Image forming apparatus

Abstract

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

Description

Technical Field

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

Background Art

[0002] As an image recording method used in an image forming apparatus such as a printer or a copier, an electrophotographic method is known. The electrophotographic method forms an electrostatic latent image on a photosensitive drum by a laser beam by using an electrophotographic process, and forms a toner image by developing the electrostatic latent image with a charged coloring material (hereinafter referred to as toner). Then, the toner image is transferred onto a recording material and fixed to perform image formation on the recording material. In recent years, for the purpose of miniaturizing the image forming apparatus, a cleanerless method has been proposed. The cleanerless method is a method of removing, collecting, and reusing the toner (transfer residual toner) remaining on the surface of the photosensitive drum after the transfer process from the photosensitive drum by developing means. In the cleanerless method, since there is no cleaning means arranged to contact the photosensitive drum, image defects may occur due to paper dust adhering to the photosensitive drum during the transfer process to the recording material. Therefore, in Patent Document 1, a configuration has been proposed in which a brush for collecting paper dust adhering to the photosensitive drum in the transfer process is arranged downstream of the transfer portion and upstream of the charging portion in the rotation direction of the photosensitive drum.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the configuration of Patent Document 1, when a large amount of images with a high printing rate are continuously passed through, the transfer residual toner gradually accumulates on the brush, and when the allowable amount is exceeded, the toner may be ejected from the brush, which may cause unnecessary images.

[0005] The object of the present invention is to suppress image defects caused by toner accumulation on a brush in an image forming apparatus having a brush that contacts a photosensitive drum. [Means for solving the problem]

[0006] The image forming apparatus according to the present invention is A rotating image carrier, A charging means that forms a charged portion opposite to the surface of the image carrier and charges the surface of the image carrier, A developing means that supplies a developer to the surface of the image carrier charged by the charging means and forms a developer image, A transfer means for forming a transfer section with the image carrier and transferring the developer image from the image carrier to the transfer target, A brush that contacts the surface of the image carrier at the brush portion, downstream of the transfer portion and upstream of the charging portion in the rotational direction of the image carrier, A voltage applying means for applying a voltage to the brush, A pre-exposure means for exposing the surface of the image carrier downstream of the brush portion and upstream of the charging portion in the rotational direction of the image carrier, Equipped with, After the developer image is transferred to the transfer target, the developer remaining on the surface of the image carrier In the image forming apparatus recovered by the developing means, The upstream end of the exposure region exposed by the pre-exposure means on the surface of the image carrier in the direction of rotation of the image carrier is upstream in the direction of rotation of the image carrier from the downstream end of the contact region that contacts the brush on the surface of the image carrier in the direction of rotation of the image carrier, and the exposure region includes at least a part of the contact region.

[0007] The image forming apparatus according to the present invention is A rotating image carrier, A charging means that forms a charged portion opposite to the surface of the image carrier and charges the surface of the image carrier, A developing means that supplies a developer charged with normal polarity to the surface of the image carrier charged by the charging means and forms a developer image, A transfer means for forming a transfer section with the image carrier and transferring the developer image from the image carrier to the transfer target, A brush that contacts the surface of the image carrier at the brush portion, downstream of the transfer portion and upstream of the charging portion in the rotational direction of the image carrier, A voltage application means for applying the voltage of the normal polarity to the brush, A pre-exposure means for exposing the surface of the image carrier downstream of the brush portion and upstream of the charging portion in the rotational direction of the image carrier, Equipped with, In an image forming apparatus in which, after the developer image is transferred to the transfer body, the developer remaining on the surface of the image carrier is recovered by the developing means, When the surface potential of the image carrier downstream of the transfer portion and upstream of the brush portion in the rotational direction of the image carrier is Va, and the surface potential of the image carrier at the brush portion on the surface of the image carrier is Vb, the surface of the image carrier is exposed by the pre-exposure means, thereby forming a surface potential of Vb in the brush portion region of the surface of the image carrier such that |Vb| < |Va|.

[0008] The image forming apparatus according to the present invention is A rotating image carrier, A charging means that forms a charged portion opposite to the surface of the image carrier and charges the surface of the image carrier, A developing means that supplies a developer to the surface of the image carrier charged by the charging means and forms a developer image, A transfer means for forming a transfer section with the image carrier and transferring the developer image from the image carrier to the transfer target, A brush that contacts the surface of the image carrier at the brush portion, downstream of the transfer portion and upstream of the charging portion in the rotational direction of the image carrier, A voltage applying means for applying a voltage to the brush, A pre-exposure means for exposing the surface of the image carrier downstream of the brush and upstream of the charging portion in the rotational direction of the image carrier, Equipped with, In an image forming apparatus in which, after the developer image is transferred to the transfer body, the developer remaining on the surface of the image carrier is recovered by the developing means, If Vb is the surface potential of the image carrier in the contact region on the surface of the image carrier that comes into contact with the brush, Vbmax is the surface potential of the image carrier at the upstream end in the rotational direction of the image carrier in the exposure region exposed by the pre-exposure means in the contact region, and Vbd is the surface potential of the image carrier near the downstream end in the rotational direction of the image carrier in the region where the exposure region and the contact region overlap on the surface of the image carrier, then In addition, the surface potential is formed such that |Vbmax|>|Vbd| by exposing the surface of the image carrier with the pre-exposure means.

[0009] The image forming apparatus according to the present invention is A rotating image carrier, A charging means that forms a charged portion opposite to the surface of the image carrier and charges the surface of the image carrier, A developing means that supplies a developer to the surface of the image carrier charged by the charging means and forms a developer image, A transfer means for forming a transfer section with the image carrier and transferring the developer image from the image carrier to the transfer target, A brush that contacts the surface of the image carrier at the brush portion, downstream of the transfer portion and upstream of the charging portion in the rotational direction of the image carrier, A voltage applying means for applying a voltage to the brush, A pre-exposure means for exposing the surface of the image carrier downstream of the brush portion and upstream of the charging portion in the rotational direction of the image carrier, Equipped with, In an image forming apparatus in which, after the developer image is transferred to the transfer body, the developer remaining on the surface of the image carrier is recovered by the developing means, When the surface potential of the image carrier when exposure is performed by the pre-exposure means is Von, and the surface potential of the image carrier when exposure is not performed by the pre-exposure means is Voff, there is a portion in the contact area where the image carrier contacts the brush on the surface of the image carrier where |Von| < |Voff|.

Advantages of the Invention

[0010] According to the present invention, in an image forming apparatus having a brush that abuts on a photosensitive drum, it is possible to suppress the occurrence of image defects due to toner accumulated on the brush.

