74 from the outer peripheral surface of the intermediate transfer belt 30. 42, a collecting roller 77 that collects the toner scraped off by the cleaning brush 42, and a scraper 78 that scrapes off the toner collected by the collecting roller 77. These members 74, 42, 77, 78 constituting the cleaning device 64 are accommodated in a housing (not shown).

  The charging brush 74 has a charging region 80 in the belt 30 portion downstream of the secondary transfer region 41 in the rotational direction of the intermediate transfer belt 30, specifically, the belt 30 portion stretched between the rollers 33 and 34. It is provided so as to face each other.

The charging brush 74 has, for example, a plate-like base portion 75 and a fiber portion 76 made of a plurality of brush fibers fixed to the base portion 75. The base 75 is made of a conductive material, and for example, a metal is used as a specific material of the base 75. The tip of the brush fiber of the charging brush 74 is disposed in contact with the outer peripheral surface of the belt 30. For the brush fibers of the charging brush 74, a conductive material is used, and a material having an electric resistance of 1 × 10 ¹³ Ω or less is preferably used. Specific materials for the brush fibers of the charging brush 74 include, for example, nylon resin, polyester resin, polyimide resin, and the like, but are not limited thereto.

  The cleaning brush 42 cleans the belt 30 portion downstream of the charging region 80 and upstream of the primary transfer region 15 in the rotational direction of the belt 30, specifically, the belt 30 portion wound around the roller 34. They are provided facing each other across the region 62.

The cleaning brush 42 is disposed on the downstream side of the charging brush 74 in the rotation direction of the belt 30. The cleaning brush 42 is a rotating brush that rotates so that the surface portions of the contact portion between the brush 42 and the belt 30 move in opposite directions. That is, the cleaning brush 42 can rotate with respect to the belt 30 in a so-called counter direction (counterclockwise direction in the drawing). A contact portion between the cleaning brush 42 and the belt 30 forms a cleaning region 62 for collecting untransferred toner on the belt 30. The cleaning brush 42 includes a cylindrical or columnar base portion 44 and a fiber portion 46 made of a plurality of brush fibers extending radially outward from the outer peripheral surface of the base portion 44. As a material of the base 44, for example, a metal such as iron, aluminum, stainless steel or the like is used. For the brush fibers of the cleaning brush 42, a conductive material is used, and a material having an electric resistance of 1 × 10 ¹³ Ω or less is preferably used. Specific materials for the brush fibers of the brush 42 include, for example, nylon resin, polyester resin, polyimide resin, but are not limited thereto.

  The collection roller 77 is disposed in contact with the cleaning brush 42. The collection roller 77 is rotatable so that the surface portions of the collection roller 77 move in the same direction at the contact portion between the roller 77 and the brush 42. That is, the collection roller 77 is rotatable in a so-called with direction (clockwise direction in the drawing) with respect to the brush 42. As the collection roller 77, a conductive material is used. Specifically, for example, a metal such as iron, aluminum, or stainless steel is used.

  The scraper 78 is a strip-shaped member that extends in a direction parallel to the axial direction of the collection roller 77, and is disposed so that one end in the short direction of the scraper 78 contacts the surface of the collection roller 77. The material of the scraper 78 is not particularly limited, but for example, a metal such as stainless steel is used.

  The charging brush 74 is grounded, and a power source 84 is connected to the collection roller 77 via a control circuit 82. In the embodiment, the current flowing from the power source 84 is subjected to constant current control by the control circuit 82. The magnitude of the constant current flowing from the power source 84 is controlled to 5 μA to 40 μA, for example.

  When the power supply 84 is turned on, a constant current having the same polarity as the secondary transfer bias, that is, a positive polarity, flows from the power supply 84 to the cleaning brush 42 via the recovery roller 77, and further from the cleaning brush 42 to the surface of the intermediate transfer belt 30. And flows to the charging brush 74. When such a constant current flows, an electric field for moving the negative toner on the belt 30 to the cleaning brush 42 is formed between the cleaning brush 42 and the belt 30, and between the charging brush 74 and the belt 30. In addition, an electric field is formed in which the positive polarity toner on the belt 30 is neutralized to make most of the toner have a negative polarity.

