JP2012123357A - Image forming apparatus and toner supply method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent toner from slipping through and prevent the fixation of toner to a photoreceptor drum.SOLUTION: An image forming apparatus according to an embodiment of the invention comprises: a first image forming unit; a second image forming unit having toner in which at least one of an abrasive amount and a lubricant amount is comparatively more than that of a developing device of the first image forming unit; a transfer body facing the first and second image forming units and conveying toner images transferred from an image carrier of each of the image forming units at the execution of a printing step; and a control unit for controlling so as to transfer a toner image from the image carrier of the second image forming unit to the transfer body at the timing other than that of the printing step, to reversely transfer the transferred toner image to the image carrier of the first image forming unit and to supply a cleaning unit with the reversely-transferred toner.

Description

  Embodiments described herein relate generally to an image forming apparatus using an electrophotographic process and a toner supply method.

  In order to form an image with good image quality, an image forming apparatus using a toner having a toner circularity close to a sphere and a small particle diameter is known. However, when a toner having a toner circularity close to a sphere and a small particle diameter is used, the cleaning performance of the residual transfer toner on the photosensitive drum is deteriorated, and the toner slips from the cleaning blade or the toner is transferred to the photosensitive drum. There are problems such as sticking.

JP 2007-114633 A

  The problem to be solved by the present invention is to prevent toner from slipping through and sticking of the toner to the photosensitive drum.

  In order to solve the above problems, an image forming apparatus according to an aspect of the present invention develops an image carrier and an electrostatic latent image formed on the image carrier to form a toner image on the image carrier. A first image forming unit having a cleaning unit for removing residual toner from the image carrier and the image carrier, and at least one of the image carrier, the amount of abrasive and the amount of lubricant of the first image forming unit. A developer that develops an electrostatic latent image formed on the image carrier and has a toner image on the image carrier having a larger amount of toner than the developer, and a cleaning that removes residual toner on the image carrier A second image forming unit having a portion, and a transfer member that faces the first and second image forming units and conveys a toner image transferred from each of the image carriers when the printing process is executed. The toner image is transferred from the image carrier of the second image forming unit at a timing other than the printing process. A controller that controls to transfer the toner image transferred to the transfer member, reversely transfer the transferred toner image to the image carrier of the first image forming unit, and supply the reversely transferred toner to the cleaning unit. And

1 is a configuration diagram illustrating an image forming apparatus according to a first embodiment. 1 is a configuration diagram illustrating an internal structure of an image forming apparatus according to a first embodiment. It is a figure which shows the toner characteristic of the image formation part of each color in 1st embodiment. It is a figure which shows the bias conditions at the time of normal printing of the image formation part in 1st embodiment. It is a figure which shows supply of the toner in 1st embodiment. It is a figure which shows the bias conditions at the time of reverse transfer of the image formation part of each color in 1st embodiment. 2 is a block diagram illustrating a control system of the image forming apparatus according to the first embodiment. FIG. It is a flowchart which shows the timing of reverse transfer in 1st embodiment. It is the flowchart 1 which shows the reverse transfer in 1st embodiment. 3 is a flowchart 2 showing reverse transfer in the first embodiment. FIG. 3 is a diagram illustrating reverse transfer of black toner to a yellow photosensitive drum in the first embodiment. FIG. 5 is a diagram illustrating reverse transfer of black toner to a cyan photosensitive drum in the first embodiment. FIG. 3 is a diagram illustrating reverse transfer of black toner to a magenta photosensitive drum in the first embodiment. FIG. 10 is a configuration diagram illustrating an internal structure of an image forming apparatus according to a second embodiment. It is a block diagram which shows the internal structure of the image forming apparatus in 3rd embodiment. It is a block diagram which shows the internal structure of the image forming apparatus in 4th embodiment. It is a block diagram which shows the internal structure of the image forming apparatus in 5th embodiment.

  Embodiments of an image forming apparatus will be described below with reference to the accompanying drawings.

(First embodiment)
In the first embodiment, in a tandem image forming apparatus, the toner characteristics of a specific image forming unit are different from the toner characteristics of other image forming units, and the toner of a specific image forming unit is used as another image forming unit. Reverse transfer to the photosensitive drum.

  FIG. 1 is a configuration diagram illustrating an image forming apparatus according to the first embodiment. The image forming apparatus is, for example, a multi-function peripheral (MFP), a printer, a copier, or the like. An example of MFP 100 in FIG. 1 will be described below.

  The MFP 100 includes an automatic document feeder (ADF) 12, an operation panel 13, a scanner unit 16, a printer unit 17, a paper feed unit (paper feed cassette) 18, and a paper discharge unit 40.

  The ADF 12 is provided on the document table so as to be openable and closable, and automatically conveys the document. The operation panel 13 includes an operation unit 14 having various keys and a touch panel type display unit 15.

