JP2007232855A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To securely remove a submicron level external additive added to toner, which has been sticking to the peripheral face of an image carrier. <P>SOLUTION: A printer 10 is configured such that the peripheral face of a photoreceptor drum 20 is charged by applying voltage from a charging roller 30 rotated around a charging roller shaft 31 in contact with the peripheral face of the photoreceptor drum 20 whose peripheral face is integrally rotated around a drum shaft 21 and such that a cleaning device 70 that wipes the peripheral face of the photoreceptor drum 20 is disposed upstream of the charging roller 30 in the rotating direction of the photoreceptor drum 20. The printer 10 is provided with a brush roller 35 rotated around a brush roller shaft 36 while its peripheral face is in contact with the peripheral face of the charging roller 30 and having brush bristles 37 planted along its entire circumference. In addition, a magnetic member 80 having a permanent magnet 811 whose magnetic pole face 81 is directed to the peripheral face of the photoreceptor drum 20 is disposed between the charging roller 30 and the cleaning device 70. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention provides an image forming method employing a so-called contact charging method in which the peripheral surface of the image carrier is uniformly charged by applying a charge from a charging roller whose peripheral surface is in contact with the peripheral surface of the image carrier. It relates to the device.

  Conventionally, there has been known a contact charging device applied to a photosensitive drum (image carrier) of an image forming apparatus as described in Patent Document 1 and Patent Document 2. In these contact charging devices, the peripheral surface of the photosensitive drum is uniformly charged by a contact method in place of the conventional non-contact charging method using corona discharge. By employing such a contact-type charging device, generation of nitrogen oxides such as NOx due to corona discharge can be suppressed.

  The contact charging device described in Patent Document 1 has a plate-like contact charging member to which a voltage from a power supply device is applied. Then, the front end side of the contact charging member is brought into contact with the peripheral surface of the photosensitive drum, so that a uniform charge is applied to the peripheral surface of the photosensitive drum. On the upstream side of the contact charging member in the rotation direction of the photosensitive drum, a first cleaning blade having a leading edge surface in contact with the peripheral surface of the photosensitive drum is provided. A second cleaning blade is provided between the contact charging member, and residual toner and paper dust remaining on the peripheral surface of the photosensitive drum are scraped off and cleaned by the first and second cleaning blades. In this state (cleaning state), the peripheral surface is directed to the contact charging member for the next image forming process.

  On the other hand, in the contact charging device described in Patent Document 2, instead of the plate-shaped contact charging member described in Patent Document 1, the peripheral surface of the contact charging device is in contact with the peripheral surface of the photosensitive drum and rotates about the axis of the photosensitive drum. A so-called charging roller that is driven is employed. A voltage from the power supply device is applied to the charging roller, whereby the peripheral surface of the photosensitive drum is subjected to a charging process via the peripheral surface of the driven charging roller.

A cleaning pad is in contact with the peripheral surface of the charging roller, and a magnet is disposed opposite to the peripheral surface with a predetermined interval, and a carbon material made of a non-magnetic material attached to the peripheral surface of the charging roller ( Toner and paper powder made of carbon black) and discharge products are wiped off by a cleaning pad, while a carrier made of a magnetic material is sucked and removed by a magnet.
JP-A-7-72709 JP 2000-122381 A

  By the way, in the contact charging device described in Patent Document 1, a large particle size such as an agglomerate of toner having a large particle diameter and paper powder adhered to the peripheral surface of the photosensitive drum (usually several tens to several hundreds μm). ) Foreign matter is captured by the first cleaning blade, and submicron order fine toner aggregates that have been rubbed through the first cleaning blade are captured by the second cleaning blade. Even if the second cleaning blade is employed, even fine toner aggregates on the order of submicron cannot be effectively removed from the peripheral surface of the photosensitive drum.

  On the other hand, the contact charging device described in Patent Document 2 removes residual toner transferred from the peripheral surface of the photosensitive drum to the peripheral surface of the charging roller by a cleaning pad and removes fine toner aggregates by suction with a magnet. Therefore, the problem of the invention described in Patent Document 1 that fine toner aggregates cannot be removed is solved.

  However, in the invention of Patent Document 2, after transferring the toner aggregate from the peripheral surface of the photosensitive drum to the peripheral surface of the charging roller, the toner aggregate adhering to the peripheral surface of the charging roller is removed. Therefore, not all toner aggregates are transferred from the peripheral surface of the photosensitive drum to the peripheral surface of the charging roller. Therefore, although the magnet is used, the peripheral surface of the photosensitive drum is not used. Concerning toner aggregates that have not shifted from the surface to the peripheral surface of the charging roller, the problem remains that the peripheral surface of the photosensitive drum remains on the peripheral surface of the photosensitive drum and the cleaning of the peripheral surface of the photosensitive drum is not realized. Exists.

  Also, once the toner aggregate has moved to the charging roller, a uniform charge is applied to the peripheral surface of the photosensitive drum by applying a voltage from the charging roller, such as when the toner aggregate is not immediately adsorbed and removed by the magnet. There is also a problem that it cannot be granted.

  The present invention has been made in order to eliminate such conventional disadvantages, and includes a cleaning means capable of reliably removing fine toner aggregates of submicron order remaining on the peripheral surface of the image carrier. An object of the present invention is to provide an image forming apparatus.

  According to the first aspect of the present invention, when the peripheral surface of the image carrier is in contact with the peripheral surface of the image carrier that rotates around the axis, voltage is applied from a charging roller that rotates around the axis, so An image forming apparatus configured to perform charging processing on a surface and provided with a cleaning device for wiping the peripheral surface of the image carrier upstream of the charging roller with respect to the rotation direction of the image carrier. A brush roller rotating around the brush shaft in a state where the tip of the brush bristle planted over the entire circumference of the predetermined brush shaft parallel to the image carrier is in contact with the peripheral surface of the charging roller And a magnet is disposed between the charging roller and the cleaning device with the magnetic pole surface facing the peripheral surface of the image carrier.

  According to this configuration, by rotating the image carrier around the axis, the peripheral surface of the image carrier can be applied by applying a voltage from the charging roller that rotates while the peripheral surface is in contact with the peripheral surface of the image carrier. Are uniformly charged. An electrostatic latent image is formed on the peripheral surface of the image carrier by a predetermined image forming process on the peripheral surface of the image carrier subjected to the charging process, and the toner image is supplied by supplying toner to the electrostatic latent image. Is formed. The toner image is transferred to a separately supplied sheet. The peripheral surface of the image carrier after the transfer process on the paper reaches the cleaning device with the rotation of the image carrier in the state where the toner image is lost, and the toner particles having a large particle size remaining on the peripheral surface are here. Foreign matter such as aggregates and paper dust will be removed, but fine toner aggregates on the order of submicron will be rubbed through without being removed by the cleaning device.

  However, according to the first aspect of the present invention, the magnetic pole surface is directed to the peripheral surface of the image carrier between the cleaning device and the charging roller for a toner aggregate that is a fine foreign matter that has passed through the cleaning device. Since the magnet member having the magnet in the state is disposed, the fine toner aggregate is adsorbed by the magnet member, and thereby the fine toner aggregate, which has been extremely difficult to remove in the past, is formed on the image carrier. It is removed from the peripheral surface, and the peripheral surface of the image carrier becomes extremely clean.

  In this state, the peripheral surface of the image carrier reaches the charging roller by rotation around the axis, so that the inconvenience that fine toner aggregates move from the peripheral surface of the image carrier to the peripheral surface of the charging roller occurs. Almost never occurs.

