JP2006113235A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain stable cleaning performance for a transfer conveying belt over a long period of time and simultaneously to restrain the turn-up of a blade. <P>SOLUTION: By disposing a cleaning brush 41 abutting on the transfer conveying belt 21 transferring a toner image while carrying paper P and cleaning the surface of the transfer conveying belt 21, and a cleaning blade 43 on the downstream side of the cleaning brush 41 in the moving direction of the transfer conveying belt 21, toner held by the cleaning brush 41 is supplied to an area where the cleaning blade 43 abuts on the transfer conveying belt 21. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a printer, and more particularly to an image forming apparatus provided with a transfer conveyance belt that electrostatically attracts a recording sheet and transfers a toner image onto the recording sheet while being conveyed.

  In an image forming apparatus such as a copying machine or a printer using an electrophotographic system, for example, a photosensitive member (photosensitive drum) formed in a drum shape is uniformly charged, and the photosensitive drum is controlled based on image information. An electrostatic latent image is formed on the photosensitive drum by exposure with the exposed light. Then, the electrostatic latent image is converted into a visible image (toner image) with toner, and the toner image is transferred from the photosensitive drum to the recording paper by the transfer device, and then heated and pressed by the fixing device to form the toner image. Fixed on recording paper.

In a transfer device used in such an image forming apparatus, in recent years, a transfer conveyance belt is disposed so as to abut on a photosensitive drum, and the transfer conveyance belt and the photosensitive drum are brought into contact with each other while the transfer conveyance belt is moved. A system in which the recording paper is sandwiched between the contact areas (transfer nip portion) and a transfer bias is applied to the transfer conveyance belt to transfer the toner image on the photosensitive drum onto the recording paper has been put into practical use.
In the transfer apparatus using such a transfer conveyance belt, a high-voltage power supply is not required as compared with the conventional corona charging method, so that the apparatus can be downsized and the manufacturing cost can be reduced. Further, there is an advantage that the generation of ozone is extremely small, and in addition, the transfer performance is stable against dirt due to adhesion of paper dust, toner, and the like. Furthermore, it is possible to configure the unit around the transfer conveyance belt so that it can be brought into contact with and separated from the photosensitive drum, or to be pulled out from the front side of the image forming apparatus. Jam processing is easy when jamming occurs. It is also possible to reduce the area occupied by the image forming apparatus.

  However, in the transfer device using the transfer conveyance belt, since the transfer conveyance belt is configured to contact the photosensitive drum at the transfer nip portion, an interimage between the image area and the image area on the photosensitive drum is formed. When the region passes through the transfer nip portion, the transfer conveyance belt and the photosensitive drum are in direct contact with each other without using the recording paper. Therefore, the toner adhering to the inter-image area on the photosensitive drum is transferred onto the transfer / conveying belt, and the surface of the transfer / conveying belt is contaminated with the toner. The toner adhering to the surface of the transfer / conveying belt stains the back surface of the newly conveyed recording paper and degrades the image quality. Furthermore, when the transfer / conveying belt carries recording paper, paper dust may adhere to the surface of the transfer / conveying belt. Therefore, in such a transfer device, a belt cleaning device is provided for removing deposits such as toner and paper dust from the surface of the transfer conveyance belt.

Here, as a related art relating to a belt cleaning device for cleaning toner or the like adhering to the surface of the transfer conveyance belt, a sponge roll that is rotatable and arranged in sliding contact with the surface of the transfer conveyance belt on the upstream side of the cleaning blade There is a technology relating to a cleaning device having a configuration including a brush roll (see, for example, Patent Document 1).
In such a system in which the surface of the transfer conveyance belt is cleaned by such a cleaning blade and a sponge roll disposed on the upstream side thereof, the sponge roll or the like first rubs against the surface of the transfer conveyance belt to remove toner or paper dust. Since the toner that could not be removed there is completely removed by the cleaning blade, there is an advantage that the surface of the transfer conveyance belt can be effectively cleaned. However, in such a configuration, for example, when continuously printing an image with a small image ratio, the amount of toner that adheres to the surface of the transfer / conveyance belt is reduced. The amount of toner that reaches the cleaning blade is extremely small. In this case, the amount of toner staying as a lubricant at the contact portion between the cleaning blade and the transfer conveyance belt is reduced, and the frictional force between the cleaning blade and the transfer conveyance belt surface is increased. As a result, there is a problem that so-called “blade turning” is easily generated, in which the front end portion of the cleaning blade is bent by the movement of the transfer conveyance belt.

  Therefore, as a conventional technique for suppressing the blade turning of the cleaning blade in contact with the transfer conveyance belt, a developer capable of applying a bias voltage on the outer periphery of the transfer conveyance belt on the upstream side of the cleaning blade. An arrangement in which a holding brush as a holding member is provided has been proposed. In this technology, a line image is formed on the photosensitive drum by operating the image forming means before the paper interval where the recording paper is not on the transfer conveyance belt, before paper passing, or after paper passing, and this line image is transferred. Transfer in the width direction on the conveyor belt. Then, after the toner supplied onto the transfer / conveying belt in this manner is attracted to the holding brush by applying a bias voltage to the holding brush, the holding brush is switched to a float as necessary. Is gradually adhered onto the transfer conveyance belt from the holding brush. As a result, toner is supplied to the contact portion between the cleaning blade and the transfer conveyance belt to suppress an increase in frictional force between the cleaning blade and the transfer conveyance belt surface, thereby suppressing the occurrence of blade turning (for example, , See Patent Document 2).

JP-A-10-171270 (page 3-4) Japanese Patent Laid-Open No. 10-186881 (page 6-7)

However, as in the technique described in Patent Document 2, in order to supply toner to the contact portion between the transfer conveyance belt and the cleaning blade, a developer holding member such as a holding brush is arranged on the upstream side of the cleaning blade. In this case, it is difficult to provide a cleaning brush or the like as a pre-stage of cleaning with the cleaning blade on the upstream side of the cleaning blade in terms of space and function. Therefore, effective cleaning cannot be performed by cooperation between the cleaning brush and the cleaning blade. Therefore, in such a configuration, even if it is possible to suppress the blade turning, a new cleaning defect is likely to occur particularly when a spherical toner having a small particle diameter such as a polymerized toner is used. Problems arise.
Further, positively supplying toner from the photosensitive drum to the transfer / conveying belt not only wastes toner, but also increases the amount of toner collected in the belt cleaning device. There is also an inconvenience that it is necessary to increase the frequency of maintenance.

The present invention has been made to solve the technical problems as described above. The object of the present invention is to maintain stable cleaning performance for the transfer conveyance belt over a long period of time, and at the same time, the occurrence of blade turning. It is to suppress.
Another object is to suppress wasteful consumption of toner and to minimize the frequency of maintenance.

  For this purpose, the image forming apparatus of the present invention moves while carrying a toner image carrier that carries a toner image and a transfer material, and transfers the toner image carried on the toner image carrier to a transfer material. A transfer conveying belt, a cleaning brush that comes into contact with the transfer conveying belt and wipes off deposits adhering to the surface of the transfer conveying belt, and a counter contact with the transfer conveying belt on the downstream side of the moving direction of the transfer conveying belt of the cleaning brush. A cleaning blade that scrapes off deposits on the surface of the transfer conveyance belt, and a toner supply unit that supplies toner held by the cleaning brush to an area where the cleaning blade contacts the transfer conveyance belt. It is characterized by.

  Here, the toner supply means mechanically peels off the toner held by the cleaning brush and scatters the toner from the cleaning brush, thereby supplying the cleaning blade to an area where the cleaning blade contacts the transfer conveyance belt. be able to. The toner supply unit electrostatically transfers the toner held on the cleaning brush to the transfer conveyance belt, and supplies the toner to an area where the cleaning blade contacts the transfer conveyance belt as the transfer conveyance belt moves. It can also be characterized.