  The scanner unit 16 is provided below the ADF 12 and reads a document sent by the ADF 12 or a document placed on the document table to generate image data. The scanner unit 16 is an example of a print document input unit. In addition to this, for example, a document created by a PC (Personal Computer) as an external terminal is received by an input unit including an external input I / F, and is used as image data. It is also possible to print.

  The paper supply unit 18 includes a plurality of cassettes 18A and 18B that store paper S of various sizes. The paper discharge unit 40 accommodates the discharged paper S on which an image has been formed.

  The printer unit 17 includes an image forming unit and a laser exposure device, which will be described later, and processes image data read by the scanner unit 16 and image data created by a PC or the like to form an image on the paper S (printing process). . The paper on which the image is formed by the printer unit 17 is discharged to the paper discharge unit 40. The printer unit 17 is a tandem color laser printer, for example, and scans the image carrier (photosensitive drum) of the image forming unit with a laser beam from the laser exposure device 19 to generate an image.

  The laser exposure device 19 includes a polygon mirror 19a, an imaging lens system 19b, and a mirror 19c, and scans the laser beam emitted from the semiconductor laser element in the axial direction of the photosensitive drum 22 (see FIG. 2).

  The printer unit 17, which will be described in detail later with reference to FIG. 2, includes black (K), yellow (Y), cyan (C), and magenta (M) image forming units 20 </ b> K, 20 </ b> Y, 20 </ b> C, and 20 </ b> M. The image forming units 20K, 20Y, 20C, and 20M are arranged below the intermediate transfer belt (transfer body) 21 in series in the above order from upstream to downstream in the moving direction of the intermediate transfer belt 21.

  A toner cartridge 2 (developer housing portion) that supplies toner to the developing devices 24K, 24Y, 24C, and 24M (see FIG. 2) is provided above the image forming portion 20. The toner cartridge 2 is adjacent to toner cartridges 2K, 2Y, 2C, and 2M of black, yellow, cyan, and magenta.

  A separation roller 36 for taking out the paper S in the paper feed cassettes 18A and 18B and a transport roller 37, between the paper feed unit 18 and the secondary transfer roller 34 in contact with the intermediate transfer belt 21 along the paper transport direction. A registration roller 38 is provided, and a fixing device 39 is provided downstream of the secondary transfer roller 34 in the sheet conveying direction.

  Further, a paper discharge unit 40 and a reverse conveyance path 41 are provided downstream of the fixing device 39. The paper S on which the toner image is fixed by the fixing device 39 is discharged to the paper discharge unit 40. The reverse conveying path 41 reverses the paper S and guides it in the direction of the secondary transfer roller 34, and is used when performing double-sided printing.

  FIG. 2 is an enlarged view of the printer unit 17 including the image forming units 20K, 20Y, 20C, and 20M. In the following description, since the image forming units 20K (black), 20Y (yellow), 20C (cyan), and 20M (magenta) of each color have the same configuration, the configuration and operation of the image forming unit 20K will be described as a representative. .

  The image forming unit 20K includes a photosensitive drum 22K that is an image carrier. Around the photosensitive drum 22K, a charging charger 23K, a developing device 24K, a primary transfer roller 25K, a cleaner 26K, and the like along the rotation direction t. A blade 27K is disposed. The exposure position of the photosensitive drum 22K is scanned by irradiating a laser beam modulated with image data corresponding to black from the laser exposure device 19 to form an electrostatic latent image on the rotationally driven photosensitive drum 22K. To do.

  The charging charger 23K of the image forming unit 20K uniformly charges the entire surface of the photosensitive drum 22K. The surface of the charged photosensitive drum is irradiated with the laser beam described above to form an electrostatic latent image. The toner supplied from the toner cartridge 2K is agitated by the agitating portion of the developing device 24K and is negatively charged. The developing device 24K supplies black toner (developer) to the photosensitive drum 22K by a developing roller to which a developing bias is applied. The electrostatic latent image on the photosensitive drum is developed (toner image) by the supplied developer. Through a primary transfer process described later, the cleaner 26K uses the blade 27K to remove toner (residual toner) that is not transferred to the transfer belt 21 and remains on the surface of the photosensitive drum 22K in the primary transfer process. .

  1 and 2, the endless intermediate transfer belt 21 moves cyclically, and for example, semiconductive polyimide is used from the viewpoint of heat resistance and wear resistance. The intermediate transfer belt 21 is stretched around the drive roller 31 and the driven rollers 32 and 33, and contacts the photosensitive drums 22K, 22Y, 22C, and 22M. A primary transfer voltage is applied to the position of the intermediate transfer belt 21 facing the photosensitive drum 22K by the primary transfer roller 25K, and the toner image on the photosensitive drum 22K is primarily transferred to the intermediate transfer belt 21 (1). Next transfer process). By this transfer step, the images of the respective colors are transferred onto the intermediate transfer belt 21, and a color transfer image (toner image) is formed.

