JP4615227B2 - Cleaning system and image forming apparatus including the cleaning system - Google Patents

Description

The present invention is a cleaning system, and, in which relates to an image forming equipment having the cleaning system.

  In this type of image forming apparatus, a transfer electric field is formed between the latent image carrier and the transferred material that moves while contacting the latent image carrier, so that the toner image on the latent image carrier is transferred onto the transferred material. Some employ an electrostatic transfer system that transfers to the surface. In such an apparatus, residual toner remains on the surface of the latent image carrier after transfer. If the latent image carrier surface portion is subjected to the next image forming process without the transfer residual toner being removed, charging failure such as uneven charging occurs on the latent image carrier surface portion, and the image quality deteriorates. Cause. Therefore, conventionally, a cleaning device is provided at a position facing the surface of the latent image carrier from the transfer region to the charging region to remove the transfer residual toner. Such a cleaning device includes a waste toner tank that stores transfer residual toner collected from the surface of the latent image carrier, a recycled toner transport passage that transports the transfer residual toner to reuse the collected transfer residual toner, and the like. Space to provide is required. This increases the size of the image forming apparatus.

  For example, there is an image forming apparatus disclosed in Patent Document 1 that can cope with the problem of enlargement of the apparatus. This image forming apparatus employs a system (hereinafter referred to as “developer recovery system”) that collects the transfer residual toner remaining on the surface of the latent image carrier using a developing device. In this developing device collection method, since the transfer residual toner is collected by a developing device installed for a purpose other than cleaning, it is not necessary to separately provide the waste toner tank and the recycled toner conveyance path as described above. Therefore, if this developer collection system is adopted, it can greatly contribute to the downsizing of the apparatus.

  Japanese Patent Application Laid-Open No. 2005-228561 describes an embodiment in which charging is performed by bringing a charging roller into contact with a latent image carrier as a charging device mounted on an image forming apparatus of a developing device collection type. Conventionally, the surface of the latent image carrier is uniformly charged by a contact / proximity charging method in which a charging member such as a charging roller is brought into contact with or close to the surface, and by a corona charger or the like. Charged charger charging methods are known. However, in the charger charging method, it is necessary to generate a large amount of discharge in order to bring the surface of the latent image carrier to a desired potential, so a large amount of discharge products such as ozone and NOx are generated, which is an environmental problem. There is. On the other hand, the contact / proximity charging method is advantageous in terms of the environment because it generates less discharge than the charger charging method.

  However, in such an image forming apparatus using both the developer collection method and the contact / proximity charging method, the transfer residual toner, the charging member, and the like are transferred while the transfer residual toner on the latent image carrier is conveyed to the development region. Will be in contact with or close to each other. For this reason, reversely charged transfer toner may adhere to the charging member. If reversely charged transfer residual toner adheres to the charging member, uniform charging is hindered by the adhered transfer residual toner, and the surface potential of the latent image carrier cannot be set to a desired potential, or charging failure such as uneven charging is caused. It occurs. As a result, there has been a problem that image density is deteriorated and background stains occur, resulting in image quality deterioration.

  In Japanese Patent Application No. 2002-254142, the present applicant has proposed an image forming apparatus that can solve the above-mentioned problems. This image forming apparatus collects, from a transfer residual toner remaining on the surface of the latent image carrier after transfer, a transfer residual toner having a polarity opposite to the polarity of the charging bias from the surface of the latent image carrier by a temporary holding means such as a fur brush. And hold. By collecting and holding the transfer residual toner having a polarity opposite to the polarity of the charging bias in this way, it is possible to prevent the transfer residual toner from adhering to the charging member. Then, the held transfer residual toner having a polarity opposite to the polarity of the charged bias is returned to the surface of the latent image carrier at a predetermined timing, for example, after one image is formed and before the next image is formed. The transfer residual toner returned onto the latent image carrier in this way is collected by the developing device, or transferred to a transfer target or a transport member for transporting the transfer target. According to this apparatus, while the returned toner passes through the charging region, the application of the charging bias is stopped or the charging member is separated from the latent image carrier. Residual toner does not adhere to the charging member.

Japanese Patent No. 3091323

  However, toner having the same polarity as the charging bias among the transfer residual toner is not collected by a temporary holding means such as a fur brush. Therefore, during the next image forming process, the latent image forming means passes through an area (hereinafter, referred to as a latent image forming area) facing and is collected by the developing device or transferred to a transfer medium. Therefore, a latent image is formed on the surface of the latent image carrier by the latent image forming means while the transfer residual toner is attached to the surface of the latent image carrier. Then, the portion where the toner is attached or the portion which is shaded by the toner is not exposed. As a result, there may be a problem that white spots occur in the solid image portion.

  Therefore, in Japanese Patent Application No. 2003-434907, the present applicant slidably contacts a magnetic brush made of magnetic particles with the surface of the latent image carrier before the transfer residual toner reaches the charging member, and the transfer residual toner is moved to the magnetic material. A temporary holding means for temporarily holding with a brush is proposed. Thus, the transfer residual toner can be held by the temporary holding unit regardless of the polarity of the transfer residual toner, and the transfer residual toner can be prevented from passing through the latent image forming area while forming the latent image on the surface of the latent image carrier. I was able to. By making the magnetic particles have a small particle diameter, it is preferable that the interval between the magnetic brushes can be increased, the number of times of contact with the transfer residual toner is increased, and the transfer residual toner can be reliably held. However, since the magnetic particles having a small particle diameter have a weak magnetic binding force, in the case of a magnetic brush formed only of a magnetic particle having a small particle diameter, the tip of the magnetic brush falls off due to sliding contact with the latent image carrier. May end up. Then, during the formation of the latent image on the surface of the latent image carrier, the dropped magnetic particles pass through the latent image forming region, thereby forming an unexposed portion on the surface of the latent image carrier. As a result, there may be a problem that white spots occur in the solid image portion. Therefore, it is conceivable to form a magnetic brush having a high magnetic binding force by using magnetic particles having a high magnetic binding force and a large particle size. However, if the particle size of the magnetic particles is increased, the spacing between the magnetic brushes becomes sparse and cannot be in close contact with the surface of the latent image carrier. As a result, the number of times of contact between the transfer residual toner and the magnetic brush is reduced, and the transfer residual toner on the surface of the photoconductor may not be temporarily held reliably. As a result, there is a problem that the transfer residual toner passes through the latent image forming area and a white spot is generated in the solid image portion during the formation of the latent image on the surface of the latent image carrier.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a cleaning system capable of suppressing the occurrence of white spots in a solid image portion and obtaining a good image, and the cleaning system. to provide the images forming apparatus provided with.

