JP2007108562A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus free of staining of a transfer material due to staining of a transfer roller caused by an image projecting from a transfer material rear end part when residual toner sticking on the transfer roller is transferred to an image carrier after a toner image on the image carrier is transferred onto the transfer material, as a frameless image. <P>SOLUTION: The image forming apparatus which has an image formation part forming a toner image on the image carrier and the transfer roller transferring the toner image to the transfer material and transfers the residual toner sticking on the transfer roller abutting against the image carrier to the image carrier by reverse bias application to clean the transfer roller controls the transfer line speed of the transfer roller when a rear end of the residual toner sticking on the transfer roller is transferred to an image formation surface of the image carrier after the toner image formed on the image carrier is transferred onto the transfer material, as the frameless image, so that the transfer line speed is faster than the image formation line speed of the image carrier. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a copying machine, a printer, a facsimile machine, and an image forming apparatus using an electrophotographic system having these functions. In particular, a toner image carried on the surface of an image carrier such as a photoconductor is transferred by a transfer roller. The present invention relates to an image forming apparatus that contacts and transfers to a transfer material, and a color image forming apparatus that superimposes and transfers a plurality of color toner images formed on an intermediate transfer body onto a transfer material.

  As an image forming apparatus that contacts and transfers a toner image carried on the surface of a toner image carrier or the like onto a transfer material by a transfer roller, those described in Patent Documents 1 and 2 are known.

  In the image forming apparatus disclosed in Patent Literature 1, when the transfer roller is cleaned, the registration roller pair restrains the movement of the transfer material, so that the roller surface of the transfer roller comes into sliding contact with the transfer material and adheres to the roller surface. This is a transfer roller cleaning means for transferring toner to the transfer material and removing the toner from the roller surface.

When the transfer roller is cleaned, the image forming apparatus disclosed in Patent Document 2 switches the charge polarity of the transfer roller to the same polarity as the toner, and determines the cleaning time based on the output from the transfer material size detection means. The transfer roller cleaning means removes toner from the toner.
Japanese Patent Laid-Open No. 7-13446 JP 7-44069 A

  In recent years, colorization has progressed in image forming apparatuses such as copiers, printers, facsimiles, and multifunction devices having these functions, and there has been a demand for higher image quality in the transfer process by employing polymerized toner and small particle size toner. Is getting bigger. The speed of image forming apparatuses is also increasing.

  In order to obtain a good image for these image forming apparatuses, a cleaning unit is used to remove residual toner adhering to a transfer roller that is in pressure contact with an image carrier such as a photosensitive member or an intermediate transfer member.

  Conventionally, it is known to apply a reverse bias voltage to the residual toner transferred to the transfer roller and return the toner to the image carrier for cleaning. At this time, the cleaning power has been increased by adjusting the magnitude of the applied electric field, the application time, etc., and selecting a plurality of cleaning means, etc., but this is not sufficient, and if there is a large amount of residual toner attached, it can be completely cleaned. Not happening.

  Further, after transferring the toner image without a margin (no margin) from the toner image on the image carrier onto the transfer material, when the residual toner adhered to the transfer roller is transferred to the image carrier, the trailing edge of the residual toner is transferred. If there is a large amount of residual toner per area on the transfer roller, the rear end of the residual toner is not transferred onto the image carrier and remains on the transfer roller. To do.

  Note that the trailing edge of the residual toner protrudes due to an error in transfer timing caused by the transfer roller or the transport roller when a borderless toner image is formed on the image carrier and contact-transferred by the transfer roller.

  In the apparatus described in Patent Document 1, when a recording paper jam occurs, the conveyance of the recording paper is stopped, the transfer roller is idled one or more times, and the toner adhering to the roller surface of the transfer roller is used as a transfer material. By transferring the toner, the toner is removed from the roller surface of the transfer roller, and when the cleaning is completed, the recording paper from which the toner has been wiped off from the transfer roller is discharged. In this apparatus, toner on the transfer roller is transferred onto the recording paper when the recording paper is jammed, and the image forming process is temporarily stopped.

