Image forming device

Abstract

To prevent, in an image forming apparatus that has a brush in contact with a photoconductor drum, the occurrence of an image defect resulting from a transfer residual toner accumulated on the brush.SOLUTION: An image forming apparatus comprises: an image carrier; electrifying means; developing means; transfer means that transfers a developer image from the image carrier to a transfer target body; a brush that is in contact with the surface of the image carrier at a brush part on the downstream side of a transfer part and on the upstream side of an electrifying part in the direction of rotation of the image carrier; voltage application means that applies voltage to the brush; and pre-exposure means that exposes the surface of the image carrier on the downstream side of the brush part and on the upstream side of the electrifying part, and in the image forming apparatus, after the developer image is transferred to the transfer target body, a developer remaining on the surface of the image carrier is recovered by the developing means. An end on the upstream side of an exposure area formed by the pre-exposure means is on the upstream of an end on the downstream side of a contact area where the brush is in contact with the surface of the image carrier, and the exposure area includes at least part of the contact area.SELECTED DRAWING: Figure 6

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, with the configuration of Patent Document 1, when a large amount of high-print-ratio images are continuously fed, the residual toner gradually accumulates on the brush, and when the allowable amount is exceeded, the toner is expelled from the brush, which can result in unnecessary images.

[0005] An object of the present invention is to prevent image defects from occurring due to toner 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 comprises: 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 means for supplying a developer to the surface of the image carrier charged by the charging means to form a developer image; a transfer means for forming a transfer portion between the image carrier and the transfer means and transferring the developer image from the image carrier to a transfer-receiving body; a brush that contacts the surface of the image carrier at a brush portion downstream of the transfer portion and upstream of the charging portion in the rotation direction of the image carrier; The brush has a base fabric and a thread portion made up of a plurality of threads extending from the base fabric. and, voltage application means for applying a voltage to the brush; a pre-exposure unit that exposes a surface of the image carrier downstream of the brush unit 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 recovered by the developing means, An upstream end of an exposure area on the surface of the image carrier that is exposed by the pre-exposure means in the rotation direction of the image carrier is located upstream of a downstream end of a contact area on the surface of the image carrier that comes into contact with the brush in the rotation direction of the image carrier, and the exposure area includes at least a part of the contact area. fruit, In the raising direction of the yarn, the arrangement of the yarn is relatively uniform near the tip of the yarn compared to near the base of the yarn portion which is close to the base fabric, A part of the light emitted by the pre-exposure means is irradiated to a part of the thread portion close to the base fabric. It is characterized by: [Effects of the Invention]

[0010] 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 toner accumulated on the brush. [Brief explanation of the drawings]

[0011] [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 cross-sectional view of the brush in the first embodiment. [Figure 4] FIG. 2 is a perspective view of a brush according to the first embodiment. [Figure 5] FIG. 10 is a cross-sectional view illustrating a conventional embodiment. [Figure 6] FIG. 1 is a cross-sectional view illustrating a first embodiment. [Figure 7] FIG. 10 is a diagram illustrating various potential relationships in a conventional embodiment. [Figure 8] 1 is a diagram illustrating three types of potential relationships in the first embodiment. FIG. [Figure 9] 1A to 1C are diagrams illustrating paper images used in a paper feed test in Example 1 and image defects that occur. [Figure 10] 1 is a cross-sectional view illustrating a method for verifying the potential relationship in Example 1. FIG. [Figure 11] FIG. 10 is a diagram comparing the brush configurations of Example 1 and Example 2. [Figure 12] 10 is a diagram comparing various potential relationships between Example 1 and Example 2. FIG. [Figure 13] 10A and 10B are cross-sectional views comparing the brush contact states of Example 1 and Example 3. [Figure 14] 10 is a diagram comparing various potential relationships between Example 1 and Example 3. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, with reference to the drawings, a detailed description will be given of an embodiment of the present invention. However, the dimensions, materials, shapes, and relative positions of the components described in the embodiment may be changed as appropriate depending on the configuration of the device to which the invention is applied and various conditions. In other words, it is not intended to limit the scope of the present invention to the following embodiment. Furthermore, terms indicating geometric shapes or relationships, such as parallel, perpendicular, center, straight line, circle, etc., are not limited to their strict mathematical meaning unless otherwise specified, and are interpreted as including the range of allowances due to manufacturing tolerances, etc.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] The charging roller 2 faces the surface of the photosensitive drum 1 and contacts it with a predetermined pressure, forming a charging portion. 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 charging roller 2 uniformly charges the surface of the photosensitive drum 1 to a predetermined potential. 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 the minute gaps between the photosensitive drum 1 and the charging roller 2, which are formed upstream and downstream of the contact point between the photosensitive drum 1 and the charging roller 2 in the rotational direction of the photosensitive drum 1. The contact point between the charging roller 2 and the photosensitive drum 1 is referred to as the charging portion.

[0017] 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.

