JP2005172946A - Charging device, process unit, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging device capable of easily and stably charging a member to be charged, with a reduced consumption of particles over a long period of time, with respect to a charging device which charges a member to be charged by making particles interposed in between a charging member and the member to be charged, and to provide a process unit with the charging device and an image forming apparatus. <P>SOLUTION: The charging device 2A, 2B, 2C or 2D has recycling mechanisms 22, 24, 25 or 26 for recovering particles 10, which stick to the member to be charged (image carrier or photoreceptor) 1 on the downstream side of points of contact of the charging member 211 and the member 1 to be charged and for resupplying the recovered particles to the gap between the charging member 211 and the member 1 to be charged. The process unit, provided with the charging device and the image forming apparatus, are also provided. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a charging device and a process device used in an electrophotographic image forming apparatus such as a copying machine and a printer, and further to an image forming apparatus.

Conventionally, in an image forming apparatus such as an electrophotographic apparatus, a corona charger using corona discharge has been mainly used as means for charging an object to be charged such as an electrophotographic photoreceptor.
The corona charger is disposed in non-contact with the object to be charged. For example, a corona discharge is generated by applying a high voltage to a wire electrode or a needle electrode, and a part of the discharge current is passed through the object to be charged. The charged body is charged to a predetermined potential.

  However, since the corona charger uses corona discharge, a large amount of ozone is generated, causing problems such as ozone odor. In addition, since the discharge product generated by corona discharge adheres to the surface of the object to be charged, the image quality is deteriorated or the surface of the object to be charged must be shaved and refreshed to shorten the life of the object to be charged. There were also problems such as. Furthermore, a high voltage power supply is necessary, and the power supply cost is high.

Therefore, in recent years, many contact chargers have been proposed and put into practical use because they have advantages such as low ozone and low power compared to corona chargers.
The contact charger applies a predetermined charging bias to a conductive charging member brought into contact with an object to be charged to charge the surface to be charged to a predetermined polarity and potential. As the charging member, for example, a charging roller, a fur brush, a blade, or the like is used.

There are two types of contact charging mechanisms. One is a charging mechanism by discharge, and the other is a charging mechanism in which charges are directly injected from a charging member to an object to be charged.
The discharge charging mechanism uses a discharge phenomenon that occurs in a minute gap between the member to be charged and the charging member. For this reason, although charging can be performed at a lower voltage than corona charging, it is necessary to apply a voltage obtained by adding a threshold voltage to a desired charging potential to the charging member. In addition, although the amount of ozone generated is smaller than that of corona charging, the charging method using the discharge phenomenon is unavoidable due to discharge products.

  In the injection charging mechanism, charges are directly injected from the contact charging member to the member to be charged without going through a discharge phenomenon. Even if the voltage applied to the charging member is equal to or lower than the discharge threshold value, the surface of the object to be charged can be charged to a voltage substantially equal to the applied voltage, so the voltage is lower than the contact charging utilizing the above discharge phenomenon. Available. Further, since no discharge occurs and no ions are generated, there is no harmful effect caused by the discharge product.

  As a means for controlling the injection charging mechanism in contact charging, a method is known in which conductive particles are interposed in the mutual contact portion between the member to be charged and the contact charging member. The presence of the conductive particles in the contact charging portion makes it possible to easily bring the object to be charged into contact with the contact charging member due to the lubricant effect of the particles. Thus, the surface of the member to be charged is intimately contacted with the contact member, and the surface of the member to be charged is contacted more frequently. As a result, the surface of the member to be charged is rubbed evenly with the conductive particles at the mutual contact portion.

  As described above, since the conductive particles are present in the contact portion between the charged body and the charging member, it is possible to maintain the close contact property and the contact resistance between the charging member and the charged body. In addition, direct injection charging with high charging ability can be performed, and direct injection charging is dominant in contact charging of the object to be charged by the contact charging member.

However, in the conventional fine particle-mediated injection charger, conductive fine particles are detached from the contact charging portion, causing the following problems.
(1) Since the number of conductive particles in the mutual contact portion is reduced and the injection charge amount is lowered, charging stability is lacking.
(2) Since exposure, development, and transfer are performed with the conductive particles still attached to the charged body, exposure, image flow, development failure, particle transfer, etc. are likely to occur, and the image quality is adversely affected. .

  Therefore, as a solution to the above point (1), for example, as disclosed in Japanese Patent Application Laid-Open No. 11-190930, conductive particles are mixed and supplied, or as disclosed in Japanese Patent Application Laid-Open No. 11-194484. There have been proposed ones that supply conductive particles using a conductive particle supply member such as a foaming roller or a fur brush.

  Regarding the point (2), for example, Japanese Patent Application Laid-Open No. 2000-81766 discloses that conductive particles are charged to a polarity opposite to that of a charging member by frictional charging with a photoreceptor, and the particles are electrically moved from the charging member. It is disclosed that it is difficult to do.

Japanese Patent Laid-Open No. 11-190930 Japanese Patent Laid-Open No. 11-194484 JP 2000-81766 A

  However, in the methods disclosed in Japanese Patent Application Laid-Open Nos. 11-190930 and 11-194484, it is necessary to constantly update the supply source of the conductive particles, and the problem of image quality degradation described in (2) above is required. It is not solved.

