JP2006113227A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent contamination on the back face of a transfer material by scattered toner in an image forming apparatus in which patch toner to be stuck to a transfer roller is electrostatically cleaned and collected, when a fur brush roller, a recovery roller and a waste toner container are arranged without leaving a wasted space in the periphery of the transfer roller. <P>SOLUTION: The image forming apparatus is provided with: a fur brush roller 12 in contact with, in a counter rotation direction, the surface of a transfer roller in an upstream of a transfer nip; a bias roller (recovery roller) 13 the rotation center axis of which is located in the surface side of a photoreceptor drum 1 before passing the transfer nip when observed on a plane including the rotation center axes of the transfer roller 6 and of the fur brush roller 12; and at least a shielding member 20 disposed in a space including the separation part (B) where the fur brush roller 12 separates from the bias roller 13, in the two spaces halved by a plane (A) including the rotation center axes of the bias roller 13 and of the fur brush roller 12, and also on a plane (C) perpendicular to the plane (A) and including the separation part (B). A bias in the same polarity as the toner is applied on the shielding member 20. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a laser printer, and more specifically, a transfer roller used for transferring a toner image formed on an image carrier such as a photosensitive drum to a transfer material such as paper. The present invention relates to an image forming apparatus that cleans the image with a fur brush or the like.

  A conventional image forming apparatus shown in FIG. 5 is known.

  That is, FIG. 5 is a cross-sectional view of a main part of a conventional image forming apparatus. In the illustrated image forming apparatus, the photosensitive drum 1 is rotationally driven in the direction of arrow A at a predetermined peripheral speed (process speed), and charging means. 2, the peripheral surface is charged to a predetermined polarity and potential (primary charging).

  The laser beam scanner 3 serving as an image exposure unit outputs laser light that is on / off modulated in accordance with image information input from an external device such as an image scanner (not shown) or a computer, and outputs on the photosensitive drum 1. The charged surface is scanned and exposed. Then, an electrostatic latent image corresponding to target image information is formed on the surface of the photosensitive drum 1 by this scanning exposure. The electrostatic latent image is developed by the developer (toner) supplied onto the surface of the photosensitive drum 1 by the developing device 4 and visualized as a toner image. In this example, a reversal development method is used as a development method in which an electrostatic latent image is developed by attaching toner to an exposed portion of the photosensitive drum 1.

  On the other hand, a recording material (hereinafter referred to as “paper”) 10 is stored in a paper supply cassette (not shown), and when a paper supply roller (not shown) is driven based on a paper supply start signal, paper supply is performed. The paper 10 in the cassette is fed one by one, and the paper 10 is conveyed in the direction of the arrow B by the registration roller 5 and has a predetermined timing at a transfer portion that is a contact nip portion between the photosensitive drum 1 and the transfer roller 6. Introduced in That is, the conveyance of the paper 10 is controlled by the registration roller 5 so as to synchronize with the timing at which the leading end of the toner image on the photosensitive drum 1 reaches the transfer site.

  Thus, the paper 10 introduced into the transfer site is held and conveyed by the transfer site. At that time, a constant voltage bias (transfer bias) controlled by the transfer bias applying unit 7 is applied to the transfer roller 6. The When a transfer bias having a polarity opposite to that of the toner is applied to the transfer roller 6, the toner image on the surface of the photosensitive drum 1 is electrostatically transferred to the surface of the paper 10 at the transfer portion.

  As described above, the paper 10 to which the toner image has been transferred at the transfer portion is separated from the photosensitive drum 1 and conveyed, and is conveyed to a fixing device (not shown) and subjected to a toner image heating / pressure fixing process.

  On the other hand, the surface of the photosensitive drum 1 after the paper 10 is transferred and separated is subjected to cleaning of residual transfer toner, paper dust, and the like by the cleaning device 8 and repeatedly subjected to an image forming process.

  Further, after the photosensitive drum 1 is charged by the charging means 2, the reference pattern for density control does not overlap with the image corresponding to the image information input from an external device such as an image scanner or a computer by the exposure of the laser beam scanner 3. As described above, the electrostatic latent image is formed on the photosensitive drum 1, and the electrostatic latent image is developed by the developing device 4 to form a density control reference pattern toner image (hereinafter “patch”). 11).