Brief Description of the Drawings

[0011] [Figure 1] It is an explanatory diagram of an image forming apparatus in Example 1. [Figure 2] It is a control block diagram in Example 1. [Figure 3] It is a cross-sectional view of a brush in Example 1. [Figure 4] It is a perspective view of a brush in Example 1. [Figure 5] It is a cross-sectional view for explaining a conventional form. [Figure 6] It is a cross-sectional view for explaining Example 1. [Figure 7] It is a diagram for explaining various potential relationships of a conventional form. [Figure 8] It is a diagram for explaining three kinds of various potential relationships of Example 1. [Figure 9] It is a diagram for explaining a paper passing image used in the paper passing test of Example 1 and image defects that occur. [Figure 10] It is a cross-sectional view for explaining a method of verifying potential relationships in Example 1. [Figure 11] It is a diagram for comparing the brush configurations of Example 1 and Example 2. [Figure 12] It is a diagram for comparing various potential relationships of Example 1 and Example 2. [Figure 13] It is a cross-sectional view for comparing the brush abutting states of Example 1 and Example 3. [Figure 14] This diagram compares the various potential relationships between Example 1 and Example 3. [Modes for carrying out the invention]

[0012] The embodiments for carrying out this invention will be described in detail below with reference to the drawings, based on examples. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately modified depending on the configuration of the device to which the invention is applied and various conditions. In other words, this invention is not intended to limit its scope to the following embodiments. No. Furthermore, unless otherwise specified, terms indicating geometric shapes or relationships such as parallel, perpendicular, center, straight line, and circle are not limited to mathematically strict meanings, but are interpreted to include the range permitted by manufacturing tolerances, etc.

[0013] (Example 1) 1. Image forming apparatus Figure 1 shows a schematic configuration of one embodiment of the image forming apparatus 100 according to the present invention. The image forming apparatus 100 of Example 1 is a monochrome laser beam printer employing a cleanerless method and a contact charging method. Because it is a cleanerless method, after the developer is transferred to the transfer target such as a recording material, the developer remaining on the surface of the image carrier is recovered by the developing means.

[0014] The image forming apparatus 100 is equipped with a photosensitive drum 1, which is a cylindrical photosensitive body that serves as an image carrier. Around the photosensitive drum 1 are a charging roller 2 as a charging means and a developing device 3 as a developing means. In Figure 1, an exposure device 4 is provided downstream of the charging roller 2 and upstream of the developing device 3 in the rotational direction of the photosensitive drum 1. A transfer roller 5 is pressed against the photosensitive drum 1 as a transfer means.

[0015] The photosensitive drum 1 is a negatively charged organic photoreceptor. This photosensitive drum 1 has a photosensitive layer on an aluminum drum-shaped substrate. The photosensitive drum 1 is driven to rotate at a predetermined process speed in the direction of the arrow in Figure 1 (clockwise when viewed parallel to the rotation axis of the photosensitive drum 1) by a drive motor 110 (see Figure 2) as a driving means. The process speed is expressed as the peripheral speed (surface moving speed) of the photosensitive drum 1. In Example 1, the process speed is set to 140 mm / sec and the outer diameter of the photosensitive drum 1 is set to 24 mm.

[0016] The charging roller 2 faces the surface of the photosensitive drum 1 and contacts it with a predetermined pressure, forming a charged area. A predetermined charging voltage (charging bias) is applied to the charging roller 2 by a charging power supply E1 (see Figure 2) as a means for applying the charging voltage. The surface of the photosensitive drum 1 is uniformly charged to a predetermined potential by the charging roller 2. In Example 1, a negative polarity DC voltage is applied to the charging roller 2 as the charging voltage, and the surface of the photosensitive drum 1 is uniformly charged to a negative polarity dark area potential Vd by the charging roller 2. In Example 1, the charging voltage is -1300V and the dark area potential Vd is -700V. The surface of the photosensitive drum 1 is charged by discharge generated in at least one of the minute gaps between the photosensitive drum 1 and the charging roller 2, which are formed on the upstream and downstream sides in the rotational direction of the photosensitive drum 1 from the contact area between the photosensitive drum 1 and the charging roller 2. The contact area between the charging roller 2 and the photosensitive drum 1 is called the charged area.

[0017] The exposure device 4 is a laser scanner device that outputs laser light L corresponding to image information input from an external device such as a host computer, and scans and exposes the surface of the photosensitive drum 1, which is uniformly charged to a dark area potential Vd. At the exposed area, the potential of the photosensitive drum 1 changes to a bright area potential Vl. This exposure forms an electrostatic latent image (electrostatic image) on the surface of the photosensitive drum 1 corresponding to the image information. In Example 1, the bright area potential Vl is set to -100V. The position on the photosensitive drum 1 that is exposed by the exposure device 4 is defined as the exposed area. Note that the exposure device 4 is not limited to a laser scanner device; for example, an LED array having multiple LEDs arranged along the longitudinal direction (parallel to the rotation axis) of the photosensitive drum 1 can also be used.

[0018] The image forming apparatus 100 uses a contact developing method. The developing apparatus 3 includes a developing roller 31 as a developer carrier, a toner supply roller 32 as a developer supply means, a developer storage chamber 33 for storing toner, and a developing blade 34. The toner supplied from the developer storage chamber 33 to the developing roller 31 by the toner supply roller 32 passes through the blade nip, which is the contact point between the developing roller 31 and the developing blade 34, and is charged to a predetermined polarity. The developing roller 31 develops the toner by contacting the photosensitive drum 1. The contact area between the developing roller 31 and the photosensitive drum 1 is called the developing section. In the developing section, the toner supported on the developing roller 31 moves from the developing roller 31 to the photosensitive drum 1 according to the electrostatic image. Here, the developing roller 31 is rotated counterclockwise (counterclockwise when viewed parallel to the rotation axis of the photosensitive drum 1) so that the photosensitive drum 1 and the developing roller 31 move in the forward direction in the developing section. Note that the drive motor 110 that drives the photosensitive drum 1 may also provide driving force to the developing roller 31, or a separate drive motor may provide driving force to the developing roller 31. During development, a predetermined developing voltage (developing bias) is applied to the developing roller 31 by a developing power supply E2 (see Figure 2) as a means for applying the developing voltage. In Example 1, the developing voltage was a negative polarity DC voltage, set to -400V. In the region of the photosensitive drum 1 where the bright area potential Vl is formed, toner charged with the same polarity as the charging polarity of the photosensitive drum 1 (negative polarity in Example 1) adheres. This development method is called the inversion development method. In addition to the one-component non-magnetic contact development method of Example 1, other development methods such as the two-component non-magnetic contact development method, non-contact development method, and magnetic development method can be employed. The two-component non-magnetic contact development method uses a two-component developer comprising non-magnetic toner and a magnetic carrier as the developer, and develops by bringing the developer (magnetic brush) supported on the developer carrier into contact with the photosensitive drum 1. The non-contact development method develops by flying toner onto the photosensitive drum from a developer carrier positioned opposite the photosensitive drum without contact. The magnetic development method develops by supporting magnetic toner by magnetic force on a developer carrier containing a magnet as a means of generating a magnetic field, which is positioned opposite the photosensitive drum, either in contact or not in contact. Example 1 uses a toner with a central average particle size of 6 μm and a normal charge polarity of negative polarity.