  And even if the external additive material that could not be removed by the magnet member moves from the peripheral surface of the image carrier to the peripheral surface of the charging roller, the peripheral surface contacts the peripheral surface of the charging roller. A brush roller with brush hairs rotating around the axis in the state is provided, and this brush roller rotates around the shaft center and the external additive on the peripheral surface of the brush roller is leveled by brushing with the brush hair. Therefore, even if a small amount of external additive is present, the external additive does not adversely affect the image forming process.

  Therefore, since the toner aggregates adhere to the peripheral surface of the charging roller, it is possible to effectively prevent the occurrence of inconvenience that the uniform charge cannot be applied to the peripheral surface of the image carrier. This effectively prevents the occurrence of defects that cause image defects in the image forming process.

The invention according to claim 2 is the invention according to claim 1, wherein the brush bristles have a single yarn fineness of 10T or less and 1.0T or more, and a planting density of 300 kF / inch. ² or less and 60 kF / inch ² or more is set.

  According to such a configuration, there is no inconvenience that the potential on the peripheral surface of the charging roller drops from a predetermined potential set in advance, and an appropriate charge can always be given to the peripheral surface of the photosensitive drum.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the magnet has a magnetic flux density set to 400 G or more and 800 G or less.

  According to such a configuration, fine toner aggregates containing a magnetic material adhering to the peripheral surface of the image carrier can be adsorbed appropriately.

  The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein a gap distance between the magnetic pole surface of the magnet and the peripheral surface of the image carrier is 300 μm or less and 50 μm. It is characterized by being set above.

  According to such a configuration, the image carrier in a state in which attenuation of magnetic force of the magnet is suppressed by a narrow gap of 300 μm or less formed between the magnetic pole surface of the magnet and the peripheral surface of the image carrier and 50 μm or more. A strong magnetic attractive force acts on fine toner aggregates adhering to the peripheral surface of the toner.

  According to the first aspect of the present invention, since the magnet member having the magnet with the magnetic pole surface facing the peripheral surface of the image carrier is disposed between the cleaning device and the charging roller, fine toner aggregation is provided. The magnetic material contained in the collecting body is attracted to the magnet member, whereby the peripheral surface of the image carrier becomes extremely clean, and in this state, the peripheral surface of the image carrier is rotated around the axis and charged roller Therefore, the inconvenience that the fine toner aggregates are transferred from the peripheral surface of the image carrier to the peripheral surface of the charging roller can be prevented.

  Even if the toner aggregate or the external additive moves from the peripheral surface of the image carrier to the peripheral surface of the charging roller, the axial center is kept in contact with the peripheral surface of the charging roller. A brush roller in which brush bristles that rotate around is provided, and this brush roller rotates around the shaft center, and the brush roller brushing process cleans and smooths the peripheral surface of the brush roller. It is possible to prevent a problem that the external additive material adversely affects the image forming process.

  As a result, since the toner aggregates adhere to the peripheral surface of the charging roller, it is possible to effectively prevent the occurrence of inconvenience that the uniform charge cannot be applied to the peripheral surface of the image carrier. Thus, it is possible to effectively prevent the occurrence of defects that cause image defects in the image forming process.

According to the second aspect of the present invention, it bristles, with the fineness of a single yarn is 10T or less, and, with is set to more than 1.0 T, planted bristle density is 300kF / inch ² or less, and 60KF / Inch ² or more, so that there is no inconvenience that the potential on the peripheral surface of the charging roller drops from a predetermined potential set in advance, and appropriate charges are always applied to the peripheral surface of the photosensitive drum. Can be given.

  According to the invention of claim 3, since the magnet has a magnetic flux density of 400 G or more and 800 G or less, a fine toner containing a magnetic material adhering to the peripheral surface of the image carrier Aggregates can be properly adsorbed.

  According to the fourth aspect of the present invention, the attenuation of the magnetic force of the magnet is suppressed by a narrow gap of 300 μm or less and 50 μm or more formed between the magnetic pole surface of the magnet and the peripheral surface of the image carrier. With this, it is possible to apply a strong magnetic attraction force to the fine toner aggregates adhering to the peripheral surface of the image carrier, thereby efficiently removing the fine toner aggregates from the peripheral surface of the image carrier. Can be removed.

  FIG. 1 is a front cross-sectional view for explaining an embodiment of the internal structure of a printer 10 according to the present invention. As shown in FIG. 1, a printer (image forming apparatus) 10 includes a sheet storage unit 12 that stores sheets P to be subjected to a printing process, and one sheet fed from a sheet bundle P1 stored in the sheet storage unit 12. The apparatus main body 11 includes an image forming unit 13 that performs an image forming process on the paper P and a fixing unit 14 that performs a fixing process on the paper P that has been transferred by the image forming unit 13. At the same time, a paper discharge unit 15 for discharging the paper P subjected to fixing processing by the fixing unit 14 is provided at the top of the apparatus main body 11.

  A predetermined number (one in this embodiment) of paper cassettes 121 is provided in the paper storage unit 12 so as to be detachable from the apparatus main body 11. A pickup roller 122 is provided at the upstream end (right side in FIG. 1) of the paper cassette 121 to feed out the paper P one by one from the paper bundle P1. The paper P fed out of the paper cassette 121 by driving the pickup roller 122 is supplied to the image forming unit 13 through the paper feed conveyance path 123 and the registration roller pair 124 provided at the downstream end of the paper feed conveyance path 123. It is supposed to be paper.

  The image forming unit 13 performs a transfer process on the paper P based on image information transmitted from a computer or the like, and is provided so as to be rotatable around a drum core extending in the front-rear direction (a direction perpendicular to the paper surface of FIG. 1). The charging roller 30, the exposure device 40, the developing device 50, the transfer roller 60, and the cleaning from the position directly above the photosensitive drum 20 in the clockwise direction along the peripheral surface of the photosensitive drum (image carrier) 20. The device 70 and the magnet member (cleaning means) 80 are disposed.

  The photosensitive drum 20 is for forming an electrostatic latent image and a toner image (visible image) S ((A) in FIG. 2) along the electrostatic latent image on the circumferential surface. Amorphous silicon layers are stacked on top of each other, and the extremely smooth smoothness and toughness of the amorphous silicon layers make them suitable for forming these images.

  The charging roller 30 forms a uniform charge on the peripheral surface of the photosensitive drum 20 rotating clockwise around the drum center, and the peripheral surface is in contact with the peripheral surface of the photosensitive drum 20. Electric charges are applied to the photosensitive drum 20 while being driven to rotate. A brush roller 35 that performs a wiping process on the peripheral surface of the charging roller 30 is provided above the charging roller 30.

  The exposure device 40 irradiates the peripheral surface of the rotating photoconductor drum 20 based on image data transmitted from an external device such as a computer, and thereby the laser beam on the peripheral surface of the photoconductor drum 20 is irradiated. The electrostatic latent image is formed on the peripheral surface of the photosensitive drum 20 by erasing the electric charge in the portion checked.

  The developing device 50 supplies toner T in the developer D (FIG. 2A) to the peripheral surface of the photoconductor drum 20 to form a toner on a portion where an electrostatic latent image is formed on the peripheral surface. T is attached, and thereby a toner image S is formed on the peripheral surface of the photosensitive drum 20. In the present invention, a so-called two-component system composed of toner T and carrier C is used as developer D.