As a solution to the above point (2), as described in, for example, Japanese Patent Application Laid-Open No. 2000-081766, the conductive particles are charged to a polarity opposite to that of the charging member by frictional charging with the photoreceptor, and the particles are electrically It is conceivable to make it difficult to move from the charging member. Alternatively, it is conceivable that the point (2) does not become a big problem even if the conductive particles remain attached to the image carrier by devising the size of the conductive particles, the triboelectric charging property, or the like.
However, in these methods, it is difficult to sufficiently suppress the problem (2), and there is also a problem that usable conductive particles are limited. Furthermore, another means for solving the problem (1) is required.

  Accordingly, the present invention provides a charging device that has a charging member that contacts a member to be charged, and charges the member to be charged by interposing particles between the member to be charged and the member to be charged. It is an object of the present invention to provide a charging device that can easily and stably charge a body over a long period of time while reducing particle consumption.

  The present invention also includes an image carrier and a charging device that charges the image carrier, the charging device having a charging member that contacts the image carrier, and between the charging member and the image carrier. A process apparatus for charging the image carrier by interposing particles therein, which can be attached to and detached from the electrophotographic image forming apparatus main body, reducing the consumption of particles and simplifying the image carrier. It is an object of the present invention to provide a process apparatus that can be stably charged over a long period of time and can be formed on a main body of an image forming apparatus to form a good image with image noise suppressed for a long period of time.

  The present invention also includes an image carrier and a charging device that charges the image carrier, the charging device having a charging member that contacts the image carrier, and between the charging member and the image carrier. An electrophotographic image forming apparatus for charging the image carrier by interposing particles therein, wherein the image carrier can be easily and stably charged over a long period of time while reducing particle consumption. Therefore, an object of the present invention is to provide an image forming apparatus capable of forming a good image in which image noise is suppressed over a long period of time.

In order to solve the above problems, the present invention provides the following charging device, process device, and image forming apparatus.
(1) Charging device A charging device having a charging member that contacts a member to be charged, and charging the member to be charged by interposing particles between the member to be charged and the member to be charged, the charging member The particles adhering to the charged body are collected downstream from the contact portion between the charged body and the charged body in the surface movement direction of the charged body, and the collected particles are collected between the charging member and the charged body. A charging device equipped with a recycling mechanism for re-supplying in between.

(2) Process device A process device comprising at least an image carrier and a charging device for charging the image carrier in a case, the process device being detachable from the main body of the image forming device, wherein the charging device is the image carrier. A charging device in contact with the charging member and charging the image carrier by interposing particles between the charging member and the image carrier, the charging member, the image carrier, For recovering the particles adhering to the image carrier on the downstream side in the direction of surface movement of the image carrier from the contact portion of the image and re-supplying the collected particles between the charging member and the image carrier Process equipment equipped with a recycling mechanism.

(3) Image forming apparatus
(3-1) First image forming apparatus An image forming apparatus in which the process apparatus is detachable.
(3-2) Second image forming apparatus At least an image carrier and a charging member that contacts the image carrier, and the image carrier with particles interposed between the charging member and the image carrier. A charging device for charging the body, a latent image forming means for forming an electrostatic latent image on the charged image carrier, and a developing device for developing the electrostatic latent image formed on the image carrier. Recovering the particles adhering to the image carrier downstream from the contact portion between the charging member and the image carrier in the surface movement direction of the image carrier, and between the charging member and the image carrier. An image forming apparatus provided with a recycling mechanism for re-supplying to the printer.

  Since the charging device according to the present invention charges particles by interposing particles between the charging member and the member to be charged, the charging voltage applied to the charging member is a voltage equal to or lower than the discharge threshold value. However, the charged object can be injected and charged to a potential substantially equal to the voltage. Therefore, the object to be charged can be charged with a low voltage at a low cost, and the adverse effect caused by the discharge product can be eliminated because of the injection charging.

  The particles attached to the member to be charged can be collected from the member to be charged by a particle recycling mechanism and re-supplied between the charging member and the member to be charged. Therefore, the reduction of particles is suppressed and the replenishment frequency of particles is remarkably reduced, so that the amount of particles consumed can be reduced to meet today's demands for resource saving and low environmental load. (Easy to use) can be realized.

  As a result, the object to be charged can be easily and stably charged over a long period of time with reduced particle consumption.

  Further, since the particles adhering to the member to be charged are collected downstream from the contact portion between the charging member and the member to be charged in the surface moving direction of the member to be charged, When used in an image forming process to charge an image carrier such as a photoreceptor, it is possible to prevent particles from adversely affecting the image forming process after charging the image carrier (such as exposure). . In addition, there is an advantage that the selection range of the particulate material is expanded.

  Also in the process apparatus and the image forming apparatus according to the present invention, the charging device charges the object to be charged by interposing particles between the charging member and the image carrier. The body can be charged and harmful effects caused by the discharge products can be eliminated.

  In the process apparatus and the image forming apparatus according to the present invention, since the particle recycling mechanism is adopted, the image carrier can be easily and stably charged over a long period of time while reducing particle consumption. Further, it is possible to prevent the particles from adversely affecting the image forming process after charging the image carrier (such as exposure).

