JP2018072749A - Image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation apparatus which has the high conveyance performance of a recording medium delivered from a transfer unit without increase in the cost and size of the apparatus, and which suppresses cleaning failure due to a blade contacting a conveyor belt.SOLUTION: An image formation apparatus includes: an intermediate transfer belt 8 (image carrier); a secondary transfer belt 72 (conveyor belt); a secondary transfer blade 73 (blade); a power source unit 91 which outputs a secondary transfer bias (transfer bias) with a prescribed polarity; and a control unit 90 which controls the power source unit 91 so as to output a bias with a reverse polarity to the prescribed polarity and different from the secondary transfer bias. The image formation apparatus supplies toner adhering to the intermediate transfer belt 8 to the secondary transfer belt 72 by performing control by the control unit 90 so as to output a non-image part bias (different bias) from the power source unit 91 at a prescribed timing when a recording medium P is not interposed in a secondary transfer nip (transfer unit).SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine thereof.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, a transfer unit is formed by bringing a conveyance belt such as a secondary transfer belt into contact with an image carrier such as an intermediate transfer belt (for example, (See Patent Document 1).

Specifically, in the image forming apparatus in Patent Document 1, toner images respectively formed on a plurality of photosensitive drums are primarily transferred onto the surface of an intermediate transfer belt (image carrier). The toner image carried on the intermediate transfer belt is secondarily transferred to a recording medium conveyed to the position of the secondary transfer nip (transfer portion). Then, the recording medium on which the toner image is secondarily transferred is conveyed by a secondary transfer belt (conveyance belt), separated from the secondary transfer belt at the position of the separation roller, and then conveyed toward the fixing device. It will be.
Here, the secondary transfer nip includes a secondary transfer belt and an intermediate transfer belt between a secondary transfer roller that stretches the secondary transfer belt and a secondary transfer counter roller that stretches the intermediate transfer belt. Is formed by being sandwiched. In addition, a secondary transfer blade (blade) is installed so as to contact the secondary transfer roller via the secondary transfer belt, and toner, paper powder, etc. adhered to the secondary transfer belt by the secondary transfer blade. Foreign matter is removed.

  On the other hand, in Patent Document 1, a lubricant is applied to the surface of the secondary transfer belt for the purpose of maintaining good cleaning performance of the secondary transfer blade (cleaning blade) in contact with the secondary transfer belt over time. A technique for installing a lubricant application device is disclosed.

Since the above-described conventional image forming apparatus forms the secondary transfer nip using the secondary transfer belt, the secondary transfer nip is formed using the secondary transfer roller (for example, Japanese Patent No. 45524164). The effect of improving the transportability of the recording medium fed from the secondary transfer nip can be greatly expected.
However, when cleaning is performed by bringing the secondary transfer blade into contact with the secondary transfer belt, cleaning defects are more likely to occur than when cleaning is performed by bringing the secondary transfer blade into contact with the secondary transfer roller. It was. In addition, such a defective cleaning causes a problem (referred to as “back stain”) in which the back surface of the recording medium conveyed to the secondary transfer nip becomes dirty.
In order to prevent such a problem, as disclosed in Japanese Patent Application Laid-Open No. H10-228707, a measure of installing a lubricant application device that applies a lubricant to the surface of the secondary transfer belt can be considered. However, in that case, the apparatus becomes expensive and large.
In addition, such a problem is not limited to an intermediate transfer type image forming apparatus using an intermediate transfer belt as an image carrier and a secondary transfer belt as a conveyance belt, but using a photosensitive drum as an image carrier. This can also occur in a direct transfer type image forming apparatus using a transfer conveyance belt as the conveyance belt.

  The present invention has been made to solve the above-described problems. The apparatus does not increase the cost and the size of the apparatus, and the transportability of the recording medium sent from the transfer unit is high. An object of the present invention is to provide an image forming apparatus in which poor cleaning due to a blade that abuts is less likely to occur.

  The image forming apparatus according to the present invention includes an image carrier, a transfer belt in contact with the image carrier, a conveyance belt that conveys a recording medium fed from the transfer unit, and a surface of the conveyance belt. A blade that abuts, a power supply unit that outputs a transfer bias of a predetermined polarity to transfer a toner image carried on the image carrier to a recording medium by the transfer unit, and a polarity opposite to the predetermined polarity , A bias having the same polarity as the predetermined polarity and having a smaller absolute value than the transfer bias, and a bias having a magnitude of zero, and a bias different from the transfer bias is output. A control unit for controlling the power supply unit, and the control unit is configured to output the different bias from the power supply unit at a predetermined timing when no recording medium is interposed in the transfer unit. Controlled by parts, and supplies the toner attached to the image carrier on the conveyor belt.

  According to the present invention, an image forming apparatus in which the recording medium sent out from the transfer unit is highly transportable without causing an increase in cost and size, and a cleaning failure due to a blade contacting the transport belt is unlikely to occur. Can be provided.

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. It is a block diagram which expands and shows a part of image forming part. FIG. 2 is a schematic diagram illustrating an intermediate transfer belt and the vicinity thereof. 6 is a timing chart illustrating bias control of a power supply unit that outputs a secondary transfer bias. FIG. 6 is a schematic diagram illustrating a relationship between a toner image and a toner pattern image formed on a surface of an intermediate transfer belt and a secondary transfer blade. FIG. 6 is a schematic enlarged view showing a state in which the secondary transfer blade is wrinkled. FIG. 3 is a schematic view showing the vicinity of a secondary transfer nip. 6 is a graph showing a change in a charge amount distribution of toner attached to the surface of a secondary transfer belt when a non-image portion bias is varied. 6 is a graph showing the relationship between the amount of toner per unit length input to the secondary transfer blade, the amount of wobbling of the secondary transfer blade, and the presence or absence of cleaning failure. 10 is a timing chart showing bias control of a power supply unit that outputs a secondary transfer bias as a modification. FIG. 10 is a table showing changes in the amount of input toner necessary to prevent the secondary transfer blade from curling when the environment changes. 6 is a graph showing a change in a non-image portion bias necessary for preventing a cleaning failure of the secondary transfer blade when the wear amount of the secondary transfer blade is changed.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

First, the overall configuration and operation of the image forming apparatus 100 will be described with reference to FIGS.
FIG. 1 is a block diagram showing a printer as an image forming apparatus, and FIG. 2 is an enlarged view showing a part of the image forming unit.
As shown in FIG. 1, an intermediate transfer belt 8 as an image carrier is installed in the center of the image forming apparatus main body 100. Further, image forming units 6Y, 6M, 6C, and 6K corresponding to the respective colors (yellow, magenta, cyan, and black) are arranged in parallel so as to face the intermediate transfer belt 8 (intermediate transfer belt).

