Image forming device

Abstract

To prevent an image defect caused by an attachment such as paper powder and residual toner attached onto a photoconductor drum in an image forming apparatus of a cleaner-less system.SOLUTION: An image forming apparatus has: electrifying means that electrifies a surface of an image carrier in an electrifying unit; developing means that forms a toner image having a predetermined polarity from an electrostatic latent image that exposure means has formed on the surface of the image carrier; transfer means that transfers the toner image to a transfer material in a transfer unit; static eliminating means that eliminates static electricity from the surface of the image carrier on the downstream of the transfer unit and on the upstream of the electrifying unit in the direction of rotation of the image carrier; conductive recovery means that recovers an attachment on the surface of the image carrier on the downstream of the transfer unit and on the upstream of the electrifying unit in the direction of rotation of the image carrier; and a voltage application unit that applies a voltage having a predetermined polarity to the recovery means, wherein after the toner image is transferred, the developing means recovers a residual toner on the surface of the image carrier. The voltage application unit sets the potential difference between the voltage applied to the recovery means and a surface potential of the image carrier to be equal to or less than a discharge threshold.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] 2. Description of the Related Art There are image forming apparatuses, such as laser printers, copying machines, and facsimiles, which obtain a recorded image by transferring a toner image formed on an image carrier using an electrophotographic method or the like to a transfer material.

[0003] As one aspect of such an image forming apparatus, a cleanerless system has been proposed in recent years, in which residual toner is collected in the developing section and reused. In this cleanerless system, toner, paper powder, and fillers that adhere to the photosensitive drum in the transfer section may affect subsequent processes. Therefore, Patent Document 1 discloses a configuration in which the toner and adhesions remaining on the photosensitive drum are collected by providing a collection member that contacts the surface of the photosensitive drum. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-279431 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the configuration of Patent Document 1 has the following problem: When a recovery member is provided downstream of the transfer unit in the rotation direction of the photosensitive drum, if toner that is not transferred to paper and remains on the photosensitive drum accumulates on the recovery member, the performance of recovering paper dust decreases, and the paper dust is recovered in the development unit, which can cause image problems.

[0006] In addition, the size of the paper dust that adheres to the photosensitive drum varies depending on the type of paper, but the largest particles are several mm in size. In areas where such large paper dust has adhered, it is not possible to remove static electricity through exposure to light, and the amount of discharge in the subsequent charging process is reduced, which can result in poor image quality.

[0007] The present invention has been made in consideration of the above problems, and its purpose is to provide a technology that suppresses image defects caused by adhesions such as paper powder and residual toner on a photosensitive drum in a cleanerless image forming apparatus. [Means for solving the problem]

[0008] The present invention employs the following configuration. A rotatable image carrier; a charging unit that contacts the image carrier to form a charging portion and charges the surface of the image carrier in the charging portion; an exposure unit for exposing the surface of the image carrier charged in the charging unit to light to form an electrostatic latent image; a developing unit that supplies a toner charged to a predetermined polarity to the electrostatic latent image formed on the surface of the image carrier to form a toner image; a transfer means for contacting the image carrier to form a transfer portion, and transferring the toner image formed on the surface of the image carrier to a transfer material in the transfer portion; 、 Guidance a brush member having electrical conductivity, the brush member being disposed on the surface of the image carrier downstream of the transfer unit and upstream of the charging unit in the rotation direction of the image carrier; Contact with said surface A brush member for collecting the adhering paper powder; a voltage application unit that applies a voltage of the predetermined polarity to the brush member; A control unit that controls the voltage application unit; having In an image forming operation for forming an image on a recording material, In an image forming apparatus, after the toner image is transferred to the transfer material in the transfer section, the toner remaining on the surface of the image carrier is recovered by the developing means, the control unit controls the voltage application unit so that a potential difference between the voltage of the predetermined polarity applied to the brush member and a surface potential of the image carrier formed on the surface of the image carrier is equal to or less than a discharge threshold value; In a non-image forming operation after the image forming operation is performed, a switching operation is performed in which the image carrier is rotated and then stopped, and the image carrier is rotated and then stopped again. The image forming apparatus is characterized in that Effect of the Invention

[0010] According to the present invention, it is possible to provide a technique for suppressing image defects caused by contaminants such as paper powder and residual toner adhering to a photosensitive drum in a cleanerless type image forming apparatus. [Brief description of the drawings]