  In the apparatus described in Patent Document 2, when the transfer roller is cleaned, the transfer roller power is switched, and the transfer roller is cleaned according to the width of the transfer material detected by the size detection unit that detects the width of the transfer material. The operating time of the cleaning means to be controlled is controlled. When the sheet passing width of the transfer material is large, the length is controlled to be short. On the other hand, when the sheet passing width is small, the length is controlled to be long. In this apparatus, when there is a large amount of toner adhering to the transfer roller, it may not be completely cleaned. In addition, there is a problem that a cleaning unit such as a blade is provided with a toner collecting unit around the transfer roller.

  However, in the electrophotographic image forming apparatus using a transfer body such as the above-described conventional transfer roller or transfer belt, there are the following problems when forming a borderless image.

  That is, the transfer material has cutting errors, paper expansion / contraction due to atmospheric environment differences, and curls, and the transfer speed of the transfer material varies in the image forming apparatus, so there is no transfer material when forming a borderless image. An image is formed on the transfer member, and the image is transferred onto the transfer member, which may contaminate the transfer member.

  If the transfer body becomes dirty to some extent, the subsequent transfer material will be placed on the dirty portion, and the back surface of the transfer material will be stained. Furthermore, if the transfer body becomes extremely dirty, the electrostatic attractive force between the transfer body and the transfer material is reduced, causing a conveyance failure and causing image defects and paper jams due to poor separation between the transfer material and the image carrier. There was a thing.

  There is also a method of detecting the transfer material position before transfer with a sensor or the like and forming an image in accordance with the transfer material position. However, it is difficult to completely match the transfer material with the image due to a measurement error or the like.

  In the cleaning blade method for preventing the transfer material from being soiled, the transfer body and the blade are rubbed against each other. Therefore, it is difficult to extend the life of the transfer body by scraping or scratching the transfer body. Further, a container for storing the residual toner collected by the blade and a means for conveying the toner to the container are necessary, and there are problems such as a container replacement operation.

  Similarly, the system for cleaning the transfer member by applying a bias voltage to the fur brush and the web cleaning system require a residual toner storage container and a residual toner conveying means, and have problems such as a container replacement operation.

  In addition, the method of returning the toner to the image carrier by applying a bias voltage having a polarity opposite to that of the toner to the transfer member, and collecting the residual toner by the cleaning means of the image carrier is a container or container for storing the collected residual toner. Since no means for transporting the film is necessary and no special cleaning means is required, the structure is simplified. However, since the transfer member cannot be cleaned during image formation, cleaning is performed only between the transfer materials, and dirt is accumulated due to insufficient cleaning, and the back surface of the subsequent transfer material may be stained. is there.

  In particular, if the transfer body has a large amount of dirt on the trailing edge of the image with a high density at the trailing edge of the image when a borderless image is passed through, when the toner is returned to the image carrier, cleaning is insufficient and the transfer material Backside contamination will occur.

  In the present invention, the toner image on the image carrier is transferred from the trailing edge of the transfer material when the residual toner adhering to the transfer roller is transferred to the image carrier after the toner image without a border is transferred onto the transfer material. Another object of the present invention is to provide an image forming apparatus that does not cause transfer material contamination due to contamination of a transfer roller by an image.

  Also, in the secondary transfer during color image formation, after the secondary transfer of the multicolor toner image formed on the intermediate transfer body onto the transfer material, the secondary transfer roller is driven by the image protruding from the rear end of the transfer material. It is an object of the present invention to provide a color image forming apparatus that does not cause stains on a transfer material due to stains.

