JP2005077576A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which ensures the formation of sharp images for a long time by preventing image flows caused on photoreceptor drums from overlapping on recording paper. <P>SOLUTION: When an image forming process is not performed, an operation control means executes a rotating operation in which the photoreceptor drums are rotated such that the photoreceptor drums are different from each other in phase at the end of rotation with reference to phase at the initiation of the rotation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a fax machine using an electrophotographic system. More specifically, the present invention relates to an image forming apparatus in which a plurality of process units having photosensitive drums are arranged along the operation direction of an endless belt.

In particular, in an image forming apparatus using a photosensitive drum on which an amorphous silicon photosensitive layer is formed, there is a problem that a phenomenon called image flow occurs such as an image fading depending on the use environment.
The cause of the image flow is that moisture in the air is adsorbed on the surface of the photosensitive drum and the surface electrical resistance decreases, and the electric charge of the formed electrostatic latent image flows in the circumferential direction, causing the potential to drop or the boundary. This is because it becomes unclear.

  Further, ozone is generated by the discharge of the charger that charges the surface of the photosensitive drum, and the components in the air are decomposed by the ozone, and ion products such as NOx and SOx are generated. Since this ion product is water-soluble, it is considered that the ion product adhering to the surface of the photosensitive drum takes in moisture in the air and the above-described image flow is likely to occur.

  In order to remove impurities such as ion products on the surface of the photosensitive drum as described above, image formation is configured such that the surface of the photosensitive drum can be polished with an abrasive-containing toner containing an abrasive such as titanium oxide. An apparatus is known (see, for example, Patent Documents 1 and 2).

JP 2000-162937 A JP 2003-5581 A

However, ion products such as NOx and SOx generated near the charger and adhering to the surface of the photosensitive drum are in a structure having a roughness of about 0.1 μm in a portion facing the charger on the surface of the photosensitive drum. In order to enter, there is a case where the degree of image flow becomes severe at that portion.
Therefore, such an image flow tends to appear remarkably on the surface of the photosensitive drum at a position facing the charger when the image forming process is completed.

  In the tandem type color image forming apparatus in which a plurality of process units are arranged, a configuration is adopted in which the rotational phases of the respective photosensitive drums are intentionally matched in order to prevent a shift at the time of color superimposition due to uneven rotation of the photosensitive drums. Therefore, the toner image of the portion that is stopped facing the charger on the surface of each photoconductive drum is transferred to the same position on the recording paper, and the image flow of that portion is superimposed, thereby degrading the image accuracy. There's a problem.

  The present invention has been made in view of the above problems, and an object of the present invention is to prevent an image flow of each photosensitive drum on a recording sheet from being superimposed and form a clear image over a long period of time. Is to provide

In order to achieve the above object, a first characteristic configuration of an image forming apparatus according to the present invention is an image forming apparatus in which a plurality of process units having photosensitive drums are arranged along the operation direction of an endless belt,
During non-image forming processing, a rotation operation is performed to rotate each photoconductor drum so that the phase of each photoconductor drum at the end of rotation with respect to the start of rotation is different for each photoconductor drum. In the point.

  According to the first characteristic configuration described above, the operation control means including a computer or the like executes the rotation operation during a predetermined rotation operation period during the non-image forming process so that the phases of the photosensitive drums are different from each other. As a result, the portions of the surface of the photosensitive drum that are located at the position facing the charging unit at the start of the rotation operation and are liable to cause image flow are different from each other at the end of the rotation operation, and during image formation processing after the rotation operation is performed. In this case, the image flows of the respective photoconductive drums can be generated at different positions on the recording paper so that the image flows of the respective photoconductive drums can be prevented from being superimposed on the recording paper. Can be formed.

  The rotation operation period indicates a part or all of the period during the non-image forming process. For example, the rotation operation period includes a period after the image forming process is finished and the charging unit is stopped, It can be a period when the power is turned off or when the power is turned on, a period provided for a certain time or every certain number of printed sheets, and the like.

In order to achieve the above object, a second characteristic configuration of the image forming apparatus according to the present invention includes a black process unit using black toner and a color process unit using color toner as the plurality of process units. Prepared,
Belt separation means capable of separating the belt from the color photosensitive drum of the color process unit;
In the rotation operation, during the non-image forming process of the color process unit, the color photosensitive drum is rotated in a state where the belt is separated from the color photosensitive drum by operating the belt separation unit. The phase of the photosensitive drums is different from each other.