[0011] [Figure 1] Schematic diagram of an image forming apparatus in the first embodiment [Diagram 2] Schematic diagram of brush member [Diagram 3] Schematic diagram of the paper dust collection test device [Figure 4] Schematic diagram of an image forming apparatus in Example 2 [Diagram 5] Schematic diagram of the photosensitive drum potential before and after the transfer process in Example 2 [Figure 6] Schematic diagram of toner adhesion to a photosensitive drum in Example 2 [Figure 7] Schematic diagram of discharge to toner on a photosensitive drum in Example 2 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the embodiments may be changed as appropriate depending on the configuration of the device to which the invention is applied and various conditions, and the scope of the present invention is not limited to the following embodiments. Furthermore, not all of the combinations of features described in the examples are necessarily essential to the solution of the invention.

[0013] <Example 1> [Overall configuration of image forming device] 1 shows a schematic configuration of an embodiment of an image forming apparatus according to the present invention. The image forming apparatus of this embodiment is a monochrome printer.

[0014] In the image forming apparatus 100 of this embodiment, a cylindrical photosensitive member serving as an image carrier, that is, a photosensitive drum 1, is provided. Around the photosensitive drum 1, a charging roller 2 serving as a charging means and a developing device 3 serving as a developing means are provided. In the figure, the charging roller 2 and the developing device An exposure device 4 serving as an exposure means is provided between the photosensitive drum 1 and the imaging device 3. A transfer roller 5 is pressed against the photosensitive drum 1.

[0015] The photosensitive drum 1 in this embodiment is a negatively charged organic photosensitive body. This photosensitive drum 1 has a photosensitive layer on a drum-shaped aluminum substrate. The photosensitive drum 1 is rotatable about its axis, and is driven to rotate at a predetermined process speed in the direction of arrow D in the figure (clockwise on the paper) by a drive device (not shown). In this embodiment, the process speed corresponds to the circumferential speed (surface moving speed) of the photosensitive drum 1.

[0016] The charging roller 2 comes into contact with the photosensitive drum 1 with a predetermined pressure, forming a charging portion P. A desired charging voltage is applied by a charging high-voltage power source (not shown) as a charging voltage supply means, and the surface of the photosensitive drum 1 is uniformly charged to a predetermined potential. In this embodiment, the photosensitive drum 1 is negatively charged by the charging roller 2, and the charging potential is approximately -500 [V].

[0017] In this embodiment, the exposure device 4 is a laser scanner device, which 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. By this exposure, an electrostatic latent image (electrostatic image) corresponding to the image information is formed on the surface of the photosensitive drum 1. Note that the potential of the exposure portion in this embodiment is approximately -100 [V]. The exposure device 4 is not limited to a laser scanner device, and may be, for example, an LED array in which a plurality of LEDs are arranged along the longitudinal direction of the photosensitive drum 1 (the axial direction of the cylinder).

[0018] In this embodiment, a contact development method is used as the development method. The development device 3 includes a development roller 31 as a developer carrier, a toner supply roller 32 as a developer supplying means, a developer storage chamber 33 that stores toner, and a development blade 34. The toner (developer) supplied from the developer storage chamber 34 to the development roller 31 by the toner supply roller 32 is charged to a predetermined polarity by passing through a contact portion with the development blade 34. Note that in this embodiment, toner with a particle size of 6 μm and a normal charging polarity of negative polarity is used. Also, although a one-component non-magnetic contact development method is adopted in this embodiment, a two-component non-magnetic contact / non-contact development method may be used.

[0019] The electrostatic latent image formed on the photosensitive drum 1 is developed into a toner image by the toner conveyed by the developing roller 31 at the portion where the developing roller 31 and the photosensitive drum 1 face each other. At this time, a developing voltage is applied to the developing roller 31 by a developing high voltage power supply (not shown) as a developing voltage application means. In this embodiment, the electrostatic latent image is developed by a reversal development method. That is, the electrostatic latent image is developed by a reversal development method on the part of the photosensitive drum 1 after the charging process where the charge has been attenuated by exposure. The electrostatic latent image is developed into a toner image by attaching toner charged with the same polarity as the charge polarity of the optical drum 1.

[0020] The transfer roller 5 can be preferably made of an elastic material such as polyurethane rubber, EPDM (ethylene-propylene-diene rubber), NBR (nitrile butadiene rubber), or other sponge rubber. The transfer roller 5 is pressed against the photosensitive drum 1 to form a transfer portion N where the photosensitive drum 1 and the transfer roller 5 are in pressure contact with each other. A transfer high voltage power supply (not shown) is connected to the transfer roller 5 as a transfer voltage application means, and a predetermined voltage is applied at a predetermined timing.