  Referring to FIG. 2, an image forming unit 6Y corresponding to yellow includes a photosensitive drum 1Y as a photosensitive member, a charging unit 4Y disposed around the photosensitive drum 1Y, a developing unit 5Y, a cleaning unit 2Y, It is composed of a lubricant supply device 3 as a photoconductor lubricant supply device, a static elimination unit, and the like. Then, an image forming process (charging process, exposure process, developing process, transfer process, cleaning process) is performed on the photosensitive drum 1Y, and a yellow image is formed on the photosensitive drum 1Y.

  The other three image forming units 6M, 6C, and 6K have substantially the same configuration as that of the image forming unit 6Y corresponding to yellow except that the color of the toner used is different. A corresponding image is formed. Hereinafter, description of the other three image forming units 6M, 6C, and 6K will be omitted as appropriate, and only the image forming unit 6Y corresponding to yellow will be described.

Referring to FIG. 2, photosensitive drum 1Y is driven to rotate counterclockwise by a motor. Then, the surface of the photosensitive drum 1Y is uniformly charged at the position of the charging unit 4Y (a charging process).
Thereafter, the surface of the photosensitive drum 1Y reaches the irradiation position of the laser beam L emitted from the exposure unit 7, and exposure in the main scanning direction at this position (in the direction perpendicular to the paper in FIGS. 1 and 2). An electrostatic latent image corresponding to yellow is formed by scanning (exposure process).

Thereafter, the surface of the photosensitive drum 1Y reaches a position facing the developing portion 5Y, and the electrostatic latent image is developed at this position to form a yellow toner image (developing process).
Thereafter, the surface of the photosensitive drum 1Y reaches the position facing the intermediate transfer belt 8 (belt member) as the image carrier and the primary transfer roller 9Y, and is formed on the surface of the photosensitive drum 1 at this position. The toner image is primarily transferred onto the surface of the intermediate transfer belt 8 (this is a primary transfer step). At this time, a small amount of untransferred toner remains on the photosensitive drum 1Y.

Thereafter, the surface of the photosensitive drum 1Y reaches a position facing the cleaning unit 2Y, and untransferred toner remaining on the photosensitive drum 1Y at this position is collected in the cleaning unit 2Y by the cleaning blade 2a (cleaning). Process.)
Here, inside the cleaning unit 2Y, a lubricant supply device 3 (a lubricant supply device for a photoconductor) including a lubricant supply roller 3a, a solid lubricant 3b, a compression spring 3c (biasing member), and the like is provided. Has been. Then, the lubricant supply roller 3a rotating in the clockwise direction in FIG. 2 scrapes the lubricant little by little from the solid lubricant 3b, and the lubricant is supplied to the surface of the photosensitive drum 1Y by the lubricant supply roller 3a. It will be.
Finally, the surface of the photosensitive drum 1Y reaches a position facing the neutralization unit, and the residual potential on the photosensitive drum 1 is removed at this position.
Thus, a series of image forming processes performed on the photosensitive drum 1Y is completed.

The image forming process described above is performed in the other image forming units 6M, 6C, and 6K in the same manner as the yellow image forming unit 6Y. That is, a laser beam L based on image information is irradiated from the exposure unit 7 disposed above the image forming unit onto the photosensitive drums 1M, 1C, and 1K of the image forming units 6M, 6C, and 6K. Is done. Specifically, the exposure unit 7 emits laser light L from a light source, and irradiates the photosensitive drum through a plurality of optical elements while scanning the laser light L with a polygon mirror that is rotationally driven.
Thereafter, the toner images of the respective colors formed on the respective photosensitive drums through the developing process are superimposed on the intermediate transfer belt 8 and primarily transferred. In this way, a color image is formed on the intermediate transfer belt 8.

  Here, referring to FIG. 3, the intermediate transfer belt device includes an intermediate transfer belt 8 (image carrier), four primary transfer rollers 9Y, 9M, 9C, and 9K, a driving roller 16, a driven roller 17, and a pre-transfer. Roller 18, tension roller 19, cleaning counter roller 20, lubricant counter roller 21, backup roller 22, intermediate transfer cleaning unit 10, lubricant supply device 30 (lubricant supply device for image carrier), secondary transfer counter roller 80 Secondary transfer devices 70 to 73 are configured. The intermediate transfer belt 8 is stretched and supported by a plurality of roller members 16 to 22, 80, and is moved endlessly in the direction of the arrow in FIG. 3 by the rotational drive of one roller member (drive roller 16) by a drive motor. Is done.

The four primary transfer rollers 9Y, 9M, 9C, and 9K respectively sandwich the intermediate transfer belt 8 with the photosensitive drums 1Y, 1M, 1C, and 1K to form a primary transfer nip. Then, a transfer voltage (primary transfer bias) having a polarity opposite to the polarity of the toner is applied to the primary transfer rollers 9Y, 9M, 9C, and 9K.
The intermediate transfer belt 8 travels in the direction of the arrow, and sequentially passes through the primary transfer nips of the primary transfer rollers 9Y, 9M, 9C, and 9K. In this way, the toner images of the respective colors on the photosensitive drums 1Y, 1M, 1C, and 1K are primarily transferred so as to overlap the surface of the intermediate transfer belt 8 (this is a primary transfer process).

  Thereafter, the intermediate transfer belt 8 on which the toner images of the respective colors are primarily transferred and overlapped reaches a position facing the secondary transfer belt 72 (secondary transfer roller 70). At this position, the secondary transfer counter roller 80 sandwiches the intermediate transfer belt 8 and the secondary transfer belt 72 between the secondary transfer roller 70 and forms a secondary transfer nip as a transfer portion. The four color toner images formed on the intermediate transfer belt 8 are secondarily transferred onto a recording medium P such as paper conveyed to the position of the secondary transfer nip (transfer portion) (secondary transfer). Process.) At this time, untransferred toner that has not been transferred to the recording medium P remains on the intermediate transfer belt 8.

Thereafter, the intermediate transfer belt 8 reaches the position of the intermediate transfer cleaning unit 10. At this position, deposits such as untransferred toner adhered to the surface of the intermediate transfer belt 8 are removed.
Further, the intermediate transfer belt 8 reaches the position of the lubricant supply device 30 (image carrier lubricant supply device). At this position, the lubricant is supplied to the surface of the intermediate transfer belt 8.
Thus, a series of transfer processes performed on the intermediate transfer belt 8 is completed.

Here, referring to FIG. 1, the recording medium P conveyed to the position of the secondary transfer nip is fed from a paper feeding unit 26 disposed below the apparatus main body 100 to a paper feeding roller 27 and a registration roller pair 28. Etc. are transported via the like.
Specifically, a plurality of recording media P such as transfer paper are stored in the paper supply unit 26 in a stacked manner. When the paper feed roller 27 is driven to rotate counterclockwise in FIG. 1, the uppermost recording medium P is fed toward the rollers of the registration roller pair 28 via the first transport path K1. Is done.

