JP2016136177A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus for preventing the degradation of an image due to the fact that the external additive of toner slips through a cleaning blade coming into contact with an image holder and stably forming an external additive dam in the part of the tip edge coming into contact with the image holder, of the cleaning blade.SOLUTION: The image forming apparatus including the image holder which receives electrification, exposure, and development by the toner including the external additive, while being rotated, to hold a toner image and transfer the toner image and fixing the transferred toner image onto a paper sheet includes a cleaning blade whose tip edge comes into contact with the region after the toner image is transferred, of the image holder, to scrape residues after the transfer on the image holder, recovery means which recovers the external additive after slipping through the cleaning blade in the region before the electrification in the rotational direction of the image holder, and returning means which returns the external additive recovered by the recovery means to a holding region just before the tip edge of the cleaning blade.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image forming apparatus.

  Patent Document 1 discloses a cleaning in which an adsorbing member that is charged to a polarity opposite to that of silica particles by frictional charging with an image carrier is provided after a cleaning portion by a cleaning blade and before a primary charging portion. An apparatus is disclosed.

  In Patent Document 2, a cleaning member that is positively charged and a cleaning member that is negatively charged are placed in contact with a charging roller disposed in contact with a photosensitive member, and electrostatic foreign matter recovery is performed along with mechanical recovery. A cleaning device is disclosed.

Japanese Patent Laid-Open No. 3-45779 Japanese Patent Laid-Open No. 6-230657

  The present invention prevents the deterioration of the image due to the toner external additive scrubbing through the cleaning blade in contact with the image carrier, and the external additive on the tip edge portion of the cleaning blade in contact with the image carrier. An object of the present invention is to provide an image forming apparatus capable of stably forming a dam.

Claim 1
An image having an image holding body that holds a toner image by being charged, exposed, and developed with toner containing an external additive while rotating, and transfers the toner image, and fixes the transferred toner image on a sheet A forming device,
A cleaning blade for bringing a tip edge into contact with a region of the image carrier after transferring the toner image and scraping off a residue after transfer of the image carrier;
A collecting means for collecting the external additive that has passed through the cleaning blade in a region before charging in the rotation direction of the image carrier;
The external additive recovered by the recovery means is upstream of the contact portion of the edge of the cleaning blade of the image carrier, and the external additive is interposed between the cleaning blade and the image carrier. An image forming apparatus comprising: a return unit configured to return to a holding area to be held.

Claim 2
2. The image forming apparatus according to claim 1, wherein the collecting unit is frictionally charged to a polarity attracting the external additive and collects the external additive by electrostatic force.

Claim 3
The return means discharges the external additive collected by the previous collecting means from the collecting means onto the image holding member, and reverses the image holding member to return the external additive to the holding region. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

Claim 4
The recovery means is housed together with the cleaning blade in a case containing an external additive;
The return means, in the case, conveying means for conveying the external additive recovered by the recovery means to the holding region;
The image forming apparatus according to claim 1, further comprising a delivery unit that delivers the external additive collected by the collection unit from the collection unit to the transport unit.

  According to the image forming apparatus of the first aspect, image deterioration is prevented and the external additive dam is stably formed as compared with the case where the external additive is not collected and returned.

  According to the image forming apparatus of the second aspect, it is possible to collect the external additive with a simple structure with reduced cost compared to the case of collecting the external additive using an external power source.

  According to the image forming apparatus of the third aspect, it is possible to return the external additive more efficiently than when the external additive is discharged to the image holding member and returned to the holding region while the image holding member is rotated forward.

  According to the image forming apparatus of the fourth aspect, it is possible to efficiently return the external additive without having a function of reversing the image carrier.

1 is a schematic configuration diagram of a color image forming apparatus to which the exemplary embodiment is applied. It is sectional drawing which shows the conceptual structure of a cleaning apparatus and an external additive collection | recovery means. It is the figure which expanded and showed the periphery of the external additive collection | recovery means. It is operation | movement explanatory drawing of the external additive collection | recovery means in the discharge mode. It is operation | movement explanatory drawing of the external additive collection | recovery means in the discharge mode. It is operation | movement explanatory drawing of the external additive collection | recovery means in the discharge mode. It is the figure which showed the verification experiment result. It is the figure which showed the running test result. It is a schematic block diagram which shows 2nd Embodiment in this invention. It is explanatory drawing of the discharge mode in this 2nd Embodiment. It is a schematic block diagram which shows 3rd Embodiment in an external additive collection | recovery means. It is explanatory drawing of the discharge mode in the 3rd Embodiment. It is the figure which showed the verification experiment result. FIG. 4 is a schematic configuration diagram of a color image forming apparatus to which the fourth and subsequent embodiments are applied. It is sectional drawing which shows the conceptual structure of a cleaning apparatus, the external additive collection | recovery means arrange | positioned in the cleaning apparatus, and an external additive conveyance means. FIG. 5 is an enlarged view showing the periphery of the external additive collecting means 94, and is a schematic configuration diagram showing an example of the external additive collecting means 94. It is the figure which showed the modification of embodiment of completion | finish shown in FIG. It is the figure which showed the cleaning apparatus provided with the external additive conveyance means of another example. Furthermore, it is the figure which showed the cleaning apparatus provided with the external additive conveyance means of another example. It is a schematic block diagram which shows 5th Embodiment in this invention. It is the figure which expanded and showed the periphery of the external additive collection | recovery means 64 in 5th Embodiment.

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

  FIG. 1 is a schematic configuration diagram of a color image forming apparatus.

  This image forming apparatus is a quadruple tandem full-color image forming apparatus, which outputs an image of each color of yellow (Y), magenta (M), cyan (C), and black (K) in order from the upstream side. Four image forming units 30 including a first image forming unit 30Y, a second image forming unit 30M, a third image forming unit 30C, and a fourth image forming unit 30K in a photographic system are sequentially arranged in parallel at a predetermined distance. Has been.

  Here, for common explanations regardless of colors, the symbols Y, M, C, and K for distinguishing colors are omitted and referred to as “image forming unit 30”. The same applies to other components. Each image forming unit 30 includes a drum-shaped photosensitive drum 1 as an image carrier having a photosensitive layer on the surface, a charging device 2 that uniformly charges the photosensitive drum 1, and a uniform charging. An exposure device 3 that forms an electrostatic latent image by irradiating the photosensitive drum 1 with image light, a developing device 4 that transfers toner to the latent image to form a toner image, and a photosensitive drum 1. A primary transfer roll 5 that transfers the toner image to the intermediate transfer belt 8, a cleaning device 6 that removes the toner remaining on the photosensitive drum 1 after the transfer, and an external that collects the external additive that has passed through the cleaning device 6. And an additive collecting means 14. Here, the intermediate transfer belt 8 is an endless belt stretched so as to be able to circulate along a path in contact with the photosensitive drum 1.

  The color image forming apparatus further includes a recording paper transport mechanism 20 that transports the recording paper P accommodated in the paper tray 21 and a fixing device 7 that fixes the toner image on the recording paper P.

  In this embodiment, toner manufactured by an emulsion polymerization method is used as the toner. However, it is not limited to this production method, and may be produced by, for example, suspension polymerization, suspension granulation, dissolution suspension, kneading and pulverization. The particle size of the toner has a great influence on the image quality, and the smaller the particle size, the better the image quality. However, when the particle size is small, the developability deteriorates and the handling becomes difficult. Further, an appropriate amount of silica or titania having an average particle diameter of about 10 to 150 nm is externally added to the toner as a charge control agent or a transfer aid. The toner used here is externally added with a silica having a relatively large particle diameter, in particular, to ensure cleaning properties and transfer maintenance properties. Specifically, silica having a number average particle diameter of 100 to 150 nm is added. I have an external attachment. The number average particle diameter is determined by a circle equivalent diameter (Heywood diameter) by a microscope method based on JIS Z 8901, and a scanning electron microscope (SEM) is used as the microscope.