  The density of the toner image of the patch 11 is detected by a patch sensor 9 installed between the developing device 4 and the transfer roller 6. Based on the detection result, the developing device 4 receives toner from a toner replenishing unit (not shown). The control device (not shown) controls the amount of toner supplied from the toner supply unit of the developing device 4 based on the output signal of the patch sensor 9 for the toner image of the patch 11. As a result, the developing capability (toner concentration of the developer) of the developing device 4 is controlled to be constant.

  However, in this type of image forming apparatus, since the transfer roller 6 comes into contact with the photosensitive drum 1, the patch 11 adheres to the transfer roller 6, which causes the backside of the paper 10 to be conveyed next. It has occurred.

  Therefore, it is conceivable to bring a cleaning blade or scraper into contact with the transfer roller 6. However, since the transfer roller 6 has elasticity in order to form a stable contact nip with the photosensitive drum 1 and to obtain a stable transfer electric field at the transfer site, it is possible to stably transfer an elastic clean blade or the like to the transfer roller. 6 cannot be brought into contact with the cleaning blade, and the cleaning blade or the like can be shaken slightly, or when a scraper such as resin is brought into contact with the surface, the surface of the transfer roller 6 is scraped to maintain the same contact force as the initial stage. The toner adhering to the transfer roller 6 could not be scraped off, and the toner slid out and eventually the back surface of the paper 10 was soiled.

  Therefore, the transfer roller 6 is separated from the photosensitive drum 1 in accordance with the timing when the patch 11 passes through the transfer portion, and the patch 11 is removed by the cleaning device 8 without attaching the patch 11 to the transfer roller 6 at the transfer portion.

  As shown in Patent Document 1, when the toner image of the image on the photosensitive drum 1 passes through the transfer portion together with the paper 10, a transfer bias (forward bias) is applied to the transfer roller 6 to patch the photosensitive drum 1. When the 11 toner image passes through the transfer portion, a bias (reverse bias) having a polarity opposite to the transfer bias is applied to the transfer roller 6 to prevent the toner of the patch 11 from adhering to the transfer roller 6. It was.

  However, in order to increase the productivity of the toner image by the photosensitive drum 1 by increasing the speed of the toner image with such a configuration, it is necessary to contact and separate the transfer roller 6 and the photosensitive drum 1 in a short time or transfer. It is necessary to switch between forward bias and reverse bias applied to the roller 6 in a short time.

  However, if the rotational speed of the photosensitive drum 1 is too high, it is not possible to ensure the time for contacting / separating the transfer roller 6 and the photosensitive drum 1 and the time for switching between the forward bias and the reverse bias applied to the transfer roller 6. 6 has a problem in that untransferred toner adheres to the paper 6 and the paper 10 is stained on the back.

  Therefore, a rotating fur brush 12 is brought into contact with the transfer roller 6, a rotating rigid bias roller 13 is brought into contact with the fur brush 12, and a cleaning blade 15 which is an elastic body is attached to the bias roller 13. By applying a bias having a polarity opposite to that of the toner to the bias roller 13 by the cleaning bias applying means 14, the patch toner adhered to the transfer roller 6 is electrostatically removed while being scraped from the transfer roller 6 to the fur brush 12. Then, the toner is electrostatically transferred from the fur brush 12 to the bias roller 13, the adhered toner is finally scraped off from the bias roller 13 by the cleaning blade 15, and the scraped toner is collected in the waste toner container 16. It was. Thereby, the transfer roller 6 can always be cleaned even if the rotational speed of the photosensitive drum 1 is increased.

  The image forming apparatus as described above is conventionally known.

Japanese Patent Laid-Open No. 7-253730

  In the conventional image forming apparatus shown in FIG. 5, it is necessary to secure a space for disposing the fur brush 12, the bias roller 13, and the waste toner container 16 around the transfer roller 6. For example, as shown in FIG. 6A, it is conceivable to arrange the fur brush 12 and the bias roller 13 vertically. However, if such an arrangement is adopted, it is necessary to secure a wide space under the transfer roller 6, and the apparatus itself needs to be enlarged vertically.

  On the other hand, as shown in FIG. 6B, when the fur brush 12 and the bias roller 13 are arranged horizontally, it is necessary to secure a wide space beside the transfer roller 6, and it is necessary to enlarge the apparatus itself horizontally. .