  As a result, for the process apparatus, the image carrier can be easily and stably charged over a long period of time with reduced particle consumption, and by being mounted on the image forming apparatus main body, image noise can be suppressed over a long period of time. It is possible to form a good image.

  In addition, with respect to the image forming apparatus, the image carrier can be easily and stably charged over a long period of time with reduced particle consumption, whereby a good image with suppressed image noise can be formed over a long period of time.

  As the particles used in the charging device, the process device, and the image forming apparatus according to the present invention, conductive particles can be used. The particle size is preferably about 0.01 μm to 100 μm from the viewpoint of good injection charging.

Examples of the recycling mechanism include those including a particle recovery member provided in contact with or in proximity to a charged body or an image carrier. A particle recovery voltage may be applied to the particle recovery member.
Examples of the particle recovery member include a brush roller, a fixed brush, a roller (excluding the brush roller), a plate-like member (for example, a blade), a film-like member, and the like.

These recovery members that are arranged in contact with the charged body or image carrier can more reliably scrape particles from the charged body or image carrier than in the case of non-contact arrangement. Even when the particles are not completely recovered, the particles can be mechanically dispersed to suppress image deterioration.
In addition, even if the toner is disposed in a non-contact manner on the member to be charged or the image carrier, it is possible to electrostatically collect particles adhering to the member to be charged or the image carrier. If the object to be charged and the image carrier are not in contact with each other, the influence on the surface is suppressed.

In addition, a member that collects particles from the charged body or the image carrier may be a rotating member, and a scraping member for scraping particles from the rotating member may be provided. Thereby, the recovered particles can be efficiently recycled.
A member that collects particles from the charged body or the image carrier may be a fixed member. In this case, the collected particles may be separated from the fixed member by attractive force such as electrostatic force. This also allows the collected particles to be efficiently recycled.
Further, the position of the particle recovery member may be arranged at a position higher than the position of the charging member, and gravity may be used to re-supply the recovered particles to the charging region.

  The process apparatus includes, for example, at least a charge of the image carrier, image exposure on the charged image carrier, development of an electrostatic latent image formed by image exposure, and a toner image transfer body (developed by development). It may be a process device for use in an image forming process for forming a toner image through transfer to an intermediate transfer member, a recording medium, or the like. In this case, the recycling mechanism can be provided in the case so as to be disposed between a charging area for charging the image carrier and a transfer area for transferring the toner image.

  In addition, the process apparatus includes, for example, an image forming process for forming a toner image through at least charging of the image carrier, image exposure on the charged image carrier, and development of an electrostatic latent image formed by image exposure. It is good also as a process apparatus for using for. In this case, the recycling mechanism can be provided in the case so as to be disposed between a charging region for charging the image carrier and an image exposure region for the image carrier.

  In any case, the process device may include one or more of a developing device and an eraser for erasing residual charges on the image carrier.

In the case of the second image forming apparatus, examples of the position where the recycling mechanism is disposed include a period from a charging region for charging the image carrier to an image exposure region for the image carrier.
The second field image forming apparatus may further include a transfer device for transferring the toner image formed by the developing device from the image carrier to a transfer target (intermediate transfer member, recording medium, etc.). In this case, the recycling mechanism may be disposed between a charging area for charging the image carrier and a transfer area for transferring the toner image.

  As described above, according to the present invention, there is provided a charging device that has a charging member that contacts a member to be charged, and charges the member to be charged by interposing particles between the charging member and the member to be charged. In addition, it is possible to provide a charging device that can easily and stably charge an object to be charged for a long period of time with reduced particle consumption.

  According to the invention, the image bearing member and a charging device for charging the image bearing member are provided, the charging device has a charging member that contacts the image bearing member, and the charging member and the image bearing member A process apparatus for charging the image carrier with intervening particles, which is detachable from the main body of an electrophotographic image forming apparatus, reducing the consumption of particles and simplifying the image carrier. In addition, it is possible to provide a process apparatus that can be stably charged over a long period of time and can be formed on a main body of an image forming apparatus to form a good image in which image noise is suppressed over a long period of time.

  According to the invention, the image bearing member and a charging device for charging the image bearing member are provided, the charging device has a charging member that contacts the image bearing member, and the charging member and the image bearing member An electrophotographic image forming apparatus in which particles are interposed to charge the image carrier, wherein the image carrier is easily and stably charged over a long period of time with reduced particle consumption. Therefore, it is possible to provide an image forming apparatus capable of forming a good image in which image noise is suppressed over a long period of time.

Embodiments of the present invention will be described below.
<First Embodiment>
FIG. 1 shows a schematic configuration of an example of an electrophotographic image forming apparatus provided with a charging device 2A according to an embodiment of the present invention.
(Configuration of image forming apparatus)
The image forming apparatus shown in FIG. 1 is an example of a member to be charged, and includes a photosensitive drum 1 which is also an example of an image carrier. A charging device 2A and an image by laser light are provided around the photosensitive drum. The exposure device 3, the developing device 4, and the transfer device 5 are arranged in this order. The developing device 4 includes a developing roller 41 to which a developing bias voltage is applied from a power supply (not shown), and the transfer device 5 faces the photosensitive drum 1 and is a transfer roller 51 to which a transfer voltage is applied from a power supply (not shown). Is included. In the drawing, a fixing device 6 is provided on the left side of the transfer roller 51.

