JP2010122249A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of obtaining high-quality images, in a short period of time without having to excessively consume toner. <P>SOLUTION: The image forming apparatus has a refreshment mode in which toner containing abrasive is supplied to a surface 31a of a photoreceptor drum 31 by a developing device 33, when an image is not formed. The refreshment mode includes operation that voltage applied to the photoreceptor drum 31 is temporarily made higher than the voltage applied at normal printing time by a charging roller 36. In the refreshment mode, the voltage applied to the charging roller 36 is made temporarily higher by increasing peak AC voltage or peak AC current. A cleaning device includes a cleaning blade 37 and a cleaning roller 36. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile.

  As charging means for uniformly charging the photosensitive member, those utilizing discharge are known. When the discharge is used, discharge products such as ozone and nitrogen oxide are generated along with the discharge. In the charging roller method, discharge occurs only between the charging roller and the photoconductor, so that the amount of discharge products generated is smaller than that in the charging charger method.

  However, since the discharge concentrates in a narrow space between the charging roller and the photoconductor, the amount of discharge products adhering to the surface of the photoconductor drum increases. In particular, in the case of a charging roller to which an AC voltage is applied, this tendency is more remarkable because the number of discharges is increased. Since the discharge product is a hydrophilic substance, if the discharge product adheres to the surface of the photosensitive drum, the electrical resistance on the surface of the photosensitive drum may be reduced in a high-humidity environment to cause image flow. In particular, when a photosensitive drum, such as an amorphous silicon photosensitive drum, in which the photosensitive layer is hard to be scraped is used, the discharge product is not removed and the image flow becomes remarkable.

  For this reason, for example, a technique has been proposed in which a heater is provided in the photosensitive drum to evaporate moisture on the surface of the photosensitive drum by heat, thereby suppressing a decrease in electrical resistance on the surface of the photosensitive drum in a high humidity environment. However, there are problems such as a temperature rise in the image forming apparatus, melting of toner in the developing device, and a large amount of power consumption.

  Alternatively, a method has been proposed in which the surface of the photosensitive drum is polished by a cleaning roller with toner containing an abrasive to remove discharge products and moisture adhering to the surface of the photosensitive drum (see Patent Document 1). In this method, titanium oxide having a controlled resistance value is added to the toner as an abrasive to transfer only the toner during transfer, while the abrasive is left on the photosensitive drum and supplied to the edge of the cleaning blade. As the cleaning roller, a foamed urethane roller or the like is used, and the surface of the photosensitive drum is polished through the supplied abrasive.

Japanese Patent Laid-Open No. 10-3333503

  By the way, in order to obtain a high-quality image, a sharp electrostatic latent image must be formed on the surface of the photosensitive drum. For this purpose, it is essential to reduce the thickness of the photosensitive member. However, since the charging performance is reduced when the photoconductor is thinned, it is necessary to increase the amount of charge supplied to the surface of the photoconductor drum. In order to increase the amount of charge supplied, the current or voltage applied to the charging roller must be increased, resulting in the generation of a large amount of discharge products.

  In order to quickly remove a large amount of discharge products adhering to the surface of the photosensitive drum by polishing, for example, the pressing force of the cleaning roller is increased, or the polishing force is increased by increasing the linear velocity difference between the photosensitive drum and the cleaning roller. It is necessary. However, it may cause mechanical problems such as jitter images. A heater system is effective in solving the jitter image. However, as described above, there are problems such as an increase in power consumption and an increase in temperature in the image forming apparatus.

  In addition, a leveling member such as a scraper or a film is brought into contact with the cleaning roller, and a large amount of toner is retained in the nip portion between the cleaning roller and the photosensitive drum, thereby quickly removing the discharge products attached to the surface of the photosensitive drum. However, there is also a problem that margins such as transport of collected toner and toner scattering are reduced.

  Therefore, a main object of the present invention is to provide an image forming apparatus capable of obtaining a high-quality image in a short time without consuming a large amount of toner.

  The invention according to claim 1 is a photoconductor, a charging device that uniformly charges the surface of the photoconductor, and an exposure unit that forms an electrostatic latent image on the surface of the photoconductor by exposing the surface of the photoconductor. An image forming apparatus comprising: a developing device that visualizes an electrostatic latent image formed on a surface of a photoreceptor with toner; and a cleaning device that contacts the surface of the photoreceptor and cleans the surface of the photoreceptor. In the non-image formation, the developing device has a refresh mode in which a toner containing an abrasive is supplied to the photosensitive member by the developing device. The refresh mode is a voltage or current applied to the surface of the photosensitive member by the charging device. An image forming apparatus comprising an operation of temporarily increasing the voltage or current during image formation.