  Therefore, as shown in FIG. 6C, it is efficient to secure the space to arrange the transfer roller 6, the fur brush 12, and the rotation center of the bias roller 13 so as to form a triangle. good. However, when the direction of gravity is the direction of arrow C as shown in FIG. 6C, it is necessary to dispose the waste toner container 16 below the bias roller 13, and the distance between the bottom surface of the waste toner container 16 and the bias roller 13. When the toner is close, the accumulated waste toner 17 comes into contact with the bias roller 13, so that a predetermined distance is secured between the bottom surface of the waste toner container 16 and the bias roller 13 as shown in FIG. There must be. As a result, it is necessary to secure a wide vertical space, and the apparatus becomes large vertically.

  Therefore, as shown in FIG. 6E, the rotation center of the bias roller 13 is located on the surface side of the photosensitive drum 1 before transfer from the line passing through the rotation center of the transfer roller 6 and the fur brush 12. The distance between the bottom surface of the waste toner container 16 and the bias roller 13 can be increased more efficiently than the arrangement shown in FIG. 6D, and the transfer roller required for the arrangement of the fur brush 12, the bias roller 13 and the waste toner container 16 can be obtained. The space around 6 can be used efficiently.

  On the other hand, when the transfer roller 6 is electrostatically cleaned with the fur brush 12, the transfer roller 6 and the fur brush are formed by causing the transfer roller 6 to enter the fur brush 12 and forming a nip with the fur brush 12 and the transfer roller 6. 12 is not a line contact but a surface contact, so that instability due to contact failure is eliminated, and stable electrostatic toner transfer is possible.

  However, at the location where the fur brush 12 and the surface of the transfer roller 6 are separated, the toner attached to the fur is disturbed by the movement of the fur brush 12 that has been laid down due to the intrusion of the transfer roller 6 to the original position. It is released from the fur, and it becomes scattered toner and stains its surroundings.

  Therefore, as shown in FIG. 7, the fur brush is rotated in the counter direction in a state where the fur brush 12 is in contact with the surface of the transfer roller 6 upstream of the transfer nip. Even if there is scattering toner A "), the scattering direction is not directed to the back of the paper 10 after transfer or the surface of the transfer roller 6 after cleaning, so that they are not soiled.

  However, the positional relationship between the transfer roller 6 and the fur brush 12 and the bias roller 13 shown in FIG. 6E disturbs the toner transferred to the bias roller 13 at the separation portion between the bias roller 13 and the fur brush 12. In some cases, the toner (“scattered toner B” in FIG. 7) that is scattered due to the surface of the transfer roller 6 after cleaning or the back surface of the paper 10 between the transfer portion and the paper guide 18 may be stained.

  The present invention has been made in view of the above problems, and its objectives are to improve image density stability and productivity, and to efficiently use the space around the transfer roller required by the fur brush and bias roller. An object of the present invention is to provide an image forming apparatus capable of suppressing the increase in size, preventing the transfer roller from being cleaned, or preventing contamination with scattered toner on the back of the paper.

  In order to achieve the above object, an invention according to claim 1 is directed to an image carrier that carries and rotates a toner image, a transfer roller that is disposed opposite to the image carrier via a transfer material, and the transfer roller. A fur brush roller that contacts the transfer roller surface upstream of the transfer nip between the image bearing member and the counter roller with respect to the transfer roller, a recovery roller that rotates in contact with the fur brush roller, and the recovery roller In an image forming apparatus having a voltage applying unit that applies a voltage having a polarity opposite to that of toner to a roller, and a cleaning member that cleans the collecting roller, transfer is performed from a surface including a rotation center axis of the transfer roller and the fur brush roller. The rotation center axis of the collection roller is arranged on the surface side of the image carrier before passing through the nip, and is divided by a plane A including the rotation center axis of the fur brush roller and the collection roller. Among the spaces, with respect to the space including the separation portion B where the fur brush roller and the collection roller separate, at least a shielding member is provided on a surface C including the separation portion B and perpendicular to the surface A, and the shielding The member is provided with potential forming means for forming a potential having the same polarity as the toner.