  A secondary transfer roller 34 is disposed opposite to the driving roller 31 that stretches the intermediate transfer belt 21. When the sheet S passes between the intermediate transfer belt 21 and the secondary transfer roller 34, a secondary transfer voltage is applied to the sheet S by the secondary transfer roller 34, and the toner image on the intermediate transfer belt 21 is applied to the sheet S 2. Next transfer (secondary transfer process). A belt cleaner 35 for cleaning toner (residual toner) that has not been transferred to the paper S in the secondary transfer process is provided near the driven roller 33 of the intermediate transfer belt 21.

  FIG. 3 is a diagram illustrating toner characteristics of the image forming unit for each color. The toner characteristics are, for example, the amount of abrasive, the amount of lubricant, the toner particle size, the toner circularity, and the type of toner. The abrasive is formed of alumina, strontium titanate, silica or the like, and the lubricant is formed of zinc stearate or the like.

  As shown in FIG. 3, the toner characteristics of the black image forming section 20K located on the most upstream side in the moving direction of the intermediate transfer belt 21 are made different from the toner characteristics of the other image forming sections. The other image forming units are yellow, cyan, and magenta image forming units 20Y, 20C, and 20M. For example, (1) the amount of abrasive contained in the toner of the black image forming unit 20K is increased as compared with the other image forming units 20Y, 20C, and 20M. For example, the amount of abrasive contained in the toner of the black image forming unit 20K is 0.2 to 1.0 wt%, and the amount of abrasive in the other image forming units 20Y, 20C, and 20M is, for example, 0 to 0.05 wt%. And

  (2) The amount of lubricant contained in the toner of the black image forming unit 20K is increased as compared with the other image forming units 20Y, 20C, and 20M. For example, the amount of lubricant contained in the toner of the black image forming unit 20K is 0.2 to 1.0 wt%, and the amount of lubricant in the other image forming units 20Y, 20C, and 20M is, for example, 0 to 0.05 wt%. And

  (3) The toner particle size of the black image forming unit 20K is made larger than those of the other image forming units 20Y, 20C, and 20M. For example, the diameter is 6.0 to 8.0 μm. The toner particle diameters of the other image forming units 20Y, 20C, and 20M are set to 4.0 to 6.0 μm, for example.

  (4) The circularity of the toner in the black image forming unit 20K is made indefinite compared to the other image forming units 20Y, 20C, and 20M. For example, the circularity of the toner is set to 0.9 or less. The circularity of the toners of the other image forming units 20Y, 20C, and 20M is, for example, 0.95 or more, and toner that is nearly spherical is used.

  (5) The type of toner in the black image forming unit 20K is pulverized toner, and the type of toner in the other image forming units 20Y, 20C, and 20M is polymerized toner. The pulverized toner particles are non-uniform in size and shape, and the polymerized toner particles are characterized by a uniform size, a nearly spherical shape, and a small particle size.

  The toner characteristics of the black image forming unit 20K and the other image forming units 20Y, 20C, and 20M are selected and combined with the above-described abrasive amount, lubricant amount, toner particle size, toner circularity, and toner type. You may do it.

  Hereinafter, with reference to FIG. 4, the transition of the bias and toner during normal printing will be described. FIG. 4 is a diagram showing bias conditions during normal printing of the image forming unit.

  During normal printing, the photosensitive drum 22 is charged to −500 V by the charging charger 23. The non-printed portion (white background portion) is not exposed to the laser beam, and the developing bias is −400 V while maintaining the potential, so that the negatively charged toner does not transfer to the photosensitive drum 22. The printed part is exposed with a laser beam, and the potential is lowered to -100V. At this time, if the developing bias is −400 V, the negatively charged toner moves to the photosensitive drum 22. Further, the toner is transferred to the intermediate transfer belt 21 by the transfer nip at a transfer bias of 1000V.

  In the first embodiment, the toner of the black image forming unit 20K is periodically reverse-transferred and supplied to the other image forming units 20Y, 20C, and 20M having different toner characteristics from the black toner. For example, a fixed amount of black toner per unit number is supplied to the other image forming units 20Y, 20C, and 20M at the end of the print job. FIG. 5 is a diagram illustrating toner supply from the black image forming unit 20K to the other image forming units 20Y, 20C, and 20M.

  Hereinafter, a method of supplying toner from the black image forming unit 20K to the other image forming units 20Y, 20C, and 20M will be described. First, at a timing other than the printing process, black toner having different toner characteristics from the other image forming units 20Y, 20C, and 20M is transferred from the black image forming unit 20K to the intermediate transfer belt 21 (for example, solid printing). Other than the printing process is between papers or before image formation, after the end of a print job, when the power is turned on, or in standby. Next, the transfer bias of the image forming portions 20Y, 20C, and 20M of yellow, cyan, and magenta is opposite to that at the time of transfer in the primary transfer step (transfer of the toner image from the photosensitive drum to the intermediate transfer belt). With the transfer bias (reverse bias), the black toner on the intermediate transfer belt 21 is reversely transferred to the photosensitive drums 22Y, 22C, and 22M (transfer opposite to the primary transfer step) (reverse transfer step).