The intermediate transfer belt 8 is wound around a primary transfer roll 5, a drive roll 9 that is driven to rotate, a tension roll 10 that adjusts tension, and a backup roll 11. The intermediate transfer belt 8 used has a surface resistivity of 10 ¹⁰ by dispersing a substance for imparting conductivity such as carbon or an ion conductive substance in a resin material such as polyimide, polyamideimide, polycarbonate, or fluorine resin. It is formed by adjusting to about 10 ¹² Ω / □ (measurement voltage: 100 V). A secondary transfer roll 12 that transfers the toner image on the intermediate transfer belt 8 onto the recording paper P conveyed by the recording paper conveyance mechanism 20 is located at a position facing the backup roll 11 with the intermediate transfer belt 8 interposed therebetween. Is provided. A toner removing device 13 is also provided for removing the toner remaining on the intermediate transfer belt 8 after the toner image is transferred onto the recording paper P by the secondary transfer roll 12.

  The recording paper transport mechanism 20 includes a pickup roll 22, a transport roll 23 and a transport belt 24, paper guides 26 and 27 for guiding the transport movement path, a paper discharge roll 25, a paper discharge tray 28, and the like. Then, the recording paper P stored in the paper tray 21 is moved from the secondary transfer position to the fixing device 7 to the secondary transfer position where the secondary transfer roll 12 and the backup roll 11 face each other with the intermediate transfer belt 8 interposed therebetween. It is transported from the fixing device 7 to the paper discharge tray 28.

  The color image forming apparatus operates as follows to form a color image.

  Since the first to fourth image forming units 30 described above have substantially the same configuration, here, the first image forming unit that forms a yellow image disposed on the upstream side in the running direction of the intermediate transfer belt 8. 30Y will be described as a representative. The same reference numerals with magenta (M), cyan (C), and black (K) are attached to members having the same functions as those of the first image unit 30Y instead of yellow (Y). Description of the second to fourth image forming units 30M, 30C, and 30K will be omitted.

  The first image forming unit 30Y includes a photosensitive drum 1Y that functions as an image carrier. Around the photosensitive drum 1Y, a charging device 2Y for charging the surface of the photosensitive drum 1Y to a predetermined potential in order in the rotation direction indicated by the arrow A of the photosensitive drum 1Y, and the charged surface is color-separated. An exposure device 3Y that forms an electrostatic latent image by exposure with a laser beam based on an image signal, a developing device 4Y that supplies charged toner to develop the electrostatic latent image, and the developed toner image is transferred to the intermediate transfer belt 8 And a photoreceptor cleaning device 6Y for removing toner remaining on the surface of the photoreceptor drum 1Y after the primary transfer. The primary transfer roll 5Y is disposed inside the intermediate transfer belt 8 and is provided at a position facing the photosensitive drum 1Y. Further, a bias power source (not shown) for applying a primary transfer bias is connected to each of the primary transfer rolls 5Y, 5M, 5C, and 5K. Each bias power source varies the transfer bias applied to each primary transfer roll under the control of a control unit (not shown).

  Hereinafter, an operation of forming a yellow image in the first image forming unit 30Y will be described. The photosensitive drum 1Y rotates in the direction of arrow A. First, the surface of the photosensitive drum 1Y is charged to a potential of about −600V to −800V by the charging device 2Y. As the charging device, in addition to the scorotron, a contact or non-contact charging device such as a solid discharger, a roll shape, or a blade shape may be used. The photoreceptor drum 1Y is formed by laminating a photosensitive layer on a conductive metal base. This photosensitive layer is a function-separated type in which a charge generation layer and a charge transport layer are sequentially stacked, and usually has a high resistance. However, when a laser beam is irradiated, the specific resistance of the portion irradiated with the laser beam changes. Have the nature of Therefore, a laser beam is output from the exposure device 3 to the surface of the charged photosensitive drum 1Y according to yellow image data sent from a control unit (not shown). The laser beam is applied to the photosensitive layer on the surface of the photosensitive drum 1Y, whereby an electrostatic latent image of a yellow print pattern is formed on the surface of the photosensitive drum 1Y. The diameter of the photosensitive drum is preferably in the range of 20 to 100 mm. The electrostatic latent image is an image formed on the surface of the photosensitive drum 1Y by charging, and the specific resistance of the irradiated portion of the photosensitive layer is lowered by the laser beam, and the charged charge on the surface of the photosensitive drum 1Y. On the other hand, it is a so-called negative latent image formed by the charge remaining in the portion not irradiated with the laser beam. The electrostatic latent image formed on the photosensitive drum 1Y in this way is rotated to a predetermined development position by the rotation of the photosensitive drum 1Y. At this development position, the electrostatic latent image on the photosensitive drum 1Y is converted into a visible image (toner image) by the developing device 4Y.

  In the developing device 4Y, yellow toner having an average particle diameter of 5.8 μm manufactured by an emulsion polymerization method is accommodated. The yellow toner is triboelectrically charged by being agitated inside the developing device 4Y, and has a charge of the same polarity (−) as the charge on the surface of the photoreceptor drum 1Y. As the surface of the photosensitive drum 1Y passes through the developing device 4Y, yellow toner is electrostatically attached only to the latent image portion on the surface of the photosensitive drum 1Y, and the latent image is developed with the yellow toner. The The photosensitive drum 1Y continues to rotate, and the toner image formed on the surface of the photosensitive drum 1Y is conveyed to the primary transfer position. When the yellow toner image on the surface of the photoreceptor drum 1Y is conveyed to the primary transfer position, a primary transfer bias is applied to the primary transfer roll 5Y, and electrostatic force directed from the photoreceptor drum 1Y to the primary transfer roll 5Y is applied to the toner. The toner image on the surface of the photosensitive drum 1Y is transferred to the surface of the intermediate transfer belt 8 by acting on the image. The transfer bias applied at this time has a polarity (+) opposite to the polarity (−) of the toner. For example, in the first image forming unit 30Y, a constant current is controlled to about +20 to 30 μA by a control unit (not shown). ing. On the other hand, the untransferred toner on the surface of the photosensitive drum 1Y is cleaned by the cleaning device 6Y. The primary transfer bias applied to the primary transfer rolls 5M, 5C, and 5K after the second image forming unit 30M is also controlled in the same manner as described above. In this way, the intermediate transfer belt 8 onto which the yellow toner image has been transferred by the first image forming unit 30Y passes through the second to fourth image forming units 30M, 30C, and 30K while being rotated in the direction of arrow B, and is conveyed. Then, the toner images of the respective colors are multiplex-transferred so as to sequentially overlap. The intermediate transfer belt 8 on which the toner images of all the colors are transferred in a multiple manner through the first to fourth image forming units further move in the direction of the arrow B, and the toner image transferred on the intermediate transfer belt 8 is transferred to the intermediate transfer belt 8. The sheet is transported to a secondary transfer section composed of a backup roll 11 in contact with the inner surface of the transfer belt 8 and a secondary transfer roll (transfer means) 12 disposed on the image holding surface side of the intermediate transfer belt 8. On the other hand, the recording paper P is fed between the secondary transfer roll 12 and the intermediate transfer belt 8 through the supply mechanism in synchronization with the toner image on the intermediate transfer belt 8, and the secondary transfer bias is applied. Applied to the secondary transfer roll 12. The transfer bias applied at this time has a polarity (+) opposite to the polarity (−) of the toner, and an electrostatic force from the intermediate transfer belt 8 toward the recording paper P acts on the toner image, and the transfer bias is applied to the intermediate transfer belt 8. The toner image is transferred to the recording paper P. The secondary transfer bias at this time is determined according to the resistance detected by a resistance detection means (not shown) for detecting the resistance of the secondary transfer portion, and is controlled by a constant voltage. Thereafter, the recording paper P is fed into the fixing device 7, and the toner image is heated and pressurized, and the color-superposed toner image is melted and permanently fixed on the surface of the recording paper P. The recording paper P on which the color image has been fixed is carried out toward the paper discharge tray 28, and a series of color image forming operations is completed.