  The toner T is a fine powder having a particle diameter of 6 to 12 μm in which an additive such as a colorant (for example, carbon black), a charge control agent including a fine magnetic material, and a wax is dispersed in a binder resin. In the present specification, the colorant and binder resin are referred to as toner aggregates, and other charge control agents and additives such as wax are referred to as external additives. The toner aggregate and the external additive are usually supplied to the peripheral surface of the photosensitive drum 20 from the developing device 50 as particles having a particle diameter of several tens to several hundreds of micrometers, and a toner image is formed on the peripheral surface. Although formed, the toner aggregate that has become fine to the order of submicron (several micrometers to several tens of micrometers) remains attached to the peripheral surface of the photosensitive drum 20 without being removed by the cleaning device 70 described later. Sometimes. In the present invention, such fine toner aggregates on the order of submicrons can be removed from the peripheral surface of the photosensitive drum 20.

The carrier C is a magnetic particle having a particle diameter of 60 to 200 μm made of magnetite (Fe ₃ O ₄ ) or the like, and is used for charging the toner T. The toner T is a consumable that is appropriately replenished from the toner cartridge 54 to the developing device 50, whereas the carrier C is preliminarily loaded in the developing device 50 so that it can be used without being consumed. In the present invention, the toner T and the carrier C (that is, the developer D) are loaded in the toner cartridge 54, and both the toner T and the carrier C are simultaneously supplied to the developing device 50. It is trying to be replenished. In some cases, magnetite (Fe ₃ O ₄ ) separated from the carrier C moves to the peripheral surface of the photosensitive drum 20 and mixes with the toner T to become a part of the toner aggregate.

  The transfer roller 60 transfers a positively charged toner image S formed on the peripheral surface of the photosensitive drum 20 to the paper P with respect to the paper P sent to a position immediately below the photosensitive drum 20. Yes, a negative charge having a polarity opposite to that of the toner image S ((A) in FIG. 2) is applied to the paper P.

  Accordingly, the sheet P that has passed the position immediately below the photosensitive drum 20 is pressed and sandwiched between the transfer roller 60 and the photosensitive drum 20, and the toner image S on the circumferential surface of the photosensitive drum 20 that is positively charged is negatively charged. The sheet P is peeled off toward the surface of the paper P, whereby the transfer process is performed on the paper P.

  The cleaning device 70 is used for the printer 10 to remove and clean the residual toner T1 remaining on the peripheral surface of the photosensitive drum 20 after the transfer process in the normal operation mode M1 ((a) in FIG. 2). (In the carrier recovery mode M2 ((b) in FIG. 2), both the toner T and the carrier C adhering to the peripheral surface of the photosensitive drum 20 are removed). The peripheral surface of the photoconductive drum 20 cleaned by the cleaning device 70 goes to the charging roller 30 again for the next image forming process.

The magnet member 80 could not be removed from the circumferential surface of the photosensitive drum 20 by the cleaning device 70 (that is, the blade blade 731 (FIG. 2) of the cleaning blade 73 described later was rubbed through). The toner aggregate is removed by adsorption by magnetic force. The magnet member 80 is provided because the toner aggregate includes a magnetic material such as magnetite (Fe ₃ O ₄ ) as described above, so that the magnetic material is adsorbed by the magnet member 80. This is because toner aggregates are caused to accompany the magnetic material to be removed from the peripheral surface of the photosensitive drum 20.

  The fixing unit 14 performs a fixing process by heating the toner image S of the paper P subjected to the transfer process by the image forming unit 13, and includes a heat roller 141 in which an energized heating element is mounted, and the heat roller 141. A pressure roller 142 having a peripheral surface facing the lower surface of the roller 141 is provided. Then, the paper P after the transfer process is composed of a heat roller 141 that is driven to rotate clockwise around the roller center, and a pressure roller 142 that is driven to rotate counterclockwise around the roller center. By passing through the nip portion between them, heat from the heat roller 141 is obtained and the fixing process is performed. The paper P subjected to the fixing process is discharged to the paper discharge unit 15 through the paper discharge conveyance path 143.

  The paper discharge unit 15 is formed by recessing the top of the apparatus main body 11, and a paper discharge tray 151 for receiving the discharged paper P is formed at the bottom of the concave portion.

  The printer 10 thus configured has an operation mode in which only the toner T in the developer D is supplied to the peripheral surface of the photosensitive drum 20 to form the toner image S on the peripheral surface, and then the toner is used. Both the operation mode M1 (T) in FIG. 2 for transferring T onto the paper P and the toner T and the carrier C in the developing device 50 are forcibly adhered to the peripheral surface of the photosensitive drum 20, and the inside of the developing device 50 It is possible to switch between the carrier recovery mode M2 for extracting a part of the carrier C ((B) in FIG. 2). The operation in the carrier recovery mode M2 is performed for the following reason.

That is, as described above, the carrier C is for subjecting the toner T to a charging treatment, and a resin coat layer is formed on the surface of a spherical magnetic body (for example, Fe ₃ O ₄ ). Is mixed in the toner T, the toner T is charged well. In the operation mode M1, since the toner T moves to the photosensitive drum 20, the carrier C stays in the developing device 50, so that the resin coat layer on the surface is formed by the operation of the developing device 50 for a long time. The quality is gradually deteriorated due to peeling or toner T adhering to the periphery. When the quality of the carrier C is deteriorated, the toner T cannot be sufficiently charged, thereby causing a so-called fog phenomenon in which the toner adheres to a place where no image data exists. In order to eliminate such image density thinning and fogging phenomenon, in the past, only the carrier C in the developer D was periodically replaced with a new one, but this replacement work is very troublesome. There was an inconvenience.

  Therefore, in the present embodiment, in order to eliminate the conventional inconvenience, the carrier C is moved from the operation mode M1 when the consumption of the toner T exceeds a preset amount based on the control of a control unit (not shown). The mode is switched to the carrier recovery mode M2 that accompanies the toner T and adheres to the image carrier, and the developer D consumed in the carrier recovery mode M2 is replenished.

  FIG. 2 is an enlarged explanatory view around the photosensitive drum 20 in the image forming unit 13 of FIG. 1 paying attention to the charge of each member. (A) is the operation mode M1, (b) is The case of the carrier recovery mode M2 is shown respectively. FIG. 3 is a perspective view showing an embodiment of the photosensitive drum 20, the charging roller 30 and the brush roller 35 in the image forming unit 13. Hereinafter, the image forming unit 13 will be described in more detail based on FIGS. 2 and 3 with reference to FIG. 1 as necessary. In FIG. 2, the constituent elements of the photosensitive drum 20 and the thickness dimension of the paper P are exaggerated.

  As shown in FIG. 2, the photosensitive drum 20 includes a drum shaft 21, an aluminum base tube 22 made of aluminum alloy that is concentrically mounted around the drum shaft 21, and a peripheral surface of the aluminum base tube 22. And an amorphous silicon layer 23 that is uniformly laminated by vapor deposition or the like. The photosensitive drum 20 is rotated clockwise by driving a drum motor (not shown).

  The amorphous silicon layer 23 is formed by solidifying a silicon (Si) or silicon compound (SiC, SiO, SiON, etc.) in a solid solution, and is usually formed by physical vapor deposition such as sputtering. Such an amorphous silicon layer 23 (particularly made of SiC) has excellent charging ability due to high resistance, and also has excellent wear resistance and environmental resistance, and forms an electrostatic latent image or toner image. It is suitable as a material to be made.