[0021] In synchronization with the timing at which the toner image formed on the photosensitive drum 1 reaches the transfer section N, a transfer material S (e.g., a recording material such as paper) stored in a cassette 6 is fed by a paper feed unit 7 and conveyed to the transfer section N through a pair of registration rollers 8. The toner image formed on the photosensitive drum 1 is transferred onto the transfer material S by a transfer roller 5 to which a predetermined transfer voltage is applied by a transfer high-voltage power supply.

[0022] The transfer material S after the toner image transfer is transported to a fixing device 9. The fixing device 9 in this embodiment is a film heating type fixing device equipped with a fixing film 91 incorporating a fixing heater and a thermistor (not shown) for measuring the temperature, and a pressure roller 92 for pressing against the fixing film 91. The fixing device 9 heats and presses the transfer material S, thereby fixing the toner image. After the fixing, the transfer material S passes through a pair of paper discharge rollers 10 and is discharged outside the machine.

[0023] A pre-exposure device 12 is provided between the transfer portion N and the charging portion P as a means for eliminating the surface potential of the photosensitive drum 1. This is to stabilize the discharge at the charging portion P by leveling out the potential unevenness of the photosensitive drum caused by the transfer, thereby obtaining a uniform charging potential.

[0024] Moreover, the transfer residual toner remaining on the photosensitive drum 1 without being transferred to the transfer material S is removed in the following process. The residual toner includes a mixture of positively charged toner and negatively charged toner that does not have a sufficient charge. The residual toner is charged negatively again by discharge at the charging section P. The residual toner that has been charged negatively again at the charging section P reaches the developing device 3 as the photosensitive drum 1 rotates. Here, as described above, an electrostatic latent image corresponding to the image information is formed on the photosensitive drum 1 that has reached the developing device 3. The behavior of the residual toner that has reached the developing device 3 will be explained separately for the exposed and non-exposed areas of the photosensitive drum 1.

[0025] Residual toner adhering to the non-exposed portion of the photosensitive drum 1 is transferred to the developing roller 31 by the potential difference between the potential of the non-exposed portion of the photosensitive drum 1 and the developing voltage in the developing device 3, and is collected in the developer storage chamber 33. The toner collected in the developer storage chamber 33 is reused for image formation. On the other hand, the residual toner adhering to the exposed portion of the photosensitive drum 1 is not transferred 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 developed toner from the developing roller 31, where it is transferred to the transfer material S and removed from the photosensitive drum 1.

[0026] In addition, the photosensitive drum 1 after transfer is neutralized by the pre-exposure device 12 described above, and the transfer residual toner can be stably charged to negative polarity by generating a uniform discharge during charging. As a result, there is no toner that cannot be sufficiently recharged to negative polarity, and the transfer residual toner can be more reliably collected by the developing device 3.

[0027] The image forming apparatus 100 may include a control unit 70. The control unit 70 is configured by an information processing device having a processor, or a processing circuit such as an FPGA or an ASIC, and is programmed. The control unit 70 performs information processing related to the operation of the image forming apparatus 100 based on the image forming system or user instructions. The control unit 70 performs, for example, control of voltage application means such as charging voltage, developing voltage, transfer voltage, and recovery voltage, voltage control, control of pre-exposure and exposure based on image information, control of driving members such as the photosensitive drum and various rollers, etc. The control unit 70 may be configured by a plurality of information processing devices operating in cooperation with each other to perform these various processes.

[0028] [Paper dust removal mechanism] When the toner is transferred from the photosensitive drum 1 to the transfer material S at the transfer portion N, paper powder fibers contained in the transfer material S may adhere to the photosensitive drum 1. In the cleaner-less method adopted in this embodiment, if the paper powder fibers adhered to the photosensitive drum 1 are not treated in any way, the paper powder fibers are collected in the developing device 3. Then, the paper powder fibers cause image defects. For example, the paper powder collected by the developing device 3 may be caught between the developing blade 34 and the developing roller 31, the toner on the developing roller 31 may be peeled off, and streaks may occur in the image (hereinafter referred to as development streaks), or the paper powder collected in the developing device 3 may hinder the charging of the toner. In addition, the paper powder fibers reach the charge removal portion by the pre-exposure 12 without being removed on the way. If large-sized paper powder adheres to the photosensitive drum 1, the light of the pre-exposure 12 does not reach the photosensitive drum surface at the paper powder adhesion portion, and charge removal is not possible. As a result, the amount of discharge on the photosensitive drum surface that was not discharged in the next charging process decreases, and the residual toner remaining in that area becomes insufficiently charged, making it impossible for the developing device 3 to collect it, resulting in poor collection.