  The image forming apparatus of the present invention also includes a toner image carrier that carries a toner image, a transfer conveyance belt that moves while carrying a transfer material, and that transfers the toner image carried on the toner image carrier to a transfer material. And a plurality of stretching rolls for stretching the transfer conveyance belt; and, while rotating in the same direction as the movement direction of the transfer conveyance belt, wiping off deposits adhering to the surface of the transfer conveyance belt, A transfer brush on the downstream side of the moving direction of the transfer conveying belt of the cleaning brush, a cleaning brush that can rotate in the reverse direction, a toner peeling member that contacts the surface of the cleaning brush and peels off the toner held on the cleaning brush A cleaning blade that counter-contacts the belt and scrapes off deposits on the surface of the transfer conveyance belt. By rotating in a direction opposite to the movement direction of the copy transport belt, is characterized in that toward the contact portion between the toner separating member to the contact portion between the transfer conveyance belt cleaning blade to scatter the toner.

Here, the cleaning blade is in contact with the transfer conveyance belt at a position where a tangent line of the cleaning brush at a position where the toner peeling member contacts the cleaning brush intersects with or near the transfer conveyance belt. be able to. In particular, the cleaning blade can be configured to come into contact with the transfer conveyance belt in a region where the transfer conveyance belt is wrapped by the tension roll. Furthermore, the tension roll can be characterized by being grounded.
In addition, a temperature / humidity detecting unit that detects temperature and humidity is further provided, and the cleaning brush rotates and rotates in a direction opposite to the moving direction of the transfer conveyance belt based on the temperature and humidity detected by the temperature / humidity detecting unit. Any one or more of the rotation time and the rotation amount can be made variable. Further, the cleaning brush may be characterized in that the length in the longitudinal direction is longer than the length in the longitudinal direction of the cleaning blade. The cleaning brush may have a resistance value of 8.0 logΩ or less.

  The image forming apparatus of the present invention also includes a toner image carrier that carries a toner image, a transfer conveyance belt that moves while carrying a transfer material, and that transfers the toner image carried on the toner image carrier to a transfer material. A tension roll that stretches the transfer conveyance belt, a cleaning brush that comes into contact with the transfer conveyance belt and wipes off deposits adhering to the surface of the transfer conveyance belt, and a downstream side of the movement direction of the transfer conveyance belt of the cleaning brush And a cleaning blade that counter-contacts the transfer conveyance belt and scrapes off deposits on the surface of the transfer conveyance belt, and the transfer conveyance belt forms a toner image with a surface potential in a region where the cleaning brush contacts. It is possible to switch between a first level potential that is the same polarity as the charging polarity of the toner and a second level potential that is set to 0V from the first level potential. It is characterized in.

Here, the surface potential of the transfer conveyance belt can be characterized in that the potential difference between the first level potential and the second level potential is set to 100 V or more. Further, a temperature / humidity detecting means for detecting temperature and humidity is further provided, and the surface potential of the transfer / conveying belt is determined based on the temperature and humidity detected by the temperature / humidity detecting means between the first level potential and the second level potential. It can also be characterized in that the potential difference is controlled.
Further, the cleaning brush may be in contact with the transfer conveyance belt in a region where the transfer conveyance belt is wrapped by the stretching roll. In particular, the cleaning brush and the tension roll can be characterized by being grounded.
The transfer / conveying belt may have a surface resistance value of 7.0 to 9.0 logΩ. Further, the cleaning brush may be characterized in that the resistance value is 8.0 logΩ or less.

  As an effect of the present invention, it is possible to maintain a good cleaning performance for a long time while suppressing the occurrence of turning of the cleaning blade, and it is possible to form a high-quality image free from backside contamination. In addition, it is possible to reduce the running cost of the image forming apparatus by suppressing unnecessary toner consumption and minimizing the frequency of maintenance.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
[Embodiment 1]
FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus to which the exemplary embodiment is applied. The image forming apparatus shown in FIG. 1 includes a charger 11 that charges the photosensitive drum 10 around the photosensitive drum 10 as an example of a toner image carrier that rotates in the direction of arrow A, and an electrostatic image on the photosensitive drum 10. A laser exposure device 12 for writing a latent image (the exposure beam is indicated by a symbol Bm in the figure), a developing device 13 that stores toner and visualizes the electrostatic latent image on the photosensitive drum 10 with toner, a transfer nip A pre-transfer charger 14 that charges the toner image on the photoconductive drum 10 prior to electrostatic transfer in the unit 15, and a recording paper (paper) that is a recording paper in the transfer nip unit 15 is transferred to the toner image formed on the photoconductive drum 10. ) A transfer unit 20 for transferring to P, an image density sensor 18 for adjusting an image density disposed in the vicinity of the photosensitive drum 10 on the downstream side of the transfer nip 15, a band of residual toner after electrostatic transfer Precleaning charger 16 to reduce the amount, electrophotographic devices, such as a drum cleaner 17 which residual toner on the photosensitive drum 10 is removed is provided. Further, a fixing device 60 for fixing the unfixed toner image transferred onto the paper P and a control unit 30 for controlling the operation of each device (each unit) are provided.

  The transfer unit 20 is disposed inside the transfer conveyance belt 21 stretched between the drive roll 22 and the idle roll 23, and is in pressure contact with the photosensitive drum 10 via the transfer conveyance belt 21. And a transfer roll 24. A function of transferring the toner image on the photosensitive drum 10 onto the paper P conveyed to the transfer nip 15, and a function of conveying the paper P onto which the toner image has been transferred at the transfer nip 15 to the fixing device 60. have.

  The image forming apparatus according to the present embodiment also includes a paper tray 50 that stores paper P, a pickup roll 51 that picks up and transports the paper P accumulated in the paper tray 50 at a predetermined timing, and a pickup as a paper transport system. A transport roll 52 that transports the paper P fed by the roll 51, a registration roll 54 that feeds the transported paper P to the transfer nip 15 at a predetermined timing, and a paper P transported by the transport roll 52 is guided to the registration roll 54. A conveyance chute 53, an inlet chute 55 that guides the paper P fed from the registration roll 54 to the transfer nip portion 15, and a fixing inlet guide 56 that guides the paper P to which the toner image is transferred by the transfer unit 20 to the fixing device 60. It has.

  Next, a basic image forming process of the image forming apparatus according to the present embodiment will be described. In the image forming apparatus as shown in FIG. 1, image data output from an image reading device (IIT) not shown or a personal computer (PC) not shown is subjected to predetermined image processing by an image processing device not shown. . In the image processing apparatus, the input reflectance data is subjected to predetermined image processing such as various kinds of image editing such as shading correction, position shift correction, gamma correction, frame deletion editing, and movement editing. The image data that has undergone image processing is output to the laser exposure unit 12.

The laser exposure unit 12 irradiates the photosensitive drum 10 with an exposure beam Bm emitted from, for example, a semiconductor laser, according to the input image data. The surface of the photosensitive drum 10 is charged to a predetermined charging potential (for example, −750 V) by a charger 11 made of scorotron, and then the surface is scanned and exposed by the laser exposure device 12 to form an electrostatic latent image. The
The formed electrostatic latent image is reversely developed with negatively charged toner by the developing device 13. That is, for example, a direct current from a power source (not shown) is applied to a developer carrying member (developing sleeve) 13a carrying a developer prepared by a polymerization method and having a toner having a shape factor SF1 of 100 to 140 mixed with a carrier made of magnetic particles. A developing bias composed of a voltage or a developing bias in which a DC voltage is superimposed on an AC voltage is applied, and a developing electric field is formed between the photosensitive drum 10 and the developing bias. As a result, the toner on the developing sleeve 13a is transferred to the image portion (exposure portion) of the electrostatic latent image, and the electrostatic latent image is visualized.

  Here, in the image forming apparatus according to the present embodiment, a setup cycle is executed every predetermined cycle. That is, prior to the actual image forming operation, a predetermined patch area is developed under predetermined conditions. At that time, as will be described later, the transfer conveyance belt 21 of the transfer unit 20 is set to be separated from the photosensitive drum 10. In this state, the developed patch area passes through the transfer nip 15 as it is, and the density of the toner image in the patch area is measured by the image density sensor 18 disposed on the downstream side of the transfer nip 15. The toner density signal measured by the image density sensor 18 is sent to the control unit 30. Then, in accordance with an instruction from the control unit 30 based on the signal from the image density sensor 18, the charging potential of the photosensitive drum 10 by the charger 11 and / or the developing bias value applied to the developing device 13 is adjusted, and a predetermined image is obtained. The density is set to be maintained.