Further, when the amorphous silicon layer 23 is made of silicon carbide (SiC), it is preferable that the ratio of silicon (Si) to carbon (C) is specific. As such a carbonized silica, the value of X in “Si _1-X C _X ” is preferably less than 0.3 to 1, and more preferably the value of X is 0.5 to 0.95.

The reason is that “Si _1-X C _X ” having such a value of _X has an extremely high resistance value of 10 ¹² to 10 ¹³ Ω (ohms). This is because there is little image flow of the electrostatic latent image in the rotation direction on the surface of the layer 23 and not only is excellent in the ability to maintain the electrostatic latent image, but also is excellent in moisture resistance.

  The charging roller 30 applies a voltage from the charging roller power supply 33 to the amorphous silicon layer 23 in a state where the peripheral surface is in contact with the peripheral surface of the photosensitive drum 20 (that is, the amorphous silicon layer 23). The charging roller shaft 31 is made of metal, and the charging roller body 32 is made of a dielectric material made of an elastomer such as synthetic rubber or flexible synthetic resin that is concentrically and integrally fitted to the charging roller shaft 31. .

  In the operation mode M1, the charging roller 30 is charged with a positive charge on the peripheral surface of the charging roller main body 32 by applying a positive voltage from the charging roller power source 33, as shown in FIG. In the formed state, the photosensitive drum 20 rotates counterclockwise around the axis while following the clockwise rotation around the drum shaft 21, thereby uniformly charging the amorphous silicon layer 23 with positive charges. It is made to form.

  The brush roller 35 performs wiping treatment on the peripheral surface of the charging roller main body 32, and is uniformly planted over the metal brush roller shaft 36 and the entire peripheral surface of the brush roller shaft 36. The brush bristles 37 are provided.

  As shown in FIG. 3, the photosensitive drum 20, the charging roller 30, and the brush roller 35 are rotated by a driving force transmitted from a predetermined driving motor 24. For this purpose, at one end of the drum shaft 21, a joint portion 211 to which a drive shaft (not shown) of the drive motor 24 is concentrically connected is provided, and the photosensitive drum 20, the charging roller 30 and the brush roller 35. A gear mechanism 25 for transmitting the driving force of the driving motor 24 is provided at one end of the motor.

  The gear mechanism 25 is charged so as to mesh with a drum gear 251 that is provided concentrically with the drum shaft 21 at the end of the charging roller body 32 on the side where the joint portion 211 is provided so as to be integrally rotatable. A charging roller gear 252 that is concentrically and integrally fitted to the roller shaft 31 and a brush roller gear 253 that is concentrically and integrally fitted to the brush roller shaft 36 so as to mesh with the charging roller gear 252 are provided. Configured.

  Therefore, when the driving force of the driving motor 24 is transmitted to the drum shaft 21 through the joint portion 211 and the drum gear 251 is driven to rotate around the drum shaft 21 in a predetermined direction, this driving rotation is transmitted to the charging roller gear 252 and The charging roller gear 252 is driven to rotate integrally around the charging roller shaft 31 in the opposite direction, and this driven rotation is transmitted to the brush roller gear 253 so that the brush roller gear 253 is driven integrally around the brush roller shaft 36. As a result, the charging roller 30 and the exposure device 40 are rotated simultaneously with the photosensitive drum 20 via the gear mechanism 25.

  In the present embodiment, the charging is performed so that the peripheral speed of the brush roller 35 is 85% of the peripheral speed of the charging roller 30 (that is, the linear speed ratio of the brush roller 35 to the charging roller 30 is 85%). The diameter dimension of the roller gear 252 and the brush roller gear 253 and the diameter dimension of the charging roller 30 and the brush roller 35 are set.

  Both ends of the charging roller shaft 31 and the brush roller shaft 36 are pivotally supported by the bearing member 26, and each bearing member 26 is urged downward by a coil spring 27 as an urging member. The peripheral surface of the charging roller body 32 is pressed against the peripheral surface of the photosensitive drum 20 with a predetermined pressing force by the urging force of the coil spring 27.

  The exposure device 40 irradiates a uniform charge surface formed on the amorphous silicon layer 23 by the charging roller 30 with a laser beam having strength and weakness based on the image information that has been sent to the drum surface 21. An electrostatic latent image is formed on the peripheral surface (amorphous silicon layer 23) of the rotating photosensitive drum 20 in a state in which the positive charges are almost lost. In the present embodiment, the charge of several hundred volts on the circumferential surface of the photosensitive drum 20 is reduced to about several tens of volts by laser beam irradiation, and an electrostatic latent image is formed at the portion of about several tens of volts. . In FIG. 2A schematically illustrated, the “+” symbol indicating the positive charge on the peripheral surface of the photosensitive drum 20 irradiated by the exposure device 40 is deleted.

  The developing device 50 supplies only the toner T (shown by small dots in FIG. 2) of the developer D to the amorphous silicon layer 23 of the photosensitive drum 20 formed by the exposure device 40 in the operation mode M1. The toner image S is formed along the electrostatic latent image, and the carrier C in the developer D (indicated by a black circle in FIG. 2) is supplied to the peripheral surface of the photosensitive drum 20 in the operation mode M1. There is no.

  Such a developing device 50 includes a box-shaped developing device main body 51 in which the developer D is loaded, and a state in which a part of the peripheral surface of the developing device main body 51 is opposed to the peripheral surface of the photosensitive drum 20. And a developing roller power source 53 for applying a voltage to the developing roller 52, and a toner cartridge 54 for replenishing the developer D in the developing device main body 51, and an operation mode M1. , The toner T in the developer D loaded in the developing device main body 51 is rotated around the drum shaft 21 from the peripheral surface of the developing roller 52 rotating around the axis parallel to the drum shaft 21 of the photosensitive drum 20. The toner image S is formed on the surface of the amorphous silicon layer 23 by supplying it to the amorphous silicon layer 23 of the photosensitive drum 20.

  A toner supply opening 511 for transferring the toner T in the developing device main body 51 to the peripheral surface of the photosensitive drum 20 is provided on the wall surface of the developing device main body 51 facing the peripheral surface of the photosensitive drum 20. The toner T in the main body 51 is supplied to the peripheral surface of the photosensitive drum 20 according to the rotation of the developing roller 52 through the toner supply opening 511.

  The developing roller 52 includes a developing roller shaft 521 disposed in parallel with the drum shaft 21 and a developing roller body 522 that is concentrically and externally fitted to the developing roller shaft 521 so as to be integrally rotatable. . The developing roller body 522 employs a surface of an aluminum sleeve that has been knurled or sandblasted, and a surface of which has been alumite or plated.

  The developing roller 52 is driven by a developing roller motor (not shown) in a state where a positive charge is applied to the developing roller shaft 521 by applying a positive voltage from the developing roller power source 53 to the developing roller shaft 521. The toner T rotates counterclockwise around the developing roller shaft 521, and thereby positively charged toner T in the developing device main body 51 is supplied to the amorphous silicon layer 23 of the photosensitive drum 20.

  At the upper edge of the toner supply opening 511 of the developing device main body 51, the thickness dimension of the toner T supplied from the peripheral surface of the developing roller main body 522 to the photosensitive drum 20 according to the rotation is made to a uniform predetermined level. A doctor blade 512 for aligning is provided, and the toner T is prevented from being excessively supplied to the photosensitive drum 20 by diving through the doctor blade 512.

