Image forming apparatus

Abstract

In a configuration that includes a brush that comes into contact with a charged roller, image artifacts are suppressed. [Solution] The device comprises a brush member having bristles that come into contact with a charging roller. In the brush portion, the bristles of the brush member are in contact with the charging roller per unit area. The ratio of the rotational component of the charging roller to the axial component of the charging roller in the direction in which the bristles extend is defined as the degree of rectification. The ratio of the area in the brush portion where the bristles of the brush member are in contact with the charging roller per unit area is defined as the contact area ratio. When the brush portion is divided into a first region located upstream from the center and a second region located downstream from the center along the rotational direction of the charging roller, i) the degree of rectification in the first region is greater than the degree of rectification in the second region, ii) the contact area ratio in the first region is 10% or more and 30% or less, and iii) the contact area ratio in the second region is 10% or more and 20% or less.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus that uses an electrophotographic recording method such as a laser printer, a copier, a facsimile machine, etc. The image forming apparatus forms an image on a recording medium using an image forming process such as an electrophotographic process, an electrostatic recording process, a magnetic recording process, etc. For example, it includes copiers, printers (such as LED printers, laser beam printers, etc.), facsimile devices, word processors, and their combined functions.

Background Art

[0002] In an electrophotographic image forming apparatus using an electrophotographic forming process, a contact charging method using a charging roller as a charging member for charging a photosensitive drum, which is an image carrier, has been put into practical use. This is to bring the charging roller into contact with the photosensitive drum, apply a charging voltage to the charging roller, and charge the surface of the photosensitive drum to a predetermined polarity and potential. Since this charging roller comes into contact with the surface of the photosensitive drum, dirt such as an external additive that controls fluidity and chargeability, which is externally added to the surface of the toner, adheres to the surface of the charging roller. Therefore, image defects may occur due to the dirt adhering to the surface of the charging roller. In particular, in a cleanerless system, since there is no cleaning means arranged in contact with the surface of the photosensitive drum, dirt such as an external additive adhering to the surface of the photosensitive drum easily adheres to the charging roller as it is.

[0003] Therefore, in Patent Document 1, a method of bringing a brush-shaped cleaning member into contact with the charging roller as a cleaning means for removing dirt on the charging roller has been proposed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, Patent Document 1 had the following problems. When the environment in which the image forming apparatus is installed is not a clean indoor environment such as an office building, but rather an outdoor environment in an area where sand and dust are constantly blown around, foreign matter such as sand and dust may enter the main body of the image forming apparatus through gaps or paper. If this foreign matter adheres to the electrostatic roller as dirt, image defects may occur.

[0006] The present invention has been made in view of the above points, and aims to suppress image artifacts in a configuration in which a brush is provided to contact a charging roller. [Means for solving the problem]

[0007] The above objective is achieved by the electrophotographic image forming apparatus according to the present invention. The image forming apparatus for forming an image on a recording material comprises: a rotatable image carrier; a rotatable charging roller that contacts the image carrier to form a charged portion and charges the surface of the image carrier with the charged portion; and a brush member that contacts the surface of the charging roller to form a brush portion, the brush member having bristles that contact the charging roller, wherein, per unit area of ​​the brush portion, the bristles of the brush member are in contact with the charging roller, and the ratio of the rotational component of the charging roller to the axial component of the charging roller in the direction in which the bristles extend When the ratio is defined as the degree of rectification, and the ratio of the area in the brush portion where the bristles of the brush member are in contact with the charging roller per unit area is defined as the contact area ratio, when the brush portion is divided into a first region located upstream from the center and a second region located downstream from the center along the rotation direction of the charging roller, the following characteristics are observed: i) the degree of rectification in the first region is greater than the degree of rectification in the second region, ii) the contact area ratio in the first region is 10% or more and 30% or less, and iii) the contact area ratio in the second region is 10% or more and 20% or less. [Effects of the Invention]

[0008] According to the present invention, in a configuration in which a brush is provided to contact the charging roller, image artifacts can be suppressed. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram of the image forming apparatus in Example 1. [Figure 2] This is a control block diagram for Example 1. [Figure 3] This is a cross-sectional view of the brush member that contacts the surface of the photosensitive drum 1 in Example 1. [Figure 4] This is a schematic diagram of the brush member that contacts the charging roller in Example 1. [Figure 5] This is a schematic diagram illustrating the effect of the brush member in contact with the charging roller in Example 1. [Figure 6] This figure shows the method for observing the contact surface using a glass plate in Example 1. [Figure 7] This figure shows the mechanism by which image defects occur due to foreign matter in Example 1. [Figure 8] This is an explanatory diagram of the drive system for the photosensitive drum and charging roller in Example 1. [Figure 9] This is an explanatory diagram of the photosensitive drum and the drive train of the charging roller in Example 1. [Figure 10] This figure shows the image artifacts in Example 1. [Figure 11] This figure shows observation images of the contact surface and the method for calculating the degree of rectification in Examples 1 and 2. [Figure 12] This figure shows examples of nip observation images with different contact area ratios in Example 1. [Figure 13] This figure shows the nip observation image of the configuration confirmed in the verification experiment in Example 2. [Figure 14] This figure shows the mechanism by which image defects occur due to paper dust accumulation in Example 2. [Figure 15] This figure shows the method for calculating the degree of rectification using actual observation images in Example 2. [Figure 16]It is a diagram showing a method for calculating the rectification degree in the actual observation image in Example 2. [Figure 17] It is a diagram showing examples of nip observation images with different rectification degrees in Example 2. [Figure 18] It is a diagram showing the relationship between the rectification degree and the ease of paper dust penetration in Example 2. [Figure 19] It is a diagram showing the relationship between the contact area ratio in the downstream part of the nip and the ease of paper dust penetration in Example 2.

Embodiments for Carrying out the Invention

[0010] Hereinafter, exemplary preferred embodiments of this invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in this embodiment are not intended to limit the scope of this invention only to those, unless otherwise specified. Also, the materials, shapes, etc. of the members once described in the following description are the same as the initial description in the subsequent description unless otherwise described again. In particular, well-known techniques or publicly known techniques in the relevant technical field can be applied to configurations and processes not specifically illustrated or described. Also, duplicate explanations may be omitted.

Examples

[0011] (Configuration of the Image Forming Apparatus) Figure 1 will be used to illustrate the outline of the image forming apparatus 100 according to Embodiment 1. When the control unit 220 issues an instruction to execute an image forming operation to the image forming apparatus 100, the photosensitive drum 1, which is the image carrier, is rotated clockwise in the direction of the arrow by the motor drive unit 223, as shown in Figure 1. The photosensitive drum 1 is a photoreceptor molded into a cylindrical shape. The photosensitive drum 1 in this embodiment has a photosensitive layer formed of a negatively charged organic photoreceptor on a drum-shaped substrate made of aluminum. More specifically, the photosensitive drum 1 is a rigid body constructed by sequentially coating a resistance layer, an undercoat layer, and a photosensitive layer on the outer surface of an aluminum cylinder with a diameter of 24 mm (also referred to as φ24) using a dipping coating method, and the photosensitive layer has a charge generation layer and a charge transport layer. The thickness of the charge transport layer is 22 μm. The charging roller 2, as a charging member, contacts the surface of the photosensitive drum 1 to form a charged area P1, and the surface of the photosensitive drum 1 is uniformly charged in the charged area P1. The charging roller 2 contacts the photosensitive drum 1 with a predetermined pressure, forming a charged portion P1. In this embodiment, the contact nip width between the charging roller 2 and the photosensitive drum 1 in the rotational direction is approximately 1 mm. Furthermore, a DC voltage charging voltage is applied from a high-voltage power supply 224, which is a charging power supply and is a charging voltage application circuit, thereby charging the surface of the photosensitive drum 1 to a predetermined potential. The charging roller 2 has a core metal with a diameter of 5 mm, a hydrin rubber base layer, and a urethane surface layer, and is configured to have an outer diameter of 10 mm. The resistance of the charging roller 2 is 1 × 10⁻¹⁰ 6 The resistance is less than Ω, and the hardness is 70 degrees according to the MD-1 rubber hardness tester. In this embodiment, a DC voltage was used for charging, but this is not the only option; a DC voltage superimposed on an AC voltage may also be used. Further details regarding the charging roller 2 will be described later.

[0012] In this embodiment, a charging brush member 11 is arranged as a first brush member that contacts the surface of the charging roller 2. Details of the charging brush member 11 will be described later.

[0013] The exposure device 3, acting as a scanner unit, irradiates the photosensitive drum 1 with a laser L based on image information received from an external source, thereby exposing the surface of the photosensitive drum 1. This forms an electrostatic latent image on the surface of the photosensitive drum 1.

[0014] This embodiment employs an inverted development method. Therefore, a charging voltage with the same negative polarity as the normal polarity of the toner developer is applied to the charging roller 2 from the high-voltage power supply 224, and the surface of the photosensitive drum 1 is charged to a negative dark area potential Vd. After charging, the bright area potential Vl, which is the region exposed by the exposure device 3, has a lower absolute value than the dark area potential. In this embodiment, Vd = -700V and Vl = -100V.

[0015] In the developing device 4, the toner contained in the toner storage section 45 is agitated by the stirring member 43 and supplied to the developing roller 41, which is the developing member, by the supply roller 42. The toner carried on the developing roller 41 is restricted to a predetermined layer thickness when it passes through the developing blade 44. The developing blade 44 is in contact with the developing roller 41 with a predetermined pressure. The developing blade 44 is mainly composed of a material (for example, iron) that is positively polarized with respect to the main component of the toner (binding resin) in the charge series. As a result, the developing blade 44 becomes charged by rubbing against the toner.

[0016] The toner, charged to the correct polarity by the rotation of the developing roller 41, is supplied to the developing unit P2, which is in contact with the photosensitive drum 1. In this embodiment, a so-called contact developing method is used. The toner, whose correct charge polarity is negative, is transferred to the photosensitive drum 1 by the potential difference between the potential of the developing roller 41 and the potential of the bright areas on the surface of the photosensitive drum 1. In this embodiment, the developing voltage is set to -350V. As a result, the electrostatic latent image on the surface of the photosensitive drum 1 is developed and visualized as a toner image. The toner image formed on the surface of the photosensitive drum 1 is transported to the transfer unit P3 while supported on the photosensitive drum 1.