[0019] As the transfer roller 5, it is preferable to use one made of an elastic material such as polyurethane rubber, EPDM (ethylene propylene diene rubber), or NBR (nitrile butadiene rubber) sponge rubber. The transfer roller 5 is pressed toward the photosensitive drum 1, forming a transfer area where the photosensitive drum 1 and the transfer roller 5 are in contact. During transfer, a predetermined transfer voltage (transfer bias) is applied to the transfer roller 5 by the transfer power supply E3 (Figure 2), which serves as a means for applying the transfer voltage. In Example 1, a DC voltage with the opposite polarity to the normal polarity of the toner (positive polarity in Example 1) is applied to the transfer roller 5 as the transfer voltage during transfer. In Example 1, the transfer voltage is set to +1000V. Then, due to the action of the electric field formed between the transfer roller 5 and the photosensitive drum 1, the developer image is electrostatically transferred from the photosensitive drum 1 to the recording material S.

[0020] The recording material S stored in the cassette 6 is fed by the paper feed unit 7 at the same time that the toner image formed on the photosensitive drum 1 reaches the transfer section, and is transported to the transfer section via the registration roller pair 8. The toner image formed on the photosensitive drum 1 is transferred onto the recording material S by the transfer roller 5, to which a predetermined transfer voltage is applied by the transfer power supply E3.

[0021] After the toner image has been transferred, the recording material S is transported to the fuser 9. The fuser 9 is a film heating type fuser equipped with a fuser heater (not shown), a fuser film 91 containing a thermistor (not shown) for measuring the temperature of the fuser heater, and a pressure roller 92 for pressing the fuser film 91 against the film. The recording material S, on which the toner image has been fixed by heating and pressurizing in the fuser 9, is discharged outside the machine by passing through the paper discharge roller pair 12.

[0022] Transfer residue toner that remains on the photosensitive drum 1 without being transferred to the recording material S is removed by the following process. The transfer residue toner is negatively charged by discharge from the charging roller 2 in the charging section. The transfer residue toner, negatively charged in the charging roller 2, reaches the developing section as the photosensitive drum 1 rotates. The electrostatic latent image formed on the surface of the photosensitive drum 1 has an image area that is at a bright area potential and a non-image area that is at a dark area potential. The behavior of the transfer residue toner that reaches the developing section will be explained separately for the image area and non-image area of ​​the photosensitive drum 1.

[0023] In the image area of ​​the photosensitive drum 1, the surface of the photosensitive drum 1 is at a bright area potential, which is higher than the potential of the developing roller 31. Therefore, negatively charged particles experience a force moving from the developing roller 31 towards the photosensitive drum 1. Consequently, the negatively charged transfer residue toner adhering to the image area of ​​the photosensitive drum 1 is not transferred from the photosensitive drum 1 to the developing roller 31 in the developing section. Instead, it moves to the transfer section along with the toner transferred from the developing roller 31, and is transferred to the recording material S for image formation.

[0024] On the other hand, in the non-image area of ​​the photosensitive drum 1, the surface of the photosensitive drum 1 is at a dark potential, which is lower than the potential of the developing roller 31 (the absolute value is large due to the negative polarity). Therefore, negatively charged particles experience a force moving from the photosensitive drum 1 towards the developing roller 31. Thus, the negatively charged transfer residue toner adhering to the non-image area of ​​the photosensitive drum 1 is transferred from the photosensitive drum 1 to the developing roller 31 in the developing section and collected in the developer storage chamber 33. The transfer residue toner collected in the developer storage chamber 33 is then used again for image formation.

[0025] The image forming apparatus 100 has a control unit 150 that controls the operation of the various functional units described above. The control unit 150 has a CPU 151 and a memory 152. The memory 152 includes volatile memory for temporarily storing information and non-volatile memory for retaining information over a long period of time. The memory 152 stores image information acquired from external devices and programs that define the control methods for the operation of the various functional units. The CPU 151 controls the operation of the image forming apparatus 100 by inputting and outputting information to and from the memory 152, acquiring and processing image information, and executing programs.

[0026] 2. Brush Configuration The image forming apparatus 100 has a brush 10 that contacts the surface of the photosensitive drum 1 at the brush portion. In Example 1, the brush 10 collects paper dust adhering to the surface of the photosensitive drum 1. The brush 10 contacts the surface of the photosensitive drum 1 downstream of the transfer portion and upstream of the charging portion in the rotational direction of the photosensitive drum 1, forming a contact portion. The area on the surface of the photosensitive drum 1 that is in contact with the brush 10 is called the contact area. The upstream end of the contact area in the rotational direction of the photosensitive drum 1 is called the upstream end, and the downstream end is called the downstream end.

[0027] Figure 3(a) shows a cross-section of the brush 10 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 brush 10 in contact with the photosensitive drum 1.

[0028] As shown in Figure 3, the brush 10 is a pile fabric having a yarn portion 11 consisting of multiple conductive nylon threads 11a that contact and rub against the surface of the photosensitive drum 1, and a base fabric 11b that supports the yarn portion 11. When the threads 11a are not in contact with the photosensitive drum 1, they extend perpendicularly from the base fabric 11b. The threads 11a are uniformly distributed on the base fabric 11b. The brush 10 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.

[0029] The brush 10 is arranged such that its longitudinal direction is parallel to the direction of the rotation axis of the photosensitive drum 1. As the material of the thread 11a, in addition to nylon (registered trademark), rayon, acrylic, polyester, etc. can be used. In Example 1, a conductive thread was used as the thread 11a, but an insulating thread may also be used. The thread 11a is not limited to being formed by twisting fibers as long as it is in a thread shape.