The object is achieved by the invention described below.
1. An image forming unit that forms a toner image on an image carrier, and a transfer roller that transfers the toner image onto a transfer material. Residual toner attached to the transfer roller that contacts the image carrier is applied by applying a reverse bias. In the image forming apparatus that transfers to the image carrier and cleans the toner image formed on the image carrier, after transferring the toner image without a border to the transfer material, after the residual toner adhering to the transfer roller An image forming apparatus, wherein the transfer line speed of the transfer roller when the end portion is transferred to the image forming surface of the image carrier is controlled to be higher than the image forming line speed of the image carrier.
2. An image forming unit that forms a toner image on an image carrier, and a transfer roller that transfers the toner image onto a transfer material. Residual toner attached to the transfer roller that contacts the image carrier is applied by applying a reverse bias. In the image forming apparatus that transfers to the image carrier and cleans the toner image formed on the image carrier, after transferring the toner image without a border to the transfer material, after the residual toner adhering to the transfer roller An image forming apparatus, wherein the transfer line speed of the transfer roller when the end portion is transferred to the image forming surface of the image carrier is controlled to be slower than the image forming line speed of the image carrier.
3. An image forming unit that forms a toner image on an image carrier, and a transfer roller that transfers the toner image onto a transfer material. Residual toner attached to the transfer roller that contacts the image carrier is applied by applying a reverse bias. In the image forming apparatus that transfers to the image carrier and cleans the toner image formed on the image carrier, after transferring the toner image without a border to the transfer material, after the residual toner adhering to the transfer roller A first control unit configured to make a transfer line speed of the transfer roller when the end portion is transferred to the image forming surface of the image carrier higher than an image formation line speed of the image carrier; and a transfer line speed of the transfer roller And a second control section that makes the image forming line speed slower than the image forming line speed of the image carrier.
4). The image carrier is a photoconductor carrying an electrostatic latent image and a toner image, and the toner image carried on the photoconductor is transferred to the transfer material by the transfer roller, and the residual toner attached to the transfer roller 4. The image forming apparatus according to any one of 1 to 3, wherein the image is transferred to the photoconductor by applying the reverse bias.
5. The image carrier is an intermediate transfer member that primarily carries and carries the toner image formed by the image forming unit, and the toner image carried on the intermediate transfer member is transferred to the transfer material by the transfer roller. 5. The image forming apparatus according to any one of 1 to 4, wherein the residual toner attached to the transfer roller is transferred to the intermediate transfer member by applying the reverse bias.
6). 4. The image forming apparatus according to claim 1, wherein the number of rotations of the transfer roller is controlled in accordance with the size of the transfer material.

  According to the first to third aspects of the present invention, it is possible to transfer the toner image on the image carrier that protrudes from the rear end portion of the transfer material to the transfer material, and a reverse bias is applied when the transfer roller is cleaned. In the image forming apparatus that performs cleaning, the relative speed difference between the transfer roller linear velocity and the image carrier linear velocity is used to assist the transfer roller cleaning effect by applying a reverse bias, and the toner per unit area. By reducing the amount of adhesion, there is provided an image forming apparatus that eliminates stains on the back surface of the transfer material due to prevention of stains on the transfer roller and obtains a high-quality image.

  The present invention will be described below with reference to embodiments, but the present invention is not limited to the embodiments described below.

[Color image forming apparatus]
FIG. 1 is a sectional view showing the overall configuration of a color image forming apparatus A according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing the main part of the color image forming apparatus A.

  The color image forming apparatus A is called a tandem type color image forming apparatus, and includes a plurality of sets of image forming units 10Y, 10M, 10C, and 10K, a belt-like intermediate transfer member 7, primary transfer units 5Y, 5M, 5C, 5K, an intermediate transfer unit including secondary transfer means 8, a fixing device 11, and a paper feeding device 20.

  Above the color image forming apparatus A, an image reading apparatus B is installed. The document placed on the document table is scanned and exposed by the optical system of the document image scanning exposure apparatus of the image reading apparatus B, and read by the line image sensor. The analog signal photoelectrically converted by the line image sensor is subjected to analog processing, A / D conversion, shading correction, image compression processing and the like in the image processing unit, and then input to the exposure means 3Y, 3M, 3C, 3K. .

  The image forming unit 10Y that forms a yellow (Y) image includes a charging unit 2Y, an exposure unit 3Y, a developing unit 4Y, and a cleaning unit 6Y disposed around the image carrier 1Y.

  The image forming unit 10M that forms a magenta (M) color image includes an image carrier 1M, a charging unit 2M, an exposure unit 3M, a developing unit 4M, and a cleaning unit 6M.

  The image forming unit 10C that forms a cyan (C) image includes an image carrier 1C, a charging unit 2C, an exposure unit 3C, a developing unit 4C, and a cleaning unit 6C.

  The image forming unit 10K that forms a black (K) image includes an image carrier 1K, a charging unit 2K, an exposure unit 3K, a developing unit 4K, and a cleaning unit 6K.