[0017] In parallel with the above process, sheets T as recording material are fed one by one from the paper feed cassette 6 by the paper feed unit 5, and the sheets T are transported to the transfer unit P3 by the transport roller 7. A transfer voltage with a positive polarity opposite to the normal polarity of toner is applied to the transfer roller 8, and the toner image is transferred from the photosensitive drum 1 to the sheet T in the transfer unit P3. Any remaining toner that was not transferred on the photosensitive drum 1 is collected by the developing roller 41 in a cleanerless manner using a drum brush member 12 as a second brush member. The drum brush member 12 is positioned so as to be in contact with the surface of the photosensitive drum 1 in the region downstream of the transfer unit P3 and upstream of the charging unit P1 in the rotational direction of the photosensitive drum 1. Details of the drum brush member 12 will be described later.

[0018] The sheet T that has passed through the transfer section P3 is transported to the fuser unit 9. The fuser unit 9 heats the sheet T while holding it in place, fixing the toner to the sheet T. The sheet T that has passed through the fuser unit 9 is discharged to the outside of the image forming apparatus 100 by the paper discharge roller 10.

[0019] In this embodiment, the photosensitive drum 1, charging roller 2, charging brush member 11, and drum brush member 12 are collectively referred to as a drum unit 201, the developing device 4 as a developing unit 202, and the drum unit 201 and the developing unit 202 together as a process unit 200. The process unit 200 may be configured to be detachable from the image forming apparatus 100, or the drum unit 201 and the developing unit 202 may be configured to be detachable from the image forming apparatus 100 as a drum cartridge and a developing cartridge, respectively. In this embodiment, the process unit 200 is fixed to the image forming apparatus 100.

[0020] (Control block diagram) The control configuration of the image forming apparatus 100 will be explained using the block diagram in Figure 2.

[0021] The main controller 211 shown in Figure 2 has a control unit 220 (Central Processing Unit: CPU) as a control means, which is the central element for performing calculations. It also has a main memory 221 such as ROM and RAM as a storage means, and an input / output (I / O) interface (I / F) 222 for input and output of information with peripheral devices. The ROM of the main memory 221 has a control program stored in advance. The control unit 220 is a control means that comprehensively controls the operation of the image forming apparatus 100, and each control target in the image forming apparatus 100 is connected via the input / output I / F 222. The control unit 220 controls the exchange of various electrical information signals and the timing of drives. The motor drive unit 223 refers to various motors and is a power source for rotating the polygon scanner, photosensitive drum 1, charging roller 2, developing roller 41, supply roller 42, etc., located inside the scanner unit 3, and operates based on control signals from the control unit 220. The high-voltage power supply 224 is a power source that applies high voltage to the photosensitive drum 1, charging roller 2, developing roller 41, supply roller 42, transfer roller 8, fixing device 9, drum brush member 12, etc. In this embodiment, the high-voltage power supply 224 includes a charging voltage application unit that applies a charging voltage to the charging roller 2 and a developing voltage application unit that applies a developing voltage to the developing roller 41. The charging voltage application unit and the developing voltage application unit may each be configured as independent high-voltage power supplies. The temperature and humidity sensor 225 is a sensor for detecting the temperature and humidity of the environment in which the image forming apparatus 100 is used, and is used to change the control according to the detected temperature and humidity. The non-volatile memory 208, which is located in the image forming unit such as a process cartridge, is connected to the main unit controller 211 via a memory communication unit 226 which acts as an acquisition unit, and information can be read and written. In this embodiment, a non-contact non-volatile memory is used as the storage means, but for example, a contact non-volatile memory, a non-contact non-volatile memory, or a volatile memory with a power supply can be used as an appropriate means.

[0022] (Cleanerless brush system) Next, we will explain the cleanerless method using the drum brush member 12 (second brush member), also known as the cleanerless brush method. In this embodiment, residual toner that remains on the surface of the photosensitive drum 1 without being transferred to the sheet T in the transfer section P3 is collected by the developing roller 41 when it reaches the developing section P2 due to the rotation of the photosensitive drum 1. The residual toner collected by the developing roller 41 is mixed with other toner in the toner storage section 45 and used again for developing.

[0023] The drum brush member 12 plays the role of dispersing residual toner that adheres to the photosensitive drum 1 after passing through the transfer section P3 on the surface of the photosensitive drum 1. If residual toner is present locally on the photosensitive drum 1, the surface of the charging roller 2 may become locally contaminated, potentially causing image defects due to poor charging. Therefore, by having the drum brush member 12 in contact with the surface of the photosensitive drum 1, the residual toner is evened out, and as a result, the above-mentioned image defects can be suppressed. The drum brush member 12 also plays a role in charging the residual toner. By causing frictional charging through contact between the drum brush member 12 and the toner, adhesion to the charging roller 2 can be suppressed, and the above-mentioned image defects can be suppressed. As described above, a brush voltage is applied to the drum brush member 12 from the high-voltage power supply 224. By applying a brush voltage of -350V to the drum brush member 12, the residual toner, which is charged with the correct polarity, electrically passes through the drum brush section P4, which is the contact point between the drum brush member 12 and the photosensitive drum 1. Furthermore, by applying +200V, residual toner charged with the correct polarity and the opposite polarity passes through the brush section. The brush voltage may be appropriately varied depending on the polarity of the toner. Alternatively, a configuration in which no brush voltage is applied to the drum brush member 12 may be adopted.

[0024] The remaining toner on the surface of the photosensitive drum 1, after passing through the contact area P4 between the drum brush member 12 and the photosensitive drum 1, reaches the charged area P1 as the photosensitive drum 1 rotates. Toner without polarity and toner with reverse polarity contained in the remaining toner is recharged by friction between the photosensitive drum 1 and the charging roller 2, and by discharge due to the potential difference generated between the photosensitive drum 1 and the charging roller 2. In this embodiment, the difference in peripheral speed between the photosensitive drum 1 and the charging roller 2 is 5%. That is, the peripheral speed of the charging roller 2, or the surface movement speed of the charging roller 2, is set to 105% of the peripheral speed of the photosensitive drum 1, or the surface movement speed of the photosensitive drum 1. This promotes triboelectric charging of the toner and suppresses the adhesion of remaining toner to the charging roller 2. Both the charging roller 2 and the photosensitive drum 1 are rotated by the motor drive unit 223. Here, the charging roller 2 may be configured to rotate in accordance with the rotation of the photosensitive drum 1.

[0025] The remaining toner on the surface of the photosensitive drum 1 that has passed through the charging section P1 reaches the developing section P2 as the photosensitive drum 1 rotates. Since the remaining toner that has passed through the charging section P1 is charged with normal polarity, the remaining toner on the surface of the photosensitive drum 1 that is carried in the region of the photosensitive drum 1 where the dark area potential Vd is formed is transferred to the developing roller 41 due to the potential difference between the dark area potential Vd and the developing potential. On the other hand, the remaining toner carried in the region of the photosensitive drum 1 where the bright area potential Vl is formed remains without being transferred to the developing roller 41 due to the potential difference between the bright area potential Vl and the developing potential. The remaining toner carried in the region of the photosensitive drum 1 where the bright area potential Vl is formed is then sent to the transfer section P3 as part of the developed toner image and transferred to the sheet T.

[0026] This method does not include a cleaning device for removing residual toner from the photosensitive drum 1, but instead has a drum brush component 12 for dispersing the toner. Therefore, it is specifically called a cleanerless brush method among cleanerless methods.

[0027] (Drum brush component) The image forming apparatus 100 has a drum brush member 12 as a second brush member that contacts the surface of the photosensitive drum 1 at the brush portion. In Example 1, the drum brush member 12 plays a role in scattering residual toner and recharging residual toner as described above, as well as collecting paper dust adhering to the surface of the photosensitive drum 1. The drum brush member 12 contacts the surface of the photosensitive drum 1 downstream of the transfer portion P3 and upstream of the charging portion P1 in the rotational direction of the photosensitive drum 1, forming a contact portion P4.

[0028] Figure 3(a) shows a cross-section of the drum brush member 12 in its standalone state (not in contact with the photosensitive drum 1) along a virtual plane perpendicular to the rotation axis of the photosensitive drum 1. Figure 3(b) shows the same cross-section of the drum brush member 12 in contact with the photosensitive drum 1.

[0029] As shown in Figure 3, the drum brush member 12 is a pile fabric having a yarn portion 12a as a second bristle material consisting of multiple conductive nylon threads that contact and rub against the surface of the photosensitive drum 1, and a base fabric 12b that supports the yarn portion 12a. When the yarn portion 12a is not in contact with the photosensitive drum 1, it extends perpendicularly from the base fabric 12b. The yarn portion 12a is uniformly distributed on the base fabric 12b. The drum brush member 12 is positioned to contact the photosensitive drum 1 downstream of the transfer portion and upstream of the charging portion in the rotational direction of the photosensitive drum 1.

[0030] The drum brush member 12 is positioned so that its longitudinal direction is parallel to the rotation axis direction, which is 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 for the thread portion 12a. Although conductive thread was used for the thread portion 12a in Example 1, insulating thread may also be used. The thread portion 12a is not limited to being formed by twisting fibers, as long as it is thread-like.

[0031] As shown in FIG. 3(a), in the state where the drum brush member 12 is in a single body, that is, in a state where no force is acting from the outside to bend the yarn portion 12a (natural state), the distance from the base fabric 12b to the tip of the yarn portion 12a is set as L1. The base fabric 12b 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 drum brush member 12 is fixed. The drum brush member 12 is fixed such that the shortest distance L2 from the base fabric 12b of the drum brush member 12 fixed to the support member to the surface of the photosensitive drum 1 becomes shorter than the length L1 of the yarn portion 12a 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 drum brush member 12 with respect to the photosensitive drum 1. Since L2 < L1, in the usage state of the drum brush member 12, that is, when the drum brush member 12 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 yarn portion 12a bends toward the rotation direction of the photosensitive drum 1. The contact portion P4 between the tip of the yarn portion 12a provided on the most upstream side among the bent yarn portions 12a and the surface of the photosensitive drum 1 is the upstream end of the contact region. The contact portion P4 between the tip of the yarn portion 12a provided on the most downstream side among the bent yarn portions 12a and the surface of the photosensitive drum 1 is the downstream end of the contact region. The contact mode between the drum brush member 12 and the surface of the photosensitive drum 1 is the contact between the yarn portion 12a 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 drum brush member 12 do not contact in the region between adjacent yarns 12a. A contact portion is formed by the surface of the photosensitive drum 1 in the contact region and the drum brush member 12 that contacts the surface of the photosensitive drum 1. The same can be said for the charging brush member 11 described later.

[0032] The dimensions of the drum brush member 12 in the longitudinal direction (parallel to the rotation axis of the photosensitive drum 1) are set so that the drum brush member 12 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. The dimensions of the drum brush member 12 in the short direction (parallel to the circumferential and rotational directions of the photosensitive drum 1) are set appropriately according to the lifespan of the image forming apparatus 100 and process unit 200.