[0029] Therefore, in this embodiment, a brush member 11 is provided as a paper dust collecting member to remove paper dust adhering to the photosensitive drum 1. As shown in Fig. 1, the brush member 11 is disposed so as to come into contact with the photosensitive drum 1 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. The brush member 11 is supported by a support member (not shown) and disposed at a fixed position relative to the photosensitive drum 1, and rubs against the surface of the photosensitive drum 1 as the photosensitive drum 1 rotates.

[0030] The brush member 11 collects paper dust transferred from the recording material S onto the photosensitive drum 1 at the transfer portion N, and reduces the amount of paper dust that moves to the charging portion P downstream of the brush member 11 in the movement direction of the photosensitive drum 1, and to the developing device 3. Paper dust that is particularly large in size and has a large impact is easily caught by the brush member 11, and the occurrence of poor collection due to insufficient neutralization described above can be suppressed.

[0031] On the other hand, the residual toner that reaches the brush member 11 is not caught by the brush member, but moves downstream while remaining attached to the photosensitive drum 1. This is because the toner is charged and therefore has a strong electrostatic adhesion to the photosensitive drum 1, and does not separate from the photosensitive drum 1 even when rubbed against the brush member 11. In other words, the brush member 11 is configured to collect paper powder, but toner is not collected as much as possible.

[0032] However, this does not apply when the toner contains a relatively low charge amount and has a weak electrostatic adhesion to the photosensitive drum 1, or when the brush prescription is not appropriate, and the toner may adhere to the brush member 11. A method for preventing toner adhesion to the brush member 11 will be described later.

[0033] Adherents such as paper dust caught in the brush member 11 are removed at an appropriate time. For example, the attitude of the brush member 11 may be changed during post-rotation after the end of a print job, as described below, to remove the paper dust together with the toner. In addition, the brush member 11 may be cleaned or replaced during device maintenance.

[0034] The optimum configuration of the brush member 11 will now be described. (Brush width) In this embodiment, the length of the brush member 11 in the circumferential direction of the photosensitive drum 1 is set to 5 mm, but is not limited to this. For example, it may be changed as appropriate depending on the life of the image forming apparatus or the process cartridge. The longer the length of the brush member 11 in the circumferential direction of the drum, the longer it can collect paper dust. In addition, the length of the brush member 11 in the longitudinal direction (drum axial direction) is set to 216 mm, but is not limited to this. For example, it may be changed as appropriate depending on the maximum paper passing width of the image forming apparatus.

[0035] (Brush fineness) In this embodiment, the fineness of the brush member 11 is 2 denier, but this may be changed as appropriate as long as the brush density conditions described below are satisfied.

[0036] (Brush Density) It is desirable to determine the density of the brush member 11 taking into consideration the toner passing property and the paper dust collecting property. In other words, if the density of the brush member 11 is too high, the toner passing property is deteriorated, the toner is piled up, and the piled up toner is scattered and may cause problems such as soiling the inside of the machine. Also, if the density of the brush member 11 is too low, the ability to collect paper dust is weakened.

[0037] Therefore, in this embodiment, the relationship between the density of the brush member 11, the paper dust collection ability, and the occurrence of dirt inside the machine due to toner scattering caused by toner remaining on the photosensitive drum 1 accumulating on the brush member 11 was examined. First, a method for determining the paper dust collecting ability will be described. In this embodiment, the paper dust collecting ability is determined based on the number of spot images caused by paper dust adhering to the photosensitive drum 1. This is because, as described above, collection failure occurs in the areas of the photosensitive drum 1 where paper dust has adhered, resulting in spot images.

[0038] In this embodiment, CenturyStar paper (product name, manufactured by CENTURY PULP AND PAPER) is used as the transfer material S, and 50,000 sheets are printed, and an all-white image printed after an all-black image is obtained every 100th sheet. The paper dust collecting ability is judged based on the maximum number of speckle images that appeared in the all-white images. In this embodiment, if the number of speckles that are 0.3 mm or larger and have a large visual impact is more than 10, the paper dust collecting ability is judged. If this is not the case, the paper dust collection capability is judged to be NG.

