JP2005122011A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of bandings by reducing the speed fluctuation of an image carrier due to secondary transfer smudge lines on a secondary transfer body. <P>SOLUTION: The image forming apparatus comprises a latent image forming means for forming an electrostatic latent image on the image carrier 3, a developing means 6a for developing the electrostatic latent image on a toner image, a primary transfer means 13 for transferring the toner image on an intermediate transfer body 12, and a secondary transfer means 15 for transferring the toner image transferred on the intermediate transfer body on a recording medium, and a cleaning blade 14 separated from and abutted against the intermediate transfer body and for removing toner left on the intermediate transfer body. The cleaning blade is separated in a non-image region on the intermediate transfer body, and the non-image region forms the latent image by the latent image forming means during transfer part passage. A primary transfer nip width, between the intermediate transfer body and the image carrier, is larger than the width of a secondary nip, and primary transfer bias is applied at all times. <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 facsimile using an electrophotographic method, and more particularly to an image forming apparatus provided with an intermediate transfer member.

  In the image forming apparatus, the toner image primarily transferred from a latent image carrier such as a photosensitive member to an intermediate transfer member such as an intermediate transfer belt is secondarily transferred onto a recording medium such as transfer paper. Then, after the secondary transfer, the transfer residual toner remaining on the intermediate transfer member is removed from the intermediate transfer member by a cleaning means such as a cleaning blade that contacts the surface of the intermediate transfer member and scrapes the transfer residual toner. ing.

  In this image forming apparatus, when the cleaning blade is separated from the surface of the intermediate transfer body, a streak-like cleaning mark (separation line) is generated. As a result, the separation line is applied to the intermediate transfer body in the next image forming process. There arises a problem that the toner image is primarily overlapped. Therefore, conventionally, the separation timing of the cleaning unit is controlled on the basis of the toner image primarily transferred onto the intermediate transfer member so that the separation line of the cleaning unit does not enter the image area.

However, even if the above-mentioned separation line is formed in the non-image area, the following problem occurs. This will be described with reference to FIG. In the figure, 3 is an image carrier, 6a is a developing roller, 10 is a backup roller (drive roller), 11 is a driven roller, 12 is an intermediate transfer member, 13 is a primary transfer roller, and 15 is a secondary transfer roller. As shown in FIG. 4A, the separation stripe formed in the non-image area is formed on the side of the secondary transfer roller 15 when the secondary transfer roller 15 contacts the intermediate transfer body 12 immediately before the secondary transfer. The two-roller stains 24 become attached (see Patent Document 1). Then, when the secondary transfer to the recording medium S is completed and the secondary transfer roller 15 is separated from the intermediate transfer body 12, as shown in FIG. Will stick. Here, the width L of the second transfer roller smear line 24 is substantially equal to the secondary transfer nip width N2 generated when the secondary transfer roller 15 and the backup roller 10 come into contact with each other.
JP 2002-82533 A

  FIG. 2 is a diagram showing a state in which the two-roller roller smear line 24 passes through the transfer position T1. FIG. (A) shows a state in which the two-roller roller streak 24 remains on the intermediate transfer body 12, and the separation position C1 advances to the primary transfer position T1, and FIG. 24 shows a state in which the primary transfer position T1 has been reached. FIG. 8C shows the two-roller roller smear line 24 passing through the primary transfer position T1, and the electrostatic latent image formed on the image carrier 3 is developed by the developing roller 6a. A state of being developed is shown.

  By the way, as a result of various experiments conducted by the present inventor, it has been found that the following problem occurs even if the separation line of the cleaning means does not enter the image area as described above. That is, as shown in FIG. 4B, when the two-roller roller smear line 24 is at the primary transfer position T1 and the two-roller roller smear line width L ≧ the primary transfer nip width N1, the latent image is formed on the image carrier 3. It has been found that when the writing operation is performed, the speed of the image carrier 3 varies, and density unevenness and color misregistration due to the speed unevenness of the image carrier 3, so-called banding occurs. This is because if there is a two-roller stain 24 (toner) between the intermediate transfer member 12 and the image carrier 3, the frictional force between them decreases, and as a result, the image carrier 3 slips and the speed changes. It is caused by waking up.