[0033] The drum brush member 12 is fixed in 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 drum brush member 12 collects (recovers) paper dust and other deposits that have been transferred from the recording material T to the photosensitive drum 1 in the transfer section P3. This reduces the amount of paper dust that moves to the charging section P1 and developing section P2 downstream of the drum brush member 12 in the direction of movement (rotation) of the photosensitive drum 1.

[0034] In Example 1, the natural length L1 of the thread portion 12a of the drum brush member 12 was 4.8 mm, and the penetration depth of the drum brush member 12 into the photosensitive drum 1 was 1.5 mm (L2 = 3.3 mm). The length L3 in the short direction of the drum brush member 12 was 5 mm, and the length in the long direction was 230 mm. The fineness (thickness) of the thread 12a was 2 denier (representing the thickness of a thread where 9000 m weighs 2 g), and the density was 240 kF / inch 2 (kF / inch 2 ¹ is a unit of brush density, indicating the number of filaments per square inch. In other words, 1 denier is the thickness of a thread where 1 gram is per 9000 meters, or 1 kF / inch. 2This indicates that there are 1000 threads per square inch. The arrangement of the thread portion 12a is almost uniform from the base of the base fabric 12b to the tip of the bristles, which is the contact point with the surface of the photosensitive drum 1. Note that the length of the drum brush member 12 in the short direction is just an example and is not limited thereto. The longer the length of the drum brush member 12 in the short direction, the longer the paper dust can be collected. The length of the drum brush member 12 in the longitudinal direction is just an example and is not limited thereto. For example, the length of the drum brush member 12 in the longitudinal direction can be set according to the maximum paper width of the image forming apparatus 100. Also, the fineness of the threads 12a of the drum brush member 12 is just an example and is not limited thereto. The fineness of the threads 12a can be determined considering the ease with which paper dust can pass through. If the fineness of the drum brush member 12 is too small, the force that blocks the paper dust is weak, and the paper dust can easily pass through. If paper dust passes through the drum brush member 12, the charging of the photosensitive drum 1 by the charging roller 2 may be hindered, potentially causing image defects. Furthermore, if the fineness of the threads 12a of the drum brush member 12 is too high, it may not be able to collect toner or fine paper dust, resulting in uneven toner adhesion in the rotation axis direction (the longitudinal direction of the charging roller 2), potentially causing uneven image density or image defects due to poor charging at the paper dust adhesion points. The density of the threads 12a of the drum brush member 12 is merely an example and is not limited to this. The density of the threads 12a can be set considering toner passability and paper dust collection. If the density of the threads 12a of the drum brush member 12 is too high, toner passability is low, causing toner to stack, which can lead to toner contamination inside the image forming apparatus 100 due to the scattering of the stacked toner. Conversely, if the density of the threads 12a of the drum brush member 12 is too low, sufficient paper dust collection performance may not be achieved. The fineness and density of yarn 12a are 1-6 denier and 150-350 kF / inch, respectively, from the perspective of paper dust collection performance. 2 It is preferable that the drum brush member 12 has a short-length L3 of 3 mm or more from the viewpoint of ensuring a long lifespan. The contact area ratio of the drum brush member 12 is 40%, and the rectification degree of the drum brush member 12 is 1.3. Details regarding the contact area ratio and rectification degree will be described later.

[0035] A high-voltage power supply 224 is connected to the drum brush member 12 as a means for applying brush voltage. During image formation, a negative polarity DC voltage is applied to the drum brush member 12 as the brush voltage by the high-voltage power supply 224.

[0036] (Charging brush member that contacts the charging roller) Next, the charging brush member 11, which serves as the first brush member that contacts the surface of the charging roller 2 in this embodiment, will be described.

[0037] Figure 4(a) is a front view (viewed from one side of the short edge) of the charging brush member 11. The charging brush member 11 is composed of a conductive thread 11a as the first bristle material, a base fabric 11b, and a support member 11c. The conductive thread 11a is in contact with the surface of the charging roller 2. The conductive thread 11a is formed of, for example, nylon fiber containing carbon as a conductive material and is fixed by being woven into the base fabric 11b. The conductive thread 11a is electrically conductive so that it is at the same potential as the charging roller 2. A conductive adhesive (not shown) is present at the contact area between the base fabric 11b and the support member 11c to prevent the conductive thread 11a from coming loose and to ensure conductivity. The conductive thread 11a is not limited to nylon; rayon or other synthetic resin fibers may also be used. The bristle length L1a is the distance from the adhesive surface between the support member 11c and the base fabric 11b to the tip of the conductive thread 11a, and L4a is the width in which the conductive thread 11a exists in the longitudinal direction LD, which is the first direction. In this embodiment, a base fabric 11b was woven into a flat support member 11c, and a brush was used in which the pile length L1a was constant within the same brush.

[0038] Figure 4(b) is a cross-sectional view of the charging brush member 11 (viewed from one side of the longitudinal direction) with respect to a virtual plane perpendicular to the rotation axis of the charging roller 2. If the short direction, which is the second direction intersecting the first direction, is denoted as SD, then the conductive thread 11a protrudes in a third direction that is perpendicular to both the longitudinal direction LD and the short direction SD. L3a is the width of the conductive thread 11a in the short direction SD. The longitudinal direction LD and the short direction SD are approximately perpendicular to each other.

[0039] Figure 4(c) is a cross-sectional view of the charging brush member 11 in contact with the charging roller 2. The support member 11c is attached to a predetermined position in the image forming apparatus 100 with fixing means such as double-sided tape and is in contact with the charging roller 2. The support member 11c is positioned so that the longitudinal direction LD and the rotation axis direction of the charging roller 2 are parallel, and the distance between the support member 11c and the charging roller 2 is constant. The shortest distance between the support member 11c and the charging roller 2 is defined as the bristle length L2a. The difference between the bristle length L1a and the bristle length L2a is defined as the amount of penetration between the charging brush member 11 and the charging roller 2. <L1aである。

[0040] Figure 4(d) is a cross-sectional view of the state in which the charging brush member 11 is in contact with the charging roller 2 with its position offset in the rotational direction. In the direction perpendicular to the longitudinal direction LD and the transverse direction SD, a straight line extending from the rotational center OA of the charging roller 2 toward the charging brush member 11 is defined as imaginary line A1. In the cross-sectional view of the charging brush member 11, a straight line parallel to this imaginary line A1 and passing through the center OB of the transverse direction SD of the support member 11c is defined as imaginary line A2. The distance between imaginary line A1 and imaginary line A2 is defined as L5a, and the length of L5a is defined as the offset amount. In this case, the center of the support member 11c in the transverse direction and the centers of the conductive thread 11a and the base fabric 11b are assumed to be approximately the same. Therefore, the offset amount is synonymous with the offset amount of the contact position of the conductive thread 11a of the charging brush member toward the charging roller 2.

[0041] Here is an example of the specific size of the charging brush member 11 in this embodiment. The thickness of the conductive thread 11a is 2 denier, and the density is 120 kF / inch. 2 The bristle lengths L1a are 4.75 mm, L3a is 3 mm, L4a is 230 mm, and L5a is 0.5 mm. If the penetration amount is 1.00 mm, L2a becomes 3.75 mm. The brush length L4a is such that the conductive threads 11a of the charging brush member 11 can contact the entire development aperture area (the maximum area where toner is developed) of the longitudinal LD. Under these conditions, when the charging roller 2 is brought into contact as shown in Figure 4(c), the contact width of the conductive threads 11a in the short direction SD is 2.5 mm.

[0042] (Electrostatic roller) The charging roller 2 in this embodiment will be described in detail. The charging roller 2 has a core metal, a 2 mm elastic layer provided on its outer circumference, and a 25 μm surface layer. The diameter of the charging roller 2 in this embodiment is 10 mm. The surface of the surface layer of the charging roller 2 is in contact with the photosensitive drum 1 and is the surface that discharges electricity to the photosensitive drum 1.

[0043] The elastic layer is made of an electronically conductive rubber material. An electronically conductive rubber material is, for example, a binder polymer that does not itself exhibit conductivity, to which carbon black is dispersed as conductive particles (electronically conductive agent) to adjust its electrical resistance.

[0044] As the binder polymer, known materials used in the conductive elastic layer of the charging roller 2 for electrophotographic devices can be used. Examples include hydrin rubber and butadiene rubber. In this example, hydrin rubber was selected.

[0045] The type of carbon black used in the elastic layer is not particularly limited, as long as it is a conductive carbon black capable of imparting conductivity to the elastic layer.

[0046] Furthermore, the elastic layer may contain, if necessary, fillers, processing aids, crosslinking aids, crosslinking accelerators, crosslinking accelerators, crosslinking retarders, softeners, dispersants, colorants, etc., which are commonly used as compounding agents for rubber.

[0047] The surface is coated with a conductive resin such as polycarbonate urethane, which causes the toner to become negatively polarized in the electrostatic series. As explained in the cleanerless brush method, in this embodiment, the peripheral speed ratio of the charging roller is set to 5% plus in the rotational direction relative to the photosensitive drum 1. This promotes the triboelectric charging of the toner, making the toner negatively polarized. Furthermore, rough particles with a polarity that does not hinder the triboelectric charging can be added to the surface. For example, one method is to particleize polycarbonate urethane similar to the surface layer and disperse it. The surface roughness Ra of the charging roller 2 in this embodiment is 1.56 μm or more and 2.36 μm or less.

[0048] In other words, the charging roller 2 does not need to be in close contact with the surface of the photosensitive drum 1 at the charging section P1, but rather contacts the surface of the photosensitive drum 1 at the peaks of the uneven surface formed by the coarse particles. Furthermore, because the surface is uneven, the member used to scrape off foreign matter adhering to the surface of the charging roller 2 is preferably a member with surface-following properties, such as the bristles of the charging brush member 11, as shown in Figures 3, 4, and 6, rather than a straight member with stiffness, such as a sheet.

[0049] (Mechanism of image defects caused by foreign objects) Next, we will explain image defects caused by foreign objects. This phenomenon is particularly likely to occur in cleanerless configurations, such as the one in this embodiment, where there is no cleaning means.