  The charging unit 2Y and the exposure unit 3Y, the charging unit 2M and the exposure unit 3M, the charging unit 2C and the exposure unit 3C, and the charging unit 2K and the exposure unit 3K constitute a latent image forming unit.

  As the image bearing members 1Y, 1M, 1C, and 1K, known ones such as an OPC photosensitive member and an aSi photosensitive member are used. An OPC photosensitive member is preferable, and in particular, a negatively charged OPC photosensitive member is preferable. In the form, negatively chargeable OPC is used.

  As the charging means 2Y, 2M, 2C, 2K, a corona discharge means such as a scorotron or a corotron is used, and a scorotron discharge means is preferably used.

  As the exposure means 3Y, 3M, 3C, and 3K, light emitting elements that emit light according to image data, such as lasers and LED arrays, are used.

  The belt-like intermediate transfer member 7 is semiconductive and is wound around a plurality of support rollers 71, 72, 73, 74 and a backup roller 75, and is supported so as to be able to circulate. In the present embodiment, the intermediate transfer member 7 is supported between the support rollers 73 and 74 in a planar shape.

  The images of the respective colors formed by the image forming units 10Y, 10M, 10C, and 10K are sequentially transferred (primary transfer) and synthesized on the rotating intermediate transfer body 7 by the primary transfer means 5Y, 5M, 5C, and 5K. A color image is formed.

  The transfer material P accommodated in the paper feeding cassette 21 of the paper feeding device 20 is fed by a paper feeding means (first paper feeding unit) 22, and is fed with paper feeding rollers 23, 24, 25 and registration rollers (second feeding). The paper is conveyed to the secondary transfer means 8 through the paper portion 26 and the like, and the color image is transferred onto the transfer material P (secondary transfer).

  The transfer material P on which the color image has been transferred is subjected to heat and pressure by the fixing device 11, and the color toner image (or single color toner image) on the transfer material P is fixed and fixed on the transfer material P. The paper is discharged from the paper roller 27 and placed on a paper discharge tray 28 outside the apparatus.

  On the other hand, after the color image is transferred to the transfer material P by the secondary transfer unit 8, the residual toner is removed by the cleaning unit 6A from the intermediate transfer body 7 from which the transfer material P is separated by curvature.

[Primary transfer means]
The primary transfer means 5Y for transferring a yellow image is composed of a primary transfer roller 5YA and a DC power source 5YE for applying a voltage to the primary transfer roller 5YA. The primary transfer roller 5YA is opposed to the image carrier 1Y with the intermediate transfer member 7 interposed therebetween, and is in sliding contact with the inner surface of the intermediate transfer member 7. The DC power supply 5YE is grounded.

  The primary transfer means 5M for transferring a magenta color image includes a primary transfer roller 5MA and a DC power source 5ME for applying a voltage to the primary transfer roller 5MA. The primary transfer roller 5MA faces the image carrier 1M through the intermediate transfer member 7 and is in sliding contact with the inner surface of the intermediate transfer member 7. The DC power source 5ME is grounded.

  The primary transfer means 5C for transferring a cyan image is composed of a primary transfer roller 5CA and a DC power source 5CE for applying a voltage to the primary transfer roller 5CA. The primary transfer roller 5 </ b> CA faces the image carrier 1 </ b> C via the intermediate transfer body 7 and is in sliding contact with the inner surface of the intermediate transfer body 7. The DC power supply 5CE is grounded.

  The primary transfer means 5K for transferring a black image is composed of a primary transfer roller 5KA and a DC power supply 5KE for applying a voltage to the primary transfer roller 5KA. The primary transfer roller 5KA is opposed to the image carrier 1K through the intermediate transfer member 7 and is in sliding contact with the inner surface of the intermediate transfer member 7. The DC power supply 5KE is grounded.

  A current value of 40 μA and a voltage value of +1.5 kV are applied to the DC power supplies 5YE, 5ME, 5CE, and 5KE of the primary transfer units 5Y, 5M, 5C, and 5K.

  Further, the primary transfer units 5Y, 5M, 5C, and 5K are moved by a driving unit (not shown) and retracted away from the inner surface of the intermediate transfer body 7 except during the primary transfer.