[0039] Regarding stains inside the machine, Century Star paper was used as transfer material S, and an image with a print rate of 5% was printed. Ten sheets were printed per print job, and 5,000 jobs, that is, 50,000 sheets, were printed. Thereafter, the occurrence of contamination inside the machine is judged based on whether or not toner contamination occurs around the brush member 11. By conducting such tests, it is possible to confirm that no malfunctions will occur over a long period of time. Note that, since most users print 10 or fewer sheets in one job, the inventors' study set the number of printed sheets per job to 10 sheets.

[0040] Table 1 shows the relationship between the density of the brush member 11, the paper dust collection performance, and the occurrence of dirt inside the machine, as examined above. The density of the brush member 11 is expressed in kF / inch^2. which indicates the number of filaments per square inch. [Table 1]

[0041] From the above results, if the density of the brush member 11 is 110 to 300 kF / inch^2, the paper dust collecting ability and function are improved. Based on the above results, in this embodiment, the density of the brush member 11 is set to 170 kF / inch^2, which can satisfy both the paper dust collecting ability and the prevention of internal staining.

[0042] (Brush penetration depth) Next, the intrusion amount of the brush member 11 into the photosensitive drum 1 (hereinafter, referred to as "intrusion amount of the brush member 11") will be described with reference to FIG. 2. FIG. 2(a) is a schematic diagram showing the brush member 11 alone in a state where it is not in contact with the photosensitive drum 1 or the like. FIG. 2(b) is a schematic diagram showing the state where the brush member 11 is in contact with the photosensitive drum 1 (the state where the brush member 11 is incorporated in the image forming apparatus). The brush member 11 includes a base fabric 111 and threads 112. Note that the term "intrusion" here does not necessarily mean only that the brush member 11 actually enters the photosensitive drum 1. Here, the term "intrusion" also refers to a state where the brush member 11 in contact with the photosensitive drum 1 is deformed and appears to have intruded into the photosensitive drum 1 when observed from the outside.

[0043] 2(a), the distance from the base fabric 111 to the tip of the thread 112 is defined as L1 when the brush member 11 is in a standalone state, that is, when no external force is being applied to bend the thread 112. Here, L1 in this embodiment is 6.5 mm.

[0044] The brush member 11 is disposed such that a base fabric 111 is fixed to a support member (not shown) by a fixing means such as double-sided tape, and the tip of the thread 112 is inserted into the photosensitive drum 1. Here, the clearance between the support member and the photosensitive drum 1 is fixed. The distance from the base fabric 111 to the photosensitive drum 1 at this time is defined as L2. In this embodiment, the difference L3 between L1 and L2 is defined as the intrusion amount of the brush member 11.

[0045] Next, a method for determining the amount of penetration of the brush member 11 will be described. The inventors' research has revealed that the penetration amount of the brush member 11 has a large effect on the paper dust collection ability of the brush member 11. However, the paper dust collection ability here means the ability to collect large-sized paper dust, for example, paper dust of 0.8 mm or more.

[0046] When the penetration amount of the brush member 11 is small, the contact length between the brush member 11 and the photosensitive drum 1 is small. Therefore, the bristles of the brush member 11 move due to the inertial force of large-sized paper dust moving on the photosensitive drum 1, making it easier for the large-sized paper dust to pass through. If the large-sized paper dust passes through, the above-mentioned development streaks may occur.

[0047] Conversely, when the penetration depth of the brush member 11 is large, the bristles of the brush member 11 lie flat against the photosensitive drum 1 (FIG. 2(b)), and the contact length between the brush member 11 and the photosensitive drum 1 becomes large. When the contact length between the brush member 11 and the photosensitive drum 1 becomes large, the bristles of the brush member 11 do not move easily when the brush member 11 comes into contact with paper dust, and large-sized paper dust does not easily slip through, improving the paper dust collection performance. As a result, the occurrence of development streaks can be suppressed. In order to ensure the ability to collect large-sized paper dust, it is desirable to make the penetration depth of the brush member 11 sufficiently large.

[0048] On the other hand, it was also found that the penetration amount of the brush member 11 has a large effect on the image in a manner other than the development streak. That is, the larger the penetration amount, the stronger the contact pressure of the brush member 11 against the photosensitive drum 1, causing unintended charging unevenness on the photosensitive drum 1, which appears as density unevenness in the image (hereinafter referred to as "friction memory").