[0050] If the image forming apparatus 100 is installed not in a clean environment such as an office building, but in an environment close to outdoors in a region where sand and dust are constantly present, which was not previously anticipated, foreign matter such as sand may enter the image forming apparatus 100. For example, this may occur when a door (not shown) is opened or closed during jam processing, or when sand adheres to a sheet T and is printed, and then carried into the image forming apparatus 100 via the sheet T. The foreign matter that enters the image forming apparatus 100 is then transferred to the surface of the photosensitive drum 1 by the transfer unit P3, passes through the drum brush contact unit P4, and reaches the charging unit P1, where it becomes jammed between the photosensitive drum 1 and the charging roller 2, scratching the charging roller 2. This can cause image defects due to the scratches on the charging roller 2.

[0051] Figure 7 illustrates the mechanism by which foreign matter causes image defects. Foreign matter adhering to the photosensitive drum 1 reaches the charged area P1 as the photosensitive drum 1 rotates (Figure 7(a)). The size of the foreign matter is 50 μm to 300 μm. Subsequently, as the charging roller 2 and the photosensitive drum 1 come into contact with each other at a predetermined contact pressure, the foreign matter may become embedded in the charging roller 2 when it comes into contact with its surface (Figure 7(b)). Here, the hardness of the surface of the charging roller 2 is lower than the hardness of the surface of the photosensitive drum 1. Hardness is represented by Martens hardness, ASKER-C hardness, and MD-1 hardness, which are due to indentation hardness. The embedded foreign matter reaches the charged area P1 again as the charging roller 2 rotates (Figure 7(c)) and becomes embedded in the charging roller 2 even more strongly. At the same time, it forms scratches on the surface of the photosensitive drum 1. By repeatedly rotating the drum 1, scratches are made at the same location (specific pitch) on the surface, gradually forming deeper grooves (Figure 7(d)). As a result, the grooves become unable to charge, and black dot-like image defects (black spots) occur at equal intervals.

[0052] Foreign objects in this context include metal fragments, resin fragments, minerals such as quartz, and dust. The harder these foreign objects are, the more likely they are to scratch the photosensitive drum 1, resulting in black dots in the image.

[0053] Next, the details of the rotational drive configuration of the charging roller 2 in this embodiment will be explained using Figures 8 and 9. Figure 8 is a diagram showing the longitudinal arrangement of the photosensitive drum 1, the charging roller 2, and the first gear 121 and second gear 112 that transmit the drive. In this embodiment, as shown in Figure 8, the gear flange 121 is fixedly attached to the end of the photosensitive drum 1 in the longitudinal direction. In the longitudinal direction, the side where the gear is located is the drive side, and the other end is the non-drive side. The drive from the drive source 110 is transmitted to the end of the gear flange 121, and the photosensitive drum 1 is rotated. The gear flange 121 has a gear-shaped portion 121a as shown in Figure 8, which meshes and engages with the gear portion 112a of the charging roller gear 112, which is press-fitted into the end of the core metal of the charging roller 2.

[0054] Furthermore, in this embodiment, as shown in Figure 9, the gear 121a of the gear flange 121 of the photosensitive drum 1 has 37 teeth, and the gear 112 of the charging roller 2 has 14 teeth. Based on the above combination of tooth counts and the outer diameters of the charging roller 2 and the photosensitive drum 1, in this embodiment, the speed ratio (surface speed of charging roller 2 / surface speed of photosensitive drum 1, hereinafter referred to as peripheral speed ratio) of the surface speed of the charging roller 2 and the surface speed of the photosensitive drum 1 during rotational drive is approximately 105%. By generating a speed difference between the charging roller 2 and the photosensitive drum 1 (charging section P1), it becomes easier to return the toner adhering to the charging roller 2 to the photosensitive drum 1 through triboelectric charging. Here, the surface speed of the charging roller 2 and the surface speed of the photosensitive drum 1 refer to the surface movement speed of the charging roller 2 and the surface movement speed of the photosensitive drum 1, respectively. These can also be rephrased as the rotational speed of the charging roller 2 and the rotational speed of the photosensitive drum 1, respectively.

[0055] In this embodiment, pressure springs (not shown) are provided on the core metal portions at both ends of the charging roller 2 at the positions indicated by the arrows in Figure 8, via bearings (not shown), to press perpendicularly to the surface of the photosensitive drum 1. The pressing force on the charging roller gear 112 side, i.e., the driving side, is 7.5N, and the pressing force on the opposite side of the charging roller gear 112, i.e., the non-driving side, is 5.6N.

[0056] The reason for the black dot image with a specific pitch is as follows. In this embodiment, as mentioned above, the charging roller 2 is driven to rotate at a constant peripheral speed ratio via the gear 112. First, foreign matter adheres to the charging roller 2, and then scratches the photosensitive drum 1 with the cycle of the charging roller 2. As mentioned above, the charging roller gear 112 has 14 teeth, so it scratches the surface of the photosensitive drum 1 with a pitch equal to the movement of 14 teeth of the gear flange 121 of the photosensitive drum 1 (=φ24×π×14 teeth / 37 teeth). Here, the gear flange 121 of the photosensitive drum 1 has 37 teeth. Therefore, when the charging roller gear 112 and the gear flange 121 of the photosensitive drum 1 are driven to rotate for 518 teeth (=14×37), which is the least common multiple of the number of teeth, it returns to the same position. During this time, the foreign matter on the charging roller 2 scratches the surface of the photosensitive drum 1 once at a pitch of approximately 2 mm (=φ24×π / 37 teeth). If foreign matter remains in the same position on the charging roller 2, it will repeatedly scratch the same spot on the surface of the photosensitive drum 1, causing the charge transport layer on the surface of the photosensitive drum 1 to gradually thin and form depressions. As a result, the accumulated charge can no longer be held in the depressions. Consequently, when the charge transport layer can no longer hold the charge, the developer is developed on the photosensitive drum 1 in the developing unit P2, resulting in a black spot image like that shown in Figure 10. In particular, under high temperature and high humidity conditions, the charge around the depressions tends to flow more easily into the depressions with lower resistance, making the black spots more visible.

[0057] As described above, the persistence of foreign matter on the charged roller 2 is the cause of the black dot image. Therefore, if the foreign matter transferred to the charged roller 2 can be quickly removed, the occurrence of the black dot image can be suppressed.

[0058] Furthermore, in this embodiment, the larger the size of the foreign object, the weaker the adhesion force, and even if it adheres temporarily, it can be removed relatively quickly. On the other hand, the smaller the size of the foreign object, the stronger the adhesion force and the harder it is to remove, but it is easily absorbed by the roughness and elastic deformation of the surface of the charging roller 2. As a result, it is less likely to damage the photosensitive drum 1 and less likely to result in image defects.

[0059] As described above, in this embodiment, due to the size and tendency of foreign matter to adhere, foreign matter in particular, with a size of about 50 to 300 μm, tends to remain on the charging roller 2. Furthermore, if the foreign matter is hard, it tends to damage the photosensitive drum 1 more easily, leading to image defects.

[0060] (Function of the charging brush component that comes into contact with the charging roller) As described above, in order to suppress black spots, it is effective to suppress the strong adhesion of foreign matter to the charging roller 2. Therefore, in this embodiment, a charging brush member 11 (first brush member), which is a cleaning member and foreign matter removal member that comes into contact with the charging roller 2 as described above, is provided.

[0061] The effect of the charging brush member 11 will be explained using Figures 5 and 7. As shown in Figure 7(a), we assume that foreign matter is attached to the surface of the photosensitive drum 1, and that the foreign matter is moved to the charging section P1 by the rotation of the photosensitive drum 1. As shown in Figure 7(b), in the charging section P1, the surface of the photosensitive drum 1 and the surface of the charging roller 2 come into contact, causing the foreign matter attached to the surface of the photosensitive drum 1 to become embedded in the surface of the charging roller 2. When the foreign matter that has begun to become embedded in the charging roller 2 (Figure 5(a)) reaches the position P5 of the charging brush member 11, the fibers of the conductive thread 11a come into contact with the foreign matter (Figure 5(b)), and the foreign matter is scraped off the charging roller 2 (Figure 5(c)). The scraped-off foreign matter may be ejected from the surface of the charging roller 2 to the outside, or it may remain on the surface of the charging roller 2. Even if foreign matter remains on the surface of the charging roller 2, it is moved by the conductive thread 11a of the charging brush member 11 with each rotation of the charging roller 2, thus reducing the likelihood of it becoming deeply embedded in the charging roller 2. Therefore, it is possible to suppress the occurrence of black spots.

[0062] (Method for calculating the contact area ratio of a 1mm square) As explained above, various image artifacts can be suppressed by the contact between the charging brush member 11 and the surface of the charging roller 2. In this case, it was found that the contact state between the conductive thread 11a of the charging brush member 11 and the charging roller 2 affects the degree to which image artifacts are suppressed.

[0063] The following describes how to calculate the contact area ratio (hereinafter referred to as the contact area ratio) of a 1 mm square between the charging roller 2 and the charging brush member 11 in this embodiment. To observe the contact state, the charging brush member 11 was brought into contact with a slide glass 15, which is a glass plate, as shown in Figure 6(a), and the contact surface was photographed with a microscope. For the purpose of photography, the slide glass 15 is used as a substitute for the charging roller 2, but it is assumed that the contact state with the charging roller 2 can be simulated. In this embodiment, considering the curvature of the charging roller 2, the glass plate 15 was tilted in the direction SD of the short side of the charging brush member 11 and brought into contact with it. If the tilt angle is α, the radius of the charging roller 2 is R (mm), and the offset amount of the charging brush member 11 is C (mm), then α can be calculated by the following equation 1.

[0064]

number

[0065] In this embodiment, R=5 and C=0.5, so the inclination angle α was 6°. When calculating, it is necessary to change R and C according to the configuration. The areas where the conductive thread 11a was in contact with the glass plate 15 and areas where it was not was determined by the color of the image. The contact surface was photographed using a Keyence VHX-6000 under the conditions of magnification ×200, ring illumination, shutter speed 67 msec (supercharge), and gain 5.3 dB. As shown in Figure 6(b), the glass plate 15 and the charging brush member 11 were divided into two parts at the nip center, with the end 15a on the side with a larger penetration amount designated as the upstream part and the end 15b on the side with a smaller penetration amount designated as the downstream part, and one photograph was taken at each point. Figure 11(a) is an image obtained by binarizing the contact area to white and the non-contact area to black based on the actual microscope images of the upstream and downstream parts. Binarization was performed after cropping the observed image to a 1 mm square at an arbitrary location. Image processing software ImageJ (National Institutes of Health: NIH) was used for the binarization process. Blue information was extracted from the RGB information of the image, and the binarization threshold was determined using the default mode (auto). Then, the number of pixels at the contact points (number of pixels in the white area) was divided by the total number of pixels to calculate the contact area ratio in the observation range.

