Image forming apparatus

Abstract

An image forming apparatus is disclosed. The image forming apparatus includes: a charging unit that charges an image bearing member; a developing unit forming a toner image on the latent image formed on the image bearing member; a transfer unit that transfers the toner image onto a transfer material; a charge canceller that cancels a charge of the image bearing member downstream of the transfer portion and upstream of the charging portion in a rotation direction of the image bearing member; and a conductive collection unit that collects a material adhering to the image bearing member downstream of the transfer portion and upstream of the charging portion, in which the developing unit collects a residual toner on the image bearing member, the voltage applying unit sets a potential difference between a voltage applied to the collecting unit and a surface potential of the image bearing member to be not greater than a discharge threshold.

Description

[0001] This application is a divisional application of the Chinese invention patent application with application number 202111525315.4, application date December 14, 2021, and titled "Image Forming Device". Technical Field

[0002] The present invention relates to an image forming apparatus. Background Art

[0003] Image forming apparatuses such as laser printers, copy machines, and facsimile machines obtain recorded images by transferring a toner image formed on an image bearing member onto a transfer material using electrophotography or the like.

[0004] In recent years, a cleaner-less system in which residual toner is collected in a developing unit and reused has been proposed as one form of such an image forming apparatus. In this cleaner-less system, toner, paper dust, and filler attached to the photosensitive drum in the transfer portion may sometimes affect downstream processing.

[0005] Japanese Patent Application Laid-Open No. 2007-279431 discloses a configuration in which a collecting member is provided, the collecting member being in contact with the surface of a photosensitive drum to collect residual toner or attached material on the photosensitive drum. Summary of the invention

[0006] The configuration of Japanese Patent Application Publication No. 2007-279431 has the following problem: With the collecting member disposed downstream of the transfer portion in the rotational direction of the photosensitive drum, the toner that cannot be transferred to the paper and remains on the photosensitive drum may accumulate on the collecting member and deteriorate its paper dust collection performance, and the paper dust collected in the developing unit will eventually cause image defects.

[0007] The paper dust attached to the photosensitive drum varies in size depending on the type of paper, etc., and can be as large as several millimeters. Where such large-sized paper dust is attached, the charge cannot be neutralized by exposure, and this sometimes causes image defects due to reduced discharge amount in subsequent charging processing.

[0008] The present invention has been made in view of the above-mentioned problems, and an object thereof is to provide a technique for reducing the occurrence of image defects caused by attached materials such as paper dust or residual toner attached to a photosensitive drum in a cleanerless type image forming apparatus.

[0009] The present invention provides an image forming device, comprising:

[0010] a rotatable image bearing member;

[0011] a charging unit that contacts the image bearing member to form a charging portion and charges a surface of the image bearing member in the charging portion;

[0012] an exposing unit that exposes the surface of the image bearing member charged in the charging portion to form an electrostatic latent image;

[0013] a developing unit that supplies a toner charged to have a predetermined polarity to the electrostatic latent image formed on the surface of the image bearing member to form a toner image;

[0014] a transfer unit that contacts the image bearing member to form a transfer portion and transfers the toner image formed on the surface of the image bearing member to a transfer material in the transfer portion;

[0015] a charge canceller that cancels the charge on the surface of the image bearing member downstream of the transfer portion and upstream of the charging portion in the rotational direction of the image bearing member;

[0016] a collecting unit having conductivity and collecting an adhered material adhered to the surface of the image bearing member downstream of the transfer portion and upstream of the charging portion in the rotation direction of the image bearing member;

[0017] a voltage applying unit that applies a voltage of a predetermined polarity to the collecting unit; and

[0018] A controller controls the voltage applying unit, wherein

[0019] After the toner image is transferred onto the transfer material in the transfer portion, the developing unit collects residual toner on the surface of the image bearing member, and

[0020] The controller controls the voltage applying unit so that a potential difference between a voltage of a predetermined polarity applied to the collecting unit and a surface potential of the image bearing member on the surface of the image bearing member is not greater than a discharge threshold value.

[0021] The present invention also provides an image forming device, comprising:

[0022] a rotatable image bearing member;

[0023] a charging unit that contacts the image bearing member to form a charging portion and charges a surface of the image bearing member in the charging portion;

[0024] an exposing unit that exposes the surface of the image bearing member charged in the charging portion to form an electrostatic latent image;

[0025] a developing unit that supplies a toner charged to have a predetermined polarity to the electrostatic latent image formed on the surface of the image bearing member to form a toner image;

[0026] a transfer unit that contacts the image bearing member to form a transfer portion and transfers the toner image formed on the surface of the image bearing member to a transfer material in the transfer portion;

[0027] a charge canceller that cancels the charge on the surface of the image bearing member downstream of the transfer portion and upstream of the charging portion in the rotational direction of the image bearing member;

[0028] a collecting unit having conductivity and collecting an adhered material adhered to the surface of the image bearing member downstream of the transfer portion and upstream of the charging portion in the rotation direction of the image bearing member;

[0029] a voltage applying unit that applies a voltage of a predetermined polarity to the collecting unit; and

[0030] A controller controls the voltage applying unit, wherein

[0031] After the toner image is transferred onto the transfer material in the transfer portion, the developing unit collects residual toner on the surface of the image bearing member, and

[0032] The collecting unit is disposed downstream of the charge canceller and upstream of the charging portion in the rotation direction of the image bearing member.