[Secondary transfer means]
The secondary transfer unit 8 includes a backup roller 75, a secondary transfer roller 8A, a DC power source 8E, and the like. The backup roller 75 made of a conductive material faces the secondary transfer roller 8 </ b> A through the intermediate transfer body 7 and is in sliding contact with the inner surface of the intermediate transfer body 7.

  The backup roller 75 is connected to a DC power source 8E that applies a DC voltage. A current value of 50 μA and a voltage value of +3 kV are applied to the DC power supply 8E of the secondary transfer unit 8. The DC power supply 8E transfers the residual toner attached to the secondary transfer roller 8A in contact with the intermediate transfer body 7 to the intermediate transfer body 7 by applying a reverse bias and cleans it.

  The backup roller 75 of the secondary transfer roller 8A has substantially the same configuration as the primary transfer rollers 5YA, 5MA, 5CA, and 5KA, and is in pressure contact with the inner surface side of the intermediate transfer body 7. The conductive backup roller 75 is formed by a roller body and an elastic layer formed on the surface of the roller body.

The intermediate transfer member 7 is a single layer or multilayer belt made of polyamide, polyimide, or the like, and has a volume resistivity of 10 ⁷ to 10 ¹² Ωcm.

  The intermediate transfer member 7 is secondarily transferred to the transfer material P by the secondary transfer unit 8 and then cleaned by passing through the cleaning unit 6A.

  The secondary transfer roller 8 </ b> A is moved by a driving unit (not shown) and retracted away from the surface of the intermediate transfer body 7 at times other than the secondary transfer.

[Image forming apparatus]
3 is a cross-sectional view showing the image forming unit 10 of the image forming apparatus. FIG. 3A is a front cross-sectional view of the image forming unit 10, and FIG. 3B is a view of the image carrier 1 and the transfer unit 9. It is a sectional side view.

  Around the image carrier 1, a charging unit 2, an exposure unit 3, a developing unit 4, a transfer unit 9, and a cleaning unit 6 are arranged in the order of the image forming process.

  The transfer unit 9 includes a transfer roller 9A, a DC power source 9E, and the like. The conductive transfer roller 9A is formed by a rotating shaft and an elastic layer formed on the surface of the rotating shaft. Both ends of the rotating shaft are rotatably supported by the bearing 9B. The DC power source 9E cleans the toner remaining on the transfer roller 9A in contact with the image carrier 1 by transferring it to the image carrier 1 by applying a reverse bias.

[Borderless transfer image]
FIG. 4 is a perspective view of the intermediate transfer member 7 and the transfer material P on which a borderless image is formed.

  The toner images formed in the image forming units 10Y, 10M, 10C, and 10K shown in FIGS. 1 and 2 and primarily transferred onto the intermediate transfer member 7 are intermediately transferred by a secondary transfer roller 8A connected to a DC power supply 8E. Secondary transfer is performed from the transfer body 7 to the transfer material P. The transfer material P on which the borderless toner image is formed by the secondary transfer is conveyed to the fixing device 11.

  On the other hand, the residual toner image Ta remaining on the intermediate transfer body 7 after the secondary transfer and the trailing edge toner that protrudes from the rear end portion of the transfer material and adheres to the secondary transfer roller 8A and then transferred onto the intermediate transfer body 7 The image Tb is attached on the intermediate transfer member 7 and removed by the cleaning unit 6A.

  The secondary transfer roller 8A is driven and rotated by the driving means 8B. The driving of the driving unit 8B is controlled by the control unit 8C.

  The first control unit of the control unit 8C transfers the toner image without a border on the transfer material P, and then transfers the trailing toner image Tb of the residual toner image Ta attached to the secondary transfer roller 8A to the intermediate transfer member 7. The line speed V1 of the secondary transfer roller 8A at the time of transfer is controlled to be faster than the line speed V2 of the intermediate transfer body 7 (V1> V2).

  Alternatively, the line speed V1 of the secondary transfer roller 8A is controlled to be slower than the line speed V2 of the intermediate transfer body 7 (V1> V2).