[0018] 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 developer supply means, a developer storage chamber 33 for storing 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 the blade nip, which is the contact portion between the developing roller 31 and the developing blade 34. The developing roller 31 performs development by contacting the photosensitive drum 1. The contact area 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. The developing roller 31 is driven to rotate in a counterclockwise direction (counterclockwise when viewed 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. Note that the drive motor 110 that drives the photosensitive drum 1 may also apply 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 apply 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 source E2 (see FIG. 2) serving as a developing voltage applying means. In Example 1, the developing voltage is a negative DC voltage of −400 V. Toner charged with the same polarity as the charge polarity of the photosensitive drum 1 (negative polarity in Example 1) 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 Example 1, other development methods may be used, such as two-component non-magnetic contact development, non-contact development, and magnetic development. The two-component non-magnetic contact development method uses a two-component developer containing non-magnetic toner and magnetic carrier as the developer, and brings the developer (magnetic brush) carried on a developer carrier into contact with the photosensitive drum 1 to perform development. The non-contact development method is a development method in which toner is ejected from a developer carrier arranged opposite the photosensitive drum but not in contact with it, onto the photosensitive drum. The magnetic development method is a development method in which magnetic toner is carried by magnetic force on a developer carrier that has a built-in magnet as a magnetic field generating means and is arranged opposite the photosensitive drum but not in contact with it. In Example 1, toner having a median average particle size of 6 μm and a normal negative charge polarity is used.

[0019] The transfer roller 5 can be preferably made of an elastic material such as polyurethane rubber, EPDM (ethylene-propylene-diene rubber), NBR (nitrile-butadiene rubber), or other sponge rubber. The transfer roller 5 is pressed against the photosensitive drum 1, forming a transfer section where the photosensitive drum 1 and the transfer roller 5 are in pressure contact. During transfer, 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 the opposite polarity to the normal polarity of the toner (positive polarity in the first embodiment) is applied to the transfer roller 5 as the transfer voltage. In the first embodiment, the transfer voltage is set to +1000 V. The developer image is then electrostatically transferred from the photosensitive drum 1 to the recording material S due to the action of the electric field formed between the transfer roller 5 and the photosensitive drum 1.

[0020] 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.

[0021] 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.

[0022] Residual toner remaining on the photosensitive drum 1 without being transferred to the recording material S is removed in the following process. The residual toner is negatively charged in the charging section by discharge from the charging roller 2. The residual toner negatively charged 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 are at a light potential and non-image areas that are at a dark potential. The behavior of the residual toner that has reached the developing section will be explained separately for the image areas and non-image areas of the photosensitive drum 1.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 2. Brush configuration The image forming apparatus 100 has a brush 10 that contacts the surface of the photosensitive drum 1 at a brush portion. 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 portion and upstream of the charging portion in the rotation direction of the photosensitive 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.

[0027] 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.

[0028] As shown in Fig. 3, the brush 10 is a pile fabric having 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 fabric 11b that supports the thread portion 11. When not in contact with the photosensitive drum 1, the threads 11a extend vertically from the base fabric 11b. The threads 11a are uniformly distributed on the base fabric 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.

[0029] 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.

[0030] As shown in FIG. 3(a), in the state where the brush 10 is a single body, that is, in a state where no external force acts to bend the thread 11a (natural state), the distance from the base fabric 11b to the tip of the thread 11a from the base fabric 11b is defined as L1. The base fabric 11b is fixed to a support member (not shown) installed at a predetermined position of the image forming apparatus 100 by fixing means such as double-sided tape. Thereby, the brush 10 is fixed. The brush 10 is fixed so 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 abuts on 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 region. 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 region. The contact mode 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 referred to as the "contact region", microscopically, the surface of the photosensitive drum 1 and the brush 10 do not contact in the region between adjacent threads 11a. A contact portion is formed by the surface of the photosensitive drum 1 in the contact region and the brush 10 that contacts the surface of the photosensitive drum 1.

[0031] 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.

[0032] 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 any adhering matter such as paper dust that has been transferred from the recording material S onto the photosensitive drum 1 in the transfer section, and reduces the amount of paper dust that moves to the charging section and developing section downstream of the brush 10 in the movement direction (rotation direction) of the photosensitive drum 1.

[0033] 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 230 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 arrangement of the threads 11a is approximately uniform from the base of the base fabric 11b to the tip of the bristles, which contact the surface of the photosensitive drum 1. Note that the lateral length of the brush 10 is an example and is not limited to this. The longer the lateral length of the brush 10, the longer it 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. Also, 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 paper dust to pass through. If the fineness of the brush 10 is too small, the paper dust retention force is weak, making it easier for paper dust to pass through. If paper dust passes through the brush 10, charging of the photosensitive drum 1 by the charging roller 2 may be hindered, resulting in poor image quality. Furthermore, if the fineness of the threads 11a of the brush 10 is too large, it will not be possible to capture toner or fine paper dust, which will result in unevenness in the amount of toner adhered in the longitudinal direction of the charging roller 2, and may cause uneven image density or poor image quality due to insufficient charging at the paper dust adhesion area. Furthermore, 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, the toner permeability will be low, causing the toner to accumulate, which may cause the accumulated toner to scatter and cause dirt inside the device. Furthermore, if the density of the threads 11a of the brush 10 is too small, it may not be possible to obtain sufficient paper dust collection ability. Fineness of the threads 11a, The density is 1 to 6 denier and 150 to 350 kF / inch from the viewpoint of paper dust collection performance. 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.

