Image forming device

Abstract

To suppress an occurrence of image defect due to deposits accumulated on a brush in an image forming device having the brush in contact with a photoconductive drum.SOLUTION: An image forming device includes: an image carrier; charging means for charging a surface of the image carrier; developing means for supplying developer to the surface of the image carrier charged by the charging means so as to form a developer image; transfer means for transferring the developer image from the image carrier to a transfer object body; and a brush coming into contact with the image carrier on a downstream side of a transfer part in a rotating direction of the image carrier and on an upstream side of a charging part. After the developer image is transferred to the transfer object part, the developer remaining on the surface of the image carrier is recovered by the developing means. In a section perpendicular to a rotation axis of the image carrier, the brush is so disposed that a contact area in contact with the brush on the surface of the image carrier overlaps with a virtual line including the rotation axis of the image carrier and extending vertically upward from the rotation axis.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] Electrophotography is a well-known image recording method used in image forming devices such as printers and copiers. Electrophotography uses an electrophotographic process to form an electrostatic latent image on a photosensitive drum using a laser beam, and then develops the electrostatic latent image with a charged colorant (hereinafter referred to as toner) to form a toner image. The toner image is then transferred to a recording material and fixed thereon, forming an image on the recording material. In recent years, cleanerless systems have been proposed to reduce the size of image forming devices. The cleanerless system uses a developing unit to remove, collect, and reuse toner remaining on the photosensitive drum after the transfer process (residual toner). Because the cleanerless system does not have a cleaning unit that contacts the photosensitive drum, paper dust adhering to the photosensitive drum during the transfer process to the recording material can cause image defects. Patent Document 1 therefore proposes a configuration in which a brush is located downstream of the transfer unit and upstream of the charging unit in the rotational direction of the photosensitive drum to collect paper dust adhering to the photosensitive drum during the transfer process. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-271030 Summary of the Invention [Problem to be solved by the invention]

[0004] However, Patent Document 1 had the following problem: In a configuration in which a brush contacts a photosensitive drum, fine paper dust accumulates on the brush as paper passes through and forms clumps. The clumps of paper dust then pass downstream of the brush and interfere with charging the surface of the photosensitive drum during the charging process, which can result in image defects such as black dots.

[0005] SUMMARY OF THE INVENTION An object of the present invention is to prevent image defects from occurring due to deposits accumulated on a brush in an image forming apparatus having a brush that contacts a photosensitive drum. [Means for solving the problem]

[0006] The image forming apparatus according to the present invention includes an image carrier that is driven to rotate, a charging unit that forms a charging portion facing the surface of the image carrier and charges the surface of the image carrier, a developing roller that supplies a developer to the surface of the image carrier charged by the charging unit and forms a developer image, a transfer roller that forms a transfer portion between the image carrier and the transfer roller and transfers the developer image from the image carrier to a transferee, and a transfer roller that contacts the surface of the image carrier downstream of the transfer portion and upstream of the charging portion in the rotation direction of the image carrier. , and is disposed fixedly relative to the image carrier. A brush and a pre-exposure unit that exposes the image carrier to light downstream of the brush and upstream of the charging unit in the rotation direction of the image carrier; and after the developer image is transferred to the transfer target body, developer remaining on the surface of the image carrier is collected by the developing roller. In this image forming apparatus, the brush is composed of a thread portion that contacts the image carrier, a first support portion that supports the thread portion, and a second support portion that supports the first support portion and extends in the direction of the rotation axis of the image carrier, and the brush is arranged so that, in a cross section perpendicular to the rotation axis of the image carrier, a contact area that contacts the thread portion on the surface of the image carrier overlaps with an imaginary line that includes the rotation axis of the image carrier and extends vertically upward from the rotation axis. If the point where the virtual line intersects with the contact area is defined as an intersection point, the distance from the intersection point to the charging unit measured along the surface of the image carrier in the rotation direction of the image carrier is The distance is shorter than the intersection point, and the pre-exposure means exposes the surface of the image carrier downstream of the downstream end of the contact area and upstream of the charging section in the rotation direction of the image carrier. It is characterized by the following. [Effects of the Invention]

[0007] According to the present invention, in an image forming apparatus having a brush that contacts a photosensitive drum, it is possible to prevent image defects from occurring due to deposits accumulated on the brush. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is an explanatory diagram of an image forming apparatus according to a first embodiment. [Figure 2] FIG. 2 is a control block diagram according to the first embodiment. [Figure 3] FIG. 2 is a schematic diagram of a brush in Example 1. [Figure 4] FIG. 1 is a cross-sectional view illustrating conventional forms 1 and 2. [Figure 5] FIG. 1 is a cross-sectional view illustrating a first embodiment. [Figure 6] 1A and 1B are cross-sectional views illustrating problems of conventional forms 1 and 2. [Figure 7] FIG. 10 is a cross-sectional view illustrating a second embodiment. [Figure 8] FIG. 10 is a cross-sectional view illustrating Example 3. [Figure 9] FIG. 10 is a cross-sectional view illustrating Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0009] The following describes in detail exemplary embodiments of the present invention with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the embodiments may be changed as appropriate depending on the configuration of the device to which the invention is applied and various conditions. In other words, the scope of the present invention is not intended to be limited to the following embodiments. Furthermore, terms indicating geometric shapes or relationships, such as parallel, perpendicular, center, straight line, and circle, are not limited to their mathematically strict meaning unless otherwise specified, but are interpreted as including a range allowed by manufacturing tolerances, etc.

[0010] Example 1 1. Image forming device 1 shows a schematic configuration of one embodiment of an image forming apparatus 100 according to the present invention. The image forming apparatus 100 of Example 1 is a monochrome laser beam printer that employs a cleanerless system and a contact charging system. Because it is a cleanerless system, after the developer is transferred to a transfer target such as a recording material, the developer remaining on the surface of the image carrier is collected by a developing means.

[0011] The image forming apparatus 100 is provided with a photosensitive drum 1, which is a cylindrical photosensitive body serving as an image carrier. A charging roller 2 serving as a charging means and a developing device 3 serving as a developing means are provided around the photosensitive drum 1. In addition, an exposure device 4 serving as an exposure means is provided downstream of the charging roller 2 and upstream of the developing device 3 in the rotation direction of the photosensitive drum 1 in FIG. 1. A transfer roller 5 serving as a transfer means is pressed against the photosensitive drum 1.