  According to the second characteristic configuration, the black photosensitive drum is not subject to the rotation operation, but only the other color photosensitive drums are subject to the rotation operation, and further, the color photosensitive drum by the belt separating means. By rotating the color photosensitive drum with a rotation operation in a state where the belt is separated from the belt, for example, when a black-and-white image forming process for forming an image only with the black photosensitive drum is performed in another color photosensitive drum As the non-image forming process, the color photosensitive drums can be rotated during the monochrome image forming process so that the phases of the photosensitive drums are different from each other.

  According to a third characteristic configuration of the image forming apparatus according to the present invention, in addition to the first or second characteristic configuration, in the rotation operation, the photosensitive drums are intermittently rotated at equal intervals for each set rotation angle. In the first rotation, the set rotation angle of each photoconductor drum is set so that the phases of the respective photoconductor drums are different from each other. In the second and subsequent rotations, the set rotation angle of each photoconductor drum is set. Are set equal to each other.

  According to the third characteristic configuration described above, in the rotation operation in which the respective photosensitive drums are intermittently rotated at each set rotation angle, the set rotation angles of the respective photosensitive drums are different from each other at, for example, less than 360 ° in the first rotation. By setting the angle, the phases of the respective photosensitive drums can be surely made different from each other, and in the second and subsequent rotations, by setting the set rotation angles of the respective photosensitive drums to be equal to each other, Different phases of the photosensitive drum can be maintained.

  According to a fourth characteristic configuration of the image forming apparatus of the present invention, in addition to any one of the first to third characteristic configurations, in the rotation operation, the phases of the photosensitive drums are made different from each other. The photosensitive drums start to rotate at different starting times, and the photosensitive drums are rotated at the same rotational speed.

  According to the fourth characteristic configuration, when the rotation operation is performed on each photoconductor drum, the rotation of each photoconductor drum is started at a different start time, thereby reliably The phases of the photosensitive drums can be made different from each other, and by maintaining the rotational speeds of the photosensitive drums equal to each other, the phases of the photosensitive drums can be kept different until the photosensitive drums are simultaneously stopped. it can.

Embodiments of the present invention will be described with reference to the drawings.
First, the configuration of the color image forming apparatus will be described with reference to FIGS.

  The image forming apparatus 50 using the intermediate transfer belt 16 has a plurality of process units 21 (21A, 21B, 21C, 21D) as image forming units arranged side by side on an endless intermediate transfer belt 16 that performs intermediate transfer. Further, a secondary transfer roller 17 is provided on the downstream side in the operation direction of the intermediate transfer belt 16 to transfer the toner primarily transferred onto the intermediate transfer belt 16 to the recording paper 15, and further on the downstream side, the transfer residue of the intermediate transfer belt 16 is transferred. A cleaning means 19 for cleaning the toner with a fur brush is arranged.

In FIG. 2, each process unit 21 is arranged in order from the most upstream side along the operation direction of the intermediate transfer belt 16, the black process unit 21A, the cyan process unit 21B, the magenta process unit 21C, and the yellow process unit. 21D.
In this embodiment, when identifying and explaining a device provided in the black process unit 21A, the cyan process unit 21B, the magenta process unit 21C, or the yellow process unit 21D, The name is prefixed with “Black”, “Cyan”, “Magenta”, or “Yellow”, and “A”, “B”, “D”, or “D” at the end of the code. Is attached.
Further, in distinction from “for black”, “for cyan”, “for magenta”, or “for yellow” may be referred to as “for color”.

  As shown in FIG. 1, each process unit 21 arranged in the image forming apparatus 50 includes a charger 5 as a charging unit that uniformly charges the surface of the photosensitive drum 1 around the photosensitive drum 1. , Exposure means (not shown) for forming an electrostatic latent image on the photosensitive drum 1, and developing means for transferring the toner to the surface of the photosensitive drum 1 to develop the electrostatic latent image on the surface of the photosensitive drum 1. A developing roller 4, a transfer roller 3 for transferring a toner image on the photosensitive drum 1 onto the intermediate transfer belt 16, a cleaner 7 for cleaning residual toner on the photosensitive drum 1 by a cleaning blade 8, and the photosensitive drum 1. Each of the static eliminators 6 for neutralizing the top is provided.