[0034] 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 −300 V.

[0035] The image forming apparatus 100 is a cleanerless system in which the developer (transfer residual toner) remaining on the surface of the photosensitive drum 1 after the developer image is transferred to the recording material S, which is the transfer target, is collected by the developing device 3. The polarity of the transfer residual toner is preferably the same as the normal polarity of the toner (negative in Example 1). If the transfer residual toner has a polarity opposite to the normal polarity (positive in Example 1), the potential relationship between the light-area potential Vl (-100 V) and the brush voltage (-300 V) causes the transfer residual toner in the light-area potential area to be electrostatically collected by the brush 10. In reality, the light-area potential area is affected by the transfer, and the potential is controlled in a direction that further reduces the absolute value. Furthermore, the positive-polarity transfer residual toner that is not collected by the brush 10 may adhere to the downstream charging roller 2 and cause density unevenness. If the transfer residual toner has the normal polarity (negative), it is less likely to electrostatically adhere to the brush 10 and charging roller 2 and can be collected in the development unit. The following description will be given on the assumption that the polarity of the transfer residual toner is normal (negative).

[0036] 3. Configuration of pre-exposure device Next, the pre-exposure device will be described. As shown in FIG. 1, the image forming apparatus 100 has a pre-exposure device 13 for equalizing the potential of the photosensitive drum 1 after the transfer process. The pre-exposure device 13 is a pre-exposure means that exposes the surface of the photosensitive drum 1 downstream of the brush 10 and upstream of the charging unit in the rotation direction of the photosensitive drum 1. The pre-exposure device 13 operates an LED attached to the side of the main body (not shown) to irradiate the photosensitive drum 1 with light parallel to the main scanning direction. A light guide or the like is used as a light guiding member to suppress uneven illumination in the main scanning direction. The pre-exposure device 13 performs an exposure operation mainly during image formation to equalize the potential on the photosensitive drum 1 after the transfer process to the recording material S, and reduces the surface potential of the photosensitive drum 1 to approximately 0 V.

[0037] 4. 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.

[0038] 5. Conventional configuration For the convenience of explaining the first embodiment, the configuration of the conventional embodiment will be explained. 5 is a diagram for clarity. Hereinafter, components according to the conventional embodiment will be assigned different reference numerals from those in Example 1 to distinguish them from Example 1. FIG. 5 is a cross-sectional view showing the arrangement of components around the photosensitive drum 1A in a conventional image forming apparatus, taken along a cross section perpendicular to the rotation axis of the photosensitive drum 1A. Among the optical paths of light used by the pre-exposure device 13A to expose the surface of the photosensitive drum 1A, the most upstream optical path in the rotation direction of the photosensitive drum 1A is indicated by the reference numeral A. In a cross section perpendicular to the rotation axis of the photosensitive drum 1A, the area on the surface of the photosensitive drum 1A upstream of an intersection B between the optical path A and the surface of the photosensitive drum 1A is a non-exposure area where exposure by the pre-exposure device 13A is not performed. In the conventional embodiment, in a cross section perpendicular to the rotation axis of the photosensitive drum 1A, the intersection B is located downstream in the rotation direction of the photosensitive drum 1A from the downstream end, in the rotation direction of the photosensitive drum 1A, of the contact area on the surface of the photosensitive drum 1A that comes into contact with the brush 10A. Therefore, the contact area between the photosensitive drum 1A and the brush 10A does not overlap with the exposure area where exposure by the pre-exposure device 13A is performed. In other words, the contact area and the exposure area do not overlap, and no part of the contact area is included in the exposure area.

[0039] 6. Configuration of Example 1 The configuration of the first embodiment will be described with reference to Fig. 6. Fig. 6 is a cross-sectional view showing 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 of the first embodiment.

[0040] In FIG. 6, among the optical paths of light when the pre-exposure device 13 exposes the surface of the photosensitive drum 1, the optical path that is most upstream in the rotation direction of the photosensitive drum 1 is indicated by the symbol A. In a cross section perpendicular to the rotation axis of the photosensitive drum 1, the area on the surface of the photosensitive drum 1 upstream of the intersection B between the optical path A and the surface of the photosensitive drum 1A is a non-exposure area where exposure by the pre-exposure device 13 is not performed. In Example 1, in a cross section perpendicular to the rotation axis of the photosensitive drum 1, the intersection B is located upstream in the rotation direction of the photosensitive drum 1 from the downstream end in the rotation direction of the photosensitive drum 1 of the contact area on the surface of the photosensitive drum 1 that comes into contact with the brush 10. Furthermore, the exposure area includes at least a portion of the contact area. In other words, the intersection B is located within the contact area. The intersection B is the upstream end of the exposure area within the contact area.

[0041] 7. Operation of Example 1 In order to explain the effects that occur in the configuration of the first embodiment, the problems in the conventional configuration will be explained.

