JP2019159108A - Electrifying device, process cartridge, and image forming apparatus - Google Patents

Abstract

To provide an electrifying device capable of suppressing the surface of a contact type electrifying member from being contaminated without increasing the size and to provide a process cartridge and an image forming apparatus.SOLUTION: The electrifying device includes an image carrier, an electrifying member which comes into contact with the image carrier and electrifies the image carrier, while being rotated, and a cleaning member which comes into contact with the surface of the electrifying member with predetermined contact pressure. The cleaning member includes magnetic field generation means for holding a magnetic developer in a rubbing part for rubbing the surface of the electrifying member. In the rubbing part, the magnetic developer and paper powder are electrified to have the same polarity as that of the surface of the image carrier and the magnetic developer and the paper powder having the same polarity are returned to the image carrier by a potential difference between the electrifying member and the image carrier.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus that forms an image by an electrophotographic process, and more particularly to a contact charging type charging device that charges the surface of an image carrier, a process cartridge, and an image forming apparatus.

As a charging device in an image forming apparatus such as a printer or a copying machine having an electrophotographic process, a contact charging method using a charging roller (charging member) is adopted because it is small and hardly generates ozone. One of the main problems of such a contact charging type charging roller is the problem of surface contamination. Since the charging roller is in contact with the image carrier, the surface is easily contaminated with the developer and external additives contained in the developer. As a result, a phenomenon such as black spots or fogging on a white background occurs as a charging failure. Resulting in.
On the other hand, from the viewpoint of reducing waste, a cleanerless system (toner recycling system) has been proposed. In this method, in the transfer type image forming apparatus, a dedicated drum cleaner which is a surface cleaning means after the transfer process on the image carrier is abolished, and the residual developer on the image carrier after the transfer is developed. To remove from the image carrier by “development simultaneous cleaning”. That is, it is an electrophotographic process in which residual developer is collected and reused by a developing device. However, since there is no drum cleaner, not only the residual developer but also paper dust derived from paper as a transfer material reaches the surface of the charging roller and becomes a serious problem.
Therefore, various configurations have been proposed in which a cleaning member is provided on the surface of the charging roller in order to prevent the surface of the charging roller from being soiled. For example, Patent Document 1 arranges a brush roller made of fibers having a fiber diameter that also enters a recess on the surface of the charging roller. When the material of the brush roller is made of a material having a polarity opposite to that of the residual developer when frictionally charged with the charging roller, the residual developer is electrically captured and held.
In Patent Document 2, a magnetic developer is used, and a magnetizing member is disposed in contact with or close to an image carrier or a charging roller. There has been proposed a configuration in which the magnetized member holds the residual magnetic developer to prevent the residual developer from reattaching to the charging roller.

JP 2014-202866 A JP 10-177292 A

However, from the viewpoint of the long life of the image forming apparatus, the charging roller cleaning member is required to prevent the surface of the charging roller from being contaminated by more residue.
As in Patent Document 1, in the configuration that keeps the residue with the brush roller, a larger volume is required to hold the residue, resulting in an increase in the size of the apparatus. In order to avoid this, complicated control is inevitably required by applying a bias or the like to the brush roller so that the residue in the brush roller is discharged onto the surface of the image carrier and collected by a cleaning device or a developing device. . As a result, the cost increases and the downtime increases.
Further, in the configuration in which the residual developer is cleaned by the magnetized member as in Patent Document 2, it is necessary to hold more residual developer by the magnetized member. Problems such as an increase in the size and cost of the member and magnetic radiation occur. Furthermore, since it is not possible to hold paper powder that does not have magnetism, a charging failure of the charging roller pitch may occur.
An object of the present invention is to provide a charging device, a process cartridge, and an image forming apparatus that can suppress the occurrence of image defects such as charging defects by cleaning the surface of the charging roller with a configuration that does not increase in size or complicated control.