  According to the first aspect of the present invention, the surface friction coefficient μ of the photosensitive member is temporarily increased by temporarily increasing the voltage or current applied to the surface of the photosensitive member by the charging device from the voltage or current at the time of image formation. Become. By increasing the surface friction coefficient μ of the photoconductor, toner having a large particle size is recovered by the cleaning device, but an abrasive having a small particle size passes through the cleaning device and is not recovered. By repeating this, a cleaning roller in which a large amount of abrasive is held is obtained. Then, by polishing the surface of the photoreceptor using this cleaning agent-rich cleaning roller, discharge products and water adhering to the surface of the photoreceptor can be efficiently removed with a minimum amount of toner.

  A second aspect of the invention is an image forming apparatus according to the first aspect of the invention, wherein the charging device is a contact charging type.

  According to the third aspect of the present invention, even in an image forming apparatus using a contact charging type charging device in which the amount of discharge products adhering to the surface of the photosensitive drum is large, the discharge products and moisture adhering to the surface of the photoconductor are removed. It can be removed reliably.

  The invention according to claim 3 is an invention subordinate to the invention according to claim 1 or claim 2, wherein the voltage or current applied to the surface of the photosensitive member by the charging device is higher than the peak AC voltage or peak AC current. The image forming apparatus is characterized in that the height is temporarily raised by the operation.

  According to the third aspect of the present invention, since the rise or fall of the voltage or current applied to the photosensitive member surface by the charging device is controlled by the peak alternating voltage or peak alternating current, the charging device becomes a small and inexpensive device.

  The invention according to claim 4 is an invention dependent on the invention according to any one of claims 1 to 3, wherein the cleaning device includes a cleaning blade and a cleaning roller. Device.

  In the invention of claim 4, since the cleaning device includes the cleaning blade and the cleaning roller, the toner having a large particle diameter is scraped off and collected by the cleaning blade by rapidly increasing the surface friction coefficient μ of the photosensitive member. Is done. On the other hand, the abrasive having a small particle diameter passes through the edge of the cleaning blade and is not recovered. This is repeated as the photoconductor rotates so that a cleaning roller in which a large amount of abrasive is held is obtained. By polishing the surface of the photoconductor with a cleaning roller that contains a large amount of this abrasive, moisture and discharge products attached to the surface of the photoconductor are reliably removed.

  A fifth aspect of the present invention is an image forming apparatus according to the first to fourth aspects of the present invention, wherein the photoconductor is made of amorphous silicon.

  According to the fifth aspect of the present invention, a good image can be provided in the long term even with an image forming apparatus using an amorphous silicon photoconductor that is liable to cause image flow.

  A sixth aspect of the present invention is an image forming apparatus according to the first to fifth aspects of the present invention, wherein the abrasive is electrically conductive.

  In the sixth aspect of the invention, since the abrasive is conductive, the abrasive easily adheres to the surface of the photoreceptor, and an abrasive-rich toner can be easily obtained.

  According to the image forming apparatus of the present invention, the toner having a large particle size is collected by the cleaning device by rapidly increasing the surface friction coefficient μ of the photoconductor, but the abrasive having the small particle size passes through the cleaning device. Will not be recovered. This is repeated by the rotation of the photoreceptor, and the cleaning roller can be made rich in abrasive. By polishing the surface of the photoreceptor using this abrasive-rich toner, it is possible to efficiently remove discharge products and moisture adhering to the surface of the photoreceptor with a minimum amount of toner. As a result, it is possible to obtain an image forming apparatus capable of suppressing the occurrence of image flow in a short time without consuming a large amount of toner.

  The above-described object, other objects, features, and advantages of the present invention will become more apparent from the following description of the best mode for carrying out the invention with reference to the drawings.

  FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus according to the present invention. The photosensitive drum 31 disposed in the central portion of the image forming apparatus 1 is driven at a predetermined speed in a clockwise direction indicated by an arrow in the drawing by a driving unit. In the vicinity of the outer periphery of the photosensitive drum 31, a charging roller 32, a developing device 33, a transfer roller 34, a cleaning device 35, and a charge eliminating lamp 38 are provided. The drum surface 31 a of the photosensitive drum 31 is uniformly charged by the charging roller 32. A laser scanning unit (optical scanning device) 8 is disposed on the downstream side of the charging roller 32 in the rotation direction of the photosensitive drum 31. The laser beam L emitted from the laser scanning unit 8 based on the image data is irradiated onto the drum surface 31a, and an electrostatic latent image is formed.

