Image forming apparatus

Abstract

To reduce accumulation of toner while ensuring the paper dust collection ability of a brush member.SOLUTION: An image forming apparatus comprises: a rotating image carrier; developing means that develops an electrostatic latent image formed on the image carrier by using developer at a developing part; transfer means that transfers a developer image developed by the developing means from the image carrier to a transfer target body at a transfer part; and a brush member that is in contact with the image carrier at a position downstream of the transfer part and upstream of the developing part in the direction of rotation of the image carrier, and the image forming apparatus collects the developer not transferred to the transfer target body at the developing part. The average interval between bristle materials of the brush member in the direction of axis of rotation of the image carrier is larger than the average particle diameter of the developer and is equal to or less than a length equivalent to the visually recognizable spatial frequency when a user sees an image formed by the image forming apparatus.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus for forming an image on a recording material. [Background technology]

[0002] In electrophotographic image forming apparatuses, a cleanerless system (simultaneous development and cleaning system) is known in which toner (developer) that remains on the photosensitive drum without being transferred to the recording material is recovered in the developing unit and reused. In the cleanerless system, it is necessary to reduce the possibility that foreign matter such as paper fibers and fillers (hereinafter collectively referred to as "paper dust") adhering to the photosensitive drum may have an undesirable effect on subsequent image forming processes. Patent Document 1 describes a method of recovering paper dust on the photosensitive drum using a brush member that contacts the surface of the photosensitive drum, thereby reducing the amount of paper dust that reaches the charging unit and developing unit downstream of the transfer unit. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-189358 [Overview of the project] [Problems that the invention aims to solve]

[0004] When using the brush component described in the above-mentioned document, if the brush component accumulates a large amount of toner, it may eject toner clumps due to some trigger, such as a change in the contact state of the brush component or a large fluctuation in the potential difference between the brush component and the photosensitive drum. Toner clumps ejected from the brush component may not be completely recovered by the developing device and may be transferred to the recording material, potentially causing image defects.

[0005] On the other hand, if the brush component is prevented from accumulating toner, the paper dust collection performance may also decrease. Paper dust that slips through the brush component can interfere with the uniform charging of the photosensitive drum surface during the charging process, potentially causing image defects (black spots) and other undesirable effects in subsequent image formation processes.

[0006] Therefore, the present invention provides an image forming apparatus that can reduce toner accumulation while ensuring the paper dust collection performance of the brush member. [Means for solving the problem]

[0007] One aspect of the present invention is an image forming apparatus comprising: a rotating image carrier; a developing means for developing an electrostatic latent image formed on the image carrier using a developer in a developing unit; a transfer means for transferring the developer image developed by the developing means from the image carrier to a transfer target in a transfer unit; and a brush member that contacts the image carrier at a position downstream of the transfer unit and upstream of the developing unit in the rotational direction of the image carrier, wherein the developer not transferred to the transfer target is recovered in the developing unit, wherein the average spacing between the bristles of the brush member in the rotational axis direction of the image carrier is greater than the average particle size of the developer, and When viewing an image formed on recording material from a distance of 300 mm Spatial frequency of 50 cycles / deg 1 cycle length equivalent to half Below the law of nature , The average spacing between the bristles of the brush member of the image carrier in the rotational direction of the image carrier is wider than the average spacing between the bristles of the brush member of the image carrier in the rotational direction of the image carrier. This is an image forming apparatus characterized by the following features.

[0008] One aspect of the present invention is an image forming apparatus including a rotating image carrier, developing means for developing an electrostatic latent image formed on the image carrier with a developer in a developing unit, transfer means for transferring the developer image developed by the developing means from the image carrier to a transfer medium in a transfer unit, and a brush member that contacts the image carrier at a position downstream of the transfer unit and upstream of the developing unit in the rotation direction of the image carrier, the image forming apparatus recovering undeveloped developer in the developing unit, wherein an average interval between bristles of the brush member in the rotation axis direction of the image carrier is larger than an average particle diameter of the developer and is 50 μm or less. the law of nature , The average spacing between the bristles of the brush member of the image carrier in the rotational direction of the image carrier is wider than the average spacing between the bristles of the brush member of the image carrier in the rotational direction of the image carrier. The image forming apparatus is characterized by this.

Effect of the Invention

[0009] According to the present invention, it is possible to reduce toner accumulation while ensuring the paper powder recovery performance of the brush member.

Brief Description of the Drawings

[0010] [Figure 1] Schematic diagram of the image forming apparatus according to Example 1 of the present disclosure. [[ID=2,1]] [Figure 2] Graph representing characteristics of human vision. [Figure 3] Perspective view of the brush member according to Example 1. [Figure 4] Schematic diagram (a) showing a state of the brush member according to Example 1 as viewed from the tip side of the bristles and schematic diagram (b) of the brush member as viewed from the upstream side in the rotation direction of the photosensitive drum. [Figure 5] Schematic diagrams (a - c) for explaining the relationship between the fiber diameter of the bristles of the brush member and the toner particle diameter. [Figure 6] Diagram for explaining the arrangement of the bundles of the bristles of the brush member.

Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments according to the present disclosure will be described with reference to the drawings.

[0012] <Example 1> FIG. 1 shows a schematic configuration of an image forming apparatus 100 according to an example (Example 1) of an embodiment of the present disclosure. The image forming apparatus 100 in this example is a monochrome printer.