  A second aspect of the invention is characterized in that, in the first aspect of the invention, the collecting roller is formed of a rigid body having conductivity, and the cleaning member is formed of a cleaning blade having elasticity.

  According to a third aspect of the present invention, in the first aspect of the present invention, the fur brush roller and the recovery roller are formed of a conductive member.

  According to a fourth aspect of the present invention, in the first aspect of the invention, the shielding member is formed of a conductive member, and the potential forming unit is configured of a bias applying unit that applies a bias having the same polarity as the toner. Features.

  According to the first aspect of the present invention, even when the toner at the separation portion of the fur brush roller and the collecting roller is disturbed by the fur tip of the fur brush roller and the toner floats and scatters, the shielding member is the same as the toner. Since a polarity potential is formed and a bias having a polarity opposite to that of the toner is applied to the collecting roller, an electric field toward the collecting roller is formed near the separation portion of the fur brush roller and the collecting roller. It is possible not to face the surface of the transfer roller after cleaning or the back of the paper before transfer. Thereby, the stain | pollution | contamination by the scattering toner of a paper back can be prevented.

  According to the second aspect of the present invention, since the recovery roller is formed of a rigid body and the cleaning member is formed of an elastic cleaning blade, the recovery roller and the cleaning blade can be stably brought into contact with each other. The mechanical removal of toner from the roller can be performed stably.

  According to the third aspect of the present invention, since the fur brush roller and the collection roller have conductivity, there is no abnormal charge accumulation on the fur brush roller or the collection roller, and noise due to abnormal discharge accompanying abnormal charge accumulation. Can prevent the malfunction of the apparatus, and it is not necessary to provide a static elimination mechanism for preventing the accumulation of abnormal charges, so that the space for that purpose can be omitted.

  According to the fourth aspect of the present invention, since the shielding member is made of a conductive member and a bias having the same polarity as that of the toner is applied to the shielding member, a potential is stably formed in the surface of the shielding member. In addition, in the vicinity of the separation portion between the fur brush roller and the collection roller, an electric field toward the toner toward the collection roller can be stably formed.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1>
1 is a cross-sectional view of a main part of an image forming apparatus according to Embodiment 1 of the present invention.

  The image forming apparatus according to the present embodiment is a laser beam printer to which an electrophotographic process is applied.

  The photosensitive drum 1 is rotationally driven in the direction of arrow A at a predetermined peripheral speed (process speed), and the peripheral surface thereof is charged to a predetermined polarity and potential by the charging unit 2 (primary charging). The laser beam scanner 3 as an image exposure unit outputs a laser beam that is modulated on / off in accordance with image information input from an external device such as an image scanner (not shown) or a computer, and performs a charging process on the photosensitive drum 1. Scan exposure of the surface. By this scanning exposure, an electrostatic latent image corresponding to target image information is formed on the surface of the photosensitive drum 1.

  The electrostatic latent image formed on the photosensitive drum 1 is developed by the developer (toner) supplied from the developing sleeve 4a onto the surface of the photosensitive drum 1 in the developing device 4 and visualized as a toner image. In the present embodiment, a reversal development method is used in which toner is attached to an exposed portion of an electrostatic latent image to develop the electrostatic latent image.

  On the other hand, a recording material (hereinafter referred to as “paper”) 10 is accommodated in a paper feed cassette (not shown), and a paper feed roller (not shown) is driven based on a paper feed start signal, The paper 10 is fed one by one, and the paper 10 is conveyed in the direction of arrow B by the registration roller 5 and introduced at a predetermined timing into a transfer portion which is a contact nip portion between the photosensitive drum 1 and the transfer roller 6. Is done. That is, the conveyance of the paper 10 is controlled by the registration roller 5 so as to synchronize with the timing at which the tip of the toner image on the photosensitive drum 1 reaches the transfer site.

  Thus, the paper 10 introduced into the transfer site is held and conveyed by the transfer site, and at that time, a predetermined voltage bias (transfer bias) controlled by the transfer bias application power source 7 is applied to the transfer roller 6. The When a transfer bias having a polarity opposite to that of the toner is applied to the transfer roller 6, the toner image on the surface of the photosensitive drum 1 is electrostatically transferred to the surface of the paper 10 at the transfer portion. In this embodiment, a constant voltage bias of +500 to +3000 V is applied to the transfer roller 6.