[0033] The present invention can provide a technique for reducing the occurrence of image defects caused by attached materials such as paper dust or residual toner attached to a photosensitive drum in a cleaner-less type image forming apparatus.

[0034] Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a diagrammatic view of the image forming apparatus in Embodiment 1;

[0036] Figure 2A and Figure 2B is a diagrammatic view of a brush member;

[0037] Figure 3 is a diagrammatic view of an apparatus for testing paper dust collection performance;

[0038] Figure 4 is a diagrammatic view of an image forming apparatus in Embodiment 2;

[0039] Figure 5A and Figure 5B is a diagrammatic view showing the potential on the photosensitive drum before and after the transfer process in Embodiment 2;

[0040] Fig. 6A and Figure 6B is a diagrammatic view showing toner adhesion on the photosensitive drum in Embodiment 2; and

[0041] Fig. 7A and Figure 7B is a diagrammatic view showing discharge occurring on the toner on the photosensitive drum in Embodiment 2. DETAILED DESCRIPTION

[0042] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the size, material, shape, relative arrangement, etc. of the constituent components described in the embodiments should be appropriately changed according to the configuration and various conditions of the device to which the present invention is applied, and it is not intended to limit the scope of the present invention to the following embodiments. Not all feature combinations described in the embodiments are essential to the solutions of the present invention. Example 1

[0043] Overall configuration of image forming apparatus

[0044] Figure 1 A schematic configuration of one embodiment of an image forming apparatus according to the present invention is illustrated. The image forming apparatus of this embodiment is a monochrome printer.

[0045] The image forming apparatus 100 in this embodiment is provided with a cylindrical photosensitive member as an image bearing member, that is, a photosensitive drum 1. Around the photosensitive drum 1, a charging roller 2 as a charging unit and a developing device 3 as a developing unit are provided. Between the charging roller 2 and the developing device 3 in the figure, an exposure device 4 as an exposure unit is provided. A transfer roller 5 is in pressure contact with the photosensitive drum 1.

[0046] The photosensitive drum 1 in this embodiment is a negatively charged organic photosensitive member. The photosensitive drum 1 has a photosensitive layer on an aluminum drum-shaped substrate. The photosensitive drum 1 can rotate about its axis and is driven by a driving device (not shown) to rotate in the direction of arrow D in the figure (clockwise on the paper) at a predetermined process speed. In this embodiment, the process speed corresponds to the peripheral speed (surface movement speed) of the photosensitive drum 1.

[0047] The charging roller 2 contacts the photosensitive drum 1 with a predetermined pressure and forms a charged portion P. A charging voltage of a desired level is applied by a high-voltage charging power source (not shown) as a charging voltage supply unit so that the surface of the photosensitive drum 1 is uniformly charged to a predetermined potential. In this embodiment, the photosensitive drum 1 is charged to negative polarity by the charging roller 2 to a potential of about -500 V.

[0048] In this embodiment, the exposure device 4 is a laser scanner device that outputs a laser beam corresponding to image information input from an external device such as a host computer to scan and expose the surface of the photosensitive drum 1. By this exposure, an electrostatic latent image (electrostatic image) corresponding to the image information is formed on the surface of the photosensitive drum 1. The potential of the exposure portion in this embodiment is about -100 V. The exposure device 4 is not limited to a laser scanner device. For example, an LED array having a plurality of LEDs aligned along the longitudinal direction (axial direction of the cylinder) of the photosensitive drum 1 may be employed.

[0049] This embodiment adopts a contact development system as a developing method. The developing device 3 includes a developing roller 31 as a developer carrying member, a toner supply roller 32 as a developer supply unit, a developer container 33 containing toner, and a developing blade 34. The toner (developer) supplied from the developer container 33 to the developing roller 31 through the toner supply roller 32 is charged to a predetermined polarity when it passes through the portion where it contacts the developing blade 34. This embodiment uses a toner with a particle size of 6 μm, and its standard polarity when charged is negative. Although this embodiment adopts a single-component, non-magnetic contact development method, a two-component, non-magnetic contact / non-contact development method may also be used.

[0050] The electrostatic latent image formed on the photosensitive drum 1 is developed into a toner image at a position where the developing roller 31 and the photosensitive drum 1 face each other, wherein the toner is conveyed to the position by the developing roller 31. At this time, a developing voltage is applied to the developing roller 31 by a high-voltage developing power source (not shown) as a developing voltage applying unit. In this embodiment, the electrostatic latent image is developed by reverse development. That is, the electrostatic latent image is developed into a toner image in which the toner charged to the same polarity as the charged photosensitive drum 1 is attached to a portion of the charged photosensitive drum 1 where the charge is attenuated by exposure.