[0049] Therefore, in this embodiment, the relationship between the penetration amount of the brush member 11, the ability to collect large-sized paper particles, and the occurrence of friction memory was examined. Here, a method for judging the large-sized paper dust collection ability will be described with reference to FIG. 3. In this embodiment, an experimental device 101 was created in which a scraper 40 was attached downstream of the brush member 11 on the photosensitive drum 1, and the paper dust collected by the scraper 40 was observed to judge the number of large-sized paper dust particles contained therein. In this embodiment, Century Star paper was used as the transfer material S, and the paper dust collected by the scraper 40 after 10 white images were printed was counted. If 10 or more pieces of paper dust with a size of 0.8 mm or more were collected, the sample was judged as NG. In addition, for friction memory, a print test of 50,000 sheets is conducted in a low temperature and low humidity environment (for example, 15°C, 10% RH), and the halftone images obtained every 100 sheets are checked to see if they occur.

[0050] Table 2 shows the relationship between the penetration amount of the brush member 11 and the ability to collect large-sized paper particles, and the occurrence of friction memory, which was examined as described above. [Table 2]

[0051] From the above results, it is possible to satisfy the requirements for both paper dust collection ability and prevention of friction memory if the penetration depth of the brush member 11 is 0.5 to 2.0 mm. Based on the above results, the penetration depth of the brush member 11 in this embodiment is set to 1.0 mm, which can achieve both paper dust collection ability for large sizes and prevention of friction memory.

[0052] [Characteristics of this embodiment] As described above, by using the brush member 11, it is possible to prevent the accumulation of toner while suppressing the influence of paper dust. However, further investigation by the present inventors has revealed that when the transfer residual toner passes through the brush member 11, a small amount of the toner adheres to the brush member 11.

[0053] Usually, when a print job is completed and there is no more supply of residual toner after transfer, post-rotation is performed to remove the toner adhering to the brush member 11. For example, there is a method in which the photosensitive drum is repeatedly driven and stopped during post-rotation after the print job is completed, thereby changing the attitude of the brush member 11 and removing the adhering toner. However, when a large number of sheets are printed continuously or during the latter half of use when the image forming device or cartridge including the photosensitive drum 1 and brush member 11 is used more frequently, the toner adhering to the brush member 11 may accumulate without being removed, which may result in the toner scattering inside the machine as described above.

[0054] In view of the above problem, in this embodiment, a conductive member is used as the brush member 11, and a bias is applied to the brush member 11, thereby suppressing toner adhesion during continuous printing. That is, the brush member 11 in this embodiment is made of a conductive nylon thread 112 woven into a conductive base fabric 111. Note that other materials such as conductive polyester or acrylic spun yarn may be used for the thread 112. A power source 13 is connected to the brush member 11 as a voltage application unit, and a voltage application is possible. There are.

[0055] A voltage of the same polarity as the normal charging polarity of the toner is applied from the power source 13 to the brush member 11. This prevents the toner from adhering to the brush member 11. Note that applying a voltage of the opposite polarity to the toner is undesirable because it will cause the toner to accumulate even more.

[0056] 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 exposed portion potential. Then, the transfer residual toner is charged twice, once by the brush member 11 and once by the charging roller 2. In that case, the transfer residual toner becomes excessively charged, and the electrostatic adhesion force with the photosensitive drum 1 becomes strong. As a result, the recovery by the developing device 3 becomes insufficient, and recovery failure may occur. On the other hand, when the absolute value of the voltage applied to the brush member 11 is small, i.e., 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 is weakened and dirt inside the machine may occur.

[0057] Therefore, in this embodiment, the relationship between the voltage applied to the brush member 11, the collection failure, and the dirt inside the machine was examined. The collection failure was judged by forming a white image after one revolution of the photosensitive drum of a black image exposed within a predetermined range, and by whether or not the transfer residual toner of the black image adheres to the white image. In addition, the dirt inside the machine was judged by printing using Century Star paper as the transfer material S. Print 1000 images with a 5% content rate per print job, and do 50 jobs, i.e. 50,000 prints. After printing, it is determined whether toner stains have occurred around the brush member 11.

[0058] Table 3 shows the relationship between the voltage applied to the brush member 11 and the collection failure and the inside of the machine stain, which was examined as described above. [Table 3]

[0059] As shown in Table 3, if the absolute value of the voltage applied to the brush member 11 is 200 V or more, some toner adheres to the brush member 11 during execution of a print job, but does not result in contamination of the inside of the machine. Note that, as described above, the toner adhered to the brush member 11 is removed by performing post-rotation when there is no more supply of residual toner after transfer.