(Charging device)
The charging device 2A includes a charging mechanism 21 for charging, and a particle recycling mechanism 22 for collecting the charging auxiliary particles 10 and resupplying the charging mechanism 21, and these are provided in the charging device case 23A. It is provided and integrated through the case 23A.

  The charging mechanism 21 includes a contact charging member 211 held by a case 23A, and the charging member 211 is disposed in contact with the photosensitive drum 1 with a predetermined pressing force. The auxiliary charging particles 10 are interposed in the mutual contact nip portion between the contact charging member 211 and the photosensitive drum drum 1.

  Here, the case where the charging mechanism 21 is a brush charging mechanism will be described. The brush charging mechanism 21 has a roller-shaped brush (brush roller) 211 as a contact charging member. The brush roller 211 is obtained by winding a brush 212 having brush hairs planted on a base cloth around a conductive support 213 (which is also a roller shaft in the example of FIG. 1).

  The brush fibers (brush hairs) of the brush 212 are made of semiconductive fibers obtained by mixing a conductive material with a resin material. Examples of the resin material include polyamide such as nylon, rayon, polyester, polyolefin, polycarbonate, polyurethane, polyvinyl alcohol (vinylon), acrylic resin, and the like. Nylon is preferable. As the conductive material, conductive carbon, metal powder, zinc oxide, titanium oxide, tin oxide, or the like can be used. There is no particular limitation as long as it can be mixed uniformly in the synthetic resin.

Since the brush charging mechanism 21 performs injection charging on the photosensitive drum 1 via the auxiliary charging particles 10, it is important that the particles 10 can sufficiently contact the photosensitive drum 1 and function as an electrode. In order to obtain sufficient chargeability and leakage resistance, the brush 212 has a brush fiber thickness of 2 to 10 denier, a brush fiber flocking density of 155 / mm ^{2 to} 10,000 / mm ² , and a brush fiber volume. A material having a resistivity in the range of 1 × 10 ¹ Ω · cm to ¹ × 10 ⁸ Ω · cm may be used.

  Examples of the material of the conductive support 213 include metals such as stainless steel and aluminum. However, the conductive support 213 is not limited to these as long as it is conductive.

  The brush charging mechanism 21 uniformly charges the surface of the photosensitive drum 1 by applying a voltage to the conductive support 213 with the brush roller 211 in contact with the surface of the photosensitive drum 1 through the particles 10. It is like that.

  As the contact charging member, in addition to the brush roller, a fixed brush, a charging roller, a charging film, a charging blade, or the like may be employed. The conductive material is not limited to these. In the case of a rotating member such as a brush roller or a charging roller, the portion that contacts the photosensitive drum 1 can be changed by rotation, so that deterioration is suppressed. Further, there is an advantage that the charging property can be controlled to some extent by adjusting the relative rotational speed with respect to the photosensitive drum 1.

The charging auxiliary particles 10 are for performing injection charging.
As the material of the auxiliary charging particles 10, metal oxides such as zinc oxide, tin oxide, titanium oxide, iron oxide, aluminum oxide, and magnesium oxide, and carbon fine particles such as carbon black, graphite, fullerene, and carbon nanotube can be used. .

  When using a metal oxide, it is also possible to use a metal oxide containing a metal element different from the main metal element. For example, zinc oxide containing aluminum, tin oxide containing antimony, or titanium oxide, aluminum borate, or barium sulfate as the core material, and the surface is covered with tin oxide containing antimony. Etc.

  The volume average particle size of the auxiliary charging particles 10 is preferably 0.01 μm to 100 μm. If the volume average particle size of the auxiliary charging particles is too small, the production cost of the auxiliary charging particles becomes high and the charging device becomes expensive. If it is too large, the contact density between the photosensitive drum 1 and the particles 10 is lowered, and it becomes difficult to perform uniform injection charging.

The volume resistivity of the auxiliary charging particles 10 is preferably 1 × 10 ¹⁰ Ω · cm or less. If it exceeds 1 × 10 ¹⁰ Ω · cm, sufficient charge cannot be supplied from the brush roller 211 to the photosensitive drum 1, and charging unevenness occurs.

  The particle recycling mechanism 22 has an elastic blade 221 as a collecting member for mainly collecting the particles 10 from the photosensitive drum 1. It is held at the upper end of the case 23A and is in contact with the photosensitive drum 1. The blade 221 collects the particles 10 adhering to the surface of the photosensitive drum 1 from the drum surface and returns them to the case 23A. Here, since the blade 221 is provided at a position higher than the brush charging mechanism 21, the auxiliary charging particles 10 can be naturally returned to the charging mechanism 21 by gravity. Therefore, the mechanism for collecting particles has a very simple configuration. The blade 221 may be vibrated so that the particles are detached from the blade 221.