In order to achieve the above object, according to the first aspect of the present invention, the surface of the latent image carrier is uniformly charged by the charging means, and a latent image is formed on the surface of the uniformly charged latent image carrier by the latent image forming means. The latent image is converted into a toner image by the developing means, the toner image is transferred to the surface moving member by the transferring means, and the transfer residual toner remaining on the surface of the latent image carrier after being transferred by the transferring means is developed by the developing means. In the cleaning system that collects the toner on the surface, two or more types of magnetic particles having different particle size distributions are built in the magnetic field generating means while the transfer residual toner reaches the charging means from the transfer means. And a temporary holding means for temporarily holding the transfer residual toner with the magnetic brush by bringing the magnetic brush into sliding contact with the surface of the latent image carrier, and the temporary holding means. Control means for returning the transfer residual toner to the surface of the latent image carrier again at a predetermined timing, and the magnetic particles include magnetic particles having an average particle diameter of 70 μm to 100 μm and an average particle diameter of 20 μm to 50 μm. consists of a magnetic particle, among them, the following magnetic particles 100μm the average particle size 70μm or Ri der than 80 wt% 40 wt% or more, the control means, the image bearing member surface after passing said transfer means A holding bias of about the same level as the potential of the latent image carrier or the same potential as the potential of the surface of the latent image carrier after passing through the transfer means and an absolute value greater than the absolute value of the potential of the surface of the latent image carrier after passing through the transfer means Application bias selection means for selectively applying a value emission bias to the magnetic brush is provided .
According to a second aspect of the present invention, in the cleaning system of the first aspect, the toner is a magnetic toner.
According to a third aspect of the present invention, in the cleaning system according to the first or second aspect , the control means performs control so that the applied bias selection means selects a discharge bias during non-image formation. is there.
According to a fourth aspect of the present invention, in the cleaning system according to the first, second, or third aspect , the temporary holding unit includes a driving unit that rotates the rotating member in the same direction as the rotation direction of the latent image carrier. It is characterized by this.
The invention of claim 5, forming a latent image forming a latent image bearing member, a charging means for uniformly charging the latent image bearing member surface, the latent image on the uniformly charged surface of the latent image carrier A transfer electric field is formed between the developing means, the developing means for attaching the toner to the latent image, and the surface moving member that moves while contacting the latent image carrier, and the developing means And a transfer unit that transfers the toner image formed on the surface of the latent image carrier onto the surface moving member. After the toner image is transferred to the surface moving member, the toner image remains on the surface of the latent image carrier. The cleaning system according to the first, second, third, or fourth aspect is used as a cleaning means for removing the transfer residual toner.

According to the present invention, before the transfer residual toner reaches the charging means, it is slidably contacted with the latent image carrier and temporarily held by the magnetic brush regardless of the polarity of the transfer residual toner. Then, when the transfer residual toner returned from the magnetic brush to the latent image carrier passes through the latent image forming area, it is held by the temporary holding unit at a predetermined timing such that the latent image forming unit is not operating. The transfer residual toner is returned to the surface of the latent image carrier again. This suppresses the transfer residual toner from adhering to the surface of the latent image carrier passing through the latent image forming area during the latent image formation. Accordingly, an unexposed portion due to the transfer residual toner is not formed. As a result, the occurrence of white spots in the solid image portion is suppressed, and there is an effect that a good image can be obtained.
The magnetic brush is formed of two or more kinds of magnetic particles having different particle size distributions. As a result, the magnetic brush has magnetic particles with a small particle size attached around the magnetic particles with a large particle size. This small magnetic particle becomes the tip of the magnetic brush and slidably contacts the surface of the latent image carrier, and the number of times the surface of the latent image carrier contacts the magnetic brush increases, so that it adheres to the latent image carrier. The transfer residual toner can be reliably held mechanically. In addition, since the magnetic particles having a large particle size have a high magnetic binding force, the magnetic particles having a small particle size around the magnetic particles having a large particle size are securely held by the magnetic particles having a large particle size. The As a result, the magnetic particles having a small particle diameter at the tip of the magnetic brush fall off due to the electrostatic force of the transfer residual toner or the sliding contact with the latent image carrier and do not adhere to the surface of the latent image carrier. Therefore, since the unexposed portion is not formed by the dropped magnetic particles, the occurrence of white spots in the solid image portion is suppressed, and an excellent image can be obtained.
Also, if the magnetic particles are formed or coated with a material that can charge the toner to a desired polarity by frictional charging, the polarity of the temporarily retained transfer toner can be made uniform. Accordingly, if the temporarily retained transfer residual toner is aligned with, for example, the same polarity as the charging bias, the transfer residual toner returned to the surface of the latent image carrier at the above timing passes through the charging unit without electrostatic adsorption. be able to.

  Hereinafter, an embodiment in which the present invention is applied to an electrophotographic printer (hereinafter simply referred to as “printer”) as an image forming apparatus will be described (hereinafter, this embodiment is referred to as “embodiment 1”). . In this printer, yellow (hereinafter referred to as “Y”), cyan (hereinafter referred to as “C”), magenta (hereinafter referred to as “M”), black (hereinafter referred to as “K”). ) Is used to form a color image.