  The recording medium P conveyed to the registration roller pair 28 (timing roller pair) temporarily stops at the position of the roller nip of the registration roller pair 28 whose rotation driving has been stopped. Then, the registration roller pair 28 is rotationally driven in synchronization with the color image on the intermediate transfer belt 8, and the recording medium P is conveyed toward the secondary transfer nip. In this way, a desired color image is transferred onto the recording medium P.

Thereafter, the recording medium P on which the color image has been transferred at the position of the secondary transfer nip is conveyed by the secondary transfer belt 72 (conveyance belt), separated from the secondary transfer belt 72, and then conveyed by the conveyance belt device 60. It is conveyed to the position of the fixing unit 50. At this position, the color image transferred to the surface is fixed on the recording medium P by the heat and pressure generated by the fixing belt and the pressure roller (fixing process).
Thereafter, the recording medium P is discharged out of the apparatus by the pair of discharge rollers via the second conveyance path K2. The recording medium P discharged out of the apparatus by the pair of paper discharge rollers is sequentially stacked on the stack unit as an output image.
Thus, a series of image forming processes in the image forming apparatus is completed.

  Note that when “double-sided printing mode” for performing printing on both sides (front side and back side) of the recording medium P is selected, the recording medium P that has completed the fixing process on the front side is Then, the paper is not discharged as it is when the “single-sided printing mode” is selected, but is guided to the third transport path K3 and the transport direction is reversed. Then, the sheet is conveyed again toward the secondary transfer nip (secondary transfer devices 70 to 73). Then, an image is formed on the back surface of the recording medium P by an image forming process (image forming operation) similar to that described above at the position of the secondary transfer nip, and then a fixing process in the fixing unit 50 is performed. Then, the sheet is discharged from the image forming apparatus main body 100 via the second conveyance path K2.

Next, the configuration and operation of the developing unit 5Y (developing device) in the image forming unit will be described in more detail with reference to FIG.
The developing unit 5Y includes a developing roller 51Y that faces the photosensitive drum 1Y, a doctor blade 52Y that faces the developing roller 51Y, two conveying screws 55Y disposed in the developer container, and a toner concentration in the developer. A density detection sensor 56Y for detecting The developing roller 51Y includes a magnet fixed inside, a sleeve rotating around the magnet, and the like. In the developer accommodating portion, a two-component developer composed of a carrier and toner is accommodated.

The developing unit 5Y configured as described above operates as follows.
The sleeve of the developing roller 51Y rotates in the direction of the arrow in FIG. The developer carried on the developing roller 51Y by the magnetic field formed by the magnet moves on the developing roller 51Y as the sleeve rotates. Here, the developer in the developing section 5Y is adjusted so that the ratio of toner in the developer (toner concentration) falls within a predetermined range.
Thereafter, the toner replenished in the developer accommodating portion circulates through the two separated developer accommodating portions while being mixed and stirred together with the developer by the two conveying screws 55Y (movement in the direction perpendicular to the paper surface of FIG. 2). .) The toner in the developer is attracted to the carrier by frictional charging with the carrier, and is carried on the developing roller 51Y together with the carrier by the magnetic force formed on the developing roller 51Y.

  The developer carried on the developing roller 51Y is conveyed in the direction of the arrow in FIG. 2 and reaches the position of the doctor blade 52Y. The developer on the developing roller 51Y is conveyed to a position facing the photosensitive drum 1Y (development area) after the developer amount is made appropriate at this position. The toner is attracted to the latent image formed on the photosensitive drum 1Y by the electric field formed in the development area. Thereafter, the developer remaining on the developing roller 51Y reaches the upper portion of the developer accommodating portion as the sleeve rotates, and is detached from the developing roller 51Y at this position.

Next, the intermediate transfer belt device in the present embodiment will be described in detail with reference to FIG.
Referring to FIG. 3, the intermediate transfer belt device includes an intermediate transfer belt 8 (intermediate transfer member) as an image carrier, four primary transfer rollers 9Y, 9M, 9C, and 9K, a driving roller 16, a driven roller 17, Pre-transfer roller 18, tension roller 19, cleaning counter roller 20, lubricant counter roller 21, backup roller 22, intermediate transfer cleaning unit 10, lubricant supply device 30 (lubricant supply device for image carrier), secondary transfer counter It comprises a roller 80, secondary transfer devices 70 to 73, and the like.

  An intermediate transfer belt 8 (intermediate transfer member) serving as an image carrier is in contact with four photosensitive drums 1Y, 1M, 1C, and 1K that respectively carry toner images of respective colors to form a primary transfer nip. The intermediate transfer belt 8 mainly includes eight roller members (a driving roller 16, a driven roller 17, a pre-transfer roller 18, a tension roller 19, a cleaning counter roller 20, a lubricant counter roller 21, a backup roller 22, and a secondary transfer counter roller 80. It is stretched and supported by.

In the present embodiment, the intermediate transfer belt 8 includes PVDF (vinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), etc. in a single layer or multiple layers. A conductive material such as carbon black is dispersed. The intermediate transfer belt 8 is adjusted so that the volume resistivity is in the range of 10 ⁶ to 10 ¹³ Ωcm and the surface resistivity on the back side of the belt is in the range of 10 ⁷ to 10 ¹³ Ωcm. The intermediate transfer belt 8 is set to have a thickness in the range of 20 to 200 μm. In the present embodiment, the thickness of the intermediate transfer belt 8 is set to about 60 μm, and the volume resistivity is set to about 10 ⁹ Ωcm.
If necessary, a release layer can be coated on the surface of the intermediate transfer belt 8. At that time, materials used for the coating are ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), PVDF (vinylidene fluoride), PEA (perfluoroalkoxy fluororesin), FEP (four A fluororesin such as fluorinated ethylene-hexafluoropropylene copolymer) or PVF (vinyl fluoride) can be used, but is not limited thereto.

The primary transfer rollers 9Y, 9M, 9C, and 9K are in contact with the corresponding photosensitive drums 1Y, 1M, 1C, and 1K via the intermediate transfer belt 8, respectively. Specifically, the yellow transfer roller 9Y contacts the yellow photosensitive drum 1Y via the intermediate transfer belt 8, and the magenta transfer roller 9M passes through the intermediate transfer belt 8 to the magenta photosensitive drum 1M. The cyan transfer roller 9C is in contact with the cyan photosensitive drum 1C via the intermediate transfer belt 8, and the black (black) transfer roller 9K is black via the intermediate transfer belt 8. It is in contact with the photosensitive drum 1K (for black). Each of the primary transfer rollers 9Y, 9M, 9C, and 9K is an elastic roller in which a conductive sponge layer having an outer diameter of about 16 mm is formed on a core metal having a diameter of about 10 mm, and has a volume resistance of 10 ^6. -10 ¹² Ω (preferably 10 ⁷ to 10 ⁹ Ω).