  The particles 10 on the photosensitive drum 1 may be charged by being rubbed by the photosensitive drum 1 and the brush roller 211 at a contact charging portion between the brush roller 211 and the photosensitive drum 1. If the charged polarity of the particles at this time is the same as the charged polarity of the photosensitive drum, the blade 221 that is a recovery member is grounded, or the blade 221 is exposed to the opposite polarity or the same polarity as the photosensitive drum 1. By applying a voltage having an absolute value smaller than the body drum surface potential, particles can be collected more efficiently.

  Further, when the charged polarity of the particles 10 is opposite to that of the photosensitive drum 1, a voltage having the same polarity as that of the photosensitive drum and an absolute value larger than the surface potential of the photosensitive drum is applied to the blade 221 efficiently. Particles can be recovered.

  When the particles to be collected are highly conductive, the particles on the photosensitive drum 1 after charging are hardly electrically charged and are detached from the surface of the photosensitive drum by mechanical rubbing by the blade 221. Therefore, the blade 221 may be electrically floated.

In the charging device shown in FIG. 1, an elastic blade is used as the particle collecting member. However, the collecting member is not limited to this, and may be, for example, a flexible film, a fixed brush, or the like, as in an embodiment described later. Alternatively, a rotating brush or a rotating roller may be used.
Alternatively, a mode may be provided in which particles adhering to a collecting member such as the blade 221 are discharged onto the photosensitive drum 1 between images for image formation, and the photosensitive drum is rotated to return the particles to the contact charging unit.

  In this embodiment, the particle recovery member is arranged between the photosensitive drum charging area by the brush roller 211 and the exposure area to the photosensitive drum by the image exposure apparatus 3. In this case, since the particles 10 are collected before the electrostatic latent image is formed, the material selection range of the particles 10 is greatly expanded unlike the method in which the charging auxiliary particles are not collected. For example, since it is not necessary to worry about exposure, colored particles and large-diameter particles can be selected. In addition, since there is no need to worry about the lateral flow of electric charges, particles with extremely high conductivity, for example, particles having a two-dimensional extent (bar-like, scaly, thread-like) or low-resistance particles can be used.

By providing the particle recovery member closer to the contact charging region, the adverse effect on image formation can be reduced, the particle recovery efficiency is increased, and resupply is facilitated.
If the pressing amount of the brush roller 211 into the photosensitive drum 1 is set in a range of 0.1 mm or more and 2 mm or less, charging unevenness can be suppressed and wear of the photosensitive drum can be reduced.

  The rotation direction of the brush roller 211 may be the same direction (with direction) or the opposite direction (counter direction) with respect to the rotation direction of the photosensitive drum 1. The rotation speed can be set to a speed at which a peripheral speed ratio with the photosensitive drum 1 is set, and charging uniformity can be improved by making the peripheral speed ratio greater than 1.

(Image formation)
In the image formation, the photosensitive drum 1 is rotationally driven in the clockwise direction in the drawing by a driving unit (not shown), and the surface is uniformly charged by the charging device 2. At this time, a voltage is applied from a photoconductor charging power supply (not shown) to the conductive support 213 of the brush roller 211 of the charging mechanism 21 in the charging device 2, and the surface of the photoconductor drum is predetermined via the above-described auxiliary charging particles 10. Is charged to a potential of Taking the case of reversal development using a negatively chargeable toner as an example, the voltage applied to the conductive support 213 is preferably about -1600 V to -800 V as a DC voltage, but is not limited to this range. In addition, when a charging bias in which an AC voltage is superimposed on a DC voltage is applied, an AC peak-to-peak voltage of 500 V to 2000 V, a frequency of 50 Hz to 2000 Hz, and a DC voltage of about −400 V to −1200 V are preferable.

  The charged photosensitive drum 1 is subjected to image exposure according to image data from the image exposure device 3 to form an electrostatic latent image. In this example, the image exposure apparatus 3 is a laser exposure apparatus incorporating a laser diode, a polygon mirror, and an optical element, but is not limited to this. The area on the photosensitive drum where the electrostatic latent image is formed moves in front of the developing device 4 as the photosensitive drum 1 rotates, and charged toner is supplied from the developing roller 41 of the developing device 4 here. The toner is attracted to the surface of the photosensitive drum 1 by electrostatic force, and a toner image is formed.

  The toner image on the photoconductive drum 1 arrives at a transfer area where the transfer roller 51 is located with the rotation of the photoconductive drum 1, and here, a recording material (in this example, a paper sheet) supplied from a recording material supply unit (not shown). S) Electrostatically transferred onto. The sheet S on which the toner image is transferred is conveyed to the fixing device 6 where the toner image is fixed and discharged.

  The image forming apparatus shown in FIG. 1 has only one photosensitive drum 1 and one developing device 4, but around one photosensitive drum 1, for example, a cyan developing device, a magenta developing device, A four-cycle type in which four developing units, a yellow developing unit and a black developing unit, are arranged, and a tandem type in which four photosensitive drums corresponding to each color are sequentially arranged in the moving direction of the intermediate transfer member A color image forming apparatus having a configuration may be used. In these cases, the toner image formed on the photosensitive drum is primarily transferred onto the intermediate transfer member, and then the toner image on the intermediate transfer member is secondarily transferred onto the recording material.