In order to achieve the above object, the present invention provides:
An image carrier;
A charging member that charges the image carrier while rotating in contact with the image carrier;
A charging member having a cleaning member that contacts the surface of the charging member at a predetermined contact pressure,
The cleaning member has a magnetic field generating means for holding a magnetic developer in a rubbing portion that rubs against the surface of the charging member,
In the rubbing portion, the magnetic developer and paper dust are charged to have the same polarity as the surface of the image carrier, and the magnetic developer and paper dust of the same polarity are charged to the charging member and the image carrier. And returning to the image carrier by a potential difference between the first and second image carriers.
In addition, the process cartridge of the present invention is configured to include at least the charging device described above.
An image forming apparatus according to the present invention includes an apparatus main body of the image forming apparatus and the process cartridge that is detachably held by the apparatus main body.
Another image forming apparatus according to the present invention forms a developer image by supplying a magnetic developer from a container while rotating with the charging device and the image carrier, and at the same time magnetic development on the image carrier. And a developing device for collecting the magnetic developer remaining on the image carrier after the agent has been transferred to the transfer material in the housing portion.

  According to the present invention, it is possible to suppress the occurrence of image defects such as defective charging by cleaning the surface of the charging roller with a configuration without increasing the size or complicated control.

1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment. FIG. 3 is a schematic cross-sectional view in the vicinity of the charging device according to the example. The schematic perspective view which shows the shape of the longitudinal direction of the charging device vicinity in an Example. FIG. 6 is a schematic cross-sectional view in the vicinity of a charging device in a comparative example.

Hereinafter, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings. The examples described below illustrate the present invention by way of example, and the dimensions, materials, shapes, relative arrangements, etc. of the components described below are not particularly specified unless otherwise specified. However, the scope of the present invention is not limited thereto.
[Entire configuration of image forming apparatus]
FIG. 1 shows an image forming apparatus 100 according to Embodiment 1 of the present invention.
First, the overall configuration of the image forming apparatus 100 will be described.
This image forming apparatus includes a charging device 2A including a photosensitive drum 1 as an image carrier and a charging roller 2 that is a contact charging member that uniformly charges the surface of the photosensitive drum 1, and a charged photosensitive member. An exposure device 3 that exposes image light to the surface of the body drum 1 to form an electrostatic latent image. Further, the developing device 4 that develops the electrostatic latent image formed by the exposure device 3 as a toner image with the magnetic toner t that is a magnetic developer, and the toner image formed on the photosensitive drum 1 on the sheet material S. And a transfer roller 5 as a transfer member to be transferred.
Further, below the developing device 4, the sheet material cassette 70 that stores the sheet material S and the sheet material S stored in the sheet material cassette 70 are directed to the transfer roller 5 and the transfer nip portion b of the photosensitive drum 1. A feeding roller 71 that feeds the paper is provided.
Further, a fixing device 7 for heating and fixing the unfixed toner image transferred onto the sheet material S is provided on the downstream side of the transfer nip b, in the illustrated example, above the photosensitive drum 1 and the charging device 2A. It has been. A paper discharge unit 8 that receives the sheet material S discharged from the fixing device 7 is provided on the upper surface of the apparatus.