  Next, in the actual image forming operation, when the toner image formed on the photosensitive drum 10 is conveyed to the transfer nip portion 15 where the photosensitive drum 10 and the transfer unit 20 abut, In this case, the pickup roll 51 rotates in accordance with the timing at which the toner image is conveyed to the transfer nip portion 15, and the paper P having a predetermined size is supplied from the paper tray 50. The paper P supplied by the pickup roll 51 is transported by the transport roll 52, and reaches the registration roll 54 through the transport chute 53. In the registration roll 54, the paper P is temporarily stopped, and the registration roll 54 rotates in accordance with the movement timing of the photosensitive drum 10 carrying the toner image. Accordingly, the position of the paper P and the position of the toner image are aligned, and the paper P is sent out from the inlet chute 55 to the transfer nip portion 15.

In the transfer nip portion 15, the sheet P conveyed at the same timing is sandwiched between the photosensitive drum 10 and the transfer roll 24 via the transfer conveyance belt 21 of the transfer unit 20. At that time, a voltage (transfer bias) having a polarity opposite to the charging polarity of the toner (here, negative polarity) is applied to the transfer roll 24, so that the transfer roller 24 is transferred to the transfer conveyance belt 21 on the photosensitive drum 10. A charge having a polarity opposite to that of the toner is applied. As a result, the unfixed toner image carried on the photosensitive drum 10 is electrostatically transferred onto the paper P in the transfer nip portion 15 pressed by the photosensitive drum 10 and the transfer roll 24.
At this time, an optimum transfer bias is applied to the transfer roll 24 by a constant current control method. In this embodiment, the optimum transfer current supplied from the transfer roll 24 varies depending on the process speed, environmental conditions such as temperature and humidity, the type of the paper P, etc., but in the present embodiment, it is set in the range of 50 to 150 μA. Is done.

Thereafter, the sheet P on which the toner image has been electrostatically transferred is peeled off and conveyed from the photosensitive drum 10 while being electrostatically attracted to the transfer conveyance belt 21 of the transfer unit 20, and downstream of the transfer unit 20 in the sheet P conveyance direction. To the fixing device 60 provided on the side. When the sheet P is not peeled off from the photosensitive drum 10 and remains adsorbed on the photosensitive drum 10, it is disposed near the surface of the photosensitive drum 10 on the downstream side of the transfer nip portion 15. The paper P is separated from the photosensitive drum 10 by the separation claw (not shown), and is electrostatically attracted to the transfer conveyance belt 21.
At the rear end of the transfer conveyance belt 21 on the fixing device 60 side, the sheet P is peeled from the transfer conveyance belt 21 due to the curvature when the transfer conveyance belt 21 is wound around the drive roll 22 and the stiffness of the sheet P. Then, the paper P is guided to the fixing inlet guide 56 and conveyed to the fixing device 60.
The unfixed toner image on the paper P conveyed to the fixing device 60 is fixed on the paper P by being subjected to fixing processing by heat and pressure in the fixing device 60. Then, the paper P on which the fixed image is formed is conveyed to a paper discharge mounting portion provided in a discharge portion of the image forming apparatus, and a series of image forming operations is completed.

  The image forming apparatus according to the present embodiment is configured to form a single color toner image. However, the present invention is a color that forms a color toner image by superimposing, for example, yellow, magenta, cyan, and black toner images. It can also be applied to an image forming apparatus.

Next, the transfer unit 20 will be described in detail.
FIG. 2 is a cross-sectional view showing the configuration of the transfer unit 20. As shown in FIG. 2, the transfer unit 20 transfers the toner image on the photosensitive drum 10 onto the paper P, and also transfers the transfer transport unit 20A and the transfer transport unit 20A for transporting the paper P on which the toner image has been transferred. A retract mechanism 20B that contacts and separates from the body drum 10, a cleaning unit 20C as an example of a belt cleaning unit that removes adhering matter such as paper dust and toner attached to the transfer conveyance unit 20A, and a transfer paper P The inlet chute part 20D led to the part 15 is configured.

  FIG. 3 is a perspective view showing the configuration of the transfer unit 20. As shown in FIG. 3, the transfer conveyance unit 20 </ b> A of the transfer unit 20 is stretched around the transfer conveyance belt 21 and the transfer conveyance belt 21 arranged in the axial direction of the photosensitive drum 10, and rotates in the arrow B direction. A drive roll 22 that is moved, an idle roll 23 that stretches the transfer conveyance belt 21 to apply a predetermined tension, and a transfer roll 24 that forms a transfer electric field with the photosensitive drum 10 to transfer a toner image onto the paper P. It is comprised by.

  The transfer / conveying belt 21 is composed of two layers including, for example, a rubber layer based on chloroprene and a surface layer obtained by coating a resin mainly composed of polyurethane with polytetrafluoroethylene (PTFE) particles dispersed therein. Is an endless belt. Further, the transfer conveyance belt 21 has a surface roughness Rz of 2.5 μm or less, a surface resistance of 7.0-9.0 logΩ, and a volume resistance of 6.0-8.0 logΩ. The transfer conveyance belt 21 is equal in speed to the surface speed of the photosensitive drum 10 by a drive roll 22 configured to transmit drive by a coupling 25 from a drive motor (not shown) on the image forming apparatus main body side. To the direction of arrow B.

The transfer roll 24 is formed of a tube of EPDM and NBR blend rubber with carbon dispersed on the surface and a roll of EPDM foam rubber with carbon dispersed on the inside, and the hardness is, for example, 20 to 50 ° (Asker C: 4. 9N load). Furthermore, the resistance is set to 5.0 to 7.0 logΩ. The transfer roll 24 is, for example, 85 μA controlled at a constant current so that a transfer bias having a polarity (positive polarity) opposite to the toner charging polarity (negative polarity) is stably applied from a transfer power source (not shown). Current is supplied. As a result, a charge having a polarity opposite to the toner charging polarity on the photosensitive drum 10 is applied from the transfer roll 24 to the transfer conveyance belt 21. The transfer bias is applied only when the image area on the photosensitive drum 10 passes through the transfer nip 15, and when the inter-image area between the image areas passes through the transfer nip 15. Is set not to be applied.
In addition, the transfer conveyance unit 20A is configured such that the idle roll 23 side is swung by the retract mechanism unit 20B with the drive roll 22 as the rocking center, and is configured to be able to contact and separate from the photosensitive drum 10. Further, a power source is connected to the idle roll 23 (not shown), and in order to suppress a minute gap discharge phenomenon at the photoconductor pre-nip portion of the transfer roll 24 according to circumstances such as environmental conditions, the transfer bias is It is comprised so that the voltage of opposite polarity can be applied.

  Next, the retract mechanism unit 20B is disposed below the transfer conveyance unit 20A. FIG. 4 is a perspective view illustrating a configuration in a state where the transfer conveyance unit 20 </ b> A is removed from the transfer unit 20. As shown in FIG. 4, the retract mechanism unit 20B is disposed at both ends in the width direction of the transfer conveyance unit 20A. The retraction mechanism unit 20B pushes up and down while supporting the idle roll 23 of the transfer conveyance unit 20A. A plate 31 is fixedly provided, and includes a link shaft 32 that swings the contact / separation plate 31, a swing arm 33 that is connected to the center of the link shaft 32, and a DC solenoid 34 that drives the swing arm 33 to swing. Yes. In the retract mechanism 20B, when a current is passed through the direct current solenoid 34, the direct current solenoid 34 moves the swing arm 33 in a downward direction. As a result, the link shaft 32 connected to the swing arm 33 rotates, and the contact / separation plates 31 fixed to both ends of the link shaft 32 swing upward.

  In the transfer unit 20, the transfer conveyance unit 20 </ b> A is set in a state of being separated from the photosensitive drum 10 at the time of measuring the toner image density in the patch area (setup cycle) or in the standby state of the image forming apparatus. FIG. 5 is a diagram illustrating a state where the transfer conveyance unit 20 </ b> A is separated from the photosensitive drum 10. As shown in FIG. 5, during the setup cycle of the image forming apparatus or during standby, the DC solenoid 34 of the retract mechanism unit 20B is not energized, and the swing arm 33 connected to the DC solenoid 34 is pushed up. Is set to the correct position. Therefore, the link shaft 32 connected to the swing arm 33 positions the contact / separation plates 31 fixed to both ends of the link shaft 32 downward. Since both ends of the idle roll 23 of the transfer conveyance unit 20A are supported by the contact / separation plate 31, the transfer conveyance unit 20A is set in a state of being separated from the photosensitive drum 10 by the contact / separation plate 31.