FIG. 3 is a diagram showing experimental data obtained by measuring the speed fluctuation of the image carrier when the primary transfer nip width N1 <the second transfer roller dirt stripe width L. In this experiment, toner images are transferred to the intermediate transfer member in the order of Bk (black), C (cyan), M (magenta), and Y (yellow). In FIG. 3, the vertical axis represents speed unevenness, the horizontal axis represents time,
(Rotation speed of the intermediate transfer member−rotation speed of the image carrier) / rotation speed of the image carrier × 100 (%). Therefore, a plus of unevenness in speed is that the image carrier is slower than the intermediate transfer member, and the speed is uneven. The minus sign indicates that the image carrier is faster than the intermediate transfer member. Here, the first large speed irregularity appears because of the disturbance of the signal that hits the belt joint of the encoder that detects the rotation, and is ignored because it does not directly indicate the disturbance of the rotation. According to this, it can be seen that when the two-roller roller smear of the intermediate transfer member comes to the primary transfer position, remarkable speed unevenness occurs as shown by the arrows in FIG.

  Hereinafter, a case where the intermediate transfer member 12 has a higher peripheral speed than the image carrier 3 will be described. Generally, a frictional force and an electrostatic attraction force act between the image carrier 3 and the intermediate transfer member 12, and the image carrier 3 is driven to be pulled by the intermediate transfer member 12 by these two forces. However, if the second transfer roller smear line (toner) 24 is locally present in the primary transfer region, the frictional force of that portion is rapidly reduced, and the force with which the intermediate transfer member 12 pulls the image carrier 3 is reduced. As a result, the image carrier is instantaneously slowed down. When a latent image is written on the image carrier at this time, the writing position is shifted and the above banding occurs.

  The speed fluctuation of the image carrier 3 is further promoted by the image carrier cleaning means. Hereinafter, a case where a cleaning blade is used as the cleaning means will be described. The cleaning blade uses a stick-slip phenomenon to remove toner. Therefore, stress is always applied to the tip of the cleaning blade, and when the speed of the image carrier is decreased for a moment, the stress at the tip of the blade is released, and this further promotes speed fluctuation.

  Further, at the primary transfer position T1, the electrostatic attraction force acts between the image carrier 3 and the intermediate transfer member 12 as described above, and the speed variation also depends on this force. That is, even if the frictional force due to the separating muscle 24 is reduced, if the electrostatic attraction force is large, the influence of the change can be reduced. On the contrary, if the electrostatic attraction force is weak, the speed fluctuation becomes large.

  The present invention solves the above-mentioned conventional problems, and can reduce the speed fluctuation of the image carrier due to secondary transfer stain on the intermediate transfer member and prevent the occurrence of banding. An object is to provide an apparatus.

Therefore, an image forming apparatus according to the present invention includes a latent image forming unit that forms an electrostatic latent image on an image carrier, a developing unit that develops the electrostatic latent image into a toner image, and the toner image as an intermediate transfer member. A primary transfer means for transferring the toner image to the recording medium, a secondary transfer means for transferring the toner image transferred to the intermediate transfer body to a recording medium, and a toner remaining on the intermediate transfer body by separating and contacting the intermediate transfer body. In the image forming apparatus, the cleaning blade is separated by a non-image area on the intermediate transfer member, and the non-image area forms a latent image by the latent image forming unit while the non-image area passes through the transfer portion. The primary transfer nip width between the transfer body and the image carrier is larger than the secondary transfer nip width, and the primary transfer bias is constantly applied.
Further, the ratio of the primary transfer nip width to the secondary transfer nip width is set within a range of 2 to 5.

  According to the present invention, it is possible to reduce fluctuations in the speed of the image carrier due to secondary transfer smears on the intermediate transfer member and to prevent banding.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 4 is a diagram showing an embodiment of an image forming apparatus according to the present invention. In FIG. Is an exposure device (latent image forming means), 6 is a developing device (developing means), 7 is a photoreceptor cleaner, 12 is an intermediate transfer member comprising an intermediate transfer belt, 13 is a pressure transfer member as a primary transfer means, and 14 is A cleaning blade, 15 is a secondary transfer roller as a secondary transfer means, 16 is a power supply device, 17 is a paper feed tray, 20 is a fixing device, and 21 is a paper discharge tray.