  As described above, the paper 10 that has received the transfer of the toner image at the transfer portion is separated from the photosensitive drum 1 and conveyed, and is conveyed to a fixing device (not shown) and subjected to a heating / pressure fixing process of the toner image. .

  The surface of the photosensitive drum 1 after the paper 10 is transferred and separated is subjected to cleaning of transfer residual toner, paper dust, and the like by a cleaning device 8 and repeatedly subjected to an image forming process.

  Further, after the photosensitive drum 1 is charged by the charging unit 2, the reference pattern for density control is overlapped with an image corresponding to image information input from an external device such as an image scanner or a computer by exposure of the laser beam scanner 3. The electrostatic latent image is formed on the photosensitive drum 1 by being written at a position corresponding to, for example, a sheet on the photosensitive drum 1 so that the electrostatic latent image is developed by the developing device 4 and is used as a density control reference. A pattern toner image (hereinafter referred to as a patch) 11 is obtained.

  The density of the toner image of the patch 11 is detected by a patch sensor 9 installed between the developing device 4 and the transfer roller 6. Based on the detection result, the developing device 4 receives a toner supply unit (not shown). Although receiving toner replenishment, a control device (not shown) controls the amount of toner replenishment from the toner replenishing unit to the developing device 4 based on the output signal of the patch sensor 9 for the toner image of the patch 11. As a result, the developing capability (toner concentration of the developer) of the developing device 4 is controlled to be constant.

By the way, in this embodiment, the transfer roller 6 is composed of an elastic layer of an ion conductive solid rubber (NBR rubber) and a cored bar, which has an outer diameter of 24 mm and a surface roughness Ra of 5. 0.0 μm or less and a resistance value (measured by applying 2 kV under N / N (temperature 23 ° C., relative humidity (RH) 50%)) of 106
~ 108 Ω rollers are used.

In FIG. 1, 12 is a fur brush roller, which is measured by applying 100 V under a hair length of 5 mm, a cored bar diameter of 8 mm, an outer diameter of 18 mm, and a resistance value (N / N (temperature 23 ° C., relative humidity (RH) 50%)). 106
~ 108 Ω are used.

  Reference numeral 13 denotes a bias roller, to which a bias having a polarity opposite to that of the toner is applied from the cleaning bias applying unit 14. In the present embodiment, a SUS metal roller having an outer diameter of 15 mm is used as the via roller 13.

  Reference numeral 15 denotes an elastic cleaning blade, which is made of polyurethane rubber.

  Thus, the transfer roller 6 and the bias roller 13 are inserted into the fur brush roller 12 by 1 to 2 mm, the fur brush roller 12 is counter-rotated in the opposite direction to the transfer roller 6, and the bias roller 13 is connected to the fur brush roller 12. It is rotated forward in the same direction. Here, since the bias roller 13 is applied with a bias having a polarity opposite to that of the toner as described above, the toner of the patch 11 adhered to the transfer roller 6 is electrostatically transferred to the fur brush 12. Then, the toner is transferred to the bias roller 13 and finally mechanically scraped off by the cleaning blade 15 and collected in the waste toner container 16.

  As shown in FIG. 2, the positional relationship among the transfer roller 6, the fur brush roller 12 and the bias roller 13 is as follows. First, the fur brush roller 12 is placed on the surface of the transfer roller 6 upstream of the transfer nip between the photosensitive drum 1 and the transfer roller 6. The rotation center axis of the bias roller 13 is positioned on the surface side of the photosensitive drum 1 before passing through the transfer nip when viewed from the surface L1 including the rotation center axes of the transfer roller 6 and the fur brush roller 12. . Thus, an arrangement that can efficiently use the space around the transfer roller 6 required by the fur brush roller 12, the bias roller 13, and the waste toner container 16 is realized.

  In FIG. 2, reference numeral 20 denotes a SUS shielding member. The shielding member 20 includes a separation portion D of the fur brush roller 12 and the bias roller 13 and a surface including the rotation center axis of the fur brush roller 12 and the bias roller 13. It is located at least on the plane L4 perpendicular to L2. Specifically, the shielding member 20 is disposed at a position with a distance of 1 to 15 mm from the separation portion D on the surface L4, and this includes a bias application power source that is a potential forming unit that forms a potential having the same polarity as the toner. A bias of −100 to −1000 V is applied by 19.