  Here, a cleaning blade 60 (see, for example, FIG. 2) is used in the cleaning device 6 of the color image forming apparatus shown in FIG. Since this cleaning blade 60 is simple in structure, small in size and low in cost, and excellent in cleaning performance and reliability, it is the most widely used cleaning method from low speed machines to high speed machines today.

  However, the cleaning blade 60 is excellent in the ability to remove toner particles, but is not necessarily excellent in the ability to remove external additives of toner. This is because the external additive added to the surface of the toner has a small particle size, and thus the blade may slip through when the scraping power of the blade is low.

  Silica is often used as an external additive, and since it has excellent functions as an external additive such as chargeability and transferability, it is externally added to almost all toners currently used in products. However, the silica released from the toner while being stirred in the developing device and the silica originally released from the toner are likely to migrate to and adhere to the surface of the photoreceptor.

  Since the silica adhering to the photosensitive member has a small particle size and is relatively firmly attached, it cannot be cleaned by the scraping force of the blade, and passes through the blade nip of the cleaning blade 60 that is in contact with the photosensitive drum 1. May end up. The silica that has passed through the blade is given a negative charge when it passes through the charging portion and reaches the developing portion. However, the silica particles charged by the charging are removed by the scavenging force acting between the developing device 4 and the silica particles. A phenomenon occurs in which the surface potential of the photoreceptor changes. In particular, when images are repeatedly formed on the same site during continuous printing and such charged silica accumulates, a so-called continuous print ghost is generated. As a result of detailed investigation, it has been found that this continuous print ghost is generated because a large amount of external additive slips through the image.

  Further, an external additive such as silica that has passed through the blade adheres to the charger and causes charging failure, resulting in image deterioration. This phenomenon occurs remarkably when a contact type charging device is used as a charger.

  On the other hand, there is an area where a certain amount of toner and external additives are accumulated in the blade pre-nip (upstream of the blade nip and in the vicinity of the nip), and these particles work like dams and have the same size. In order to prevent the particles from slipping through in order to prevent the external additive from slipping through, it is necessary that an external dam be formed at the most distal end portion of the prenip. The reason why the externally added dam is formed at the foremost part of the pre-nip is that particle size segregation occurs due to movement and stirring in the dam. Such an external dam does not prevent all external additives from slipping through, but plays an important role in maintaining a stable blade posture.

  Therefore, even when the external additive slips through, it is necessary to always supply the external additive to the blade pre-nip so that the external dam is not depleted.

  As will be described below, according to the present embodiment, the problem of continuous print ghost that occurs when the external additive slips through the image is solved, and the external additive that slips through the blade adheres to the charger. Image deterioration can be prevented, and an external additive dam can be stably formed in the blade pre-nip.

  Next, the cleaning device 6 and the external additive recovery means that is the main part of the present embodiment will be described in detail.

  FIG. 2 is a cross-sectional view showing a conceptual configuration of the cleaning device and the external additive recovery means in the first embodiment. FIG. 3 is an enlarged view of the periphery of the external additive collecting means in the first embodiment.

  The cleaning device 6 includes a cleaner housing 64 that is disposed in the vicinity of the photosensitive drum 1 and opens to the side facing the photosensitive drum 1. A seal member 65 is fixed to the lower opening end of the cleaner housing 64. The seal member 65 substantially closes the gap between the photosensitive drum 1 and the cleaner housing 64 and prevents waste toner or the like stored in the cleaning device 6 from leaking or scattering to the outside. For the seal member 65, for example, a thermoplastic polyurethane film having a thickness of 0.1 mm is used.

  Inside the cleaner housing 64, a cleaning blade 60 as a cleaning member is disposed downstream of the seal member 65 in the rotation direction of the photosensitive drum 1 (indicated by an arrow A in the figure). In addition, an auger 63 is disposed in the lower portion of the cleaner housing 64.

  The cleaning blade 60 is formed in a plate shape with a predetermined thickness by an elastic material. As the blade material, for example, thermosetting polyurethane rubber having excellent mechanical properties such as wear resistance, chipping resistance, and creep resistance is used. The material of the blade is not limited to urethane rubber, and functional rubber materials such as silicone rubber, fluorine rubber, ethylene / propylene / diene rubber are used. The cleaning blade 60 is bonded to a sheet metal 61 and is fixed to the cleaner housing 64 by a set screw 62, and the tip edge portion thereof is provided in contact with the surface of the photosensitive drum 1.

  The blade pressurization method in the present embodiment employs a constant displacement method with a simple structure and low cost. For example, the applied pressure is set to 39.2 N / m (4 gf / mm). However, the blade pressing method is not limited to the constant displacement method, and a constant load method in which the contact pressure hardly changes with time may be used.

  In the cleaning device 6 having such a configuration, as shown in FIG. 2, the transfer residual toner T remaining on the surface of the photosensitive drum 1 passes through the front of the seal member 65 as it is and is scraped off by the cleaning blade 60. . The toner scraped off by the cleaning blade 60 is once accommodated in the cleaner housing 64, and finally transported and discharged by the auger 63 to the side of the cleaning device 6 (in the direction perpendicular to the paper surface of FIG. 2). The cleaning device 6 is configured as at least a unit (process cartridge) integrated with the photosensitive drum 1, and is detachable from the image forming apparatus in the state of the unit.

  In such a cleaning device 6, the tip of the cleaning blade 60 is irregularly worn when the tip of the cleaning blade 60 is abraded by rubbing against the photosensitive drum 1 or the coefficient of friction of the surface of the photosensitive drum is high. When the blocking force is reduced due to deformation or the like, the external additive having a small particle size is likely to slip through the blade. In particular, silica used as an external additive has a small particle size and is firmly attached to the surface of the photosensitive member by van der Waals force or the like, so that it cannot be cleaned with the scraping force of the blade and easily passes through the blade nip. The externally added dam AD shown in FIG. 2 effectively acts to prevent this slip-through, and the externally added dam AD is formed at the forefront of the cleaning blade pre-nip. Similarly, the toner dam TD contributes to toner slipping. As described above, in order to prevent the particles of the same size from slipping out by the action of such a dam, it is possible to slightly suppress the slipping of the external additive. However, when a large amount of external additive reaches the cleaning area as in continuous printing, it is difficult to suppress the occurrence of continuous print ghost (image defects in which the afterimage of the previous image appears slightly on the subsequent image). Become.

In order to avoid such a problem, the image forming apparatus according to the present embodiment is provided with the external additive collecting means 14. The external additive recovery means 14 is for recovering the external additive, particularly silica, that has passed through the cleaning blade. This is because silica having a relatively large particle size tends to cause continuous print ghosts and image quality deterioration.
FIG. 3 is an enlarged view of the periphery of the external additive collecting means, and is a schematic configuration diagram showing an example of the external additive collecting means. The external additive recovery means 14 of the present embodiment has a roll shape, and a recovery layer 140 is formed on a metal core 141. In the present embodiment, the core bar has a diameter of 10 mm and the recovery layer has a thickness of 5 mm. In the present embodiment, a solid recovery layer is used, but any form of member such as a sponge shape (porous body) or a brush shape can be used as the recovery layer.