  As shown in FIG. 4, the image forming apparatus 1 according to the present embodiment includes a paper discharge tray 21 formed on an upper portion of the main body case 2 and a front cover 2 a that is openably and detachably inserted on the front surface. In the main body case 2, a developing device 6 having a plurality of developing cartridges, an image carrier 3 on which an electrostatic latent image is formed and developed to form a toner image, and a toner image on the image carrier 3 are transferred. An intermediate transfer unit, a control unit for controlling each drive motor and bias, a power supply device 16, a paper feed tray 17 for storing a recording medium, a fixing device 20 for fixing a toner image on the recording medium, and the like are disposed. A paper transport unit 19 for transporting the recording medium from the paper feed tray 17 to the fixing device 20 through the secondary transfer roller 15 is disposed in the front cover 2a. Each unit and device is configured to be detachable from the main body, and can be removed and repaired or replaced integrally during maintenance or the like.

  The photoreceptor 3 as an image carrier has a thin cylindrical conductive substrate and a photosensitive layer formed on the surface thereof. On the outer periphery of the photosensitive member 3, a charging device 4 for uniformly charging the photosensitive member 3 along the rotation direction, an exposure device 5 for forming an electrostatic latent image on the photosensitive member 3, an electrostatic latent A developing device 6 for developing an image, an intermediate transfer belt 12 for transferring a toner image on the photoreceptor 3, a photoreceptor cleaner 7 for cleaning the surface of the photoreceptor 3 after primary transfer, and the like are provided. Yes.

  The intermediate transfer unit is composed of a driving roller 10 and a driven roller 11 and an endless intermediate transfer belt 12. The intermediate transfer unit is wound around both rollers 10 and 11 and is driven in the direction of the arrow in the drawing to transfer the toner image on the photoreceptor 3. An intermediate transfer belt 12, a pressure transfer member 13 disposed on the back surface of the intermediate transfer belt 12 so as to face the photosensitive member 3 and primarily for transferring a toner image on the photosensitive member 3 to the intermediate transfer belt 12; A transfer belt cleaning blade 14 that removes residual toner on the belt 12 and a drive roller 10 are arranged to face the four-color full-color toner image formed on the intermediate transfer belt 12 as a recording medium (paper or the like). ) And a secondary transfer roller 15 for secondary transfer.

  A power supply device 16 is disposed below the exposure device 5, and a paper feed cassette 17 is disposed at the bottom of the main body case 2. A recording medium in the paper feed cassette 17 is a pickup roller 18, a sheet material conveyance path. 19, the secondary transfer roller 15, and the fixing device 20 are conveyed to the paper discharge tray 21. The paper feed cassette 17 is attached to the front of the apparatus by a handle 17b so that it can be pulled out, and an auxiliary cassette 17a is attached so that it can be pulled out so as to protrude toward the rear of the apparatus so as to cope with a large paper size. Yes.

  In the image forming apparatus 1 configured as described above, when an image forming signal is input to the exposure device 5, the photoreceptor 3, the developing roller 6 a of the developing device 6, and the intermediate transfer belt 12 are controlled in accordance with the drive motor and bias control by the control unit. Is rotated, and first, the outer peripheral surface of the photoreceptor 3 is uniformly charged by the charging device 4. Thereafter, the exposure device 5 selectively exposes the surface of the photoreceptor 3 in accordance with the image information to form an electrostatic latent image. At this time, the developing device 6 rotates so that the developing roller 6 a of the developing cartridge comes into contact with the photoreceptor 3. As a result, a toner image of an electrostatic latent image is formed on the photoreceptor 3. The toner image formed on the photoreceptor 3 is transferred onto the intermediate transfer belt 12 by the pressure transfer member 13 to which a primary transfer voltage having a polarity opposite to the toner charging polarity is applied, and remains on the photoreceptor 3. The remaining toner is removed by the photoreceptor cleaner 7.