Next, an image forming process in the image forming apparatus will be described.
When an image information signal from a personal computer (not shown) is received by a CPU (not shown) of the image forming apparatus, a sheet material S as a recording material is fed by a feeding roller 71 from a sheet material cassette 70 mounted at the lower part of the apparatus. To feed. In synchronization with the feeding of the sheet material S, the photosensitive drum 1 serving as an image carrier starts to rotate.
[Description of image forming process]
The photosensitive drum 1 in this embodiment is, for example, a negative OPC photosensitive member having a diameter of 24 mm. The photosensitive drum 1 is driven to rotate in the direction of arrow A at a constant speed of 100 mm / sec (= process speed PS, printing speed).
Then, a predetermined charging bias is applied to a charging roller 2 as a charging member from a charging power source (not shown) to uniformly charge the surface of the photosensitive drum 1. The charging roller 2 is, for example, a conductive elastic roller having a diameter of 10 mm, and includes a core metal 2a and a conductive elastic layer 2b as shown in FIG. The diameter of the cored bar 2a is set to about φ6 mm, for example.
In this embodiment, a DC voltage is applied from the charging power source to the cored bar 2a. The DC voltage to be applied is set to a value such that the potential difference between the surface of the photosensitive drum 1 and the charging roller 2 is equal to or higher than the discharge start voltage. Specifically, a DC voltage of -1300 V is applied as the charging bias. At this time, the surface of the photosensitive drum 1 is contact-charged uniformly at a charging potential (dark portion potential) of −700V.
The charging roller 2 is energized with a predetermined pressure F (3 to 9 N), and is pressed against the photosensitive drum 1 with this pressure to form a charging region (c in the figure) having a predetermined width in the rotation direction. Yes. In this embodiment, the charging roller 2 rotates in the opposite direction (arrow B direction) to the rotation of the photosensitive drum 1 (arrow A direction). In the illustrated example, it is described that the photosensitive drum 1 rotates in the clockwise direction and the charging roller 2 rotates in the counterclockwise direction.
The exposure apparatus 3 is constituted by a laser beam scanner including a laser diode, a polygon mirror, and the like. The exposure apparatus 3 outputs a laser beam L whose intensity is modulated in accordance with a time-series electric digital pixel signal of target image information, and is uniformly charged at the exposure position d of the photosensitive drum 1 with the laser beam L. Scan exposure of the surface. When the uniformly charged surface of the photosensitive drum 1 is exposed entirely with the laser beam L, the laser power is adjusted so that the potential of the photosensitive drum 1 surface becomes −150V. When the exposure device 3 exposes the photosensitive drum 1, an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 1.

In the present embodiment, the developing device 4 uses, as a magnetic developer, a negative-polarity one-component magnetic toner t having styrene acrylic as a main binder. The developing device 4 is provided with a developing sleeve 13 and a developing blade 14 which are developer carriers. The developing sleeve 13 is formed of a rubber layer having a thickness of 1 mm on an aluminum base tube having an outer diameter of 12 mm and an inner diameter of 9 mm, and is driven to rotate in the direction of arrow C. The magnetic toner t is attracted to the developing sleeve 13 by the magnetic force of the magnet 12 that is a magnetic field generating means contained in the developing sleeve 13. The magnetic toner t has a certain negative triboelectric charge while being regulated to a predetermined layer thickness by the developing blade 14. Thereafter, an electrostatic latent image on the photosensitive drum 1 is visualized in the developing region a by a developing bias applied between the developing sleeve 13 and the photosensitive drum 1 from a developing bias application power source (not shown). . That is, the latent image on the photosensitive drum is developed by the developing sleeve 13, whereby a toner image (developer image) is formed on the photosensitive drum 1.
The transfer roller 5 is a medium-resistance member, and is pressed against the photosensitive drum 1 with a predetermined pressure to form a transfer nip portion b. The transfer roller 5 used in this embodiment has a configuration in which a medium resistance foam layer is formed on a core metal, has a roller resistance value of 5 × 10 ⁸ Ω, and is transferred by applying a voltage of +2.0 kV to the core metal. Is made. That is, the toner image is transferred from the photosensitive drum 1 to the sheet material S by the transfer roller 5 (transfer device, transfer member).
In this embodiment, the transfer roller 5 directly transfers the toner image from the photosensitive drum 1 to the sheet material S. However, instead of transferring directly, the toner image may be transferred from the photosensitive drum 1 to the intermediate transfer member at one end and indirectly transferred from the intermediate transfer member to the sheet material S. At this time, the intermediate transfer member is a transfer material onto which the toner image is transferred from the photosensitive drum 1.
The sheet material S on which the toner image is transferred through the transfer roller 5 is separated from the photosensitive drum 1 and conveyed to the fixing device 7. Then, the toner image is heated and fixed on the sheet material S, and is discharged to the paper discharge unit 8 as an image formed product (print copy).