  The configuration for forming the electric field between the cleaning brush 42 and the belt 30 and between the charging brush 74 and the belt 30 is not limited to the above configuration. For example, when the scraper 78 is made of a conductive material, the power source 84 may be connected to the scraper 78. Control of the current flowing from the power supply 84 is not limited to constant current control, and constant voltage control may be performed. Further, a power source different from the power source 84 may be connected to the charging brush 74, and a negative bias may be applied to the charging brush 74 by this power source.

  A specific example of the operation of removing the untransferred toner from the outer peripheral surface of the intermediate transfer belt 30 using the cleaning device 64 configured as described above will be described.

  During a series of operations of development, primary transfer, and secondary transfer, untransferred toner that is not transferred from the belt 30 to the recording sheet 36 in the secondary transfer region 41 and remains on the belt 30 is caused by the rotation of the belt 30. It is conveyed downstream from the secondary transfer area 41. Here, the normal charging polarity of the toner is negative, but the untransferred toner that has not been electrostatically transferred from the belt 30 to the recording sheet 36 is composed of particles having a small charge amount or positive electrodes as shown in FIG. The non-transferred toner contains various electrically charged particles and has various charges for each particle.

  When the untransferred toner on the belt 30 is conveyed to the contact portion with the charging brush 74 by the rotation of the belt 30, the non-transferred toner is transferred by the charging brush 74 in which the constant current supplied from the power source 84 flows as described above. Most of the particles are negatively charged and are conveyed further downstream in the moving direction of the belt 30.

  At the contact portion between the belt 30 and the charging brush 74, most of the untransferred toner particles have a negative polarity, but there are toner particles having a small charge amount and toner particles having a positive charge. Most of the positively charged toner particles are electrostatically adsorbed to the brush fibers of the charging brush 74, and some of the toner particles having a small charge amount are mechanically entangled with the brush fibers of the charging brush 74. It is done. Thus, the toner adsorbed on the charging brush 74 or mechanically entangled is accumulated inside the charging brush 74.

  The non-transferred toner charged to the negative polarity by the charging brush 74 and conveyed to the contact portion between the belt 30 and the cleaning brush 42 by the rotation of the belt 30 is a brush in which the constant current supplied from the power source 84 flows as described above. 42 is electrostatically attracted to the brush fibers 42, and is thereby collected by the brush 42 and removed from the outer peripheral surface of the belt 30.

  When the toner collected by the cleaning brush 42 is conveyed to the contact portion between the brush 42 and the collection roller 77 by the rotation of the brush 42, the toner is electrostatically attracted to the surface of the collection roller 77 having a higher potential than the brush 42. As a result, it is recovered by the recovery roller 77.

  When the toner collected by the collecting roller 77 is conveyed to the contact portion between the roller 77 and the scraper 78 by the rotation of the roller 77, it is mechanically scraped off by the scraper 78.

  When the untransferred toner is removed using the cleaning device 64 by the above operation, the toner is accumulated inside the charging brush 78 as described above. When the next image forming operation is started in a state where a large amount of toner is accumulated in the charging brush 74, the tip of the brush fiber of the charging brush 74 is attached to the belt 30 as the intermediate transfer belt 30 starts to rotate. When pulled in the moving direction, the charging brush 74 vibrates, and as a result, toner is discharged from the inside of the charging brush 74 to the surface of the belt 30. The toner accumulated in the charging brush 74 has a small charge amount or a large number of particles that are positively charged. Therefore, when the toner (discharge toner) discharged from the inside of the charging brush 74 to the surface of the belt 30 is conveyed to the contact portion between the belt 30 and the cleaning brush 42 by the rotation of the belt 30, the brush fibers of the brush 42 are discharged. Since it is not electrostatically attracted to the belt 30, it is difficult to remove from the outer peripheral surface of the belt 30. Therefore, most of the discharged toner remains on the outer peripheral surface of the belt 30 even after passing through the cleaning region 62.

  The discharged toner remaining on the belt 30 after passing through the cleaning region 62 is collected by the photoreceptor 4 disposed in contact with the belt 30.