[0051] For the transfer roller 5, anything made of an elastic material such as sponge rubber composed of polyurethane rubber, EPDM (ethylene propylene diene monomer rubber), NBR (nitrile rubber) can be appropriately used. The transfer roller 5 is pressed against the photosensitive drum 1, and forms a transfer portion N where the photosensitive drum 1 and the transfer roller 5 are in pressure contact. A predetermined voltage is applied to the transfer roller 5 from a high-voltage transfer power source (not shown) as a transfer voltage applying unit connected to the transfer roller at a predetermined timing.

[0052] The transfer material S (e.g., recording material such as paper) stored in the cassette 6 is fed out by the paper feed unit 7 to match the timing of the toner image formed on the photosensitive drum 1 arriving at the transfer portion N, and is conveyed to the transfer portion N through a pair of resist rollers 8. The toner image formed on the photosensitive drum 1 is transferred onto the transfer material S by the transfer roller 5 to which a predetermined voltage is applied by a high-voltage transfer power source.

[0053] The transfer material S after the toner image is transferred thereon is conveyed to the fixing unit 9. The fixing unit 9 of this embodiment is a film heating type fixing unit including a fixing film 91 including a fixing heater and a thermistor (not shown) for measuring the temperature of the heater, and a pressure roller 92 for pressure contact with the fixing film 91. The toner image is fixed in the fixing unit 9 applying heat and pressure to the transfer material S. After fixing, the transfer material S is discharged to the outside of the machine by a pair of discharge rollers 10.

[0054] A pre-exposure device 12 as a charge canceller for canceling the charge on the surface of the photosensitive drum 1 is provided between the transfer portion N and the charging portion P. This is to minimize the potential variation on the photosensitive drum caused by transfer to stabilize the discharge at the charging portion P and achieve a uniform potential.

[0055] The untransferred toner that is not transferred to the transfer material S and remains on the photosensitive drum 1 is removed in the following process. The untransferred toner is a mixture of positively charged toner and insufficiently negatively charged toner. At the charged portion P, the untransferred toner is negatively charged again by discharge. Thereafter, as the photosensitive drum 1 rotates, the untransferred toner negatively charged again at the charged portion P reaches the developing device 3. As mentioned above, when the toner reaches the developing device 3, an electrostatic latent image corresponding to the image information is formed on the photosensitive drum 1. How the untransferred toner behaves in the exposed portion and the non-exposed portion of the photosensitive drum 1 after reaching the developing device 3 will be described respectively.

[0056] The untransferred toner attached to the non-exposed portion of the photosensitive drum 1 moves to the developing roller 31 in the developing device 3 by the potential difference between the non-exposed portion of the photosensitive drum 1 and the developing voltage, and is collected back to the developer container 33. The toner collected back to the developer container 33 is used again for image formation. On the other hand, the untransferred toner attached to the exposed portion of the photosensitive drum 1 does not move from the photosensitive drum 1 to the developing roller 31 in the developing device 3, but moves to the transfer portion N together with the toner supplied from the developing roller 31 for development, and is transferred to the transfer material S, that is, is removed from the photosensitive drum 1.

[0057] The above-mentioned pre-exposure device 12 offsets the charge on the photosensitive drum 1 after transfer to ensure uniform discharge so that the untransferred colorant can be uniformly negatively charged. This eliminates the toner that cannot be sufficiently negatively charged again, so that the untransferred colorant can be collected more reliably in the developing device 3.

[0058] The image forming apparatus 100 may further include a controller 70. The controller 70 is composed of an information processing device including a processor or a processing circuit such as an FPGA or an ASIC, and performs information processing related to the operation of the image forming apparatus 100 based on a program or a user instruction. The controller 70 performs, for example, control of a voltage or a voltage applying unit applied for charging, developing, transferring, and collecting, control of pre-exposure or exposure based on image information, and control of driving members for a photosensitive drum and various rollers. The controller 70 may be composed of a plurality of information processing devices configured to operate in cooperation with each other for performing these various types of processing.