  The photoreceptor drum 1 has a photoreceptor having a thickness of 10 to 25 μm including an amorphous silicon photosensitive layer on the surface. That is, the photosensitive drum 1 is configured by providing a photosensitive member formed by sequentially laminating a blocking layer, an amorphous silicon (a-Si) photosensitive layer, and a surface protective layer on a base material. . The material for the photosensitive layer of the photosensitive drum 1 is not particularly limited. As the amorphous silicon, for example, an inorganic material such as a-Si, a-SiC, a-SiO, or a-SiON can be used.

  Further, the thickness t of the surface protective layer is 0.3 to 5 μm. Moreover, as a material of a surface protective layer, it is desirable to use a specific ratio of Si (silicon) and C (carbon) among a-SiC. As such a-SiC, a-Si (1-x) CX (0.3 ≦ X <1.0) is preferable, and further, a-Si (1-X) CX (0.5 ≦ X ≦ 1.0). 0.95) is more preferable. The reason is that such a-SiC has a particularly high resistance value of 1012 to 1013 Ω · cm, and an excellent saturation charging potential, wear resistance, and environmental resistance (humidity resistance) can be obtained. is there.

  The developing device 4 is provided with a developing roller 9. The developing device 4 contains a non-magnetic toner and a carrier, and is configured to be stirred by a stirring means (not shown). The non-magnetic toner has an average particle size of 9 μm and is configured to be positively charged in the developing device. The photosensitive drum 1 is disposed so as to face the developing roller 9.

  The cleaner 7 is provided with a cleaning blade that collects toner adhering to the surface of the photosensitive drum 1 and a rubbing roller 10 that functions as a rubbing means for rubbing the surface of the photosensitive drum 1. The rubbing roller 10 is urged against the surface of the photosensitive drum 1 by a spring, can be driven to rotate with the photosensitive drum 1, and is further stopped by the clutch 12, thereby sliding the photosensitive drum 1. It is configured to be rubbed.

  The transfer roller 3 is disposed opposite to the surface of the photosensitive drum 1 via the intermediate transfer belt 16, and a negative DC voltage of −300 V to −1000 V is applied while the intermediate transfer belt 16 is pressed against the surface of the photosensitive drum 1. Accordingly, the toner image on the photosensitive drum 1 is transferred to the intermediate transfer belt 16.

  The transfer roller 3 described above is configured to be movable to a position that is in close contact with and separated from the photosensitive drum 1 by a cam mechanism 22 as a belt separating means. Then, the intermediate transfer belt 16 tensioned in the direction away from the photosensitive drum 1 is moved from the photosensitive drum 1 by moving the transfer roller 3 to a position away from the photosensitive drum 1 by the cam mechanism 22. The photosensitive drum 1 can be rotated regardless of the operation of the intermediate transfer belt 16. For example, at the time of color image forming processing, as shown in FIG. 2A, all the transfer rollers 3 are placed in close contact with the photosensitive drums 1, and the intermediate transfer belt 16 is brought into close contact with all the photosensitive drums 1, so At the time of the image forming process, as shown in FIG. 2B, the color transfer rollers 3B, 3C, and 3D are placed at positions separated from the photosensitive drums 1B, 1C, and 1D, and the black transfer roller 3A is set to the photosensitive drum. As the position close to 1A, the intermediate transfer belt 16 is brought into close contact with only the black photosensitive drum 1A, and the color photosensitive drums 1B, 1C, and 1D are not related to the operation of the intermediate transfer belt 16 by the monochrome image forming process. Can be rotated freely.

  The secondary transfer roller 17 is disposed so as to face the driven roller 12 via the intermediate transfer belt 16, and the recording paper 15 supplied between the secondary transfer roller 17 and the intermediate transfer belt 16 is pressed against the intermediate transfer belt 16 while being −300 V to By applying a negative DC voltage of −2500 V, the toner primarily transferred onto the intermediate transfer belt 16 is collectively transferred onto the recording paper 15.

  The secondary transfer roller 17 and the transfer roller 3 are formed by rolling foamed EPDM that is impregnated with carbon to adjust resistance.

  The cleaning unit 19 is arranged to face the driving roller 11 and is configured to remove residual toner on the intermediate transfer belt 16 by applying a reverse bias to the fur brush.