  When printing in the full color mode, as shown in FIG. 7, since the four photosensitive members 4 are arranged in contact with the belt 30, the discharged toner is transferred to the secondary transfer area 41 before being transferred to the secondary transfer area 41. Pass 15 through 4 times. In each primary transfer region 15, an electric field that moves toner charged to a negative polarity (regular charging polarity) from the photoreceptor 4 to the belt 30 is formed. Therefore, a part of the discharged toner containing many particles charged to positive polarity (polarity opposite to the normal charging polarity) moves from the belt 30 to the photoreceptor 4 in each primary transfer region 15. In this way, in each of the four primary transfer regions 15, a part of the discharged toner is collected by the photoconductor 4, and thus most of the discharged toner is collected by the four photoconductors 4.

  On the other hand, assuming that the discharge toner collecting operation described later is not performed when printing in the monochrome mode, as shown in FIG. 8, only the black photosensitive member 4K is placed in contact with the belt 30, and yellow, magenta, The cyan photoconductors 4Y, 4M, and 4C are separated from the belt 30. Therefore, a part of the discharged toner is collected by the photoconductor 4K, but most of the discharged toner is conveyed to the secondary transfer area 41 while remaining on the belt 30, and the recording sheet 36 is transferred to the secondary transfer area 41. Alternatively, it may transfer to the secondary transfer roller 40 and cause the recording sheet 36 to become dirty.

[3. Discharge toner recovery operation]
In order to prevent such a problem, in the present invention, when the rotation of the intermediate transfer belt 30 is started during the image forming operation in the monochrome mode under the control of the control unit 70, a plurality of toners are discharged on the intermediate transfer belt 30. The discharged toner collecting operation (corresponding to the toner collecting operation in claims) collected by the photoconductor 4 is performed.

  Specifically, the discharged toner collecting operation is an operation in which the plurality of photosensitive members 4 are brought into contact with the outer peripheral surface of the intermediate transfer belt 30 for a predetermined time. In the embodiment, the contact between the intermediate transfer belt 30 and the photosensitive member 4 is intermediate. This is started after the rotation driving of the transfer belt 30 is started and before the image formation on the photosensitive member 4K is started. However, in the present invention, the contact between the intermediate transfer belt 30 and the photosensitive member 4 may be started before the rotation of the intermediate transfer belt 30 is started or simultaneously with the start of the rotation of the intermediate transfer belt 30.

  In the embodiment, during the discharging toner collecting operation, as shown in FIG. 2, the black photosensitive member 4K and the yellow photosensitive member 4Y are controlled to contact the outer peripheral surface of the intermediate transfer belt 30 for a predetermined time. When the photoreceptors 4Y and 4K are in contact with the belt 30, while the contact state is maintained, a primary transfer bias having a polarity opposite to the normal charging polarity of the toner, that is, a positive primary transfer bias is applied to the primary transfer rollers 14Y and 14K. Is done. As a result, an electric field is formed in the primary transfer areas 15Y and 15K to move the discharged toner charged to the positive polarity from the belt 30 to the photoreceptors 4Y and 4K. The magnitude of the primary transfer bias at the time of discharging toner collecting operation is set to the same magnitude as the primary transfer bias at the time of development, for example, but may be set to a magnitude different from that at the time of development. Specifically, the primary transfer bias during the discharge toner collecting operation is set to 100 V to 3000 V, for example. The movement of the discharged toner from the belt 30 to the photosensitive member 4 can be realized even if the photosensitive member 4 is not charged as long as the primary transfer bias is applied. However, in order to positively collect the discharged toner. In addition, the discharged toner may be collected while the photosensitive member 4 is charged as in the image formation. In this case, since the reversal image is used in this embodiment, the charging polarity of the photoconductor 4 becomes negative, and it becomes easy to collect the discharged toner charged to positive polarity.

  By configuring the discharge toner collecting operation in this way, when the discharge toner on the belt 30 is conveyed to the primary transfer region 15Y by the rotation of the belt 30, the discharge is generated by the above-described electric field formed in the primary transfer region 15Y. Part of the toner moves from the belt 30 to the photoreceptor 4Y. When the discharged toner remaining on the belt 30 after passing through the primary transfer area 15Y is conveyed to the primary transfer area 15K by the rotation of the belt 30, most of the remaining discharged toner is transferred to the primary transfer area 15K as described above. The belt 30 moves from the belt 30 to the photosensitive member 4K by the electric field formed.