  On the other hand, during a normal image forming operation, the transfer conveyance unit 20A is set in a state of being in contact with the photosensitive drum 10. FIG. 6 is a diagram illustrating a state where the transfer conveyance unit 20 </ b> A is in contact with the photosensitive drum 10. During the image forming operation, the paper P that has been fed to the registration roll 54 and has been waiting is sent out by the registration roll 54 in accordance with the movement timing of the photosensitive drum 10 carrying the toner image. At that time, the sensor (not shown) detects that the leading end of the paper P is guided to the inlet chute 55 and has reached the vicinity of the contact portion between the photosensitive drum 10 and the transfer conveyance belt 21. When the control unit 30 inputs a signal from this sensor, the control unit 30 turns on the DC solenoid 34 of the retract mechanism unit 20B and starts energization. As a result, the DC solenoid 34 moves the swing arm 33 in a downward direction. When the swing arm 33 is pushed down, the link shaft 32 connected to the swing arm 33 rotates, and the contacting / separating plates 31 fixed to both ends of the link shaft 32 swing upward. Then, the idle roll 23 of the transfer conveyance unit 20 </ b> A whose both end portions are supported by the contact / separation plate 31 is set in a state of being in contact with the photosensitive drum 10. At this time, a transfer nip portion 15 is formed at a contact portion between the photosensitive drum 10 and the transfer conveyance belt 21.

  When the transfer conveyance unit 20 </ b> A comes into contact with the photosensitive drum 10, the paper P on the transfer conveyance belt 21 conveyed by the rotational drive of the drive roll 22 is transferred to the transfer nip portion 15 between the photosensitive drum 10 and the transfer conveyance belt 21. Then, a transfer bias having a polarity (plus polarity) opposite to the toner charging polarity (minus polarity) is applied to the transfer roll 24 from a transfer power source (not shown). As a result, a charge having a polarity opposite to the toner charging polarity on the photosensitive drum 10 is applied to the transfer / conveying belt 21. Then, the toner on the photosensitive drum 10 is transferred to the paper P. Thereafter, the paper P is transported in a state of being electrostatically attracted to the transfer transport belt 21 and sent to the fixing device 60.

Further, the inlet chute 20D is disposed on the upstream side of the transfer conveyance unit 20A in the transfer unit 20, and is integrally joined to the housing 70 (see FIG. 2). The photosensitive drum inlet chute 55a integrally formed with the photosensitive drum unit that supports the photosensitive drum 10 and the resist roll inlet chute 55b integrally formed with the resist roll unit that supports the resist roll 54 (FIG. Inlet chute 55 is configured in combination with an upper inlet chute consisting of 1). In this case, the inlet chute 20D constitutes the lower inlet chute of the inlet chute 55. That is, the inlet chute 55 is composed of a separate upper inlet chute and lower inlet chute, and the lower inlet chute is integrally configured with the transfer unit 20 as an inlet chute portion 20D.
The inlet chute 55 supports one surface (lower surface) of the sheet P conveyed from the resist roll 54 by the inlet chute 20D, and the other surface (upper surface) of the photosensitive drum inlet chute 55a and the resist roll. While being regulated by the inlet chute 55b, it is carried into the nip portion between the photosensitive drum 10 and the transfer conveyance belt 21 in the transfer nip portion 15 while maintaining an accurate posture without being inclined.

Next, the cleaning unit 20C will be described.
As shown in FIG. 2, the cleaning unit 20 </ b> C is configured to remove the adhering matter adhered to the cleaning brush 41 and the cleaning brush 41 by wiping off adhering matters such as paper dust and toner adhering to the surface of the transfer conveying belt 21 of the transfer conveying unit 20 </ b> A. A flicker bar 42 serving as a toner peeling means disposed so as to bite into the cleaning brush 41 so as to be struck down, and disposed on the downstream side of the cleaning brush 41 in the transport direction of the transfer transport belt 21, and the surface of the transfer transport belt 21 The cleaning blade 43 that scrapes off the attached matter, the cleaning brush 41 and the cleaning box 44 that receives the toner and paper dust removed from the surface of the transfer and transport belt 21 by the cleaning blade 43, and the toner and paper dust in the cleaning box 44 are removed. Transport to collection bottle (not shown) Osamu coil 45, the cleaning blade 43 the blade holder 46 as a supporting member for supporting the is held in a blade holder 46 is constituted by a shielding seal 47 for shielding the downstream side of the cleaning blade 43.

The cleaning brush 41 has a configuration in which a brush roll is formed around the brush shaft. The brush roll, for example, has a fiber weight of 10 denier, a fiber flocking density of 30000 / inch ² and is made of conductive polyester fiber. The outer diameter of the brush roll is 15 mm, and the outer diameter of the brush shaft made of metal is 6 mm. The resistance of the brush roll is measured by, for example, fixing the metal plate so as to bite 1 mm, grounding the brush shaft, applying a voltage of 100 V to the metal plate, and measuring the flowing current with an ammeter, and the resistance value is 5 logΩ here. It has been adjusted to be. The brush fibers of the cleaning brush 41 are formed so as to be inclined in the forward direction with respect to the transfer direction of the transfer conveyance belt 21 and arranged so as to bite into the transfer conveyance belt 21 by about 1 mm. In the normal cleaning operation, the transfer conveyance belt 21 rotates in the forward direction and the forward direction. The surface speed at that time is set 30% faster than the rotation speed of the transfer conveyance belt 21.
The flicker bar 42 is formed of a metal round bar having an outer diameter of φ5 mm, and is approximately the counterclockwise direction on the downstream side of the rotation direction of the transfer conveyance belt 21 from the position where the cleaning brush 41 contacts the transfer conveyance belt 21. The cleaning brush 41 is arranged so as to bite 1 mm at a position inclined by 90 °. Then, when the cleaning brush 41 rotates, the brush fibers on the surface collide with the flicker bar 42, so that the toner and paper dust collected on the brush fibers are knocked down and collected in the cleaning box 44. In addition, the brush fibers are thereby refreshed, and the recovery ability of the cleaning brush 41 such as toner and paper dust is recovered.

  On the other hand, the cleaning blade 43 is a plate-like member made of polyurethane rubber having a thickness of 2 mm, for example, and is disposed in counter contact with the transfer conveyance belt 21. The angle formed with the transfer / conveying belt 21 at this time is set to 27 °. The cleaning blade 43 has one end in the short direction bonded to the blade holder 46 in the longitudinal direction, and the free length in the short direction toward the transfer conveyance belt 21 is set to 7 mm.

The cleaning brush 41 rotates in the forward direction with the transfer conveyance belt 21 during image formation, and wipes off deposits such as toner and paper dust adhering to the transfer conveyance belt 21 surface. Are collected from the surface of the transfer / conveyance belt 21 to the cleaning box 44, and have a function of reducing the adhesion force of the adhered matter to the surface of the transfer / conveyance belt 21.
Further, the cleaning blade 43 disposed on the downstream side of the cleaning brush 41 scrapes off deposits that could not be wiped off by the cleaning brush 41 and collects them in the cleaning box 44.
As described above, in the cleaning unit 20C of the present embodiment, the cleaning brush 41 and the cleaning blade 43 are made to cooperate with each other, so that the particle size is fine and the shape is particularly like the toner generated by the polymerization method. Since it is nearly spherical, it is possible to effectively clean the surface of the transfer / conveyance belt 21 even for toner having high adhesion to the transfer / conveyance belt 21.

  After being cleaned in this manner, the collection coil 45 rotates in the direction of arrow C in FIG. 2 and conveys toner, paper dust, and the like in the cleaning box 44 to a collection bottle (not shown) outside the transfer unit 20. The collection coil 45 is in the direction of arrow C, that is, the direction in which toner or paper dust collected on the bottom surface of the cleaning box 44 is separated from the fixing device 60 side (upstream side in the direction of conveying the paper P of the transfer conveyance belt 21). By rotating so as to be moved, toner, paper dust, and the like are conveyed along the side wall 44a in the cleaning box 44 opposite to the fixing device 60 side. Therefore, the collected toner is difficult to receive heat from the fixing device 60, and the fusion between the toners can be suppressed. Therefore, the collected toner, paper dust, and the like can be smoothly conveyed to the collection bottle. .