[0013] The image forming apparatus 100 has a cylindrical photoreceptor as an image carrier, that is, a photosensitive drum 1. Around the photosensitive drum 1, a charging roller 2 as charging means and a developing device 3 as developing means are provided. Also, an exposure device 4 as exposure means is provided between the charging roller 2 and the developing device 3 in the figure. Further, a transfer roller 5 as transfer means is pressed against the photosensitive drum 1.

[0014] The photosensitive drum 1 in this example is a negatively chargeable organic photoreceptor. The photosensitive drum 1 has a photosensitive layer on a drum-shaped substrate made of aluminum. The photosensitive drum 1 is rotatable about its axis and is rotationally driven in the direction of arrow A in the figure (clockwise direction in the figure) at a predetermined process speed by a driving device (not shown). In this example, the process speed corresponds to the peripheral speed (surface movement speed) of the photosensitive drum 1.

[0015] The charging roller 2 contacts the photosensitive drum 1 with a predetermined pressing force to form a charging portion P1. At the time of image formation, the charging roller 2 is applied with a predetermined charging voltage by a charging high-voltage power source (not shown) as charging voltage supply means, and the surface of the photosensitive drum 1 is uniformly charged to a predetermined potential. In this example, the photosensitive drum 1 is charged negatively by the charging roller 2, and its charging potential (the surface potential of the photosensitive drum 1 immediately after passing through the charging portion P1. Dark portion potential) is approximately -700 [V].

[0016] In this embodiment, the exposure apparatus 4 is a laser scanner device that outputs laser light 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. This exposure forms an electrostatic latent image (electrostatic image) on the surface of the photosensitive drum 1 corresponding to the image information. The potential of the exposed area (bright area potential) in this embodiment is approximately -100[V]. The exposure apparatus 4 is not limited to a laser scanner device; for example, an LED array in which multiple LEDs are arranged along the longitudinal direction (axial direction of the cylinder) of the photosensitive drum 1 may be used.

[0017] In this embodiment, a contact development method is used as the development method. The development 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 34 for containing toner, a stirring member 33 for stirring the toner in the developer storage chamber 34, and a developing blade 35. The toner (developer) supplied from the developer storage chamber 34 to the developing roller 31 by the toner supply roller 32 is charged to a predetermined polarity by passing through the contact area with the developing blade 35. In this embodiment, a toner with a particle size of 7 μm and a normal charge polarity (normal polarity) of negative polarity is used. In this embodiment, a one-component non-magnetic developer consisting of toner is used as the developer, but a two-component developer including non-magnetic toner and a magnetic carrier may also be used. Alternatively, a two-component non-magnetic contact / non-contact development method may be used.

[0018] The electrostatic latent image formed on the photosensitive drum 1 is developed as a toner image (developer image) by toner transported by the developing roller 31 at the opposing section (developing section P2) between the developing roller 31 and the photosensitive drum 1. During image formation, a developing voltage of -400V is applied to the developing roller 31 by a developing high-voltage power supply (not shown) as a means for applying the developing voltage. In this embodiment, the electrostatic latent image is developed using an inversion developing method. That is, the electrostatic latent image is developed as a toner image by attaching toner charged with the same polarity as the charging polarity of the photosensitive drum 1 to the portion (bright area) on the surface of the photosensitive drum 1 after charging treatment where the charge has been attenuated by exposure by the exposure device 4.

[0019] The transfer roller 5 can preferably be made of an elastic material such as polyurethane rubber, EPDM (ethylene propylene diene rubber), or sponge rubber formed from NBR (nitrile butadiene rubber). The transfer roller 5 is pressed toward the photosensitive drum 1, forming a transfer section N where the photosensitive drum 1 and the transfer roller 5 are in contact. A transfer high-voltage power supply (not shown) is connected to the transfer roller 5 as a means of applying the transfer voltage, and a predetermined transfer voltage is applied at a predetermined timing. In addition, a corona discharge type transfer device may be used as a direct transfer means.

[0020] As the toner image formed on the photosensitive drum 1 reaches the transfer section N, the transfer material S stored in the cassette 6 is fed by the feeding unit 7 and transported to the transfer section N via the registration roller pair 8. A variety of sheet materials of different sizes and materials can be used as the transfer material S (recording material), including plain paper and cardboard, plastic film, cloth, coated paper, and specially shaped sheet materials such as envelopes and index paper. The toner image formed on the photosensitive drum 1 is transferred onto the transfer material S by the transfer roller 5 to which a transfer voltage is applied.

[0021] After the toner image has been transferred, the transfer material S is transported to a fuser 9, which serves as a fixing means. The fuser 9 in this embodiment is a film heating type equipped with a fixing film 91 that incorporates a fixing heater and a thermistor (not shown) for measuring its temperature, and a pressure roller 92 for pressing the fixing film 91 against the film. The fuser 9 fixes the toner image by heating and pressurizing the transfer material S. After fixing, the transfer material S passes through a pair of discharge rollers 10 and is discharged outside the machine.

[0022] Between the transfer section N and the charging section P1, a pre-exposure device 12 is provided as a means for removing static electricity from the surface potential of the photosensitive drum 1. This is to stabilize the discharge at the charging section P1 by leveling out the potential unevenness of the photosensitive drum 1 after it has passed through the transfer section N, thereby obtaining a uniform charging potential.