<Cleanerless system>
Next, the cleanerless system in the present embodiment will be described in detail.
Most of the transfer residual toner and paper dust remaining on the photosensitive drum 1 after the transfer process is charged positively by the transfer bias in the transfer region (b in the figure). The transfer residual toner and paper dust are charged to a negative polarity like the photosensitive drum 1 by a discharge generated between the charging roller 2 and the photosensitive drum 1 in a charging region (c in the figure). At this time, the surface of the photosensitive drum 1 is charged to −700V. The transfer residual toner and paper dust charged to negative polarity pass through the charging portion without adhering to the charging roller 2 due to the potential difference (surface potential of the photosensitive drum 1 = −700 V, charging roller potential = −1300 V). become.
However, depending on the usage situation, if there is a large amount of transfer residual toner or paper powder, there may be a case where the negative polarity cannot be obtained, and a part of the toner adheres to the surface of the charging roller 2. Therefore, in the present invention, the cleaning member 20 that contacts the surface of the charging roller 2 and charges the negatively charged toner having the same polarity as the surface of the photosensitive drum 1 by rubbing the transfer residual toner or paper powder that has adhered thereto. Is arranged. The cleaning member 20 will be described in detail later.
The transfer residual toner that has passed through the charging unit reaches the laser irradiation position on the surface of the photosensitive drum 1 where the laser beam is irradiated from the exposure device 3. Since the transfer residual toner is not so large as to block the laser beam of the exposure device 3, it does not affect the process of forming an electrostatic image (latent image) on the photosensitive drum 1. Of the toner that has passed through the laser irradiation position, the toner in the non-exposed portion (the surface of the photosensitive drum 1 that has not been irradiated with the laser) is collected in the developing sleeve 31 by electrostatic force in the developing portion. Such toner is further collected in the housing portion of the developing device 4 via the developing sleeve 31.

On the other hand, of the toner that has passed through the laser irradiation position d, the toner in the exposed portion (the surface of the photosensitive drum 1 that has been irradiated with the laser) is not recovered electrostatically and remains on the photosensitive drum 1 as it is. Subsequently, it becomes part of forming a toner image. However, a part of the toner may be collected by a physical force due to a difference in peripheral speed between the developing sleeve 13 and the photosensitive drum 1. The toner remaining on the photosensitive drum 1 without being transferred in this manner is generally collected by the developing device 4 except for the toner in the exposed portion. The toner collected in the developing device 4 is mixed with the toner stored in the storage unit 15 of the developing device 4 and used again.
That is, the developing device 4 supplies the magnetic toner t from the storage unit 15 while being rotationally driven with the photosensitive drum 1 to form a developer image. At the same time, after the magnetic toner on the photosensitive drum 1 is transferred to the sheet material S as a transfer material, the magnetic toner remaining on the photosensitive drum 1 is collected in the storage unit 15.
In the present embodiment, the process cartridge P is detachable from the apparatus main body of the image forming apparatus 100. That is, the charging device 2A, the developing device 4 and the like, in which the photosensitive drum 1, the charging roller 2, and the cleaning member 20 are integrated, are detachable from the apparatus main body as a part of the process cartridge P. . The apparatus main body is a part obtained by removing the process cartridge P from the image forming apparatus 100.
The process cartridge P may be divided into a cartridge including the charging device 2A and a cartridge including the developing device 4, and may be configured to be detachable from the apparatus main body independently. In addition, the charging device 2 </ b> A may be directly assembled to the image forming apparatus 100 instead of the configuration built into the process cartridge P.