  Reference numeral 20b denotes a guide for guiding the paper 10 to the transfer site, and this is constituted by a SUS plate grounded via a resistor (not shown) of 1 to 100 MΩ. Reference numeral 20a denotes an insulating member having a thickness of 0.05 to 5 mm arranged between the guide 20b and the shielding member 20.

  With the above configuration, as shown in FIG. 2, an electric field E acts between the shielding member 20 and the bias roller 13, so that the scattered toner floating near the separation portion D is returned to the surface of the bias roller 13. As a result, the cleaned transfer roller 6 and the back surface of the paper 10 viewed from between the guide 20b and the transfer roller 6 are not contaminated with scattered toner floating from the vicinity of the separation portion D. The toner returned to the bias roller 13 is scraped off by the cleaning blade 15 and stored in the waste toner container 16.

  As described above, according to the present embodiment, the transfer roller 6 that is contaminated with the patch toner used for stabilizing the image density is constantly cleaned by the fur brush roller 12 while the image density is constantly stabilized. Therefore, even if there is toner scattered by the fur brush roller 12, the back surface of the paper 10 is not soiled.

<Embodiment 2>
Next, a second embodiment of the present invention will be described.

  FIG. 3 is a cross-sectional view of the main part of the image forming apparatus according to the present embodiment. In FIG. 3, reference numeral 1 denotes a photosensitive drum (latent image carrier), which is accompanied by rotation in the direction of arrow A. Then, an electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum 1 by a known electrophotographic process using a charging means 2, a laser beam scanner 3 that performs exposure based on the image information, and the like. The electrostatic latent image is developed by the developer (toner) supplied from the developing sleeve 4a onto the surface of the photosensitive drum 1 in the developing device 4 and visualized as a toner image. In this embodiment, a reversal development method is used in which toner is attached to an exposure portion of an electrostatic latent image to develop the electrostatic latent image.

  Reference numeral 26 denotes an intermediate transfer belt disposed so as to be in contact with the surface of the photosensitive drum 1, and this intermediate transfer belt 26 is stretched around a plurality of stretching rollers 22, 23, 24 and is moved to an arrow G Rotate in the direction. In this embodiment, the tension roller 23 is a tension roller that controls the tension of the intermediate transfer belt 26 to be constant, the tension roller 24 is a driving roller for the intermediate transfer belt 26, and the tension roller 22 is a secondary roller. This is a counter roller for transfer. Incidentally, the transfer residual toner remaining on the intermediate transfer belt 26 is removed by the belt cleaner 25 that contacts the intermediate transfer belt 26.

In the present embodiment, as the intermediate transfer belt 26, an appropriate amount of carbon black is added as an antistatic agent to resins such as polyimide, polycarbonate, polyester, polypropylene, polyethylene terephthalate, acrylic, vinyl chloride, or various rubbers. Volume resistivity is 1 × 10 8
˜1 × 10 13 Ω · cm and a thickness of 0.07 to 0.1 mm are used.

  Further, a primary transfer roller 21 is disposed on the back side of the intermediate transfer belt 26 at a primary transfer position of the intermediate transfer belt 26 facing the photosensitive drum 1, and a toner charging polarity is provided to the primary transfer roller 21. The toner image on the photosensitive drum 1 is primarily transferred onto the intermediate transfer belt 26 by applying a primary transfer bias having a polarity opposite to that of the positive polarity. A drum cleaning device 8 removes toner remaining on the photosensitive drum 1 after the primary transfer.

  Further, in the present embodiment, the secondary transfer roller 6 disposed in pressure contact with the toner image carrying surface side of the intermediate transfer belt 26 is disposed on the secondary transfer portion of the intermediate transfer belt 26 facing the conveyance path of the paper 10. A stretching roller 22 is disposed on the back side of the transfer belt 26 and forms a counter electrode of the secondary transfer roller 6 to which a bias having the same polarity as the toner is applied. The secondary transfer roller 6 is grounded.

  Further, in the present embodiment, a belt cleaner 26 for removing toner remaining on the intermediate transfer belt 26 after the secondary transfer is provided on the downstream side of the secondary transfer portion.