Here, the contact position of the cleaning blade 43 with respect to the transfer conveyance belt 21 will be described.
FIG. 7 is a cross-sectional configuration diagram illustrating a state in which the cleaning blade 43 is in contact with the transfer conveyance belt 21. As shown in FIG. 7, the cleaning blade 43 is arranged so that the leading edge portion contacts in the region where the transfer conveyance belt 21 is wrapping the drive roll 22. As described above, the cleaning blade 43 is configured to contact the transfer conveyance belt 21 in the region where the drive roll 22 is wrapped, so that the drive roll 22 supports the transfer conveyance belt 21 from the back, and the transfer conveyance is performed. The cleaning blade 43 can stably come into contact with the belt 21 against the belt 21.
The leading edge portion of the cleaning blade 43 is in the vicinity of the transfer conveyor belt 21 in the vicinity of the position where the tangent line of the cleaning brush 41 intersects the transfer conveyor belt 21 at the position where the flicker bar 42 contacts the cleaning brush 41. It is set to contact the surface.

The cleaning brush 41 rotates in the forward direction with respect to the transfer direction of the transfer transfer belt 21 during a normal cleaning operation, but can be rotated in a direction opposite to the normal rotation direction at a predetermined timing. ing.
When the cleaning brush 41 rotates in the direction opposite to the normal rotation direction and in the forward direction, the toner and the like struck by colliding with the flicker bar 42 are as shown in FIG. It is dropped downward in the vertical direction mainly with the rotation of the cleaning brush 41 and collected in the cleaning box 44. On the other hand, when the cleaning brush 41 is rotated in the reverse direction, as shown in FIG. 8B, the toner adhering mainly to the cleaning brush 41 is mainly at the position where the flicker bar 42 contacts the cleaning brush 41. The tangential direction of 41 is the center of the vertical direction. In particular, the brush fibers of the cleaning brush 41 are formed so as to be inclined in the forward direction with respect to the transport direction of the transfer transport belt 21, and therefore when the cleaning brush 41 is rotated in the direction opposite to the transport direction of the transfer transport belt 21. The brush fibers collide with the flicker bar 42 in the reverse eye direction (direction in which the brush fibers are turned upside down), so that a relatively large amount of toner can be sprinkled.

The toner thus struck adheres to the surface of the transfer conveyance belt 21 and the surface of the cleaning blade 43 in the vicinity of the tip edge area of the cleaning blade 43 positioned above the flicker bar 42 in the vertical direction. That is, since the tip edge portion of the cleaning blade 43 is located in the tangential direction of the cleaning brush 41 at the position where the flicker bar 42 contacts the cleaning brush 41, the toner scooped up by the reverse rotation of the cleaning brush 41 is The cleaning blade 43 adheres to a peripheral region around the tip edge portion.
In this way, the collected toner can be supplied to the leading edge portion of the cleaning blade 43. That is, the cleaning brush 41 and the flicker bar 42 function as a toner supply unit that supplies recovered toner to the tip edge portion of the cleaning blade 43.

  Here, the position where the tip edge portion of the cleaning blade 43 is set is centered on the tangent line of the cleaning brush 41 at the position where the toner sprinkled by the reverse rotation of the cleaning brush 41 contacts the cleaning brush 41. Therefore, it is sufficient if the tangent line is in the vicinity region centering on the position intersecting with the transfer conveyance belt 21. For example, it is preferable that the flicker bar 42 has a spread angle of 20 to 30 ° from the position where the flicker bar 42 contacts the cleaning brush 41 around the tangent. However, since the leading edge portion of the cleaning blade 43 needs to abut on the transferring and conveying belt 21 in the region where the transfer conveying belt 21 is wrapping the drive roll 22, the leading edge portion of the cleaning blade 43 is set. The position where the transfer conveyance belt 21 wraps the drive roll 22 is within a region having a spread of 20 to 30 ° centered on the tangent line as viewed from the position of the flicker bar 42. Preferably there is. The cleaning brush 41 may be driven from the drive roll 22 via a gear. In this case, when the cleaning brush 41 rotates in the reverse direction, the transfer conveyance belt 21 also rotates in the reverse direction.

  Incidentally, the recovered toner is supplied to the leading edge portion of the cleaning blade 43 for the following reason. As described above, in the transfer unit 20 of the present embodiment, the transfer conveyance belt 21 is formed with a rubber layer as a base, and a surface layer mainly composed of urethane resin is formed on the outer surface thereof. Further, the cleaning blade 43 is also made of rubber such as urethane rubber. Further, in the transfer / conveying belt 21, since the surface layer of the transfer / conveying belt 21 is formed of urethane resin or the like, it is difficult to finish the surface smoothly like a mirror surface, and some surface roughness is generated. . Due to such a configuration, a large frictional force acts on the contact portion between the transfer conveyance belt 21 and the cleaning blade 43. For this reason, at the contact portion between the transfer conveyance belt 21 and the cleaning blade 43, fine particles such as toner are used as a lubricant to reduce the frictional force between the transfer conveyance belt 21 and the cleaning blade 43. ing.

However, there are cases where the amount of toner adhering to the transfer / conveying belt 21 decreases due to the continuous printing of a large number of images with a low image ratio or the influence of the temperature and humidity environment. In that case, the toner acting as a lubricant is insufficient due to staying in the contact portion between the transfer conveyance belt 21 and the cleaning blade 43, and the frictional force cannot be sufficiently reduced. In such a situation, so-called blade turning is easily generated in which the cleaning blade 43 is dragged and curved in the moving direction of the transfer conveyance belt 21.
In particular, in a high-temperature and high-humidity environment, moisture is adsorbed on the surface of the transfer / conveyance belt 21, so that the coefficient of friction between the transfer / conveyance belt 21 and the cleaning blade 43 increases, and the resilience elastic modulus of rubber of the cleaning blade 43 increases. Since it increases, blade turning is likely to occur.

  Therefore, in the cleaning unit 20 </ b> C according to the present embodiment, the cleaning blade is located in the vicinity region centered on the position where the tangent line of the cleaning brush 41 intersects the transfer conveyance belt 21 at the position where the flicker bar 42 contacts the cleaning brush 41. 43 is set so that the leading edge portion 43 contacts the surface of the transfer conveyance belt 21. At a predetermined timing, the cleaning brush 41 is rotated in the direction opposite to the conveyance direction of the transfer conveyance belt 21. Accordingly, the toner collected by the cleaning brush 41 is supplied to the leading edge portion of the cleaning blade 43, so that an appropriate amount of toner that is always a lubricant is interposed at the contact portion between the transfer conveyance belt 21 and the cleaning blade 43. Can be made. Therefore, it is possible to reduce the frictional force between the transfer conveyance belt 21 and the cleaning blade 43, and it is possible to suppress the occurrence of blade turning.

  Here, the timing for rotating the cleaning brush 41 in the reverse direction (reverse rotation cycle) can be set to be performed every predetermined number of prints (for example, every 200 sheets). Moreover, it can also set so that a reverse rotation cycle may be changed according to a temperature / humidity environment. That is, the image forming apparatus includes a temperature / humidity sensor (not shown) as temperature / humidity detection means for detecting temperature and humidity. For example, as described above, blade turning is likely to occur in a high-temperature and high-humidity environment. It is also effective to make a changeable setting so that the reverse rotation cycle in a high-temperature and high-humidity environment is performed in a short cycle based on the detection value of the temperature and humidity sensor. Furthermore, the cleaning brush 41 can be set to rotate in the reverse direction only in a high temperature and high humidity environment. In addition, the frequency, the rotation time, and the rotation amount may be changed based on the detection value of the temperature / humidity sensor.

  Further, the rotation amount when rotating the cleaning brush 41 in the reverse direction is preferably rotated more than an arc that moves at least the position of contact with the flicker bar 42 to the position of contact with the transfer conveyance belt 21. This is because the collected toner accumulates on the flicker bar 42, so that the collected collected toner is effectively used. That is, the toner collected on the flicker bar 42 is wiped off by the cleaning brush 41, and an appropriate amount of the toner is ejected in the direction of the tip edge portion of the cleaning blade 43, and applied directly to the transfer conveyance belt 21 while being carried on the cleaning brush 41. It is because it can supply. However, the reverse rotation amount is set to a predetermined rotation amount (for example, 2 to 3 rotations) or less so as not to increase too much. This is because if an excessive amount of toner is supplied to the tip edge portion of the cleaning blade 43 beyond an appropriate amount, it causes a cleaning failure.