  In the present embodiment, a negative / positive image forming method in which the image portion causes the charge on the photoreceptor to disappear and toner is attached to a portion having no charge by a developing bias will be described, but the present invention is not limited to this. Alternatively, a positive / positive image forming method may be used.

First, the basic configuration of the printer will be described.
FIG. 1 is a schematic configuration diagram of a printer according to the first embodiment. The printer includes four photosensitive members 1Y, 1C, 1M, and 1K as latent image carriers. Here, a drum-shaped photoconductor is taken as an example, but a belt-shaped photoconductor can also be adopted. Each of the photoreceptors 1Y, 1C, 1M, and 1K is rotationally driven in the direction of the arrow in the drawing while contacting the intermediate transfer belt 10 that is an endless moving member as a surface moving member. In the present embodiment, each of the photoreceptors 1Y, 1C, 1M, and 1K is rotationally driven in the direction of the arrow in the drawing while contacting the intermediate transfer belt 10 that is an endless moving member as a surface moving member. Each of the photoreceptors 1Y, 1C, 1M, and 1K is formed by forming a photosensitive layer on a relatively thin cylindrical conductive substrate and further forming a protective layer on the photosensitive layer, and has an outer diameter of 30 [ mm] and its inner diameter is 28.5 [mm]. In the present embodiment, an organic photoconductor is used from the viewpoints of cost reduction, freedom of photoconductor design, non-pollution, and the like.

FIG. 2 is a diagram showing a schematic configuration around each of the photoreceptors 1Y, 1C, 1M, and 1K. Since the configuration around each of the photoconductors 1Y, 1C, 1M, and 1K is the same, only one photoconductor is illustrated, and reference numerals Y, C, M, and K for color coding are omitted.
Around the surface of the photoreceptor 1, a toner holding device 40 as a temporary holding unit, a charging device 3 as a charging unit, and a developing device 5 as a developing unit are arranged in this order along the surface movement direction. A space is secured between the charging device 3 and the developing device 5 so that light emitted from the exposure device 4 as a latent image forming unit can pass to the photosensitive member 1.

  The charging device 3 uniformly charges the surface of the photoreceptor 1 to a negative polarity. The charging device 3 according to the first embodiment includes a charging roller 3a as a charging member that performs a charging process by a so-called contact / proximity charging method. That is, the charging device 3 uniformly charges the surface of the photosensitive member 1 by bringing the charging roller 3a into contact with the surface of the photosensitive member 1 and applying a negative bias to the charging roller 3a. In the first embodiment, a DC charging bias of about −1000 V is applied to the charging roller 3a so that the surface potential of the photoreceptor 1 is uniformly − (minus) 500 [V].

  An electrostatic latent image corresponding to each color is formed on the surface of the photoreceptor 1 thus uniformly charged by exposure by the exposure device 4. The exposure device 4 writes an electrostatic latent image corresponding to each color on the photoreceptor 1 based on image information corresponding to each color. The exposure apparatus 4 of the present embodiment is a laser type exposure apparatus, but other types of exposure apparatuses such as an exposure apparatus including an LED array and an image forming unit may be employed.

  Further, in the developing device 5, the developing roller 5a as the developer carrying member is partially exposed from the opening of the casing. In the developing device 5 used in the first exemplary embodiment, a two-component developer including a toner and a carrier is used. However, a one-component developer that does not include a carrier may be used. The developing device 5 receives toner of the corresponding color from the toner bottles 31Y, 31C, 31M, and 31K shown in FIG. The toner bottles 31Y, 31C, 31M, and 31K are configured to be attachable to and detachable from the printer body so that they can be replaced individually. With such a configuration, only the toner bottles 31Y, 31C, 31M, and 31K may be replaced at the time of toner end. Therefore, other components that have not yet reached the end of their life when the toner ends can be used as they are, and the user's expense can be reduced.

  The toner replenished into the developing device 5 from the toner bottles 31Y, 31C, 31M, and 31K is conveyed while being agitated with the carrier by the agitating and conveying screw 5b, and is carried on the developing roller 5a. The developing roller 5a is composed of a magnet roller as magnetic field generating means and a developing sleeve that rotates coaxially therearound. The carrier in the developer is transferred to the developing area facing the photosensitive member 1 in a state where it stands on the developing roller 5a by the magnetic force generated by the magnet roller. Here, the developing roller 5a moves in the same direction at a linear velocity faster than the surface of the photoreceptor 1 in the developing region. Then, the carrier spiked on the developing roller 5 a supplies the toner adhering to the carrier surface to the surface of the photoreceptor 1 while rubbing the surface of the photoreceptor 1. At this time, a developing bias of −300 [V] is applied to the developing roller 5a from a power source (not shown), whereby a developing electric field is formed in the developing region. Then, between the electrostatic latent image on the photoreceptor 1 and the developing roller 5a, an electrostatic force directed toward the electrostatic latent image side acts on the toner on the developing roller 5a. As a result, the toner on the developing roller 5 a adheres to the electrostatic latent image on the photoreceptor 1. By this adhesion, the electrostatic latent image on the photoreceptor 1 is developed into a corresponding color toner image.

  The intermediate transfer belt 10 is stretched around three support rollers 11, 12, and 13, and is configured to endlessly move in the direction of the arrow in the figure. On the intermediate transfer belt 10, the toner images on the photoreceptors 1Y, 1C, 1M, and 1K are transferred so as to overlap each other by an electrostatic transfer method. Although there is a configuration using a transfer charger in the electrostatic transfer system, in this embodiment, a configuration using a transfer roller that generates less transfer dust is adopted. Specifically, primary transfer rollers 14Y, 14C, 14M, and 14K as transfer means are disposed on the back surface of the portion of the intermediate transfer belt 10 that is in contact with each of the photoreceptors 1Y, 1C, 1M, and 1K. In the first embodiment, a primary transfer nip portion is formed by the portions of the intermediate transfer belt 10 pressed by the primary transfer rollers 14Y, 14C, 14M, and 14K and the photoreceptors 1Y, 1C, 1M, and 1K. The When the toner images on the photoconductors 1Y, 1C, 1M, and 1K are transferred onto the intermediate transfer belt 10, a positive polarity bias is applied to each primary transfer roller 20. As a result, a transfer electric field is formed at each primary transfer nip, and the toner images on the photoreceptors 1Y, 1C, 1M, and 1K are electrostatically attached to the intermediate transfer belt 10 and transferred.