  FIG. 3 is a block diagram for controlling the operation of the image forming apparatus. The input terminal of the control circuit 31 is connected to temperature / humidity detection means 30 for detecting the temperature in the apparatus and the humidity in the apparatus, and temperature / humidity data. A storage means 37 for storing a grouped table or the like corresponding to is connected. The output end of the control circuit 31 is connected to a drive circuit 32 that drives each drive unit. The drive circuit 32 is a drum drive means 33 that rotates the photosensitive drum 1 and an intermediate transfer belt 16 (or a conveyance belt described later). 2) is connected to a belt driving means 34, a recording paper driving means 35, a process unit driving means 36, and the like.

Next, a description will be added regarding the image forming process.
The toner in the developing device 4 is frictionally charged by the image formation start signal from the control circuit 31 and adheres to the surface of the carrier, and a magnetic brush is formed on the surface of the magnetic roller (not shown) by the carrier. A thin layer of toner is formed.

  The charging of the photosensitive drum 1 by the charger 5, exposure to the photosensitive drum 1 by an image signal from the exposure device, and the electrostatic latent image so that the intermediate transfer belt 16 reaches the photosensitive drum 1 of each color. When the electrostatic latent image is developed with toner on the developing roller 9 and the intermediate transfer belt 16 reaches the photosensitive drum 1, a reverse bias of reverse polarity is applied to the transfer roller 3, and the intermediate transfer belt 16 is applied. Different color toner images are successively transferred in color.

Specifically, the surface of the photosensitive drum 1 is uniformly charged to +250 V by the charger 5, and an electrostatic latent image is formed by exposure means (not shown).
On the other hand, a developing bias (positive bias) that is a rectangular wave having an amplitude of 1.1 KV, a frequency of 3.0 Hz, and a DUTY ratio of 45% is applied to the developing roller 9 disposed in a non-contact state with the photosensitive drum 1. A toner thin layer is formed on the surface of the developing roller 9 with toner.
Then, the toner in the thin toner layer of the developing roller 9 flies according to the electrostatic latent image formed on the surface of the photosensitive drum 1, and the electrostatic latent image becomes a toner image and is developed.

  In the present application, applying a positive bias means applying a voltage having the same polarity as the toner charging polarity, and applying a reverse bias means applying a voltage having a polarity opposite to the charging polarity of the toner. is there.

A reverse bias is applied to the transfer roller 3 that presses the intermediate transfer belt 16 against the surface of the photosensitive drum 1, and the developed toner image on the surface of the photosensitive drum 1 is transferred to the intermediate transfer belt 16.
The black, cyan, magenta, and yellow toner images formed in each process unit 21 in this way are sequentially superimposed and transferred onto the intermediate transfer belt 16, and are collectively transferred onto the recording paper 15 by the secondary transfer roller 17. The

Similarly, a reverse bias is applied to the secondary transfer roller 17 that presses the recording paper 15 against the intermediate transfer belt 16, and the toner image on the intermediate transfer belt 16 is transferred to the recording paper 15.
In other words, the recording paper 15 conveyed from a paper feed cassette (not shown) is conveyed between a secondary transfer roller 17 and an intermediate transfer belt 16 that are disposed opposite to the driven roller 12 via the intermediate transfer belt 16, and is intermediate. The color toner image on the transfer belt 16 is transferred, fixed by a fixing device (not shown), and discharged.

  A reverse bias is applied to the cleaning unit 19, and residual toner on the intermediate transfer belt 16 is removed by a fur brush.

  Next, the rotation operation of the photosensitive drum 1 during the non-image forming process will be described.

  The image forming apparatus 50 is configured to execute a rotation operation for rotating the photosensitive drum 1 by the control circuit 31 during the non-image forming process in which the charger 5 is stopped.

During the non-image forming process, a period immediately after the image forming process is terminated and the charger 5 is stopped, a sleep period after a certain period of time has elapsed after the charger 5 is stopped, A period when the power is turned on, a period provided for a certain period of time or every certain number of printed sheets, and the like are set as the rotation operation period.
In the rotation operation period, the control circuit 31 performs a rotation operation for rotating the photosensitive drum 1 while moving the transfer roller 3 in a direction away from the photosensitive drum 1 by the cam mechanism 22. Impurities that float near the surface of the photosensitive drum 1 are prevented from adhering to the surface of the photosensitive drum 1.