[0030] As shown in FIG. 3(a), in the state where the brush 10 is a single body, that is, in a state where no external force acts to bend the thread 11a (natural state), the distance from the base fabric 11b to the tip of the thread 11a from the base fabric 11b is defined as L1. The base fabric 11b is fixed to a support member (not shown) installed at a predetermined position of the image forming apparatus 100 by fixing means such as double-sided tape. Thereby, the brush 10 is fixed. The brush 10 is fixed such that the shortest distance L2 from the base fabric 11b of the brush 10 fixed to the support member to the surface of the photosensitive drum 1 is shorter than the length L1 of the thread 11a in the single body state. The clearance between the support member and the photosensitive drum 1 is constant. The difference between L2 and L1 is referred to as the intrusion amount of the brush 10 with respect to the photosensitive drum 1. Since L2 < L1, in the usage state of the brush 10, that is, when the brush 10 is fixed to the image forming apparatus 100 and abuts on the surface of the photosensitive drum 1, as shown in FIG. 3(b), the tip of the thread 11a bends toward the rotation direction of the photosensitive drum 1. The contact portion between the tip of the thread 11a provided on the most upstream side among the bent threads 11a and the surface of the photosensitive drum 1 is the upstream end of the contact area. The contact portion between the tip of the thread 11a provided on the most downstream side among the bent threads 11a and the surface of the photosensitive drum 1 is the downstream end of the contact area. The contact mode between the brush 10 and the surface of the photosensitive drum 1 is the contact between each of the plurality of threads 11a and the surface of the photosensitive drum 1. Even when referring to the "contact area", microscopically, the surface of the photosensitive drum 1 and the brush 10 do not contact in the area between adjacent threads 11a. A contact portion is formed by the surface of the photosensitive drum 1 in the contact area and the brush 10 contacting the said surface of the photosensitive drum 1.

[0031] The dimensions of the brush 10 in the longitudinal direction (parallel to the rotation axis of the photosensitive drum 1) are set so that the brush 10 contacts the entire image forming area (the area where a toner image can be formed) on the photosensitive drum 1 in the direction of the rotation axis of the photosensitive drum 1. The dimensions of the brush 10 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 and process cartridge.

[0032] The brush 10 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 brush 10 collects (recovers) paper dust and other deposits transferred from the recording material S to the photosensitive drum 1 in the transfer section, and reduces the amount of paper dust that moves downstream of the brush 10 to the charging section and developing section in the direction of movement (rotation) of the photosensitive drum 1.

[0033] In Example 1, the natural length L1 of the thread 11a of the brush 10 is 4.8 mm, the penetration depth of the brush 10 into the photosensitive drum 1 is 1.5 mm, the length L3 of the brush 10 in the short direction is 5 mm, and the length in the long direction is 230 mm. The fineness (thickness) of the thread 11a is 2 denier (representing the thickness of a thread where 9000 m weighs 2 g), and the density is 240 kF / inch 2 (kF / inch 2( is a unit of brush density, indicating the number of filaments per square inch). The arrangement of the threads 11a is almost uniform from the base of the base fabric 11b 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 brush 10 in the short direction is just an example and is not limited thereto. The longer the length of the brush 10 in the short direction, the longer the paper dust can be collected. The length of the brush 10 in the long direction is just an example and is not limited thereto. For example, the length of the brush 10 in the long direction can be set according to the maximum paper width of the image forming apparatus 100. Also, the fineness of the threads 11a of the brush 10 is just an example and is not limited thereto. The fineness of the threads 11a can be determined considering the ease with which paper dust can pass through. If the fineness of the brush 10 is too small, the force that blocks the paper dust will be weak, and the paper dust will easily pass through. If paper dust passes through the brush 10, the charging of the photosensitive drum 1 by the charging roller 2 will be inhibited, which may result in image defects. Furthermore, if the fineness of the threads 11a of the brush 10 is too high, toner and fine paper dust cannot be collected, resulting in uneven toner adhesion along the longitudinal direction of the charging roller 2, which may cause uneven image density and image defects due to poor charging at the paper dust adhesion area. Also, the density of the threads 11a of the brush 10 is just an example and is not limited to this. The density of the threads 11a can be set considering toner passability and paper dust collection performance. If the density of the threads 11a of the brush 10 is too high, toner passability is low, toner may stack, and the stacked toner may scatter, causing contamination inside the device. Also, if the density of the threads 11a of the brush 10 is too low, sufficient paper dust collection performance may not be obtained. Fineness of threads 11a, In terms of paper dust collection performance, the densities are 1-6 denier and 150-350 kF / inch. 2 It is preferable that this is the case. Furthermore, the length L3 of the brush 10 in the shorter direction is preferably 3 mm or more from the viewpoint of ensuring a long lifespan.

[0034] A brush power supply E4 (see Figure 2) is connected to the brush 10 as a means for applying brush voltage. During image formation, a negative polarity DC voltage is applied to the brush 10 as the brush voltage by the brush power supply E4. In Example 1, the brush voltage during image formation is -300V.

[0035] The image forming apparatus 100 is a cleanerless system in which, after the developer image is transferred to the recording material S, the developer (transfer residue toner) remaining on the surface of the photosensitive drum 1 is recovered by the developing apparatus 3. Preferably, the polarity of the transfer residue toner is the same as the normal polarity of the toner (negative polarity in Example 1). If the transfer residue toner has the opposite polarity to the normal polarity (positive polarity in Example 1), the transfer residue toner in the bright area potential Vl (-100V) and the brush voltage (-300V) will be electrostatically collected by the brush 10. In reality, the bright area potential is affected by the transfer, and the potential is controlled in a direction that further reduces the absolute value. Also, positive polarity transfer residue toner that is not collected by the brush 10 may adhere to the downstream charging roller 2 and cause density unevenness. If the transfer residue toner has the normal polarity (negative polarity), it is less likely to adhere electrostatically to the brush 10 and the charging roller 2 and can be recovered in the developing section. The following explanation assumes that the polarity of the transferred toner is the correct polarity (negative polarity).

[0036] 3. Configuration of the pre-exposure apparatus Next, the pre-exposure device will be described. As shown in Figure 1, the image forming apparatus 100 has a pre-exposure device 13 to equalize the potential of the photosensitive drum 1 after the transfer process. The pre-exposure device 13 is a pre-exposure means that exposes the surface of the photosensitive drum 1 downstream of the brush 10 and upstream of the charging part in the rotation direction of the photosensitive drum 1. The pre-exposure device 13 operates an LED attached to the side of the main body (not shown) and irradiates light parallel to the main scanning direction of the photosensitive drum 1. Light guides and the like are used as light guide members to suppress uneven irradiation in the main scanning direction. The pre-exposure device 13 mainly performs exposure operations during image formation to equalize the potential on the photosensitive drum 1 after the transfer process to the recording material S, and lowers the surface potential of the photosensitive drum 1 to approximately 0V.