  A belt cleaning device 15 for removing toner remaining on the surface of the intermediate transfer belt 10 is provided around the intermediate transfer belt 10. The belt cleaning device 15 is configured to collect unnecessary toner adhering to the surface of the intermediate transfer belt 10 with a fur brush and a cleaning blade. The collected unnecessary toner is transported from the belt cleaning device 15 to a waste toner tank (not shown) by a transport means (not shown).

  Further, a secondary transfer roller 16 is disposed in contact with the portion of the intermediate transfer belt 10 stretched around the support roller 13. A secondary transfer nip portion is formed between the intermediate transfer belt 10 and the secondary transfer roller 16, and transfer paper as a recording material is fed into this portion at a predetermined timing. The transfer paper is accommodated in a paper feed cassette 20 on the lower side of the exposure device 4 in the drawing, and is conveyed to the secondary transfer nip portion by a paper feed roller 21, a registration roller pair 22, and the like. Then, the toner images superimposed on the intermediate transfer belt 10 are collectively transferred onto the transfer paper at the secondary transfer nip portion. At the time of the secondary transfer, a positive bias is applied to the secondary transfer roller 16, and the toner image on the intermediate transfer belt 10 is transferred onto the transfer paper by the transfer electric field formed thereby.

  A heat fixing device 23 as a fixing unit is disposed downstream of the secondary transfer nip portion in the transfer paper conveyance direction. The heat fixing device 23 includes a heating roller 23a with a built-in heater and a pressure roller 23b for applying pressure. The transfer paper that has passed through the secondary transfer nip is sandwiched between these rollers and receives heat and pressure. As a result, the toner on the transfer paper is melted and the toner image is fixed on the transfer paper. Then, the fixed transfer paper is discharged by a paper discharge roller 24 onto a paper discharge tray on the upper surface of the apparatus.

  In the present embodiment, the process cartridge 30 in which the photosensitive members 1Y, 1C, 1M, and 1K, parts such as a developing device disposed around the photosensitive members 1Y, 1C, 1M, and 1K, the exposure device 4, the intermediate transfer belt 10, and the belt cleaning device 15 are integrated. It is configured as. The process cartridge 30 is detachable from the printer body. Therefore, when the life of a component housed in the process cartridge 30 reaches the end of its life or when maintenance is required, the process cartridge 30 can be replaced, which improves convenience. In the first exemplary embodiment, the toner bottles 31Y, 31C, 31M, and 31K described above are configured to be detachable from the printer main body separately from the process cartridge 30.

  Next, cleaning of transfer residual toner remaining on the surfaces of the photoreceptors 1Y, 1C, 1M, and 1K, which is a characteristic part of the present invention, will be described. FIG. 3A is a graph showing the charge potential distribution immediately before the transfer of the toner carried on the photoreceptor 1. FIG. 3B is a graph showing the charge potential distribution of the untransferred toner remaining on the photoreceptor 1 after the transfer. As shown in FIG. 3A, the charge amount of the toner immediately before the transfer is distributed around -30 [μC / g], and most of the charge is normally charged negatively. On the other hand, the charge amount of the transfer residual toner is distributed around about −2 [μC / g]. In general, most of the untransferred toner is a defective toner that cannot obtain a desired charging characteristic due to a defective composition of the toner. Therefore, a part of the transfer residual toner is subjected to charge injection by the positive bias applied to the primary transfer roller 14, and the charge polarity of the toner is reversed to the positive polarity. As a result, in the transfer residual toner, there is a reversely charged toner that has been reversed to the positive polarity as indicated by the hatched portion in FIG.

Residual transfer toner in which regular charged toner T ₀ charged to −20 [μC / g] to −5 [μC / g] and reversely charged toner T ₁ reversed to positive polarity are mixed on the surface of the photoreceptor. Is temporarily held by the toner holding device 40.
FIG. 4 is a schematic configuration diagram showing the toner holding device 40. The toner holding device 40 includes a magnetic brush roller 41. The magnetic brush roller 41 includes a rotating sleeve 41a and a magnet roller 41b as magnetic field generating means fixedly disposed inside the rotating sleeve 41a. The rotating sleeve 41a is rotated in the clockwise direction in the drawing similarly to the photosensitive member 1 by a driving device (not shown). As a result, at the position where the rotating sleeve 41a and the photosensitive member 1 face each other, the surface of the rotating sleeve 41a moves in the opposite direction to the moving direction of the photosensitive member surface. As a result, the tips of a large number of magnetic brushes come into contact while the surface of the photoreceptor passes through the holding nip. Therefore, it is possible to reliably retain the transfer residual toner attached to the surface of the photoreceptor. Further, since the number of times of contact between the magnetic brush and the untransferred toner increases, the triboelectric charge of the untransferred toner proceeds, and the reversely charged toner can be reliably reversed to be a normally charged toner. Inside the magnet roller 41b, N-pole magnets and S-pole magnets are alternately arranged. Further, the toner holding device 40 includes a casing 46 that houses magnetic particles (carriers) 47. The contact width (holding nip) between the magnetic brush and the photosensitive member is set to about 5 to 6 mm.