  By the way, in the present embodiment, after the paper 10 is once positioned and stopped by the registration roller 5, the paper 10 is sent to the secondary transfer portion at a predetermined timing. The paper 10 is transported to a fixing device (not shown) by a transport means (not shown), and the toner image is melted and fixed by heat and pressure.

  Further, after the photosensitive drum 1 is charged by the charging unit 2, the density control reference pattern does not overlap with the image corresponding to the image information input from an external device such as an image scanner or a computer by the exposure of the laser beam scanner 3. As described above, the electrostatic latent image is written on the photosensitive drum 1 at a position corresponding to, for example, a sheet of paper, and an electrostatic latent image is formed on the photosensitive drum 1. A pattern toner image (hereinafter referred to as a patch) 11 is obtained. The patch 11 is primarily transferred onto the intermediate transfer belt 16, and the density is detected by the patch sensor 9 disposed opposite to the stretching roller 23. Based on the detection result, the developing device 4 supplies toner (not shown). The control device (not shown) controls the amount of toner replenished from the toner replenishing unit to the developing device 4 based on the output signal of the patch sensor 9 for the toner image of the patch 11. As a result, the developing capability (toner concentration of the developer) of the developing device 4 is controlled to be constant.

By the way, in the present embodiment, the secondary transfer roller 6 is composed of an elastic layer of an ion conductive solid rubber (NBR rubber) and a cored bar, which has an outer diameter of φ24 mm and a surface roughness Ra. Is 5.0 μm or less, and the resistance value (measured by applying 2 kV under N / N (temperature 23 ° C., relative humidity (RH) 50%)) is 1 × 10 6.
A roller of ˜1 × 10 8 Ω is used.

In FIG. 3, 12 is a fur brush roller, which has a bristle length of 5 mm, a cored bar diameter of 8 mm, an outer diameter of 18 mm, and a resistance value (N / N (temperature 23 ° C., relative humidity (RH) 50). %) Measured with 100V applied under)
˜1 × 10 8 Ω is used.

  Reference numeral 13 denotes a bias roller to which a bias having a polarity opposite to that of the toner is applied from the cleaning bias applying unit 14, and a SUS metal roller having an outer diameter of φ15 mm is used. Reference numeral 15 denotes an elastic polyurethane rubber cleaning blade.

  Thus, in the present embodiment, the secondary transfer roller 6 and the bias roller 13 are inserted into the fur brush roller 12 by 1 to 2 mm, and the fur brush roller 12 is counter-rotated in the opposite direction to the transfer roller 6 to thereby bias the roller. 13 is forward rotated in the same direction as the fur brush roller 12. Here, as described above, since the bias roller 13 is applied with a bias having a polarity opposite to that of the toner, the toner of the patch 11 adhered to the secondary transfer roller 6 is electrostatically applied to the fur brush 12. , Then transferred to the bias roller 13, and finally mechanically scraped off by the cleaning blade 15 and collected into the waste toner container 16.

  As shown in FIG. 4, the positional relationship among the secondary transfer roller 6, the fur brush roller 12 and the bias roller 13 is such that the fur brush roller 12 first contacts the surface of the secondary transfer roller 6 upstream of the transfer nip. 6 and the rotation center axis of the bias roller 13 are located on the surface side of the intermediate transfer belt 26 before passing through the secondary transfer nip when viewed from the surface L1 including the rotation center axis of the fur brush roller 12. Thus, the space around the secondary transfer roller 6 required by the fur brush roller 12, the bias roller 13, and the waste toner container 16 can be efficiently used.

  20 is a shielding member made of SUS, and this shielding member 20 includes a separation portion D of the fur brush roller 12 and the bias roller 13 as shown in FIG. 4 and the rotation center axis of the fur brush roller 12 and the bias roller 13. At least on a surface L4 perpendicular to the surface L2 and the distance between the surface and the separation portion D is 1-15 mm, and this is a potential forming means for forming a potential of the same polarity as the toner. A bias of −100 to −1000 V is applied by a bias application power source 19.