[0023] Furthermore, any remaining toner on the photosensitive drum 1 that was not transferred to the transfer material S is removed by the following process. The remaining toner contains a mixture of positively charged toner and negatively charged toner that does not have sufficient charge. The remaining toner is recharged to a negative polarity by discharge in the charging unit P1. The remaining toner, recharged to a negative polarity in the charging unit P1, reaches the developing unit 3 as the photosensitive drum 1 rotates and is collected. Therefore, the "brush member" in this embodiment is different from a brush member used as a cleaning device (drum cleaner) for the purpose of removing remaining toner from the photosensitive drum 1.

[0024] [toner] The toner used in this embodiment is a non-magnetic spherical toner produced by suspension polymerization, with an average particle size of 7 μm. While the toner particle size has some distribution, more than 90% of the toner falls between 4 and 10 μm. From the viewpoint of image accuracy and stability, toner with an average particle size of, for example, 4 to 10 μm is preferably used, and an average particle size of 6 to 8 μm is even more preferable.

[0025] This document describes the method for measuring the average particle size dt (weight-average particle size) of toner. The average particle size dt was measured using the "Coulter Counter Multisizer 3" (registered trademark, manufactured by Beckman Coulter), a precision particle size distribution analyzer using the pore electrical resistance method with a 100 μm aperture tube, and the accompanying dedicated software "Beckman Coulter Multisizer 3 Version 3.51" (manufactured by Beckman Coulter) for setting measurement conditions and analyzing measurement data, with an effective measurement channel count of 25,000. The measurement data was then analyzed and calculated.

[0026] The electrolytic aqueous solution used for measurement is prepared by dissolving special grade sodium chloride in deionized water to a concentration of approximately 1% by mass; for example, "ISOTON II" (manufactured by Beckman Coulter) can be used.

[0027] Before performing the measurement and analysis, the dedicated software was configured as follows: In the "Change Standard Measurement Method (SOMME)" screen of the dedicated software, the total count for the control mode was set to 50,000 particles, the number of measurements to 1, and the Kd value was set to the value obtained using "Standard Particle 10.0 μm" (manufactured by Beckman Coulter). The threshold and noise level were automatically set by pressing the measurement button for threshold / noise level. In addition, the current was set to 1600 μA, the gain to 2, the electrolyte to ISOTON II, and the option to flush the aperture tube after measurement was checked. In the "Pulse to Particle Size Conversion Settings" screen of the dedicated software, the bottle spacing was set to logarithmic particle size, the particle size bottles to 256 particle size bottles, and the particle size range from 2 μm to 60 μm.

[0028] The specific measurement method is as follows: (1) Place approximately 200 mL of electrolytic solution into a 250 mL round-bottom glass beaker specifically designed for the Multisizer 3, set it on the sample stand, and stir the mixture with the stirrer rod at 24 revolutions per second in a counterclockwise direction. Then, use the "Aperture Flash" function of the dedicated software to remove any dirt and air bubbles from inside the aperture tube.

[0029] (2) Place approximately 30 mL of the above electrolytic aqueous solution into a 100 mL flat-bottomed glass beaker. Add approximately 0.3 mL of a diluted solution of "Contaminon N" (a 10% by mass aqueous solution of a pH 7 neutral detergent for cleaning precision measuring instruments, consisting of a nonionic surfactant, anionic surfactant, and organic builder, manufactured by Wako Pure Chemical Industries, Ltd.) diluted three times by mass with deionized water as a dispersant.

[0030] (3) Two oscillators with an oscillation frequency of 50 kHz are built in with a phase difference of 180 degrees, and an electrical output of 120 W is added to the tank of an ultrasonic dispersion device called "Ultrasonic Dispersion System Tetora150" (manufactured by Nikko Bios Co., Ltd.). 3.3 L of deionized water is placed in the tank, and approximately 2 mL of Contaminon N is added to this tank.

[0031] (4) Place the beaker from (2) above into the beaker fixing hole of the ultrasonic disperser and operate the ultrasonic disperser. Then, adjust the height of the beaker so that the resonance state of the liquid surface of the electrolytic solution inside the beaker is maximized.

[0032] (5) While irradiating the electrolytic aqueous solution in the beaker described in (4) above with ultrasound, add approximately 10 mg of toner to the electrolytic aqueous solution in small amounts and disperse it. Continue the ultrasonic dispersion treatment for another 60 seconds. During ultrasonic dispersion, adjust the water temperature in the tank to be between 10°C and 40°C as appropriate.

[0033] (6) Using a pipette, add the electrolytic aqueous solution (5) containing the dispersed toner to the round-bottom beaker (1) placed in the sample stand, adjusting the concentration to approximately 5%. Continue the measurement until the number of particles reaches 50,000.

[0034] (7) The measurement data is analyzed using the dedicated software provided with the device to calculate the weight-average particle size. Note that the "Average Diameter" on the Analysis / Volume Statistics (Arithmetic Mean) screen when the dedicated software is set to Graph / Volume % is the weight-average particle size. This weight-average particle size corresponds to the average particle size dt of the toner in this embodiment.