  As described above, when printing in the monochrome mode, as in the case of printing in the full color mode, most of the discharged toner on the belt 30 is collected by the plurality of photosensitive members 4, so that the recording sheet 36 is stained by the discharged toner. Can be prevented.

  Next, a specific example of the flow of each process performed after a print instruction is given and the rotation driving of the intermediate transfer belt 30 is started will be described with reference to the flowchart shown in FIG.

  As shown in FIG. 4, when the rotational driving of the intermediate transfer belt 30 is started, it is first determined in step 1 whether or not the image forming mode is a monochrome mode. If it is determined in step 1 that the mode is the monochrome mode, the process proceeds to step 2, and if it is determined that the mode is the full color mode, the process is terminated, and the image formation of the image instructed to be printed is started.

  In step 2, the yellow photoconductor 4Y and the black photoconductor 4K are pressed against the belt 30 at a predetermined timing after the rotation driving of the belt 30 is started, and the process proceeds to step 3. The pressure contact between the yellow photoconductor 4Y and the black photoconductor 4K to the belt 30 is performed before the discharged toner discharged from the charging brush 74 onto the belt 30 as the belt 30 starts to rotate passes through the primary transfer region *. These timings may be performed at the same time or at different timings. When the photoreceptors 4Y and 4K are pressed against the belt 30, they are rotationally driven in the clockwise direction in the drawing.

  In Step 3, a primary transfer bias having a polarity opposite to the normal charging polarity of the toner, that is, a positive primary transfer bias is applied to the primary transfer rollers 14Y and 14K. As a result, an electric field is formed in the primary transfer regions 15Y and 15K in which the discharged toner charged to the positive polarity moves from the belt 30 to the photosensitive members 4Y and 4K. Therefore, the electric field is formed on most of the discharged toner. By passing through the two primary transfer areas 15Y and 15K, they are recovered by the photoreceptors 4Y and 4K.

  In the next step 4, image formation on the black photosensitive member 4K is started, and the process proceeds to step 5. Note that the process of step 4 may be performed after the process of step 5 described below.

  In step 5, the yellow photoconductor 4Y is separated from the belt 30, and the process ends. The contact state between the photoconductor 4Y and the belt 30 is maintained for a predetermined time until the photoconductor 4Y is separated from the belt 30. The contact time between the photosensitive member 4Y and the belt 30 is set to a time required for the discharged toner to completely pass through the primary transfer region 15 after the photosensitive member 4Y is pressed against the belt 30, and specifically, for example, 1 Set to seconds to 5 seconds. When the yellow photoconductor 4Y is separated from the belt 30, the black photoconductor 4K is maintained in contact with the belt 30.

  When the above processing is completed, image formation is continued with the black photoconductor 4K, and the image instructed to print is printed on the recording sheet 36 by a series of image forming operations such as development, primary transfer, secondary transfer, and fixing. The Since black image formation is started immediately after the yellow and black photoreceptors 4Y and 4K are pressed against the belt 30, the time from when the print command is issued until the first print is completed increases. In this case, the discharged toner can be collected. In collecting the discharged toner, the photosensitive member 4 pressed against the belt 30 together with the black photosensitive member 4K is not limited to the yellow photosensitive member 4Y, but the yellow photosensitive member 4Y is farthest from the black photosensitive member 4K. With the above-described configuration in which the yellow photoconductor 4Y is pressed against the belt 30, the influence of the separation of the other photoconductors 4M and 4C is least likely to occur during black image formation.

  FIG. 5 shows another embodiment of the present invention. In the embodiment shown in FIG. 5, the amount of discharged toner that detects the amount of discharged toner in the vicinity of the belt 30 portion downstream of the cleaning brush 42 and upstream of the primary transfer region 15 </ b> Y in the rotation direction of the belt 30. A sensor (corresponding to the discharged toner amount detecting means in claims) 90 is arranged. As the discharged toner amount sensor 90, for example, a reflection type sensor, a displacement sensor, a surface potential sensor, or the like is used.