  The driving roller 16 is positioned downstream of the four photosensitive drums in the running direction of the intermediate transfer belt, and the inner transfer belt 8 is wound on the inner periphery of the intermediate transfer belt 8 at a winding angle of about 120 degrees. It arrange | positions so that it may contact | abut on a surface. The driving roller 16 is rotationally driven in the clockwise direction in FIG. 3 by a driving motor controlled by the control unit 90. As a result, the intermediate transfer belt 8 travels in a predetermined traveling direction (clockwise in FIG. 3).

  The driven roller 17 is located in the intermediate transfer belt 8 at a position upstream of the four photosensitive drums in the running direction of the intermediate transfer belt 8 with the intermediate transfer belt 8 wound at a winding angle of about 180 degrees. It arrange | positions so that it may contact | abut to a surrounding surface. In the intermediate transfer belt 8, a portion from the driven roller 17 to the driving roller 16 is set to be substantially horizontal. The driven roller 17 is driven to rotate clockwise in FIG. 3 as the intermediate transfer belt 8 travels.

The tension roller 19 is in contact with the outer peripheral surface of the intermediate transfer belt 8. The pre-transfer roller 18, the cleaning counter roller 20, the lubricant counter roller 21, the backup roller 22, and the secondary transfer counter roller 80 are in contact with the inner peripheral surface of the intermediate transfer belt 8.
An intermediate transfer cleaning unit 10 (cleaning blade) is installed between the secondary transfer counter roller 80 and the lubricant counter roller 21 so as to contact the cleaning counter roller 20 via the intermediate transfer belt 8.
Between the cleaning facing roller 20 and the tension roller 19, a lubricant supply device 30 is installed so as to contact the lubricant facing roller 21 via the intermediate transfer belt 8. The lubricant supply device 30 includes a lubricant supply roller, a solid lubricant, a compression spring (biasing member), and the like, like the lubricant supply device 3 for the photosensitive drum. Then, the lubricant supply roller rotating counterclockwise in FIG. 3 scrapes the lubricant little by little from the solid lubricant, and the lubricant is supplied to the surface of the intermediate transfer belt 8 by the lubricant supply roller. Become.
All of the roller members 17 to 22 and 80 excluding the drive roller 16 are driven to rotate clockwise in FIG. 3 as the intermediate transfer belt 8 travels.

Referring to FIG. 3, the secondary transfer counter roller 80 is in contact with the secondary transfer roller 70 via the intermediate transfer belt 8 (image carrier) and the secondary transfer belt 72 (conveyance belt). The secondary transfer counter roller 80 has an NBR having a volume resistance of about 10 ⁷ to 10 ⁸ Ω and a hardness (JIS-A hardness) of about 48 to 58 degrees on the outer peripheral surface of a cylindrical metal core made of stainless steel or the like. An elastic layer 83 (layer thickness is about 5 mm) made of rubber is formed.

  In the present embodiment, the secondary transfer counter roller 80 is electrically connected to the power supply unit 91 (bias output means), and the secondary transfer bias becomes a high voltage of about −5 kV from the power supply unit 91. (Transfer bias) is applied. The secondary transfer bias applied to the secondary transfer counter roller 80 is obtained by transferring the toner image primarily transferred onto the surface of the intermediate transfer belt 8 onto the recording medium P conveyed to the secondary transfer nip as a transfer portion. A secondary transfer bias (DC voltage) for the next transfer and having the same polarity as the polarity of the toner (in this embodiment, a negative polarity). As a result, the toner carried on the toner carrying surface (outer circumferential surface) of the intermediate transfer belt 8 is electrostatically moved from the secondary transfer counter roller 80 side to the secondary transfer devices 70 to 73 side by the secondary transfer electric field. It will be.

  Referring to FIG. 3 (or FIG. 7A), the secondary transfer device includes a secondary transfer belt 72 (conveyance belt), a secondary transfer roller 70, a separation roller 71, and a secondary transfer blade 73 (blade). , Etc. Since the secondary transfer device according to the present embodiment is not provided with a lubricant supply device that supplies lubricant directly to the surface of the secondary transfer belt 72, the cost of the device is increased, the size is increased, and the weight is increased. Can be reduced.

  The secondary transfer belt 72 as a conveyance belt is an endless belt stretched and supported by two rollers (a secondary transfer roller 70 and a separation roller 71), and is substantially the same material as the intermediate transfer belt 8. It is formed with. The secondary transfer belt 72 (conveyance belt) is in contact with the intermediate transfer belt 8 (image carrier) and a secondary transfer nip as a transfer portion (a portion surrounded by a broken line in FIG. 7A). The recording medium P is formed and conveyed from the secondary transfer nip (transfer portion).

The secondary transfer roller 70 forms a secondary transfer nip (transfer portion) with the intermediate transfer belt 8 and the secondary transfer belt 72 sandwiched between the secondary transfer counter roller 80. The secondary transfer roller 70 is formed by forming (coating) an elastic layer having a hardness (Asker C hardness) of about 40 to 50 degrees on a hollow core bar made of stainless steel, aluminum or the like. The elastic layer of the secondary transfer roller 70 is made of a solid or foamed sponge by dispersing a conductive filler such as carbon or containing an ionic conductive material in a rubber material such as polyurethane, EPDM, or silicone. Can be formed. In this embodiment, the elastic layer is set to have a volume resistance of about 10 ^6.5 to 10 ^7.5 Ω in order to suppress concentration of transfer current. In the present embodiment, the secondary transfer roller 70 is grounded (earthed).
Further, the secondary transfer roller 70 is rotationally driven in the counterclockwise direction of FIG. 3 by the drive mechanism to cause the secondary transfer belt 72 to run in the counterclockwise direction of FIG. 3 and to move the separation roller 71 counterclockwise in FIG. Rotate following direction.

The separation roller 71 is disposed at a position downstream of the secondary transfer nip in the conveyance direction of the recording medium P. The recording medium P sent out from the secondary transfer nip is conveyed along the secondary transfer belt 72 running in the counterclockwise direction of FIG. 3 and then along the outer periphery of the separation roller 71 at the position of the separation roller 71. Thus, the secondary transfer belt 72 having a curved surface is separated (curvature separation) from the secondary transfer belt 72.
In this embodiment, the secondary transfer belt 72 is stretched by the two rollers of the secondary transfer roller 70 and the separation roller 71. However, the secondary transfer belt 72 is stretched by three or more rollers. It can also be configured to be stretched.

  The secondary transfer blade 73 as a blade is in contact with the surface of the secondary transfer belt 72 and removes foreign matters such as toner and paper dust attached to the surface of the secondary transfer belt 72. The secondary transfer blade 73 is in pressure contact with the secondary transfer roller 70 via the secondary transfer belt 72 so as to contact the running direction of the secondary transfer belt 72 in the counter direction. The secondary transfer blade 73 is obtained by holding a plate-like member made of a rubber material such as urethane rubber and having a thickness of about 1 to 5 mm by a sheet metal holder.