  The toner cartridge 54 is detachably attached to the developing device main body 51. The toner cartridge 54 includes a developer discharge port 541 communicating with the inside of the developing device main body 51 and a shutter 542 that covers the developer discharge port 541 at the bottom thereof. 541 is opened and closed. The shutter 542 is opened for a predetermined time at the same time as the operation mode of the printer 10 is switched from the operation mode M1 to the carrier recovery mode M2 because the toner T in the developing device main body 51 is consumed by an amount corresponding to a preset reference value. Thus, the developer D corresponding to the consumed amount is supplied into the developing device main body 51.

  In the present embodiment, the surface potential (dark potential) Sp of the photosensitive drum 20 in the operation mode M1 is 400 V, the DC development bias (DC) Vdc is 300 V, and the AC development frequency (frequency f = 6 kHz). (AC) Vpp is set to 2 kV. On the other hand, the surface potential Sp of the photosensitive drum 20 in the carrier recovery mode M2 is 600V, the DC development bias (DC) Vdc is 300V, and the AC (frequency f = 6 kHz) development bias (AC) Vpp is 2 kV. Is set to That is, in the present embodiment, the potential difference is set to the target value by changing the surface potential of the photosensitive drum 20, but instead, the development bias may be set to the target potential difference.

  The transfer roller 60 gives a toner image from the amorphous silicon layer 23 by applying a polarity (negative polarity in the present embodiment) opposite to the polarity of the charge of the toner image S formed on the peripheral surface of the photosensitive drum 20. S is peeled off, and the peeled toner image S is transferred onto the sheet P being conveyed between the peripheral surface of the transfer roller 60 and the amorphous silicon layer 23.

  The transfer roller 60 includes a transfer roller shaft 61 that is parallel to the drum shaft 21 of the photosensitive drum 20 and a transfer roller body 62 that is concentrically and externally fitted to the transfer roller shaft 61. A negative voltage from the transfer roller power supply 63 is applied in a state where the printer 10 is set to the operation mode M1. Accordingly, the sheet P is transported between the transfer roller main body 62 and the amorphous silicon layer 23 of the photosensitive drum 20 in close contact with the peripheral surface of the transfer roller main body 62. The image S is electrostatically attracted to the surface side of the negatively charged paper P, whereby the toner image S formed on the peripheral surface of the photosensitive drum 20 is transferred to the paper P.

  The cleaning device 70 is for removing residual toner T1 remaining on the amorphous silicon layer 23 after the toner image S on the surface of the amorphous silicon layer 23 of the photosensitive drum 20 is transferred to the paper P. The cleaning device 70 includes a cleaning roller 72 having a peripheral surface attached to a lower portion in a box-shaped cleaning device main body 71 and a peripheral surface of the photosensitive drum 20 (amorphous silicon layer 23), and a tip at the photosensitive drum 20. The cleaning blade 73 is mounted on the upper part of the cleaning device main body 71 so as to abut on the peripheral surface of the cleaning device main body 71.

  The cleaning roller 72 is formed concentrically and integrally around a roller shaft parallel to the drum shaft 21. The cleaning roller 72 is made of a synthetic resin material that can be elastically deformed and has excellent toughness.

  Such a cleaning roller 72 rotates in the direction opposite to the photosensitive drum 20 (counterclockwise in the example shown in FIG. 2) at a peripheral speed faster than the peripheral speed of the photosensitive drum 20 around the roller axis. Residual toner T1 mainly composed of the toner aggregate and paper powder adhering to the amorphous silicon layer 23 remaining on the amorphous silicon layer 23 adhering to the silicon layer 23 are scraped off, thereby cleaning the amorphous silicon layer 23. It is processed.

  The cleaning blade 73 is a finishing cleaning member for the peripheral surface of the photosensitive drum 20, and is formed in a plate shape by an elastic material such as rubber. The cleaning blade 73 is mounted at an upper position in the cleaning device main body 71 in a state where the cleaning blade 73 is inclined downward toward the amorphous silicon layer 23 on the peripheral surface of the photosensitive drum 20, and the blade blade at the tip is slightly elastically deformed. 731 is in contact with the amorphous silicon layer 23. Accordingly, the residual toner T1 that could not be removed by the cleaning roller 72 is scraped off from the amorphous silicon layer 23 that has reached the blade blade 731 via the cleaning roller 72 in accordance with the clockwise rotation of the photosensitive drum 20. become.

  Then, the residual toner T1 of the amorphous silicon layer 23 removed by the cleaning roller 72 and the cleaning blade 73 is introduced into the cleaning device main body 71 and temporarily stored, and then driven by a predetermined conveying means to drive the device main body 11 (FIG. 1). ) Is collected in an unillustrated collection bottle provided in a proper position.

  The magnet member 80 removes fine toner aggregates that could not be removed from the peripheral surface of the photosensitive drum 20 by the cleaning device 70 by a magnetic force, and is disposed between the cleaning device 70 and the charging roller 30. Has been. As shown in FIGS. 2 and 3, the magnet member 80 includes a permanent magnet 81 that extends in the axial direction of the photosensitive drum 20 and has a rectangular parallelepiped shape that is substantially the same length as the photosensitive drum 20. The casing 82 is configured to hold the permanent magnet 81.

  The permanent magnet 81 is held by the casing 82 with its magnetic pole surface 811 facing the peripheral surface of the photosensitive drum 20 with a predetermined gap d. The magnetic pole surface 811 is formed in a concave arc shape with the center of curvature coinciding with the center of the photosensitive drum 20, whereby the gap d is constant in the circumferential direction of the photosensitive drum 20.

  In the present embodiment, a permanent magnet 81 having a magnetic flux density value of 400G or more and 800G or less is employed. This range is set for the magnetic flux density because if the magnetic flux density is less than 400 G, the magnetic force is too weak to effectively adsorb the external additive, and the magnetic flux density exceeds 800 G. This is because there is no difference in effect.

  In the present embodiment, the gap d between the magnetic pole surface 811 of the permanent magnet 81 and the peripheral surface of the photosensitive drum 20 is set to 300 μm or less and 50 μm or more. The reason why the gap d is set in such a range is that when the gap d exceeds 300 μm, the magnetic force becomes too weak to reliably attract the external additive. Also, if the gap d is set to be less than 50 μm, the magnetic pole surface 811 of the permanent magnet 81 may come into contact with the peripheral surface of the photosensitive drum 20 due to an assembly error or the like.

  According to the magnet member 80, even if the external additive is removed from the peripheral surface of the photosensitive drum 20 by the cleaning device 70, the portion where the cleaning blade 73 is in sliding contact with the tip of the peripheral surface of the photosensitive drum 20. When the photosensitive drum 20 reaches the position facing the magnetic pole surface 811 of the permanent magnet 81 by the rotation of the photosensitive drum 20, the remaining external additive on the peripheral surface of the photosensitive drum 20 is attracted to the magnetic pole surface 811. The peripheral surface of the photoconductive drum 20 is surely cleaned.

  Next, operation mode switching of the printer 10 will be described. First, when the operation of the printer 10 in the operation mode M1 as shown in FIG. 2 (a) is continued, the carrier C staying in the developing device main body 51 becomes the toner T and other carriers C, Furthermore, quality degradation such as a reduction in the amount of charge occurs due to rubbing against the peripheral surface of the developing roller 52.