[0059] Paper dust removal mechanism

[0060] When the toner is transferred from the photosensitive drum 1 to the transfer material S in the transfer portion N, sometimes, paper dust fibers contained in the transfer material S adhere to the photosensitive drum 1. If this paper dust fiber attached to the photosensitive drum 1 is not processed in the cleaner-less system adopted in this embodiment, the paper dust fiber will be collected in the developing device 3. The paper dust fiber may deteriorate the image quality later. For example, when the paper dust collected in the developing device 3 and adhered between the developing blade 34 and the developing roller 31 scrapes off the toner on the developing roller 31, the image will have streaks (hereinafter referred to as development streaks), or the paper dust collected in the developing device 3 may hinder the charging of the toner. If the paper dust fiber is not removed, it may reach the portion where the charge is offset by the pre-exposure device 12. The large-sized paper dust attached to the photosensitive drum 1 will block the light from the pre-exposure device 12, so that the charge on the photosensitive drum surface to which the paper dust is attached cannot be offset. This results in a reduction in the amount of discharge in locations on the photosensitive drum surface that cannot be offset in the subsequent charging process and causes collection failure, i.e., the untransferred toner remaining in these locations will be insufficiently charged and cannot be collected in the developing device 3.

[0061] Therefore, in this embodiment, the brush member 11 is provided as a paper dust collecting member for removing paper dust attached to the photosensitive drum 1. Figure 1 As shown in the figure, the brush member 11 is disposed downstream of the transfer portion N and upstream of the charging portion P in the rotation direction (rotation direction D) of the photosensitive drum 1, and contacts the photosensitive drum 1. The brush member 11 is supported by a supporting member (not shown) and disposed at a fixed position relative to the photosensitive drum 1, and rubs on the surface of the photosensitive drum 1 as the photosensitive drum 1 rotates.

[0062] The brush member 11 captures the paper dust moving from the transfer material S onto the photosensitive drum 1 in the transfer portion N to reduce the amount of paper dust moving to the charging portion P and the developing device 3 further downstream of the brush member 11 in the moving direction of the photosensitive drum 1. In particular, large-sized paper dust causing a large impact tends to be captured by the brush member 11, so that collection failure due to insufficient cancellation of the above-mentioned charge can be prevented.

[0063] On the other hand, in this configuration, the untransferred toner that has reached the brush member 11 is not captured by the brush member, but stays on the photosensitive drum 1 and moves further downstream. This is because, due to the high electrostatic adhesion acting between the toner and the photosensitive drum 1, the toner is charged and does not fall off the photosensitive drum 1 even when the brush member 11 is rubbed on the drum. That is, when the brush member 11 collects paper dust, it avoids collecting toner as much as possible.

[0064] This does not apply to toner particles that carry a relatively small amount of charge and have weak electrostatic adhesion to the photosensitive drum 1, or if the brush specification is inappropriate, in which case the toner may adhere to the brush member 11. A method of preventing the toner from adhering to the brush member 11 will be described later.

[0065] Any material such as paper dust captured by the brush member 11 is removed at appropriate timing. For example, during post-processing rotation after a print job is completed as will be described later, by changing the posture of the brush member 11, the paper dust can be removed together with the toner.

[0066] Alternatively, the brush member 11 may be cleaned or replaced during maintenance of the device.

[0067] Hereinafter, an optimum configuration of the brush member 11 will be described.

[0068] Brush width

[0069] The length of the brush member 11 along the circumferential direction of the photosensitive drum 1 in this embodiment is 5 mm, but the length is not limited thereto. For example, the length can be appropriately changed according to the service life of the image forming device or the process cartridge. The longer the length of the brush member 11 along the circumferential direction of the drum, the longer the time period for collecting paper dust. Here, the length of the brush member 11 along the longitudinal direction of the brush member 11 (the axial direction of the drum) is 216 mm, but the length is not limited thereto. For example, the length can be appropriately changed according to the maximum paper feed width of the image forming device.

[0070] Brush fineness

[0071] The brush member 11 in this embodiment has a fineness of 2 denier, which can be appropriately changed as long as the brush density requirements to be described later are satisfied.

[0072] Brush Density

[0073] The brush member 11 should have a density determined in consideration of toner passability and paper dust collection performance. That is, too high a density of the brush member 11 will reduce toner passability and may cause malfunction because toner may be stuck and then may be scattered and contaminate the inside of the machine. If the density of the brush member 11 is too low, the paper dust collection performance will be reduced.

[0074] Therefore, the relationship between the density of the brush member 11 and the paper dust collection performance and the occurrence of the machine internal contamination caused by the toner scattering caused by the accumulation of the residual toner on the photosensitive drum 1 in the brush member 11 was studied. First, how to judge the paper dust collection performance will be described. In this embodiment, the paper dust collection performance is judged based on the number of dots that appear in the image due to the attachment of paper dust to the photosensitive drum 1. This is because, as mentioned before, the dots in the image are caused by the collection failure of the part of the photosensitive drum 1 to which the paper dust is attached.

[0075] In this embodiment, Century Star paper (product name, produced by CENTURY PULP AND PAPER) was used as the transfer material S, 50,000 copies were printed, and every 100 times, a full white image was printed after printing a full black image. The paper dust collection performance was judged based on the maximum value of the number of dots appearing in the full white image. In this embodiment, when the number of dots of 0.3 mm or more having a large visual impact was greater than 10, the paper dust collection performance was judged to be poor (NG).