[0042] When an image forming operation (job) is performed in the image forming apparatus 100 and conveyance of the recording material S is initiated, residual toner that was not transferred onto the recording material S during the transfer process is generated on the photosensitive drum 1A. The residual toner moves to the contact area with the brush 10A, but in some cases, this residual toner does not pass through the contact area and remains in the contact area. This phenomenon will be explained using FIG. 7. FIG. 7 is a diagram showing changes in the surface potential of the photosensitive drum 1A after transfer at the transfer unit in a conventional configuration. In FIG. 7, section (a) shows changes in the surface potential Va of the photosensitive drum 1A downstream from the transfer unit and upstream from the contact area, while section (b) shows changes in the surface potential Vb of the photosensitive drum 1A in the contact area. Section (c) shows changes in the surface potential of the photosensitive drum 1A downstream from the contact area and upstream from the exposure area (non-exposure area), and section (d) shows changes in the surface potential Vd of the photosensitive drum 1A in the exposure area. It can also be said that the section (d) shows the change in the surface potential of the photosensitive drum 1A downstream from the lower end of the contact area and upstream from the charging portion.

[0043] First, the surface potential Va of the photosensitive drum 1A after transfer in the transfer section in the conventional embodiment is -80V. Here, the light area potential Vl is -100V in the first embodiment, but as described above, the absolute value of the surface potential Va after transfer in the part that was the light area potential due to the influence of transfer is reduced from the light area potential Vl, and is -80V in the first embodiment. The value of the surface potential is an example. Even if changes in surface potential due to the influence of the brush 10A are not taken into consideration, the effects of the present invention, described below, can be similarly achieved. Subsequently, while passing through the contact area, the surface potential Vb of the photosensitive drum 1A gradually increased, reaching −230 V when the photosensitive drum 1A passed the downstream end of the contact area. Note that, here, the term “potential increasing” refers to an increase in the absolute value of the negative potential. Although the surface potential Vb while passing through the contact area with the brush 10A cannot be directly measured, the following can be inferred from the potential change before and after passing through the contact area. That is, while passing through the contact area, negative charges are injected from the brush 10A onto the surface of the photosensitive drum 1A due to the brush voltage, resulting in an increase in the surface potential. Because the brush voltage is constant at −300 V, the potential difference between the brush voltage and the surface potential Vb of the photosensitive drum 1A gradually decreases while passing through the contact area. There is no part of the contact area where |Vb|<|Va|; |Vb|≧|Va| is always true. Furthermore, the surface potential Vb of the photosensitive drum 1A does not decrease in the contact area, and the surface potential Va upstream of the contact area is higher than the surface potential Vd in the exposure area downstream of the contact area. Therefore, there is no part in the contact area where |Va-Vb|>|Vb-Vd|, and |Va-Vb|≦|Vb-Vd| is always true.

[0044] Therefore, in the contact area, the electrostatic force acting on the negative residual toner acts in the direction from the brush 10A toward the photosensitive drum 1A, but the magnitude of this force decreases toward the downstream end of the contact area. Therefore, it is thought that the negative residual toner is more likely to be collected by the brush 10A near the downstream end of the contact area.

[0045] As a result, in the conventional configuration, the amount of transfer residual toner remaining near the downstream end of the contact area increases, and the transfer residual toner that can no longer be held by brush 10 A is expelled from brush 10 A. If this transfer residual toner is not collected in the developing unit, a toner expulsion image may be formed as an image on the recording material.

[0046] Taking into account the above-described problems of the conventional configuration, the operation of the first embodiment will be described with reference to FIG. 8. FIG. 8 is a diagram showing changes in the surface potential of the photosensitive drum 1 after transfer at the transfer unit in the first embodiment. In FIG. 8, section (a) shows changes in the surface potential Va of the photosensitive drum 1 downstream of the transfer unit and upstream of the contact area, and section (b) shows changes in the surface potential Vb of the photosensitive drum 1 in the contact area. Section (c) shows changes in the surface potential of the photosensitive drum 1 downstream of the contact area and upstream of the exposure area (non-exposure area), and section (d) shows changes in the surface potential Vd of the photosensitive drum 1 in the exposure area. It can also be said that section (d) shows changes in the surface potential of the photosensitive drum 1 downstream of the lower end of the contact area and upstream of the charging unit.

[0047] In the first embodiment, as shown in Fig. 6, in a cross section perpendicular to the rotation axis of the photosensitive drum 1, an intersection B between the most upstream optical path A of the optical paths irradiated by the pre-exposure device 13 and the surface of the photosensitive drum 1 is located upstream of the downstream end of the contact area in the rotation direction of the photosensitive drum 1. As a result, part of the light irradiated by the pre-exposure device 13 irradiates the thread portion 11 of the brush 10, and the light not blocked by the threads 11a of the thread portion 11 exposes the surface of the photosensitive drum 1. Therefore, as shown in Fig. 8(A), the changes in the surface potential Va of the photosensitive drum 1 after transfer and the surface potential Vb of the photosensitive drum 1 in the non-exposed area in the contact area are the same as those in the conventional embodiment up to the intersection B, i.e., before entering the exposure area.