For the cyan photosensitive drum 1B, the magenta photosensitive drum 1C, and the yellow photosensitive drum 1D, the black and white image forming process in which only the black process unit 21A is operated is defined as the rotation operation period. A rotating operation can be performed.
That is, during the monochrome image forming process, as shown in FIG. 2B, only the cyan transfer roller 3B, the magenta transfer roller 3C, and the yellow transfer roller 3D are moved away from the photosensitive drum 1. The rotation operation may be performed on the cyan photosensitive drum 1B, the magenta photosensitive drum 1C, and the yellow photosensitive drum 1D.

  The control circuit 31 executes such a rotation operation until the rotation operation time elapses or until an image forming process start signal is input. At the end of the rotation operation, the photosensitive drum The rotation of the photosensitive drum 1 is stopped so that the posture of 1 is different from that at the start of the rotation operation. Therefore, the portion of the surface of the photosensitive drum 1 that was at the position facing the charger 5 at the start of the rotation operation is prevented from stopping at the position facing the charger 5 at the end of the rotation operation. The generated ion product is prevented from locally attaching to the surface of the photosensitive drum 1.

  In about 30 minutes after the charger 5 stops, the ozone concentration in the apparatus falls below the allowable level and the amount of ion products decreases. Therefore, the rotation operation can be started as soon as possible after the charger 5 stops. Preferably, the rotation operation time is set within a range of 20 minutes to 1 hour. That is, by setting the rotation operation time to 20 minutes or more, it is possible to suppress power consumption by setting the rotation operation time to 1 hour or less while suppressing the adhesion of ion products to the photosensitive drum 1. .

  The control circuit 31 is configured to intermittently rotate the photosensitive drum 1 for every set rotation angle, for example, every minute in the rotation operation in order to suppress waste of electric power.

Further, in the rotation operation for rotating the photosensitive drum 1 intermittently, the set rotation angle is set to an angle excluding a divisor of 360 ° within a range of less than 360 °.
That is, by setting the set rotation angle to such an angle, it is avoided that the same part of the surface of the photosensitive drum 1 stops at a position facing the charger 5 every rotation, and is generated near the charger 5. It is further suppressed that the ion product to be deposited locally adheres to the photosensitive drum surface 1.

  The control circuit 31 applies a reverse bias having a polarity opposite to the developing bias to the developing roller 9 of the developing unit 4 in order to suppress toner flying to the photosensitive drum 1 and prevent waste of the toner in the rotation operation. Is configured to do.

  Further, as described above, the reverse bias potential applied to the developing roller 9 in the rotation operation is set to 1/5 or less of the developing bias potential, thereby charging the low-charged or uncharged toner in the developing device 4. The toner is allowed to fly and adhere to the surface of the photosensitive drum 1, and further, an abrasive such as titanium oxide can be contained in the toner and used for a polishing process by a rubbing roller 10 described later.

  Further, it is preferable that the stirring means of the developing machine 4 is stopped during the rotation operation.

  Further, in the rotation operation, the control circuit 31 sets the photosensitive drums 1 so that the phases of the photosensitive drums 1 at the end of the rotation operation are different from each other for each photosensitive drum 1 with reference to the start of the rotation operation. It is configured to rotate.

  That is, at the end of the rotation operation, the phases of the respective photoconductive drums 1 are different from each other, so that the surface of each photoconductive drum 1 on the surface of the photoconductive drum 1 where the image flow is likely to occur at the position facing the charger 5 when the rotation operation starts. The portions are at different positions when the rotation operation ends. Therefore, during the image forming process after the rotation operation, the image flows by the respective photosensitive drums 1 are generated at different positions on the recording paper 15, and the image flows on the photosensitive drum 1 are superimposed on the recording paper 15. It is prevented.

  When the black and white image forming process in which the control circuit 31 performs the image forming process only with the black process unit 21A is the non-image forming process in which the color process units 21B, 21C and 21D are in the non-operating state, the black and white image forming process is performed. At the time of processing, the color transfer rollers 3B, 3C, 3D are moved to positions away from the color photosensitive drums 1B, 1C, 1D by the color cam mechanisms 22B, 22C, 22D, so that the intermediate transfer belt 16 is used for color. The color photosensitive drums 1B, 1C, and 1D are rotated independently of the operation of the intermediate transfer drum 16 while being separated from the photosensitive drums 1B, 1C, and 1D, and a rotating operation and a polishing process are executed. Can do.