<Configuration of cleaning member and its effect>
Next, the cleaning member 20 in the present embodiment will be described in detail with reference to FIG.
The cleaning member 20 abuts on the surface of the charging roller 2 and is disposed so as to be charged by rubbing the transfer residual toner and paper powder adhering to the charging roller 2 and returning to the surface of the photosensitive drum 1. The cleaning member 20 includes a rubbing portion 21 and a flexible support portion 22, and has the same longitudinal dimension as the conductive elastic layer of the charging roller 2. The cleaning member 20 is fixed by being attached with a frame 200 and a double-sided tape or the like so as not to be wavy so as to support the opposite side of the support portion 22 that is rubbed against the charging roller 2. The cleaning member 20 has a contact pressure on the surface of the charging roller 2 of 1.0 g / cm ² so that the edge of the rubbing portion 21 does not contact the surface of the charging roller 2 in the forward direction with respect to the rotation direction B of the charging roller ^2. The contact is made in the range of ˜200 g / cm ² . The contact portion between the charging roller 2 and the cleaning member 20 is arranged so that there is no gap in the longitudinal direction.
As shown in FIG. 3, the rubbing portion 21 has a sheet shape with a predetermined thickness, as a magnetic field generating means, mainly composed of ferrite, and multipolar magnetization with N poles and S poles in a longitudinal direction on only one side at a pitch of about 2 mm. A single-sided multi-pole magnetized magnet sheet is used. The magnetized surface is installed so as to be in contact with the charging roller 2.
The surface magnetic flux density is measured by connecting a magnetic probe with a magnetic sensor embedded at the tip to a teslamator, placing the magnetic probe perpendicular to the measurement object, and setting the height to a predetermined position. Thereby, the magnetic strength applied perpendicularly to the magnetic sensor surface is detected. In this example, the magnetic toner was measured at a height of 1 mm from the surface of the magnet sheet so that at least one layer could be held in the rubbing portion 21 and set to 5 mT or more. The term “at least one layer” means that it is not scraped off, and it is sufficient that at least one layer can be held, and two or more layers may be used.
In addition to single-sided multipole magnetization, there are double-sided multipole magnetization in which NS is alternately poled on the front and back, and double-sided magnetization in which N-pole and S-pole are applied on both sides. It is only necessary that the magnetic toner can be held in the portion 21 in the longitudinal direction. Thus, frictional charging between the surface of the charging roller 2 and the magnetic roller can be performed while the magnetic toner is held on the surface of the rubbing portion 21 without scraping off transfer residual toner or the like adhering to the charging roller 2 at the rubbing portion 21. it can.
Further, in this embodiment, the rubbing portion 21 of the cleaning member 20 is configured by a sheet-shaped magnet sheet, but may be a roller shape.

The effects of this embodiment will be described below.
In this embodiment, since magnetic toner is used, the rubbing portion 21 having a magnetic field can hold a certain amount of transfer residual toner attached to the charging roller 2 on the surface of the rubbing portion 21 by magnetic force. On the other hand, foreign matters such as paper dust are hardly held by the rubbing portion 21 because they have little magnetism. For this reason, the magnetic toner held on the rubbing portion 21 becomes a lubricant between the surface of the charging roller 2 and the rubbing portion 21, and foreign matters such as paper powder are likely to slip through the rubbing portion 21. Further, there is a peripheral speed difference between the surface of the charging roller 2 and the rubbing portion 21. For this reason, the toner held on the rubbing portion 21 is rubbed with the surface of the charging roller 2 or the rubbing portion 21 and is discharged from the charging roller 2, so that foreign matters such as toner and paper dust are negatively charged. The toner that tends to be negative in triboelectric chargeability is charged negatively. When the rubbing portion 21 holds a certain amount of magnetic toner, the toner layer becomes thick and the magnetic force decreases. Therefore, foreign matters such as negatively charged toner and paper powder that can no longer be held by magnetic force adhere to the surface of the charging roller 2 by the electrostatic adhesion force to the surface of the charging roller 2 and are conveyed to the charging unit. Thereafter, foreign matters such as negative toner and paper dust adhering to the surface of the charging roller 2 return to the surface of the photosensitive drum 1 due to a potential difference in the charging unit and are used for forming a toner image or collected by the developing device 4. Is done.