Further, the resistance of the cleaning brush 41 is preferably set to 8.0 logΩ or less from the viewpoint of supplying a sufficient amount of collected toner from the cleaning brush 41 to the tip edge portion of the cleaning blade 43. This is because, when the resistance of the cleaning brush 41 is greater than 8.0 logΩ, the cleaning brush 41 itself is frictionally charged, which hinders the action of electrostatic force when the toner adhering to the surface of the transfer conveyance belt 21 is collected. It is. In that case, a sufficient amount of recovered toner held by the cleaning brush 41 cannot be obtained, and even if the cleaning brush 41 is rotated in the reverse direction, an appropriate amount of recovered toner is supplied to the tip edge portion of the cleaning blade 43. It becomes difficult.
The fiber density of the cleaning brush 41 is preferably 15000 / inch ² or more. As the fiber density is higher than 15000 lines / inch ² , the ability to collect the toner adhering to the surface of the transfer conveyance belt 21 increases, and a sufficient amount of toner is collected by the cleaning brush 41 so that the cleaning brush 41 is moved in the reverse direction. This is because an appropriate amount of collected toner can be supplied to the leading edge portion of the cleaning blade 43 when rotating.

Further, at this time, it is preferable that the drive roll 22 that supports the transfer conveyance belt 21 from the back is grounded in a region where the tip edge portion of the cleaning blade 43 contacts. By grounding the drive roll 22, the toner supplied by the reverse rotation of the cleaning brush 41 can easily adhere electrostatically to the area of the transfer conveyance belt 21 supported by the drive roll 22, and efficiently. This is because the toner can be supplied to the leading edge portion of the cleaning blade 43.
In addition, the blade turning of the cleaning blade 43 tends to occur in both end regions in the longitudinal direction. Therefore, the lengths of the cleaning brush 41 and the flicker bar 42 in the longitudinal direction are longer than the length of the cleaning blade 43 so that an appropriate amount of toner can be supplied also to the both end regions in the longitudinal direction. In addition, it is preferable that the toner can be supplied to the entire cleaning blade 43 throughout.

  Here, a paper passing test for continuously printing a low density image having an image density of 1% under a high temperature and high humidity environment (28 ° C./85% RH (Relative Humidity)) was performed. In this paper passing test, (1) a configuration in which the cleaning brush 41 is not provided and only the cleaning blade 43 is disposed, and (2) the cleaning brush 41 is provided on the upstream side of the cleaning blade 43 but the above-described reverse rotation operation is not performed. (3) The cleaning brush 41 is provided to perform the above-described reverse rotation operation, and the arrangement position of the flicker bar 42 is arranged at the lowest vertical point of the cleaning brush 41, (4) the cleaning brush 41 is provided, The reverse rotation operation described above is performed, and the arrangement position of the flicker bar 42 is also arranged on the downstream side of the transfer conveyance belt 21 in the rotation direction and inclined at about 90 ° in the counterclockwise direction (in the present embodiment). Configuration). The result is shown in FIG.

As shown in FIG. 9, in the configuration of (1), the blade was turned over when 1000 sheets of paper P were passed. This is because the condition of the paper passing test is continuous printing of a low-density image having an image density of 1% under a high-temperature and high-humidity environment (28 ° C./85% RH). In addition to an increase in the coefficient of friction between the transfer conveyance belt 21 and the cleaning blade 43 due to the adsorption, and a decrease in rubber elasticity of the cleaning blade 43, the contact portion between the transfer conveyance belt 21 and the cleaning blade 43. Insufficient toner as a lubricant staying in the toner. Therefore, it can be inferred that blade turning occurred at an early stage of 1000 sheets of paper P.
In the case of (2), blade turning occurred on 1200 sheets of paper P. In this case as well, the situation is substantially the same as in the case of (1), but the cleaning brush 41 cleans the surface of the transfer conveyance belt 21 so that the toner adheres to the brush fibers. However, the occurrence of blade turning is slightly delayed from the configuration of (1), which is 1200 sheets of paper P. This is thought to have occurred.

In the case of (3), blade turning occurred after 1500 sheets of paper P were passed. In this case, although the reverse rotation operation described above is performed, the toner scattered by the reverse rotation operation of the cleaning brush 41 because the flicker bar 42 is disposed at the lowest vertical point of the cleaning brush 41. Is not directed toward the leading edge portion of the cleaning blade 43, so that a sufficient amount of toner cannot be supplied to the leading edge portion of the cleaning blade 43. For this reason, it can be estimated that blade turning has occurred as early as 1500 sheets of paper P.
On the other hand, in the configuration of the present embodiment of (4), an appropriate amount and a sufficient amount of toner are collected by the toner collected on the brush fibers of the cleaning brush 41 by cleaning the surface of the transfer conveyance belt 21. Since it can be supplied to the edge portion, it is possible to suppress the occurrence of blade turning even at the time of 10,000 sheets of paper P even under severe conditions such as this paper passing test.

  As described above, in the image forming apparatus according to the present embodiment, in addition to the configuration in which the cleaning blade 43 and the cleaning brush 41 are arranged on the upstream side of the cleaning blade 43 in the cleaning unit 20C of the transfer unit 20. Thus, the cleaning blade 43 has a tip edge portion of the cleaning blade 43 in the vicinity region centering on the position where the tangent of the cleaning brush 41 intersects the transfer conveyance belt 21 at the position where the flicker bar 42 contacts the cleaning brush 41. It is set so as to come into contact with the surface of the transfer conveyance belt 21. At a predetermined timing, the cleaning brush 41 is rotated in the direction opposite to the conveyance direction of the transfer conveyance belt 21. With such a configuration, it is possible to supply the toner collected by the cleaning brush 41 to the tip edge portion of the cleaning blade 43, so that at the contact portion between the transfer conveyance belt 21 and the cleaning blade 43, it is always possible. An appropriate amount of toner as a lubricant can be interposed. For this reason, by cooperating the cleaning brush 41 and the cleaning blade 43, transfer and conveyance of toner having a fine particle diameter such as toner produced by a polymerization method and having high adhesion to the transfer and conveyance belt 21 is possible. The surface of the belt 21 can be effectively cleaned, and at the same time, the frictional force between the transfer conveyance belt 21 and the cleaning blade 43 can be reduced, and the occurrence of blade turning can be suppressed. .

  In particular, in the image forming apparatus of the present embodiment, when the toner is supplied to the tip edge portion of the cleaning blade 43, the toner collected by the cleaning brush 41 is used, so that wasteful consumption of the toner is suppressed and the collection is performed. Since the amount of toner collected in the bottle does not increase, the maintenance frequency can be minimized.

[Embodiment 2]
In the first embodiment, the cleaning blade 43 and the cleaning brush 41 are arranged, and the leading edge portion of the cleaning blade 43 is tangent to the transfer brush 21 at the contact position of the flicker bar 42 with the cleaning brush 41. The configuration in which the cleaning brush 41 is rotated in the direction opposite to the conveyance direction of the transfer conveyance belt 21 at a predetermined timing has been described. In the present embodiment, a configuration in which the toner collected by the cleaning brush 41 is electrostatically attached to the transfer conveyance belt 21 and the toner is supplied to the leading edge portion of the cleaning blade 43 will be described. In addition, the same code | symbol is used about the structure similar to Embodiment 1, and the detailed description is abbreviate | omitted here.

  Also in the transfer unit 20 of the present embodiment, as in the first embodiment, the cleaning unit 20C includes the cleaning blade 43 and the cleaning brush 41 on the upstream side of the cleaning blade 43. The cleaning brush 41 is grounded. Further, the transfer conveyance belt 21 is stretched, and the driving roll 22 disposed in a region facing the cleaning blade 43 and the cleaning brush 41 is also grounded. Further, in the present embodiment, the surface potential of the transfer conveyance belt 21 is the first level potential and the second level potential (| second level potential | <| first) having the same polarity as the toner charging polarity in the cleaning region. The level potential can be switched to |).