  By setting a speed difference that changes the relative speed between the line speed V1 of the secondary transfer roller 8A and the line speed V2 of the intermediate transfer body 7, the outer peripheral surface of the intermediate transfer body 7 and the secondary transfer roller 8A Friction due to the difference in peripheral speed is generated at the pressure contact position with the outer peripheral surface, and the rear end toner image Tb formed on the secondary transfer roller 8A is spread to reduce the amount of toner adhering per unit area. By transferring the rear end toner image Tb, the back surface contamination of the transfer material P due to the occurrence of contamination of the secondary transfer roller 8A is eliminated, and an image forming apparatus that obtains a high quality image is provided.

  3 is transferred onto the transfer material P, the rear end portion of the residual toner adhering to the transfer roller 9A is transferred to the image carrier 1 after the toner image on the image carrier 1 shown in FIG. At this time, the line speed V1 of the transfer roller 9A is controlled to be faster than the line speed V2 of the image carrier 1 (V1> V2). Alternatively, the second control unit of the control unit 8C controls the line speed V1 of the transfer roller 9A to be slower than the line speed V2 of the image carrier 1 (V1> V2).

  By setting a speed difference that changes the relative speed between the line speed V1 of the transfer roller 9A and the line speed V2 of the image carrier 1, the outer peripheral surface of the image carrier 1 and the outer peripheral surface of the transfer roller 9A are set. Friction due to the difference in peripheral speed is generated at the pressure contact position, and the rear end toner image Tb formed on the transfer roller 9A is spread to reduce the amount of toner adhering per unit area, and the rear end toner image Tb is applied to the image carrier 1. Is transferred, so that the back surface contamination of the transfer material P due to prevention of contamination of the transfer roller 9A is eliminated, and an image forming apparatus that obtains a high-quality image is provided.

[Secondary transfer roller control]
FIG. 5 is a block diagram showing the configuration of the control means of the secondary transfer means 8 according to the present invention. FIG. 6 is a flowchart showing the residual toner cleaning process in the present embodiment.

  Step 1: The size of the transfer material P is set in an operation unit (not shown) of the color image forming apparatus A.

  Step 2: A negative transfer bias is applied to the secondary transfer roller 8A.

  Step 3: In the operation unit (not shown) of the color image forming apparatus A, a borderless image forming mode is set.

  Step 4: The transfer material front end detection sensor PS disposed in the vicinity of the registration roller 26 detects the passage of the transfer material P at the front end.

  Step 5: The control means 8C predicts the timing from the front end passage to the rear end passage of the transfer material P by dividing the length L (see FIG. 4) of the transfer material P in the conveyance direction by the conveyance speed of the intermediate transfer body 7. . For example, when the transfer material P is A6 size, the time t1 for the transfer material P to pass is 477 ms.

  Step 6: The driving unit 8B rotates the secondary transfer roller 8A at a line speed V1 (440 mm / sec) for a time t2 (10 ms).

  Step 7: After the elapse of time t3 (550 ms), a positive voltage transfer bias is applied to the secondary transfer roller 8A by the DC power supply 8E, and the driving means 8B moves the secondary transfer roller 8A to the line speed V2 (73 mm / sec). Rotate at low speed for time t4 (60 ms).

  Step 8: The same control is performed for the subsequent transfer material P.

  Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In this embodiment, an image is formed by the color image forming apparatus A provided with the primary transfer means 5Y, 5M, 5C, 5K and the secondary transfer means 8 shown in FIG.

[Image formation conditions]
Image forming apparatus: Tandem-type full-color copier (Konica Minolta 8050 (registered trademark) modified machine, see FIG. 2), continuous copying speed: full-color mode, output 51 sheets per minute on A4-size image carrier 1Y, 1M, 1C 1K: Outer diameter φ60mm
Transfer line speed of transfer material P: 220 mm / sec
Developer: Carrier average particle size 20-60 μm, polymerization toner average particle size 3-7 μm
Charging means 2Y, 2M, 2C, 2K: charging voltage V0 is -700V (variable: standard values on the left)
Exposure means 3Y, 3M, 3C, 3K: semiconductor laser (wavelength 780 nm), image forming body surface potential Vi during exposure is -50V
Developing means 4Y, 4M, 4C, 4K: Development sleeve potential Vdc is -500 V (variable: standard value on the left), development bias voltage AC component Vac is 1 kVp-p rectangular wave (frequency 5 kHz)
Primary transfer rollers 5YA, 5MA, 5CA, 5KA: use of conductive roller, roller pressing 50N (Newton), transfer current 40 μA, transfer voltage +1.5 kV are applied. In this embodiment, the secondary transfer shown in FIG. 1 and FIG. An image was formed by the color image forming apparatus A provided with the means 8.