[0076] In order to determine the occurrence of contamination inside the machine, Century Star paper was used as the transfer material S, and 5,000 print jobs were performed, each time 10 copies of an image with a coverage of 5% were printed, that is, 50,000 copies were printed. Thereafter, whether there was contamination inside the machine was determined based on whether any toner contamination occurred around the brush member 11. These tests can confirm that no malfunction occurs over a long period of time. Because in most cases the number of copies printed by the user in one job is 10 or less, in the study conducted by the inventor of the present application, the number of printed copies per job was set to 10.

[0077] Table 1 shows the relationship between the density of the brush member 11 and the paper dust collection performance and the occurrence of contamination inside the machine studied as described above. The density of the brush member 11 is expressed in units of "kF / inch 2 ” indicates the number of filaments per square inch.

[0078] [Table 1]

[0079] The above results show that if the density of the brush member 11 is 110 kF / inch 2 Up to 300kF / inch 2 , it is possible to simultaneously meet the requirements of paper dust collection performance and prevention of internal pollution of the machine. In this embodiment, based on the above results, the brush member 11 has a 170 kF / inch 2 The density makes it possible to achieve both paper dust collection performance and prevent internal pollution of the machine.

[0080] Inroad Amount

[0081] Next, we will refer to Figure 2A and Figure 2B The intrusion amount of the brush member 11 on the photosensitive drum 1 (referred to herein as “intrusion amount of the brush member 11 ”) is described. Figure 2A 1 is a diagrammatic view illustrating the brush member 11 which is separate and does not contact the photosensitive drum 1 or the like. Figure 2B 1 is a diagrammatic view of a state of a brush member 11 (brush member 11 incorporated in an image forming apparatus) in contact with a photosensitive drum 1. The brush member 11 includes a base cloth 111 and a thread 112. Here, the term "intrusion" does not necessarily mean only that the brush member 11 intrudes on the photosensitive drum 1. Here, the term "intrusion" should also mean a state in which the brush member 11 in contact with the photosensitive drum 1 is deformed and looks like the brush member 11 is intruding on the photosensitive drum 1 when viewed from the outside.

[0082] like Figure 2A As shown in , L1 represents the distance from the base cloth 111 to the tip of the wire 112 of the brush member 11 itself (ie, in a state where no force is applied to bend the wire 112). In this embodiment, L1 is 6.5 mm.

[0083] The brush member 11 is fixed to a supporting member (not shown) by a fixing member such as a double-sided tape, and is arranged so that the tip of the wire 112 invades the photosensitive drum 1. The gap between the supporting member and the photosensitive drum 1 is fixed here. L2 represents the distance between the base cloth 111 and the photosensitive drum 1. In this embodiment, the intrusion amount of the brush member 11 is defined as the difference L3 between L1 and L2.

[0084] Next, it will be described how to determine the intrusion amount of the brush member 11. Through research, the inventors of the present application have found that the intrusion amount of the brush member 11 has a large influence on the paper dust collection performance of the brush member 11. Note that here, the paper dust collection performance refers to the performance of collecting large paper dust having a particle size of 0.8 mm or more, for example.

[0085] The small intrusion amount of the brush member 11 means that the contact length between the brush member 11 and the photosensitive drum 1 is short. Therefore, the inertial force of the large-sized paper dust traveling on the photosensitive drum 1 will displace the brush tip of the brush member 11, and the paper dust will easily pass through. Any large-sized paper dust that has passed through may cause the above-mentioned development streaks to occur.

[0086] In contrast, a large intrusion amount of the brush member 11 means a large contact length between the brush member 11 and the photosensitive drum 1, wherein the brush tip lies flat and the middle portion of the brush member 11 abuts against the photosensitive drum 1 ( Figure 2B ). By utilizing the large contact length between the brush member 11 and the photosensitive drum 1, when paper dust contacts the brush member 11, the brush tip of the brush member 11 is hardly displaced because large-sized paper dust is less likely to pass through, so that the paper dust collection performance is improved. Therefore, the occurrence of development streaks can be prevented. In order to ensure the performance of collecting large-sized paper dust, it is preferable to make the intrusion amount of the brush member 11 sufficiently large.

[0087] On the other hand, it was also found that in addition to the development streaks, the intrusion amount of the brush member 11 has a great influence on the image. That is, the larger the intrusion amount, the higher the contact pressure applied to the photosensitive drum 1 by the brush member 11 when rubbing on the photosensitive drum 1, thereby generating unintentional charge unevenness on the photosensitive drum 1 and causing image density unevenness (hereinafter referred to as friction memory).