[0037] 4. Image output operation The image forming apparatus 100 executes a series of operations to form an image on one or more recording materials S in response to a start instruction for one image output operation (job) from an external device (not shown), such as a personal computer. A job generally includes a pre-rotation process, an image forming process (printing process), a paper-intermediate process when forming an image on multiple recording materials S, and a post-rotation process. The image forming process is a process that performs the formation of an electrostatic image on the photosensitive drum 1, development of the electrostatic image (formation of a toner image), transfer of the toner image, fixing of the toner image, etc., and the image forming time refers to the period during which this image forming process is performed. During the image forming time, that is, within the period during which the image forming process is performed, the timing of each operation, such as the formation of the electrostatic image, the formation of the toner image, the transfer of the toner image, and the fixing of the toner image, is different. The pre-rotation process is a process that performs preparatory operations before the image forming process. The inter-paper process is a process performed between the image forming process for the first recording material S and the image forming process for the second recording material S that follows the first recording material S when the image forming process is performed consecutively on multiple recording materials S (continuous image forming). The post-rotation process is a process that performs the sorting operation (preparation operation) after the image forming process. Non-image forming time refers to the period other than the image forming time, and includes the pre-rotation process, the inter-paper process, and the post-rotation process. The pre-multi-rotation process, which is a preparation operation when the image forming apparatus 100 is powered on or when it returns from sleep mode, is also included in non-image forming time.

[0038] 5. Conventional Configuration For the sake of explaining Example 1, the configuration of the conventional form will be described. Figure 5 illustrates the conventional form. This is a diagram for clarity. Hereinafter, components relating to the conventional embodiment will be denoted by different reference numerals than those in Embodiment 1 to distinguish them from Embodiment 1. Figure 5 is a cross-sectional view showing the arrangement of each component around the photosensitive drum 1A in a conventional image forming apparatus, in a cross-section perpendicular to the rotation axis of the photosensitive drum 1A. Of the optical paths of light when the pre-exposure device 13A exposes the surface of the photosensitive drum 1A, the optical path furthest upstream in the rotation direction of the photosensitive drum 1A is indicated by the numeral A. In a cross-section perpendicular to the rotation axis of the photosensitive drum 1, the region on the surface of the photosensitive drum 1A upstream of the intersection point B between optical path A and the surface of the photosensitive drum 1A is a non-exposure region where exposure by the pre-exposure device 13A does not occur. In the conventional embodiment, in a cross-section perpendicular to the rotation axis of the photosensitive drum 1, the intersection point B is located downstream in the rotation direction of the photosensitive drum 1 from the downstream end in the rotation direction of the photosensitive drum 1A of the contact area that contacts the brush 10A on the surface of the photosensitive drum 1A. Therefore, the contact area between the photosensitive drum 1A and the brush 10A and the exposure area where exposure is performed by the pre-exposure device 13A do not have any common area. In other words, the contact area and the exposure area do not overlap, and there is no portion of the contact area that is included in the exposure area.

[0039] 6. Configuration of Example 1 The configuration of Example 1 will be explained with reference to Figure 6. Figure 6 is a cross-sectional view showing the arrangement of each component around the photosensitive drum 1 in a cross section perpendicular to the rotation axis of the photosensitive drum 1 in the image forming apparatus of Example 1.

[0040] In Figure 6, the optical path furthest upstream in the rotational direction of the photosensitive drum 1 among the optical paths of light when the pre-exposure device 13 exposes the surface of the photosensitive drum 1 is indicated by the symbol A. In a cross section perpendicular to the rotational axis of the photosensitive drum 1, the region of the surface of the photosensitive drum 1 upstream of the intersection B between optical path A and the surface of the photosensitive drum 1A is an unexposed region where exposure by the pre-exposure device 13 does not occur. In Embodiment 1, in a cross section perpendicular to the rotational axis of the photosensitive drum 1, the intersection B is located upstream in the rotational direction of the photosensitive drum 1 from the downstream end in the rotational direction of the photosensitive drum 1 of the contact region that contacts the brush 10 on the surface of the photosensitive drum 1. Furthermore, the exposed region includes at least a part of the contact region. In other words, the intersection B is located within the contact region. The intersection B is the upstream end of the exposed region within the contact region.

[0041] 7. Action of Example 1 To explain the effects that occur with the configuration of Example 1, we will first describe the problems of the conventional configuration.

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

[0043] First, in the conventional configuration, the surface potential Va of the photosensitive drum 1A after transfer is -80V. Here, in Example 1, the bright area potential Vl is -100V, but as described above, due to the effect of transfer, the surface potential Va of the area that was the bright area potential after transfer is reduced in absolute value from the bright area potential Vl, and in Example 1 it is -80V. The surface potential value is just an example. Also, the transfer... Even without considering the change in surface potential due to the influence, the effects of the present invention, as described later, can be obtained similarly. Subsequently, as the photosensitive drum 1A passes through the contact region, the surface potential Vb gradually increases, reaching -230V when it passes the downstream end of the contact region. Here, an increase in the absolute value of the negative potential is expressed as "the potential increases." Although it is not possible to directly measure the surface potential Vb while passing through the contact region with the brush 10A, the following can be inferred from the potential change before and after passing through the contact region. That is, it is inferred that while passing through the contact region, negative charges are injected from the brush 10A to the surface of the photosensitive drum 1A by the brush voltage, and as a result the surface potential increases. Since the brush voltage is constant at -300V, the potential difference between the brush voltage and the surface potential Vb of the photosensitive drum 1A and the brush voltage gradually decreases as it passes through the contact region. There is no part in the contact region where |Vb|<|Va|, and |Vb|≧|Va| is always the case. Furthermore, the surface potential Vb of the photosensitive drum 1A does not decrease in the contact region, and the surface potential Va upstream of the contact region is higher than the surface potential Vd in the exposure region downstream of the contact region. Therefore, there is no part in the contact region where |Va-Vb|>|Vb-Vd|, and |Va-Vb|≦|Vb-Vd| is always true.

[0044] Therefore, in the contact area, the electrostatic force acting on the negatively polarized transfer residue toner acts in the direction from the brush 10A towards the photosensitive drum 1A, but the magnitude of this force decreases as it moves towards the downstream end of the contact area. As a result, it is thought that the negatively polarized transfer residue toner is more easily collected by the brush 10A near the downstream end of the contact area.