[0012] The photosensitive drum 1 is a negatively charged organic photosensitive member. This photosensitive drum 1 has a photosensitive layer on a drum-shaped aluminum substrate. The photosensitive drum 1 is driven to rotate at a predetermined process speed in the direction indicated by the arrow in FIG. 1 (clockwise when viewed parallel to the rotation axis of the photosensitive drum 1) by a drive motor 110 (see FIG. 2) serving as a driving means. The process speed is represented by the peripheral speed (surface movement speed) of the photosensitive drum 1. In Example 1, the process speed is set to 140 mm / sec, and the outer diameter of the photosensitive drum 1 is set to 24 mm.

[0013] The charging roller 2 faces the surface of the photosensitive drum 1 and contacts it with a predetermined pressure to form a charging portion. In addition, a predetermined charging voltage (charging bias) is applied to the charging roller 2 by a charging power source E1 (see FIG. 2) serving as a charging voltage application means. The surface of the photosensitive drum 1 is uniformly charged to a predetermined potential by the charging roller 2. In Example 1, a negative DC voltage is applied to the charging roller 2 as the charging voltage, and the surface of the photosensitive drum 1 is uniformly charged to a negative dark potential Vd by the charging roller 2. In Example 1, the charging voltage is −1300 V, and the dark potential Vd is −700 V. The surface of the photosensitive drum 1 is charged by discharge generated in at least one of minute gaps between the photosensitive drum 1 and the charging roller 2, which are formed upstream and downstream in the rotation direction of the photosensitive drum 1 from the contact portion between the photosensitive drum 1 and the charging roller 2. The contact portion between the charging roller 2 and the photosensitive drum 1 is called the charging portion.

[0014] The exposure device 4 is a laser scanner device that outputs laser light L corresponding to image information input from an external device such as a host computer, and scans and exposes the surface of the photosensitive drum 1, which is uniformly charged to a dark area potential Vd. The potential of the photosensitive drum 1 at the exposed area changes to a light area potential Vl. This exposure forms an electrostatic latent image (electrostatic image) corresponding to the image information on the surface of the photosensitive drum 1. In the first embodiment, the light area potential Vl is -100 V. The position on the photosensitive drum 1 that is exposed by the exposure device 4 is referred to as the exposure area. Note that the exposure device 4 is not limited to a laser scanner device, and for example, an LED array having a plurality of LEDs arranged along the longitudinal direction of the photosensitive drum 1 (the direction parallel to the rotation axis) can also be used.

[0015] The image forming apparatus 100 employs a contact development system. The developing device 3 includes a developing roller 31 as a developer carrier, a toner supply roller 32 as a developer supply means, a developer storage chamber 33 that stores toner, and a developing blade 34. The toner supplied from the developer storage chamber 33 to the developing roller 31 by the toner supply roller 32 is charged to a predetermined polarity by passing through a blade nip, which is the contact point between the developing roller 31 and the developing blade 34. The developing roller 31 performs development by coming into contact with the photosensitive drum 1. The contact point between the developing roller 31 and the photosensitive drum 1 is called the developing unit. The toner carried on the developing roller 31 moves from the developing roller 31 to the photosensitive drum 1 in accordance with the electrostatic image in the developing unit. Here, the developing roller 31 is driven to rotate in a counterclockwise direction (counterclockwise when viewed in a direction parallel to the rotation axis of the photosensitive drum 1) so that the photosensitive drum 1 and the developing roller 31 move forward in the developing unit. The drive motor 110 that drives the photosensitive drum 1 may also provide a driving force to the developing roller 31, or a drive motor separate from the drive motor 110 that drives the photosensitive drum 1 may provide a driving force to the developing roller 31. During development, a predetermined developing voltage (developing bias) is applied to the developing roller 31 by a developing power supply E2 (see FIG. 2) that serves as a developing voltage application means. In the first embodiment, the developing voltage is a negative DC voltage of −400 V. Toner charged with the same polarity as the charging polarity of the photosensitive drum 1 (negative in the first embodiment) adheres to the area of ​​the photosensitive drum 1 where the light area potential Vl is formed. This development method is called a reversal development method. In addition to the one-component non-magnetic contact development method of the first embodiment, other development methods such as two-component non-magnetic contact development, non-contact development, and magnetic development may also be used. The two-component non-magnetic contact development method uses a two-component developer containing non-magnetic toner and magnetic carrier as the developer, and develops by bringing the developer (magnetic brush) carried on a developer carrier into contact with the photosensitive drum 1. The non-contact development method develops by scattering toner onto the photosensitive drum from a developer carrier arranged opposite the photosensitive drum but in a non-contact manner. The magnetic development method develops by magnetically carrying magnetic toner on a developer carrier that incorporates a magnet as a magnetic field generating means and is arranged opposite the photosensitive drum but in contact or in a non-contact manner.In Example 1, toner having a median average particle size of 6 μm and a normal polarity of negative polarity is used.

[0016] The transfer roller 5 is preferably made of an elastic material such as polyurethane rubber or sponge rubber made of EPDM (ethylene propylene diene rubber), NBR (nitrile butadiene rubber), etc. The transfer roller 5 is pressed against the photosensitive drum 1, forming a transfer portion where the photosensitive drum 1 and the transfer roller 5 are in pressure contact. During transfer, the transfer roller 5 A predetermined transfer voltage (transfer bias) is applied to the transfer roller 5 by a transfer power supply E3 (FIG. 2) serving as a transfer voltage application means. In the first embodiment, a DC voltage of a polarity opposite to the normal polarity of the toner (positive polarity in the first embodiment) is applied to the transfer roller 5 as a transfer voltage during transfer. In the first embodiment, the transfer voltage is set to +1000 V. Then, the developer image is electrostatically transferred from the photosensitive drum 1 to the recording material S by the action of an electric field formed between the transfer roller 5 and the photosensitive drum 1.

[0017] A recording material S stored in a cassette 6 is fed by a paper feed unit 7 in synchronization with the timing at which the toner image formed on the photosensitive drum 1 reaches the transfer section, and is conveyed to the transfer section via a pair of registration rollers 8. The toner image formed on the photosensitive drum 1 is transferred onto the recording material S by a transfer roller 5 to which a predetermined transfer voltage is applied by a transfer power source E3.