  Therefore, in order to eliminate such inconvenience, in this embodiment, the operation of the printer 10 is changed from the operation mode M1 ((A) in FIG. 2) to the carrier when the consumption of the toner T exceeds a preset reference value. The mode is switched to the collection mode M2 ((b) in FIG. 2), whereby the carrier C in the developing device 50 is forcibly attached to the peripheral surface of the photosensitive drum 20 and is extracted from the developing device 50, and the extracted amount is set. Appropriate new developer D is supplied into the developing device main body 51.

  In the carrier recovery mode M2, as shown in FIG. 2B, a positive voltage is applied to the charging roller 30 from the charging roller power source 33, so that the peripheral surface of the photosensitive drum 20 is positively applied. While the charge is formed, no voltage is applied to the transfer roller 60 from the power supply 63 for the transfer roller, and the transfer roller 60 is slightly separated from the peripheral surface of the photosensitive drum 20. As a result, a positive charge is formed in the amorphous silicon layer 23 of the photosensitive drum 20. In this embodiment, the charge is set so that the difference from the surface voltage of the photosensitive drum 20 is −300 V as a developing bias sufficient to attract the carrier C reliably.

  In the carrier recovery mode M2, a reverse bias may be applied to the transfer roller 60 instead of separating the transfer roller 60 from the peripheral surface of the photosensitive drum 20. By doing so, the transfer of the carrier C on the circumferential surface of the photosensitive drum 20 to the transfer roller 60 can be prevented.

  In this state, the photosensitive drum 20 is rotated around the drum shaft 21 in the clockwise direction, and the developing roller 52 is rotated around the developing roller shaft 521 in the counterclockwise direction. At this time, voltage application to the developing roller 52 from the developing roller power source 53 may or may not be performed. Incidentally, FIG. 2B illustrates a state in which a voltage is applied from the developing roller power source 53 to the developing roller 52.

  Then, the positively charged carrier C (quality deteriorated carrier C1) attached to the peripheral surface of the developing roller main body 522 is negatively charged and the peripheral surface of the photosensitive drum 20 is negatively charged with the opposite polarity. Therefore, the quality deteriorated carrier C1 is separated from the developing device main body 51 from the toner T with the toner T by being sequentially peeled off from the peripheral surface of the developing roller 52 according to the rotation of the developing roller 52. It will be extracted while accompanying.

  The quality deteriorated carrier C1 transferred from the developing roller 52 to the photosensitive drum 20 is in a state where contact with the peripheral surface of the transfer roller 60 separated from the peripheral surface of the photosensitive drum 20 is avoided. Is moved to the cleaning device 70 by rotation in the clockwise direction, where a part is first removed from the peripheral surface of the photosensitive drum 20 by the cleaning roller 72, and the remaining part is subsequently scraped off by the blade blade 731 of the cleaning blade 73. Then, it is collected in the cleaning device main body 71.

  After such operation in the carrier recovery mode M2 is continued for a predetermined time, the shutter 542 of the toner cartridge 54 is opened for a predetermined time, and the toner cartridge corresponding to the developer D (quality deteriorated carrier C1 and toner T) consumed thereby. The developer D in 54 is supplied to the developing device main body 51 via the developer discharge port 541, and the operation of the printer 10 is subsequently returned from the carrier recovery mode M2 to the operation mode M1.

  In this embodiment, the developer D is set to a mixing ratio of 50 g of the carrier C to 500 g of the toner T (that is, the mixing ratio of the carrier C to the toner T is 10 wt%). The capacity of the developing device main body 51 is set to 350 g as the developer D. If the developer D has a toner mixing ratio of 5%, the toner T is 16.7 g and the carrier C is 333.3 g. To say. The capacity of the toner cartridge 54 is set to 550 g (toner T500 g + carrier C50 g).

Further, every time 100 g of toner T is consumed in the operation in the operation mode M1, the mode is changed to the carrier recovery mode M2. In determining the timing at which this mode change should be performed, the printer 10 according to the present embodiment performs processing by replacing the analog amount, which is the original document information, with a digital amount (specifically, dot information on a plane). Because of this, the characteristics of this digital machine are used. Specifically, whether or not 100 g of toner T has been consumed is determined by integrating the number of dots in the image data. That is, since the amount of toner T consumed for one dot is 2 × 10 ⁵ mg, the number of dots corresponding to 100 g of toner T is 4.96 × 10 ⁹ mg dots.

  Incidentally, if it is assumed that the printing rate is 5% on A4 size paper P, the toner consumption amount of one sheet of paper is about 35 mg as a result, and therefore when 100 g of toner is consumed, 100 g / 0.00. 035g = 2857 sheets. That is, as a rough estimate, the operation mode of the printer 10 is changed from the operation mode M1 to the carrier recovery mode M2 for every 2857 sheets of A4 size paper P.

  In the present embodiment, 10 g of quality-degraded carrier C1 is extracted from the developing device 50 in the carrier recovery mode M2. The developing device 50 is loaded with about 330 g of carrier C. To replace all the carriers C, 3.3 kg (330 g / 0.1 (10%)) of toner T needs to be consumed. is there. This amount of toner corresponds to 94300 sheets (approximately 100k sheets) in terms of the number of output sheets of A4 size paper P. If the carrier C is transferred to, for example, A4 size paper P in a solid black state, 1 g of the carrier C is consumed as an actual numerical value. Therefore, if 10 g of carrier C is discharged in one carrier recovery mode M2, the carrier recovery mode M2 is operated for every 2857 sheets on average for the transfer time of 10 sheets of A4 size paper P. It will be a good calculation.

  In the present invention, by arranging the magnet member 80 between the cleaning device 70 and the charging roller 30, it is conventionally difficult to remove the magnet member 80 from the peripheral surface of the photosensitive drum 20. The submicron-order external additive material that has passed through the cleaning blade 73 of the 70 can be removed with certainty, so that the peripheral surface of the photosensitive drum 20 can be reliably cleaned, and thereby the photosensitive drum The amount of fine toner aggregates transferred from the peripheral surface of 20 to the peripheral surface of the charging roller 30 can be suppressed as much as possible.

  In addition, since the brush roller 35 for wiping the peripheral surface of the charging roller 30 by brushing is provided, the external additive moves from the peripheral surface of the photosensitive drum 20 to the peripheral surface of the charging roller 30. Even in such a case, the external additive is leveled on the peripheral surface of the brush roller 35 by the brushing process by the brush roller 35, thereby preventing an adverse effect on the image forming process.

  In the present invention, in order to make the brushing process by the brush roller 35 effective, various ideas are added to the brush bristle 37 that is a component of the brush roller 35. Specifically, the brush bristle 37 is made of a tough, strong fluororesin such as PTFE (polytetrafluoroethylene), nylon, vinylon, or the like. The brush bristles 37 have a fineness (single yarn fineness) which is the thickness of one hair, set to 10T or less and 1.0T or more. Incidentally, “T (decitex)” is a unit indicating 1/10 of the tex (count) which is a unit of the thickness of the fiber. Moreover, in this invention, what was proposed in 1956 by the textile special committee of an international standard organization (ISO) as a tex (counter), that is, what expresses the weight of a 1000-m yarn in grams is adopted. Therefore, “T (decitex)” is a unit indicating the thickness of a fiber in which the weight of a fiber having a length of 10,000 m is expressed in grams.