[0066] Figure 12 shows three images with different contact area ratios. Figure 12(a) has a contact area ratio of 20%, Figure 12(b) has a contact area ratio of 30%, and Figure 12(c) has a contact area ratio of 40%. As shown in Figure 12(c), the higher the contact area ratio, the narrower the gaps between the conductive threads 11a. In order to scrape foreign matter from the surface of the charging roller 2, it is necessary to move the conductive threads 11a against the foreign matter, so a higher contact area ratio is better. For black spots, it is necessary to prevent the foreign matter attached to the charging roller 2 from becoming fixed in the same position on the charging roller 2 by moving it against the conductive threads 11a. In order to make foreign matter come into contact with the conductive threads 11a, it is important to increase the contact area ratio across the entire nip so that foreign matter between 50 μm and 200 μm does not pass straight through the nip P5. In other words, if a contact area ratio of a certain value or higher can be secured, it is possible to move the foreign matter and scrape it off the charging roller 2.

[0067] (Explanation of effects) This section describes a verification experiment to demonstrate the effectiveness of the black spot prevention measures. The penetration amount and offset amount L5 of the charged brush member 11 were varied, and the contact area ratio of 1 mm square was measured for both the upstream and downstream sections for each configuration. Subsequently, a durability evaluation of 50,000 sheets of paper was conducted under conditions of 23°C / 50% humidity to check for the occurrence of image defects.

[0068] Table 1 summarizes the occurrence of black spots in this experiment. ○ indicates that no image defects occurred or were within acceptable limits. × indicates that black spots outside the acceptable limits occurred.

[0069] [Table 1]

[0070] When the contact area ratio of the upstream section (first contact area ratio) was 5% and 10%, black spots occurred in the configuration where the contact area ratio of the downstream section (second contact area ratio) was 5%. Also, when the contact area ratio of the upstream section was 5%, black spots occurred in the configuration where the contact area ratio of the downstream section was 5% and 10%. Figure 13(a) is a nip image taken with a configuration where the contact area ratio of the upstream section was 5% and the contact area ratio of the downstream section was 5%. The reason for the occurrence of black spots is thought to be that the contact area ratio of the charging brush member 11 was too low, causing the gaps between the conductive threads 11a to widen, and some foreign matter, especially small foreign matter around 50 μm, passed through the nip section P5 without contacting the conductive threads 11a. Figure 13(c) is a nip image taken with a configuration where the contact area ratio of the upstream section was 10% and the contact area ratio of the downstream section was 5%. Under these conditions as well, the reason for the occurrence of black spots is thought to be the low contact area ratio of the charging brush member 11 and the wide gaps between the conductive threads 11a.

[0071] On the other hand, when the contact area ratio of the upstream and downstream sections exceeded 20%, the occurrence of black spots was suppressed even if a region with a contact area ratio of 5% was included. Figure 13(b) is a nip image taken with a configuration in which the contact area ratio of the upstream section was 20% and the contact area ratio of the downstream section was 10%, and Figure 13(d) is a nip image taken with a configuration in which the contact area ratio of the upstream section was 30% and the contact area ratio of the downstream section was 30%. The reason why black spots were suppressed is thought to be that, on average, the contact area ratio of the charged brush member 11 was high, so when foreign matter of 50 μm to 300 μm passed through, it passed through the nip section P5 while in contact with the conductive thread 11a, causing the foreign matter to roll.

[0072] Based on the above results, it is desirable that the contact conditions of the electrostatic brush member 11 for suppressing image defects caused by foreign matter be such that the contact area ratio of the upstream part is 10% or more and the contact area ratio of the downstream part is 10% or more. Alternatively, it is desirable that the contact area ratio of the upstream part is 20% or more and the contact area ratio of the downstream part is 5% or more, or the contact area ratio of the upstream part is 5% or more and the contact area ratio of the downstream part is 20% or more. Therefore, it can be said that setting the contact area ratio of the electrostatic brush member 11 to 20% or more will contribute to suppressing black spots.

[0073] (Charging brush member and drum brush member) As described above, the roles of the charging brush member 11 and the drum brush member 12 are significantly different. The charging brush member 11 prevents foreign matter present on the surface of the charging roller 2 from becoming fixed by moving it with the conductive thread 11a. On the other hand, the drum brush member 12 uses the conductive thread 12a to capture paper dust, filler, and debris attached to the surface of the photosensitive drum 1, preventing them from accumulating inside the image forming apparatus 100 and the developing container 45. Therefore, although both the charging brush member 11 and the drum brush member 12 contain conductive threads 11a and 12a, their physical properties are different. For example, the amount L2 that the drum brush member 12 penetrates into the photosensitive drum 1 is set to be greater than the amount L2a that the charging brush member 11 penetrates into the charging roller 2. This is because the drum brush member 12 needs to have a higher scraping ability against paper dust and the like. On the other hand, the amount L2a that the charging brush member 11 penetrates is smaller than that of the drum brush member 12, making it easier for foreign matter to move. For similar reasons, the short-side width L3 of the drum brush member 12 is made longer than the short-side width L3a of the charging brush member 11. A longer short-side width provides a greater opportunity to scrape up paper dust and other foreign matter. Therefore, the short-side width L3 of the drum brush member 12 needs to be set to be longer than the short-side width L3a of the charging brush member 11. The density of the conductive threads 11a and 12a also has an effect. The density of the conductive thread 12a of the drum brush member 12 is made greater than the density of the conductive thread 11a of the charging brush member 11. Furthermore, the contact area ratio is also set to be larger for the drum brush member 12 than for the charging brush member 11. This is also to improve the scraping ability of the drum brush member 12 to remove paper dust and other foreign matter. Since the purpose of the charging brush member 11 is to roll over foreign matter present on the surface of the charging roller 2, the pressure exerted by the bristles 11a should be reduced compared to that exerted by the bristles 12a of the drum brush member 12. Thus, in this embodiment, the settings are adjusted appropriately based on the difference in the required functions of the charging brush member 11 and the drum brush member 12.

[0074] Example 1 has the following characteristics:

[0075] An image forming apparatus 100 for forming an image on a recording material T includes a photosensitive drum 1 as a rotatable image carrier, and a rotatable charging roller 2 as a charging member that contacts the surface of the photosensitive drum 1 to form a charging portion P1 and charges the surface of the photosensitive drum 1 with the charging portion P1. It also includes a charging brush member 11 as a first brush member that contacts the surface of the charging roller 2 to form a charging brush portion P5, which is a first brush portion. The charging brush member 11 includes a thread portion 11a that contacts the surface of the charging roller 2. It also includes an exposure unit 3 as an exposure apparatus for exposing the surface of the photosensitive drum 1 that has been charged by the charging roller 2. It includes a developing member and a developing roller 41 as a developing agent carrier that supplies toner as a developer to the surface of the photosensitive drum 1 exposed by the exposure unit 3. The developing roller 41 contacts the surface of the photosensitive drum 1 to form a developing portion P2, and in the developing portion P2, it forms a developing image by supplying the developer to the electrostatic latent image formed by exposure by the exposure unit 3. The photosensitive drum 1 has a transfer roller 8 as a transfer member that transfers the developer image formed on the surface of the photosensitive drum 1 to the recording material T. The transfer roller 8 contacts the surface of the photosensitive drum 1 to form a transfer section P3. The remaining toner that remains on the surface of the photosensitive drum 1 without being transferred to the recording material T by the transfer section P3 passes through the drum brush section P4, which is the contact area between the charging brush member 11 and the photosensitive drum 1, downstream of the transfer section P3 and upstream of the charging section P1, in the rotational direction of the photosensitive drum 1. The toner that has passed through the drum brush section P4 as a second brush section is recharged by the charging section P1, passes through the charging section P1, and then reaches the developing section P2. Then, due to the potential difference between the surface potential formed on the surface of the photosensitive drum 1 and the developing voltage applied to the developing roller 41, it moves to the developing roller 41 and is collected in the developing container 45. At the contact section P5 between the charging brush member 11 and the charging roller 2, the contact area ratio of the charging brush member 11 is defined as follows. The contact area ratio is defined as the value relating to the contact area of ​​the thread portion 11a, obtained from images of the contact surface between the charging brush member 11 and the slide glass 15 taken using an optical microscope. For the purpose of imaging, the slide glass 15 is used as a substitute for the charging roller 2, but it is assumed that the contact state with the charging roller 2 can be simulated.As an example, the contact area is binarized to white and the non-contact area to black, and the number of pixels at the contact point (number of pixels in the white area) is divided by the total number of pixels to calculate the contact area ratio in the observation range. Therefore, in the brush section P5, the contact area ratio is defined as the ratio of the area in contact per unit area where the bristles 11a of the charged brush member 11 are in contact with the charged roller 2. It is preferable that the contact area ratio of the charged brush member 11 to the charged roller 2 at the nip section P5, which is the contact area between the charged brush member 11 and the charged roller 2, is 20% or more with respect to the rotation direction of the charged roller 2. Furthermore, consider the case where the nip section P5 is divided into an upstream and downstream section in the rotation direction of the charged roller 2 with respect to the center of the nip section P5. That is, when the charged brush section P5 is divided into a first region which is the upstream section in the rotation direction of the charged roller 2 with respect to the center of the charged brush section P5 and a second region which is the downstream section in the rotation direction of the charged roller 2 with respect to the center of the charged brush section P5, the settings are as follows. It is also effective if the contact area ratio of the first region in the upstream section of the nip section is 10% or more and the downstream section is also 10% or more. Alternatively, the contact area ratio of the first region is 20% or more and 5% or more in the downstream section, or the contact area ratio of the first region is 5% or more and the contact area ratio of the second region downstream is 20% or more. In particular, it is desirable that the contact area ratio of the first region be 10% to 30%, and the contact area ratio of the second region be 10% to 20%. [Examples]

[0076] Next, we will describe Example 2. The same reference numerals are used for components similar to those in Example 1 described above, and detailed explanations are omitted.

[0077] As explained in Example 1, as shown in Figure 12(c), the higher the contact area ratio of the charging brush member 11, the narrower the gaps between the conductive threads 11a become. In order to scrape foreign matter from the surface of the charging roller 2, it is necessary to move the conductive threads 11a in contact with the foreign matter, so a higher contact area ratio of the charging brush member 11 is desirable. However, if the contact area ratio of the charging brush member 11 is too high, the gaps through which fine paper dust and filler can pass become narrow, and they may get trapped and accumulate in the conductive threads 11a. Depending on the number of sheets of paper passed through and the type of paper used, fine paper dust and filler may accumulate in the charging brush member 11, causing image defects. The mechanism of this will be explained using Figure 14.