Secondary transfer means 8: a configuration in which the intermediate transfer member 7 is sandwiched between a backup roller 75 and a secondary transfer roller 8A. Both electric resistance values are 1 × 10 ⁷ Ω, and a predetermined current value is selected from a current value table in which a matrix is formed of temperature and humidity and a counter and applied.

Pressing force F: 50 N (Newton), transfer material conveyance direction nip width: 3 mm
Elastic layer of secondary transfer roller 8A: semiconductive NBR solid rubber (acrylonitrile butadiene rubber), volume resistance 4 × 10 ⁷ Ω, outer diameter φ40 mm,
Axial length of the elastic layer of the secondary transfer roller 8A: LA = 150 mm, LB = 250 mm, LC = 330 mm,
Intermediate transfer body 7: polyimide resin, seamless semiconductive belt (volume resistivity 10 ⁹ Ωcm), tension tension 50N, linear velocity 220 mm / sec,
Amount of toner adhering to the intermediate transfer member 7 after passing through the image carrier 1K and reaching the secondary transfer means 8: 10 g / M ²
The height of the toner on the intermediate transfer member 7 after passing through the image carrier 1K and reaching the secondary transfer means 8: 30 μm
Reverse bias application cleaning control for the secondary transfer roller 8A: During continuous printing, if the toner image is transferred from the rear end of the transfer material P to the secondary transfer roller 8A, 1 second (transfer) When the normal conveyance line speed V1 of the material P is 220 mm / sec (V1 = V2), the secondary transfer roller 8A having an outer diameter of 40 mm is rotated twice), and secondary transfer is performed by applying a positive polarity charge. The roller 8A is cleaned.

[Example 1]
In the image forming apparatus having the above configuration, when the secondary transfer is performed from the secondary transfer roller 8A to the transfer material P, the line speed V1 of the secondary transfer roller 8A is set to 440 mm / sec (the secondary transfer roller 8A having an outer diameter of 40 mm). In this case, the height of the toner on the secondary transfer roller 8A is about 10 μm. The height of the toner is about 10 μm because when the secondary transfer roller 8A has a normal line speed of 220 mm / sec (V1 = V2), the height of the toner on the secondary transfer roller 8A is about 20 μm. That is, the height of the trailing edge toner image Tb is about half, and the length of the trailing edge toner image Tb is doubled.

  With this configuration, cleaning is performed by applying a reverse bias to the secondary transfer roller 8A to form a borderless image on 1000 sheets of A6 size (147.5 mm × 105 mm) transfer material P. As a result, the secondary transfer roller 8A There were no problems such as dirt on the back surface of the transfer material P due to dirt.

[Example 2]
In the image forming apparatus having the above-described configuration, when residual toner is transferred from the secondary transfer roller 8A onto the intermediate transfer member 7 and cleaned, that is, when the trailing end toner image Tb passes through the nip portion of the secondary transfer. Only the line speed V1 of the secondary transfer roller 8A is switched from 220 mm / sec (V2) to 73 mm / sec (V1 <V2), and the secondary transfer from the secondary transfer roller 8A to the transfer material P is performed. In this configuration, a reverse bias is applied to the secondary transfer roller 8A to perform cleaning, and an edgeless image is formed on 1000 sheets of A6 size transfer material P. As a result, the transfer material P is stained by the secondary transfer roller 8A. There were no problems such as dirt on the back.

[Example 3]
In the image forming apparatus configured as described above, when the toner image is transferred from the intermediate transfer body 7 to the transfer material P, the line speed of the secondary transfer roller 8A is switched from 220 mm / sec to 440 mm / sec, and the secondary transfer roller 8A. When the secondary transfer from the secondary transfer roller 8A to the transfer material P is performed, the line speed of the secondary transfer roller 8A is switched to 73 mm / sec (V2) (V1> V2), and the secondary transfer from the secondary transfer roller 8A to the transfer material P is performed. . In this configuration, a reverse bias is applied to the secondary transfer roller 8A to perform cleaning, and an edgeless image is formed on 1000 sheets of A6 size transfer material P. As a result, the transfer material P is stained by the secondary transfer roller 8A. There were no problems such as dirt on the back.