  In the present invention, the fineness of the brush bristle 37 implanted on the peripheral surface of the brush roller shaft 36 is set to a range of 10T or less and 1.0T or more for the following reason. That is, when the fineness of the brush bristle 37 exceeds 10T, the potential of the surface of the charging roller 30 with which the brush bristle 37 abuts is lowered to a target surface potential (250 V in this embodiment) or less. This is because an appropriate charge cannot be applied to the peripheral surface of the photosensitive drum 20 whose peripheral surface is in contact with the peripheral surface of the charging roller 30. On the contrary, if the fineness of the brush bristles 37 is less than 1.0T, the waist of the bristles 37 becomes too weak to secure the rigidity, so that the outer surface adhering to the surface of the charging roller main body 32 cannot be secured. This is because foreign materials such as additives cannot be removed. These are things that were derived after many confirmation tests with actual machines.

In the present invention, the density of the bristle 37 implanted on the peripheral surface of the brush roller shaft 36 is set to 300 kF / inch ² or less and 60 kF / inch ² or more. In addition, kF is the number of single yarns (filaments) of the brush hair 37 in which the brush roller shaft 36 is implanted.

The reason why such a range is set for the density of the brush bristles 37 implanted in the brush roller shaft 36 is as follows. That is, when the density of the brush hairs 37 exceeds 300 kF / inch 2, the surface potential of the charging roller 30 with which the brush hairs 37 are in contact decreases to become a target surface potential (250 V in this embodiment) or less, This is because an appropriate charge cannot be applied to the peripheral surface of the photosensitive drum 20 whose peripheral surface is in contact with the peripheral surface of the charging roller 30. Conversely, if the fineness of the brush bristle 37 is less than 60 kF / inch ² , the brush bristle 37 becomes too sparse, thereby removing foreign substances such as external additives adhering to the surface of the charging roller body 32. Because it becomes impossible. These things have been confirmed after many confirmation tests using actual machines.

  As described above in detail, the printer 10 according to the present invention has a charging device that rotates around the charging roller shaft 31 while the peripheral surface is in contact with the peripheral surface of the photosensitive drum 20 that rotates integrally with the drum shaft 21. The peripheral surface of the photosensitive drum 20 is charged by applying a voltage from the roller 30, and the circumference of the photosensitive drum 20 is upstream of the charging roller 30 with respect to the rotation direction of the photosensitive drum 20. Since the cleaning device 70 for wiping the surface is provided, the peripheral surface is in contact with the peripheral surface of the photosensitive drum 20 by rotating the photosensitive drum 20 around the drum shaft 21. A uniform charging process is performed on the peripheral surface of the photoconductive drum 20 by applying a voltage from the charging roller 30 that rotates at (1). An electrostatic latent image is formed on the peripheral surface of the photosensitive drum 20 by the exposure processing based on the image information from the exposure device 40 on the peripheral surface of the photosensitive drum 20 subjected to the charging process. By supplying the toner T from the developing device 50 toward the image, a toner image is formed on the peripheral surface of the photosensitive drum 20.

  The sheet P is supplied to the nip portion between the rotating photosensitive drum 20 and the transfer roller 60 with the toner image formed on the peripheral surface of the photosensitive drum 20, whereby the photosensitive drum 20. The toner image S on the peripheral surface is transferred onto the paper P. The peripheral surface of the photosensitive drum 20 after the transfer process on the paper P reaches the cleaning device 70 as the photosensitive drum 20 rotates with the toner image S disappeared, and remains on the peripheral surface here. The toner T1 and foreign matters such as paper dust adhering to the peripheral surface are removed, but the sub-micron-order toner aggregate that cannot be completely removed by the cleaning blade 73 rubs through the cleaning blade 73. End up.

  In the present invention, with the external additive that has passed through the cleaning blade 73 as a target, the magnetic pole surface 811 faces the peripheral surface of the photosensitive drum 20 between the charging roller 30 and the cleaning device 70. Since the magnet member 80 having the permanent magnet 81 is disposed, the magnetic material contained in the external additive is adsorbed by the magnet member 80, and thus the external additive that has been extremely difficult to remove in the past can be obtained. It is removed from the peripheral surface of the photosensitive drum 20, and the peripheral surface of the photosensitive drum 20 becomes extremely clean.

  In this state, the peripheral surface of the photosensitive drum 20 reaches the charging roller 30 by rotation around the drum shaft 21, so that fine toner aggregates on the order of submicrons are from the peripheral surface of the photosensitive drum 20 to the periphery of the charging roller 30. The occurrence of inconveniences such as shifting to the surface hardly occurs.

  Even if the external additive material moves from the peripheral surface of the photosensitive drum 20 to the peripheral surface of the charging roller 30, the brush roller shaft is in a state where the peripheral surface is in contact with the peripheral surface of the charging roller 30. The brush roller 35 is provided around the entire circumference of the brush roller shaft 36 and is rotated around the brush roller 35. The brush roller 35 rotates around the brush roller shaft 36 and is brushed by the brush hair 37. Since the external additive transferred to the peripheral surface of the brush roller 35 in the process is leveled, the image forming process is not adversely affected.

  As a result, since fine toner aggregates adhere to the peripheral surface of the charging roller 30, there is an inconvenience that a uniform charge cannot be applied to the peripheral surface of the photosensitive drum 20. Thus, it is possible to effectively prevent the occurrence of a malfunction that causes an image defect in the image forming process in the image forming unit 13.

In the present invention, the brush bristle 37 implanted in the brush roller shaft 36 has a single yarn fineness of 10 T or less and 1.0 T or more, and an implantation density of 300 kF / inch 2 or less. In addition, since it is set to 60 kF / inch ² or more, there is no inconvenience that the potential of the peripheral surface of the charging roller 30 is lowered from a predetermined potential set in advance, and an appropriate charge is always sensitized. It can be applied to the peripheral surface of the body drum 20.

  Further, since the permanent magnet 81 of the magnet member 80 is set to have a magnetic flux density of 400 G or higher and 800 G or lower, the external additive attached to the peripheral surface of the photosensitive drum 20 can be appropriately adsorbed. Can do.

  Further, since the gap d between the magnetic pole surface 811 of the permanent magnet 81 and the peripheral surface of the photosensitive drum 20 is set to 300 μm or less and 50 μm or more, the magnetic force of the permanent magnet 81 is set by this narrow gap d. A strong suction force can be applied to the external additive adhering to the peripheral surface of the photosensitive drum 20 in a state in which the attenuation of the photosensitive drum 20 is suppressed.

  The present invention is not limited to the above embodiment, and includes the following contents.

  (1) In the above embodiment, the printer 10 is employed as the image forming apparatus. However, the present invention is not limited to the printer 10 being an image forming apparatus, and may be a copying machine or a facsimile apparatus. There may be.

  (2) In the above embodiment, the printer 10 is capable of mode switching between the operation mode M1 and the carrier recovery mode M2. However, in the present invention, the printer 10 has the operation mode M1 and the carrier recovery mode. It is not limited to that the mode can be switched with M2, and the mode setting of only the operation mode M1 may always be performed.

  (3) In the above embodiment, the permanent magnet 81 is employed for the magnet member 80. However, the present invention is not limited to the permanent magnet 81, and an electromagnet is employed as the magnet. May be. When an electromagnet is employed, the external additive adsorbed on the electromagnet can be easily removed by interrupting the supply of electric power to the electromagnet.

  (4) In the above embodiment, the mixture of toner T and carrier C is supplied from the toner cartridge 54 to the developing roller 52 as a developer. However, in the present invention, the developing roller 52 is supplied. The developer is not limited to the mixture of the toner T and the carrier C, and a system in which only the toner T is supplied to the developing roller 52 may be used.