[0078] Figure 14(a) is a cross-sectional view of the charging brush member 11 in its initial state (new shipment state) as measured by a virtual plane perpendicular to the rotation axis of the charging roller 2. Figure 14(b) is a cross-sectional view of the charging brush member 11 as the number of sheets of paper has increased and fine paper dust and filler have accumulated. Paper dust adheres to the photosensitive drum 1 in the transfer section P3, and some of it is blocked by the drum brush member 12. Fine paper dust and filler that slip through the drum brush member 12 adhere to the charging roller 2 and reach the contact section P5, which is the charging brush portion between the charging roller 2 and the charging brush member 11. When paper dust accumulates on the conductive threads 11a of the charging brush member 11, the conductive threads 11a become clogged, and the toner and external additives that would normally pass through are pressed against the charging roller 2 and adhere to the surface of the charging roller 2 (Figure 14(c)). The surface of the charging roller 2 to which toner and external additives have adhered becomes charged up, causing a phenomenon in which the density decreases, such as in halftones. For example, differences in the contact state of the electrostatic brush member 11 in the longitudinal direction, and differences in the longitudinal positions where paper dust is likely to be generated due to the paper feed cassette 6 and transfer properties, and where it is not likely to be generated, can cause uneven accumulation of paper dust on the conductive thread 11a in the longitudinal direction. Under such circumstances, differences in the density of toner and external additives adhering to the surface of the electrostatic roller 2 become apparent as white streaks.

[0079] For the reasons stated above, in environments where white streaks occur, such as low-temperature, low-humidity environments where the surface of the charging roller 2 is prone to charging up, there is an appropriate range for the contact area ratio of the charging brush member 11 and the contact area ratio of the drum brush member 12.

[0080] From the above, in the configuration of this embodiment, fine paper dust and filler that slip through the gaps in the conductive threads 12a of the drum brush member 12 that contacts the photosensitive drum 1 reach the charging brush member 11 that contacts the charging roller 2, and accumulate on the conductive threads 11a, causing image defects. Therefore, in order to suppress the occurrence of image defects caused by accumulation on the charging brush member 11, it is desirable that the contact area ratio of the drum brush member 12 be higher than that of the charging brush member 11. The contact area ratio of the drum brush member 12 can be calculated from the captured image of the contact surface with the glass plate 15, similar to the charging brush member 11. The inclination angle of the glass plate 15 when making contact can be calculated by setting the value of R to the radius of the photosensitive drum 1 and the value of C to the offset amount of the drum brush member 12 in the above calculation formula. In this embodiment, the radius of the photosensitive drum 1 is 24 mm and the offset amount is 0 mm. In this embodiment, the contact area ratio of the drum brush member 12 is set to 40%. The contact area ratio of the drum brush member 12 was set to 40% for both the upstream and downstream sides in the rotational direction of the photosensitive drum 1. However, if the contact area ratio is higher than that of the electrostatic brush member 11, different values ​​may be used for the upstream and downstream sides. In particular, it is desirable to make the contact area ratio on the upstream side in the rotational direction of the photosensitive drum 1 higher than that of the electrostatic brush member 11.

[0081] (Calculation of the degree of rectification in a 1mm square area) Next, the degree of flow rectification of the electrostatic brush member 11 will be explained. The degree of flow rectification of the electrostatic brush member 11 is a numerical value that indicates the degree of hair flow at the contact portion P5 between the electrostatic roller 2 and the electrostatic brush member 11, with respect to the rotational direction of the electrostatic roller 2. The higher the value of the degree of flow rectification, the more the bristles 11a flow in the rotational direction. Like the contact area ratio, the degree of flow rectification is one of the important parameters in defining the contact state of the electrostatic brush member 11 with the electrostatic roller 2. In other words, the degree of flow rectification is the ratio of the rotational component of the electrostatic roller 2 to the axial component of the electrostatic roller 2 in the direction in which the bristles 11a extend, and is an indicator of how parallel the bristles 11a are to the rotational direction.

[0082] This section describes an example of a method for calculating the degree of rectification (hereinafter referred to as "degree of rectification") in a 1 mm square area of ​​the charging roller 2 and the charging brush member 11 in this embodiment. In this embodiment, the degree of rectification was calculated only in the upstream part of the nip. After capturing a binarized image of the contact surface using the method described in the previous section (Method for calculating longitudinal contact area ratio), the image was converted into a numerical map such that the value of the part where the conductive threads 11a are in contact with each other is 255, and the value of the part where the conductive threads 11a are not in contact with each other is 0. To explain the specific method for calculating the degree of rectification, consider an image with 6x6 pixels as an example. Figure 11(b) is a schematic diagram in which each pixel of the 6x6 image is assigned a number. Using Figure 11(b), the method for calculating the degree of rectification is described below. S1: Calculate the average value of the rotation direction and row N11 (N11, N12, ..., N16). Perform S2:S1 up to row N61. S3: Extract the maximum and minimum values ​​from the average values ​​of the calculation results of S1 and S2, rows N11, N21, ..., and N61, and calculate the difference. S4: Calculate the average value of the longest column, N11 (N11, N21, ..., N61). Perform S5:S4 up to column N16. Extract the maximum and minimum values ​​from the mean values ​​of columns N11, N12, ..., N16, which are the calculation results for S6:S5, and calculate the difference between them. S7: Calculate (Result of calculation in S3) / (Result of calculation in S6) (This will be written as S3 / S6)

[0083] The calculation result of S7 above represents the degree of rectification in this embodiment. Here, the degree of rectification is not limited to the above evaluation method, as long as it is a relationship value that allows for a comparison of the contact state in the rotational direction and the longitudinal direction. For example, it may be S6 / S3, or a difference such as S3-S6 may be used.

[0084] Figures 15 and 16 will be used to explain the specific calculation results of the rectification degree. Figure 15(a) is a 900x900 pixel binarized image of a 1 mm square area upstream of the nip, taken using Example 1. Figure 15(b) is an example of the charging brush member 11 that is the source of the image in Figure 15(a), and Figure 15(c) shows the arrangement of the conductive threads 11a when the charging brush member 11 in Figure 15(b) is viewed from the direction of arrow A. Figure 16 is a graph plot of the profile of the charging brush member 11 in Figure 15(b), obtained by taking the average value for each pixel in a 900x900 pixel area using the same calculation method as described in Figure 11(b).

[0085] As shown in Figure 15(c), the charging brush member 11 in Figure 15(b) has conductive threads 11a arranged so that they flutter regularly in the direction of rotation of the charging roller 2 and are arranged regularly in the longitudinal direction. As shown in Figure 13(a), the more the conductive threads 11a are aligned in the direction of rotation of the charging roller 2, the larger the gap parallel to the direction of rotation becomes, and the greater the difference between the contact and non-contact values ​​in the longitudinal direction, resulting in a larger difference between the maximum and minimum values ​​in the longitudinal direction. On the other hand, in Figure 13(b), the conductive threads 11a are distributed almost uniformly in the longitudinal direction, so the difference between the maximum and minimum values ​​in the direction of rotation becomes smaller. That is, the value of the degree of rectification calculated by the ratio of the calculation results in the two directions becomes larger. In this case, the degree of rectification was 3.

[0086] Figure 17 shows images of three nip sections with different degrees of rectification. Figure 17(a) has a rectification degree of 1, (b) has a rectification degree of 2.5, and (c) has a rectification degree of 0.2. As shown in Figure 17(a), when the rectification degree is 1, the conductive thread 11a is in contact with the charging roller 2 at an oblique angle to the direction of rotation. As shown in Figure 17(b), the closer the conductive thread 11a is aligned with the direction of rotation of the charging roller 2, the higher the value of the rectification degree. To suppress image defects caused by trapping paper dust, it is desirable for the conductive thread 11a to be aligned with the direction of rotation. Therefore, the higher the value of the rectification degree, the better the level of vertical streaks. Conversely, as the rectification degree is less than 1 and approaches 0, the orientation of the contacting conductive thread 11a becomes aligned in the longitudinal direction, as shown in Figure 17(c). Alignment in the longitudinal direction makes it easier to trap paper dust, and image defects are more likely to occur. To suppress image defects caused by trapping and accumulating paper dust, it is desirable that the value of the downstream rectification degree, which serves as the second rectification degree, be 1 or greater.

[0087] Furthermore, in the configuration of this embodiment, by suppressing the passage of paper dust through the drum brush member 12 that contacts the photosensitive drum 1, the amount of paper dust reaching the charging brush member 11 is reduced, making it possible to further reduce the occurrence rate of image defects. For this reason, it is desirable that the rectification degree of the drum brush member 12 is lower than that of the charging brush member 11. The rectification degree of the drum brush member 12 can be calculated from the captured image of the contact surface with the glass plate 15, similar to the calculation method for the rectification degree of the charging brush member 11. In this embodiment, the rectification degree of the drum brush member 12 is set to 1.3. The rectification degree of the drum brush member 12 is set to 1.3 for both the upstream and downstream directions of rotation of the photosensitive drum 1, but if it is lower than the rectification degree of the charging brush member 11, different values ​​may be used for the upstream and downstream directions.

[0088] (Explanation of effects) For vertical streaks, it is necessary to prevent paper dust from accumulating in the nip portion P5 of the charged brush member 11. In order for the paper dust not to be trapped by the conductive thread 11a, a gap larger than the size of the paper dust (50 μm to 300 μm) must extend in the direction of rotation of the charged roller 2 in the upstream part of the nip where the paper dust first enters. Therefore, the degree of rectification in the upstream part of the nip and the contact area ratio throughout the entire nip are important. Figure 18 is a schematic diagram showing how paper dust passes through in two configurations with a constant contact area ratio and different degrees of rectification. Figure 18(a) is the configuration when the degree of rectification is high. In this case, the direction of the conductive thread 11a is parallel to the direction of rotation of the charged roller 2. Therefore, a gap is created for the paper dust to pass through, and the paper dust passes through the nip portion P5 without being trapped. On the other hand, Figure 18(b) is the configuration when the degree of rectification is low. In this case, the direction of the conductive thread 11a is not parallel to the direction of rotation of the charged roller 2. Therefore, the conductive thread 11a obstructs the progress of paper dust, and the accumulation of paper dust on the conductive thread 11a causes vertical streaks to form. Thus, even with the same contact area ratio, a higher degree of rectification can improve the appearance of vertical streaks.