  A developing device 33 is disposed on the downstream side of the laser scanning unit 8. The developing device 33 forms a toner image on the drum surface 31a by applying toner to the drum surface 31a on which the electrostatic latent image is formed.

  A transfer roller 34 is disposed on the downstream side of the developing device 33. Further, on the downstream side of the transfer roller 34, a cleaning device 35 for removing the toner remaining on the drum surface 31a and a neutralization lamp 38 for neutralizing the potential remaining on the surface of the drum surface 31a after cleaning are arranged. ing.

  On the other hand, the pickup roller 22 takes out a sheet as a recording medium from the sheet feeding cassette 21 in synchronization with the toner image, and feeds the sheet to the horizontal portion of the transport path R1 by the sheet feeding rollers 23, 24, 25, and 26. Further, after the paper is temporarily put on standby by the registration roller 27, it is fed to the photosensitive drum 31 at a predetermined timing. The pickup roller 29 takes out the paper placed on the manual feed tray 28 and sends the paper to the horizontal portion of the transport path R1 by the paper feed rollers 24 and 26.

  The sheet fed to the photosensitive drum 31 is transferred with the toner image formed on the drum surface 31 a of the photosensitive drum 31 by the transfer roller 34, and sent to the fixing rollers 41 and 42. The sheet on which the toner image has been transferred is fixed to the toner image by heat and pressure by the fixing rollers 41 and 42, and then sent out to the vertical portion of the transport path R1, and is discharged out of the apparatus by the discharge roller 51 as a printed matter. It is loaded on the discharge tray 5.

  Further, a reverse conveyance path R2 is provided between the horizontal portion of the conveyance path R1 and the paper feed cassette 21 so that images can be formed on both sides of the sheet. Further, a conveyance roller 7 is disposed at an appropriate position between the fixing rollers 41 and 42 and the discharge roller 51 and on the reverse conveyance path R2.

  Next, an example of the refresh mode of the image forming apparatus 1 will be described with reference to FIG. FIG. 2 is an enlarged schematic configuration diagram of the periphery of the photosensitive drum 31. A control device (not shown) performs switching between the refresh mode and the print mode, application bias control in the refresh mode, rotation control of the photosensitive drum 31 and the like.

  The photosensitive drum 31 has a cylindrical metal base made of an aluminum base tube and a photosensitive layer made of amorphous silicon (typically 20 μm in thickness) disposed on the surface of the metal base. The metal base is integrally supported by a drive shaft, and the drive shaft is drivingly connected to an electric motor as a drive source via a power transmission device such as a gear (none of which is shown). The outer diameter is 28 to 32 mm, and it is rotationally driven at a linear velocity of 340 mm / sec.

  The charging roller 32, which is a contact charging type charging device, has a shaft core having an outer diameter of 12 mm and an elastic body disposed on the shaft core. The elastic body is formed of a semiconductive elastic member such as a synthetic rubber, and in this embodiment is made of epichlorohydrin rubber. The surface of the charging roller 32 (the surface of the elastic body) is in contact with the drum surface 31 a of the photosensitive drum 31. The shaft core of the charging roller 32 is connected to voltage supply means that can supply a voltage necessary for discharge.

  The toner accommodated in the developing device 33 contains a conductive abrasive for polishing the drum surface 31 a of the photosensitive drum 31. In this embodiment, titanium oxide is used as the conductive abrasive.

  The cleaning device 35 includes a cleaning roller 36 that contacts the drum surface 31a of the photosensitive drum 31 and polishes the drum surface 31a, and a cleaning blade 37 that removes toner remaining on the drum surface 31a. The cleaning roller 36 has a shaft core having an outer diameter of 10 mm and an elastic body having an outer diameter of 14 mm formed on the shaft core. The elastic body of the cleaning roller 36 and the cleaning blade 37 are preferably made of soft rubber or soft plastic having elasticity. Material is used.