[0048] However, after passing intersection B, that is, after entering the exposure area by the pre-exposure device 13, the surface potential Vb of the photosensitive drum 1 gradually decreases, and |Vb| becomes smaller as it approaches the downstream end of the contact area. This is because the light emitted by the pre-exposure device 13 passes through the gaps in the threads 11a of the brush 10 and exposes the surface of the photosensitive drum 1 in the contact area. As a result, after passing intersection B, the potential difference between the brush voltage and the surface potential Vb of the photosensitive drum 1 increases. At this time, as is clear from FIG. 8(A), there exists a region where |Vb|<|Va| is satisfied.

[0049] Regarding the surface potential Vb of the photosensitive drum 1 in the contact area, the potential at intersection B is Vbmax, the potential upstream of intersection B near the upstream end of the non-exposed area in the contact area is Vba, and the potential downstream of intersection B near the downstream end of the exposed area in the contact area is Vbd. Vbmax is the surface potential of the photosensitive drum 1 at the upstream end of the exposed area in the contact area. That is, Vbmax has the largest absolute value among Vb because the upstream end of the exposed area in the contact area is the area where the most charge is injected without being neutralized. Vbd is the surface potential near the downstream end of the area where the contact area and the exposed area overlap. After passing intersection B, |Vb| gradually decreases from |Vbmax| to |Vbd|. Therefore, in Example 1, the brush member and pre-exposure device 13 are positioned so that |Vbmax| > |Vbd| is satisfied. This change in Vb increases the potential difference between the brush voltage and Vb, making it difficult for the brush 10 to collect the residual toner. Here, the larger the difference between |Vbmax| and |Vbd|, the larger the potential difference between the brush voltage and the surface potential Vb of the photosensitive drum 1, and therefore the more the collection of the residual toner after transfer is suppressed. Note that in the above-described conventional configuration, |Vbmax|=|Vbd|, so the amount of residual toner remaining near the downstream end of the contact area increases.

[0050] For example, Figure 8(A) shows a case where the surface potential Vb of the photosensitive drum 1 changes from rising to falling in the contact area and becomes lower than Va within the contact area. In this case, the relationship between Va, Vbd, and Vbmax is |Vbd|<|Vba|<|Vbmax|. Therefore, in a case like Figure 8(A), the relationship between Va, Vb (Vbd), and Vd is |Vba-Vbmax|<|Vbmax-Vbd|, which indicates that the change in potential from Vbmax to Vbd is large.

[0051] On the other hand, if the brush 10 is densely packed and the exposure intensity of the pre-exposure device 13 in the contact area is low, making it difficult for the surface potential Vb of the photosensitive drum 1 in the exposed area to decrease, |Vbd| ≧ |Vba| may be satisfied, as shown in Figure 8(B). Note that even in the case of Figure 8(B), the presence of intersection B in the contact area causes the potential difference between the brush voltage and the surface potential Vb of the photosensitive drum 1 to increase in the downstream area of ​​the contact area, just like in the case of Figure 8(A). However, the degree of this increase is smaller than in the case of Figure 8(A).

[0052] In Example 1, the contact area includes an exposure area by the pre-exposure device 13. However, because the irradiated light is blocked to some extent by the threads 11 of the brush 10, the degree of decrease in surface potential due to exposure is thought to be smaller within the contact area than outside the contact area. Therefore, as shown in FIG. 8C, within the exposure area, a potential change occurs in which the surface potential decreases discontinuously at the downstream end of the contact area, i.e., the point where the influence of light blocking by the brush 10 disappears. Even in this case, as shown in FIG. 8C, the presence of intersection B within the contact area increases the potential difference between the brush voltage and the surface potential Vb of the photosensitive drum 1 in the downstream area of ​​the contact area, so that |Vbmax| > |Vbd| holds. This provides the effect of making it difficult for the residual toner to be collected by the brush 10.

[0053] 8(A) to 8(C) all have in common the essential feature of the present invention that there is a location within the contact area where the surface potential of the photosensitive drum 1 changes from increasing to decreasing due to exposure by the pre-exposure device 13. In other words, there is a location within the contact area where the potential difference between the surface potential of the photosensitive drum 1 and the brush voltage changes from decreasing to increasing due to exposure by the pre-exposure device 13. Therefore, in all of the cases of FIGS. 8(A) to 8(C), it can be said that the surface potential of the photosensitive drum 1 is formed so that |Vbmax|>|Vbd| by exposing the surface of the photosensitive drum 1 with the pre-exposure device 13.

[0054] Therefore, in the contact area downstream of the intersection point B, the negative polarity residual toner is The electrostatic force applied acts in a direction from the brush 10 toward the photosensitive drum 1, and the magnitude of this force increases toward the downstream end of the contact area. Therefore, even near the downstream end of the contact area, the transfer residual toner is less likely to be collected by the brush 10, and the accumulation of transfer residual toner is suppressed.

[0055] As a result, in the first embodiment, it is possible to suppress the occurrence of toner-throw-up images caused by an increase in the transfer residual toner remaining near the downstream end of the contact area.