  In the full-color image forming apparatus, yellow Y, magenta M, cyan C, and black K developing cartridges 6Y, 6M, 6C, and 6K are detachably mounted on the developing device 6. In the image forming operation, the exposure device 5 selectively exposes the surface of the photoreceptor 3 in accordance with image information of the first color, for example, yellow Y, to form a yellow Y electrostatic latent image. At this time, the developing device 6 rotates so that the developing roller 6a of the yellow Y developing cartridge 6Y contacts the photoreceptor 3, and a yellow Y electrostatic latent image toner image is formed on the photoreceptor 3. Subsequently, the toner image is transferred onto the intermediate transfer belt 12 by the pressure transfer member 13 to which a primary transfer voltage having a polarity opposite to the charging polarity of the toner is applied.

  During this time, the transfer belt cleaning blade 14 and the secondary transfer roller 15 are separated from the intermediate transfer belt 12. A four-color full-color image is obtained by repeating this series of processes corresponding to the second color, the third color, and the fourth color of the image formation signal, thereby obtaining yellow Y, Magenta M, cyan C, and black K toner images are sequentially superimposed and transferred from the photoreceptor 3 onto the intermediate transfer belt 12. Note that the order of yellow Y, magenta M, cyan C, and black K is arbitrary.

  The recording medium on the paper feed tray 17 is conveyed from the pickup roller 18 to the secondary transfer roller 15 through the registration roller and the sheet material conveyance path 19 at the timing when the superimposed image of each color toner image reaches the secondary transfer roller 15. The secondary transfer roller 15 is pressed against the intermediate transfer belt 12 and a secondary transfer voltage is applied to transfer the toner image on the intermediate transfer belt 12 onto the recording medium. The recording medium onto which the toner image has been transferred in this manner is conveyed to the fixing device 20, and the toner image on the recording medium is heated and pressed by the fixing device 20 to be fixed. The toner remaining on the intermediate transfer belt 12 is removed by the cleaning blade 14.

  In the case of double-sided printing, the recording medium exiting the fixing device 20 is switched back so that its trailing edge is the leading edge, and is supplied again to the secondary transfer roller 15 via the double-sided printing conveyance path 22. The full-color toner image on the intermediate transfer belt 12 is transferred onto the recording medium, is heated and pressed again by the fixing device 20, and is discharged onto the paper discharge tray 21.

  In the developing device 6 of the present embodiment, the four developing cartridges 6Y, 6M, 6C, and 6K are detachably mounted as described above to form a four-color full-color image forming device, but a monochrome image forming device. As shown in FIG. 2, only the black K developing cartridge 6K is mounted and mounted, the developing cartridge 6K waits at the standby position (home position), and the black K developing cartridge 6K rotates and moves from the standby position during image formation. The electrostatic latent image on the photoreceptor 3 may be developed into a toner image at the position. This makes it possible to use the developing device 6 with the same design specifications for full color and mono color, and maintenance management and design compared to designing an image forming apparatus dedicated to full color and mono color by sharing full color and mono color. Manufacturing costs can be greatly reduced.

  FIG. 5 is a diagram for explaining a drive system for the image carrier 3 and the intermediate transfer member 12 of FIG. A drive gear 3a is connected to one end of the image carrier 3, and the drive gear 3a is connected to an output gear 23a of the drive motor 23 via transmission gears 3b and 3c. A driving gear 10a is connected to one end of the driving roller 10 that drives the intermediate transfer body 12, and is connected to an output gear 23a of the driving motor 23 through a transmission gear 10b.

  FIG. 6 shows an example of the pressure transfer member 13 of FIG. 4, in which the transfer roller 13a is shown in FIG. (A), the transfer blade 13b in FIG. (B), and the back side of the intermediate transfer body 12 by an urging member (not shown). To the image carrier 3. Reference numeral 26 denotes a primary transfer power source.

  7 to 10 are diagrams for explaining one embodiment of the present invention. FIG. 7 is a diagram for explaining the relationship between the two-roller roller stain streak width and the primary transfer nip width. FIG. FIG. 9 is a diagram showing an operation sequence of the embodiment, FIG. 9 is a diagram showing measurement data, and FIG. 10 is a diagram showing measurement data showing a relationship between primary transfer nip width / secondary transfer nip width and speed unevenness.