  The surface of the external additive collecting unit 14 is in contact with friction charging units 15 and 16 that are rubbed and charged with the surface of the external additive collecting unit. The friction charging means 15 is for negatively charging the surface of the external additive collecting means, and the friction charging means 16 is for positively charging the surface of the external additive collecting means. The frictional charging means 15 of the present embodiment is a rotating brush, which has a configuration in which a brush portion 150 is bonded to a metal core 151, and the brush portion 150 is obtained by planting nylon fibers on a base fabric. In the present embodiment, the diameter of the core metal is 5 mm, and the pile height of the brush is 3.5 mm. The friction charging unit 15 includes a scattering prevention housing 153 that prevents the external additive scattering portion.

  In addition, a fixed brush is used for the frictional charging means 16 of the present embodiment, and is constituted by a brush portion 160 and a base member 161. The brush part 160 is obtained by flocking fibers on a base fabric. In the present embodiment, a metal plate having a brush width in the rotation direction of 10 mm, a pile height of 6.5 mm, and a base member 161 of 2 mm is used. In this embodiment, a brush is used. However, a member of any shape such as a solid shape or a sponge shape can be used as the friction charging member.

  The material of the recovery layer 140 is composed of a material having a positive charge column from silica, specifically, urethane rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber, chloroprene rubber, nitrile rubber, butylene rubber, polysulfide type. Synthetic rubber such as rubber, acrylic rubber and ethylene propylene rubber, natural rubber and the like can be used, and those having relatively high hardness and a low friction coefficient are preferable. In addition, plastic materials such as polyethylene, polyethylene terephthalate (PET), polypropylene, polyvinyl chloride, acrylic resin, polystyrene, polyacetal, polyimide, polyamideimide, phenol resin, epoxy resin, polyester resin, melamine resin, and polyurethane can also be used. Furthermore, glass is suitable because it has a strong positive chargeability.

  The material of the frictional charging means 15 is selected from materials whose charge train is on the plus side with respect to the material of the recovery layer of the external additive recovery means. Further, the material of the frictional charging means 16 is selected from materials whose charging column is on the minus side of the material of the recovery layer of the external additive recovery means. By sliding the charge train with the material on the plus side and the material on the minus side, friction charging can be performed on both the minus side and the plus side. As a specific example, when a polyester resin is used as the material for the recovery layer, nylon fiber or rayon fiber can be used as the material for the friction charging means 15, and polyethylene fiber or acrylic fiber can be used as the material for the friction charging means 16. . These material selections need only satisfy the following relationship, and are not limited to the materials described.

Charge train positive tendency: material of friction charging means 15> material of external additive recovery means 14 Charge train negative tendency: material of friction charging means 16> material of external additive recovery means 14 Note that each material is in the charge train. Thus, better charging can be performed by selecting a material that is further away.

  A polyester resin is used for the recovery layer 140 of the present embodiment, a nylon fiber brush is used as the material of the friction charging means 15, and a polyethylene fiber brush is used as the material of the friction charging means 16.

  As shown in FIG. 3, the external additive recovery means of the present embodiment is supported such that the surface of the recovery layer 140 is not in contact with the surface of the photosensitive drum 1. By making such contactless, the external additive collecting means does not frictionally charge by rubbing against the surface of the photosensitive drum, so that it is not affected regardless of the surface material of the photosensitive drum. And can be charged to a desired polarity. In addition, the smaller the gap of the non-contact portion, the higher the silica recovery efficiency, which is preferable. However, since the gap setting has a limit of mechanical tolerance, the gap at the closest position is set to about 0.1 to 0.5 mm. It is appropriate to do.

  The image forming apparatus according to the present embodiment has two modes, ie, a recovery mode and a discharge mode. First, the collection mode will be described with reference to FIG. The external additive recovery means 14 of the present embodiment can be rotated by a drive system (not shown), and rotates counterclockwise as indicated by an arrow C as shown in FIG. As the external additive collecting means rotates, the collecting layer 140 is positively charged by rubbing with the friction charging means 16. The rotational speed needs to be set so as to be an appropriate peripheral speed in consideration of friction charging performance, recovery performance, mechanical performance, and the like. In this embodiment, the photosensitive drum peripheral speed is 0.5 to 2.5. It is appropriate to set to about double. If it is too slow, the charging performance will be insufficient, and if it is too fast, the drive motor will be overloaded and the external additive collecting means 14 will vibrate. On the other hand, silica tends to be negatively charged, and as shown in FIG. 3, silica A1 that has passed through the blade is negatively charged. (Refer to part A2), adsorbed to the external additive recovery means 14 and recovered. The recovered silica passes through the region where the frictional charging means 15 is in contact, but the frictional charging means 15 rotates in the clockwise direction indicated by the arrow D at the same peripheral speed as the external additive recovery means 14. Since the rubbing force hardly acts, the recovery layer 140 retains a positive charge without being frictionally charged and passes through while adsorbing silica. Strictly speaking, the brush tip receives a slight rubbing force due to irregular movement of the brush tip, but the generated charge is minute and can be ignored.

  Next, the discharge mode will be described.

  4 to 6 are operation explanatory views of the external additive recovery means in the discharge mode.

  First, as shown in FIG. 4, at the beginning of this mode, the photosensitive drum 1 is stopped. The frictional charging means 15 rotates counterclockwise as indicated by the arrow D and the surface of the recovery layer 140 is negatively charged. Therefore, the negatively charged silica is repelled from the surface of the recovery layer 140 and released. The released silica flies in the direction of the photosensitive drum 1 along the flow of the air flow generated by the brush rotation, and adheres to the surface of the photosensitive drum 1 (see A3). Part of the silica is in a cloud state, but is collected without being scattered around because of the scattering prevention housing 153.

  As the next operation, as shown in FIG. 5, the photosensitive drum 1 rotates in the reverse direction of the arrow A ′, which is different from the normal one, and the silica adhering to the surface of the photosensitive drum has the cleaning blade 60 on the upstream side. To get there. When the photosensitive drum is rotated in the reverse direction, the cleaning blade 60 comes into contact with the so-called “wiz contact”, so that the blocking force is remarkably reduced, and fine particles such as external additives easily pass the blade nip. To reach the blade pre-nip A4. Then, as the next operation, as shown in FIG. 6, when the photosensitive drum 1 is rotated (forward rotation) in the normal rotation direction (A direction), the cleaning blade is in a so-called against contact and is blocked. Since the force becomes high, even fine particles such as an external additive are blocked, and the external dam is reformed.

  Note that the discharge mode timing can be set before or after a print job, when the print job is stopped and idle (adjustment / correction / cleaning, etc.), or every time an appropriate number is output. preferable.

  In order to make it easy for the external additive to pass through the blade nip, a retract mechanism for temporarily releasing the pressure of the cleaning blade on the surface of the photosensitive drum may be provided.

  Here, the reason why it is preferable to re-feed the external additive to the blade pre-nip will be described.

  As described above, there is a region where a certain amount of toner and external additives are accumulated in the blade pre-nip, and these particles act like a dam to prevent the same size particles from slipping through. Therefore, in order to prevent the external additive from slipping through, an external dam needs to be formed at the most distal end portion of the prenip. As described above, the external additive tends to accumulate at the leading edge of the prenip due to particle size segregation, but the external additive adhering to the surface of the photosensitive drum is carried by the rotation of the photosensitive drum, and the particle size is compared with that of the toner. Therefore, since it is 1/10 or less (small-diameter external additive is 1/100 or less), it easily passes through the toner dam and reaches the blade nip leading edge easily. Accordingly, the external additive re-supplied to the blade pre-nip quickly reaches the leading edge and forms an external dam.