[0035] [Paper dust removal mechanism] When toner is transferred from the photosensitive drum 1 to the transfer material S in the transfer section N, foreign matter such as fibers and fillers contained in the transfer material S, i.e., paper dust, may adhere to the photosensitive drum 1. In this embodiment, a brush member 11 is provided as a paper dust collection member (foreign matter removal member) to remove the paper dust adhering to the photosensitive drum 1. As shown in Figure 1, the brush member 11 is positioned to contact the photosensitive drum 1 downstream of the transfer section N and upstream of the charging section P1 in the rotation direction of the photosensitive drum 1 (arrow A). In other words, the brush member 11 in this embodiment contacts the image carrier at a position downstream of the transfer section N and upstream of the developing section P2 in the rotation direction of the image carrier. The brush member 11 is supported by a support member (not shown) and is positioned 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 rotates.

[0036] The brush member 11 collects paper dust transferred from the transfer material S onto the photosensitive drum 1 at the transfer section N, and reduces the amount of paper dust that moves downstream of the brush member 11 to the charging section P1 and developing device 3 in the direction of movement of the photosensitive drum 1. If the paper dust is not collected by the brush member 11, the paper dust may get into the charging section P1 and inhibit charging. In this case, the potential of the part of the surface of the photosensitive drum 1 where the paper dust was attached after passing through the charging section P1 becomes lower than the surrounding potential, which may cause the corresponding part on the transfer material S to be developed as black unintentionally. This problem can appear, for example, as black spots on a solid white image (a completely white image).

[0037] If the paper dust not collected by the brush member 11 is small, the level of the above-mentioned problems is small, but if the paper dust is large, it tends to worsen the level of the above-mentioned problems. The size of the uncollected paper dust and the size of the black spots causing image defects are almost the same. As described in the "IEICE Knowledge Base" S3 Group-2, Chapter 5, etc., the spatial frequency that the human eye can perceive is 50-60 cycles / deg. Beyond this spatial frequency, it becomes difficult for the human eye to perceive (Figure 2). Figure 2 shows the contrast sensitivity characteristics of the human eye to sinusoidal grid patterns for each spatial frequency. This limit of spatial frequency that the human eye can perceive is also called grid visual acuity.

[0038] Let's assume a typical user views an image formed on recording material from a distance of 300 mm. In this case, a viewing angle of 1° is 300 * 2π / 360 = 5.235 (mm), and one period at a frequency of 50 cycles / deg is 105 μm. The spatial frequency test is performed by checking whether a black-white-black-white-black... striped pattern can be seen, so the thickness of the black areas in the striped pattern corresponds to half of one period, or 52.5 μm. In other words, black areas smaller than 52.5 μm are difficult for the average user to perceive.

[0039] In other words, although it depends on the user's eyesight and the distance at which they view the image, it can be said that even if paper dust with a diameter of approximately 50 μm or less passes through the brush member 11, the black spots mentioned above will not be perceived by the user. Conversely, if paper dust with a diameter of approximately 50 μm or more passes through the brush member 11, the black spots will begin to become slightly visible. If the diameter of the black spots becomes larger than that, for example, 100 μm or more, they will be easily visible as image defects. Also, the more black spots there are, the worse the impression of image quality will be for the user.

[0040] On the other hand, it is preferable that the remaining toner that reaches the brush member 11 does not accumulate (get caught in) the brush member 11, but instead remains attached to the photosensitive drum 1 and moves downstream in the direction of rotation (arrow A). If toner adheres to and accumulates on the brush member 11, it will exist on the brush member 11 as a toner clump, and there is a risk that it will be ejected from the brush member 11 onto the photosensitive drum 1 at an unintended time, causing image defects. Hereinafter, the ejection of toner clumps from the brush member 11, or the image defects caused thereby, will also be referred to as "toner ejection".

[0041] Toner clumps are ejected from the brush member 11 when, for example, the contact state of the brush member 11 with the photosensitive drum 1 changes when the photosensitive drum 1 stops rotating and then starts rotating again. Also, if the surface potential of the photosensitive drum 1 fluctuates greatly when the leading or trailing end of the transfer material S passes through the transfer section N, the contact state of the brush member 11 may change as the area of ​​surface potential fluctuation passes through the brush member 11, causing toner clump ejection. If the amount of toner clumps ejected onto the photosensitive drum 1 is small, they can be recovered by the developing device 3. However, if the amount of toner clumps ejected onto the photosensitive drum 1 is large, it becomes difficult for the developing device 3 to recover them. In that case, some of the toner clumps that were not recovered may be transferred to the transfer material S in the transfer section N, potentially resulting in image defects.

[0042] In other words, it is desirable for the brush member 11 to collect as much paper dust as possible and to collect as little toner as possible.

[0043] [Composition of brush components] The configuration of the brush member 11 in this embodiment will be described below. Figure 3 is an external view of the brush member 11 according to this embodiment. The length of the brush member 11 in the short direction (the rotation direction of the photosensitive drum 1; arrow A) is set to 5 mm. The length of the brush member 11 in the long direction (the rotation axis direction of the photosensitive drum 1; arrow B) is set to 216 mm. The lengths of the brush member 11 in the long and short directions are not limited to these and may be changed as appropriate, for example, according to the maximum paper feed width of the image forming apparatus. The maximum paper feed width of the image forming apparatus is the width of the transfer material with the largest width in the rotation axis direction of the photosensitive drum 1 among the transfer materials that the image forming apparatus can image (feed).