(Cartridge)
The charging device 2 may be installed alone in the image forming apparatus. However, as shown by a broken line in FIG. 1, the charging device 2, the photosensitive drum 1 as an image carrier, and other process equipment (here, a developing device). ) May be formed integrally with the cartridge case CA to form a process apparatus (process cartridge) that can be attached to and detached from the image forming apparatus main body. This also applies to the following embodiments.

Second Embodiment
The image forming apparatus according to the second embodiment is obtained by replacing the charging device 2A with the charging device 2B shown in FIG. 2 in the image forming apparatus of FIG.
A charging device 2B shown in FIG. 2 employs a particle recycling mechanism 24 having a recovery member for promoting the recovery of particles, instead of the particle recycling mechanism 22 in the charging device 2A.

  The recycling mechanism 24 is provided with a roller-type recovery brush 241 as a particle recovery member in a container (case) 23 </ b> B having an opening on the photosensitive drum 1 side so as to be rotationally driven, and at a position in contact with the brush 241. A mesh plate 23 ′ for removing the particles 10 from is provided. Inside the container 23B, the same charging mechanism 21 as in the case of the charging device 2A is provided on the upstream side in the rotational direction of the photosensitive drum from the collection brush 241, and the collected particles 10 move inside the collection container 23B. The structure is again supplied to the contact charging unit. A scattering prevention member 242 is provided at the opening of the collection container 23B in order to prevent the particles 10 from scattering.

  The collection brush 241 is brought into contact with the surface of the photosensitive drum 1 and at a peripheral speed faster than that of the photosensitive drum so that the respective contact portions move in the opposite direction to each other in the same direction as the photosensitive drum rotation direction. It is preferable to rotate.

  The mesh plate 23 ′ is used for separating the particles 10 collected by the collecting brush 241 from the brush and re-supplying the particles to the contact charging unit by the charging mechanism 21. As the collection brush 241 rotates, the bristle comes in contact with the mesh plate 23 'one after another to cause a flick action, and the particles 10 are detached from the brush.

  By providing a member that promotes the collection of particles as in this embodiment, the particles are more reliably scraped off from the member to be charged (photosensitive drum in this example). Further, since the particles are mechanically moved to the charging mechanism side by the rotating member, the resupply of the particles to the charging region is promoted. Further, by providing a member for detaching particles adhering to the particle recovery member, the resupply of particles to the charged region is promoted also in this respect.

<Third Embodiment>
The image forming apparatus according to the third embodiment is obtained by replacing the charging device 2A with the charging device 2C shown in FIG. 3 in the image forming apparatus shown in FIG.
The charging device 2C shown in FIG. 3 is obtained by changing the particle recycling mechanism 24 in the charging device 2B.

The particle cycle mechanism 25 in the charging device 2C of FIG. 3 includes an insulating roller 251 for particle recovery provided in a case 23C having an opening on the photosensitive drum 1 side so as to be rotationally driven. In the case 23C, the same charging mechanism 21 as that in the case of the charging device 2A is provided upstream of the collection roller 251 in the rotation direction of the photosensitive drum, and particles collected on the collection roller 251 from the photosensitive drum 1 are provided. 10 is scraped off by the charging brush roller 211 in the charging mechanism 21 and supplied again to the contact charging unit. An anti-scattering member 252 is provided at the opening of the case 23C in order to prevent the particles 10 from scattering.
In this embodiment, it is possible to increase the efficiency of particle recovery and resupply to the charged region with a relatively simple structure.

<Fourth embodiment>
The image forming apparatus according to the fourth embodiment is obtained by replacing the charging device 2A with the charging device 2D shown in FIG. 4 in the image forming apparatus shown in FIG.
The charging device 2D shown in FIG. 4 is obtained by changing the particle recycling mechanism 22 in the charging device 2A.

The particle recycling mechanism 26 of the charging device 2D in FIG. 4 is provided with a particle recovery fixed brush 261 in a recovery container (case) 23D having an opening on the photosensitive drum 1 side. Inside the container 23D, the same charging mechanism 21 as that in the case of the charging device 2A is provided upstream of the fixed brush 261 in the rotation direction of the photosensitive drum.
A potential controller 262 is connected to the fixed brush 261, and the potential of the brush 261 can be selected between float and ground.
The potential control device 262 causes the brush 261 to float when collecting particles. When the particles accumulated on the brush 261 are supplied again to the contact charging unit, the charging mechanism 21 charges the photosensitive drum 1 and the electric control device 262 places the collection brush 261 in the ground state.

  The auxiliary charging particles 10 charged to a predetermined polarity by friction with the photosensitive drum are easily transferred to the photosensitive drum 1 by grounding the recovery brush 262. The auxiliary charging particles that have moved onto the photosensitive drum move to the contact charging unit as the photosensitive drum 1 rotates, and are supplied again.

<Experimental example>
Hereinafter, experimental examples and comparative experimental examples in which the charging device according to the present invention is employed to evaluate the chargeability of the photoreceptor and the image quality of the formed image will be described. In the following experimental examples and comparative experimental examples, a monochrome printer of the type shown in FIG. 1 was used. However, a photosensitive drum used in a commercially available printer (magicolor 2200 DeskLaser manufactured by Minolta QMS Co., Ltd.) was used as the photosensitive drum.