  Regarding the role of this external additive dam, the present inventor visualized and observed the external additive dam at a high magnification using a transparent photoconductive drum, or made a prototype of a toner with a different external additive formulation and evaluated the actual machine As a result of conducting extensive studies, it was found that it plays a very important role in stabilizing the blade posture. This is presumably because the external additive supplied from the externally added dam performs a roll-like action by passing through uniformly and appropriately, and substantially reduces the friction between the blade and the photoreceptor surface. That is, the frictional force works non-uniformly and the blade is not pulled strongly by the photoconductor in some places. As a result, the cleaning properties against external additives, toner, and other foreign matters are improved. Further, it is possible to prevent a problem that an external additive such as silica or toner that has passed through the blade adheres to the charger and causes a charging failure to cause image deterioration. Further, as a result of friction reduction, blade wear is reduced and photoreceptor wear is also reduced, greatly contributing to a longer life of the apparatus.

  For these reasons, it is necessary to always supply the external additive to the blade pre-nip so that the external dam is not exhausted even if the external additive slips through. The external additive dam can be regenerated immediately by re-supplying the external additive to the blade pre-nip as in the present invention, and even when an image having a low area coverage is continuously printed. There is no need to worry about running out of external dams due to lack of chemicals. Even when images with different area coverage are continuously printed in the direction of the photoconductor axis, there is no concern that there will be a region where the external additive is insufficient. In particular, even when an image in which an image portion and a non-image portion are mixed is printed in the process direction, there is no fear that the external dam is exhausted in the non-image portion.

  Further, the amount of the external additive added is determined in consideration of the amount that contributes to the cleaning performance as an external dam that is originally released or detached from the toner. Therefore, the toner cost can be reduced and the running cost of the apparatus can be reduced.

  Furthermore, in the conventional image forming apparatus, in order to effectively function the external dam of the prenip, an image called a “toner band” is developed and sent to the blade prenip for the purpose of preventing the shortage of external additives. Although the operation is performed at regular intervals, according to the present invention, there is a merit that such an operation becomes unnecessary. Accordingly, this point also contributes to lower running costs.

  Thus, by re-supplying the external additive to the blade pre-nip, the external dam can be stably formed over a long period of time, and a highly reliable image forming apparatus can be provided over a long period of time.

  Next, a verification experiment conducted to confirm the effect of this embodiment will be described.

  In the verification experiment, Fuji Xerox on-demand printing machine DocuColor 8000 was used, and the case where the external additive collecting means was added to the cleaning device with the configuration as shown in FIG. 2 was compared with the case where it was not added (conventional example).

The evaluation method was that 50 ghost evaluation charts were printed continuously, and the ghost level of the 50th sheet was evaluated based on the brightness difference ΔL ^{* based} on the brightness L ^* before printing.

  FIG. 7 is a diagram showing the result of the verification experiment.

In FIG. 7, the smaller the value of the lightness difference ΔL ^* , the better the ghost level. From FIG. 7, in the case where the external additive recovery means is not added (conventional example), the value of ΔL ^* is 2.0 and continuous print ghosts are generated, whereas the external additive recovery means is added. In the embodiment, it has been found that the value of the lightness difference ΔL ^* is reduced to 0.05, which is improved to a level where the continuous print ghost is not recognized.

  In addition, a running test was conducted to confirm the maintainability of the external additive recovery means.

  FIG. 8 is a diagram showing a running test result.

The total number of running cycles (total number of rotations of the photosensitive drum) is 100,000 cycles. As a result of performing the ghost evaluation in the same manner as described above every 10,000 cycles, the value of the brightness difference ΔL ^* changes from 0.05 to 0.10 as shown in FIG. 8, and changes if the measurement variation is taken into consideration. Therefore, the maintainability of the external additive collecting means was confirmed.

  FIG. 9 is a schematic configuration diagram showing a second embodiment of the present invention. The external additive collecting means in the present embodiment is different in friction charging means from the first embodiment, but the basic configuration is the same. That is, the frictional charging means 16 that was a fixed brush in the first embodiment is replaced with the frictional charging means 18 of the rotating brush, and the frictional charging means 18 negatively charges the surface of the external additive collecting means. The friction charging means 17 is different in that the surface of the external additive collecting means is positively charged. The friction charging means 17 and 18 are rotary brushes similar to the friction charging means 15, and specifically, have a configuration in which the brush portions 170 and 180 are bonded to metal cores 171 and 181, respectively. The brush part 170 is obtained by flocking polyethylene fibers on a base cloth, and the brush part 180 is obtained by flocking nylon fibers on a base cloth. In this embodiment, the diameters of the core bars 171 and 181 are 5 mm, and the pile heights of the brush portions 170 and 180 are 3.5 mm. In this embodiment, a brush is used. However, a member of any shape such as a solid shape or a sponge shape can be used as the friction charging member.

  Next, the collection mode and the discharge mode in the present embodiment will be described. First, the recovery mode will be described with reference to FIG. The external additive recovery means 14 of the present embodiment is rotatable by a drive system (not shown) and rotates counterclockwise (arrow C direction). The friction charging unit 17 is also rotated in a clockwise direction indicated by an arrow E by another drive system (not shown), and is rotated at a peripheral speed different from that of the external additive collecting unit 14. By rotating with a difference in peripheral speed, the collection layer 140 is positively charged by rubbing with the friction charging means 17. This peripheral speed difference needs to be set so as to be an appropriate peripheral speed difference in consideration of frictional charging performance, recovery performance, mechanical performance, and the like. In this embodiment, the peripheral speed difference of the external additive recovery means 14 is set. It is appropriate to set to about 0.5 to 2.5 times. If it is too slow, the charging performance will be insufficient, and if it is too fast, the collected external additive will be scattered around and the drive motor will be overloaded. In addition, since a certain amount of scattering is unavoidable, a scattering prevention housing 173 is provided to prevent this.

  On the other hand, silica tends to be negatively charged, and as shown in FIG. 9, silica A1 that has passed through the blade is negatively charged. (Refer to part A2), adsorbed to the external additive recovery means 14 and recovered. The recovered silica passes through the area where the frictional charging means 18 is in contact, but the frictional charging means 18 rotates in the clockwise direction indicated by the arrow F at the same peripheral speed as the external additive recovery means 14, and slides. Since the rubbing force hardly acts, the recovery layer 140 is not triboelectrically charged but holds a positive charge and passes through while adsorbing silica. Strictly speaking, the brush tip receives a slight rubbing force due to irregular movement of the brush tip, but the generated charge is minute and can be ignored. Further, a scattering prevention housing 183 is provided so that even if silica is scattered, it is not scattered around.

  FIG. 10 is an explanatory diagram of the discharge mode in the second embodiment.

  Here, the discharge operation of the external additive performed at the beginning of the discharge mode will be described with reference to FIG. As shown in FIG. 10, in this discharge mode, the photosensitive drum 1 is stopped. The external additive recovery means 14 rotates in the clockwise direction indicated by the arrow C ', which is the opposite direction to that in the recovery mode. The frictional charging means 18 rotates in the same clockwise direction as in the recovery mode, and the surface of the recovery layer 140 is negatively charged. Therefore, the negatively charged silica is repelled from the surface of the recovery layer 140 and released. . The released silica flies in the direction of the photosensitive drum along the airflow generated by the rotation of the brush and adheres to the surface of the photosensitive drum (see A6). Part of the silica is in a cloud state, but is collected without being scattered around because of the scattering prevention housing 183.

  Further, the friction charging means 17 rotates counterclockwise as indicated by an arrow E ′, which is different from that in the recovery mode, and rotates at the same peripheral speed as the external additive recovery means 14, so that almost no frictional force is generated. The recovery layer 140 does not act and retains a negative charge without being rubbed or charged. Since the subsequent operation in the discharge mode is exactly the same as in the first embodiment, the details are omitted, but finally the tip of the cleaning blade is reached and the external dam is re-formed.