[0044] The brush member 11 comprises conductive nylon 6 threads 11a as multiple bristles for rubbing against the surface of the photosensitive drum 1, a base fabric 11b for supporting the threads 11a, and a sheet metal 11c for attaching and fixing the base fabric 11b. In addition to nylon, rayon, acrylic, polyester, etc. may be used as the material for the threads 11a. In this embodiment, conductive threads 11a were used, but threads made of an insulating material may also be used. Furthermore, the brush may be manufactured using a woven brush or a brush made by an electrostatic flocking method. In this embodiment, a woven brush was used.

[0045] In this embodiment, a bias voltage (brush voltage) of -400V is applied to the sheet metal 11c by a brush power supply 13 (Figure 1) as a voltage application means when the photosensitive drum 1 rotates. This brush voltage has the same polarity as the normal charge polarity of the toner attached to the photosensitive drum 1, thus helping to pass the toner over the photosensitive drum 1 without being collected. Preferably, the brush voltage is a value that has the same polarity as the normal charge polarity of the toner with respect to the surface potential of the photosensitive drum 1 after it has passed through the transfer section N. Note that a configuration in which no brush voltage is applied to the brush member 11 is also possible.

[0046] In this embodiment, the length (bristle length) of the thread 11a of the brush member 11 is 5 mm, and the brush member 11 is positioned so that it penetrates the surface of the photosensitive drum 1 by 1 mm. Here, a penetration amount of 1 mm for the brush member 11 means that the shortest distance from the base fabric 11b to the surface of the photosensitive drum 1, measured in the direction of the thread 11a protruding from the base fabric 11b, is 1 mm shorter than the length of the thread 11a. In other words, assuming there is no interference with the photosensitive drum 1, the brush member 11 is positioned so that a 1 mm range from the tip of the thread 11a penetrates the inside of a virtual cylindrical surface corresponding to the surface position of the photosensitive drum 1.

[0047] The fineness of the yarn 11a used in this embodiment is 6d, and its density is 180 kF / inch. 2 The fineness of the brush member 11 is measured in "d (denier)," which represents the weight of a 9000m length of yarn. A higher fineness indicates a thicker fiber diameter. In this embodiment, the fiber diameter was 27μm, as observed under a microscope. The density of the brush member 11 is measured in "kF / inch." 2 This is expressed as "kF / inch," which indicates the number of filaments per square inch. 2 This represents a density of 1000 lines per square inch.

[0048] Based on these values, a schematic diagram showing how the brush member 11 contacts the photosensitive drum 1 is shown in Figure 4(a, b). Figure 4(a) shows the unit area (1 mm²) when the brush member 11 is observed from directly above (towards the tip of the thread 11a). 2 This is a schematic diagram representing the region of ). Figure 4(b) is a schematic diagram of the brush member 11 as seen from the upstream side in the rotational direction of the photosensitive drum 1.

[0049] In the diagram, "dens" represents the brush density (kF / mm²). 2 ) represents the fiber diameter (μm) of the yarn 11a, and I represents the average spacing between fibers in the longitudinal direction (μm). The density of the yarn 11a of the brush member 11 in this embodiment is 180 kF / inch 2 Since 1 inch = 25.4 mm, dens = 279 (F / mm 2) can be converted to this. In this embodiment, the tips of the threads 11a are isotropically distributed with respect to the short direction (direction of rotation of the photosensitive drum 1; arrow A) and the long direction (axis direction of rotation of the photosensitive drum 1; arrow B) of the brush member 11. Therefore, by taking the square root of the density dens, it is possible to estimate how many threads 11a are in contact with the photosensitive drum 1 for a 1 mm width in the long direction of the photosensitive drum 1. In this embodiment, √279 = 16.7 (threads). Since the fiber diameter of the threads 11a is 27 μm, if the threads 11a exist at equal intervals, the gap between the threads 11a (average distance between bristles; hereafter also called the average distance between fibers) is I = (1000 - 16.7 × 27) / 16.7 = 33 (μm).

[0050] Paper dust larger than the average inter-fiber distance I is physically difficult to pass through the brush member 11. Paper dust smaller than or equal to the average inter-fiber distance I can pass through the brush member 11, but if the size of the paper dust is 50 μm or less, as mentioned above, due to the characteristics of human vision, it is difficult for the user to see it as black spots as long as they use the normal viewing method described above. In other words, if the average inter-fiber distance I is 50 μm or less, it is possible to collect paper dust that is visible to the user. Furthermore, regarding toner ejection, if the average inter-fiber distance I is greater than or equal to the particle size of the toner, the toner can easily pass through the brush member 11. Specifically, since the average particle size of the toner is 7 μm, if the average inter-fiber distance I is greater than 7 μm, it is considered that the brush member 11 can easily pass the toner without collecting it.

[0051] [Method of Consideration] The performance of the brush member 11 in this embodiment was evaluated and examined. Using CenturyStar paper (manufactured by CENTURY PULP AND PAPER, product name) as the transfer material S, 50,000 sheets were printed, and every 100 sheets, a completely black image (solid black image) was printed, followed by a completely white image (solid white image) that was then acquired. The paper dust recovery performance was determined based on the maximum number of spotted images that appeared on the completely white image. In this example, if the number of visible black spots was greater than 10, the paper dust recovery performance was judged as × (unacceptable), if it was between 3 and 10, it was judged as △ (acceptable), and if it was less than 3, it was judged as ○ (good).