In both experiments, measurement of photoreceptor surface potential for evaluation of charging unevenness and image formation for evaluation of image deterioration were performed in an environment of 25 ° C. and 50% RH.
The charged potential on the surface of the photosensitive drum was measured using a surface potential meter MODEL 344 and a probe 6000B-16 manufactured by Trek Japan. At the time of measurement, the above probe is arranged on the downstream side of the charging portion of the photosensitive member, the surface of the photosensitive drum is charged by applying a DC bias of −600 V to the fur brush roller, and the photosensitive member is not exposed. The surface potential of the drum was measured for a predetermined time. The difference between the maximum value and the minimum value of the surface potential measured during that time was defined as charging potential unevenness | ΔV |.
As image patterns in image formation, three types of patterns, a 2-dot line pattern, a 2-dot × 2-dot halftone pattern, and a white pattern were used in all experiments.

(Experimental example 1)
As the charging device, a charging device described next of the type shown in FIG. 2 was adopted to measure the surface potential of the photosensitive drum and form an image.
The charging brush roller in the charging device has a configuration in which a brush in which brush hairs (brush fibers) are planted on a base fabric is wound around a 6 mm diameter stainless steel shaft. As the brush fiber, nylon in which conductive carbon is dispersed was used. The thickness of one brush fiber was 2.2 denier, the flocking density was 465 fibers / mm ² , the volume resistivity of the brush fiber was 1.7 × 10 ³ Ω · cm, and the outer diameter of the brush roller was 15 mm.
The charging brush rollers employed in Experimental Examples 2 to 4 and Comparative Experimental Examples 1 and 2 are the same.

The particle recovery brush has the same basic configuration as the charging brush roller, the brush fiber thickness is 6 denier, the flocking density is 90 / mm ² , and the brush fiber volume resistivity is 6.8 ×. 10 ⁴ Ω · cm and a brush outer diameter of 15 mm were used. The particle recovery brush is brought into contact with the surface of the photosensitive drum, and the circumferential speed ratio is 2 with respect to the photosensitive drum so that the contact portions move in the same direction as the rotation direction of the photosensitive drum, and thus the contact portions of the two move in opposite directions. Rotated.

As the charging auxiliary particles, conductive zinc oxide particles having a particle size of 0.05 μm and a volume resistivity of 100 Ω · cm were employed. The printer setting conditions were as follows.
-Photosensitive drum outer diameter: 30 mm
・ Rotation direction of charging brush roller: Rotating at a peripheral speed ratio of 2 in the same direction as the photosensitive drum (each contact portion moves in the opposite direction to each other) ・ Photosensitive drum for charging brush roller and collecting brush Pushing amount to 0.5mm
・ Development method: One-component non-contact development (reversal development with negatively chargeable toner)
-System speed: 160 mm / sec.

(Experimental example 2)
The surface potential of the photosensitive drum was measured under the same conditions as in Experimental Example 1 except that multi-walled carbon nanotubes having a length of 50 μm and a volume resistivity of 0.05 Ω · cm were used as charging auxiliary particles, and an image was formed.

(Experimental example 3)
An image was formed by measuring the surface potential of the photosensitive drum under the same conditions as in Experimental Example 1 except that the charging device of the type shown in FIG. 3 was used as the charging device.
In this charging device, an insulating roller made of polyurethane having a volume resistivity of 10 ¹⁵ Ω · cm and an outer diameter of 12 mm was used as a charging auxiliary particle collection roller. The particle recovery roller was brought into contact with the surface of the photosensitive drum and rotated at a peripheral speed ratio of 2 in the same direction as the rotation direction of the photosensitive drum.

(Experimental example 4)
An image was formed by measuring the surface potential of the photosensitive drum under the same conditions as in Experimental Example 1 except that a charging device of the type shown in FIG. 4 was used as the charging device.
The brush part of the fixed brush for particle recovery in this charging device has the same configuration as the brush part of the brush for particle recovery in Experimental Example 1.
At the time of collection of the charging auxiliary particles, the collection brush was set in a float state. Further, when the particles accumulated on the brush were supplied again to the contact charging unit, the collection brush was grounded while charging the photosensitive drum with the charging brush roller.

  Since the conductive zinc oxide used in this experimental example is positively charged by friction with the photosensitive drum, the particles are easily transferred to the photosensitive drum by grounding the particle recovery brush. The particles that have moved onto the photosensitive drum move to the contact charging unit as the photosensitive drum rotates, and are re-supplied.

(Comparative Experimental Examples 1 and 2)
For comparison, a charging device in which the particle recovery blade 221 is removed from the charging device shown in FIG. 1 (in the case of Comparative Experimental Example 1), a particle recovery brush 241, a mesh plate 23 ′, and a scattering prevention member from the charging device shown in FIG. The surface potential of the photosensitive drum was measured under the same conditions as in Experimental Example 1 except that the charging device (in the case of Comparative Experimental Example 2) from which 242 was removed was used to form an image.