Here, the surface potential in the cleaning region of the transfer conveyance belt 21 will be described.
First, in the transfer nip portion 15, when the image area on the photosensitive drum 10 passes through the transfer nip portion 15, the paper P is carried on the transfer conveyance belt 21 and from the transfer roll 24 to the transfer conveyance belt 21. The transfer bias is applied (transfer bias ON), and a positive charge having a polarity opposite to the toner charging polarity (minus) on the photosensitive drum 10 is applied to the transfer conveyance belt 21. Therefore, since the back surface of the paper P has a positive potential opposite to the toner charging polarity, the toner on the photosensitive drum 10 is transferred to the paper P. At that time, a phenomenon occurs in which the surface of the paper P is charged by a negative charge having the same polarity as that of the photosensitive drum 10. This is because, when the paper P comes into contact with the surface of the photosensitive drum 10 in the transfer nip portion 15, it is pulled by the positive potential of the transfer conveyance belt 21 on the back surface of the paper P, and the surface of the photosensitive drum 10 on the surface of the paper P. This is presumably because the surface charge is transferred.
The positively charged paper P is conveyed in a state of being electrostatically attracted to the transfer conveyance belt 21 and is sent to the fixing device 60. When the paper P is peeled off from the transfer / conveyance belt 21, the negative charges carried on the surface of the paper P are transferred to the transfer / conveyance belt 21 by the peeling discharge. Therefore, in the cleaning area located downstream of the area where the paper P is peeled off from the transfer conveyance belt 21, the surface of the transfer conveyance belt 21 is negatively charged, and a predetermined negative potential is formed. Here, the potential is referred to as a first level potential.

On the other hand, when the inter-image area between the image areas on the photosensitive drum 10 passes through the transfer nip portion 15, the sheet P is not carried on the transfer conveyance belt 21, and the transfer roll The transfer bias from 24 to the transfer conveyance belt 21 is cut (transfer bias OFF). Then, no transfer bias is applied to the region of the transfer conveyance belt 21 that is in contact with the inter-image region of the photosensitive drum 10, and the charge on the surface of the photosensitive drum 10 is not transferred. The surface potential of the transfer / conveying belt 21 becomes a minus potential close to 0V by the driven roll 22. Here, the potential is referred to as a second level potential.
FIG. 10 is a diagram illustrating the first level potential and the second level potential. As shown in FIG. 10, in the image forming cycle of the image forming apparatus, as described above, the surface potential of the cleaning area in the transfer conveyance belt 21 is transferred by turning on / off the transfer bias of the transfer roll 24. The first level potential when the bias is turned on and the second level potential when the transfer bias is turned off are switched.

  Also, it has been found through experiments that the potential of the grounded cleaning brush 41 is set between the first level potential and the second level potential by forming the resistance of the cleaning brush 41 to 8.0 logΩ or less. ing. The method for measuring the brush resistance is the same as that described in the first embodiment. This is presumably because the resistance of the cleaning brush 41 is set to 8.0 logΩ or less and the grounding of the cleaning brush 41 suppresses frictional charging with the transfer conveyance belt 21.

As a result of the potential relationship as shown in FIG. 10, the area where the transfer bias is turned on, that is, the area where the paper P is carried on the transfer conveyance belt 21 and the toner image on the photosensitive drum 10 is transferred ( In the transfer bias ON region), the surface potential of the transfer conveyance belt 21 is higher than the potential of the cleaning brush 41 on the negative side. Therefore, in the transfer bias ON region, the negatively charged toner is transferred from the surface of the transfer conveyance belt 21 to the cleaning brush 41. Thereby, the cleaning effect of the transfer conveyance belt 21 can be enhanced.
On the other hand, in the area where the transfer bias is turned off, that is, in the area where the paper P is not carried on the transfer conveyance belt 21 and is in contact with the inter-image area on the photosensitive drum 10 (transfer bias ON area), the potential of the cleaning brush 41. Becomes higher than the surface potential of the transfer conveyance belt 21 on the negative side. Therefore, in the transfer bias OFF region, the negatively charged toner is transferred from the cleaning brush 41 to the surface of the transfer conveyance belt 21. The toner transferred to the surface of the transfer conveyance belt 21 is supplied to the leading edge portion of the cleaning blade 43 on the downstream side of the cleaning brush 41 as the transfer conveyance belt 21 rotates.

As described above, the surface potential of the cleaning region in the transfer conveyance belt 21 is changed to the first level potential and the second level potential (| second level potential | <| first level potential) that are the same polarity (minus) as the charging polarity of the toner. )) And setting the potential of the cleaning brush 41 between the first level potential and the second level potential, so that the toner collected by the cleaning brush 41 in a predetermined cycle is transferred to the tip of the cleaning blade 43. It becomes possible to supply to the edge part. Accordingly, an appropriate amount of toner that is always a lubricant can be interposed at the contact portion between the transfer conveyance belt 21 and the cleaning blade 43. Therefore, it is possible to reduce the frictional force between the transfer conveyance belt 21 and the cleaning blade 43, and it is possible to suppress the occurrence of blade turning.
In this case, the transfer conveyance belt 21 and the cleaning brush 41 function as a toner supply unit that supplies the collected toner to the leading edge portion of the cleaning blade 43.

  Incidentally, in order to sufficiently transfer the toner from the cleaning brush 41 to the surface of the transfer conveyance belt 21, it is preferable to set the potential difference between the cleaning brush 41 and the surface of the transfer conveyance belt 21 to a certain value or more. In order to verify the appropriate potential difference, a low-density image having an image density of 1% is used in a high-temperature and high-humidity environment (28 ° C./85% RH (Relative Humidity)) using a transfer conveyance belt 21 having different surface resistance values. A paper passing test for continuously printing was performed. Specifically, as the surface resistance value of the transfer conveyance belt 21, those of 6.0, 7.0, 8.0, 9.0, 10.0 logΩ are used. FIG. 11 shows the result. Here, the belt surface resistance value was measured by the following method. That is, 500 V was applied with an ADVANTEST R8340A / HR (HIRESTA) probe, and the measured value 10 seconds after the application was used as the belt surface resistance value. Further, an acrylic plate (insulating) was used for the facing surface of the probe via the transfer conveyance belt 21.

As shown in FIG. 11, the first level potential and the second level potential change depending on the surface resistance value of the transfer conveyance belt 21, and the higher the resistance value of both, the lower the potential attenuation and the larger the potential. Indicates. It was found that the potential difference (ΔV) between the first level potential and the second level potential is 100 V at the maximum when the surface resistance value of the transfer conveyance belt 21 is 7.0 to 9.0 logΩ. At that time, it was proved in the paper passing test that the cleaning blade 43 was not turned over even when 10,000 sheets were passed.
On the other hand, when the surface resistance value of the transfer conveyance belt 21 is 6.0 logΩ or 10.0 logΩ, the potential difference between the first level potential and the second level potential is 30 V and 70 V, respectively. Blade turning occurred before 10000 sheets of paper passed. This is because when the surface resistance of the transfer / conveying belt 21 is less than 7.0 logΩ, the transfer / conveying belt 21 is hardly charged. On the other hand, when the surface resistance of the transfer / conveying belt 21 exceeds 9.0 logΩ, this time the transfer / conveying belt 21 is not charged. This is presumed to be because the potential difference between the first level potential and the second level potential cannot be obtained because 21 cannot be neutralized. Thus, when the potential difference between the first level potential and the second level potential is smaller than 100 V, it is not sufficient to transfer the toner from the cleaning brush 41 to the surface of the transfer conveyance belt 21, and the cleaning blade 43 It has been found that blade turning occurs. Therefore, the potential difference between the first level potential and the second level potential is preferably set to 100 V or more. For this purpose, the surface resistance value of the transfer conveyance belt 21 is preferably set to 7.0 to 9.0 logΩ. Is preferred.
Since the first level potential and the second level potential may fluctuate depending on the temperature and humidity environment, the image forming apparatus is provided to maintain the potential difference between the first level potential and the second level potential at 100 V or more. It is also effective to change the transfer current value from the transfer roll 24 in accordance with the temperature and humidity environment based on the detected value of the temperature and humidity sensor. Further, by controlling the ON / OFF time of the transfer bias and further controlling the magnitude / time of the reverse bias applied to the idle roll 23, the above-described potential difference value can be adjusted to some extent, By combining this with a temperature / humidity sensor, the toner supply amount to the blade edge can be controlled according to environmental conditions.