  FIG. 6 shows the bias condition of each image forming unit 20 when the black toner is reversely transferred to the photosensitive drums 22Y, 22C, and 22M. The potential of the photosensitive drum 22 of each color is −100V.

  First, toner transfer (development) to the photoconductive drum 22K and toner transfer (transfer) from the photoconductive drum 22K to the intermediate transfer belt 21 will be described. The development bias of the black image forming unit 20K is set to −400V, and the transfer bias is set to 1000V. When the developing bias is −400 V, the negatively charged toner is transferred to the −100 V photosensitive drum 22K. The toner transferred to the photosensitive drum 22K is further transferred to the intermediate transfer belt 21 in order to set the transfer bias to 1000V. The black toner transferred to the intermediate transfer belt 21 is conveyed downstream in the moving direction of the intermediate transfer belt 21 as shown in FIG.

  As shown in FIG. 6, the developing bias of the image forming units 20Y, 20C, and 20M other than black during the reverse transfer process is 0V, and each color is transferred from the developing units 24Y, 24C, and 24M to the photosensitive drums 22Y, 22C, and 22M. The toner does not migrate. The transfer bias of the yellow image forming unit 20Y is set to −400 V, and the black toner transferred to the intermediate transfer belt 21 upstream is transferred to the yellow photosensitive drum 22Y by 1/3 (reverse transfer). The 2/3 black toner that has not transferred to the yellow photosensitive drum 22Y remains on the intermediate transfer belt 21 and is conveyed downstream.

  When the transfer bias of the cyan image forming unit 20C is set to −400 V, the black toner that has not shifted to the yellow photosensitive drum 22Y upstream is shifted to 1/3 (reverse transfer) to the cyan photosensitive drum 22C. Here, 1/3 means 1/3 of the amount transferred to the intermediate transfer belt 21 in the black image forming unit 20K. The 1/3 black toner that has not transferred to the cyan photosensitive drum 22C remains on the intermediate transfer belt 21 and is conveyed downstream.

  Assuming that the transfer bias of the magenta image forming unit 20M is −400 V, the remaining black toner that has not shifted to the cyan photosensitive drum 22C upstream is transferred (reverse transfer) to the magenta photosensitive drum 22M.

  The black toner transferred to the yellow, cyan, and magenta photosensitive drums 22Y, 22C, and 22M is scraped off by the blades 27Y, 27C, and 27M of the respective colors. The yellow, cyan, and magenta blades 27Y, 27C, and 27M, for example, contain a large amount of abrasives and lubricants, and scrape off black toner having a large particle size, whereby each color toner onto the photosensitive drums 22Y, 22C, and 22M. Prevents sticking and deterioration of cleaning properties. That is, even if there is a toner having a small particle size remaining on the photosensitive drum without being scraped off by the blades 27 of each color during image formation and having a circularity close to a sphere, it contains a large amount of the above-mentioned abrasive and lubricant, and the particle size is small. It is scraped off with black toner that is large and irregular in roundness.

  FIG. 7 is a block diagram showing a control system of the MFP 100, and mainly shows a control system of the developing device 50.

  In FIG. 7, the control unit 101 includes a CPU, a memory (storage unit), and the like, and controls the operation of the entire MFP 100. An operation panel 13, a scanner unit 16, and a printer unit 17 are connected to the control unit 101, respectively. As shown in FIG. 2, the image forming unit 20 of the printer 17 includes a photosensitive drum 22 that is an image carrier, and around the photosensitive drum 22, a charging charger 23, a developing device 24, a primary transfer roller 25, and a cleaner 26. Etc. The controller 101 changes the bias of the developing device 24 (development bias) and the bias of the primary transfer roller 25 (transfer bias) in the primary transfer process and the reverse transfer process. For example, the number of printed sheets is counted by a memory included in the control unit 101, and black toner is transferred to the intermediate transfer belt 21 in accordance with the count, and then the photosensitive drum 22Y of the image forming unit other than black is transferred from the intermediate transfer belt 21. Control is performed so that the toners reversely transferred to 22C and 22M are supplied to the cleaning unit.

  Hereinafter, the timing of reverse transfer of the black toner will be described. FIG. 8 is a flowchart showing the timing of reverse transfer.

  First, in 1000, the number of printed sheets is set to 0, and in 1001, a development bias and a transfer bias for normal printing are applied to the paper S to perform printing. The number of printed sheets is counted in the memory of the control unit 101. The development bias during normal printing is set to −400V, and the transfer bias is set to 1000V.

  Next, in 1002, it is determined whether or not the number of printed sheets is 100. If the number of printed sheets is not 100 (No in 1002), it is determined in 1003 whether or not printing is finished. If printing is finished (Yes in 1003), the process is finished. If printing is not finished (No in 1003), the process returns to 1001, and normal printing is performed.