Also, as shown in FIG. 4, the rotation start timing of each photoconductor drum 1 is shifted, and the phase of each photoconductor drum 1 is different at the end of the rotation operation.
That is, in the non-image forming process, the control circuit 31 does not start the rotation operations of the respective photosensitive drums 1 at the same time but sequentially starts them with different start times. That is, the yellow photosensitive drum 1D is first started to rotate intermittently, for example, every 50 °, and when the yellow photosensitive drum 1D rotates for the second time, the magenta photosensitive drum 1C is rotated every 50 °. When the magenta photoconductor drum 1C rotates for the second time, the cyan photoconductor drum 1B also starts to rotate intermittently every 50 °, and the black photoconductor When rotating the drum 1A as well, when the cyan photosensitive drum 1B is rotated for the second time, the black photosensitive drum 1B starts to rotate intermittently every 50 °. At the end of the rotation operation, the photosensitive drums 1 are stopped at a phase of 50 °.

In addition, as shown in FIG. 5, it is also possible to set different rotation angles in the rotation operation of the respective photosensitive drums 1 so as to be different from each other in the first rotation. The phase can be different.
That is, the control circuit 31 simultaneously starts the rotation operation of the respective photosensitive drums 1 in the non-image forming process, but only the set rotation angles of the respective photosensitive drums 1 in the first rotation are different from each other. Set. Specifically, the setting rotation angle in the first rotation of the yellow photosensitive drum 1D is set to 80 °, the setting rotation angle in the first rotation of the magenta photosensitive drum 1C is set to 70 °, and the yellow photosensitive drum 1D is rotated. The set rotation angle in the first rotation of the photosensitive drum 1B is set to 60 °, the set rotation angle in the first rotation of the black photosensitive drum 1A is set to 50 °, and the rotation operation of each photosensitive drum 1 is performed. The photosensitive drums 1 have a phase of 10 ° with each other at the end of the rotation operation by simultaneously starting the rotation of the photosensitive drums 1 and setting the set rotation angles in the second and subsequent rotations of the photosensitive drums 1 to 50 °. And then stop.

Next, the polishing process for the surface of the photosensitive drum 1 will be described.
The control circuit 31 is a polishing agent containing an abrasive on the surface of the photosensitive drum 1 for at least one rotation of the photosensitive drum 1 at a predetermined timing of the rotation operation in order to recover the sensitivity of the photosensitive drum 1. With the contained toner attached, the clutch 12 is operated to stop the rotation of the rubbing roller 10, and the surface of the photosensitive drum 1 is rubbed by the rubbing roller 10 to polish the surface of the photosensitive drum 1. Is configured to run.

  As the black toner held in the black process unit as the first process unit, an abrasive-containing black toner containing an abrasive such as titanium oxide is used, and the color process unit 21B as the other second process unit. , 21C, 21D does not contain an abrasive.

  Then, the control circuit 31 applies an abrasive-containing black toner containing an abrasive before performing the above polishing process on the color photoconductor drums 1B, 1C, and 1D as the second photoconductor drums. From the black process unit 21A, an abrasive-containing toner transfer operation for transferring and adhering to the surface of the color photosensitive drums 1B, 1C, 1D is executed.

  That is, in the abrasive-containing toner transfer operation, the control circuit 31 applies the abrasive-containing black toner held in the black process unit 21A to the black photosensitive drum 1A and the intermediate transfer belt 16 in the same manner as in a normal image forming process. After the transfer, a positive bias opposite to the normal image forming process is applied to the transfer roller 3 on the color process unit 21B, 21C, 21D side which receives the transfer of the abrasive-containing black toner, and the intermediate transfer belt 16 is applied. The abrasive-containing black toner is transferred to the surface of the color photosensitive drums 1B, 1C, and 1D.

  That is, the black toner-containing black toner transferred to the color photosensitive drums 1B, 1C, and 1D from the black developing device 4A to the intermediate transfer belt 16 through the black photosensitive drum 1A is sequentially transferred, A positive bias is sequentially applied to the color transfer rollers 3B, 3C, and 3D, and the abrasive-containing black toner sequentially transferred to the intermediate transfer belt 16 is transferred and supplied to the surfaces of the photosensitive drums 1B, 1C, and 1D.