  In FIG. 7, FIG. (A) shows a state in which the two-roller roller smear line 24 remains on the intermediate transfer body 12, and this position C1 advances to the primary transfer position T1, and FIG. FIG. 4C shows a state in which the roller smear stripe 24 has reached the primary transfer position T1, and FIG. (C) shows the development of the electrostatic latent image formed on the image carrier 3 when the two-roller roller stain stripe 24 has passed the primary transfer position T1. A state of being developed by the roller 6a is shown.

  In the image forming apparatus of the present invention, as shown in FIG. 5B, when the two-roller roller smear line 24 is at the primary transfer position T1, the two-roller roller smear line width L (secondary transfer nip width N2) <1. The next transfer nip width N1 is set. In the primary transfer portion, if there is a two-roller roller smear line 24 (toner) between the intermediate transfer member 12 and the image carrier 3, the frictional force between the two rapidly decreases. Since there is a portion where there is no toner in the next transfer nip width N, it is possible to maintain the frictional force in that portion. Further, since the image bearing member 3 and the intermediate transfer member 12 are in direct contact with each other in the toner-free portion, the electrostatic attraction force due to the primary transfer bias is increased, and as a result, the image bearing generated when the image bearing member 3 slips. The speed unevenness of the body 3 can be reduced.

  FIG. 8 shows the vsync signal, the image signal, the color switching operation of the developing device, the developing operation, the primary transfer position, the secondary transfer roller, and the primary transfer bias. This operation sequence will be described with reference to FIG. The surface of the image carrier 3 is uniformly charged by the charging device 4 and the image signal is turned on in synchronization with the vsync signal. Exposure is performed to form an electrostatic latent image. At this time, the developing device 6 rotates so that the first color developing roller 6a contacts the image carrier 3, and a toner image of the first color is formed on the image carrier 3, and then the primary transfer voltage. The toner image of the first color is transferred onto the intermediate transfer body 12 by the pressure transfer member 13 to which is applied.

  During this time, the transfer belt cleaning blade 14 and the secondary transfer roller 15 are separated from the intermediate transfer body 12. In a four-color full-color image, this series of processing is repeatedly executed corresponding to the second color, the third color, and the fourth color of the image formation signal, so that a toner image corresponding to the content of each image formation signal is obtained. From the image carrier 3, the images are sequentially superimposed and transferred onto the intermediate transfer body 12. The recording medium S is conveyed to the secondary transfer roller 15 at a timing when the superimposed image of each color toner image reaches the secondary transfer roller 15, and the secondary transfer roller 15 is pressed against the intermediate transfer belt 12 and 2. The next transfer voltage is applied, and the toner image on the intermediate transfer body 12 is transferred onto the recording medium S.

  Next, the toner remaining on the intermediate transfer belt 12 is removed by the cleaning blade 14. The cleaning blade 14 is brought into contact with the non-image area of the intermediate transfer body 12 after the rear end of the third color image has passed the cleaning blade position, and the first color of the image formed in the next step (second sheet). The leading edge of the image is separated from the intermediate transfer body 12 before reaching the cleaning blade position. By the separation contact of the cleaning blade 14, the toner image on which the fourth color is superimposed is transferred to the recording medium S, and the toner remaining on the intermediate transfer body 12 is removed by the cleaning blade 14.

  As shown in FIG. 7, when the secondary transfer roller 15 is separated from the intermediate transfer body 12, a second transfer roller smear line 24 is generated. In this embodiment, the second transfer roller smear line 24 is at the primary transfer position T1. Control is performed so as to form an electrostatic latent image by turning on the image signal before a predetermined time t and starting image writing. In this case, in the image forming apparatus of the present invention, as described above, the primary transfer nip width N1 is made larger than the secondary roller smear stripe width L (that is, the secondary transfer nip width N2), and the primary transfer bias is always set. Therefore, even if the 2-roller roller smear line 24 passes through the primary transfer position T1, there is no sudden fluctuation in the frictional force between the image carrier 3 and the intermediate transfer member 12, and the speed of the image carrier 3 is increased. Unevenness can be reduced.