[0056] 8. Effects of Example 1 Next, a paper feed test conducted to confirm the effects of Example 1 will be described. The paper feed test was conducted under the following conditions: a temperature of 23°C, a relative humidity of 50%, and Xerox Vitality Multipurpose Paper (Letter size, 20 lb) was used as the recording material S. The evaluation image used was an image in which the upper half of the image formation area was a black image and the lower half was a white image, as shown in FIG. 9(a). By using this evaluation image, the transfer residual toner generated during the image formation of the upper half of the black image was sent to the brush. If the transfer residual toner that did not pass through the brush accumulates on the brush, this transfer residual toner causes a toner-spit image in the white image area in the lower half, as shown in FIG. 9(b). Therefore, based on the presence or absence of a toner-spit image in the white image area, it is possible to determine whether the transfer residual toner is accumulating or being spit out by the brush. In the paper feed test, 50 sheets of the evaluation image were continuously fed, and it was confirmed whether a toner-spit image occurred in the white image area in the lower half of the image during the continuous paper feed. A paper feed test was carried out using the conventional configuration and the configuration of Example 1, and the number of sheets on which toner-spit images occurred was counted in units of 10 sheets. Table 1 shows the results. [Table 1]

[0057] The results shown in Table 1 indicate that Example 1 can suppress the occurrence of toner-spit images compared to the conventional configuration. Note that the values ​​in Table 1 are the number of sheets on which toner-spit images occurred, and do not take into account the degree of toner-spit images (number, size), but even when comparing the degree, Example 1 is considered to have a lower degree than the conventional configuration.

[0058] As described above, the configuration of Example 1 makes it possible to suppress toner-spit images that occur due to the accumulation of residual toner on the brush. In Example 1, the light of the pre-exposure device 13 is disposed so as to irradiate the area between the brush 10 and the charging roller 2. However, the same effect can be obtained even if the pre-exposure device 13 is disposed further upstream from the position shown in FIG. 6, and light is emitted from downstream of the brush 10, and the light passes behind the brush 10 and irradiates the surface of the photosensitive drum 1 upstream of the brush 10.

[0059] Next, a verification method for confirming whether the exposure area by the pre-exposure device 13 extends upstream from the downstream end of the contact area as in the first embodiment will be described with reference to Fig. 10. Fig. 10 is a diagram showing the brush 10 of Fig. 6 removed and the measurement probe 14 of a surface potential meter (Trek Model 344) placed in its place. The measurement portion 14a of the measurement probe 14 is positioned so as to measure the surface potential of the photosensitive drum 1 at a position close to the downstream end of area C, within area C corresponding to the contact area before the brush 10 is removed.

[0060] Under the above measurement conditions, the surface potential of the photosensitive drum 1 during the image forming operation is measured. First, the surface potential Von of the photosensitive drum 1 is measured while the pre-exposure device 13 is in the exposure state. Next, Next, a state is created in which the surface of the photosensitive drum 1 is not exposed by the pre-exposure device 13, and the surface potential Voff of the photosensitive drum 1 in this state is measured. If there is a portion in region C corresponding to the contact area where |Von|<|Voff|, it can be said that there is a portion in the contact area where |Von|<|Voff|. This means that the exposure area by the pre-exposure device 13 extends upstream from the downstream end of the contact area, in other words, it can be determined that the exposure area and the contact area have a shared portion and overlap each other.

[0061] Example 2 Next, 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 description thereof will be omitted.

[0062] The fineness of the threads 11a of the brush 10 of Example 2 and the density of the threads 11a in the thread portion 11 are set to 1 to 6 denier and 150 to 350 kF / inch, respectively, in terms of paper dust collection performance, similarly to Example 1. 2 On the other hand, the higher the fineness and density, the more easily the light from the pre-exposure device 13 is blocked, and the smaller the effect of lowering the surface potential of the photosensitive drum 1 in the contact area, and the smaller the effect of promoting the passage of the transfer residual toner. Therefore, in Example 2, a configuration will be described that allows the transfer residual toner to pass through the brush more effectively while ensuring the paper dust collection performance of the brush.

[0063] 1. Configuration of Example 2 The configuration of the brush 10 in Example 2 will be described with reference to FIG. 11 . FIG. 11 is a perspective view of the brush 10 as viewed from the downstream side in the rotation direction of the photosensitive drum 1. Light from the pre-exposure device 13 is irradiated from the front side to the back side of the page in FIG. 11 . FIG. 11(a) is a diagram showing the brush 10 in Example 1, and FIG. 11(b) is a diagram showing the brush 10 in Example 2. In the brush 10 in Example 1, the arrangement of the threads 11a in the thread portion 11 is almost uniform from the base of the base fabric 11b to the tip of the bristles, where the bristles abut against the surface of the photosensitive drum 1. In contrast, the brush 10 in Example 2 has a pile fabric configuration in which multiple pile threads emerge from the base fabric 11b at regular intervals and the threads 11a spread uniformly as they approach the tip of the bristles. In other words, in the raising direction of the thread portion 11, the arrangement of the threads 11a is relatively uniform near the tip of the bristles compared to near the base of the base fabric 11b.