  In FIG. 4, reference numeral 20b denotes a guide for guiding the paper 10 to the transfer unit, and this is composed of a SUS plate grounded via a resistance of 1 to 100 MΩ (not shown). Reference numeral 20a denotes an insulating member disposed between the guide 20b and the shielding member 20, and the thickness thereof is 0.05 mm to 5 mm.

  With the above configuration, an electric field E acts between the shielding member 20 and the bias roller 13 as shown in FIG. 4, so that the scattered toner floating near the separation portion D is returned to the surface of the bias roller 13. As a result, the secondary transfer roller 6 after cleaning and the back surface of the paper 10 viewed from between the guide 20b and the secondary transfer roller 6 are not stained with the scattered toner floating from the vicinity of the separation portion D. The toner returned to the bias roller 13 is scraped off by the cleaning blade 15 and stored in the waste toner container 16.

  As described above, according to the present embodiment, the secondary transfer roller 6 that is contaminated with the patch toner used for stabilizing the image density is constantly cleaned by the fur brush roller 12 while the image density is constantly stabilized. Therefore, even if there is toner scattered by the fur brush roller 12, the back surface of the paper 10 is not soiled.

  The present invention is useful for an image forming apparatus in which a transfer roller used for transferring a toner image formed on an image carrier onto a transfer material such as paper is cleaned with a fur brush or the like.

1 is a cross-sectional view of a main part of an image forming apparatus according to Embodiment 1 of the present invention. 2 is a cross-sectional view of a transfer portion of the image forming apparatus according to Embodiment 1 of the present invention. FIG. It is sectional drawing of the image forming apparatus principal part which concerns on Embodiment 2 of this invention. It is sectional drawing of the secondary transfer part of the image forming apparatus principal part which concerns on Embodiment 2 of this invention. It is sectional drawing of the conventional image forming apparatus principal part. (A)-(e) is sectional drawing which shows the arrangement | positioning form of each roller in the transfer part of the conventional image forming apparatus. FIG. 10 is a cross-sectional view illustrating a toner scattering state in a transfer unit of a conventional image forming apparatus.

Explanation of symbols

1 Photosensitive drum (image carrier)
2 Charging means 3 Laser beam scanner 4 Developing device 5 Registration roller 6 (Secondary) transfer roller 7 Transfer bias application power supply 8 Cleaning device 9 Patch sensor 10 Paper (transfer material)
11 Patch 12 Fur brush roller 13 Bias roller (collection roller)
14 Cleaning bias application means (voltage application means)
15 Cleaning blade (cleaning member)
16 Waste toner container 17 Waste toner accumulated in the waste toner container 19 Bias applied power supply (potential forming means)
18 Guide 20 Shielding member 20a Insulating member 20b Guide 21 Primary transfer roller 22 Stretching roller (opposing roller)
23 Tension roller
24 Tension roller (drive roller)
25 Belt cleaner 26 Intermediate transfer belt

Claims (4)

An image carrier that carries a toner image and rotates, a transfer roller disposed opposite to the image carrier via a transfer material, and a transfer roller upstream of the transfer nip between the transfer roller and the image carrier. A fur brush roller that contacts and rotates counter to the transfer roller, a collection roller that rotates in contact with the fur brush roller, and a voltage applying unit that applies a voltage having a polarity opposite to that of the toner to the collection roller. An image forming apparatus having a cleaning member for cleaning the recovery roller,
The rotation center axis of the recovery roller is arranged on the surface of the image carrier before passing through the transfer nip from the surface including the rotation axis of the transfer roller and the fur brush roller, and the rotation center of the fur brush roller and the recovery roller. Of the space divided into two by the surface A including the shaft, the space including the separation portion B where the fur brush roller and the collecting roller separate from each other, on the surface C including the separation portion B and perpendicular to the surface A An image forming apparatus, wherein at least a shielding member is provided, and a potential forming means for forming a potential having the same polarity as the toner is provided on the shielding member.   2. The image forming apparatus according to claim 1, wherein the collecting roller is made of a conductive rigid body, and the cleaning member is made of an elastic cleaning blade.   The image forming apparatus according to claim 1, wherein the fur brush roller and the collection roller are made of a conductive member.   The image forming apparatus according to claim 1, wherein the shielding member is formed of a conductive member, and the potential forming unit is configured of a bias applying unit that applies a bias having the same polarity as the toner.

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