[0088] Therefore, the relationship between the intrusion amount of the brush member 11 and the large-size paper dust collection performance and the occurrence of friction memory was studied. Figure 3 Describe how to judge the large-size paper dust collection performance. In this embodiment, a test device 101 is prepared, in which a scraper 40 is installed downstream of the brush member 11 on the photosensitive drum 1 to observe the paper dust collected by the scraper 40, and a judgment is made based on the number of large-size paper dust particles contained therein. In this embodiment, the paper dust collected by the scraper 40 after printing 10 copies of a white image using Century Star paper as a transfer material S is observed. When 10 or more paper dust particles of 0.8 mm or larger are collected, it is judged to be bad (NG). In order to check whether there is friction memory, a printing test is performed in which 50,000 copies of a halftone image are printed in a low temperature, low humidity environment (e.g., 15°C and 10% RH), and the image of each 100 copies is checked for the presence of friction memory.

[0089] Table 2 shows the relationship between the intrusion amount of the brush member 11 and the large-sized paper dust collecting performance and the occurrence of friction memory studied as described above.

[0090] [Table 2]

[0091] The above results show that if the intrusion amount of the brush member 11 is 0.5 mm to 2.0 mm, the requirements of paper dust collection performance and friction memory prevention can be met at the same time. Based on the above results, the intrusion amount of the brush member 11 in this embodiment is set to 1.0 mm, thereby achieving large-size paper dust collection performance and friction memory prevention at the same time. Characteristic features of this embodiment

[0092] As described above, using the brush member 11, toner deposition can be prevented and the influence of paper dust is also suppressed. However, further studies by the inventors of the present application revealed that when untransferred toner passes through the brush member 11, the toner adheres to the brush member 11, albeit only slightly.

[0093] After a print job, generally, the post-processing rotation after the supply of the untransferred toner stops removes the toner attached to the brush member 11. For example, by repeatedly driving and stopping the photosensitive drum to change the posture of the brush member 11 in the post-processing rotation after the print job, any attached toner can be removed. However, in the case of continuously printing a large number of copies, or in the latter half of the service life of an image forming apparatus or cartridge including the photosensitive drum 1 and the brush member 11, the toner that is attached to the brush member 11 and cannot be removed may accumulate after many years of use, and thus the toner scattering in the interior of the machine mentioned above may occur.

[0094] In view of the above problems, the present embodiment adopts a configuration in which a conductive member is used as the brush member 11 to apply a bias voltage in order to reduce toner adhesion during continuous printing. That is, the brush member 11 in this embodiment uses a wire 112 of a conductive nylon material woven into a base cloth 111 having conductivity. Other materials such as conductive polyester or acrylonitrile yarn may also be used for the wire 112. A power source 13 as a voltage applying unit is connected to the brush member 11 so that a voltage can be applied thereto.

[0095] A voltage of the same polarity as the standard polarity of the toner when charged is applied from the power source 13 to the brush member 11. This suppresses the toner from adhering to the brush member 11. Applying a voltage of the opposite polarity to the polarity of the toner is undesirable because it will promote toner deposition.

[0096] When the absolute value of the voltage applied to the brush member 11 is large, that is, when the potential difference between the surface of the photosensitive drum 1 and the voltage applied to the brush member 11 is large, discharge occurs between the brush member and the exposure portion. This means that the untransferred toner will be charged twice by the brush member 11 and the charging roller 2. In this case, the excess charge of the untransferred toner will then increase the electrostatic adhesion to the photosensitive drum 1. This may sometimes cause insufficient toner collection in the developing device 3 and cause a collection failure. On the other hand, when the absolute value of the voltage applied to the brush member 11 is small, that is, when the potential difference between the surface of the photosensitive drum 1 and the voltage applied to the brush member 11 is small, the effect of suppressing toner adhesion may be impaired and the inside of the machine may be contaminated.

[0097] Therefore, the relationship between the voltage applied to the brush member 11 and the collection failure and the machine internal contamination was studied. A white image was formed after one rotation of the photosensitive drum 1 after the black image was formed by exposure in a predetermined range, and it was determined whether the collection failure occurred based on whether the untransferred toner from the black image portion adhered to the white image portion. In order to determine the occurrence of the machine internal contamination, Century Star paper was used as the transfer material S, 50 printing jobs were performed, 1000 copies of the image with a coverage of 5% were printed each time, that is, 50000 copies were printed, and it was determined whether the toner contamination occurred around the brush member 11.

[0098] Table 3 shows the relationship between the voltage applied to the brush member 11 and the collection failure and the contamination inside the machine.

[0099] [Table 3]

[0100] As shown in Table 3, when the absolute value of the voltage applied to the brush member 11 is 200 V or more, machine contamination does not occur even if some toner adheres to the brush member 11 during execution of a print job. As mentioned above, the post-processing rotation after the supply of the untransferred toner is stopped removes the toner adhered to the brush member 11.

[0101] Table 3 also shows that when the absolute value of the voltage applied to the brush member 11 is less than 600 V, excessive charging of the untransferred toner does not occur and collection failure is prevented. It is assumed that this is because the untransferred toner is not charged by the brush member 11 if the potential difference between the voltage applied to the brush member 11 and -100 V of the exposed portion of the photosensitive drum 1 is not greater than a normal discharge threshold value (i.e., 500 V or less).