  If the number of printed sheets is 100 (Yes in 1002), the reverse transfer process is performed in 1004, the black toner is transferred to the intermediate transfer belt 21, and then the photosensitive drum 22Y of the image forming unit other than black. , 22C and 22M, the black toner on the intermediate transfer belt 21 is reversely transferred. After reverse transfer, the process returns to 1000, the count of the number of printed sheets is reset, the count is set to 0, and the process is repeated until the printing is completed at 1003 (Yes in 1003).

  In step 1002, it is determined whether the number of printed sheets is 100 or not. However, the number of counted sheets is not limited to 100, and may take other values. The method is not limited to the above-described method in which a constant amount of black toner per unit number is reversely transferred, and black toner may be reversely transferred every time a print job is completed. In addition, when printing 500 print sheets or more, for example, when printing 500 sheets or more, even when 500 sheets are printed even during the job, image formation is temporarily stopped and reverse transfer of black toner is performed. Image formation may be resumed.

  Next, reverse transfer will be described. 9 and 10 are flowcharts showing reverse transfer. First, in 1100, black toner is transferred to the intermediate transfer belt 21 from the black image forming unit 20 </ b> K. The amount of black toner transferred to the intermediate transfer belt 21 is, for example, about 3 cm in the transport direction of the toner transferred on the intermediate transfer belt 21 (the moving direction of the intermediate transfer belt 21). The development bias and transfer bias at this time are the same as those in normal printing.

  After the transfer of black toner, in 1101, it is determined whether or not the black toner T1 on the intermediate transfer belt 21 is in a position in contact with the yellow primary transfer roller 25Y. When the black toner T1 is in a position in contact with the yellow primary transfer roller 25Y (Yes in 1101), in 1102, the black toner T1 is reversely transferred to the yellow photosensitive drum 22Y. At the time of reverse transfer, the developing bias is set to 0 V, the yellow toner is not transferred to the photosensitive drum 22Y, the transfer bias is set to −400 V, and the black toner T1 is reversely transferred to the yellow photosensitive drum 22Y.

  FIG. 11 is a diagram illustrating reverse transfer of black toner to a yellow photosensitive drum. T1, T2, and T3 shown in FIG. 11 represent black toner transferred to the intermediate transfer belt 21 from the black image forming unit 20K. The transferred black toner is about 3 cm in the conveying direction of the transferred toner on the intermediate transfer belt 21, and the lengths of T1, T2, and T3 are about 1 cm, respectively. At the time of reverse transfer, the black toner T1 is reversely transferred to the yellow photosensitive drum 22Y, conveyed in the direction of the arrow u as the photosensitive drum 22Y rotates, and supplied to the blade 27Y.

  Next, in 1103 of FIG. 9, it is determined whether or not the black toner T1 has passed through the yellow primary transfer roller 25Y. If the black toner T1 does not pass through the yellow primary transfer roller 25Y (No in 1103), the process returns to 1102.

  If the black toner T1 has passed the yellow primary transfer roller 25Y (Yes in 1103), the reverse transfer of the black toner T1 to the yellow photosensitive drum 22Y is stopped in 1104. By changing the transfer bias at the time of reverse transfer from −400 V to 0 V, the reverse transfer of the black toner T1 to the yellow photosensitive drum 22Y is stopped.

  After the reverse transfer of the black toner T1 is stopped, in 1105, it is determined whether or not the black toner T2 on the intermediate transfer belt 21 is in a position in contact with the cyan primary transfer roller 25C. If the black toner T2 is not in contact with the cyan primary transfer roller 25C (No in 1105), the determination is repeated until contact.

  If the black toner T2 is in contact with the cyan primary transfer roller 25C (Yes in 1105), the black toner T2 is reversely transferred to the cyan photosensitive drum 22C in 1106 of FIG. FIG. 12 is a diagram illustrating reverse transfer of black toner to the cyan photosensitive drum 22C. At the time of reverse transfer, the developing bias is set to 0V, the cyan toner is not transferred to the photosensitive drum 22C, the transfer bias is set to −400V, and the black toner T2 is reversely transferred to the cyan photosensitive drum 22C. As shown in FIG. 12, the black toner T2 is reversely transferred to the cyan photosensitive drum 22C, conveyed in the direction of the arrow v as the photosensitive drum 22C rotates, and supplied to the blade 27C.

  In 1107 of FIG. 10, it is determined whether or not the black toner T2 has passed through the cyan primary transfer roller 25C. If the black toner T2 has not passed the cyan primary transfer roller 25C (No in 1107), the process returns to 1106.

  If the black toner T2 has passed the cyan primary transfer roller 25C (Yes in 1107), in 1108, the reverse transfer of the black toner T2 to the cyan photosensitive drum 22C is stopped. The reverse transfer of the black toner T2 to the cyan photosensitive drum 22C is stopped by changing the transfer bias at the time of reverse transfer from −400V to 0V.