  In the present embodiment, since the frictional charging means 18 is a rotating brush, the rubbing force is increased and good frictional charging is possible.

  Also in the present embodiment, a verification experiment was performed using a Fuji Xerox on-demand printing machine DocuColor 8000 as in the first embodiment, with a total cycle number of 100,000.

As a result, the value of the lightness difference ΔL ^* changed from 0.05 to 0.1, and it was confirmed that continuous print ghosting could be prevented over a long period of time.

  FIG. 11 is a schematic configuration diagram showing a third embodiment of the external additive collecting means. The external additive collecting means in the present embodiment is different from the first and second embodiments in that the surface of the external additive collecting means 19 is in contact with the surface of the photosensitive drum. Further, the external additive collecting means 19 of the present embodiment has a brush shape, and a brush portion 190 as a collecting layer is bonded to a metal core 191. In the present embodiment, the external additive collecting means uses a brush-shaped one, but is not limited to that form. For example, a collecting layer is formed on the surface of a metal core, and the collecting is performed. Any other means can be used as long as the external additive can be recovered, such as a roll-shaped external additive recovery means using a solid or sponge shape (porous body) as the layer.

  The material of the brush part 190 that constitutes the external additive collecting means 19 is composed of a material in which the charged column is on the plus side with respect to the surface material of the photosensitive drum. In the present embodiment, since the surface material of the photosensitive drum uses a polycarbonate resin, the material of the brush portion 190 is made of a material having a charged column on the plus side of the polycarbonate resin. Specifically, as a material for the brush portion 190, synthetic fibers such as nylon fibers and rayon fibers, glass fibers, animal hair such as wool, and the like can be used.

  The material selection of the external additive collecting means is not limited to the described materials as long as the following relationship is satisfied.

Charging column plus tendency: material of brush portion> material of surface of photosensitive drum It should be noted that each material can be charged better by selecting a more distant material in the charging column.

  A nylon fiber brush was used as the material of the brush portion 190 of the external additive collecting means 19 of the present embodiment. The brush portion 190 is obtained by flocking nylon fibers on a base fabric. In this embodiment, the core bar 191 has a diameter of 10 mm, and the pile height of the brush portion 190 is 5 mm.

  As shown in FIG. 11, the external additive collecting means 19 of the present embodiment is supported so that the surface of the brush portion 190 is in contact with the surface of the photosensitive drum 1. Further, the external additive collecting means of the present embodiment can be rotated by a drive system (not shown) and rotates clockwise as indicated by an arrow G. As the external additive collecting means rotates, the brush portion 190 is positively charged by rubbing against the surface of the photosensitive drum. The rotational speed needs to be set so as to be an appropriate peripheral speed in consideration of friction charging performance, recovery performance, mechanical performance, and the like. In this embodiment, the speed is set to about 0.1 to 0.2 times the peripheral speed of the photosensitive drum.

  The brush portion 190 of the external additive collecting means 19 is in contact with the friction charging means 20 that is rubbed and charged with the brush portion 190. The friction charging means 20 negatively charges the surface of the brush portion 190. . The frictional charging means 20 of the present embodiment has a roll shape, and a surface layer 200 is formed on a metal cored bar 201. The diameter of the cored bar 201 is 5 mm, the thickness of the surface layer 200 is 3.5 mm, and the material of the surface layer 200 is polyacetal (POM). In the present embodiment, a solid surface layer is used, but any shape member such as a sponge shape (porous body) or a brush shape can be used as the surface layer. Further, the material of the frictional charging means 20 is not limited to that described, and the frictional charging system only needs to be on the plus side with respect to the surface material of the brush portion 190. For example, if the nylon brush portion 190 is used as in the present embodiment, animal hair such as glass, quartz, glass fiber or wool can be used as the material of the frictional charging means 20.

  Next, the collection mode and the discharge mode in the present embodiment will be described. First, the collection mode will be described with reference to FIG. Silica has a strong tendency to be negatively charged, and silica A1 that has passed through the cleaning blade is negatively charged. Therefore, when the external additive collecting means 19 passes through a position facing the photosensitive drum 1, the brush of the external additive collecting means 19 that is positively frictionally charged by sliding with the surface of the photosensitive drum 1. The unit 190 adsorbs and collects negatively charged silica by electrostatic force (see A5). At this time, the mechanical scraping force by the brush part 190 is also acting, and the silica is also mechanically scraped, but the electrostatic force is mainly acting at the time of recovery.

  FIG. 12 is an explanatory diagram of the discharge mode in the third embodiment. Here, the discharge operation of the external additive performed at the beginning of the discharge mode will be described with reference to FIG.

As shown in FIG. 12, in this discharge mode, the photosensitive drum 1 is stopped. The external additive collecting means 19 rotates in the counterclockwise direction indicated by the arrow G ′, which is the opposite direction to that in the collecting mode. The frictional charging means 20 rotates in the counterclockwise direction indicated by the arrow H, which is the same as in the recovery mode, and the surface of the brush portion 190 is negatively charged. Therefore, the negatively charged silica is repelled from the surface of the brush portion 190. Released with power. The released silica flies in the direction of the photosensitive drum 1 along the airflow generated by the rotation of the brush and adheres to the surface of the photosensitive drum 1 (see A6). Part of the silica is in a cloud state, but is collected without being scattered around because of the scattering prevention housing 202. Since the subsequent operation in the discharge mode is exactly the same as in the first embodiment, the details are omitted, but finally the tip of the cleaning blade is reached and the external dam is re-formed.
Also in the present embodiment, a verification experiment was performed using a Fuji Xerox on-demand printing machine DocuColor 8000 as in the first embodiment, with a total cycle number of 100,000.

  FIG. 13 is a diagram showing a verification experiment result.

As a result of conducting this verification experiment, as shown in FIG. 13, the value of the lightness difference ΔL ^* was changed from 0.05 to 0.15, and it was confirmed that continuous print ghosting could be prevented over a long period of time.

  Next, a fourth embodiment will be described. In each of the fourth and subsequent embodiments, the structure is slightly different from that of the color image forming apparatus shown in FIG. 1, and therefore, the color image forming apparatus will be described here again.

  FIG. 14 is a schematic configuration diagram of a color image forming apparatus to which the fourth and subsequent embodiments are applied.

  Here, elements common to the elements of the color image forming apparatus shown in FIG. 1 are denoted by the same reference numerals as those shown in FIG. 1, and only differences will be described.

  The color image forming apparatus shown in FIG. 14 differs from the color image forming apparatus shown in FIG. 1 in that the cleaning apparatuses 9Y, 9M, and 6K are replaced with the cleaning apparatuses 6Y, 6M, 6C, and 6K in the color image forming apparatus shown in FIG. The color image forming apparatus shown in FIG. 14 and the color image forming apparatus shown in FIG. 14 are externally provided separately from the cleaning apparatuses 6Y, 6M, 6C, and 6K. The agent recovery means 14 is not present. However, the color image forming apparatus shown in FIG. 14 does not have an external additive collecting means that is separate from the cleaning apparatus, so that the external additives in FIG. 1 are provided inside the cleaning apparatuses 9Y, 9M, 9C, and 9D. An external additive recovery means is provided in place of the agent recovery means 14. In the case of the color image forming apparatus shown in FIG. 14, the photosensitive drum 1 rotates only in the direction of arrow A shown in FIG. 14, and does not reversely rotate as in the first to third embodiments. Instead of this, in the case of the color image forming apparatus shown in FIG. 14, in addition to the external additive collecting means, the external additive collected by the external additive collecting means is transported into the cleaning blade 9 to the pre-nip of the cleaning blade. An additive conveying means is also provided.

  Next, the cleaning device 9 and the external additive collecting means and external additive transport means which are the main parts of the present embodiment will be described in detail.