[0102] Based on the above results, a voltage (specifically, −400 V) that can simultaneously achieve prevention of collection failure and prevention of contamination inside the machine is applied to the brush member 11 .

[0103] As described above, by adopting the configuration of this embodiment, it is possible to suppress the scattering of toner inside the machine caused by the deposition of toner on the brush member 11, reduce the appearance of dot images caused by paper dust attached to the photosensitive drum, and reduce the occurrence of collection failures. The present invention is also applicable to an image forming apparatus having a plurality of photosensitive drums corresponding to a plurality of color toners. In addition, the present invention is also applicable to an image forming apparatus of a type that directly transfers an image from the photosensitive drum 1 to a transfer material S conveyed toward a transfer portion by a belt or an image forming apparatus using an intermediate transfer member such as an intermediate transfer belt. Example 2

[0104] Hereinafter, this embodiment will be described mainly focusing on the differences from the first embodiment. Figure 4 The configuration of the image forming apparatus 100 in this embodiment is illustrated. Unlike Embodiment 1, in this embodiment, the brush member 11 is disposed downstream of the pre-exposure device 12 and upstream of the charging roller 2. In this embodiment, the potential of the photosensitive drum 1 charged by the charging roller 2 is about -700 V, which is higher than that of Embodiment 1. The potential of the exposed portion is about -100 V, which is the same level as that of Embodiment 1. The bias voltage applied to the brush member 11 is -400 V, which is the same level as that of Embodiment 1. Other configurations and operations are similar to those of Embodiment 1, and will not be described again.

[0105] The difference between the charged potential and the potential of the exposed portion (referred to as "latent image contrast") can be set as desired for each type of image forming apparatus. For example, when a toner having a high charge amount is used, the latent image contrast is set high. Figure 5A and Figure 5B To describe the problem when setting a high latent image contrast.

[0106] Figure 5A The figure shows the change in potential before and after transfer when the latent image contrast is relatively low. In this case, due to the transfer voltage, there is almost no potential difference between the exposed part and the non-exposed part after the transfer process. On the other hand, Figure 5B The change in potential before and after transfer is shown when the latent image contrast is relatively high. In this case, the high potential of the non-exposed portion is not completely reduced even after the transfer process, so that the potential difference remains between the exposed portion and the non-exposed portion.

[0107] The same amount of -400 V as in Embodiment 1 is applied to brush member 11. As described in Embodiment 1, brush member 11 has some toner thereon even if there is no contamination inside the machine, and the toner moves to photosensitive drum 1 because of the potential difference between itself and photosensitive drum 1. Fig. 6A and Figure 6B The diagram shows how this happens.

[0108] Fig. 6A Corresponds to Figure 5A , and shows the case where the latent image contrast is relatively low, so that the potential difference between the exposed portion and the non-exposed portion after the transfer process is small. In this case, the toner t is uniformly attached to the photosensitive drum 1. The toner uniformly attached in this way can be easily charged in the charging process and collected in the developing device 3, so that no problem is caused. Figure 6B Corresponds to Figure 5B , and shows the following situation: the latent image contrast is relatively high, so that the potential difference between the exposed part and the non-exposed part after the transfer process is large. In this case, the toner is gathered in the exposed part because of the electric field concentrated in the exposed part. The toner gathered in this way is less charged in the charging process and is therefore less collected into the developing device 3, so that a collection failure occurs.

[0109] Reference Fig. 7A and Figure 7B Describes collection failures in more detail. Fig. 7A Corresponds to Fig. 6A , illustrates a case where the toner t is uniformly attached to the photosensitive drum 1. In this case, the toner can be uniformly given the charge from the charging roller 2, that is, uniformly charged, so that all the toner can be collected in the developing device 3. Figure 7B Corresponds to Figure 6B , illustrates a case where there is a portion where toner is gathered into a layer on the photosensitive drum 1. In this case, the toner located closer to the photosensitive drum 1 (the layer on the lower side in the paper) cannot be given the charge from the charging roller 2. The toner in this portion cannot be charged, and therefore cannot be collected in the developing device 3, causing a collection failure.

[0110] Therefore, in this embodiment, the brush member 11 is disposed downstream of the pre-exposure device 12 and upstream of the charging roller 2 to cancel the charge on the photosensitive drum 1 before the brush member 11 contacts the photosensitive drum 1 so as to cancel the potential difference between the exposed portion and the non-exposed portion after the transfer process. By adopting this configuration, since the toner is uniformly attached to the photosensitive drum 1 when the brush member 11 contacts, it can be easily collected in the developing device 3, so even when a high latent image contrast is to be used, the occurrence of collection failure can be reduced.