[0060] In addition, as shown in Table 3, if the voltage applied to the brush member 11 is a voltage with an absolute value smaller than 600 [V], the residual toner is not excessively charged and the occurrence of collection failure can be prevented. If the potential difference between the transfer pad and the discharge pad is less than the general discharge threshold, i.e., 500V or less, the transfer residual toner will not be transferred to the discharge pad. This is thought to be because the brush member 11 does not charge the battery.

[0061] Based on the above results, the voltage applied to the brush member 11 is a voltage that can prevent both poor collection and contamination inside the machine, specifically, -400 [V].

[0062] As described above, by adopting the configuration of this embodiment, it is possible to prevent toner from scattering inside the machine due to toner accumulation on the brush member 11, prevent spotted images caused by paper powder adhering to the photosensitive drum, and prevent collection failures. The present invention can also be applied to an image forming apparatus having multiple photosensitive drums corresponding to multiple color toners. The present invention can also be applied to a transfer method in which the transfer material S is transported to the transfer section by a belt and directly transferred from the photosensitive drum 1 to the transfer material S, or an image forming apparatus using an intermediate transfer body such as an intermediate transfer belt.

[0063] <Example 2> The present embodiment will be described below, focusing on the differences from the first embodiment. The configuration of the image forming apparatus 100 in this embodiment is shown in FIG. 4. In this embodiment, unlike the first embodiment, a brush member 11 is disposed downstream of the pre-exposure device 12 and upstream of the charging roller 2. In this embodiment, the charging potential of the photosensitive drum 1 charged by the charging roller 2 is set to about -700 [V], which is higher than that in the first embodiment. The potential is about -100 [V], which is the same as in Example 1. The bias is −400 [V], the same as in Example 1. Other configurations and operations are the same as in Example 1, so a description thereof will be omitted.

[0064] The difference between the charge potential and the exposed area potential (called the latent image contrast) can be set arbitrarily for each model of image forming apparatus, and for example, the latent image contrast is increased when a toner with a high charge amount is used. Here, referring to FIG. 5, the problem of setting a large latent image contrast will be described.

[0065] Figure 5(a) shows the change in potential before and after transfer when the latent image contrast is relatively small. In this case, the potential difference between the exposed and unexposed areas after the transfer process is almost eliminated due to the action of the transfer voltage. On the other hand, Figure 5(b) shows the potential before and after transfer when the latent image contrast is relatively large. In this case, the potential of the non-exposed area is high, so the potential does not decrease completely even after the transfer process, and the potential difference between the exposed and non-exposed areas remains.

[0066] Here, a voltage of -400 [V] is applied to the brush member 11 as in the first embodiment. As explained in Example 1, no dirt was generated inside the machine, but toner was attached to the brush member 11. The toner moves due to the potential difference with the photosensitive drum 1 and adheres to the photosensitive drum 1. This state will be described with reference to FIG.

[0067] Figure 6(a) corresponds to Figure 5(a), and is a case where the latent image contrast is relatively small and the potential difference between the exposed and non-exposed areas after the transfer process is small. At this time, the toner t adheres uniformly to the photosensitive drum 1. Toner that adheres uniformly in this way is easily charged in the charging process, and is collected by the developing device 3, so no problems arise. On the other hand, Figure 6(b) corresponds to Figure 5(b), and shows a case where the latent image contrast is relatively large and the potential difference between the exposed and non-exposed areas after the transfer process is large. In this case, the electric field is concentrated on the exposed areas, so the toner is concentrated and adheres to the exposed areas. The toner that is concentrated and adheres in this way is difficult to charge in the charging process and difficult to collect by the developing device 3, resulting in poor collection.

[0068] The collection failure will be described in detail with reference to Fig. 7. Fig. 7(a) corresponds to Fig. 6(a), and is a case where toner t is uniformly attached on the photosensitive drum 1. At this time, all of the toner can receive discharge from the charging roller 2, and all of the toner is charged, so that all of the toner can be collected by the developing device 3. On the other hand, Figure 7(b) corresponds to Figure 6(b), and shows a case where there is a toner concentration area on the photosensitive drum 1 and the toner becomes a layer. In this case, the toner on the photosensitive drum 1 side (the lower layer side on the paper surface) cannot receive the discharge from the charging roller 2. Since the toner is not charged, it is not collected by the developing device 3, resulting in a collection failure.