Hereinafter, the configuration and operation of the image forming apparatus 100, which are characteristic in the present embodiment, will be described in detail with reference to FIGS.
As described above with reference to FIG. 3, the image forming apparatus 100 has the toner first transferred onto the surface of the intermediate transfer belt 8 (image carrier) onto the recording medium P conveyed to the secondary transfer nip. In order to perform secondary transfer of an image, a power supply unit 91 (bias output unit) that outputs a secondary transfer bias as a transfer bias having a predetermined polarity (in this embodiment, a negative polarity) is provided. The secondary transfer process in the present embodiment uses a repulsive transfer method, and a secondary transfer bias (image part bias) or a non-image part bias described later is applied from the power supply unit 91 to the secondary transfer counter roller 80. (Different biases) will be applied.

Here, the control unit 90 has a polarity opposite to the predetermined polarity (secondary transfer bias polarity) (a positive polarity bias) and the same polarity as the predetermined polarity (secondary transfer bias polarity). A bias having an absolute value smaller than the secondary transfer bias and a bias having a magnitude of zero, which is different from the secondary transfer bias (transfer bias) (hereinafter referred to as “non-image portion” as appropriate). The power supply unit 91 is controlled so that “bias” is output. In the present embodiment, the non-image part bias (different bias) output from the power supply unit 91 is a bias having a polarity opposite to the polarity of the secondary transfer bias (image part bias) (+0.5 kV bias). ) Is used.
The power supply unit 91 is configured to be able to vary the output voltage (bias) output toward the secondary transfer counter roller 80, and the output voltage is varied under the control of the control unit 90. Specifically, the voltage applied from the power supply unit 91 to the secondary transfer counter roller 80 can be switched between −5 kV and +0.5 kV by the control of the control unit 90.

With reference to FIG. 4, in this embodiment, a non-image portion bias (different bias) is output from the power supply portion 91 at a predetermined timing at which the recording medium P does not intervene in the secondary transfer nip (transfer portion). Thus, the toner attached to the intermediate transfer belt 8 (image carrier) is supplied to the secondary transfer belt 72 (conveyance belt) under the control of the control unit 90. Specifically, the non-image portion bias (different bias) is applied from the power supply unit 91 at the timing when the secondary transfer belt 72 is in direct contact with the intermediate transfer belt 8 without the recording medium P interposed in the secondary transfer nip. The toner adhering to the intermediate transfer belt 8 is supplied to the secondary transfer belt 72 under the control of the control unit 90 so that is output.
That is, referring to FIG. 5, the time for the image portion on the intermediate transfer belt 8 to pass the position of the secondary transfer nip is from the power source portion 91 to the secondary transfer counter roller 80 in order to perform the secondary transfer step. A secondary transfer bias (image portion bias) of 5 kV is applied. In contrast, the time during which the non-image portion of the intermediate transfer belt 8 passes through the position of the secondary transfer nip is determined by the power supply unit 91 while the secondary transfer belt 72 is in direct contact with the intermediate transfer belt 8. A non-image portion bias of +0.5 kV is applied to the secondary transfer counter roller 80.

  The “image portion” is a sub-scanning direction (a direction orthogonal to the main scanning direction) in which the toner image T to be secondarily transferred to the recording medium P is formed, and in the same direction as the traveling direction of the intermediate transfer belt 8. The “non-image portion” is a region in the sub-scanning direction other than the image portion. Therefore, the “non-image area” includes the area before and after the image area, the area corresponding to the space between continuous sheets, the entire area when the apparatus is idled without forming the image area, etc. Will be included.

As described above, when the non-image portion of the intermediate transfer belt 8 passes through the position of the secondary transfer nip, the power supply units 91 to 2 are in a state where the secondary transfer belt 72 is in direct contact with the intermediate transfer belt 8. By applying a non-image portion bias of +5 kV to the secondary transfer counter roller 80, toner containing a large amount of reversely charged toner or weakly charged toner is supplied from the intermediate transfer belt 8 to the secondary transfer belt 72. . These toners are input to the edge portion of the secondary transfer blade 73 (the tip portion that is in sliding contact with the secondary transfer belt 72).
Here, the toner supplied from the intermediate transfer belt 8 to the secondary transfer belt 72 at the timing of the non-image portion may be a scumming toner adhering to the surface of the intermediate transfer belt 8, or the intermediate transfer as shown in FIG. There is also a toner pattern image TP positively formed on the non-image portion of the belt 8, and there are also a patch pattern for adjusting the image of the toner image and adjusting the color shift of the four color toner images.

  More specifically, referring to FIG. 8, the charge amount distribution of the toner carried on the intermediate transfer belt 8 has a normal distribution width, and the charge amount varies among the negatively charged ones. Some are weakly charged. Furthermore, there are also those that are reversely charged to a positive polarity.

  When the non-image part bias output from the power supply unit 91 at the non-image part timing is set to be equal to the secondary transfer bias (image part bias), the electrostatically charged negatively charged toner is transferred to the intermediate transfer. A large amount of toner is transferred from the belt 8 to the secondary transfer belt 72, and the toner having such characteristics is input to the edge portion of the secondary transfer blade 73. The toner that is normally charged to the negative polarity in this way has a strong electrostatic attraction force to the secondary transfer belt 73 and thus easily slips out from the edge portion of the secondary transfer blade 73. When the toner does not stay on the edge portion of the secondary transfer blade 73 as described above, the sliding resistance of the secondary transfer blade 73 with respect to the secondary transfer belt 72 increases, and as shown in FIG. The edge portion of the transfer blade 73 is bent (a portion surrounded by a broken line). In such a portion where the wrinkle occurs, foreign matter such as toner adhering to the surface of the secondary transfer belt 72 is not removed, and the toner that has not been removed reaches the position of the secondary transfer nip again, and the secondary transfer is performed. The recording medium P that is conveyed to the nip adheres to the back surface (the front surface in the double-sided printing mode) as back dirt.

  On the other hand, when the non-image portion bias output from the power supply unit 91 at the non-image portion timing is set to a reverse polarity with respect to the secondary transfer bias (image portion bias), weakly charged toner or reversely charged toner However, a large amount of toner is transferred from the intermediate transfer belt 8 to the secondary transfer belt 72, and the toner having such characteristics is input to the edge portion of the secondary transfer blade 73. The weakly charged toner and the reversely charged toner are removed by the secondary transfer blade 73 and are subjected to the secondary transfer because the electrostatic attraction force to the secondary transfer belt 73 is weaker than that of the normally charged toner. It tends to stay at the edge portion of the blade 73. Then, the toner remaining on the edge portion of the secondary transfer blade 73 acts like a lubricant to prevent the edge portion from curling as shown in FIG. For this reason, the cleaning property by the secondary transfer blade 73 is maintained well, and the problem that the recording medium P conveyed to the secondary transfer nip is soiled is also reduced.