  As described above, in the image forming apparatus of the present embodiment, the surface potential of the transfer conveyance belt 21 can be switched between the first level potential and the second level potential having the same polarity as the charging polarity of the toner in the cleaning region. It is configured to be able to. With this configuration, as in the first embodiment, the toner collected by the cleaning brush 41 can be supplied to the leading edge portion of the cleaning blade 43 in a predetermined cycle. Accordingly, an appropriate amount of toner that is always a lubricant can be interposed at the contact portion between the transfer conveyance belt 21 and the cleaning blade 43. Therefore, it is possible to reduce the frictional force between the transfer conveyance belt 21 and the cleaning blade 43, and it is possible to suppress the occurrence of blade turning.

In this case, the potential difference between the first level potential and the second level potential is preferably set to 100 V or more. For this purpose, the resistance value of the transfer conveyance belt 21 is formed to 7.0 to 9.0 logΩ. Is preferred. The resistance of the cleaning brush 41 is preferably formed to 8.0 logΩ or less.
Also in the image forming apparatus of the present embodiment, when the toner is supplied to the leading edge portion of the cleaning blade 43, the toner collected by the cleaning brush 41 is used, so that wasteful consumption of toner is suppressed, Since the amount of toner collected in the collection bottle does not increase, the maintenance frequency can be minimized.
Note that the configuration of the present embodiment can be further combined with the configuration of the first embodiment to further enhance the effect of suppressing blade turning.

  Examples of utilization of the present invention include application to copying machines, printers, facsimiles, and multifunctional machines using electrophotography.

1 is a schematic configuration diagram of an image forming apparatus of the present invention. It is sectional drawing which shows the structure of a transfer unit. It is a perspective view which shows the structure of a transfer unit. FIG. 3 is a perspective view illustrating a configuration of a transfer unit in a state where a transfer conveyance unit is removed. FIG. 6 is a diagram illustrating a state where a transfer conveyance unit is separated from a photosensitive drum. FIG. 6 is a diagram illustrating a state where a transfer conveyance unit is in contact with a photosensitive drum. FIG. 6 is a cross-sectional configuration diagram illustrating a state in which a cleaning blade is in contact with a transfer conveyance belt. FIG. 6 is a diagram for explaining the scattering direction of toner that is scooped up from a cleaning brush by a flicker bar. It is the figure which showed the result of having evaluated the presence or absence of generation | occurrence | production of the blade turning at the time of performing a paper passing test. It is a figure explaining the 1st level potential and the 2nd level potential. FIG. 6 is a diagram showing the results of evaluating the potential difference between the first level potential and the second level potential when using transfer / conveying belts having different surface resistance values and the presence / absence of blade turn-up during a paper passing test. is there.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Photosensitive drum, 11 ... Charger, 12 ... Laser exposure device, 13 ... Developing device, 15 ... Transfer nip part, 17 ... Drum cleaner, 20 ... Transfer unit, 20A ... Transfer conveyance part, 20B ... Retract mechanism part, 20C: Cleaning unit, 20D: Inlet chute unit, 21: Transfer conveyance belt, 22 ... Drive roll, 23 ... Idle roll, 30 ... Control unit, 31 ... Contact / separation plate, 32 ... Link shaft, 33 ... Swing arm, 34 DESCRIPTION OF SYMBOLS ... DC solenoid, 41 ... Cleaning brush, 42 ... Flicker bar, 43 ... Cleaning blade, 44 ... Cleaning box, 45 ... Collection coil, 46 ... Blade holder, 47 ... Shield seal, 54 ... Registration roll, 55 ... Inlet chute, 60 ... Fixer

Claims (17)

A toner image carrier for carrying a toner image;
A transfer conveyance belt that moves while carrying a transfer material and transfers the toner image carried on the toner image carrier to the transfer material;
A cleaning brush that abuts on the transfer and transport belt and wipes off deposits adhering to the surface of the transfer and transport belt;
A cleaning blade that counter-contacts the transfer conveyance belt on the downstream side of the cleaning conveyance belt in the movement direction of the transfer conveyance belt and scrapes the deposits on the surface of the transfer conveyance belt;
An image forming apparatus comprising: a toner supply unit that supplies toner held by the cleaning brush to a region where the cleaning blade contacts the transfer conveyance belt.   The image forming apparatus according to claim 1, wherein the toner supply unit mechanically peels off the toner held by the cleaning brush and supplies the toner to the region by scattering the toner from the cleaning brush. .   The toner supply means electrostatically transfers the toner held on the cleaning brush to the transfer / conveyance belt, and supplies the toner to the region as the transfer / conveyance belt moves. Item 2. The image forming apparatus according to Item 1. A toner image carrier for carrying a toner image;
A transfer conveyance belt that moves while carrying a transfer material and transfers the toner image carried on the toner image carrier to the transfer material;
A tension roll that stretches the transfer conveyance belt;
A cleaning brush that rotates in the same direction as the transfer conveyance belt while wiping off deposits adhering to the surface of the transfer conveyance belt and rotatable in a direction opposite to the movement direction of the transfer conveyance belt;
A toner peeling member that comes into contact with the surface of the cleaning brush and peels off the toner held by the cleaning brush;
A cleaning blade that counter-contacts the transfer conveyance belt on the downstream side of the transfer conveyance belt in the movement direction of the cleaning brush and scrapes off the deposits on the surface of the transfer conveyance belt;
The cleaning brush rotates in a direction opposite to the moving direction of the transfer / conveying belt, so that the toner is scattered from the contact portion with the toner peeling member toward the contact portion between the cleaning blade and the transfer / conveying belt. An image forming apparatus.   The cleaning blade is in contact with the transfer conveyance belt at a position where a tangent of the cleaning brush at a position where the toner peeling member abuts on the cleaning brush intersects with the transfer conveyance belt or a region in the vicinity thereof. The image forming apparatus according to claim 4.   The image forming apparatus according to claim 5, wherein the cleaning blade is in contact with the transfer conveyance belt in an area where the transfer conveyance belt is wrapped by the tension roll.   The image forming apparatus according to claim 6, wherein the tension roll is grounded. A temperature / humidity detection means for detecting temperature and humidity is further provided,
Based on the temperature and humidity detected by the temperature / humidity detection means, the cleaning brush rotates at least one of timing, frequency, rotation time, and rotation amount in the direction opposite to the moving direction of the transfer conveyance belt. The image forming apparatus according to claim 4, wherein the image forming apparatus is variable.   The image forming apparatus according to claim 4, wherein a length of the cleaning brush in a longitudinal direction is longer than a length of the cleaning blade in a longitudinal direction.   The image forming apparatus according to claim 4, wherein the cleaning brush has a resistance value of 8.0 logΩ or less. A toner image carrier for carrying a toner image;
A transfer conveyance belt that moves while carrying a transfer material and transfers the toner image carried on the toner image carrier to the transfer material;
A tension roll that stretches the transfer conveyance belt;
A cleaning brush that abuts on the transfer and transport belt and wipes off deposits adhering to the surface of the transfer and transport belt;
A cleaning blade that counter-contacts the transfer conveyance belt on the downstream side of the transfer conveyance belt in the movement direction of the cleaning brush and scrapes off the deposits on the surface of the transfer conveyance belt;
The transfer conveyance belt has a surface potential at a region where the cleaning brush contacts a first level potential having the same polarity as the charging polarity of the toner constituting the toner image, and 0V side of the first level potential. An image forming apparatus capable of switching to a set second level potential.   12. The image forming apparatus according to claim 11, wherein the surface potential of the transfer / conveying belt is set such that a potential difference between the first level potential and the second level potential is 100 V or more. A temperature / humidity detection means for detecting temperature and humidity is further provided,
The surface potential of the transfer / conveying belt is characterized in that a potential difference between the first level potential and the second level potential is controlled based on temperature and humidity detected by the temperature / humidity detecting means. Item 12. The image forming apparatus according to Item 11.   The image forming apparatus according to claim 11, wherein the cleaning brush contacts the transfer conveyance belt in a region where the transfer conveyance belt is wrapped by the tension roll.   The image forming apparatus according to claim 14, wherein the cleaning brush and the stretching roll are grounded.   The image forming apparatus according to claim 11, wherein the transfer conveyance belt has a surface resistance value of 7.0 to 9.0 logΩ.   The image forming apparatus according to claim 11, wherein the cleaning brush has a resistance value of 8.0 logΩ or less.

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