[0018] After the toner image has been transferred, the recording material S is conveyed to a fixing device 9. The fixing device 9 is a film heating type fixing device that includes a fixing film 91 incorporating a fixing heater (not shown) and a thermistor (not shown) that measures the temperature of the fixing heater, and a pressure roller 92 that presses against the fixing film 91. The recording material S, on which the toner image has been fixed by being heated and pressed by the fixing device 9, passes through a pair of paper discharge rollers 12 and is discharged outside the apparatus.

[0019] Residual toner remaining on the photosensitive drum 1 without being transferred to the recording material S is removed in the following process. Residual toner is a mixture of positively charged toner and negatively charged toner that does not have a sufficient charge. The residual toner is negatively charged by discharge from the charging roller 2 in the charging section. The negatively charged residual toner by the charging roller 2 reaches the developing section as the photosensitive drum 1 rotates. The electrostatic latent image formed on the surface of the photosensitive drum 1 has image areas that have a light potential and non-image areas that have a dark potential. The behavior of residual toner that has reached the developing section will be explained separately for the image and non-image areas of the photosensitive drum 1.

[0020] In the image area of ​​the photosensitive drum 1, the surface of the photosensitive drum 1 is at a light area potential, which is higher than the potential of the developing roller 31, and therefore the negatively charged particles are subjected to a force from the developing roller 31 toward the photosensitive drum 1. Therefore, the negatively charged residual toner adhering to the image area of ​​the photosensitive drum 1 is not transferred from the photosensitive drum 1 to the developing roller 31 in the developing section, but moves to the transfer section together with the toner transferred from the developing roller 31, and is transferred to the recording material S for image formation.

[0021] On the other hand, in the non-image areas of the photosensitive drum 1, the surface of the photosensitive drum 1 is at a dark potential, which is lower than the potential of the developing roller 31 (the absolute value is large because of the negative polarity), and therefore the negatively charged particles are subjected to a force from the photosensitive drum 1 toward the developing roller 31. Therefore, the negatively charged residual toner adhering to the non-image areas of the photosensitive drum 1 is transferred from the photosensitive drum 1 to the developing roller 31 in the developing section and is collected in the developer storage chamber 33. The residual toner collected in the developer storage chamber 33 is used again for image formation.

[0022] Image forming apparatus 100 has a control unit 150 that controls the operation of the various functional units described above. Control unit 150 has a CPU 151 and memory 152. Memory 152 includes a volatile memory that temporarily stores information and a non-volatile memory that retains information for a long period of time. Memory 152 stores image information acquired from an external device and programs that define methods for controlling the operation of the various functional units. CPU 151 inputs and outputs information to and from memory 152, acquires and processes image information, and executes programs to control the operation of image forming apparatus 100.

[0023] 2. Brush configuration The image forming apparatus 100 has a brush 10 that contacts the surface of the photosensitive drum 1. In the first embodiment, the brush 10 collects paper dust adhering to the surface of the photosensitive drum 1. The brush 10 contacts the surface of the photosensitive drum 1 downstream of the transfer unit and upstream of the charging unit in the rotation direction of the drum 1 to form a contact portion. The area on the surface of the photosensitive drum 1 that is in contact with the brush 10 is called the contact area. The upstream end of the contact area in the rotation direction of the photosensitive drum 1 is called the upstream end, and the downstream end is called the downstream end.

[0024] 3(a) is a diagram showing a cross section of the brush 10 in a standalone state (not in contact with the photosensitive drum 1) taken along an imaginary plane perpendicular to the rotation axis of the photosensitive drum 1. FIG. 3(b) is a diagram showing the same cross section of the brush 10 in a state in which it is in contact with the photosensitive drum 1.

[0025] As shown in Fig. 3, the brush 10 has a thread portion 11 made of multiple threads 11a made of conductive nylon bristles that contact and rub against the surface of the photosensitive drum 1, and a base cloth 11b that supports the thread portion 11. When not in contact with the photosensitive drum 1, the threads 11a extend vertically from the base cloth 11b. The threads 11a are evenly distributed on the base cloth 11b. The brush 10 is disposed so as to contact the photosensitive drum 1 downstream of the transfer unit and upstream of the charging unit in the rotation direction of the photosensitive drum 1.

[0026] The brush 10 is arranged such that its longitudinal direction is parallel to the direction of the rotation axis of the photosensitive drum 1. In addition to nylon (registered trademark), rayon, acrylic, polyester, etc. can be used as the material of the thread 11a. Although a conductive thread was used as the thread 11a in Example 1, an insulating thread may also be used. The thread 11a is not limited to being formed by twisting fibers as long as it is in a thread shape.

[0027] As shown in Fig. 3(a), in the state where the brush 10 is a single body, that is, in the state where no force is acting from the outside to bend the thread 11a (natural state), the distance from the base fabric 11b to the tip of the thread 11a extending from the base fabric 11b is defined as L1. The base fabric 11b is fixed by fixing means such as double-sided tape to a support member (not shown) installed at a predetermined position of the image forming apparatus 100, whereby the brush 10 is fixed. The brush 10 is fixed such that the shortest distance L2 from the base fabric 11b of the brush 10 fixed to the support member to the surface of the photosensitive drum 1 is shorter than the length L1 of the thread 11a in the single body state. The clearance between the support member and the photosensitive drum 1 is constant. The difference between L2 and L1 is referred to as the intrusion amount of the brush 10 with respect to the photosensitive drum 1. Since L2 < L1, in the usage state of the brush 10, that is, when the brush 10 is fixed to the image forming apparatus 100 and is in contact with the surface of the photosensitive drum 1, as shown in Fig. 3(b), the tip of the thread 11a bends toward the rotation direction of the photosensitive drum 1. The contact portion between the tip of the thread 11a provided on the most upstream side among the bent threads 11a and the surface of the photosensitive drum 1 is the upstream end of the contact area. The contact portion between the tip of the thread 11a provided on the most downstream side among the bent threads 11a and the surface of the photosensitive drum 1 is the downstream end of the contact area. The mode of contact between the brush 10 and the surface of the photosensitive drum 1 is the contact between each of the plurality of threads 11a and the surface of the photosensitive drum 1. Even if it is called the "contact area", microscopically, the surface of the photosensitive drum 1 and the brush 10 are not in contact in the area between adjacent threads 11a.