Since the image forming apparatus 100 according to the present embodiment forms a secondary transfer nip using the secondary transfer belt 72, the secondary transfer roller 70 is used as shown in FIG. Compared with the transfer nip formed, the transportability of the recording medium P sent out from the secondary transfer nip can be improved. This is because the secondary transfer belt 72 functions to guide the conveyance of the recording medium P fed from the secondary transfer nip.
In particular, in the case where the secondary transfer nip is formed using the secondary transfer belt 72, the recording medium P sent out from the secondary transfer nip when the recording medium P (thin paper) having a small thickness is passed. Separation is improved. Unlike the secondary transfer roller 70, the separation roller 71 has no side effect in the secondary transfer process even if the outer diameter is relatively small, and the outer diameter for performing the curvature separation is set relatively freely. This is because it can.

  On the other hand, when cleaning is performed by bringing the secondary transfer blade 73 into contact with the secondary transfer belt 72 as in this embodiment, as shown in FIG. As compared with the case where cleaning is performed by bringing the secondary transfer blade 73 into contact with the secondary transfer blade 73, a cleaning defect is likely to occur. As shown in FIG. 7A, when the secondary transfer nip is formed by using the secondary transfer belt 72, the intermediate transfer belt 8 and the secondary transfer belt 72 are arranged downstream of the secondary transfer nip. When the secondary transfer nip is formed using the secondary transfer roller 70 as shown in FIG. 7B and the angle θ1 of the space formed by the intermediate transfer belt 8 on the downstream side of the secondary transfer nip. And the angle θ2 of the space formed by the secondary transfer roller 70, it can be considered that the former is smaller than the latter (θ1 <θ2). That is, the electric field formed by the secondary transfer bias at the position of angle θ1 shown in FIG. 7A is stronger than the electric field formed by the secondary transfer bias at the position of angle θ2 shown in FIG. Therefore, the toner that is normally charged to the negative polarity is easily transferred to the secondary transfer belt 72. Accordingly, as described above, a large amount of toner having a strong electrostatic attraction force adheres to the secondary transfer belt 73 and a lot of toner slips from the edge portion of the secondary transfer blade 73, and the secondary transfer blade. The cleaning failure due to the wrinkling of the edge portion 73 is likely to occur.

On the other hand, in the present embodiment, the non-image part bias output from the power supply unit 91 at the timing of the non-image part is set to a reverse polarity with respect to the secondary transfer bias (image part bias). A lot of weakly charged toner and reversely charged toner are supplied to the secondary transfer belt 72 and stored in the edge portion of the secondary transfer blade 73. Accordingly, it is possible to make it difficult to cause a cleaning failure due to the edge portion of the secondary transfer blade 73.
FIG. 8 is a graph showing a change in the charge amount distribution of the toner attached to the surface of the secondary transfer belt 72 when the non-image portion bias applied to the secondary transfer counter roller 80 is varied. Indicates the charge amount, and the vertical axis indicates the frequency (toner amount). From the results shown in FIG. 8, it is also possible to apply the secondary transfer bias (image portion bias) as the non-image portion bias, rather than applying -0.5 kV having the same polarity as the secondary transfer bias (image portion bias) as the non-image portion bias. It can be seen that when +0.5 kV having a reverse polarity is applied, the proportion of weakly charged toner and reversely charged toner adhering to the surface of the secondary transfer belt 72 increases.
In this embodiment, the total charge amount of toner supplied from the intermediate transfer belt 8 to the secondary transfer belt 72 at the timing of the non-image portion is set to about +8.7 μC / g.

  In the present embodiment, a non-image portion bias (different bias) applied to the secondary transfer counter roller 80 is a reverse polarity bias to the polarity of the secondary transfer bias (image portion bias). 8, the non-image portion bias has the same polarity as the secondary transfer bias (image portion bias) and has a smaller absolute value than the secondary transfer bias, or a zero magnitude ( Even when a bias of 0 kV) is used, it can be seen that the proportion of weakly charged toner and reversely charged toner adhering to the surface of the secondary transfer belt 72 tends to increase. Therefore, it can be seen that even in such a case, a similar effect can be obtained although the effect is smaller than in the case of using a reverse polarity bias.

  Here, referring to FIG. 4, in the present embodiment, the control unit 90 always outputs a non-image portion bias (different bias) from the power supply unit 91 at the timing between sheets during continuous sheet passing. Is controlling. Therefore, at least at the timing between papers during continuous paper feeding, at least the scumming toner adhering to the non-image portion of the intermediate transfer belt 8 (particularly, the weakly charged and reversely scumming toner) is secondary. The toner is supplied to the transfer belt 72 (secondary transfer blade 73). Accordingly, it is possible to make it difficult to cause a cleaning failure due to the edge portion of the secondary transfer blade 73.

Referring to FIG. 5, in this embodiment, the toner image is positively supplied from the intermediate transfer belt 8 toward the secondary transfer belt 72 at the timing of the non-image portion. The toner pattern image is formed on the surface of the photosensitive drum at a timing different from the timing at which T (image portion) is formed, and the toner pattern image TP is primarily transferred onto the surface of the intermediate transfer belt 8. doing.
That is, a substantially belt-like toner pattern image TP is formed on the non-image portion of the intermediate transfer belt 8 by the image forming process described above with reference to FIGS. 1 and 2, and the intermediate transfer is performed at the timing of the non-image portion. More toner is positively supplied from the belt 8 toward the secondary transfer belt 72. Specifically, in the present embodiment, a halftone toner pattern image TP of black color is formed between papers at a frequency of about once every 10 sheets in continuous paper feeding.
As a result, more weakly charged toner and reversely charged toner are supplied to the edge portion of the secondary transfer blade 73, and it becomes difficult to cause a cleaning failure due to curl of the edge portion of the secondary transfer blade 73. it can.
In the present embodiment, the toner pattern image TP of only one color is formed, but a toner pattern image TP of two to four colors can also be formed.

Referring to FIG. 5, in the present embodiment, the toner pattern image TP has a range in the main scanning direction (vertical direction in FIG. 5) of the contact width of the secondary transfer blade 73 (FIG. 5). 3 in the direction perpendicular to the plane of the drawing and the range in the vertical direction of FIG. 5).
As a result, the weakly charged toner and the reversely charged toner are uniformly supplied to the edge portion of the secondary transfer blade 73 over the entire contact width, and the edge portion of the secondary transfer blade 73 is cleaned by curling. Defects can be made difficult to occur.