[0064] 2. Operation of Example 2 Next, the effects of the configuration of the second embodiment will be described. In the brush 10 of the first embodiment shown in FIG. 11(a), the gaps between the threads 11a through which the light of the pre-exposure device 13 passes are constant from the tip to the root. In contrast, in the brush 10 of the second embodiment shown in FIG. 11(b), the gaps between the threads 11a through which the light of the pre-exposure device 13 passes are wider near the root D than near the tip. A portion of the light irradiated by the pre-exposure device 13 irradiates the portion of the thread portion 11 of the brush 10 that is closer to the base fabric 11b, i.e., the root portion of the thread portion 11. In the second embodiment, the gaps between the threads 11a are wider near the root portion of the thread portion 11 than near the tip. This makes it difficult for the light irradiated by the pre-exposure device 13 to be blocked, allowing the light to easily pass through the brush 10. As a result, the light irradiated by the pre-exposure device 13 reaches a more upstream side of the surface of the photosensitive drum 1. Therefore, the intersection B between the most upstream optical path A of the light irradiated by the pre-exposure device 13 and the surface of the photosensitive drum 1 is located more upstream. 12, the start position of the exposure area in the contact area (the position of intersection B) is located further upstream, and the potential of the surface of the photosensitive drum 1 in the contact area decreases from the upstream side. Therefore, it is possible to more effectively suppress toner-spit images caused by accumulation of residual toner after transfer.

[0065] 3. Effects of Example 2 In order to confirm the effect of Example 2, a paper feed test similar to that described in Example 1 was carried out, and the results are shown in Table 2. [Table 2]

[0066] From the results in Table 2, it is clear that in Example 2, the occurrence of toner-spit images can be more reliably suppressed than in Example 1.

[0067] As described above, the configuration of the second embodiment can suppress the occurrence of toner-throw-up images caused by the accumulation of transfer residual toner on the brush.

[0068] Example 3 Next, a description will be given of a third embodiment of the present invention. The basic configuration and operation of the image forming apparatus of the third embodiment are the same as those of the image forming apparatus of the first embodiment. Therefore, in the image forming apparatus of the third embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of the first embodiment are given the same reference numerals as those of the image forming apparatus of the first embodiment, and detailed description thereof will be omitted.

[0069] In the third embodiment, a configuration will be described in which the paper dust collecting ability of the brush is ensured and the transfer residual toner can pass through the brush more effectively.

[0070] 1. Configuration of Example 3 The configuration of the brush 10 in Example 3 will be described with reference to Fig. 13. Fig. 13 is a diagram showing a cross section of the brush 10 taken along an imaginary plane perpendicular to the rotation axis of the photosensitive drum 1. Fig. 13(a) shows the brush 10 of Example 1, and Fig. 13(b) shows the brush 10 of Example 3. In the brush 10 of Example 1, the length of each thread 11a of the thread portion 11 is uniform, and the base fabric 11b is fixed so as to be parallel to an imaginary tangent plane P of the surface of the photosensitive drum 1 in the center of the contact area. Therefore, the penetration amount of the thread 11a is approximately uniform throughout the entire contact area (from the upstream end to the downstream end), and 11a abuts uniformly against the surface of the photosensitive drum 1 within the contact area.

[0071] On the other hand, in the brush 10 of Example 3, the length of each thread 11a of the thread portion 11 is uniform, and the base fabric 11b is inclined by an angle θ toward the upstream side in the rotation direction of the photosensitive drum 1 (the opposite direction to the rotation direction) with respect to the imaginary tangent plane P of the surface of the photosensitive drum 1 at the center of the contact area. As a result, the penetration amount of the thread 11a is greatest at the upstream end of the contact area and gradually decreases toward the downstream end.

[0072] In Example 1, the penetration amount of the thread 11a is approximately uniform at 1.5 mm from the upstream end to the downstream end of the contact area, whereas in Example 3, the penetration amount of the thread 11a is 2.5 mm at the upstream end of the contact area and 0.5 mm at the downstream end.

[0073] 2. Operation of Example 3 The effect of the configuration of Example 3 will be explained. In Example 1, as shown in FIG. 13(a), the penetration depth of the bristles of the threads 11a of the brush 10 is uniform at about 1.5 mm throughout the entire contact area. On the other hand, in Example 3, as shown in FIG. 13(b), the penetration depth of the bristles of the threads 11a near the upstream end of the contact area is about 2.5 mm, which is larger than that of Example 1, and the paper dust blocking effect at the upstream end is higher than that of Example 1. Also, the penetration depth of the threads 11a near the downstream end of the contact area is about 0.5 mm. Since the contact area between the yarn 11a and the surface of the photosensitive drum 1 is smaller than that of Example 1, the contact area between the yarn 11a and the surface of the photosensitive drum 1 is small, and light from the pre-exposure device 13 is easily irradiated onto the surface of the photosensitive drum 1. Therefore, the surface potential of the photosensitive drum 1 due to exposure by the pre-exposure device 13 can be more effectively reduced near the downstream end of the contact area.

[0074] As a result, the brush 10 of Example 3 has paper dust collecting performance equal to or greater than that of Example 1, and can more reliably suppress the occurrence of toner-spit images due to accumulation of transfer residual toner.