  In this embodiment, a configuration in which a blade is brought into contact with the surface of the photoreceptor 1 is not employed. Therefore, the load torque applied to the driving device of the photosensitive member 1 can be greatly reduced as compared with the configuration in which the blade contacts. However, on the other hand, the holding ability to hold the transfer residual toner remaining on the surface of the photoreceptor 1 is inferior. For this reason, when used over time, a filming phenomenon may occur in which the additive released from the toner adheres to the surface of the photosensitive drum 1 in the form of a film. By using a so-called spherical toner as the toner to be used, the amount of residual toner as described above becomes relatively small. However, if it is used for a long period of time, a filming phenomenon may occur. However, in the present embodiment, as described above, a configuration in which the magnetic brush roller 41 is driven in the opposite direction with respect to the surface of the photoreceptor 1 is employed. Therefore, the addition of toner adhered to the surface of the photoconductor 1 is compared with the configuration in which the magnetic brush roller 41 is rotated with respect to the surface of the photoconductor 1 or the configuration in which the magnetic brush roller 41 is driven in the same direction with respect to the surface of the photoconductor drum 1. The action to scrape off the agent is strong. As a result, the occurrence of the filming phenomenon can be prevented.

  A bias is applied to the magnetic brush roller 41 from either the first power supply 43 or the second power supply 44. Specifically, a changeover switch 45 is provided between the power supplies 43 and 44 and the brush roller 41, and the power supply connected to the brush roller 41 is selected by the operation of the changeover switch 45. The operation of the changeover switch 45 is controlled by the control unit of the printer. In the present embodiment, the first power source 43 applies a holding bias such that the potential of the surface portion of the brush roller 41 is −50 to 100 [V], and the second power source 44 has the potential. An emission bias is applied such that becomes −300 to 400 [V].

  The carrier 47 of the holding device 40 is a carrier for minus toner manufactured by a known manufacturing method, and ferrite or magnetite is coated with a silicone resin to improve toner charging property and carrier durability. The carrier 47 of the holding device 40 includes a small carrier 47a having an average particle diameter of 20 to 50 μm and a large carrier 47b having an average particle diameter of 70 to 100 μm.

  The carrier 47 accommodated in the casing 46 is carried on the rotating sleeve 41 a and conveyed to the photoreceptor 1. At this time, the carrier 47 is raised by the magnetic field of the magnet roller 41b to form a magnetic brush. In this magnetic brush, a small carrier 47a having an average particle diameter of 20 to 50 μm is attached around a large carrier 47b having an average particle diameter of 70 to 100 μm. The carrier 47a having a small particle size can be slidably contacted with the surface of the photoconductor without any gap, and the transfer residual toner attached to the photoconductor can be reliably held. In addition, since the carrier 47a having a small particle diameter is reliably held by the magnetic force of the carrier 47b having a large particle diameter, the carrier 47a having a small particle diameter is not scattered and attached to the surface of the photoreceptor. As a result, an unexposed portion is formed by the transfer residual toner and the scattered carrier, and deterioration of the image such as white spots on the solid portion can be suppressed.

  At this time, a holding bias is applied to the magnetic brush from the first power supply unit 43. As the holding bias, a voltage substantially the same as the photoreceptor surface potential (−50 to −100 V) after transfer is applied. As a result, no potential difference occurs between the photoreceptor 1 and the magnetic brush roller 41. Therefore, the electrostatic attraction force generated by the potential difference between the photosensitive member and the magnetic brush roller 41 does not act on the untransferred toner. As a result, the untransferred toner can be reliably held by the frictional force of the magnetic brush regardless of the polarity of the untransferred toner.

  Further, by using magnetic toner as the toner, the transfer residual toner can be reliably held on the magnetic brush by the magnetism of the magnetic brush. In particular, black toner has poor light transmission compared to color toner. For this reason, black toner is used as the color toner when the latent image is formed with the black toner attached to the surface of the photoconductor and when the latent image is formed with the color toner attached to the surface of the photoconductor. Compared with color toner, the surface of the photoreceptor is less likely to be neutralized because it is less likely to transmit light. As a result, the solid white spots formed by the black toner are more noticeable than the solid white spots formed by the color toner. Therefore, by using only the black toner as the magnetic toner, the white spots on the solid portion become inconspicuous and image deterioration can be suppressed.

  The magnetic toner can be obtained by adding a known magnetic fine powder such as iron oxide, magnetite or ferrite to the toner. The amount of magnetic fine powder added is preferably 5 to 60 parts by weight, more preferably 15 to 45 parts by weight.

Further, when the charge amount of the transfer residual toner held by the magnetic brush was examined, it was -10 to -15 [μC / g] on average, and the charge amount of the transfer residual toner after transfer (−2 [μC / g] ], The negative charge amount increased. The transfer residual toner held in the magnetic brush has been a normally charged toner T _0. This is because the transfer residual toner is frictionally charged by the magnetic brush when the transfer residual toner is held on the magnetic brush from the surface of the photoreceptor. Therefore, the reverse charged toner T ₁ which is positively charged within the transfer residual toner is caused to polarity reversal to a negative polarity normally charged toner T ₀ of the friction with the magnetic brush. Similarly, the negatively charged toner T ₀ of the transfer residual toner also increases the negative charge amount due to friction with the magnetic brush. As a result, the negative charge amount of the transfer residual toner held on the magnetic brush is increased as compared with the charge amount of the transfer residual toner after the transfer.

  In this way, the untransferred toner held on the magnetic brush is returned to the surface of the photoreceptor at a predetermined timing. Specifically, the changeover switch 45 is switched from the first power supply unit 43 to the second power supply unit 44 at a predetermined timing, and a discharge bias of −350 V is applied to the magnetic brush roller 41. As a result, a potential difference is generated between the photosensitive member 1 (about −50 V) and the magnetic brush roller 41 (−350 V). As a result, the transfer residual toner that is normally charged to the negative polarity by frictional charging is electrostatically adsorbed to the photoconductor having a higher potential than the magnetic brush. As a result, the untransferred toner held by the magnetic brush is returned to the surface of the photoreceptor again.