(Chargeability evaluation)
Regarding the charging property of the photosensitive drum, as described above, the difference between the maximum value and the minimum value of the surface potential of the photosensitive member when the photosensitive drum is charged by applying a DC bias of −600 V to the brush roller for charging the photosensitive member. The charging potential unevenness | ΔV | defined in (1) was measured and evaluated according to the following criteria. The evaluation is based on unevenness of the charged potential on the surface of the photosensitive drum at the start of use of a new charging brush roller, and a photosensitive member after printing 5000 images of a B / W ratio 5% chart on an A4 size longitudinal recording sheet. The measurement was performed by measuring the uneven charging potential on the drum surface.
◎ (very good): | ΔV | <20V
○ (Good): 20V ≦ | ΔV | <50V
× (defect): 50V ≦ | ΔV |

(Image quality evaluation)
The line pattern was checked for the presence or absence of image flow, the halftone pattern was checked for the presence or absence of image unevenness due to exposure, and the white pattern was checked for the presence or absence of particle transfer or dot discharge by visual observation.
A: Almost no
○: Some are recognized, but there is no practical problem.
X: Image quality is significantly deteriorated and there is a problem in practical use.

  The evaluation results are shown in the following table. As can be seen from the following table, in the comparative experimental examples (comparative examples) 1 and 2, since the particle recycling mechanism was not provided, the charging ability was lowered due to the low particle retention property, and the particles on the photosensitive drum during image formation. There was a decrease in image quality due to the presence of. In the experimental example employing the particle recycling mechanism, neither charging ability nor image quality was observed.

  The present invention can be used to provide a good image over a long period of time.

1 is a diagram illustrating a schematic configuration of an example of an image forming apparatus according to the present invention. It is a figure which shows the other example of a charging device. It is a figure which shows the further another example of a charging device. It is a figure which shows schematic structure of the example of an image forming apparatus provided with the further another example of the charging device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 2A Charging device 21 Charging mechanism 211 Brush roller 212 Brush 213 Conductive support 22 Particle recycling mechanism 221 Particle recovery elastic blade 23A Charging device case 3 Image exposure device 4 Developing device 41 Developing roller 5 Transfer device 51 Transfer roller 6 Fixing device 10 Charge assisting particle S Transfer paper CA Cartridge case 2B Charging device 23B Charging device case 23 'Mesh plate 24 Particle recycling mechanism 241 Particle recovery brush 242 Particle scattering prevention member 2C Charging device 23C Charging device case 25 Particle recycling mechanism 251 Particles Recovery roller 252 Particle scattering prevention member 2D Charging device 23D Charging device case 26 Particle recycling mechanism 261 Particle recovery fixed brush 262 Potential control device

Claims (10)

A charging device having a charging member in contact with a member to be charged, and charging the member to be charged by interposing particles between the member to be charged and the member to be charged, the charging member and the member to be charged The particles adhering to the object to be charged are collected downstream from the contact portion with the surface movement direction of the object to be charged, and the collected particles are supplied again between the charging member and the object to be charged. A charging device comprising a recycling mechanism for the purpose. The charging device according to claim 1, wherein the particles are conductive particles having a particle diameter of 0.01 μm to 100 μm. The charging device according to claim 1, wherein the recycling mechanism includes a particle recovery member provided in contact with or in proximity to the member to be charged, and a particle recovery voltage is applied to the particle recovery member. A process device comprising at least an image carrier and a charging device for charging the image carrier in a case, the process device being detachable from the main body of the image forming apparatus, wherein the charging device contacts the image carrier And a process device for charging the image carrier by interposing particles between the charging member and the image carrier, and a contact portion between the charging member and the image carrier. A recycling mechanism is provided for recovering the particles attached to the image carrier downstream in the surface movement direction of the image carrier and re-supplying the recovered particles between the charging member and the image carrier. A process device characterized by that. A toner image is obtained through at least charging of the image carrier, image exposure on the charged image carrier, development of an electrostatic latent image formed by image exposure, and transfer of a toner image obtained by development to a transfer target. A process apparatus for use in an image forming process to be formed, wherein the recycling mechanism is disposed between a charging area for charging the image carrier and a transfer area for transferring the toner image. The process apparatus according to claim 4, which is provided in the apparatus. A process device for use in an image forming process for forming a toner image through at least charging of the image carrier, image exposure on the charged image carrier and development of an electrostatic latent image formed by image exposure. 5. The process apparatus according to claim 4, wherein the recycling mechanism is provided in the case so as to be disposed between a charging region for charging the image carrier and an image exposure region for the image carrier. A detachable image forming apparatus as the process apparatus according to claim 4, 5 or 6. A charging device including at least an image carrier and a charging member in contact with the image carrier, and charging the image carrier by interposing particles between the charging member and the image carrier; A latent image forming means for forming an electrostatic latent image on the image carrier, a developing device for developing the electrostatic latent image formed on the image carrier, the charging member, and the image carrier. A recycling mechanism for collecting the particles adhering to the image carrier downstream from the contact portion in the surface movement direction of the image carrier and re-supplying the particles between the charging member and the image carrier; An image forming apparatus. The image forming apparatus according to claim 8, wherein the recycling mechanism is disposed between a charging region for charging the image carrier and an image exposure region for the image carrier. The image forming apparatus further includes a transfer device for transferring a toner image formed by the developing device from the image carrier to a transfer target, and the recycling mechanism transfers the toner image from a charging region that charges the image carrier. The image forming apparatus according to claim 8, wherein the image forming apparatus is disposed between the transfer areas.