  Further, the black process unit 21A having the abrasive-containing black toner is disposed on the upstream side of the other color process units 21B, 21C, and 21D along the operation direction of the intermediate transfer belt 16, so that the intermediate A color in which the abrasive-containing black toner transferred from the black photosensitive drum 1A onto the intermediate transfer belt 16 is subjected to the polishing process in a relatively short time while the transfer belt 16 is driven in the same direction as the image forming process. Can be transferred to the photosensitive drums 1B, 1C, and 1D.

  Further, the black process unit 21 </ b> A as the first process unit holding the abrasive-containing toner is used for color as the second process unit holding the abrasive-free toner along the operation direction of the intermediate transfer belt 16. Even if it is not arranged upstream of the process units 21B, 21C, and 21D, the intermediate transfer belt 16 is driven in the opposite direction, or the intermediate transfer belt 16 to which the abrasive-containing toner is transferred is rotated substantially once so as to be used for black. The abrasive-containing black toner transferred from the process unit 21A onto the intermediate transfer belt 16 can be transferred to the color process units 21B, 21C, and 21D.

  Further, after the polishing process as described above is executed, the photosensitive drum 1 is rotated once or more at least before the image forming process in order to completely remove the abrasive-containing black toner adhering to the surface of the photosensitive drum 1. Then, the charger 5 and the charge eliminator 6 are operated to charge and charge the surface of the photosensitive drum 1.

  Further, during the polishing process for the black photosensitive drum 1A, a positive bias is applied to the primary transfer roller 3 to transfer the abrasive-containing black toner adhered to the surface of the black photosensitive drum 1A to the intermediate transfer belt 16. Without being supplied to the rubbing roller 10 side for black.

Conditions such as the set rotation angle and rotation operation time in the above rotation operation, and conditions such as the polishing time in the polishing process are adjusted according to the temperature and humidity data detected by the temperature and humidity detection means 30.
That is, a table in which the various conditions are grouped according to the temperature and humidity data is stored in the storage unit 37 in advance, and the control circuit 31 refers to the table at the time of starting the rotation operation or the polishing process. To determine various conditions. For example, the table is configured to increase the rotation operation time and the polishing time when the humidity is high and the image flow phenomenon of the photosensitive drum 1 is likely to occur.

Further, the positive bias potential applied to the transfer roller 3 to transfer the abrasive-containing black toner from the intermediate transfer belt 16 to the color photosensitive drums 1B, 1C, 1D in the above-described abrasive-containing toner transfer operation is also as follows. A table grouped corresponding to the temperature and humidity data is stored in the storage means 37, and is determined with reference to the table.
That is, the control circuit 31 refers to the table and sets the positive bias potential applied to the transfer roller 3 in the abrasive-containing toner transfer operation based on the temperature / humidity data detected by the temperature / humidity detection means 30. For example, such a table increases the positive bias potential applied to the transfer roller 3 when the humidity is high and the charging potential on the surface of the color photosensitive drums 1B, 1C, and 1D is small. The black toner containing the abrasive is reliably transferred from the transfer belt 16 to the surface of the color photoreceptors 1B, 1C, 1D.

〔Example〕
When the color image forming apparatus 50 described in the above embodiment is turned on in an environment of 33 ° C. and 85% humidity, a rotation operation is performed so that the phases of the photosensitive drums 1 are different from each other, and an initial state ( First image), 10,000 images, 50,000 images, and 100,000 images were formed, and the image flow state was evaluated. As a result, even when the number of images reached 100,000, the image did not move.

[Comparative Example 1]
When the color image forming apparatus 50 described in the above embodiment is turned on in an environment of 33 ° C. and 85% humidity without performing the above rotation operation, the initial state (first sheet) and 10,000 sheets, 50,000th and 100,000th images were formed, and the image flow state was evaluated. Although it was an acceptable level at 10,000 sheets, it became an image flowing state, and an image flowing state exceeded the allowable level at 50,000 sheets, and then the degree of the image flowing state deteriorated until reaching the 100,000th sheet.

[Comparative Example 2]
When the color image forming apparatus 50 described in the above embodiment is turned on in a 33 ° C. and 85% humidity environment, a rotation operation is performed so that the phases of the photosensitive drums 1 do not differ from each other. (First sheet), 10,000 sheets, 50,000 sheets, and 100,000 sheets of images were formed, and the image flow state was evaluated. Although it was an acceptable level at 10,000 sheets, the image flow state became minute, and the image flow state exceeded the allowable level at 50,000 sheets, and then the degree of the image flow state deteriorated until reaching the 100,000th sheet.