  In FIG. 8, the image signal is turned on and image writing is started a predetermined time t before the 2nd-roller smear stripe 24 reaches the primary transfer position T1. Since the speed unevenness of the image carrier 3 can be reduced, an image signal is output while a non-image area (area where a transfer image is not formed) of the intermediate transfer body 12 including the two-roller roller smear lines 24 passes through the primary transfer position T1. The image writing may be started by turning on.

FIG. 9 is a diagram showing experimental data obtained by measuring the speed fluctuation of the image carrier when primary transfer nip width N1> secondary transfer nip width N2 × 2. In FIG. 9, the vertical axis represents speed variation, the horizontal axis represents time, and the speed variation is
(Rotation speed of the intermediate transfer member−rotation speed of the image carrier) / rotation speed of the image carrier × 100 (%). Therefore, a plus of unevenness in speed is that the image carrier is slower than the intermediate transfer member, and the speed is uneven. The minus sign indicates that the image carrier is faster than the intermediate transfer member. Here, the first large speed irregularity appears because of the disturbance of the signal that hits the belt joint of the encoder that detects the rotation, and it is ignored because it does not directly indicate the disturbance of the rotation.
According to FIG. 9, it can be seen that when the two-roller roller smear line passes the primary transfer position, the speed unevenness is reduced at the position of the arrow.

  FIG. 10 shows measurement data in which the horizontal axis indicates (primary transfer nip width N1 / 2 and secondary transfer nip width N2), and the vertical axis indicates the peak value of speed unevenness. The peak value of the speed unevenness is an average value of five times of the peak value during magenta printing. According to this, it has been found that the speed unevenness can be reduced when N1 / N2 is in the range of 2 to 5.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, in the above embodiment, the electrostatic latent image is formed on the image carrier by the exposure device. However, the electrostatic latent image may be formed by the charging / writing device. It is defined as forming means. Although the intermediate transfer belt has been described in the above embodiment, it can be applied to an intermediate transfer drum, and in the present invention, these are defined as intermediate transfer members.

It is a figure for demonstrating generation | occurrence | production of the 2 rolling-roller stain | pollution | contamination stripe based on this invention. It is a figure which shows the state in which 2 rolling-roller stain | pollution | contamination stripe | line passes a transfer position. It is a figure for demonstrating the subject of this invention, and is a figure which shows the experimental data which measured the speed fluctuation | variation of the image carrier. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 5 is a diagram for explaining a drive system for the image carrier and the intermediate transfer member in FIG. 4. It is a figure which shows the example of the press-contact transfer member of FIG. It is a figure for demonstrating one Embodiment of this invention, and is a figure for demonstrating the relationship between the 2 rolling-roller stain | pollution | contamination streak stripe width | variety, and a primary transfer nip width | variety. It is a figure which shows the operation | movement sequence of embodiment of FIG. It is a figure which shows the measurement data of embodiment of FIG. It is a figure which shows the measurement data which show the relationship between the transfer nip width | variety and speed nonuniformity of embodiment of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Image carrier, 5 ... Latent image formation means, 6 ... Developing means, 12 ... Intermediate transfer body 13 ... Primary transfer means, 14 ... Cleaning blade, 15 ... Secondary transfer means N1 ... Primary transfer nip width, N2 ... secondary transfer nip width

Claims (2)

A latent image forming means for forming an electrostatic latent image on the image bearing member; a developing means for developing the electrostatic latent image into a toner image; a primary transfer means for transferring the toner image to an intermediate transfer member; A secondary transfer means for transferring the toner image transferred to the intermediate transfer member to a recording medium; and a cleaning blade for separating and contacting the intermediate transfer member to remove the toner remaining on the intermediate transfer member. In an image forming apparatus in which a latent image is formed by the latent image forming means while being separated by a non-image area on an intermediate transfer body and the non-image area is passing through a transfer portion, primary transfer between the intermediate transfer body and the image carrier is performed. An image forming apparatus characterized in that a nip width is larger than a secondary transfer nip width and a primary transfer bias is constantly applied. 2. The image forming apparatus according to claim 1, wherein a ratio of the primary transfer nip width to the secondary transfer nip width is set in a range of 2 to 5.

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