[0052] Furthermore, regarding toner ejection, we checked for any image defects caused by toner ejection in the solid white image when printing six images consecutively (five full-halftone images and one solid white image). If no image defects due to toner ejection were observed, the toner ejection performance was marked as ○ (acceptable), and if clear image defects due to toner ejection were observed, the toner ejection performance was marked as × (unacceptable). In addition, for those with a toner ejection performance of ○, if no image defects due to toner ejection were observed in the solid white image even when printing eleven images consecutively (ten full-halftone images and one solid white image), the performance was judged as ◎ (good).

[0053] Table 1 shows the relationship between the configuration of the brush member 11 and the paper dust collection performance and toner ejection performance, as examined above.

[0054] [Table 1]

[0055] As shown in Table 1, the configuration of Example 1 was confirmed to be superior in both paper dust recovery and toner ejection performance. Table 1 also includes the results for the following examples, modifications, and comparative examples.

[0056] <Variation 1-1> As an example of variation 1-1, the fineness is 4d and the density is 240kF / inch. 2A brush member 11 was prepared and its performance was confirmed. The fiber diameter was 21 μm and the average distance between fibers was 31 μm. Conditions other than the brush member 11 were the same as in Example 1. It was confirmed that, as in Example 1, it was excellent in both the performance of paper dust recovery and toner ejection.

[0057] <Modified Example 1-2> As Modified Example 1-2, a brush member 11 with a fineness of 4 d and a density of 180 kF / inch 2 was prepared and its performance was confirmed. The fiber diameter was 21 μm and the average distance between fibers was 39 μm. Conditions other than the brush member 11 were the same as in Example 1. It was confirmed that, as in Example 1, it was excellent in both the performance of paper dust recovery and toner ejection.

[0058] In the above Example 1 and its modified examples, since the average distance I between fibers was sufficiently narrow, it is considered that the ability to collect paper dust of a size that can be visually recognized by the user as an image defect was sufficient and good results were obtained for paper dust recovery. Also, since the average distance I between fibers was larger than the toner size (7 μm), it is considered that good results were obtained for toner ejection as well.

[0059] <Example 2> In Example 2, a brush member 11 using a yarn 11a with a smaller fineness than that in Example 1 as the hair material was prepared. The fineness was 2 d and the density was 180 kF / inch 2 The fiber diameter was 15 μm and the average distance between fibers was 45 μm. Other conditions were the same as in Example 1.

[0060] When evaluating the brush member 11 of this example, it was excellent in paper dust recovery and was even more excellent in toner ejection than in Example 1.

[0061] <Modified Example 2-1> As Modified Example 2-1, a fineness of 2 d and a density of 240 kF / inch 2A brush member 11 was prepared and its performance was confirmed. The fiber diameter was 15 μm and the average inter-fiber distance was 37 μm. All conditions other than the brush member 11 were the same as in Example 1. In this modified example, as in Example 2, the paper dust recovery performance was excellent, and the toner ejection performance was even better than in Example 1.

[0062] In Example 2 and its modifications described above, a yarn 11a with a smaller fineness than that used in Example 1 is used. This is thought to be what makes it possible to further improve the toner ejection performance compared to Example 1. Figures 5(a-c) show the relationship between the size of the yarn 11a and the toner t. In the figure, the surface of the photosensitive drum 1 is moving in the direction of the arrow A from bottom to top. Figures 5(a-c) show the behavior of the toner t when the fiber diameter D of the yarn 11a of the brush member 11 is changed at three levels. In the figure, dt indicates the toner diameter (μm).

[0063] As shown in Figure 5(a), when D < 3dt, even if the toner t collides with the thread 11a of the brush member 11, the curvature of the thread 11a is large from the perspective of the toner t (the radius of curvature of the surface of the thread 11a is small), and the toner t is unstable on the thread 11a. Therefore, the toner t moves to the side of the thread 11a (the side of the thread 11a in the longitudinal direction of the brush member 11) due to the adhesive force with the photosensitive drum 1 or the frictional force received from the photosensitive drum 1. The thread 11a cannot adsorb and hold the toner that has moved to the side, and as a result, the toner t is not collected by the thread 11a and easily slips through to the downstream of the brush member 11.

[0064] As shown in Figure 5(b), when D=3dt, the curvature of the thread 11a decreases (the radius of curvature of the surface of the thread 11a increases), and the surface facing the direction of travel of the photosensitive drum 1 increases, making it easier for the thread 11a to hold toner t. As shown in Figure 5(c), when D>>3dt, the thread 11a can hold more toner, and the held toner will further accumulate.

[0065] As described above, in Example 2 and Modification 2-1, where the fiber diameter D is 15 μm, which is less than three times the average toner particle size of 7 μm, particularly excellent toner ejection performance was observed.

[0066] <Comparative Example 1> Comparative Example 1: Fineness 6d, Density 70kF / inch 2 A brush member 11 was prepared and its performance was confirmed. The fiber diameter was 27 μm, and the average inter-fiber distance was 69 μm. All conditions other than the brush member 11 were the same as in Example 1. In this comparative example, the average inter-fiber distance was larger than the 50 μm diameter of paper dust that is visible as an image defect, resulting in significantly inferior paper dust recovery compared to the above-mentioned example and modification.