<About Comparative Example>
Next, a comparative example for comparing the effects of the present embodiment will be described.
In the comparative example, as shown in FIG. 4, the rubbing portion 21 of the cleaning member 24 does not have a magnetic field generating means. Specifically, a flexible polyimide sheet having a thickness of 25 μm is pasted in the same manner as in Example 1. Since the polyimide sheet makes the toner negative in terms of the charge train, the toner becomes negative by providing a peripheral speed difference between the surface of the charging roller 2 and the surface of the cleaning member 24. However, the rubbing portion 21 does not have a magnetic force.
Table 1 shows the results of confirming the effects and harmful effects of this example and the comparative example.
This is a result of performing a printing operation at a printing rate of 4% and confirming the presence or absence of HT unevenness due to charging failure at the time of a predetermined number of prints and streaks due to paper powder being caught. In each item, ◯ indicates that there is no image defect, Δ indicates that there is an image defect but there is no problem in actual use, and × indicates that there is an image defect.

As shown in Table 1, in the examples, it was confirmed that there was no generation of HT unevenness due to charging failure and no streaks due to the inclusion of foreign matter, and it could be used. On the other hand, with respect to paper dust, in Comparative Example 1, the transfer residual toner adhering to the surface of the charging roller 2 is made negative by rubbing and the surface of the charging roller 2 is returned from the charging roller 2 to the surface of the photosensitive drum 1. Dirt was able to be prevented. However, streaks due to uneven soiling due to paper dust sandwiched in the early stage occurred.
As a modification of the present embodiment, even if a member that makes the toner negative polarity, for example, a polyimide sheet, is interposed between the surface of the charging roller 2 and the magnet sheet as the rubbing portion 21, the effect is further exhibited.

1 Photosensitive drum (image carrier)
2 Charging roller (charging member)
4 Developing device 13 Developing sleeve 15 Housing portion 20 Cleaning member 21 Rub portion (magnetic force generating means)
22 Support unit 100 Image forming apparatus t Magnetic toner (magnetic developer)
P Process cartridge

Claims (11)

An image carrier;
A charging member that charges the image carrier while rotating in contact with the image carrier;
A charging member having a cleaning member that contacts the surface of the charging member at a predetermined contact pressure,
The cleaning member has a magnetic field generating means for holding a magnetic developer in a rubbing portion that rubs against the surface of the charging member,
In the rubbing portion, the magnetic developer and paper dust are charged to have the same polarity as the surface of the image carrier, and the magnetic developer and paper dust of the same polarity are charged to the charging member and the image carrier. The charging device is returned to the image carrier by a potential difference between the charging device and the image carrier.   2. The charging device according to claim 1, wherein the magnetic field generation unit is set to a magnetic flux density capable of holding at least one layer of the magnetic developer in the rubbing portion.   The charging device according to claim 2, wherein the magnetic flux density is measured at a height of 1 mm from the cleaning member and is set to 5 mT or more. The charging device according to any one of claims 1 to 3 contact pressure to the surface of the charging member of the cleaning member is set in the range of ^{1.0g / cm 2 ~200g / cm 2} .   5. The charging according to claim 1, wherein the cleaning member has a sheet shape, and is disposed by being fixed to a frame body on a side opposite to a rubbing portion with the charging member. apparatus.   The charging device according to claim 5, wherein the cleaning member is installed such that a magnetized surface is in contact with the charging member.   The charging device according to claim 1, wherein the cleaning member has a roller shape.   A process cartridge comprising at least the charging device according to claim 1.   The magnetic developer is supplied from a container while being rotated with the image carrier to form a developer image. At the same time, the magnetic developer on the image carrier is transferred to a transfer material, and then the image carrier is used. The process cartridge according to claim 8, wherein the process cartridge is integrated with a developing device for collecting the magnetic developer remaining on the body in the container.   An image forming apparatus comprising: an apparatus main body of the image forming apparatus; and the process cartridge according to claim 8, which is detachably held by the apparatus main body. The charging device according to any one of claims 1 to 7,
The magnetic developer is supplied from a container while being rotated with the image carrier to form a developer image. At the same time, the magnetic developer on the image carrier is transferred to a transfer material, and then the image carrier is used. An image forming apparatus comprising: a developing device for collecting the magnetic developer remaining on the body in the housing unit.

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