[0089] Furthermore, in order to prevent paper dust from accumulating in the nip section P5, it is necessary to avoid trapping paper dust in the downstream section of the nip as well. To this end, it is important to make the contact area ratio of the downstream section lower than that of the upstream section. Figure 19 shows how paper dust passes through in two configurations with different contact area ratios of the downstream section. Figure 19(a) shows a configuration where the contact area ratio of the downstream section is higher than that of the upstream section. In this case, even if paper dust slips through in the upstream section, the high contact area ratio of the downstream section traps the paper dust, resulting in vertical streaks. Figure 19(b) shows a configuration where the contact area ratio of the downstream section is lower than that of the upstream section. In this case, the paper dust that slips through in the upstream section also slips through in the downstream section, so the paper dust passes through without being trapped. In the case of flow rectification, it is better if the flow rectification of the upstream section is higher than that of the downstream section.

[0090] This section explains the effect of increasing the degree of flow straightening in the upstream section compared to the downstream section. If the degree of flow straightening differs between the upstream and downstream sections, the state of paper dust and other particles entering the brush section P5 will differ slightly between the upstream and downstream sections. Upstream, paper dust containing relatively large fibers may enter, so a higher degree of flow straightening in the upstream section makes it easier to loosen the paper dust as it passes through. On the other hand, downstream, the paper dust that enters is already somewhat loosened from passing through the upstream section, so even with a lower degree of flow straightening than in the upstream section, the accumulation of paper dust can be suppressed. Therefore, when comparing the upstream and downstream sections, it is important to increase the degree of flow straightening in the upstream section.

[0091] Here, we will describe the verification experiment to demonstrate the effectiveness of achieving both vertical streaks and black spots. To conduct the verification experiment, the rectification degree and contact area ratio of a 1 mm square area were measured upstream and downstream for each configuration. Subsequently, a paper feed durability evaluation of 50,000 sheets was conducted under a temperature of 15°C and humidity of 10%, and the occurrence of image defects was checked.

[0092] Table 2 summarizes the occurrence of vertical streaks and black spots in this experiment. ○ indicates that no image defects occurred or were within acceptable limits. △ indicates that some vertical streaks and black spots occurred, although they were not outside the acceptable range of image defects. × indicates that vertical streaks and black spots occurred outside the acceptable range.

[0093] [Table 2]

[0094] When the flow rectification of the upstream section, which is the first degree of flow rectification, was less than 1.5, black spots or vertical streaks occurred. Specifically, black spots occurred in configurations where the flow rectification of the upstream section was less than 1.5 and the contact area ratio was 5% or 10%, while vertical streaks occurred in configurations where the flow rectification of the upstream section was less than 1.5 and the contact area ratio was 20% or more. Figures 13(a) and (b) are NIP images of configurations where the flow rectification of the upstream section was less than 1.5. Figure 13(a) is a NIP image of configurations where the flow rectification of the upstream section was less than 1.5, the contact area ratio was 5%, and the contact area ratio of the downstream section was 5%. Figure 13(b) is a NIP image of configurations where the flow rectification of the upstream section was less than 1.5, the contact area ratio was 20%, and the contact area ratio of the downstream section was 10%. The reason for the black spots is thought to be that, as mentioned above, the contact area ratio was too low, which widened the gaps between the conductive threads 11a, preventing foreign matter between 50 μm and 300 μm from contacting the conductive threads 11a and thus preventing it from being scraped off by the nip section P5. The reason for the vertical streaks is thought to be that the rectification degree in the upstream section was low and the contact area ratio was high, resulting in insufficient gaps extending in the direction of rotation of the charging roller 2 for 50 μm to 300 μm paper dust to pass through. As a result, the paper dust was trapped by the conductive threads 11a and accumulated.

[0095] Next, let's consider the case where the flow rectification degree of the upstream section is 1.5 or higher. When the flow rectification degree of the upstream section is 1.5 or higher and the contact area ratio is 5% and 10%, black spots occurred in the configuration where the contact area of ​​the downstream section is 5%, or when the flow rectification degree of the upstream section is 1.5 or higher and the contact area ratio is 5%, and the contact area of ​​the downstream section is 10%. Figure 13(c) is a nip image taken with a configuration where the flow rectification degree of the upstream section is 1.5 or higher and the contact area ratio is 10%, and the contact area ratio of the downstream section is 5%. The reason for the occurrence of black spots is thought to be that, as mentioned above, the contact area ratio was too low, which widened the gap between the conductive threads 11a, preventing foreign matter of 50 μm to 300 μm from contacting the conductive threads 11a and thus preventing it from being scraped off by the nip section P5. Furthermore, minor vertical streaks within the acceptable range occurred in configurations where the flow rectification degree in the upstream section was 1.5 or higher, with a contact area ratio of 30% in the upstream section and 30% in the downstream section, and in configurations where the contact area ratio in the upstream section was 40% and 20% in the downstream section. Figure 13(d) is a nip image taken with a configuration where the flow rectification degree in the upstream section was 1.5 or higher, with a contact area ratio of 30% in both sections. The reason for the occurrence of vertical streaks is that although the flow rectification degree in the upstream section was high, the contact area ratio across the entire nip was high on average. Therefore, it is thought that the gap was not wide enough in the direction of rotation of the charging roller 2 to allow 50 μm to 300 μm paper dust to pass through, causing the paper dust to be trapped by the conductive thread 11a and accumulate.

[0096] On the other hand, in other configurations where the flow rectification degree of the upstream section was 1.5 or higher, neither vertical streaks nor black spots occurred, or were within acceptable limits. No configurations where both vertical streaks and black spots were within acceptable limits existed in configurations where the flow rectification degree of the upstream section was less than 1.5. Compared to configurations with a flow rectification degree of less than 1.5, the flow of the conductive threads 11a was aligned with the rotation direction of the charging roller 2, causing the gaps between the conductive threads 11a to extend in the rotation direction. This is thought to be because, even with a high contact area ratio of the charging brush member 11, sufficient gaps were secured for paper dust of 50 μm to 300 μm to pass through, making it less likely for paper dust to be trapped in the conductive threads 11a.

[0097] From the above results, it can be said that the preferred contact conditions for the electrostatic brush member 11 are when the flow straightening degree in the upstream section is 1.5 or higher. Furthermore, in order to prevent paper dust from accumulating in the nip section P5 and to prevent paper dust from being trapped in the downstream section of the nip, the contact area ratio in the downstream section is set to be less than or equal to the contact area ratio in the upstream section in the rotation direction of the electrostatic roller 2 in the nip section P5. It is also effective to set the flow straightening degree in the downstream section to be less than or equal to the flow straightening degree in the upstream section. In particular, it is desirable that the contact area ratio is 10-30% in the upstream section and 10-20% in the downstream section, and that the flow straightening degree is 1.5 or higher in the upstream section and 1 or higher in the downstream section.

[0098] (Charging brush member and drum brush member) As described above, the roles of the charging brush member 11 and the drum brush member 12 are significantly different. As described in Example 1, the charging brush member 11 plays the role of preventing foreign matter present on the surface of the charging roller 2 from becoming fixed by moving it with the conductive thread 11a. Furthermore, it is necessary to prevent paper dust and other particles from being trapped by the conductive thread 11a of the charging brush member 11. On the other hand, the drum brush member 12 plays the role of capturing paper dust, fillers, and debris attached to the surface of the photosensitive drum 1 with the conductive thread 12a to prevent them from accumulating inside the image forming apparatus 100 and the developing container 45. Therefore, although both the charging brush member 11 and the drum brush member 12 contain conductive threads 11a and 12a, their physical properties are different. As described above, the amount L2 that the drum brush member 12 penetrates into the photosensitive drum 1 is set to be greater than the amount L2a that the charging brush member 11 penetrates into the charging roller 2. This is because the charging brush member 11 is designed to allow less foreign matter to enter than the drum brush member 12, making it easier for foreign matter to move, and also to reduce the amount of paper dust that can be scraped off and the accumulation of paper dust. For similar reasons, the short side width L3a of the charging brush member 11 is shorter than the short side width L3 of the drum brush member 12. A shorter short side width reduces the opportunities to scrape off paper dust and other foreign matter, making it less likely for paper dust to accumulate. The density of the conductive threads 11a and 12a also has an effect. The density of the conductive thread 11a of the charging brush member 11 is lower than the density of the conductive thread 12a of the drum brush member 12. Furthermore, the contact area ratio of the charging brush member 11 is set to be smaller than that of the drum brush member 12. In addition, in this embodiment, the degree of rectification of the charging brush member 11 is greater than that of the drum brush member 12. This is also to suppress the accumulation of paper dust and other foreign matter on the charging brush member 11. The purpose of the electrostatic brush member 11 is to suppress the accumulation of paper dust and other foreign matter, and to roll away foreign matter present on the surface of the electrostatic roller 2. Thus, in this embodiment, the settings are appropriately adjusted according to the difference in the required functions of the electrostatic brush member 11 and the drum brush member 12.

[0099] The configuration of Example 2 has the following additional features in addition to the configuration of Example 1.

[0100] At the contact point P5 between the charging brush member 11 and the charging roller 2, the contact area ratio and flow rectification of the charging brush member 11 are defined as follows. The flow rectification is defined as a value relating to the direction of flow of the thread portion 11a generated by the contact between the charging brush member 11 and the slide glass 15, obtained from an image of the contact surface between the charging brush member 11 and the slide glass 15 taken using an optical microscope. For the purpose of photography, the slide glass 15 is used as a substitute for the charging roller 2, but it is assumed that the contact state with the charging roller 2 can be simulated. As an example of calculating the flow rectification, the following calculation method is adopted. After taking a binarized image of the contact surface, the image is converted into a numerical map such that the value of the part where the conductive threads 11a are in contact with each other is 255 and the value of the part where the conductive threads 11a are not in contact with each other is 0 for each pixel of the image. After conversion, the average values ​​in the rotational direction and longitudinal direction of the charging roller 2 are calculated, the maximum and minimum values ​​are extracted from the average values, and the difference is calculated. The degree of rectification is calculated by calculating the ratio S3 / S6 of the difference S3 in the rotational direction of the charging roller 2 and the difference S6 in the longitudinal direction of the charging roller 2. In other words, the degree of rectification is defined as the ratio of the rotational component of the charging roller 2 to the axial component of the charging roller 2 in the direction in which the bristles 11a of the charging brush member 11 are in contact with the charging roller 2 per unit area in the charging brush section P5. It is assumed that the degree of rectification of the bristles 11a of the charging brush member 11 in the nip section P5, which is the contact point between the charging brush member 11 and the charging roller 2, is 1.5 or higher with respect to the rotational direction of the charging roller 2. At the same time, in the rotational direction of the charging roller 2 in the nip section P5, the contact area ratio of the downstream part is set to be less than or equal to the contact area ratio of the upstream part. It is desirable that the contact area ratio of the charging brush member 11 is 10-30% in the upstream part and 10-20% in the downstream part.