  FIG. 15 is a cross-sectional view showing a conceptual configuration of a cleaning device and external additive recovery means and external additive transport means arranged in the cleaning device according to the fourth embodiment.

  FIG. 16 is an enlarged view of the periphery of the external additive collecting means in the fourth embodiment.

  The cleaning device 9 includes a cleaner housing 87 that is disposed in the vicinity of the photosensitive drum 1 and opens to the side facing the photosensitive drum 1. A lower seal member 85 is fixed to the lower opening end of the cleaner housing 87, and an upper seal member 86 is fixed to the upper opening end. The seal members 85 and 86 substantially block the gap between the photosensitive drum 1 and the cleaner housing 87, and prevent waste toner or the like stored in the cleaning device 9 from leaking or scattering to the outside. For the seal members 85 and 86, for example, a thermoplastic polyurethane film having a thickness of 0.1 mm is used.

  In the cleaner housing 87, a cleaning blade 91 as a cleaning member is disposed downstream of the seal member 85 in the rotation direction of the photosensitive drum 1 (indicated by an arrow A in the figure). In addition, an auger 84 is disposed in the lower portion of the cleaner housing 87.

  The cleaning blade 91 is formed in a plate shape having a thickness predetermined by an elastic material. As the blade material, for example, thermosetting polyurethane rubber having excellent mechanical properties such as wear resistance, chipping resistance, and creep resistance is used. The material of the blade is not limited to urethane rubber, and functional rubber materials such as silicone rubber, fluorine rubber, ethylene / propylene / diene rubber are used. The cleaning blade 91 is bonded to a sheet metal 92, is fixed to the cleaner housing 87 by a set screw 93, and is provided such that a tip edge portion thereof is in contact with the surface of the photosensitive drum 1.

  The blade pressurization method in the present embodiment employs a constant displacement method with a simple structure and low cost. For example, the applied pressure is set to 39.2 N / m (4 gf / mm). However, the blade pressing method is not limited to the constant displacement method, and a constant load method in which the contact pressure hardly changes with time may be used.

  In the cleaning device 9 having such a configuration, as shown in FIG. 15, the transfer residual toner T remaining on the surface of the photosensitive drum 1 passes through the front of the seal member 85 as it is and is scraped off by the cleaning blade 91. . The toner scraped off by the cleaning blade 91 is once accommodated in the cleaner housing 87, and then finally transported and discharged by the auger 84 to the side of the cleaning device 9 (direction perpendicular to the paper surface of FIG. 15). The cleaning device 9 is configured as at least a unit (process cartridge) integrated with the photosensitive drum 1, and is detachable from the image forming apparatus in the state of the unit.

  In such a cleaning apparatus, the tip of the cleaning blade 91 is irregularly deformed when the tip of the cleaning blade 91 is worn by rubbing against the photosensitive drum 1 or when the coefficient of friction of the surface of the photosensitive drum is high. If the blocking force is reduced, the external additive having a small particle size is likely to slip through the blade. In particular, silica used as an external additive has a small particle size and is firmly attached to the surface of the photosensitive member by van der Waals force or the like, so that it cannot be cleaned by the scraping force of the blade and easily passes through the blade nip. As described above, the external additive that has passed through the blade causes image quality degradation such as continuous print ghost.

  Therefore, in order to avoid such a problem, the image forming apparatus according to the present embodiment is provided with the external additive collecting means 94. The external additive recovery means 94 is for recovering the external additive that has passed through the cleaning blade 91, particularly silica. This is because silica having a relatively large particle size tends to cause continuous print ghosts (image defects in which an afterimage of the previous image appears slightly on the subsequent image) and image quality degradation.

  FIG. 16 is an enlarged view of the periphery of the external additive recovery means 94, and is a schematic configuration diagram showing an example of the external additive recovery means 94. The external additive collecting means 94 of the present embodiment has a brush shape, and a brush portion 942 is bonded to a metal cored bar 941. In the present embodiment, the external additive collecting means uses a brush-shaped one, but is not limited to that form. For example, a collecting layer is formed on the surface of a metal core, and the collecting is performed. Any other means can be used as long as the external additive can be recovered, such as a roll-shaped external additive recovery means using a solid or sponge shape (porous body) as the layer.

  The material of the brush portion 942 constituting the external additive collecting means 94 is composed of a material having a charged column on the plus side with respect to the surface material of the photosensitive drum.

  In the present embodiment, since the surface material of the photosensitive drum 1 uses polycarbonate resin, the material of the brush portion 942 is made of a material having a charged column on the plus side of the polycarbonate resin. Specifically, as the material of the brush portion 942, synthetic fibers such as nylon fibers and rayon fibers, glass fibers, and animal hair such as wool can be used.

  The material selection of the brush portion 942 of the external additive collecting means 94 is not limited to the described materials as long as the following relationship is satisfied.

Charging column plus tendency: material of brush portion> material of surface of photosensitive drum It should be noted that each material can be charged better by selecting a more distant material in the charging column.

A nylon fiber brush was used as the material of the brush portion 942 of the external additive collecting means 94 of the present embodiment. The brush portion 942 is obtained by implanting nylon fibers in a base fabric. In this embodiment, the diameter of the core metal 941 is 10 mm, and the pile height of the brush portion 942 is 5 mm.
As shown in FIG. 16, the external additive collecting means 94 of the present embodiment is supported so that the surface thereof is in contact with the surface of the photosensitive drum 1. Further, the external additive recovery means 94 of the present embodiment is rotatable by a drive system (not shown) and rotates in the clockwise direction indicated by an arrow J. As the external additive collecting means 94 rotates, the brush portion 942 of the external additive collecting means 94 is positively charged by sliding with the surface of the photosensitive drum 1.

  The rotational speed needs to be set so as to be an appropriate peripheral speed in consideration of friction charging performance, recovery performance, mechanical performance, and the like. In this embodiment, the speed is set to about 0.1 to 0.2 times the peripheral speed of the photosensitive drum.

  The external additive collecting means 94 is provided with a flicker bar 95 for separating the silica collected from the brush. It is preferable that the material of the flicker bar 95 itself is not frictionally charged. The flicker bar 95 of this embodiment is made of metal, specifically, a SUS square bar, and is connected to the ground.

  Next, the operation of the external additive collecting means 94 will be described. Silica has a strong tendency to be negatively charged, and as shown in FIG. 16, the silica S that has passed through the cleaning blade 91 is negatively charged. Therefore, when the external additive collecting means 94 passes through a position facing the photosensitive drum 1, the brush 942 of the external additive collecting means 94 that is positively frictionally charged by sliding with the surface of the photosensitive drum 1 is used. The negatively charged silica S is adsorbed and recovered by electrostatic force. At this time, the mechanical scraping force by the brush is also acting, and the silica S is also mechanically scraped, but the electrostatic force is mainly acting at the time of recovery.

  The silica recovered by the external additive recovery means 94 is scraped off by the mechanical scraping force by the flicker bar 95 and falls onto the external additive transport means 98. The external additive collecting means 94 is always refreshed by scraping off the silica from the external additive collecting means 94, so that the desired silica collecting performance can be stably maintained.

  The external additive conveying means 98 of the present embodiment is a plate-like member, and the external additive is conveyed by utilizing a descending action due to gravity. For this reason, a slippery member is appropriate for the surface of the plate. Specifically, a metal such as SUS, a resin material such as a fluororesin, a silicone resin, or polyacetal (POM) can be used, but unnecessary charging is prevented. Therefore, a conductive material is preferable. The external additive conveying means 98 according to this embodiment uses a SUS plate having a thickness of 1 mm and is connected to the ground in order to prevent the influence of charging. Silica that has fallen on the surface of the external additive conveying means 98 slides down the surface downward and falls into the pre-nip of the cleaning blade 91. In the prenip, toner and external additives are convected in a cloud shape, and when silica is added to it, it rides on the surface and adheres to the surface of the photoreceptor, reaching the external dam at the most advanced part of the prenip. To do.