In the above embodiment, the case where the image forming apparatus according to the present invention is applied to the image forming apparatus 50 using the intermediate transfer belt 16 has been described. However, the image forming apparatus according to the present invention uses the conveyance belt 2. The present invention can also be applied to the image forming apparatus 51.
That is, the image forming apparatus 51 using the conveying belt 2 shown in FIG. 6 has a plurality of process units 21 (21A, 21B, 21C, 21C, 21C, 21C, 21C) on the endless conveying belt 2 that conveys the recording paper 15. 21D) are arranged side by side, and an adsorption roller 13 for adsorbing the recording paper 15 to the conveyance belt 2 is provided on the upstream side in the rotation direction of the conveyance belt 2, and the recording paper is separated from the conveyance belt 2 on the downstream side. The separation means 14 is provided.
Even when the transport belt 2 is used in this way, the transport belt 2 is used in the same manner as the intermediate transfer belt 16 in the state where the recording paper 15 is not transported, and the abrasive-containing toner transport operation is executed. be able to.
Further, when the abrasive-containing toner transfer operation is executed using the transport belt 2 as described above, the same cleaning means 19 as described above is provided to clean the residual toner on the transport belt 2.

  In addition, the order of the process units 21 may not be particularly limited. However, if the process unit containing the abrasive in the toner is arranged on the most upstream side along the operation direction of the belts 16 and 2, The toner containing the abrasive can be conveyed to other process units via the belts 16 and 2.

  In the above embodiment, various conditions in the rotation operation and the polishing process are changed depending on the temperature and humidity conditions. However, these conditions may be fixed conditions, and the conditions such as the rotation operation time and the polishing time may be set. You may comprise so that it may extend for every total printed sheet number (for example, 3000 sheets).

  In the above embodiment, non-magnetic toner is used, but magnetic toner may be used.

  In the above embodiment, a photosensitive drum having an amorphous silicon photosensitive layer is used as the photosensitive drum 1, but another photosensitive drum such as a photosensitive drum having an organic semiconductor photosensitive layer or a selenium arsenic photosensitive layer is used. You may use.

Schematic diagram of a process unit having a developing device for developing the surface of the photosensitive drum Schematic diagram of a tandem color image forming apparatus with multiple process units Block configuration diagram for controlling the operation of the image forming apparatus Timing chart showing the rotation state of each photosensitive drum during rotation operation Timing chart showing the rotation state of each photosensitive drum during rotation operation Schematic diagram showing another embodiment of a tandem color image forming apparatus

Explanation of symbols

1: Photosensitive drum 1A: Black photosensitive drums 1B, 1C, 1D: Color photosensitive drum 2: Transport belt 3: Transfer roller 4: Developer (developing means)
5: Charger (charging means)
6: neutralizer 7: cleaner 8: cleaning blade 9: developing roller 10: rubbing roller (rubbing means)
12: Clutch 15: Recording paper 16: Intermediate transfer belt 21: Process unit 21A: Black process units 21B, 21C, 21D: Color process unit 22: Cam mechanism 30: Temperature / humidity detection means 31: Control circuit

Claims (4)

An image forming apparatus in which a plurality of process units having photosensitive drums are arranged along the operation direction of an endless belt,
During non-image forming processing, a rotation operation is performed to rotate each photoconductor drum so that the phase of each photoconductor drum at the end of rotation with respect to the start of rotation is different for each photoconductor drum. An image forming apparatus configured as described above. As the plurality of process units, a black process unit using black toner and a color process unit using color toner are provided,
Belt separation means capable of separating the belt from the color photosensitive drum of the color process unit;
In the rotation operation, during the non-image forming process of the color process unit, the color photosensitive drum is rotated in a state where the belt is separated from the color photosensitive drum by operating the belt separation unit. The image forming apparatus according to claim 1, wherein the phases of the photosensitive drums are different from each other.   In the rotation operation, the photosensitive drums are intermittently rotated at equal intervals for each set rotation angle, and the phases of the photosensitive drums are different from each other in the first rotation. The image forming apparatus according to claim 1, wherein the set rotation angle is set so that the set rotation angle of each of the photosensitive drums is set equal in the second and subsequent rotations. 2. In the rotation operation, rotation of the photosensitive drums is started at different start times so that the phases of the photosensitive drums are different from each other, and the photosensitive drums are rotated at equal rotational speeds. Or the image forming apparatus according to 2;

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