  First, when the power of the image forming apparatus 1 is turned on, the ambient temperature / humidity is detected by an external temperature / humidity sensor to determine whether the environment is a high temperature / humidity environment. That is, when the condition of the temperature of 26 ° C. or higher and the humidity of 70% or higher (condition in which moisture easily adheres to the drum surface 31a of the photosensitive drum 31) is satisfied, it is determined that the external environment is high temperature and high humidity. In order to remove moisture and discharge products 31a, the image forming apparatus 1 performs a refresh operation.

  On the other hand, if the above conditions are not satisfied, it is determined that the external environment is not high temperature and high humidity (because moisture hardly adheres to the drum surface 31a of the photoconductive drum 31, the image flow due to the discharge product is unlikely to occur) Without performing the refresh operation, the printer is ready for printing, and printing is performed as appropriate. As a result, the number of refresh operations to be described later, which temporarily increases the voltage or current applied to the charging roller 32, is suppressed, and the occurrence of surface contamination of the cleaning roller 36 and damage to the cleaning blade edge is avoided.

  The refresh operation is performed in a state where the photosensitive drum 31 is rotationally driven clockwise by an electric motor (not shown). The charging roller 32 is rotated by the rotation of the photosensitive drum 31. The developing roller 33a of the developing device 33 is rotationally driven counterclockwise by an electric motor (not shown). A voltage obtained by superimposing an AC voltage on a DC voltage is applied to the charging roller 32 by voltage supply means. In this embodiment, as shown in Table 1, the DC voltage Vdc = 400 V, the peak AC voltage Vpp = 1350 V, the frequency f = 2000 Hz, and temporarily set the peak AC voltage Vpp higher than the voltage value during normal printing. Has been. As a result, the drum surface 31a of the photosensitive drum 31 is uniformly charged to the positive polarity by the charging roller 32, and the surface friction coefficient μ of the drum surface 31a of the photosensitive drum 31 is rapidly increased. The peak AC voltage Vpp is preferably about 1350V to 1600V. When the peak AC voltage Vpp is higher than the voltage value during normal printing, more discharge products are generated than usual, but since the cleaning roller is in an abrasive-rich state as will be described later, it is generated more than usual. The discharged product is removed quickly, so there is no problem.

  Thereafter, toner is supplied from the developing device 33 to the photosensitive drum 31 by bias development, and the toner is uniformly adhered to the drum surface 31a. By setting the transfer bias to a reverse bias, most of the toner is sent to the cleaning roller 36 without being transferred. The cleaning roller 36 rubs the drum surface 31a of the photosensitive drum 31 through the toner. Since the toner contains an abrasive, the drum surface 31 a is polished by the cleaning roller 36. Therefore, moisture and discharge products on the drum surface 31a are removed together with the toner.

  However, since the surface friction coefficient μ of the drum surface 31a is increased, the cleaning blade 37 causes a phenomenon that the edge of the cleaning blade 37 is caught by the drum surface 31a and slips. As a result, the edge of the cleaning blade 37 is turned up (bound), and an abrasive having a small diameter (for example, about 0.08 μm) slips through the cleaning blade 37. On the other hand, toner having a large diameter (for example, about 6 μm) can hardly pass through the cleaning blade 37, and is scraped off into the housing of the cleaning device 35 and discharged to the toner collection container by the toner collection member and collected. (Both not shown). The electric potential remaining on the drum surface 31a after the cleaning is discharged by the discharging lamp 38.

  The photosensitive drum 31 with the abrasive adhered on the drum surface 31a is again charged uniformly by the charging roller 32 whose peak AC voltage Vpp is set higher than the voltage value during normal printing. An increase in the coefficient of friction μ results. Thereafter, toner is supplied from the developing unit 33 to the photosensitive drum 31. At this time, since the abrasive is attached on the drum surface 31a, the ratio of the abrasive to the toner is relatively increased.

  Thereafter, most of the toner is transferred to the cleaning roller 36 without being transferred. The cleaning roller 36 rubs against the drum surface 31 a of the photosensitive drum 31 through the relatively abrasive-rich toner. Further, since the ratio of the abrasive entering the cleaning blade 37 is larger than that in the previous time, the amount of abrasive slipping from the cleaning blade 37 is larger than that in the previous time. Thus, each time the photosensitive drum 31 rotates, the proportion of the abrasive in the toner increases. In this embodiment, this operation is performed for 30 seconds (about 10 rotations of the photosensitive drum 31) (hereinafter, this time is referred to as “high Vpp application time”).