  FIG. 17 is a view showing a modification of the fourth embodiment shown in FIG.

  In the case of the modification shown in FIG. 17, a supply brush 99 is provided in order to more reliably supply silica to the prenip. The supply brush 99 can be rotated by a drive system (not shown), and rotates clockwise as shown in FIG. The supply brush 99 mechanically scrapes the silica from the surface of the external additive conveying means 98, rotates counterclockwise as indicated by an arrow K, and scrapes the silica by striking the tip of the brush at the corner of the blade edge tip. , Put it in the cloud of the pre-nip. By this operation, the silica rides on the convection in the prenip and adheres to the surface of the photoreceptor, and is supplied to the externally added dam at the most advanced portion of the prenip.

  Next, the external additive conveying means will be described in detail.

  FIG. 18 is a view showing a cleaning device including another example of the external additive conveying means.

  The external additive conveying means 98 used in the embodiment shown in FIG. 15 is a plate-like member, and the external additive is conveyed by utilizing a descent action due to gravity. The external additive conveying means is not limited to such a system, and may be a belt conveyor type using a belt 80 stretched around a conveying roll 81 as shown in FIG. As the belt material, metals such as steel and resin materials such as polyimide, polyamideimide, polycarbonate, and fluorine resin can be used. However, in order to prevent unnecessary charging, conductive materials (carbon and ion conductive materials are used in the case of resin materials). A substance in which conductivity is imparted by dispersing a substance or the like is preferable, and it is used by connecting to a ground.

  FIG. 19 is a view showing a cleaning device including an external additive transporting unit of still another example.

  As the external additive conveying means used in the cleaning apparatus shown in FIG. 19, a plate-like member 82 having a piezoelectric vibration element 83 bonded thereto is used. The main conveying force of this method is vibration, and the plate-like member is vibrated by the piezoelectric vibration element 83, so that silica is conveyed in the direction in which gravity acts. Since fine particles such as silica have a strong adhesive force, they can be easily separated from the adhesion surface when such vibrations are applied, thus providing an efficient conveying means.

  As in the first to third embodiments, the basic form of the present embodiment shown in FIG. 15 is verified using a Fuji Xerox on-demand printing machine Docu Color 8000 with a total cycle number of 100,000. Was done.

As a result, the value of the lightness difference ΔL ^* changes from 0.05 to 0.15, and it can be determined that it has not changed in consideration of measurement variation, and the maintainability of the cleaning device 9 is confirmed. .

  FIG. 20 is a schematic configuration diagram showing a fifth embodiment of the present invention. FIG. 21 is an enlarged view of the periphery of the external additive collecting means in the fifth embodiment.

  The external additive collecting means in the present embodiment differs from the fourth embodiment in the periphery of the external additive collecting means, but the basic configuration is the same. That is, the fifth embodiment is different in that friction charging means 96 and 97 are added around the external additive collecting means 94.

  The surface of the external additive collecting means 94 in this embodiment is in contact with friction charging means 96 and 97 that are rubbed and charged with the surface of the external additive collecting means 94. The friction charging means 96 is for negatively charging the surface of the external additive collecting means, and the friction charging means 97 is for positively charging the surface of the external additive collecting means 94. The friction charging means 96, 97 of the present embodiment uses block resin, and is constituted by resin portions 961, 971 and base members 962, 972, respectively, as shown in FIG. In this embodiment, the friction charging means 96 and 97 both use a circumferential width of 10 mm, the resin part 961 uses polyacetal (POM), the resin part 971 uses Teflon (registered trademark), and the base member uses a 2 mm thick metal plate. did. In this embodiment, a solid shape is used. However, any shape member such as a brush shape or a sponge shape can be used as the friction charging member. The materials of the friction charging means 96, 97 are not limited to those described, and the material of the friction charging means 96 only needs to have a friction charging series on the plus side with respect to the surface material of the external additive collecting means. The material of the charging unit 97 may be such that the charging series is on the minus side of the surface material of the external additive collecting unit. For example, when a nylon external additive collecting means is used as in the present embodiment, animal hair such as glass, quartz, glass fiber or wool can be used as the material of the friction charging means 96, and friction charging As a material of means 97, synthetic rubber such as urethane rubber, silicone rubber, fluoro rubber, natural rubber, polyethylene terephthalate (PET), polyethylene resin, acrylic resin, polystyrene resin, phenol resin, polyester resin, polyurethane resin, etc. Can be used.

  The reason why the frictional charging means is provided in this way is to make it easier to release the silica collected from the external additive collecting means 94, to send the silica to the external dam more stably, and to refresh more steadily. is there. That is, the frictional charging means 96 is intended to be charged with the same polarity as the recovered silica and released using the repulsive force. Further, the frictional charging means 97 is provided as an auxiliary in order to steadily return to the charging at the time of silica recovery after charging to the same polarity.

  In addition, the flicker bar 95 for separating the silica collected from the brush is attached to the external additive collecting means, as in the fourth embodiment. The material of the flicker bar 95 is preferably not frictionally charged by itself, and the flicker bar is also connected to the ground using a SUS square bar in this embodiment.

  With this setting, as in the first to fourth embodiments, a verification experiment was performed on the fifth embodiment using a Fuji Xerox on-demand printing machine DocuColor 8000 with a total cycle number of 100,000. It was.

As a result, the value of the lightness difference ΔL ^* changed from 0.05 to 0.1, and it was confirmed that continuous print ghosting could be prevented over a long period of time.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging device 3 Exposure device 4 Developing device 5 Primary transfer device 6 Cleaning device 7 Fixing device 8 Intermediate transfer belt 20 Recording paper transport mechanism 21 Paper tray 30Y First image forming unit 30M Second image forming unit 30C Second image forming unit 30C 3 image forming unit 30K 4th image forming unit 60, 91 Cleaning blade 61, 92 Sheet metal 62, 93 Set screw 63, 84 Auger 64, 87 Cleaner housing 65, 85, 86 Seal member 80 Belt 83 Piezo vibration element 85 Lower seal 86 Upper seal 95 Flicker bar 99 Supply brush 140 Collection layer 150, 160, 170, 180, 190, 942 Brush part 153, 173, 183 Anti-scattering housing

Claims (4)

An image having an image holding body that holds a toner image by being charged, exposed, and developed with toner containing an external additive while rotating, and transfers the toner image, and fixes the transferred toner image on a sheet A forming device,
A cleaning blade for bringing a tip edge into contact with a region of the image carrier after transferring the toner image and scraping off a residue after transfer of the image carrier;
A collecting means for collecting the external additive that has passed through the cleaning blade in a region before charging in the rotation direction of the image carrier;
The external additive recovered by the recovery means is upstream of the contact portion of the edge of the cleaning blade of the image carrier, and the external additive is interposed between the cleaning blade and the image carrier. An image forming apparatus comprising: a returning unit that returns the holding area to the holding area.   The image forming apparatus according to claim 1, wherein the recovery unit is frictionally charged to a polarity attracting the external additive and recovers the external additive by electrostatic force.   The return means discharges the external additive collected by the previous collecting means from the collecting means onto the image holding member, and reverses the image holding member to return the external additive to the holding region. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The recovery means is housed together with the cleaning blade in a case containing an external additive;
The return means, in the case, conveying means for conveying the external additive recovered by the recovery means to the holding region;
The image forming apparatus according to claim 1, further comprising: a delivery unit that delivers the external additive collected by the collection unit from the collection unit to the transport unit.

Images