  In order to confirm the relationship between the single yarn fineness of the brush bristles 37 used for the brush roller 35 and the peripheral voltage V0 of the charging roller 30, the actual printer 10 is used to apply 10,000 sheets of paper P to the printer 10. Then, the voltage on the peripheral surface of the photosensitive drum 20 for each single yarn fineness of the used bristle 37 was measured. The peripheral surface voltage V0 of the initial photosensitive drum 20 was set to 255V. Moreover, as the brush roller 35, the brush roller 37 in which the planting density of the brush bristles 37 is set to 300 kF / inch2 or less is employed. The measurement results are as shown in the graph of FIG.

  That is, as shown in the graph of FIG. 4, until the single yarn fineness of the brush bristles 37 exceeds 10T, the peripheral voltage V0 of the charging roller 30 is a value that is substantially close to the initial set voltage of 255V. However, when the single yarn fineness exceeds 10T, the value of the circumferential voltage V0 gradually decreases as the excess amount increases. This is the basis for setting the single yarn fineness of the bristles 37 to 10 T or less in the present invention.

  In order to confirm the relationship between the density of the bristle 37 used for the brush roller 35 and the peripheral voltage V0 of the charging roller 30, the actual printer 10 is used to process 10,000 sheets of paper P to the printer 10. Then, the voltage on the circumferential surface of the photosensitive drum 20 for each density of the used bristle 37 was measured. The peripheral surface voltage V0 of the initial photosensitive drum 20 was set to 255V. Further, as the brush roller 35, a brush roller 37 in which the single yarn fineness of the bristle 37 is set to 10T or less is employed. The measurement results are as shown in the graph of FIG.

  That is, as shown in the graph of FIG. 5, until the density of the bristle 37 exceeds 300 kF / inch2, the circumferential voltage V0 of the charging roller 30 is a value that is substantially close to the initial set voltage of 255V. However, when the density exceeds 300 kF / inch 2, the value of the peripheral voltage V 0 rapidly decreases as the amount exceeding the density increases. This is the basis for setting the density of the bristles 37 to 300 kF / inch 2 or less in the present invention.

  The gap d between the magnetic pole surface 811 of the permanent magnet 81 and the peripheral surface of the photosensitive drum 20 is changed variously, and the actual printer 10 for each gap d for 400 G, 600 G, and 800 G with respect to the magnetic flux density of the permanent magnet 81. After the transfer processing was performed on 10,000 sheets of paper P, the adsorption state of the external additive adsorbed by the permanent magnet 81 was visually observed to determine whether the adsorption state was good or bad. As the dimension of the gap d, five types of 0 μm (no gap), 100 μm, 200 μm, 300 μm and 400 μm were adopted. The test results are as shown in Table 1. By the way, in Table 1, ○ indicates that the adsorption status was good, x indicates that the adsorption status was poor, and Δ indicates that the adsorption status was slightly good. Show. In Table 1, “scraping” indicates that the peripheral surface of the photosensitive drum 20 is scraped by sliding contact with the charging roller 30.

  As shown in Table 1, when the gap d between the magnetic pole surface 811 of the permanent magnet 81 and the peripheral surface of the photosensitive drum 20 is 100 μm, 200, and 300 μm, the magnetic flux density of the permanent magnet 81 is 400 G, 600 G, and 800 G. In either case, it was confirmed that the external adsorbent was attracted by the permanent magnet 81 in a good state. On the other hand, when the gap d is 400 μm, it was confirmed that the permanent magnet 81 hardly adsorbs the external additive when the magnetic flux density of the permanent magnet 81 is 400 G and 600 G. However, even when the gap d is 400 μm, when the magnetic flux density of the permanent magnet 81 is 800 G, the adsorbing condition of the external additive by the permanent magnet 81 is slightly good. This is based on the fact that the magnetic flux density of 81 is set to 400 μm or less.

It is explanatory drawing of front sectional view for demonstrating one Embodiment of the internal structure of the printer which concerns on this invention. FIG. 2 is an enlarged explanatory view around the photosensitive drum in the image forming unit of FIG. 1 with attention paid to the charge of each member, where (A) is in the operation mode M1 and (B) is in the carrier recovery mode M2. Respectively. FIG. 3 is a perspective view illustrating an embodiment of a photosensitive drum, a charging roller, and a brush roller in an image forming unit. It is a graph which shows the relationship between the single yarn fineness of a bristle, and the surrounding surface potential of the charging roller after performing image formation processing with respect to 10,000 sheets of paper. It is a graph which shows the relationship between the density of a bristle, and the surrounding surface potential of the charging roller after performing an image formation process with respect to 10,000 paper.

Explanation of symbols

10 Printer (image forming device)
DESCRIPTION OF SYMBOLS 11 Apparatus main body 12 Paper storage part 121 Paper cassette 122 Pickup roller 123 Paper feed conveyance path 124 Registration roller pair 13 Image forming part 14 Fixing part 141 Heat roller 142 Pressure roller 143 Paper discharge conveyance path 15 Paper discharge part 151 Paper discharge tray 20 Photosensitive drum (image carrier)
DESCRIPTION OF SYMBOLS 21 Drum shaft 211 Joint part 22 Aluminum elementary pipe 23 Amorphous silicon layer 24 Drive motor 25 Gear mechanism 251 Drum gear 252 Charging roller gear 253 Brush roller gear 26 Bearing member 27 Coil spring 30 Charging roller 31 Charging roller shaft 32 Charging roller main body 33 For charging roller Power supply 35 Brush roller 36 Brush roller shaft 37 Brush bristle 40 Exposure device 50 Developing device 51 Developing device main body 511 Toner supply opening 512 Doctor blade 52 Developing roller 521 Developing roller shaft 522 Developing roller main body 53 Developing roller power supply 54 Toner cartridge 541 Developer Discharge port 542 Shutter 60 Transfer roller 61 Transfer roller shaft 62 Transfer roller body 63 Transfer roller power supply 70 Cleaning device 71 Cleaning device body 72 Cleaning Roller 73 Cleaning blade 731 Blade blade 80 Magnet member (cleaning means)
81 Permanent magnet 811 Magnetic pole surface 82 Casing D Developer C Carrier C1 Quality deteriorated carrier d Gap M1 Operation mode M2 Carrier recovery mode P Paper P1 Paper bundle S Toner image T Toner T1 Residual toner

Claims (4)

The peripheral surface of the image carrier is subjected to a charging process by applying a voltage from a charging roller that rotates about the axis while the peripheral surface is in contact with the peripheral surface of the image carrier that rotates around the axis. In an image forming apparatus configured and provided with a cleaning device for wiping the peripheral surface of the image carrier upstream of the charging roller with reference to the rotation direction of the image carrier,
A brush roller that rotates about the brush shaft in a state in which the tip of the brush bristle planted over the entire circumference of a predetermined brush shaft parallel to the image carrier is in contact with the peripheral surface of the charging roller; And
An image forming apparatus, wherein a magnet is disposed between the charging roller and the cleaning device with a magnetic pole surface facing the peripheral surface of the image carrier. The brush bristles have a single yarn fineness of 10 T or less and 1.0 T or more, and a planting density of 300 kF / inch ² or less and 60 kF / inch ² or more. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the magnet has a magnetic flux density set to 400 G or more and 800 G or less.   4. The gap distance between the magnetic pole surface of the magnet and the peripheral surface of the image carrier is set to 300 μm or less and 50 μm or more. 5. Image forming apparatus.

Images