  Thereafter, as shown in Table 1, the peak AC voltage Vpp of the charging roller 32 is set to a voltage value of 1200 V in normal printing. The photosensitive drum 31 having a large amount of abrasive adhered to the drum surface 31 a is uniformly charged by the charging roller 32. However, since the voltage value of the charging roller 32 is a voltage value during normal printing, the surface friction coefficient μ of the drum surface 31a does not increase. The photosensitive drum 31 supplied with toner from the developing unit 33 goes around the cleaning roller 36 and the cleaning blade 37 in order.

  In the cleaning blade 37, since the surface friction coefficient μ of the drum surface 31a is not increased, the edge of the cleaning blade 37 is not easily caught on the drum surface 31a, and the edge turning (bound) is reduced. For this reason, the amount of the small-diameter abrasive dammed up by the cleaning blade 37 increases and stays, or is scraped off on the cleaning roller 36. As a result, the amount that the cleaning roller 36 holds the abrasive is rapidly increased. This was rotated about 10 times for 30 seconds by the number of rotations of the photosensitive drum 31 (hereinafter, this time is referred to as “polishing time”). That is, the drum surface 31a of the photosensitive drum 31 is polished in a state where a large amount of abrasive is held and the cleaning roller 36 having increased polishing power is completed. By doing so, the surface friction coefficient μ of the drum surface 31a is reduced compared to the refresh mode of the normal printing condition, and the image flow can be suppressed. Thus, a printable state is entered, and printing is performed as appropriate.

  Specifically, when the “high Vpp application time” for increasing the surface friction coefficient μ of the drum surface 31a is performed for 30 seconds and then the “polishing time” for 30 seconds is set to one refresh mode, it is performed once. As a result of performing the refresh mode, the surface friction coefficient μ of the drum surface 31a of the photosensitive drum 31 decreased to 0.32, and no image flow occurred.

  On the other hand, in the refresh mode in which the peak AC voltage Vpp of the charging roller 32 is set to the voltage value for normal printing without increasing it, the surface friction coefficient μ decreases only to 0.51 in one execution, and the image flow Did not go away. Then, the refresh mode was executed four times, the surface friction coefficient μ finally decreased to 0.30, and the image flow was eliminated.

  With the above refresh mode, discharge products and moisture adhering to the drum surface 31a can be efficiently removed with a minimum amount of toner. As a result, it is possible to suppress the occurrence of image flow in a short time without consuming a large amount of toner. Even in the image forming apparatus 1 using the contact charging type charging roller 32 having a large amount of discharge products adhering to the drum surface 31a or the photosensitive drum 31 made of amorphous silicon which easily causes image flow, the image forming apparatus 1 can be used for a long time. A good image can be provided.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is carried out within the range of the summary. In the embodiment, voltage control is adopted as a method for increasing the surface friction coefficient μ of the drum surface of the photosensitive drum, but current control may be adopted. In addition, this refresh mode is not performed only when the image forming apparatus is activated, and may be designed so that the refresh mode is automatically performed for each preset number of printed sheets even during continuous operation.

1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 3 is an enlarged schematic configuration diagram of the periphery of a photosensitive drum.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 31 Photosensitive drum 32 Charging roller 33 Developing device 35 Cleaning device 36 Cleaning roller 37 Cleaning blade

Claims (6)

A photosensitive member, a charging device that uniformly charges the surface of the photosensitive member, an exposure unit that forms an electrostatic latent image on the surface of the photosensitive member by exposing the surface of the photosensitive member, and a surface of the photosensitive member An image forming apparatus comprising: a developing device that visualizes the electrostatic latent image formed on the toner with a toner; and a cleaning device that contacts the surface of the photoreceptor and cleans the surface of the photoreceptor.
In the non-image formation, the developing device has a refresh mode in which toner containing an abrasive is supplied to the photoconductor, and the refresh mode is a voltage or current applied to the surface of the photoconductor by the charging device. The image forming apparatus includes an operation for temporarily increasing the voltage higher than the voltage or current during image formation.   The image forming apparatus according to claim 1, wherein the charging device is of a contact charging type.   The voltage or current applied to the surface of the photoconductor by the charging device is temporarily increased by increasing the peak AC voltage or the peak AC current. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the cleaning device includes a cleaning blade and a cleaning roller.   The image forming apparatus according to claim 1, wherein the photoconductor is made of amorphous silicon.   The image forming apparatus according to claim 1, wherein the abrasive is conductive.