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

[0046] Based on the problems of the conventional configuration described above, the operation of Example 1 will be explained using Figure 8. Figure 8 is a diagram showing the change in the surface potential of the photosensitive drum 1 after transfer in the transfer section in Example 1. In Figure 8, section (a) shows the change in the surface potential Va of the photosensitive drum 1 downstream of the transfer section and upstream of the contact area, and section (b) shows the change in the surface potential Vb of the photosensitive drum 1 in the contact area. Section (c) shows the change in the surface potential of the photosensitive drum 1 downstream of the contact area and upstream of the exposure area (non-exposure area), and section (d) shows the change in the surface potential Vd of the photosensitive drum 1 in the exposure area. Section (d) can also be said to show the change in the surface potential of the photosensitive drum 1 downstream of the lower end of the contact area and upstream of the charged section.

[0047] In Example 1, as shown in Figure 6, in a cross-section perpendicular to the rotation axis of the photosensitive drum 1, the intersection point B between the upstream light path A of the irradiation light path by the pre-exposure device 13 and the surface of the photosensitive drum 1 is located upstream of the downstream end of the contact area in the rotation direction of the photosensitive drum 1. As a result, a portion of the irradiation light from the pre-exposure device 13 irradiates the thread portion 11 of the brush 10, and the irradiation light that is not blocked by the thread 11a of the thread portion 11 exposes the surface of the photosensitive drum 1. Therefore, as shown in Figure 8(A), the change in the surface potential Va of the photosensitive drum 1 after transfer and the change in the surface potential Vb of the photosensitive drum 1 in the non-exposed area of ​​the contact area are the same as in the conventional form up to intersection point B, that is, before entering the exposure area.

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

[0049] Regarding the surface potential Vb of the photoreceptor in the contact region, let Vbmax be the potential at intersection B, Vba be the potential upstream of intersection B and near the upstream end of the unexposed region in the contact region, and Vbd be the potential downstream of intersection B and near the downstream end of the exposed region in the contact region. Vbmax is the surface potential of the photosensitive drum 1 at the upstream end of the exposed region in the contact region. In other words, Vbmax has the largest absolute value among Vb because the upstream end of the exposed region in the contact region is the region where the most charge is injected without being discharged. Vbd is the surface potential near the downstream end of the region where the contact region and the exposed region overlap. After passing intersection B, |Vb| gradually decreases from |Vbmax| to |Vbd|. Therefore, in Example 1, the brush member and the pre-exposure device 13 are arranged so that |Vbmax|>|Vbd| is satisfied. This change in Vb increases the potential difference between the brush voltage and Vb, making it more difficult for residual toner to be collected by the brush 10. Here, a larger difference between |Vbmax| and |Vbd| leads to a greater potential difference between the brush voltage and the surface potential Vb of the photosensitive drum 1, thus further suppressing the collection of residual toner. However, in the conventional configuration described above, |Vbmax| = |Vbd|, which increases the amount of residual toner that accumulates near the downstream end of the contact area.

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

[0051] On the other hand, if the brush 10 is densely packed and the exposure intensity of the pre-exposure device 13 in the contact area is low, and the surface potential Vb of the photosensitive drum 1 in the exposure area does not decrease easily, then, as shown in Figure 8(B), |Vbd|≧|Vba| may occur. Note that even in the case of Figure 8(B), the presence of intersection B in the contact area causes the potential difference between the brush voltage and the surface potential Vb of the photosensitive drum 1 to expand in the downstream region of the contact area, similar to the case in Figure 8(A). However, the degree of expansion is smaller compared to the case in Figure 8(A).

[0052] In Example 1, although an exposure area by the pre-exposure device 13 exists within the contact area, the irradiation light is partially blocked by the thread portion 11 of the brush 10. Therefore, the degree of decrease in surface potential due to exposure is likely to be smaller within the contact area than outside the contact area. Consequently, as shown in Figure 8(C), within the exposure area, a potential change occurs where the surface potential drops discontinuously and significantly, with respect to the downstream end of the contact area, i.e., the position where the effect of blocking light by the brush 10 disappears. Even in this case, as shown in Figure 8(C), the presence of intersection B within the contact area causes the potential difference between the brush voltage and the surface potential Vb of the photosensitive drum 1 to expand in the downstream region within the contact area, so that |Vbmax|>|Vbd| holds true. As a result, the effect of making it difficult for residual toner to be collected by the brush 10 is obtained.

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

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

[0055] As a result, in Example 1, it is possible to suppress the occurrence of toner ejection images caused by an increase in residual toner accumulating near the downstream end of the contact area.

[0056] 8. Effects of Example 1 Next, we will describe the paper feeding test conducted to confirm the effect of Example 1. The paper feeding experiment was conducted under the following conditions: Xerox Vitality Multipurpose Paper (Letter size, 20 lb) was used as the recording material S in an environment with a temperature of 23°C and a relative humidity of 50%. As the evaluation image, an image was used in which the upper half of the image formation area was a black image and the lower half was a white image, as shown in Figure 9(a). By using this evaluation image, the residual toner generated during the formation of the black image in the upper half is fed to the brush. If residual toner that could not pass through the brush remains on the brush, a toner ejection image is generated in the white image area of ​​the lower half, as shown in Figure 9(b), due to this residual toner. Therefore, it is possible to determine whether residual toner is accumulating and being ejected on the brush based on the presence or absence of a toner ejection image in the white image area. In the paper feeding test, 50 evaluation images were fed continuously, and it was confirmed whether a toner ejection image was generated in the white image area of ​​the lower half of the image during continuous feeding. Table 1 shows the results of paper feeding tests conducted with the conventional configuration and the configuration of Example 1, and the number of sheets on which toner ejection images occurred in units of 10 sheets. [Table 1]

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

[0058] As described above, by having the configuration of Example 1, it is possible to suppress toner ejection images that occur due to the accumulation of residual toner on the brush. Furthermore, in Example 1, the light from the pre-exposure device 13 was described as irradiating between the brush 10 and the charging roller 2 due to its arrangement. However, the same effect can be obtained even if the position of the pre-exposure device 13 is moved further upstream from the position in Figure 6, so that light is irradiated from downstream of the brush 10, and then passes behind the brush 10 to irradiate the surface of the photosensitive drum 1 upstream of the brush 10.