Further, in this embodiment, when the toner pattern image TP is formed at the timing of the non-image portion, the toner per unit length in the contact width direction from the intermediate transfer belt 8 to the secondary transfer belt 72. The toner is configured to be supplied with an amount of 0.6 mg / m or more.
FIG. 9 shows the amount of toner per unit length (shown on the horizontal axis) input to the secondary transfer blade 73, the amount of deflection of the secondary transfer blade 73 (shown on the vertical axis), and It is a graph which shows the relationship between the presence or absence of cleaning failure (indicated by ◯, Δ, ×). In FIG. 9, “◯” indicates the result of no cleaning failure, “Δ” indicates the result of acceptable cleaning failure, and “x” indicates the unacceptable level. This shows the result of cleaning failure.
From the result of FIG. 9 also, the toner pattern image TP and the non-image are printed at the timing of the non-image portion so that the toner having a toner amount per unit length of 0.6 mg / m or more is input to the secondary transfer blade 73. It can be seen that by setting the partial bias, the amount of deflection of the edge portion of the secondary transfer blade 73 can be reduced, thereby making it difficult to cause a cleaning failure.

Further, the image forming apparatus 100 according to the present embodiment is provided with a lubricant supply device 30 (an image carrier lubricant supply device) that directly supplies a lubricant to the surface of the intermediate transfer belt 8.
Therefore, a part of the lubricant supplied (applied) to the intermediate transfer belt 8 moves from the intermediate transfer belt 8 to the surface of the secondary transfer belt 72 at the timing of the non-image portion. Therefore, the sliding resistance between the secondary transfer belt 72 and the secondary transfer blade 73 is reduced by the lubricant supplied to the surface of the secondary transfer belt 72, and the edge of the secondary transfer blade 73 is curled. It is possible to make it difficult for cleaning defects to occur.
Since the secondary transfer blade 73 has the highest sliding resistance with the secondary transfer belt 72 when it is new, the secondary transfer devices 70 to 73 are new, or the secondary transfer blade 73. When the replacement is performed, the recording medium P is not passed, and the intermediate transfer belt 8 and the secondary transfer belt 72 are driven idle for about 6 minutes.

In addition, the image forming apparatus 100 according to the present embodiment includes a lubricant supply device 3 (photosensitive member lubricant supply device) that directly supplies a lubricant to the surfaces of the photosensitive drums 1Y, 1M, 1C, and 1K. is set up.
Therefore, a part of the lubricant supplied (applied) to the photoconductive drums 1Y, 1M, 1C, and 1K moves to the surface of the intermediate transfer belt 8, and further from the intermediate transfer belt 8 to 2 at the timing of the non-image portion. The surface of the next transfer belt 72 is transferred. Therefore, the sliding resistance between the secondary transfer belt 72 and the secondary transfer blade 73 is reduced by the lubricant supplied to the surface of the secondary transfer belt 72, and the edge of the secondary transfer blade 73 is curled. It is possible to make it difficult for cleaning defects to occur.
When the intermediate transfer belt 8 and the secondary transfer belt 72 described above are driven idle, the above-described effects are further exhibited by performing the idle driving of the photosensitive drums 1Y, 1M, 1C, and 1K. It will be.

<Modification>
FIG. 10 is a timing chart showing bias control of the power supply unit 91 that outputs the secondary transfer bias as a modified example, and corresponds to FIG. 4 in the present embodiment. FIG. 11 is a table showing changes in the amount of input toner necessary to prevent the secondary transfer blade 73 from curling when the environment (particularly temperature) changes. Further, FIG. 12 is a graph showing changes in the non-image portion bias necessary for preventing the cleaning failure of the secondary transfer blade 73 when the wear amount of the secondary transfer blade 73 changes with time. In FIG. 11 and FIG. 12, “◯” indicates the result of no cleaning failure, and “X” indicates the result of cleaning failure.

As shown in FIG. 10, in the modification, the value of the non-image portion bias (different bias) is varied based on a predetermined condition.
Specifically, referring to FIG. 3, a temperature sensor 92 as temperature detecting means for indirectly detecting the temperature of the secondary transfer blade 73 is installed in the vicinity of the secondary transfer blade 73. The control unit 90 has a non-image portion bias (different bias) when the temperature detected by the temperature sensor 92 (temperature detection means) is high compared to when the temperature detected by the temperature sensor 92 is low. The power supply unit 91 is controlled so as to greatly change toward the opposite polarity side. Specifically, referring to FIG. 10, when the temperature detected by temperature sensor 92 is equal to or lower than a predetermined value A, the non-image portion bias is set to +0.5 kV, and the temperature detected by temperature sensor 92 is a predetermined value. When A exceeds A, the non-image portion bias is set to +0.7 kV. The reason why such control is performed is that the secondary transfer blade 73 becomes soft and tends to bend at high temperatures, and such a phenomenon can be seen from the results shown in FIG. Further, as described above with reference to FIG. 8, when the non-image portion bias changes to the plus side, the amount of weakly charged toner and reversely charged toner supplied to the secondary transfer belt 72 increases. As the temperature detecting means, a means for directly detecting the temperature of the secondary transfer blade 73 can be used.

  In the modification, referring to FIG. 3, a counter 93 (time detecting means for directly or indirectly detecting the accumulated time that the secondary transfer blade 73 is in sliding contact with the secondary transfer belt 72 from a new state) Or a timer) is installed. When the time detected by the counter 93 (time detection means) is long, the control unit 90 has a non-image portion bias (different bias) having a reverse polarity as compared with the case where the time detected by the counter 93 is short. The power supply unit 91 is controlled so as to change greatly toward the side. Specifically, referring to FIG. 10, when the accumulated time detected by counter 93 is equal to or less than predetermined value B, the non-image portion bias is set to +0.5 kV and the accumulated detected by counter 93 is set. When the time exceeds the predetermined value B, the non-image portion bias is set to +0.7 kV. The reason why such control is performed is that the secondary transfer blade 73 wears over time and is liable to bend, and such a phenomenon can be seen from the results shown in FIG. Further, as described above, when the non-image portion bias changes to the plus side, weakly charged toner and reversely charged toner supplied to the secondary transfer belt 72 increase.

As described above, the image forming apparatus 100 according to the present embodiment includes the intermediate transfer belt 8 (image carrier), the secondary transfer belt 72 (conveyance belt), the secondary transfer blade 73 (blade), and a predetermined number. The power supply unit 91 that outputs a secondary transfer bias (transfer bias) of a negative polarity, or the power supply unit 91 is controlled so that a bias having a polarity opposite to a predetermined polarity and different from the secondary transfer bias is output. A control unit 90 is provided. Then, the intermediate transfer is controlled by the control unit 90 so that a non-image part bias (different bias) is output from the power supply unit 91 at a predetermined timing when the recording medium P is not interposed in the secondary transfer nip (transfer unit). The toner attached to the belt 8 is supplied to the secondary transfer belt 72.
As a result, the transportability of the recording medium P sent from the secondary transfer nip is high without increasing the cost and size of the apparatus, and the cleaning failure due to the secondary transfer blade 73 contacting the secondary transfer belt 72 is achieved. Can be made difficult to occur.