  After the reverse transfer of the black toner T2 is stopped, in 1109, it is determined whether or not the black toner T3 on the intermediate transfer belt 21 is in a position in contact with the magenta primary transfer roller 25M. If the black toner T3 is not in contact with the magenta primary transfer roller 25M (No in 1109), the determination is repeated until contact.

  If the black toner T3 is in contact with the magenta primary transfer roller 25M (Yes in 1108), at 1110, the black toner T3 is reversely transferred to the magenta photosensitive drum 22M. FIG. 13 is a diagram illustrating reverse transfer of the black toner T3 on the intermediate transfer belt 21 to the magenta photosensitive drum 22M. At the time of reverse transfer, the developing bias is set to 0V, the magenta toner is not transferred to the photosensitive drum 22M, and the transfer bias is set to −400V, and the black toner T3 is transferred to the magenta photosensitive drum 22M in reverse. As shown in FIG. 13, the black toner T3 is reversely transferred to the magenta photosensitive drum 22M, conveyed in the direction of the arrow w along with the rotation of the photosensitive drum 22M, and supplied to the blade 27M.

  In 1111 of FIG. 10, it is determined whether or not the black toner T3 has passed through the magenta primary transfer roller 25M. If the black toner T3 does not pass through the magenta primary transfer roller 25M (No in 1111), the process returns to 1110.

  If the black toner T3 has passed the magenta primary transfer roller 25M (Yes in 1111), the reverse transfer of the black toner T3 to the magenta photosensitive drum 22M is stopped in 1112. By changing the transfer bias at the time of reverse transfer from −400 V to 0 V, the reverse transfer of the black toner T3 to the magenta photosensitive drum 22M is stopped.

  In the above description, the black toner is transferred to the intermediate transfer belt 21, divided into T1, T2, and T3, and reversely transferred to the photosensitive drums 22Y, 22C, and 22M of the respective colors. For example, the yellow transfer bias at the time of reverse transfer is -200 V, the cyan transfer bias is -300 V, the magenta transfer bias is -400 V, and black toner is applied to the photosensitive drums 22Y, 22C, and 22M for each color by 1/3. Reverse transfer may be performed.

  In the above description, when the number of printed sheets reaches 100, about 1 cm of black toner is transferred in the toner transfer direction of the intermediate transfer belt 21 to the one-color image forming unit. The width of the black toner transferred to the intermediate transfer belt 21 may be changed according to the number of printed sheets to start copying. For example, when the number of printed sheets reaches 500, about 5 cm of black toner may be transferred in the toner transfer direction of the intermediate transfer belt 21 to one color image forming unit.

  As described above, the first embodiment includes a large amount of abrasives and lubricants from the black image forming unit 20K, and has a large particle size and is transferred to the intermediate transfer belt 21, and the toner is yellow. When reaching the cyan and magenta image forming units 20Y, 20C, and 20M, a transfer bias opposite in polarity to that at the time of printing is applied to cause reverse transfer from the intermediate transfer belt 21 to each photosensitive drum 22, and to each blade 27. Supply toner. This black toner containing a large amount of abrasive or lubricant stays in the vicinity of the blade tip or is scraped off by the blade 27, thereby preventing the toner from slipping through the cleaning blade and fixing the toner to the photosensitive drum. Can do.

  When the amount of lubricant is large, there is a problem that the toner charge amount becomes unstable. In the first embodiment, the toner of the first image forming unit is black toner. If the amount of lubricant is increased with toners of color (yellow, cyan, magenta) and the development amount is decreased, the color of the color image may change and the influence may be significant. However, the black toner is less likely to affect the color, and the influence of increasing the amount of lubricant can be minimized.

  In addition, toner with a toner circularity close to a sphere and a small particle diameter can form an image with good image quality. In the first embodiment, in the yellow, cyan, and magenta image forming units, toner having a circularity of toner close to a sphere and a small particle diameter is used. That is, it is possible to prevent the deterioration of the cleaning property and prevent the toner from adhering to the photosensitive drum while forming an image with good image quality.

(Second embodiment)
In the second embodiment shown in FIG. 14, in the tandem image forming apparatus, the photosensitive drum of the black image forming unit 20K has a larger diameter than the photosensitive drums of the other image forming units. The toner characteristics of the black image forming unit 20K are different from those of the yellow, cyan, and magenta image forming units, and the toner of the black image forming unit is reversely transferred to the photosensitive drum of the other image forming unit. The difference from the first embodiment is that the photosensitive drum of the black image forming unit has a large diameter. In the figure, the same components as those in the first embodiment are denoted by the same reference numerals.

  FIG. 14 is a configuration diagram showing an internal structure of the MFP 100 according to the second embodiment. As shown in FIG. 14, the photosensitive drum 22K of the black image forming unit 20K has a large diameter.

  When the amount of the abrasive is large, the photosensitive drum that comes into contact with the toner containing a large amount of abrasive during normal printing may have a problem that the film of the photosensitive drum is scraped and the life is shortened. On the other hand, shortening the life can be prevented by increasing the diameter of the photosensitive drum 22K of the black image forming unit 20K.