The changeover switch 45 is switched at a timing such that a latent image is not formed when the transfer residual toner returned from the magnetic brush to the photosensitive member 1 passes through the latent image formation region. For example, when the rear end of the image portion on the photosensitive member formed in one image forming process reaches the holding nip, the changeover switch 45 is switched from the first power supply portion 43 to the second power supply portion 44 to thereby change the magnetic brush. An emission bias is applied to. Then, when the surface portion of the photosensitive member 1 that is started to be uniformly charged by the charging device 3 in the next image forming process reaches the holding nip, the changeover switch 45 is changed from the second power supply unit 44 to the first power supply unit. Switch to 33. Then, the voltage applied to the magnetic brush is switched from the discharge bias to the holding bias, and the transfer residual toner held on the magnetic brush is not released to the photoconductor. By switching the changeover switch 45 at such timing, when the latent image is formed on the surface of the photoconductor by the exposure device 4, no transfer residual toner exists on the surface of the photoconductor. As a result, an unexposed portion is formed by the transfer residual toner, and deterioration of an image such as a white spot on the solid portion can be suppressed.
In addition, a cleaning mode may be provided at the time of starting the apparatus, at the end of the image forming operation, or after a certain number of image forming operations, and the changeover switch 45 may be switched to the second power supply unit 44 in this cleaning mode. In this cleaning mode, since no image is formed, the untransferred toner released from the magnetic brush does not form an unexposed portion.

  The untransferred toner returned from the magnetic brush roller 41 to the surface of the photoreceptor passes through a contact area with the charging roller 3a. Since the transfer residual toner at this time is a regular charged toner having the same polarity as the charging bias, it passes without adhering to the charging roller 3a. The untransferred toner that has passed through the contact area with the charging roller 3a passes through the latent image forming area. At this time, the exposure device 4 is not operating, and no latent image is formed on the surface of the photoreceptor. The untransferred toner moves to the development area. The developing roller 41 is applied with a bias having a polarity opposite to the developing bias necessary for image formation, that is, a bias of + 200V. As a result, the transfer residual toner charged negatively has an electrostatic force acting toward the developing roller in the developing region. As a result, the transfer residual toner is electrostatically attracted to the carrier on the developing roller and collected by the developing device 4. The transfer residual toner collected in the developing device 4 by the developing roller is agitated and transported inside and then contributes again to the development.

  In the present embodiment, the process cartridge 30 in which the photosensitive members 1Y, 1C, 1M, and 1K, parts such as a developing device disposed around the photosensitive members 1Y, 1C, 1M, and 1K, the exposure device 4, the intermediate transfer belt 10, and the belt cleaning device 15 are integrated. However, the present invention is not limited to this. As shown in FIG. 2, a process cartridge in which a photosensitive member and parts such as a developing device arranged around the photosensitive member, an exposure device 4 and a holding device 40 are integrated may be provided for each color.

Next, the weight ratio between the small carrier 47a and the large carrier 47b of the carrier 47 of the holding device 40 was varied, and the degree of image degradation at that time was examined. The degree of image degradation was determined by printing five A4 size black solid images and visually confirming the number of white spots at that time. The average of 5 white spots was 10 or more and x was 10 or less. The average particle size of the small carrier 47a was 30 μm, and the average particle size of the large carrier 47b was 80 μm. Further, these carriers are carriers for minus toners manufactured by a known manufacturing method, and ferrite or magnetite is coated with a silicone resin to improve toner charging properties and carrier durability. The minimum particle size in the carrier 47 was 25 μm, and the maximum particle size was 100 μm. The results are shown below.

  As can be seen from Table 1, No. 1 comprising only a large carrier 47b of 80 μm. One carrier had an average number of white spots of 28.5, and a deteriorated image was obtained. Also, white streaks were confirmed in these images. This is because the carrier particle size is large, and the spacing between the magnetic brushes on the rotating sleeve becomes sparse, and the carrier surface cannot be intimately contacted. As a result, the number of times of contact with the magnetic brush before the surface of the photosensitive member passes through the holding nip is small, and the transfer residual toner cannot be sufficiently collected. As a result, a large amount of untransferred toner passes through the latent image forming area while adhering to the surface of the photoreceptor, and as a result, it seems that many white spots are confirmed in the black solid image. Further, there is a portion on the surface of the photoconductor where no transfer residual toner is collected by the magnetic brush, and the transfer residual toner remains in a streak shape on the surface of the photoconductor. This portion is considered to have passed through the latent image forming area and formed a white streak image.

  Further, when the weight ratio of the carrier 47a having a small particle diameter is 80 wt% or more, the number of white spots is 20 or more, and the image is remarkably deteriorated. As a result, the ratio of carriers having a small particle size has increased, and as a result, a magnetic brush is often formed only from carriers having a small particle size. At the tip of the magnetic brush formed by only the carrier having a small particle diameter, the magnetic attractive force to the magnet roller 41 is small. For this reason, the tip of the magnetic brush adheres to the surface of the photoreceptor by sliding contact with the surface of the photoreceptor or electrostatically adhering to the transfer residual toner on the surface of the photoreceptor. As a result, it is considered that an unexposed portion was formed on the carrier attached to the surface of the photoreceptor, and the average number of white spots increased.

  On the other hand, when the weight ratio of the carrier having a large particle diameter is 40 to 80 Wt%, the average number of white spots is 10 or less, and a good image can be obtained. What is constituted by such a weight ratio is a magnetic brush in which a small carrier is attached around a large carrier. The carrier having a small particle diameter is in sliding contact with the surface of the photoconductor without any gap, so that the transfer residual toner can be reliably held. Further, since the number of times of contact between the magnetic brush and the surface of the photoconductor increases, the transfer residual toner attached to the photoconductor can be reliably held. In addition, since the carrier having a small particle size is securely held by the magnetic force of the carrier having a large particle size, the carrier having a small particle size is not scattered and attached to the surface of the photoreceptor. As a result, it is considered that an unexposed portion was not formed by the attached carrier, and a good image with a small average number of white spots could be obtained.