[0059] Next, a verification method to confirm whether the exposure area by the pre-exposure device 13 extends upstream from the downstream end of the contact area, as in Example 1, will be explained using Figure 10. Figure 10 shows the brush 10 from Figure 6 removed, with the measurement probe 14 of a surface potential meter (Model 344 manufactured by Trek) placed in its place. The measurement part 14a of the measurement probe 14 is positioned to measure the surface potential of the photosensitive drum 1 at a location near the downstream end of region C, which corresponds to the contact area before the brush 10 was removed.

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

[0061] (Example 2) Next, Embodiment 2 of the present invention will be described. The basic configuration and operation of the image forming apparatus in Embodiment 2 are the same as those of the image forming apparatus in Embodiment 1. Therefore, in the image forming apparatus in Embodiment 2, elements having the same or corresponding functions or configurations as those of the image forming apparatus in Embodiment 1 are denoted by the same reference numerals as those in the image forming apparatus in Embodiment 1, and detailed descriptions are omitted.

[0062] The fineness of the yarn 11a of the brush 10 in Example 2 and the density of the yarn 11a in the yarn portion 11 are 1 to 6 denier and 150 to 350 kF / inch, respectively, from the viewpoint of paper dust collection performance, as in Example 1. 2 It is preferable that this is the case. On the other hand, the higher the fineness and density, the easier it is for light from the pre-exposure device 13 to be blocked, and the effect of lowering the surface potential of the photosensitive drum 1 in the contact area becomes smaller, thus reducing the effect of promoting the passage of residual toner.Therefore, in Example 2, a configuration is described in which residual toner can pass through the brush more effectively while ensuring the paper dust collection performance of the brush.

[0063] 1. Configuration of Example 2 The configuration of the brush 10 in Example 2 will be explained using Figure 11. Figure 11 is a perspective view of the brush 10 from the downstream side in the rotational direction of the photosensitive drum 1. Light from the pre-exposure device 13 is irradiated from the front to the back of the paper in Figure 11. Figure 11(a) shows the brush 10 of Example 1, and Figure 11(b) shows the brush 10 of Example 2. In the brush 10 of Example 1, the arrangement of the yarns 11a in the yarn portion 11 is almost uniform from the root of the base fabric 11b to the tip of the bristles, which is the part that contacts the surface of the photosensitive drum 1. In contrast, in the brush 10 of Example 2, multiple pile yarns emerge from the base fabric 11b at regular intervals, and the yarns 11a spread out uniformly as they approach the tip of the bristles, forming a pile fabric. In other words, in the napping direction of the yarn portion 11, the arrangement of the yarns 11a is relatively more uniform near the tip of the bristles than near the root close to the base fabric 11b.

[0064] 2. Action of Example 2 Next, we will explain the effects that occur with the configuration of Example 2. In the brush 10 of Example 1 shown in Figure 11(a), the gaps between the threads 11a through which the light from the pre-exposure device 13 passes are constant from the tip to the base. In contrast, in the brush 10 of Example 2 shown in Figure 11(b), the gaps between the threads 11a through which the light from the pre-exposure device 13 passes are wider near the base D than near the tip. A portion of the light irradiated by the pre-exposure device 13 irradiates the part of the thread portion 11 of the brush 10 that is close to the base fabric 11b, that is, the base portion of the thread portion 11. In Example 2, since the gaps between the threads 11a are wider near the base of the thread portion 11 than near the tip, the light irradiated by the pre-exposure device 13 is less likely to be blocked, the light irradiated by the pre-exposure device 13 is more likely to pass through the brush 10, and the light irradiated by the pre-exposure device 13 reaches further upstream on the surface of the photosensitive drum 1. Therefore, the intersection point B between the upstreammost optical path A of the light irradiated by the pre-exposure device 13 and the surface of the photosensitive drum 1 is located further upstream. As a result, as shown in Figure 12, the starting position of the exposure area in the contact area (position of intersection B) is moved further upstream, so the potential of the surface of the photosensitive drum 1 in the contact area becomes lower from further upstream. Therefore, toner ejection images caused by the accumulation of residual toner can be suppressed more effectively.

[0065] 3. Effects of Example 2 Table 2 shows the results of a paper-passing test conducted in the same manner as described in Example 1 to confirm the effect of Example 2. [Table 2]

[0066] The results in Table 2 show that Example 2 can suppress the generation of toner ejection images even more effectively than Example 1.

[0067] As described above, the configuration of Example 2 makes it possible to suppress toner ejection images that occur due to the accumulation of residual toner on the brush.

[0068] (Example 3) Next, Embodiment 3 of the present invention will be described. The basic configuration and operation of the image forming apparatus in Embodiment 3 are the same as those of the image forming apparatus in Embodiment 1. Therefore, in the image forming apparatus in Embodiment 3, elements having the same or corresponding functions or configurations as those of the image forming apparatus in Embodiment 1 are denoted by the same reference numerals as those in the image forming apparatus in Embodiment 1, and detailed descriptions are omitted.

[0069] In Example 3, we will also describe a configuration that ensures paper dust collection by the brush while allowing residual toner to pass through the brush more effectively.

[0070] 1. Configuration of Example 3 The configuration of the brush 10 in Example 3 will be explained with reference to Figure 13. Figure 13 is a diagram showing a cross-section of the brush 10 with respect to a virtual plane perpendicular to the rotation axis of the photosensitive drum 1. Figure 13(a) shows the brush 10 of Example 1, and Figure 13(b) shows the brush 10 of Example 3. In the brush 10 of Example 1, the length of each thread 11a of the thread portion 11 is uniform, and the base fabric 11b is fixed so as to be parallel to the virtual tangent plane P of the surface of the photosensitive drum 1 in the central part of the contact area. Therefore, the amount of penetration of the threads 11a is almost uniform throughout the entire contact area (from the upstream end to the downstream end), and 11a contacts the surface of the photosensitive drum 1 uniformly within the contact area.

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

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

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

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

[0075] 3. Effects of Example 3 Table 3 shows the results of a paper-passing test conducted in the same manner as described in Example 1 to confirm the effect of Example 3. [Table 3]

[0076] The results in Table 3 show that Example 3 can suppress the generation of toner ejection images even more effectively than Example 1.