[0028] The dimension of the brush 10 in the longitudinal direction (the direction parallel to the rotation axis of the photosensitive drum 1) is set so that the brush 10 contacts the entire image forming area (the area where a toner image can be formed) on the photosensitive drum 1 in the direction of the rotation axis of the photosensitive drum 1. In addition, the dimension of the brush 10 in the lateral direction (the circumferential direction of the photosensitive drum 1, the direction parallel to the rotation direction) is set appropriately depending on the life of the image forming apparatus and the process cartridge.

[0029] The brush 10 is fixed at a fixed position relative to the photosensitive drum 1, and rubs against the surface of the photosensitive drum 1 as the photosensitive drum 1 moves (rotates). The brush 10 collects (recovers) from the photosensitive drum 1 deposits such as paper dust transferred from the recording material S onto the photosensitive drum 1 in the transfer section, and removes the deposits from the charging section and developing section downstream of the brush 10 in the moving direction (rotation direction) of the photosensitive drum 1. This reduces the amount of paper dust that moves to the printing section.

[0030] In Example 1, the length L1 of the thread 11a of the brush 10 in its natural state is 4.8 mm, the penetration amount of the brush 10 into the photosensitive drum 1 is 1.5 mm, the length L3 in the lateral direction of the brush 10 is 5 mm, and the length in the longitudinal direction is 216 mm. The fineness (thickness) of the thread 11a is 2 denier (representing the thickness of a thread such that 9000 m weighs 2 g), and the density is 240 kF / inch. 2 (kF / inch 2is a unit of brush density, indicating the number of filaments per square inch. The transverse length of the brush 10 is an example and is not limited to this. The longer the transverse length of the brush 10, the longer the brush can collect paper dust. The longitudinal length of the brush 10 is an example and is not limited to this. For example, the longitudinal length of the brush 10 can be set according to the maximum paper passing width of the image forming apparatus 100. The fineness of the threads 11a of the brush 10 is an example and is not limited to this. The fineness of the threads 11a can be determined taking into account the ability of the paper dust to pass through. If the fineness of the brush 10 is too small, the force that blocks the paper dust will be weak, and the paper dust will easily pass through. If the paper dust passes through the brush 10, the charging of the photosensitive drum 1 by the charging roller 2 will be hindered, which may result in image defects. Furthermore, if the fineness of the threads 11a of the brush 10 is too large, toner and fine paper dust cannot be captured, resulting in uneven toner adhesion in the longitudinal direction of the charging roller 2, which may cause uneven image density or image defects due to insufficient charging at the paper dust adhesion area. The density of the threads 11a of the brush 10 is an example and is not limited to this. The density of the threads 11a can be set taking into consideration the toner permeability and paper dust collection ability. If the density of the threads 11a of the brush 10 is too large, toner permeability will be low, causing toner to accumulate, which may scatter and cause contamination inside the device. If the density of the threads 11a of the brush 10 is too small, sufficient paper dust collection performance may not be achieved. From the perspective of paper dust collection performance, the fineness and density of the threads 11a should be 1 to 6 denier and 150 to 350 kF / inch, respectively. 2 In addition, it is preferable that the length L3 of the brush 10 in the lateral direction is 3 mm or more from the viewpoint of long life.

[0031] A brush power supply E4 (see FIG. 2) serving as a brush voltage application means is connected to the brush 10. During image formation, a negative DC voltage is applied as a brush voltage from the brush power supply E4 to the brush 10. In the first embodiment, the brush voltage during image formation is −400 V.

[0032] 3. Image output operation The image forming apparatus 100 executes a series of operations for forming an image on one or more recording materials S in response to a start instruction for one image output operation (job) from an external device (not shown) such as a personal computer. A job generally includes a pre-rotation process, an image formation process (printing process), an inter-sheet process when forming images on multiple recording materials S, and a post-rotation process. The image formation process includes forming an electrostatic image on the photosensitive drum 1, developing the electrostatic image (forming a toner image), transferring the toner image, fixing the toner image, etc., and the image formation time refers to the period during which this image formation process is performed. During image formation, i.e., during the period during which the image formation process is performed, the timing of each operation, such as forming an electrostatic image, forming a toner image, transferring the toner image, and fixing the toner image, varies. The pre-rotation process is a process for performing a preparatory operation before the image formation process. The sheet interval process is a process that is executed between the image formation process on a first recording material S and the image formation process on a second recording material S that follows the first recording material S when image formation processes are performed continuously on multiple recording materials S (continuous image formation). The post-rotation process is a process that performs a tidying up operation (preparatory operation) after the image formation process. Non-image formation time is a period other than image formation time, and includes the pre-rotation process, sheet interval process, and post-rotation process. The pre-multiple rotation process, which is a preparatory operation when the image forming apparatus 100 is turned on or when it returns from a sleep state, is also included in non-image formation time.

[0033] 4. Conventional configuration Next, the configuration of the first embodiment will be described in comparison with the configuration of a conventional embodiment. Fig. 4 is a diagram for explaining the conventional embodiment.

[0034] The conventional embodiments will be described using two configurations. Hereinafter, conventional embodiment 1 will be described using FIG. 4(a), and conventional embodiment 2 will be described using FIG. 4(b). FIGS. 4(a) and 4(b) are schematic cross-sectional views showing the arrangement of each member around the photosensitive drum in a cross section perpendicular to the rotation axis of the photosensitive drum in image forming apparatuses of conventional embodiments 1 and 2, respectively. Hereinafter, members relating to the conventional embodiments will be assigned different reference numerals from those in Example 1 to distinguish them from Example 1.

[0035] A conventional photosensitive drum 1A is driven to rotate clockwise around its rotation axis as viewed in the direction of the rotation axis. A transfer roller 5A, a brush 10A, a charging roller 2A, and a developing roller 31A are arranged circumferentially around the photosensitive drum 1A. Point O in FIG. 4 indicates the rotation axis of the photosensitive drum 1A. The dashed line A in FIG. 4 indicates an imaginary line that includes the rotation axis of the photosensitive drum 1A and extends vertically upward from the rotation axis in a cross section of the photosensitive drum 1A perpendicular to the rotation axis. Point B in FIG. 4 indicates the intersection of this imaginary line with the surface of the photosensitive drum 1A.

[0036] In conventional form 1, as shown in Fig. 4(a), the contact area between the brush 10A and the surface of the photosensitive drum 1A is located closer to the transfer roller 5A than the intersection B (upstream of the intersection B in the rotation direction of the photosensitive drum 1A). On the other hand, in conventional form 2, as shown in Fig. 4(b), the contact area between the brush 10A and the surface of the photosensitive drum 1A is located closer to the charging roller 2A than the intersection B (downstream of the intersection B in the rotation direction of the photosensitive drum 1A).