  In this embodiment, an example in which an intermediate transfer belt is used as the intermediate transfer body 7 has been described. However, the present invention is also applicable to an apparatus using an intermediate transfer body of another shape (for example, an intermediate transfer drum). I can do it. In addition, the electrical characteristics, thickness, layer configuration, material, and the like of the intermediate transfer member 7 can be selected and used according to image forming conditions.

FIG. 3 is a cross-sectional view showing the overall configuration of the color image forming apparatus. FIG. 3 is a cross-sectional view illustrating a main part of the color image forming apparatus. FIG. 3 is a front sectional view and a side sectional view showing an image forming unit of the image forming apparatus. FIG. 3 is a perspective view of an intermediate transfer member and a transfer material on which a borderless image is formed. The block diagram which shows the structure of the control means of a secondary transfer means. 6 is a flowchart showing a cleaning process of residual toner.

Explanation of symbols

1, 1Y, 1M, 1C, 1K Image carrier 7 Intermediate transfer body 75 Backup roller 8 Secondary transfer means 8A Secondary transfer roller 8B Drive means 8C Control means 8E DC power supply 9 Transfer means 9A Transfer rollers 10, 10Y, 10M, 10C, 10K Image forming unit A Color image forming apparatus P Transfer material V1, V2 Line speed Ta Residual toner image Tb Rear end toner image

Claims (6)

An image forming unit that forms a toner image on an image carrier, and a transfer roller that transfers the toner image onto a transfer material. Residual toner attached to the transfer roller that contacts the image carrier is applied by applying a reverse bias. In the image forming apparatus for transferring and cleaning the image carrier,
When a toner image formed on the image carrier is transferred to the transfer material, and a rear end portion of residual toner attached to the transfer roller is transferred to the image forming surface of the image carrier. An image forming apparatus, wherein a transfer line speed of the transfer roller is controlled to be higher than an image forming line speed of the image carrier. An image forming unit that forms a toner image on an image carrier, and a transfer roller that transfers the toner image onto a transfer material. Residual toner attached to the transfer roller that contacts the image carrier is applied by applying a reverse bias. In the image forming apparatus for transferring and cleaning the image carrier,
When a toner image formed on the image carrier is transferred to the transfer material, and a rear end portion of residual toner attached to the transfer roller is transferred to the image forming surface of the image carrier. An image forming apparatus, wherein a transfer line speed of the transfer roller is controlled to be slower than an image forming line speed of the image carrier. An image forming unit that forms a toner image on an image carrier, and a transfer roller that transfers the toner image onto a transfer material. Residual toner attached to the transfer roller that contacts the image carrier is applied by applying a reverse bias. In the image forming apparatus for transferring and cleaning the image carrier,
When a toner image formed on the image carrier is transferred to the transfer material, and a rear end portion of residual toner attached to the transfer roller is transferred to the image forming surface of the image carrier. A first control unit that makes the transfer line speed of the transfer roller faster than the image forming line speed of the image carrier, and a first controller that makes the transfer line speed of the transfer roller slower than the image forming line speed of the image carrier. And an image forming apparatus. The image carrier is a photoconductor carrying an electrostatic latent image and a toner image, and the toner image carried on the photoconductor is transferred to the transfer material by the transfer roller, and the residual toner attached to the transfer roller The image forming apparatus according to claim 1, wherein the image is transferred to the photoconductor by the reverse bias application. The image carrier is an intermediate transfer member that primarily carries and carries the toner image formed by the image forming unit, and the toner image carried on the intermediate transfer member is transferred to the transfer material by the transfer roller. 5. The image forming apparatus according to claim 1, wherein residual toner attached to the transfer roller is transferred to the intermediate transfer member by applying the reverse bias. 6. The image forming apparatus according to claim 1, wherein the number of rotations of the transfer roller is controlled in accordance with the size of the transfer material.

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