[0111] In this embodiment, when the pre-exposure device 12 cancels the charge, the paper dust is not removed. Therefore, as described in Embodiment 1, in the portion where the paper dust adheres, the discharge amount in the charging process may be reduced, so the untransferred colorant cannot be sufficiently charged and may not be collected in the developing device 3, that is, the occurrence of a collection failure may be expected. However, this is not the case, because the charging potential, that is, the charging voltage is high in this embodiment, so that even in the portion where the paper dust adheres, a sufficiently high discharge amount can be achieved. Therefore, the untransferred colorant is sufficiently charged and can be collected in the developing device 3, so the occurrence of image defects can be reduced.

[0112] As described above, by adopting the configuration of this embodiment, even when the latent image contrast is high, it is possible to prevent toner scattering inside the machine, prevent the occurrence of dot images caused by paper dust attached to the photosensitive drum, and prevent collection failure.

[0113] The configuration of Embodiment 1 or Embodiment 2 can be appropriately selected based on the level of latent image contrast to be used.

[0114] It should be understood that by providing the brush member 11 both upstream and downstream of the pre-exposure device 12, all the effects described in Embodiment 1 and Embodiment 2 can be achieved.

[0115] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. An image forming device, comprising: a rotatable image bearing member; a charging unit that contacts the image bearing member to form a charging portion and charges a surface of the image bearing member in the charging portion; an exposure unit that exposes the surface of the image bearing member charged in the charging portion to form an electrostatic latent image; a developing unit that supplies a toner charged to have a predetermined polarity to the electrostatic latent image formed on the surface of the image bearing member to form a toner image; a transfer unit that contacts the image bearing member to form a transfer portion and transfers the toner image formed on the surface of the image bearing member to a transfer material in the transfer portion; a charge canceller that cancels charges on a surface of the image bearing member downstream of the transfer portion and upstream of the charging portion in the rotational direction of the image bearing member; a collecting unit having conductivity and collecting the attached material attached to the surface of the image bearing member downstream of the transfer portion and upstream of the charging portion in the rotation direction of the image bearing member; a voltage applying unit, wherein the voltage applying unit applies a voltage of a predetermined polarity to the collecting unit; as well as A controller controls the voltage applying unit, wherein: After the toner image is transferred onto the transfer material in the transfer portion, the developing unit collects residual toner on the surface of the image bearing member, and The controller controls the voltage applying unit so that a potential difference between a voltage of a predetermined polarity applied to the collecting unit and a surface potential of the image bearing member on the surface of the image bearing member is not greater than a discharge threshold value.

2. The image forming apparatus according to claim 1, wherein: The controller controls the voltage applying unit so that a voltage of a level capable of suppressing the toner from being attached to the collecting unit is applied to the collecting unit.

3. The image forming apparatus according to claim 1 or 2, wherein: The collecting unit is disposed downstream of the transfer portion in the rotational direction of the image bearing member and upstream of the charge canceller.

4. The image forming apparatus according to claim 1 or 2, wherein: The collecting unit is disposed downstream of the charge canceller and upstream of the charging portion in the rotational direction of the image bearing member.

5. The image forming apparatus according to claim 1, wherein: As the image bearing member rotates, the collecting unit rubs against the image bearing member.

6. The image forming apparatus according to claim 5, wherein: The collecting unit includes a brush member.

7. The image forming apparatus according to claim 6, wherein: A portion of the brush member of the collecting unit that rubs against the image bearing member is composed of a conductive wire.

8. The image forming apparatus according to claim 7, wherein: The wire of the brush member has a 110 kF / inch 2 Up to 300kF / inch 2 Line density.

9. The image forming apparatus according to claim 7, wherein: The wire of the brush member has an intrusion amount of 0.5 mm to 2 mm on the image bearing member.

10. An image forming device comprising: a rotatable image bearing member; a charging unit that contacts the image bearing member to form a charging portion and charges a surface of the image bearing member in the charging portion; an exposure unit that exposes the surface of the image bearing member charged in the charging portion to form an electrostatic latent image; a developing unit that supplies a toner charged to have a predetermined polarity to the electrostatic latent image formed on the surface of the image bearing member to form a toner image; a transfer unit that contacts the image bearing member to form a transfer portion and transfers the toner image formed on the surface of the image bearing member to a transfer material in the transfer portion; a charge canceller that cancels charges on a surface of the image bearing member downstream of the transfer portion and upstream of the charging portion in the rotational direction of the image bearing member; a collecting unit having conductivity and collecting the attached material attached to the surface of the image bearing member downstream of the transfer portion and upstream of the charging portion in the rotation direction of the image bearing member; a voltage applying unit, wherein the voltage applying unit applies a voltage of a predetermined polarity to the collecting unit; as well as A controller controls the voltage applying unit, wherein: After the toner image is transferred onto the transfer material in the transfer portion, the developing unit collects residual toner on the surface of the image bearing member, and The collecting unit is disposed downstream of the charge canceller and upstream of the charging portion in the rotation direction of the image bearing member.

Images