[0037] 5. Configuration of Example 1 Next, the configuration of the first embodiment will be described with reference to FIG. 5. FIG. 5 shows a cross section perpendicular to the rotation axis of the photosensitive drum 1 in the image forming apparatus 100 of the first embodiment, illustrating the arrangement of various components around the photosensitive drum 1. The photosensitive drum 1 is driven to rotate clockwise as viewed in the direction of the rotation axis. A transfer roller 5, a brush 10, a charging roller 2, and a developing roller 31 are arranged around the photosensitive drum 1. The definitions of dashed line A and intersection B are the same as those in FIG. 4. In the first embodiment, as shown in FIG. 5, intersection B is located within the contact area with the brush 10 on the surface of the photosensitive drum 1. Furthermore, intersection B is located at the center of the contact area in the rotation direction of the photosensitive drum 1. The brush 10 of the first embodiment is arranged so that the contact area with the brush 10 on the surface of the photosensitive drum 1 overlaps with an imaginary line that includes the rotation axis of the photosensitive drum 1 and extends vertically upward from the rotation axis, in a cross section perpendicular to the rotation axis of the photosensitive drum 1. This positional relationship between the contact area and the intersection B includes a case where the upstream end or downstream end of the contact area in the rotation direction of the photosensitive drum 1 includes the intersection B.

[0038] 6. Operation of Example 1 Next, in order to describe the effects that occur in the configuration of the first embodiment, problems in the conventional configuration will be described.

[0039] 6(a) is a diagram for explaining the problem in Conventional Form 1. When an image forming operation (job) of the image forming apparatus is executed and conveyance of recording material S is started, some of the paper dust on recording material S is transferred onto photosensitive drum 1A during the transfer process. After that, the paper dust transferred to photosensitive drum 1A is collected by brush 10A.

[0040] Most of the paper dust collected by the brush 10A is blocked at the upstream end of the contact area, but some small pieces of paper dust are not blocked at the upstream end of the contact area and gradually move downstream in the direction of rotation within the contact area as the photosensitive drum 1A rotates, reaching the vicinity of the downstream end of the contact area.

[0041] Any paper dust P that has reached the downstream end of the contact area is removed by the rotation of the photosensitive drum 1A. The paper dust P moves downstream from the contact area as it is. On the other hand, because the downstream end of the contact area is closer to the transfer roller 5A than the intersection B, as shown in Figure 6(a), some of the paper dust P that has reached the vicinity of the downstream end of the contact area is subjected to a force FA that has a vertically downward component due to gravity. Therefore, some of the paper dust P that has reached the vicinity of the downstream end of the contact area remains near the downstream end of the contact area.

[0042] As the image formation operation is repeatedly performed and further sheets of recording material S are fed, the amount of paper dust P remaining near the downstream end of the contact area increases, and the remaining paper dust becomes entangled and forms a paper dust mass. Then, while the photosensitive drum 1A is rotating, this paper dust mass may leave the area near the downstream end of the contact area and move downstream of the contact area due to some reason, such as a change in the drum potential. When this paper dust mass passes through the charging section, the portion of the photosensitive drum 1A surface where this paper dust mass is located is not properly charged and becomes at a higher potential than the voltage of the developing roller 31A, causing the toner on the developing roller 31A to move in the developing section, resulting in the formation of black dots on the image.

[0043] 6(b) is a diagram for explaining the problem in Conventional Form 2. In Conventional Form 2, as in Conventional Form 1, the paper dust transferred to the photosensitive drum 1A in the transfer process is blocked at the upstream end of the contact area. When the image forming operation is repeatedly performed and further recording material S is passed through, a lump of paper dust is formed at the upstream end of the contact area.

[0044] In Conventional Form 2, because the upstream end of the contact area is closer to the charging roller 2A than the intersection B, the blocked paper dust P is subjected to a force FB with a vertically downward component due to gravity in addition to the force caused by the rotation of the photosensitive drum 1A, as shown in Figure 6(b). As a result, some of the paper dust mass formed at the upstream end of the contact area is gradually pushed downstream through the brush 10B and may pass through the downstream end of the contact area. As with Conventional Form 1, this paper dust mass that passes through the contact area may form black spots.

[0045] In consideration of the above-described problems of Conventional Forms 1 and 2, the operation of Example 1 will be described. In Example 1, in the cross section of the photosensitive drum 1, intersection B is located within the contact area where the brush 10 contacts the surface of the photosensitive drum 1, and intersection B is located in the center of the contact area in the rotation direction of the photosensitive drum 1. In other words, the downstream end of the contact area is located closer to the charging roller 2 than intersection B (downstream of intersection B in the rotation direction of the photosensitive drum 1). Therefore, the force due to gravity acting on the paper dust that has reached the downstream end of the contact area does not act in a direction that tries to keep the paper dust at the downstream end of the contact area (toward the upstream side in the rotation direction) as in Conventional Form 1, but acts in a direction away from the downstream end of the contact area. Therefore, the generation of paper dust clumps near the downstream end of the contact area as described in Conventional Form 1 is suppressed.

[0046] Furthermore, the upstream end of the contact area is located closer to the transfer roller 5 than the intersection point B (upstream of the intersection point B in the rotation direction of the photosensitive drum 1). Therefore, even if a lump of paper powder is formed at the upstream end of the contact area, the force due to gravity acting on the lump of paper powder does not act in a direction that tries to insert the lump of paper powder into the contact area and move it downstream (towards the downstream side in the rotation direction), as in conventional form 2. The force due to gravity acting on the lump of paper powder acts in a direction away from the upstream end of the contact area. Therefore, even if a lump of paper powder is formed, it is prevented from passing through the contact area and moving downstream of the contact area.

[0047] The above-described operation of Example 1 makes it possible to suppress the occurrence of black spots caused by paper dust clumps, which was a problem in Conventional Modes 1 and 2.