In the present embodiment, a repulsive transfer system in which the power supply unit 91 is configured to apply a secondary transfer bias (image portion bias) or a non-image portion bias (different bias) to the secondary transfer counter roller 80. The present invention is applied to the image forming apparatus 100.
In contrast, an attractive transfer type image forming apparatus in which a power supply unit is configured to apply a secondary transfer bias (image portion bias) or a non-image portion bias (different bias) to the secondary transfer roller 70. However, the present invention can be applied. In this case, the secondary transfer bias (image portion bias) has a polarity opposite to that of the repulsive transfer type. The present invention can also be applied to an image forming apparatus in which both the repulsive force transfer method and the attractive force transfer method are used.
In addition, for a direct transfer type image forming apparatus that transfers a toner image on a photosensitive drum to a recording medium at a transfer nip between a photosensitive drum as an image carrier and a transfer conveyance belt as a conveyance belt. The present invention can be applied.
The present invention can also be applied to an image forming apparatus that uses a drum-shaped intermediate transfer drum as an intermediate transfer body instead of an intermediate transfer belt as an intermediate transfer body.
Further, the present invention can also be applied to a configuration in which the secondary transfer belt 72 is separated from the intermediate transfer belt 8 in a non-image portion (between sheets). When the secondary transfer belt 72 is separated from the intermediate transfer belt 8 in the non-image portion (between sheets), or when the secondary transfer belt 72 and the intermediate transfer belt 8 remain in contact with each other in the non-image portion (between sheets). As compared with the above, the amount by which the toner pattern image TP moves to the secondary transfer belt 72 is reduced. However, since an electric field is formed in the secondary transfer portion by the non-image portion bias, at least a part of the toner pattern image TP can be transferred to the secondary transfer belt 72 in the secondary transfer portion. It is possible to make it difficult for cleaning failure due to the secondary transfer blade 73 to occur. The distance between the secondary transfer belt 72 and the intermediate transfer belt 8 in the non-image area (between paper), that is, the gap between the secondary transfer belt 72 and the intermediate transfer belt 8 causes the toner pattern image TP to be transferred to the secondary transfer belt. In order to facilitate the transition to 72, it is preferably within 3 mm, more preferably within 1 mm.
And even if it is such a case, the effect similar to the thing of this Embodiment can be acquired.

  It should be noted that the present invention is not limited to the present embodiment, and it is obvious that the present embodiment can be modified as appropriate within the scope of the technical idea of the present invention, other than suggested in the present embodiment. is there. In addition, the number, position, shape, and the like of the constituent members are not limited to the present embodiment, and the number, position, shape, and the like suitable for implementing the present invention can be achieved.

1Y, 1M, 1C, 1K photosensitive drum,
3 Lubricant supply device (lubricant supply device for photoconductor),
8 Intermediate transfer belt (image carrier),
30 Lubricant supply device (lubricant supply device for image carrier),
70 secondary transfer roller (roller),
71 Separation roller (roller),
72 secondary transfer belt (conveyor belt),
73 secondary transfer blade (blade),
80 Secondary transfer counter roller (roller member),
90 control unit,
91 Power supply section (secondary transfer power supply),
92 Temperature sensor (temperature detection means),
93 counter (time detection means),
100 Image forming apparatus (image forming apparatus main body), P recording medium.

Japanese Patent Laying-Open No. 2015-161941

Claims (11)

An image carrier;
A transfer belt that abuts on the image carrier to form a transfer portion, and that transports a recording medium sent from the transfer portion;
A blade that contacts the surface of the conveyor belt;
A power supply unit that outputs a transfer bias of a predetermined polarity in order to transfer the toner image carried on the image carrier to a recording medium by the transfer unit;
A bias having a polarity opposite to the predetermined polarity, a bias having the same polarity as the predetermined polarity and having an absolute value smaller than the transfer bias, and a bias having a magnitude of zero, and the transfer bias A control unit that controls the power supply unit so that a bias different from that is output;
With
At the predetermined timing when no recording medium is interposed in the transfer unit, the control unit controls the bias so that the different bias is output from the power supply unit, and supplies the toner adhered to the image carrier to the transport belt. An image forming apparatus.   A toner pattern image is formed on the surface of the image carrier at a timing different from the timing at which the toner image is formed so that toner is supplied from the image carrier to the conveyance belt at the predetermined timing. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The image forming apparatus according to claim 2, wherein the toner pattern image is formed such that a range in a main scanning direction is equal to a contact width of the blade.   When the toner pattern image is formed at the predetermined timing, toner having a toner amount per unit length of 0.6 mg / m or more is supplied from the image carrier toward the conveyance belt. The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus. Comprising temperature detecting means for directly or indirectly detecting the temperature of the blade;
When the temperature detected by the temperature detecting means is high, the control unit changes the different bias toward the opposite polarity side compared to when the temperature detected by the temperature detecting means is low. The image forming apparatus according to claim 1, wherein the power supply unit is controlled to do so. A time detecting means for directly or indirectly detecting the accumulated time when the blade is in sliding contact with the conveyor belt from a new state;
When the time detected by the time detection means is long, the control unit changes the different bias toward the opposite polarity side compared to when the time detected by the time detection means is short. The image forming apparatus according to claim 1, wherein the power supply unit is controlled.   The image forming apparatus according to claim 1, further comprising a lubricant supply device that supplies a lubricant to a surface of the image carrier.   8. The control unit according to claim 1, wherein the control unit performs control so that the different bias is always output from the power supply unit at a timing between sheets during continuous sheet passing. Image forming apparatus.   9. The timing according to claim 1, wherein the predetermined timing is a timing at which the conveyance belt is in direct contact with the image carrier without a recording medium interposed in the transfer portion. The image forming apparatus described in 1. The image carrier is an intermediate transfer belt that is stretched around a plurality of roller members and that contacts a plurality of photosensitive drums,
The conveyance belt is stretched around a plurality of rollers, and abuts against the intermediate transfer belt to form a secondary transfer nip as the transfer portion, and conveys a recording medium fed from the secondary transfer nip. A secondary transfer belt,
The plurality of rollers are:
A secondary transfer roller that forms the secondary transfer nip between the intermediate transfer belt and the secondary transfer belt between a secondary transfer counter roller as one of the plurality of roller members;
A separation roller disposed at a position downstream of the secondary transfer nip in the conveyance direction of the recording medium;
Comprising at least
The power supply unit applies a secondary transfer bias as the transfer bias or the different bias to the secondary transfer counter roller or / and the secondary transfer roller,
The blade is a secondary transfer blade that is in pressure contact with the secondary transfer roller via the secondary transfer belt so as to come into contact with the running direction of the secondary transfer belt in a counter direction. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 10, further comprising a photoconductor lubricant supply device that supplies a lubricant to a surface of the photoconductor drum.

Images