  With the image forming apparatus having the above-described configuration, it is possible to prevent the toner from slipping through the cleaning blade and the toner from adhering to the photosensitive drum while forming an image with good image quality. In addition, shortening of the life of the photosensitive drum can be prevented.

(Third embodiment)
In the third embodiment shown in FIG. 15, in the tandem image forming apparatus, an image forming unit (0th image) which is not involved in printing an image on a sheet further upstream in the moving direction of the intermediate transfer belt of the black image forming unit. The toner of the 0th image forming unit has the same characteristics as the toner of the black image forming unit of the first embodiment. In the figure, the same components as those in the first embodiment are denoted by the same reference numerals.

  FIG. 15 is a configuration diagram showing the internal structure of the MFP 100 according to the third embodiment. In addition to the black, yellow, cyan, and magenta image forming units 20K, 20Y, 20C, and 20M, a 0th image forming unit 20T that is not involved in image formation for printing is provided. The 0th image forming unit 20T includes a photosensitive drum 22T, a charging charger 23T, a developing device 24T, and a blade 27T.

  The toner characteristics of the 0th image forming unit 20T are a pulverized toner which is an irregularly shaped toner containing a large amount of abrasive and lubricant, having a large particle size. On the other hand, the toner characteristics of the black, yellow, cyan, and magenta image forming portions are polymer toners that have a small amount of abrasive and lubricant, a small particle size, and a nearly spherical shape. As in the first embodiment, the amount of abrasive, the amount of lubricant, the toner particle size, the toner circularity, and the type of toner are not all different, but some may be selected and combined.

  Further, after printing 100 sheets, the toner may be transferred from the 0th image forming unit 20T by about 1 cm of the moving width of the intermediate transfer belt 21 and the image forming unit of each color. About 4 cm of toner is transferred from the 0th image forming unit 20T to the intermediate transfer belt 21, and the transferred toner is reversely transferred by about 1 cm to the photosensitive drum of the image forming unit of each color.

  With the image forming apparatus having the above-described configuration, it is possible to prevent toner from slipping through the cleaning blade and fixing the toner to the photosensitive drum while forming an image with better image quality.

(Fourth embodiment)
In the fourth embodiment shown in FIG. 16, in the tandem image forming apparatus, a polishing agent and a toner in each color image forming unit are used instead of the 0th image forming unit in the third embodiment. A supply unit configured to supply toner containing a large amount of at least one of the lubricants; In the figure, the same components as those in the first embodiment are denoted by the same reference numerals.

  FIG. 16 is a block diagram showing the internal structure of the MFP 100 in the fourth embodiment. A supply unit 30 is provided upstream of the moving direction (toner transport direction) of the intermediate transfer belt 21 of each color image forming unit 20K, 20Y, 20C, 20M. That is, the supply unit 30 is arranged at a position where the 0th image forming unit of the third embodiment is provided.

  The supply unit 30 is formed of, for example, a rotatable brush or roller. The supply unit 30 supplies toner containing a large amount of at least one of an abrasive and a lubricant little by little while rotating in a state where the supply unit 30 is always in contact with the intermediate transfer belt 21. The toner supplied from the supply unit 30 is used only for cleaning the photosensitive drums 22 of the respective colors.

  The brush or roller of the supply unit 30 may always be in contact with the intermediate transfer belt 21 as described above, or may be moved by a solenoid and supplied at the end of each job. For example, at the end of the job, the solenoid is turned on, the supply unit 30 is raised, and is brought into contact with the intermediate transfer belt 21. After the supply, the solenoid is turned off and the supply unit 30 is lowered.

  Further, after printing 100 sheets, the moving width of the intermediate transfer belt 21 and the image forming portions of the respective colors may be supplied for about 1 cm.

  With the image forming apparatus having the above-described configuration, it is possible to prevent toner from slipping through the cleaning blade and fixing the toner to the photosensitive drum while forming an image with better image quality. Further, as compared with the 0th image forming unit of the third embodiment, the supply unit does not take up space and can be downsized.

(Fifth embodiment)
In the fifth embodiment shown in FIG. 17, when changing from a tandem color image forming apparatus to a monochrome image forming apparatus, two image forming portions are left instead of one, and the intermediate transfer belt moves. The image forming unit upstream in the direction is defined as the 0th image forming unit of the third embodiment. In the figure, the same components as those in the first embodiment are denoted by the same reference numerals.

  FIG. 17 is a configuration diagram showing the internal structure of the MFP 100 according to the fifth embodiment. For example, the upstream image forming unit is a 0th image forming unit 20T, and the downstream image forming unit is a black image forming unit (black toner) 20K. Not only the black toner but also a different color may be used.