[0048] Next, a paper feed test conducted to confirm the effect of Example 1 will be described. The paper feed test was conducted under the following conditions: In an environment of a temperature of 15°C and a relative humidity of 10% (low temperature and low humidity environment), Century Star paper (trade name, manufactured by Century Pulp and Paper Co.) was used as the recording material S, and 1000 white images were printed consecutively. From the 901st sheet onwards, 100 sheets were taken as samples, and the number of black dots that appeared on the samples was counted. At this time, only black dots larger than 1.2 mm, which are highly visible, were counted. A paper feed test was conducted with the configurations of Conventional Forms 1 and 2 and Example 1, and the results of comparing the number of black dots are shown in Table 1. [Table 1]

[0049] From the results in Table 1, many black spots larger than 1.2 mm were observed in Conventional Forms 1 and 2, but no black spots were observed in Example 1.

[0050] As described above, the configuration of Example 1 has made it possible to prevent adhesions accumulated on the brush 10 from forming clumps and detaching from the brush 10, causing image defects, in an image forming device 100 having a brush 10 that contacts the photosensitive drum 1.

[0051] Example 2 A description will be given of Example 2 of the present invention. The basic configuration and operation of the image forming apparatus of Example 2 are the same as those of the image forming apparatus of Example 1. Therefore, in the image forming apparatus of Example 2, elements having the same or corresponding functions or configurations as those of the image forming apparatus of Example 1 are given the same reference numerals as those of the image forming apparatus of Example 1, and detailed descriptions thereof will be omitted.

[0052] 1. Configuration of Example 2 The arrangement of the brushes in the second embodiment will be described with reference to Fig. 7. Fig. 7 is a schematic cross-sectional view for explaining the arrangement of each member around the photosensitive drum 1 in a cross section perpendicular to the rotation axis of the photosensitive drum 1 in the image forming apparatus 100 in the second embodiment.

[0053] In the second embodiment, similarly to the first embodiment, the photosensitive drum 1 is driven to rotate in a clockwise direction when viewed in a direction parallel to the rotation axis of the photosensitive drum 1. A transfer roller 5, a brush 10, a charging roller 2, and a developing roller 31 are arranged around the photosensitive drum 1. Furthermore, a pre-exposure device 13 is provided between the brush 10 and the charging roller 2 in the rotation direction of the photosensitive drum 1.

[0054] The pre-exposure device 13 operates an LED attached to the side of the main body (not shown) to irradiate light parallel to the main scanning direction of the photosensitive drum 1. A light guide or the like is used as a light guiding member to suppress uneven illumination in the main scanning direction.

[0055] 2. Operation of Example 2 Next, differences from Example 1 will be described to explain the action that occurs in the configuration of Example 2. In the configuration of Example 1, when paper dust accumulates near the upstream end of the contact area with the brush 10 on the surface of the photosensitive drum 1 to form a paper dust lump, the force due to gravity acting on the paper dust lump acts in a direction away from the upstream end of the contact area. Therefore, even if a paper dust lump is formed at the upstream end of the contact area, it is possible to prevent the paper dust lump from passing through the contact area and moving toward the charging roller 2. On the other hand, in the case of paper dust that is not clumped, the force due to gravity is small, so it is possible that it will move from the upstream end of the contact area in the direction of rotation of the photosensitive drum 1 and pass through the contact area. Even if small pieces of paper dust that are not clumped move toward the charging roller 2, they will not immediately cause black spots. However, if this paper dust adheres to the photosensitive drum 1 and continues to rotate, toner will eventually fuse to the paper dust, and black spots may occur at intervals corresponding to the rotation cycle of the photosensitive drum 1.

[0056] In this regard, in the second embodiment, the pre-exposure device 13, which is disposed between the brush 10 and the charging roller 2 in the rotation direction of the photosensitive drum 1, neutralizes the surface of the photosensitive drum 1 downstream of the brush 10. This allows for uniform discharge during charging, and small paper particles that pass through the contact area can be stably charged to negative polarity. As a result, this paper particle can be more reliably collected in the developing unit, and the occurrence of black spots originating from paper particles at intervals corresponding to the rotation cycle of the photosensitive drum 1 can be suppressed.

[0057] Next, a paper feed test conducted to confirm the effects of Example 2 will be described. The paper feed test was conducted under the following conditions: A white image was continuously printed on 10,000 sheets of Century Star paper (trade name, manufactured by Century Pulp and Paper Co.) as the recording material S in an environment of 23°C temperature and 50% relative humidity. A full-page halftone image was printed on one out of every 2,000 sheets, and the number of black or white dots appearing at intervals corresponding to the rotation cycle of the photosensitive drum 1 was counted. Here, black and white dots of 0.5 mm or larger were counted. The above paper feed test was conducted with the configurations of Example 1 and Example 2, and the results of comparing the number of black and white dots counted are shown in Table 2. [Table 2]

[0058] From the results in Table 2, in the configuration of Example 1, as the number of sheets of paper increased, small black and white spots occurred at intervals corresponding to the rotation period of the photosensitive drum 1, whereas in the configuration of Example 2, no black or white spots occurred as the number of sheets of paper increased.

[0059] As described above, with the configuration of Example 2, in the image forming apparatus 100 having the brush 10 in contact with the photosensitive drum 1, it was possible to suppress the occurrence of image defects caused by deposits accumulated on the brush 10.

[0060] Example 3 A description will be given of Example 3 of the present invention. The basic configuration and operation of the image forming apparatus of Example 3 are the same as those of the image forming apparatus of Example 1. Therefore, in the image forming apparatus of Example 3, elements having the same or corresponding functions or configurations as those of the image forming apparatus of Example 1 are given the same reference numerals as those of the image forming apparatus of Example 1, and detailed descriptions thereof will be omitted.

[0061] 1. Configuration of Example 3 The arrangement of the brushes in the third embodiment will be described with reference to Fig. 8. Fig. 8 is a schematic cross-sectional view for explaining the arrangement of each member around the photosensitive drum 1 in a cross section perpendicular to the rotation axis of the photosensitive drum 1 in the image forming apparatus 100 in the third embodiment.

[0062] In the third embodiment, similarly to the first embodiment, the photosensitive drum 1 is driven to rotate in a clockwise direction when viewed in a direction parallel to the rotation axis of the photosensitive drum 1. Around the photosensitive drum 1, a transfer roller 5, a brush 10, a charging roller 2, and a developing roller 31 are arranged.