[0069] Therefore, in this embodiment, the brush member 11 is disposed downstream of the pre-exposure 12 and upstream of the charging roller 2, thereby discharging the photosensitive drum 1 before the brush member 11 comes into contact with it, thereby eliminating the potential difference between the exposed and non-exposed areas after the transfer process. With this configuration, even when a large latent image contrast is used, the toner adheres uniformly to the photosensitive drum 1 when the brush member 11 comes into contact with it, making it easy to collect it with the developing device 3, thereby suppressing collection failures.

[0070] Incidentally, in this embodiment, paper dust is not removed when discharging in pre-exposure 12. Therefore, as explained in embodiment 1, the amount of discharge in the charging process decreases in the paper dust adhesion portion, and there is a concern that the transfer residual toner will not be sufficiently charged and will not be able to be collected by the developing device 3, resulting in the occurrence of image defects. However, in this embodiment, the charging potential is high, that is, the charging voltage is high, so that a sufficient amount of discharge can be obtained even in the portion where paper dust was attached, and the transfer residual toner will not be sufficiently charged and will be able to be collected by the developing device 3, thereby suppressing the occurrence of image defects.

[0071] As described above, by adopting the configuration of this embodiment, it is possible to prevent toner from scattering inside the machine even when the latent image contrast is high, prevent spotted images caused by paper powder adhering to the photosensitive drum, and prevent recovery failures.

[0072] The configurations of the first and second embodiments can be appropriately selected based on the magnitude of the latent image contrast to be used.

[0073] Moreover, it goes without saying that by providing the brush members 11 upstream and downstream of the pre-exposure 12, all of the effects described in the first and second embodiments can be obtained. [Explanation of symbols]

[0074] 1: photosensitive drum, 2: charging roller, 3: developing device, 4: exposure device, 5: transfer roller, 11: brush member, 12: pre-exposure device, 13: power supply, 70: control unit, 100: image forming device

Claims

1. A rotatable image carrier; a charging unit that contacts the image carrier to form a charging portion and charges the surface of the image carrier in the charging portion; an exposure unit for exposing the surface of the image carrier charged in the charging unit to light to form an electrostatic latent image; a developing unit that supplies a toner charged to a predetermined polarity to the electrostatic latent image formed on the surface of the image carrier to form a toner image; a transfer unit that forms a transfer section by contacting the image carrier and transfers the toner image formed on the surface of the image carrier in the transfer section to a transfer material; a brush member having conductivity, the brush member contacting a surface of the image carrier downstream of the transfer unit and upstream of the charging unit in a rotation direction of the image carrier to collect paper powder adhering to the surface; a voltage application unit that applies a voltage of the predetermined polarity to the brush member; A control unit that controls the voltage application unit; having In an image forming operation for forming an image on a recording material, after the toner image is transferred to the transfer material in the transfer section, toner remaining on the surface of the image carrier is recovered by the developing means, the control unit controls the voltage application unit so that a potential difference between the voltage of the predetermined polarity applied to the brush member and a surface potential of the image carrier formed on the surface of the image carrier is equal to or less than a discharge threshold value; an image forming apparatus characterized in that, in a non-image forming operation after the image forming operation has been performed, a switching operation is performed in which the image carrier is rotated and then stopped, and the image carrier is rotated and stopped again after the image carrier is rotated.

2. An image forming apparatus as described in claim 1, further characterized in that it further has a de-electrification means for de-electrifying the surface of the image carrier downstream of the transfer section and upstream of the charging section in the rotation direction of the image carrier.

3. The brush member is provided downstream of the transfer unit and upstream of the charge removing unit in a rotation direction of the image carrier.

3. The image forming apparatus according to claim 2, wherein the image forming apparatus further comprises:

4. The brush member is provided downstream of the charge removing means and upstream of the charging unit in the rotation direction of the image carrier.

3. The image forming apparatus according to claim 2,

5. The amount of penetration of the threads of the brush member into the image carrier is 0.5 to 2 mm.

5. The image forming apparatus according to claim 1, wherein the image forming apparatus is a multi-color image forming apparatus.

6. An image forming apparatus as described in any one of claims 1 to 4, characterized in that the brush member has a portion that rubs against the image carrier made of conductive thread, and the density of the thread is 110 to 300 kF / inch^2.

Images