Next, using the carrier used in the above experiment, it was examined whether there was a difference in the average number of white spots between the magnetic black toner and the nonmagnetic black toner. As for the average number of white spots, five A4 size black solid images were printed and the number of white spots at that time was confirmed visually. The magnetic toner can be obtained by adding a known magnetic fine powder such as iron oxide, magnetite, or ferrite to the toner. The magnetic toner used this time was added with 15 to 45 parts by weight of magnetic fine powder. The results are shown in Table 2.

  As can be seen from Table 2, the use of magnetic toner reduces the average number of white spots compared to non-magnetic toner, and it can be seen that a better image can be obtained. This is presumably because the transfer residual toner can be reliably held on the magnetic brush by the magnetic force of the magnetic brush by using the magnetic toner.

As described above, according to this embodiment, the transfer residual toner remaining on the surface of the photoreceptor 1 without being electrostatically transferred to the intermediate transfer belt 10 at the primary transfer nip is temporarily held by the magnetic brush of the toner holding device 40 regardless of the polarity. Is done. When the transfer residual toner passes through the latent image forming region, the transfer residual toner is returned from the holding device 40 to the surface of the photoconductor again at a timing at which writing is not performed on the surface of the photoconductor by the exposure device 4. Then, during the formation of the non-latent image, the transfer residual toner passes through the latent image area and is collected by the developing device. As a result, during the formation of the latent image by the exposure device 4, the transfer residual toner is suppressed from adhering to the surface of the photoreceptor passing through the latent image formation region. Therefore, the transfer residual toner can be collected by the developing device without forming an unexposed portion due to the transfer residual toner. As a result, the occurrence of white spots in the solid image portion is suppressed, and a good image can be obtained.
In the magnetic brush, a small carrier having an average particle size of 20 to 50 μm is attached around a large carrier having an average particle size of 70 to 100 μm. The carrier having a small particle diameter can be slidably contacted with the surface of the photoconductor without any gap, and the transfer residual toner attached to the photoconductor can be reliably held. In addition, since the surface of the photoconductor is in contact with the magnetic brush many times, the frictional charge of the transfer residual toner proceeds, and the negative charge amount of the transfer residual toner is increased by friction with the magnetic brush, or the reversely charged toner is normally charged. The toner can be reversed. As a result, the untransferred toner returned to the surface of the photosensitive member at the above timing is a normally charged toner having the same polarity as the charging bias, and therefore can pass through without being electrostatically attracted to the charging roller 3a. In addition, since the carrier having a small particle size is securely held by the magnetic force of the carrier having a large particle size, the carrier having a small particle size at the tip of the magnetic brush is in contact with the electrostatic force of the transfer residual toner on the photoconductor or the sliding contact with the photoconductor And will not adhere to the surface of the photoreceptor. Therefore, since the unexposed portion is not formed by the dropped carrier, the occurrence of white spots in the solid image portion is suppressed, and a good image can be obtained.
If the carrier having a large particle size is 40 Wt% or less, the proportion of the carrier having a small particle size of 20 to 50 μm increases, and the proportion of the magnetic brush formed only by the carrier having a small particle size increases. The carrier at the tip of the magnetic brush formed only with the carrier having the small particle diameter has a weak magnetic coupling force. Will fall off and adhere to the surface of the photoreceptor. As a result, the unexposed portion is formed by the dropped carrier, and white spots occur in the solid image portion. On the other hand, when the carrier having a large particle size with an average particle size of 70 to 100 μm is 80 Wt% or more, the amount of the carrier having a small particle size attached around the carrier having a large particle size is reduced. Then, the magnetic brush cannot be brought into sliding contact with the surface of the photoconductor without any gap, and the transfer residual toner attached to the photoconductor cannot be reliably held by the magnetic brush. As a result, an unexposed portion is formed by the transfer residual toner, and white spots occur in the solid image portion. Therefore, among the carriers forming the magnetic brush, by setting the carrier having a large average particle size of 70 to 100 μm to 40 Wt% to 80 Wt%, the transfer residual toner can be reliably held, and the small carrier is transferred. The remaining toner does not fall off due to the electrostatic force of the remaining toner or the sliding contact with the photoreceptor, and does not adhere to the surface of the photoreceptor. As a result, it is possible to suppress the formation of an unexposed portion due to the transfer residual toner, the dropped carrier, and the like, and it is possible to suppress the occurrence of white spots in the solid image portion, thereby obtaining a good image.
Further, by using the magnetic toner, the transfer residual toner can be reliably held on the magnetic brush by the magnetism of the magnetic brush. Therefore, the formation of an unexposed portion due to the transfer residual toner is further suppressed. As a result, the occurrence of white spots in the solid image portion is further suppressed, and a better image can be obtained.
In the present embodiment, while the exposure apparatus 4 is in operation, a holding bias having substantially the same potential as the surface potential of the photoreceptor after transfer is applied from the first power source 43. As a result, no potential difference occurs between the magnetic brush and the surface of the photoreceptor. For this reason, the negatively charged regular charged toner and the positively charged reversely charged toner are prevented from being electrostatically adsorbed on the surface of the photoreceptor. As a result, the transfer residual toner can be reliably held by the frictional force of the magnetic brush. Therefore, the exposure device 4 suppresses the transfer residual toner from adhering to the surface of the photoreceptor passing through the latent image forming area during the latent image formation. Then, while the exposure apparatus 4 is not operating, that is, during non-image formation, the selector switch 45 as the selection unit is switched from the first power source 43 to the second power source 44. As a result, a discharge bias having a negative polarity having the same polarity as the surface of the photoreceptor after transfer and a potential (350 V) larger than the absolute value (50 V) of the surface potential of the photoreceptor after transfer is applied to the magnetic brush. Then, a potential difference is generated between the surface of the photoreceptor and the magnetic brush. The untransferred toner held on the magnetic brush is uniformly charged normally due to frictional charging with the magnetic brush. For this reason, the untransferred toner held on the magnetic brush is discharged from the magnetic brush and electrostatically attracted to the surface of the photosensitive member having a high potential. Thereby, the transfer residual toner of the magnetic brush can be returned to the surface of the photoreceptor again. In this way, the transfer residual toner held by the holding device 40 during non-image formation is returned to the surface of the photoreceptor, so that the transfer residual toner can pass through the latent image forming area while the exposure device 4 is not operating.
In this embodiment, during the image operation, the transfer residual toner is held by the holding device 40 so that the transfer residual toner does not pass through the latent image forming area. Then, during the non-image formation, the transfer residual toner is collected by the developing device through the latent image forming area. Thereby, the transfer residual toner can be collected in the developing device without forming an unexposed portion by the transfer residual toner. As a result, the occurrence of white spots in the solid image portion is suppressed, and a good image can be obtained.
In the present embodiment, the rotating sleeve 41 a rotates in the same rotation direction as that of the photoreceptor 1. As a result, at the position where the rotating sleeve 41a and the photosensitive member 1 face each other, the surface of the rotating sleeve 41a moves in the opposite direction to the moving direction of the photosensitive member surface. As a result, the tips of a large number of magnetic brushes come into contact while the surface of the photoreceptor passes through the holding nip. Therefore, it is possible to reliably retain the transfer residual toner attached to the surface of the photoreceptor. Further, since the number of times of contact between the magnetic brush and the untransferred toner increases, the triboelectric charge of the untransferred toner proceeds, and the reversely charged toner can be reliably reversed to be a normally charged toner.
Further, compared to a configuration in which the magnetic brush roller 41 is rotated with respect to the surface of the photoconductor 1 or a configuration in which the magnetic brush roller 41 is driven in the same direction with respect to the surface of the photoconductor drum 1, the addition of toner attached to the surface of the photoconductor 1 is added. The action to scrape off the agent is strong. As a result, the occurrence of the filming phenomenon can be prevented.
Further, when the process cartridge is used, when the life of the components accommodated in the process cartridge 30 reaches the end of its life or when maintenance is required, the process cartridge 30 may be replaced, and the convenience is improved.