  The toner characteristics of the 0th image forming unit 20T include a large amount of an abrasive and a lubricant as compared with the toner of the image forming unit 20K. On the other hand, the toner characteristics of the image forming unit 20K are polymerized toners having a small amount of an abrasive and a lubricant, a small particle size, and a nearly spherical shape. As in the first embodiment, the amount of abrasive, the amount of lubricant, the toner particle size, the toner circularity, and the type of toner are not all different, but some may be selected and combined.

  In the above embodiment, after printing 100 sheets, the toner may be transferred to the intermediate transfer belt 21 from the 0th image forming unit 20T by the moving width of the intermediate transfer belt 21 and about 1 cm of the image forming unit 20K. .

  With the image forming apparatus having the above-described configuration, it is possible to prevent toner from slipping through the cleaning blade and fixing the toner to the photosensitive drum while forming an image with better image quality. Further, when changing from a tandem color image forming apparatus to a monochrome image forming apparatus, the image forming unit is left as one and changed to the 0th image forming unit, thereby enabling cost reduction. .

  Although several embodiments have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the gist of the invention, and in the invention described in the claims and the equivalents thereof.

12 Automatic Document Conveying Section 13 Operation Panel 14 Operation Section 15 Display Section 16 Scanner Section 17 Printer Section 18 Paper Feed Cassette 20 Image Forming Section 21 Intermediate Transfer Belt (Transfer)
22 Photosensitive drum (image carrier)
23 Charger 24 Developer 25 Primary transfer roller 26 Cleaner 27 Blade 100 Image forming apparatus 101 Control unit

Claims (11)

The image carrier, a developing unit that develops the electrostatic latent image formed on the image carrier and forms a toner image on the image carrier, and a first cleaning unit that removes residual toner from the image carrier An image forming unit;
An electrostatic latent image formed on the image carrier having at least one of the image carrier, the amount of abrasive, and the amount of lubricant having a larger amount of toner than the developer of the first image forming unit. A developing unit for developing and forming a toner image on the image carrier, a second image forming unit having a cleaning unit for removing residual toner on the image carrier;
A transfer member that faces the first and second image forming units and conveys a toner image transferred from each of the image carriers when the printing process is performed;
At a timing other than the printing process, the toner image is transferred from the image carrier of the second image forming unit to the transfer member, and the transferred toner image is reversely transferred to the image carrier of the first image forming unit. A control unit for controlling the reversely transferred toner to be supplied to the cleaning unit;
An image forming apparatus comprising:   The color of the toner of the second image forming unit is black, and the second image forming unit is upstream of the first image forming unit in the toner image conveyance direction by the transfer body. The image forming apparatus according to claim 1.    The image forming apparatus according to claim 1, wherein a plurality of the first image forming units are arranged along a toner image conveying direction of the transfer body.   The image carrier of the first and second image forming units is a photosensitive drum, and the photosensitive drum of the second image forming unit has a larger diameter than the photosensitive drum of the first image forming unit. The image forming apparatus according to claim 1.   The control unit includes a storage unit that counts the number of printed sheets, and when the count number is equal to or greater than a threshold value in the storage unit, the toner image transferred from the image carrier of the second image forming unit to the transfer member The image forming apparatus according to claim 1, wherein the image is reversely transferred to an image carrier of the first image forming unit.   3. The image formation according to claim 1, wherein the toner of the developing unit of the second image forming unit has a toner particle size larger than the toner of the developing unit of the first image forming unit. apparatus.   7. The image forming apparatus according to claim 1, wherein the toner of the developing unit of the second image forming unit has a smaller circularity of the toner than the toner of the developing unit of the first image forming unit. . An image carrier having a developing unit that develops an electrostatic latent image formed on the image carrier and forms a toner image on the image carrier, and a cleaning unit that removes residual toner from the image carrier. When,
A transfer member that faces the image forming unit and conveys a toner image transferred from an image carrier of the image forming unit when performing a printing process;
Compared with the toner of the developing device of the image forming unit, the supply unit has a toner containing a lot of at least one of an abrasive and a lubricant, and supplies the toner to the rotating body;
Control to supply toner from the supply unit to the transfer body at a timing other than the printing process, reversely transfer the supplied toner to the image carrier of the image forming unit, and supply the reversely transferred toner to the cleaning unit. A control unit,
An image forming apparatus comprising:   The image forming apparatus according to claim 8, wherein a plurality of the image forming units are arranged along a toner image conveying direction of the transfer body. A first image forming unit having toner, a second image forming unit having a toner containing more of at least one of an abrasive and a lubricant than the toner of the first image forming unit, and a transfer body. Image forming device
A toner supply method, wherein the toner of the second image forming unit is supplied to the first image forming unit via the transfer body at a timing other than the printing process. By an image forming apparatus comprising: an image forming unit having toner; a supply unit having a toner containing more of at least one of an abrasive and a lubricant than toner in the image forming unit; and a transfer body.
A toner supply method comprising: supplying toner from the supply unit to the image forming unit via the transfer body at a timing other than a printing process.

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