  The arrangement of the discharged toner amount sensor 90 is not limited to the above-described configuration, and may be in the vicinity of the belt 30 portion on the downstream side of the charging brush 74 and the upstream side of the primary transfer region 15Y in the rotation direction of the belt 30.

  With respect to the discharge toner collecting operation according to the embodiment shown in FIG. 5, a specific example of the flow of each process performed after a print instruction is given and the rotation driving of the intermediate transfer belt 30 is started will be described with reference to the flowchart shown in FIG. 6. While explaining.

  As shown in FIG. 6, when the rotational driving of the intermediate transfer belt 30 is started, first, in step 11, it is determined whether or not the image forming mode is a monochrome mode. If it is determined in step 11 that the mode is the monochrome mode, the process proceeds to step 12, and if it is determined that the mode is the full color mode, the process is terminated, and the image formation of the image instructed to be printed is started.

  In step 12, it is determined whether or not the toner amount detected by the discharged toner amount sensor * is equal to or greater than a predetermined amount. If it is determined in step 12 that the toner amount is equal to or greater than the predetermined amount, the process proceeds to step 13, and if it is determined that the toner amount is less than the predetermined amount, the process is terminated and the image for which printing is instructed Is started.

  In step 13, the yellow photosensitive member 4 </ b> Y and the black photosensitive member 4 </ b> K are pressed against the belt 30 at a predetermined timing after the rotation driving of the belt 30 is started, and the process proceeds to step 14. The pressure contact between the yellow photoconductor 4Y and the black photoconductor 4K to the belt 30 is performed before the discharged toner discharged from the charging brush 74 onto the belt 30 as the belt 30 starts to rotate passes through the primary transfer region *. These timings may be performed at the same time or at different timings. When the photoreceptors 4Y and 4K are pressed against the belt 30, they are rotationally driven in the clockwise direction in the drawing.

  In step 14, a primary transfer bias having a polarity opposite to the normal charging polarity of the toner, that is, a positive primary transfer bias is applied to the primary transfer rollers 14Y and 14K. As a result, an electric field is formed in the primary transfer areas 15Y and 15K in which the discharged toner charged to the positive polarity moves from the belt 30 to the photoreceptors 4Y and 4K. By passing through the primary transfer areas 15Y and 15K, most of them are recovered to the photoreceptors 4Y and 4K.

  In the next step 15, image formation on the black photoconductor 4 </ b> K is started, and the process proceeds to step 16. The process of step 15 may be performed after the process of step 16 described below.

  In step 16, the yellow photoconductor 4Y is separated from the belt 30, and the process ends. The contact state between the photoconductor 4Y and the belt 30 is maintained for a predetermined time until the photoconductor 4Y is separated from the belt 30. The contact time between the photoreceptor 4Y and the belt 30 is set in the same manner as in the above embodiment. When the yellow photoconductor 4Y is separated from the belt 30, the black photoconductor 4K is maintained in contact with the belt 30.

  When the above processing is completed, image formation is continued with the black photoconductor 4K, and the image instructed to print is printed on the recording sheet 36 by a series of image forming operations such as development, primary transfer, secondary transfer, and fixing. The

  While the present invention has been described with reference to the above-described embodiments, the present invention is not limited to the above-described embodiments.

  For example, in the above-described embodiment, the configuration in which the black photoconductor 4K and the yellow photoconductor 4Y are brought into contact with the belt 30 during the discharge toner collecting operation has been described. If it is the structure which contacts, it will not be limited to the above-mentioned embodiment. However, it is preferable to contact the belt 30 with the photoreceptor 4 corresponding to the color to be imaged (black in the above embodiment) and one or more other photoreceptors 4.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to the present invention. FIG. 4 is a diagram illustrating an intermediate transfer belt and members around the intermediate transfer belt. It is an enlarged view which shows the principal part of FIG. 7 is a flowchart showing a flow of processing of discharged toner collection operation. It is a figure which shows the member of the intermediate transfer belt which concerns on other embodiment, and its peripheral part. 6 is a flowchart showing a process flow of a discharge toner collecting operation according to the embodiment shown in FIG. 5. FIG. 4 is a diagram illustrating a state around an intermediate transfer belt when printing in a full color mode. FIG. 4 is a diagram illustrating a state around an intermediate transfer belt when printing in a monochrome mode. It is a figure which shows the prior art example of the cleaning apparatus for intermediate transfer belts.