[0063] 8, the brush 10 is disposed so that, in a cross section perpendicular to the rotation axis of the photosensitive drum 1, the contact area where the brush 10 comes into contact with the surface of the photosensitive drum 1 overlaps with an imaginary line that includes the rotation axis of the photosensitive drum 1 and extends vertically upward from the rotation axis. In other words, the brush 10 is disposed so that the contact area includes intersection B. Furthermore, intersection B is located closer to the charging roller 2 than the center of the contact area in the rotation direction of the photosensitive drum 1 (downstream in the rotation direction of the photosensitive drum 1). In other words, the center of the contact area in the rotation direction of the photosensitive drum 1 is located closer to the transfer roller 5 than intersection B (upstream in the rotation direction of the photosensitive drum 1).

[0064] 2. Operation of Example 3 Next, we will explain the effects that occur in the configuration of Example 3. First, Table 3 shows the results of a paper feed test in which black dots of 1.2 mm and black dots of 0.8 mm to 1.2 mm in size were counted for each of the configurations of Conventional Forms 1 and 2 and Example 1 under the same paper feed test conditions as Example 1. [Table 3]

[0065] The results in Table 3 show that, when sizes smaller than 1.2 mm are taken into consideration, black spots occur even in Example 1, although the number is kept low. Furthermore, when comparing Conventional Forms 1 and 2, it is found that more black spots of all sizes occur in Conventional Form 2. From this, it is thought that the occurrence of black spots in Conventional Form 2 is largely influenced by the mass of paper powder that accumulates at the upstream end of the contact area with the brush 10A on the surface of the photosensitive drum 1A, which is the cause of black spots in Conventional Form 2.

[0066] In the configuration of the first embodiment, the upstream end of the contact area between the surface of the photosensitive drum 1 and the brush 10 is When a paper dust lump is formed, it gradually enters the contact area from the upstream end and moves downstream due to the rotation of the photosensitive drum 1. The force due to gravity acting on this paper dust lump acts upstream in the direction of rotation of the photosensitive drum 1, but the magnitude of the component of this force parallel to the surface of the photosensitive drum 1 decreases as the paper dust lump approaches intersection B. When the paper dust lump moves to a position closer to the charging roller 2 than intersection B (downstream of intersection B in the direction of rotation of the photosensitive drum 1), the force due to gravity acting on the paper dust lump begins to act downstream in the direction of rotation of the photosensitive drum 1. Therefore, the paper dust lump that passes intersection B can more easily pass through the contact area.

[0067] In Example 3, as in Example 1, intersection B is located within the contact area between the surface of the photosensitive drum 1 and the brush 10. However, as shown in FIG. 8, the size of the area from the upstream end of the contact area to intersection B is larger than in Example 1. In other words, the upstream end of the contact area is closer to the transfer roller 5 in the rotation direction of the photosensitive drum 1 than in Example 1. As a result, even if a paper dust mass is formed at the upstream end of the contact area, the force due to gravity acting on the paper dust mass is stronger in the direction toward the upstream side of the rotation direction of the photosensitive drum 1. Therefore, even if a paper dust mass is formed, the paper dust mass is prevented from passing through the contact area by being inserted from the upstream end of the contact area into the downstream side of the contact area. Furthermore, as in Example 1, the downstream end of the contact area is located closer to the charging roller 2 than intersection B (downstream in the rotation direction of the photosensitive drum 1). Therefore, the accumulation of paper dust near the downstream end of the contact area, which is the cause of black spots in Conventional Example 1, is less likely to occur.

[0068] Table 4 shows the results of a paper feed test conducted under the same conditions as in Example 1 for each of the configurations of Examples 1 and 3, and counting the number of black dots of 1.2 mm and 0.8 mm to 1.2 mm. [Table 4]

[0069] As shown in Table 4, in Example 3, the occurrence of black spots having sizes of 0.8 mm to 1.2 mm was reduced compared to Example 1.

[0070] As described above, the configuration of Example 3 has made it possible to prevent adhesions accumulated on the brush 10 from forming clumps and detaching from the brush 10, causing image defects, in an image forming device 100 having a brush 10 that contacts the photosensitive drum 1.

[0071] It should be noted that a pre-exposure device similar to that in the second embodiment may be provided in the configuration of the third embodiment, thereby making it possible to suppress black dots that appear at intervals corresponding to the rotation period of the photosensitive drum 1.

[0072] Example 4 A fourth embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of the fourth embodiment are the same as those of the image forming apparatus of the third embodiment. Therefore, in the image forming apparatus of the fourth embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of the third embodiment are assigned the same reference numerals as those of the image forming apparatus of the third embodiment, and detailed descriptions thereof will be omitted.

[0073] 1. Configuration of Example 4 The fourth embodiment differs from the third embodiment in the arrangement of the brush 10 and other members in the circumferential direction of the photosensitive drum 1. The other members are, for example, a developing roller 31. The configuration of the fourth embodiment will be described below with reference to Fig. 9. Fig. 9 is a schematic cross-sectional view illustrating the arrangement of the members around the photosensitive drum 1 in a cross section perpendicular to the rotation axis of the photosensitive drum 1 in the image forming apparatus 100 of the fourth embodiment, and the relationship between the forces acting on the photosensitive drum 1.

[0074] In the fourth embodiment, similarly to the third embodiment, the photosensitive drum 1 is driven to rotate in a clockwise direction when viewed in a direction parallel to the rotation axis of the photosensitive drum 1. A transfer roller 5, a brush 10, a charging roller 2, and a developing roller 31 are arranged around the photosensitive drum 1. The brush 10 is arranged in the same manner as in the third embodiment.

[0075] The pressure that the brush 10 exerts on the surface of the photosensitive drum 1 is designated as F1. The pressure that the developing roller 31, which is a contact member other than the brush that abuts on the surface of the photosensitive drum 1, exerts on the surface of the photosensitive drum 1 is designated as F2. In the fourth embodiment, the magnitude of the pressure F1 is equal to or less than the magnitude of the component of the pressure F2 in a direction parallel to the pressure F1.

[0076] In addition, in the cross section of the photosensitive drum 1, an imaginary line C passes through the center of the contact area on the surface of the photosensitive drum 1 that comes into contact with the brush 10 in the rotation direction of the photosensitive drum 1 and the rotation axis O of the photosensitive drum 1. In the fourth embodiment, the developing roller 31, which is the contact member, and the upstream end of the contact area are located on opposite sides of the imaginary line C.