1 is a schematic configuration diagram of a printer according to an embodiment. FIG. 2 is a schematic configuration diagram showing a configuration around a photoconductor. FIG. 6A is a graph showing a charge potential distribution immediately before transfer of toner carried on the photosensitive drum. (B) is a graph showing the charge potential distribution of the transfer residual toner remaining on the photosensitive drum after transfer. FIG. 3 is a schematic configuration diagram illustrating a toner holding device.

Explanation of symbols

1Y, 1C, 1M, 1K Each photosensitive drum 3a Charging roller 3,203 Charging device 4 Exposure device 5 Developing device 10 Intermediate transfer belt 14Y, 14C, 14M, 14K Primary transfer roller 15 Belt cleaning device 16 Secondary transfer roller 30 Process cartridge 31Y, 31C, 31M, 31K Toner bottle 40 Toner holding device 41 Magnetic brush roller 41a Rotating sleeve 41b Magnet roller 42 Blade 43 First power supply 44 Second power supply 45 Changeover switch 46 Casing 47 Carrier

Claims (5)

The surface of the latent image carrier is uniformly charged by a charging unit, a latent image is formed on the surface of the uniformly charged latent image carrier by a latent image forming unit, and the latent image is converted into a toner image by a developing unit. In the cleaning system in which the toner image is transferred to the surface moving member by the transfer unit, and the transfer residual toner remaining on the surface of the latent image carrier after being transferred by the transfer unit is collected by the developing unit.
While the transfer residual toner reaches the charging unit from the transfer unit, a rotating member that has a magnetic field generating unit and supports two or more kinds of magnetic particles having different particle size distributions on the surface as a magnetic brush is disposed. A magnetic brush is brought into sliding contact with the surface of the latent image carrier to temporarily hold the transfer residual toner with the magnetic brush, and the transfer residual toner held on the temporary hold means is again latent at a predetermined timing. Control means for returning to the surface of the image carrier,
The magnetic particles are composed of magnetic particles having an average particle diameter of 70 μm or more and 100 μm or less, and magnetic particles having an average particle diameter of 20 μm or more and 50 μm or less, of which 40% by weight or more of the magnetic particles having an average particle diameter of 70 μm or more and 100 μm or less are included. 80% by weight or less der is,
The control means has the same holding bias as the potential of the surface of the latent image carrier after passing through the transfer means or the same polarity as the potential of the surface of the latent image carrier after passing through the transfer means, and passes through the transfer means. A cleaning system comprising application bias selection means for selectively applying a discharge bias having an absolute value larger than the absolute value of the potential of the latent image carrier surface to the magnetic brush . 2. The cleaning system according to claim 1 , wherein the toner is a magnetic toner. 3. The cleaning system according to claim 1 , wherein the control means performs control so that the applied bias selection means selects a discharge bias during non-image formation. According to claim 1, 2 or 3 of the cleaning system, the temporary retaining means, cleaning system, characterized in that the rotating member comprising a drive unit that rotates in the same direction as the rotational direction of the latent image carrier. A latent image bearing member, a charging means for uniformly charging the latent image bearing member surface, a latent image forming means for forming a latent image uniformly charged surface of the latent image bearing member, a toner to the latent image A transfer electric field is formed between the developing means for attaching and developing and the surface moving member that moves while contacting the latent image carrier, and is formed on the surface of the latent image carrier by the developing means. An image forming apparatus including a transfer unit that transfers the toner image formed on the surface moving member;
5. An image using the cleaning system according to claim 1, 2, 3 or 4 as cleaning means for removing residual toner remaining on the surface of the latent image carrier after the toner image is transferred to the surface moving member. Forming equipment.

Images