[0067] <Comparative Example 2> As comparative example 2, we used a fiber with a fineness of 4d and a density of 120kF / inch. 2 A brush member 11 was prepared and its performance was confirmed. The fiber diameter was 21 μm, and the average inter-fiber distance was 52 μm. All conditions other than the brush member 11 were the same as in Example 1. In this comparative example as well, the average inter-fiber distance was slightly larger than the 50 μm diameter of paper dust that is visible as an image defect, resulting in slightly inferior paper dust recovery performance.

[0068] <Comparative Example 3> As comparative example 3, we used a fiber with a fineness of 2d and a density of 120kF / inch. 2 A brush member 11 was prepared and its performance was confirmed. The fiber diameter was 15 μm, and the average inter-fiber distance was 58 μm. All conditions other than the brush member 11 were the same as in Example 1. In this comparative example as well, the average inter-fiber distance was larger than the 50 μm diameter of paper dust that is visible as image defects, resulting in slightly inferior paper dust recovery performance. However, due to the small fiber diameter, the toner ejection performance was excellent for the reasons explained using Figure 5(a~c).

[0069] <Comparative Example 4> As comparative example 3, a fineness of 10d and density of 70kF / inch 2A brush member 11 was prepared and its performance was confirmed. The fiber diameter was 35 μm and the average inter-fiber distance was 61 μm. All conditions other than the brush member 11 were the same as in Example 1. In this comparative example as well, the average inter-fiber distance I was larger than the diameter of paper dust (50 μm) that is visible as image defects, resulting in poor paper dust recovery. Furthermore, the fiber diameter D was even larger than 3 times the average toner particle size dt, being 5 times, resulting in a state like D>>3dt shown in Figure 5(c), which resulted in poor toner ejection. Therefore, to suppress toner ejection, it is preferable that the fiber diameter D is less than 5 times the average toner particle size dt (D<5dt).

[0070] Based on the above results, in the examples and modifications where the average distance between fibers is greater than the average particle size dt (7 μm) of the toner and less than or equal to the length corresponding to human lattice visual acuity (50 μm), image defects due to paper dust were prevented, and excellent results were also shown in toner ejection. In other words, according to the embodiments of this disclosure, it is possible to reduce toner accumulation while ensuring the paper dust collection performance of the collection member.

[0071] Furthermore, in Example 2 and Modification 2, where the fiber diameter D is less than three times the average toner particle size dt (D < 3dt), particularly excellent toner ejection was observed.

[0072] Although no significant difference was observed in the verification shown in Table 1, it is thought that the smaller the size of the paper dust passing through the brush member 11, the less likely image distortion caused by the paper dust will be to become apparent, even with variations in the user's visual acuity and observation distance. For this reason, the average distance between fibers of the brush member 11 is more preferably 45 μm or less, and even more preferably 40 μm or less.

[0073] Furthermore, while toner can pass through the brush member 11 if the average distance between fibers is greater than the average particle size of the toner, it is considered that the toner passes more easily when the average distance between fibers is significantly greater than the average particle size than when it is close to the average particle size of the toner. From the viewpoint of more reliably reducing toner ejection, it is preferable, for example, to set the average distance between fibers of the brush member 11 to twice or more the average particle size of the toner (7 μm), more preferably four times or more.

[0074] Furthermore, while we have discussed preferred values ​​for the average inter-fiber distance I in the direction perpendicular to the direction of movement of the photosensitive drum surface (arrow A) (the longitudinal direction of the brush member 11), we will now explain the spacing between the bristles of the brush member 11 in the direction of movement of the photosensitive drum surface. It is preferable that the spacing between the bristles in the direction of movement of the photosensitive drum surface (average inter-fiber distance) is wider than the average inter-fiber distance I in the longitudinal direction. This allows the toner that reaches the brush member 11 to flow more smoothly downstream in the direction of movement of the photosensitive drum surface 1, making toner ejection less likely. Regarding paper dust recovery, the average inter-fiber distance I, which is the fiber spacing in the longitudinal direction of the brush member 11, is important, so even if the fiber spacing in the direction of movement of the photosensitive drum surface is somewhat wider, paper dust recovery is maintained.

[0075] Specifically, in the case of the woven brush used in Example 1, as shown in Figure 6, the arrangement of the flocks of yarn 11a of the brush member 11 (each point on the left of Figure 6) should be relatively sparse in the direction of movement of the photosensitive drum surface (arrow A) and relatively dense in the longitudinal direction of the brush member 11 (arrow B). The position of the flocks of the bristles is the starting point of the bundle of yarn 11a supported at the same location on the base fabric 11b. If the spacing between the flocks in the direction of movement of the photosensitive drum surface is PA, and the spacing between the flocks in the longitudinal direction of the brush member 11 (arrow B) is PB, then it is sufficient that PA > PB. In the figure, the yarn 11a in each flock extends almost uniformly (i.e., isotropically) in all directions when viewed from the normal direction of the base fabric 11b, and the number of yarns 11a in each flock is also assumed to be almost uniform.