[0077] More specifically, in the cross section of the photosensitive drum 1, an imaginary line D passes through the contact point between the surface of the photosensitive drum 1 and the developing roller 31 and the rotation axis O of the photosensitive drum 1. The angle θ between imaginary line C and imaginary line D is defined as a counterclockwise direction in FIG. 9 . The pressure with which the brush 10 contacts the surface of the photosensitive drum 1 is defined as F1 (force in the direction of the rotation axis O), and the pressure with which the developing roller 31 contacts the surface of the photosensitive drum 1 is defined as F2 (force in the direction of the rotation axis O). In the fourth embodiment, F1 and the component of F2 (F2·cosθ) parallel to the imaginary line C satisfy F1≦F2·cosθ (θ≧0). For example, the contact pressure F1 of the brush 10 is 4.9 N, the contact pressure F2 of the developing roller 31 is 9.6 N, and the angle θ between imaginary line C and imaginary line D is in the range of 0°≦θ≦58.6°.

[0078] A small desktop testing machine (Shimadzu Corporation, EZ-S) was used to measure the contact pressure F1 of the brush 10. Specifically, the brush was sandwiched between upper and lower pressure plates with a diameter of 118 mm, and the repulsive force was measured when the brush was penetrated 1.5 mm. The measured value was converted according to the longitudinal length of the brush 10 used in the experimental system. The contact pressure F2 of the developing roller 31 was the contact pressure when stationary, calculated based on the characteristics of a pressure spring (not shown).

[0079] 2. Operation of Example 4 Next, the operation of the fourth embodiment will be described. The brush 10 contacts the photosensitive drum 1, and a pressure F1 is applied from the brush 10 to the photosensitive drum 1. If the photosensitive drum 1 is bent by the pressure F1, a gap may be created between the brush 10 and the surface of the photosensitive drum 1, allowing paper dust to slip through. Meanwhile, a pressure F2 from the developing roller 31 acts on the photosensitive drum 1, and a component F2·cosθ (>0) parallel to the imaginary line C acts as a force to reduce the bending of the photosensitive drum 1 caused by the pressure F1 of the brush 10. In the fourth embodiment, F1≦F2·cosθ is satisfied, which results in suppressing bending of the photosensitive drum 1 and suppressing the creation of a gap between the brush 10 and the photosensitive drum 1. In the configuration of the fourth embodiment, F1≦F2·cosθ is satisfied when |θ|≦58.6°.

[0080] As explained in Example 3, the occurrence of black dot images is largely caused by the phenomenon in which a mass of paper powder that has accumulated at the upstream end of the contact area with the brush 10 on the surface of the photosensitive drum 1 passes through the contact area, as in Conventional Form 2. Therefore, it is preferable to arrange F2·cosθ in the range of 0°≦θ≦58.6° to make it work more upstream of the contact area.

[0081] As described above, by arranging the developing roller relative to the brush 10 in the circumferential direction of the photosensitive drum 1 as in Example 4, the paper dust collection performance at the upstream end of the contact area is stabilized, and the occurrence of black spots can be suppressed. Note that, although the arrangement of the developing roller 31 has been described in Example 4, the same effect can be obtained by arranging the contact members, such as the charging roller 2 and transfer roller 5, that contact the photosensitive drum 1 in a way that suppresses bending of the photosensitive drum 1 due to contact of the brush 10. [Explanation of symbols]

[0082] 1: photosensitive drum, 2: charging roller, 3: developing device, 5: transfer roller, 10: brush, 31: developing roller

Claims

1. an image carrier that is driven to rotate; a charging unit that forms a charging portion facing the surface of the image carrier and charges the surface of the image carrier; a developing roller that supplies a developer to the surface of the image carrier charged by the charging means to form a developer image; a transfer roller that forms a transfer portion between itself and the image carrier and transfers the developer image from the image carrier to a transfer target; a brush that is fixed to the image carrier and that comes into contact with the surface of the image carrier downstream of the transfer unit and upstream of the charging unit in the rotation direction of the image carrier; a pre-exposure unit that exposes the image carrier to light downstream of the brush and upstream of the charging unit in the rotation direction of the image carrier; Equipped with In an image forming apparatus, after the developer image is transferred to the transfer object, the developer remaining on the surface of the image carrier is collected by the developing roller, the brush is composed of a thread portion that contacts the image carrier, a first support portion that supports the thread portion, and a second support portion that supports the first support portion and extends in the direction of the rotation axis of the image carrier, In a cross section perpendicular to the rotation axis of the image carrier, the brush is disposed so that a contact area on the surface of the image carrier where the brush comes into contact with the thread portion overlaps with an imaginary line that includes a rotation axis of the image carrier and extends vertically upward from the rotation axis, If the point where the virtual line intersects with the contact area is defined as an intersection point, then a distance from the intersection to the charging unit, measured along the surface of the image carrier in a rotation direction of the image carrier, is shorter than a distance from the transfer unit to the intersection; The image forming apparatus is characterized in that the pre-exposure means exposes the surface of the image carrier downstream of the downstream end of the contact area and upstream of the charging unit in the rotation direction of the image carrier.

2. The magnitude of the pressure F1 that the brush exerts on the surface of the image carrier is 2. The image forming apparatus according to claim 1, wherein the magnitude of a component of a pressure F2 applied to the surface of the image carrier by a contact member other than the brush in a direction parallel to the pressure F1 is equal to or less than the magnitude of the component of the pressure F2 applied to the surface of the image carrier.

3. 3. The image forming apparatus according to claim 2, wherein, in a cross section perpendicular to the rotation axis of the image carrier, the abutment member and the upstream end of the contact area in the rotation direction of the image carrier are located on opposite sides of an imaginary line passing through the rotation axis of the image carrier and the center of the contact area in the rotation direction of the image carrier.

4. 3. The image forming apparatus according to claim 2, wherein the contact member is the developing roller.

5. 2. The image forming apparatus according to claim 1, wherein the charging means is a rotatable charging roller, the charging roller contacting the image carrier to form a charging portion, and the image carrier is charged at the charging portion.

6. The density of the thread portion is 150 kF / inch ２ ~350kF / inch ２ 2. The image forming apparatus according to claim 1, wherein:

7. 2. The image forming apparatus according to claim 1, wherein the brush collects paper dust adhering to the surface of the image carrier.

8. 2. The image forming apparatus according to claim 1, wherein the fineness of the thread portion is 1 to 6 denier.

9. 2. The image forming apparatus according to claim 1, wherein the brush is configured to block the paper dust collected by the thread portion at an upstream end of the contact area in the rotation direction of the image carrier.

Images