Explanation of symbols

2: image forming apparatus, 4: photoconductor, 14: primary transfer roller, 15: primary transfer area, 30: intermediate transfer belt, 36: recording sheet, 40: secondary transfer roller, 41: secondary transfer area, 42: Cleaning brush, 62: cleaning area, 64: power supply, 68: power supply, 70: control unit, 74: charging brush, 80: charging area, 82: control circuit, 84: power supply, 90: discharge toner amount sensor.

Claims (5)

A plurality of image carriers that carry toner images of predetermined colors different from each other;
A rotatable intermediate transfer member that faces the plurality of image carriers with a primary transfer region interposed therebetween, and in which the toner image is transferred from the image carrier in the primary transfer region;
The image formation mode is switched between a single color mode for forming an image composed of only one color toner image and a multi-color mode for forming an image formed by superimposing a plurality of color toner images. When the rotation of the intermediate transfer member is started during operation, the plurality of image carriers are brought into contact with the intermediate transfer member for a predetermined time, and the toner recovery is performed such that the toner on the intermediate transfer member is recovered by the plurality of image carriers. An image forming apparatus comprising: a control unit that controls to perform an operation. A plurality of primary transfer members provided corresponding to each image carrier so as to sandwich the intermediate transfer member together with the image carrier;
A primary transfer bias applying device that applies a primary transfer bias of a first polarity to the primary transfer member;
A secondary transfer member provided opposite to the intermediate transfer member portion downstream of the primary transfer region in the rotational direction of the intermediate transfer member with the secondary transfer region interposed therebetween;
In the rotation direction, the intermediate transfer member portion downstream of the secondary transfer region is provided opposite to the charging region, and the toner remaining on the intermediate transfer member after passing through the secondary transfer region is A charging member for charging to a second polarity different from the first polarity;
The intermediate transfer member is provided downstream of the charging area and upstream of the primary transfer area in the rotation direction, with the cleaning area sandwiched therebetween, and is charged to the second polarity in the charging area. A cleaning member that removes the toner from the surface of the intermediate transfer member,
2. The image forming apparatus according to claim 1, wherein the controller applies the primary transfer bias of the first polarity to the primary transfer member by the primary transfer bias applying device during the toner collecting operation. . A discharge toner amount detecting means for detecting the amount of toner discharged from the charging member to the intermediate transfer body as the intermediate transfer member starts to rotate;
3. The image according to claim 1, wherein the control unit performs the toner collecting operation when the toner amount detected by the discharged toner amount detection unit is equal to or greater than a predetermined amount. 4. Forming equipment. Using an image forming apparatus comprising a plurality of image carriers that carry toner images of predetermined colors different from each other, and a rotatable intermediate transfer member that faces the plurality of image carriers across a primary transfer region. An image forming method in which an image is formed by switching between a single color mode for forming an image composed of only one color toner image and a multi-color mode for forming an image formed by superimposing a plurality of color toner images. ,
When starting rotation of the intermediate transfer member during image formation in the monochrome mode, a toner recovery operation is performed to recover the toner on the intermediate transfer member with a plurality of the image carriers,
The toner collecting operation is
Bringing two or more image carriers into contact with the intermediate transfer member for a predetermined time;
The toner on the intermediate transfer member is electrostatically transferred from the intermediate transfer member to the image carrier in a plurality of primary transfer regions formed between the two or more image carriers and the intermediate transfer member. Forming an electric field to be moved;
And a step of separating an image carrier other than the image carrier on which image formation is performed, of the two or more image carriers, from the intermediate transfer member. Detecting the amount of toner discharged from the member in contact with the intermediate transfer member to the intermediate transfer member as the intermediate transfer member starts to rotate;
The image forming method according to claim 4, wherein the toner collecting operation is performed when the detected toner amount is a predetermined amount or more.

Images