[0077] As described above, the configuration of Example 3 has paper dust collection performance equivalent to or better than that of Example 1, and can suppress toner ejection images caused by the accumulation of residual toner on the brush. [Explanation of Symbols]

[0078] 1: Photosensitive drum, 2: Charging roller, 3: Developing unit, 5: Transfer roller, 10: Brush, 13: Pre-exposure unit

Claims

1. an image carrier that is rotated; a charging unit which forms a charging portion facing the surface of the image carrier and charges the surface of the image carrier; a developing means for supplying a developer to the surface of the image carrier charged by the charging means to form a developer image; a transfer unit which forms a transfer portion between the image carrier and the transfer unit and transfers the developer image from the image carrier to a transfer target; a brush that contacts a surface of the image carrier at a brush portion downstream of the transfer portion and upstream of the charging portion in a rotation direction of the image carrier; A voltage applying means for applying a voltage to the brush; a pre-exposure unit for exposing a surface of the image carrier downstream of the brush unit and upstream of the charging unit in a rotation direction of the image carrier; Equipped with In an image forming apparatus, after the developer image is transferred to the transfer medium, the developer remaining on the surface of the image carrier is recovered by the developing means, An image forming apparatus characterized in that the upstream end, in the direction of rotation of the image carrier, of an exposure area on the surface of the image carrier exposed by the pre-exposure means is upstream, in the direction of rotation of the image carrier, of a contact area on the surface of the image carrier that contacts the brush, and the exposure area includes at least a portion of the contact area.

2. The brush has a base fabric and a thread portion including a plurality of threads extending from the base fabric, 2. The image forming apparatus according to claim 1, wherein, in the raising direction of the yarn, the arrangement of the yarn is relatively uniform near the tip of the yarn portion compared to near the base close to the base fabric.

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

4. 4. The image forming apparatus according to claim 2, wherein a part of the light emitted by the pre-exposure means is incident on a portion of the yarn portion close to the base fabric.

5. 5. The image forming apparatus according to claim 2, wherein the base fabric is parallel to a virtual tangent plane that contacts the surface of the image carrier at a center of the contact area in the rotation direction of the image carrier.

6. 5. An image forming apparatus according to claim 2, wherein the base fabric is inclined in a direction opposite to the rotation direction of the image carrier with respect to a virtual tangent plane that contacts the surface of the image carrier at the center of the contact area in the rotation direction of the image carrier.

7. The length of each thread of the thread portion is uniform, 5. The image forming apparatus according to claim 2, wherein the amount of penetration of each of the threads of the thread portion into the surface of the image carrier is uniform over the entire contact area.

8. The length of each thread of the thread portion is uniform, 5. The image forming apparatus according to claim 2, wherein an intrusion amount of each thread of the thread portion into the surface of the image carrier decreases toward a downstream end of the contact area in the rotation direction of the image carrier.

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

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

11. an image carrier that is rotated; a charging unit which forms a charging portion facing the surface of the image carrier and charges the surface of the image carrier; a developing means for supplying a developer charged to a normal polarity to the surface of the image carrier charged by the charging means to form a developer image; a transfer unit which forms a transfer portion between the image carrier and the transfer unit and transfers the developer image from the image carrier to a transfer target; a brush that contacts a surface of the image carrier at a brush portion downstream of the transfer portion and upstream of the charging portion in a rotation direction of the image carrier; a voltage applying means for applying a voltage of the normal polarity to the brush; a pre-exposure unit for exposing a surface of the image carrier downstream of the brush unit and upstream of the charging unit in a rotation direction of the image carrier; Equipped with In an image forming apparatus, after the developer image is transferred to the transfer medium, the developer remaining on the surface of the image carrier is recovered by the developing means, An image forming apparatus characterized in that, when the surface potential of the image carrier downstream of the transfer section and upstream of the brush section in the rotation direction of the image carrier is Va, and the surface potential of the image carrier in a contact area on the surface of the image carrier that comes into contact with the brush is Vb, by exposing the surface of the image carrier by the pre-exposure means, a surface potential is formed in the area of ​​the brush section on the surface of the image carrier so that |Vb|<|Va|.

12. An image forming apparatus as described in claim 11, wherein by exposing the surface of the image carrier by the pre-exposure means, a surface potential of Vb is formed in a region of the brush portion on the surface of the image carrier downstream from the center in the direction of rotation of the image carrier, so that |Vb|<|Va|.

13. an image carrier that is rotated; a charging unit which forms a charging portion facing the surface of the image carrier and charges the surface of the image carrier; a developing means for supplying a developer to the surface of the image carrier charged by the charging means to form a developer image; a transfer unit which forms a transfer portion between the image carrier and the transfer unit and transfers the developer image from the image carrier to a transfer target; a brush that contacts a surface of the image carrier at a brush portion downstream of the transfer portion and upstream of the charging portion in a rotation direction of the image carrier; A voltage applying means for applying a voltage to the brush; a pre-exposure unit for exposing a surface of the image carrier downstream of the brush and upstream of the charging unit in a rotation direction of the image carrier; Equipped with In an image forming apparatus, after the developer image is transferred to the transfer medium, the developer remaining on the surface of the image carrier is recovered by the developing means, an image forming apparatus characterized in that, when the surface potential of the image carrier in the contact area on the surface of the image carrier that comes into contact with the brush is Vb, the surface potential of the image carrier at the upstream end in the rotation direction of the image carrier of the exposure area exposed by the pre-exposure means in the contact area is Vbmax, and the surface potential of the image carrier near the downstream end in the rotation direction of the image carrier of the area where the exposure area and the contact area overlap on the surface of the image carrier is Vbd, by exposing the surface of the image carrier by the pre-exposure means, a surface potential is formed so that |Vbmax|>|Vbd|.

14. an image carrier that is rotated; a charging unit which forms a charging portion facing the surface of the image carrier and charges the surface of the image carrier; a developing means for supplying a developer to the surface of the image carrier charged by the charging means to form a developer image; a transfer unit which forms a transfer portion between the image carrier and the transfer unit and transfers the developer image from the image carrier to a transfer target; a brush that contacts a surface of the image carrier at a brush portion downstream of the transfer portion and upstream of the charging portion in a rotation direction of the image carrier; A voltage applying means for applying a voltage to the brush; a pre-exposure unit for exposing a surface of the image carrier downstream of the brush unit and upstream of the charging unit in a rotation direction of the image carrier; Equipped with In an image forming apparatus, after the developer image is transferred to the transfer medium, the developer remaining on the surface of the image carrier is recovered by the developing means, An image forming apparatus characterized in that, when the surface potential of the image carrier is Von when exposure by the pre-exposure means is performed and the surface potential of the image carrier is Voff when exposure by the pre-exposure means is not performed, there is a portion among the contact areas on the surface of the image carrier that come into contact with the brush such that |Von|<|Voff|.

15. The image forming apparatus according to claim 1, wherein the brush has bristles that contact the surface of the image carrier, and the density of the bristles is 150 to 350 kF / inch 2 .

Images