[0101] Summary of this disclosure This disclosure includes at least the following:

[0102] (Composition 1) In an image forming apparatus that forms an image on a recording material, A rotatable image carrier, A rotatable charging roller that contacts the image carrier to form a charging portion and charges the surface of the image carrier at the charging portion, A brush member that contacts the surface of the charging roller to form a brush portion, comprising a brush member having bristles that contact the charging roller, In the brush portion, the amount of the bristles of the brush member in contact with the charging roller per unit area is defined as the degree of rectification, and the ratio of the rotational component of the charging roller to the axial component of the charging roller in the direction in which the bristles extend is defined as the contact area ratio, When the brush portion is divided along the rotation direction of the charging roller into a first region located upstream from the center and a second region located downstream from the center, i) The degree of rectification in the first region is greater than the degree of rectification in the second region. ii) The contact area ratio of the first region is 10% or more and 30% or less. iii) The contact area ratio of the second region is 10% or more and 20% or less. An image forming apparatus characterized by being such.

[0103] (Configuration 2) In an image forming apparatus that forms an image on a recording material, A rotatable image carrier, A rotatable charging roller that contacts the image carrier to form a charging portion and charges the surface of the image carrier at the charging portion, A first brush member that contacts the surface of the charging roller to form a first brush portion, the brush member having a first bristle material that contacts the charging roller, A developing member that supplies developer to the surface of the image carrier which has been charged by the charging roller; a transfer member that contacts the surface of the image carrier to form a transfer portion and transfers the developer supplied to the surface of the image carrier to a recording material in the transfer portion; A second brush member that forms a second brush portion by contacting the surface of the image carrier downstream of the transfer portion and upstream of the charging portion in the rotational direction of the image carrier, the second brush member having a second bristle material that contacts the surface of the image carrier, In the first brush section, the ratio of the area in which the first bristles of the first brush member are in contact with the charging roller per unit area is defined as the first contact area ratio, and in the second brush section, the ratio of the area in which the second bristles of the second brush member are in contact with the image carrier per unit area is defined as the second contact area ratio. An image forming apparatus characterized in that the first contact area ratio is smaller than the second contact area ratio.

[0104] (Composition 3) In an image forming apparatus that forms an image on a recording material, A rotatable image carrier, A rotatable charging roller that contacts the image carrier to form a charging portion and charges the surface of the image carrier at the charging portion, A first brush member that contacts the surface of the charging roller to form a first brush portion, the brush member having a first bristle material that contacts the charging roller, A developing member that supplies developer to the surface of the image carrier which has been charged by the charging roller; a transfer member that contacts the surface of the image carrier to form a transfer portion and transfers the developer supplied to the surface of the image carrier to a recording material in the transfer portion; A second brush member that forms a second brush portion by contacting the surface of the image carrier downstream of the transfer portion and upstream of the charging portion in the rotational direction of the image carrier, the second brush member having a second bristle material that contacts the surface of the image carrier, An image forming apparatus characterized in that the density of the first bristles is less than the density of the second bristles.

[0105] (Composition 4) In an image forming apparatus that forms an image on a recording material, A rotatable image carrier, A rotatable charging roller that contacts the image carrier to form a charging portion and charges the surface of the image carrier at the charging portion, A first brush member that contacts the surface of the charging roller to form a first brush portion, the brush member having a first bristle material that contacts the charging roller, A developing member that supplies developer to the surface of the image carrier which has been charged by the charging roller; a transfer member that contacts the surface of the image carrier to form a transfer portion and transfers the developer supplied to the surface of the image carrier to a recording material in the transfer portion; A second brush member that forms a second brush portion by contacting the surface of the image carrier downstream of the transfer portion and upstream of the charging portion in the rotational direction of the image carrier, the second brush member having a second bristle material that contacts the surface of the image carrier, In the first brush section, per unit area, the first bristles of the first brush member are in contact with the charging roller, and the ratio of the rotational component of the charging roller to the axial component of the charging roller in the direction in which the first bristles extend is defined as the first rectification degree, and in the second brush section, per unit area, the second bristles of the second brush member are in contact with the image carrier, and the ratio of the rotational component of the image carrier to the axial component of the image carrier in the direction in which the second bristles extend is defined as the second rectification degree, An image forming apparatus characterized in that the first degree of rectification is greater than the second degree of rectification.

[0106] (Composition 5) A first gear for rotating the image carrier, A second gear for rotating the charging roller, comprising a second gear that engages with the first gear, An image forming apparatus according to any one of configurations 1 to 4, characterized by having a drive source that rotates the image carrier and the charging roller by transmitting drive to the first gear.

[0107] (Composition 6) The image forming apparatus according to configuration 2, characterized in that the density of the first bristles is less than the density of the second bristles.

[0108] (Composition 7) In the first brush section, per unit area, the first bristles of the first brush member are in contact with the charging roller, and the ratio of the rotational component of the charging roller to the axial component of the charging roller in the direction in which the first bristles extend is defined as the first rectification degree, and in the second brush section, per unit area, the second bristles of the second brush member are in contact with the image carrier, and the ratio of the rotational component of the image carrier to the axial component of the image carrier in the direction in which the second bristles extend is defined as the second rectification degree, The image forming apparatus according to configuration 2 or 3, characterized in that the first degree of rectification is greater than the second degree of rectification. [Explanation of symbols]

[0109] 1. Image carrier (photosensitive drum) 2 Charging rollers 11 Charging brush member 12 Drum brush component

Claims

1. In an image forming apparatus that forms an image on a recording material, A rotatable image carrier, A rotatable charging roller that contacts the image carrier to form a charging portion and charges the surface of the image carrier at the charging portion, A brush member that contacts the surface of the charging roller to form a brush portion, comprising a brush member having bristles that contact the charging roller, In the brush portion, the amount of the bristles of the brush member in contact with the charging roller per unit area is defined as the degree of rectification, and the ratio of the rotational component of the charging roller to the axial component of the charging roller in the direction in which the bristles extend is defined as the contact area ratio, When the brush portion is divided along the rotation direction of the charging roller into a first region located upstream from the center and a second region located downstream from the center, i) The degree of rectification in the first region is greater than the degree of rectification in the second region. ii) The contact area ratio of the first region is 10% or more and 30% or less. iii) The contact area ratio of the second region is 10% or more and 20% or less. An image forming apparatus characterized by being such.

2. In an image forming apparatus that forms an image on a recording material, A rotatable image carrier, A rotatable charging roller that contacts the image carrier to form a charging portion and charges the surface of the image carrier at the charging portion, A first brush member that contacts the surface of the charging roller to form a first brush portion, the brush member having a first bristle material that contacts the charging roller, A developing member that supplies developer to the surface of the image carrier which has been charged by the charging roller; a transfer member that contacts the surface of the image carrier to form a transfer portion and transfers the developer supplied to the surface of the image carrier to a recording material in the transfer portion; A second brush member that forms a second brush portion by contacting the surface of the image carrier downstream of the transfer portion and upstream of the charging portion in the rotational direction of the image carrier, the second brush member having a second bristle material that contacts the surface of the image carrier, In the first brush section, the ratio of the area in which the first bristles of the first brush member are in contact with the charging roller per unit area is defined as the first contact area ratio, and in the second brush section, the ratio of the area in which the second bristles of the second brush member are in contact with the image carrier per unit area is defined as the second contact area ratio. An image forming apparatus characterized in that the first contact area ratio is smaller than the second contact area ratio.

3. In an image forming apparatus that forms an image on a recording material, A rotatable image carrier, A rotatable charging roller that contacts the image carrier to form a charging portion and charges the surface of the image carrier at the charging portion, A first brush member that contacts the surface of the charging roller to form a first brush portion, the brush member having a first bristle material that contacts the charging roller, A developing member that supplies developer to the surface of the image carrier which has been charged by the charging roller; a transfer member that contacts the surface of the image carrier to form a transfer portion and transfers the developer supplied to the surface of the image carrier to a recording material in the transfer portion; A second brush member that forms a second brush portion by contacting the surface of the image carrier downstream of the transfer portion and upstream of the charging portion in the rotational direction of the image carrier, the second brush member having a second bristle material that contacts the surface of the image carrier, An image forming apparatus characterized in that the density of the first bristles is less than the density of the second bristles.

4. In an image forming apparatus that forms an image on a recording material, A rotatable image carrier, A rotatable charging roller that contacts the image carrier to form a charging portion and charges the surface of the image carrier at the charging portion, A first brush member that contacts the surface of the charging roller to form a first brush portion, the brush member having a first bristle material that contacts the charging roller, A developing member that supplies developer to the surface of the image carrier which has been charged by the charging roller; a transfer member that contacts the surface of the image carrier to form a transfer portion and transfers the developer supplied to the surface of the image carrier to a recording material in the transfer portion; A second brush member that forms a second brush portion by contacting the surface of the image carrier downstream of the transfer portion and upstream of the charging portion in the rotational direction of the image carrier, the second brush member having a second bristle material that contacts the surface of the image carrier, In the first brush section, per unit area, the first bristles of the first brush member are in contact with the charging roller, and the ratio of the rotational component of the charging roller to the axial component of the charging roller in the direction in which the first bristles extend is defined as the first rectification degree, and in the second brush section, per unit area, the second bristles of the second brush member are in contact with the image carrier, and the ratio of the rotational component of the image carrier to the axial component of the image carrier in the direction in which the second bristles extend is defined as the second rectification degree, An image forming apparatus characterized in that the first degree of rectification is greater than the second degree of rectification.

5. A first gear for rotating the image carrier, A second gear for rotating the charging roller, comprising a second gear that engages with the first gear, The image forming apparatus according to any one of claims 1 to 4, characterized in that it has a drive source that rotates the image carrier and the charging roller by transmitting drive to the first gear.

6. The image forming apparatus according to claim 2, characterized in that the density of the first bristles is less than the density of the second bristles.

7. In the first brush section, per unit area, the first bristles of the first brush member are in contact with the charging roller, and the ratio of the rotational component of the charging roller to the axial component of the charging roller in the direction in which the first bristles extend is defined as the first rectification degree, and in the second brush section, per unit area, the second bristles of the second brush member are in contact with the image carrier, and the ratio of the rotational component of the image carrier to the axial component of the image carrier in the direction in which the second bristles extend is defined as the second rectification degree, The image forming apparatus according to claim 2 or 3, characterized in that the first degree of rectification is greater than the second degree of rectification.

Images