[0076] (Other variations) In the embodiments described above, a typical user was assumed to be, for example, an office or home printer user, and it was explained that the average distance between fibers of the brush member 11 is preferably 50 μm or less, which corresponds to the grid visual acuity when viewing an image with the naked eye from a distance of 30 cm. However, this is not limited to this, and depending on the application of the image forming apparatus, it may be common for the printed image to be observed from a position farther than 30 cm (or closer than 30 cm). Therefore, the preferred value for the average distance between fibers of the brush member 11 may change depending on the average viewing distance of the image mainly output by the image forming apparatus.

[0077] For example, in the case of a large-format printer mainly used for printing posters, the average observation distance is considered to be greater than 30 cm. In this case, if the user views the image formed on the recording material from a distance of 1 m, the length corresponding to the spatial frequency that the user can perceive (the diameter of the visible black spot) will be approximately 175 μm, so it is conceivable to set the average inter-fiber distance of the brush member 11 to 175 μm or less. Conversely, in the case of an image forming apparatus that mainly outputs images that are typically observed using a magnifying glass, for example, the length corresponding to the spatial frequency that the user can perceive (the diameter of the visible black spot) will be shorter than 52.5 μm. In this case, it is conceivable to set the average inter-fiber distance of the brush member 11 to a predetermined value less than 50 μm.

[0078] (Other embodiments) In the embodiments described above, a monochrome printer was used as an example, but this technology can also be applied to direct transfer color printers. A direct transfer color printer is, for example, an image forming apparatus in which multiple process units, each equipped with an image carrier (photosensitive drum), are arranged along a transport path for the recording material. In this case, a color image is formed on the recording material by sequentially transferring the toner images of each color formed by each process unit onto the recording material.

[0079] Furthermore, although the above-described embodiment described a direct transfer method in which the toner image is directly transferred from the photosensitive drum 1 (image carrier) to the transfer material (recording material) as the transfer target, this technology may also be applied to an image forming apparatus using an intermediate transfer method. In the case of an intermediate transfer method, the transfer member refers to, for example, a transfer roller (primary transfer roller) that first transfers the toner image from the photosensitive drum 1 as the image carrier to the intermediate transfer target as the transfer target. As the intermediate transfer target, an endless belt member stretched across multiple rollers can be used. The toner image first transferred to the intermediate transfer target is then secondarily transferred from the intermediate transfer target to a sheet (recording material) by a secondary transfer means such as a secondary transfer roller that forms a secondary transfer nip between itself and the intermediate transfer target. Even in such an intermediate transfer method configuration, the same effects as in the above-described embodiment can be obtained by replacing the transfer roller in the above-described embodiment with a primary transfer roller. [Explanation of Symbols]

[0080] 1…Image carrier (photosensitive drum) / 3…Developing device / 5…Transfer means (transfer roller) / 11…Brush member

Claims

1. A rotating image carrier, A developing means for developing the electrostatic latent image formed on the image carrier using a developer in a developing unit, A transfer means for transferring the developer image developed by the developing means from the image carrier to the transfer target in the transfer unit, A brush member that contacts the image carrier at a position downstream of the transfer section and upstream of the developing section in the rotational direction of the image carrier, An image forming apparatus comprising, which recovers the developer that was not transferred to the transfer object in the developing unit, The average spacing between the bristles of the brush member in the rotation axis direction of the image carrier is greater than the average particle size of the developer, and is less than half the length corresponding to one period of a spatial frequency of 50 cycles / deg when the image formed on the recording material is viewed from a distance of 300 mm. The average spacing between the bristles of the brush member in the rotational direction of the image carrier is wider than the average spacing between the bristles of the brush member in the rotational direction of the image carrier. An image forming apparatus characterized by the following features.

2. The average interval is 50 μm or less. The image forming apparatus according to feature 1.

3. A rotating image carrier, A developing means for developing the electrostatic latent image formed on the image carrier using a developer in a developing unit, A transfer means for transferring the developer image developed by the developing means from the image carrier to the transfer target in the transfer unit, A brush member that contacts the image carrier at a position downstream of the transfer section and upstream of the developing section in the rotational direction of the image carrier, An image forming apparatus comprising, which recovers the developer that was not transferred to the transfer object in the developing unit, The average spacing between the bristles of the brush member in the rotation axis direction of the image carrier is greater than the average particle size of the developer and 50 μm or less. The average spacing between the bristles of the brush member in the rotational direction of the image carrier is wider than the average spacing between the bristles of the brush member in the rotational direction of the image carrier. An image forming apparatus characterized by the following features.

4. The average interval is 45 μm or less. The image forming apparatus according to any one of claims 1 to 3.

5. If the fiber diameter of the bristles of the brush member is D (μm) and the average particle size of the developer is d (μm), then D < 5d. The image forming apparatus according to any one of claims 1 to 4.

6. If the fiber diameter of the bristles of the brush member is D (μm) and the average particle size of the developer is d (μm), then D < 3d. The image forming apparatus according to any one of claims 1 to 4.

7. The system further comprises a voltage application means for applying a voltage with the same polarity as the normal charging polarity of the developer to the surface potential of the image carrier that has passed through the transfer portion, relative to the brush member. The image forming apparatus according to any one of claims 1 to 6.

8. The material to be transferred is a recording material. The image forming apparatus according to any one of claims 1 to 7.

9. The aforementioned transcribed material is an intermediate transcribed material, The system further comprises a secondary transfer means for transferring the toner image transferred to the intermediate transfer medium to a recording material. The image forming apparatus according to any one of claims 1 to 7.

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