[0075] 3. Effects of Example 3 In order to confirm the effect of Example 3, a paper feed test similar to that described in Example 1 was carried out, and the results are shown in Table 3. [Table 3]

[0076] From the results in Table 3, it is clear that in Example 3, the occurrence of toner-spit images can be more reliably suppressed than in Example 1.

[0077] As described above, the configuration of Example 3 has paper dust collection performance equal to or better than that of Example 1, and can suppress toner-spit images that occur due to the accumulation of residual toner on the brush. [Explanation of symbols]

[0078] 1: photosensitive drum, 2: charging roller, 3: developing device, 5: transfer roller, 10: brush, 13: pre-exposure device

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 means for supplying a developer to the surface of the image carrier charged by the charging means to form a developer image; a transfer means for forming a transfer portion between the image carrier and the transfer means and transferring the developer image from the image carrier to a transfer-receiving body; a brush having a brush portion 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, the brush having a base fabric and a thread portion made of a plurality of threads extending from the base fabric; voltage application means for applying a voltage to the brush; a pre-exposure unit that exposes a surface of the image carrier downstream of the brush unit 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 recovered by the developing means, an upstream end of an exposure area on the surface of the image carrier that is exposed by the pre-exposure unit in the rotation direction of the image carrier is located upstream of a downstream end of a contact area on the surface of the image carrier that comes into contact with the brush in the rotation direction of the image carrier, and the exposure area includes at least a part of the contact area; In the raising direction of the yarn, the arrangement of the yarn is relatively uniform near the tip of the yarn compared to near the base of the yarn portion which is close to the base fabric, An image forming apparatus, characterized in that a part of the light emitted by the pre-exposure means is irradiated to a part of the thread portion close to the base fabric.

2. 2. The image forming apparatus according to claim 1, wherein a part of the light emitted by said pre-exposure means is irradiated onto said thread portion of said brush, and the light not shielded by said thread portion exposes the surface of said image carrier.

3. 3. The image forming apparatus according to claim 1, wherein the base fabric is parallel to a virtual tangent plane that contacts the surface of the image carrier at a center of the contact area in the rotation direction of the image carrier.

4. 3. An image forming apparatus according to claim 1, wherein the base fabric is inclined in a direction opposite to the rotation direction of the image carrier with respect to a virtual tangent plane that contacts the surface of the image carrier at the center of the contact area in the rotation direction of the image carrier.

5. The length of each thread of the thread portion is uniform, 3. The image forming apparatus according to claim 1, wherein the penetration amount of each thread of the thread portion into the surface of the image carrier is uniform over the entire contact area.

6. The length of each thread of the thread portion is uniform, 3. The image forming apparatus according to claim 1, wherein the penetration amount of each thread of the thread portion into the surface of the image carrier decreases toward the downstream end of the contact area in the rotation direction of the image carrier.

7. 7. The image forming apparatus according to claim 1, wherein the brush is made of pile fabric.

8. 8. The image forming apparatus according to claim 1, wherein the polarity of the voltage applied by said voltage applying means is the same as the normal charging polarity of said developer.

9. The developing means supplies a developer charged to a normal polarity to the surface of the image carrier charged by the charging means to form a developer image, the voltage applying means applies a voltage of the normal polarity to the brush; The image forming apparatus of claim 1, characterized in that when the surface potential of the image carrier downstream of the transfer section and upstream of the brush section in the rotation direction of the image carrier is Va, and the surface potential of the image carrier in the contact area on the surface of the image carrier that comes into contact with the brush is Vb, by exposing the surface of the image carrier by the pre-exposure means, a surface potential is formed in the area of ​​the brush section on the surface of the image carrier so that |Vb|<|Va|.

10. An image forming apparatus as described in claim 9, wherein by exposing the surface of the image carrier by the pre-exposure means, a surface potential of Vb is formed so that |Vb| < |Va| in the area of ​​the brush portion on the surface of the image carrier downstream from the center in the direction of rotation of the image carrier.

11. An image forming apparatus as described in claim 1, characterized in that when the surface potential of the image carrier in the contact area where the surface of the image carrier comes into contact with the brush is Vb, the surface potential of the image carrier at the upstream end in the rotation direction of the image carrier of the exposure area exposed by the pre-exposure means in the contact area is Vbmax, and the surface potential of the image carrier near the downstream end in the rotation direction of the image carrier of the area where the exposure area and the contact area overlap on the surface of the image carrier is Vbd, by exposing the surface of the image carrier by the pre-exposure means, the surface potential is formed so that |Vbmax|>|Vbd|.

12. An image forming apparatus as described in claim 1, characterized in that when the surface potential of the image carrier when exposure by the pre-exposure means is Von and the surface potential of the image carrier when exposure by the pre-exposure means is not performed is Voff, there is a portion of the contact area on the surface of the image carrier that comes into contact with the brush such that |Von| < |Voff|.

13. The brush has bristles that come into contact with the surface of the image carrier, and the density of the bristles is 150 to 350 kF / inch. ２ 13. Any one of claims 1 to 12, characterized in that Item 1. The image forming apparatus according to item 1.

Images