JP4978961B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus using a photosensitive drum, and in particular, a method for polishing a surface of a photosensitive drum capable of suppressing image flow when an amorphous silicon (hereinafter referred to as a-Si) photosensitive drum is used. It is about.

  In recent years, an a-Si photosensitive drum has been widely used as an image carrier of an image forming apparatus using an electrophotographic process. The a-Si photoconductor drum has high hardness and excellent durability, and its characteristics as a photoconductor are hardly deteriorated even after long-term use. In addition, the image carrier is excellent in environmental safety.

  In an image forming apparatus using such an a-Si photosensitive drum, it is known that image flow tends to occur due to its characteristics. That is, when charging is performed using the charging unit, ozone is generated by discharging of the charging unit. The components in the air are decomposed by the ozone, and ion products such as NOx and SOx are generated. Since this ion product is water-soluble, it adheres to the photosensitive drum and enters into a roughness structure of about 0.1 μm on the surface of the photosensitive drum, so that it can be removed by a cleaning system used in a general-purpose machine. In addition, the resistance of the surface of the photosensitive drum is lowered by taking in moisture in the atmosphere. As a result, the lateral flow of the potential occurs at the edge portion of the electrostatic latent image formed on the surface of the photosensitive drum, and as a result, the image flow may occur.

  Conventionally, by putting a heater in the photosensitive drum, energy is given to release the moisture taken in by the ion products, and the resistance decrease on the surface of the photosensitive drum in a high humidity environment is suppressed. Already generalized. However, in such an apparatus, the number of parts for configuring the heater increases, a heater installation space is required, and power consumption increases, leading to an increase in the size and cost of the apparatus. In addition, it takes time for the surface of the photoreceptor to be heated to a predetermined temperature, which requires a long processing time and is not preferable from the viewpoint of safety.

  In view of this, a method for reducing the image flow by suppressing a decrease in resistance on the surface of the photosensitive drum with a simple configuration has been proposed. Patent Documents 1 and 2 describe a developer (abrasive toner) mixed with an abrasive and an abrasive. A method of removing ozone products without using a heater or the like by executing a refresh mode in which a photosensitive member is polished by the interaction of members (a rubbing roller and a cleaning blade) at a predetermined timing is disclosed. In the above Patent Documents 1 and 2, the developer is printed or developed at the time of non-printing (when the apparatus is started up or in a standby mode after printing), and the polishing means in the photoreceptor unit is transferred without transferring the developer to the recording medium. To be used for polishing the surface of the photoreceptor.

However, in the methods of Patent Documents 1 and 2, when the amount of developer supplied increases, a multilayer developer adheres to the surface of the photoreceptor. Here, since the developer layer close to the surface of the photoreceptor has a strong adhesion to the surface of the photoreceptor, it moves at the same speed as the photoreceptor. On the other hand, since the developer layer close to the polishing member is pressed against and adhered to the polishing member, the developer layer moves at the same speed as the polishing member. For this reason, slipping occurs between the layers of the developer and the polishing effect is lowered. In order to compensate for this, it is necessary to take a long polishing time. In particular, in a high temperature and high humidity environment, the amount of ion product adhering is large and polishing takes time, so that there is a problem that the printing waiting time for the user becomes long and the amount of developer necessary for polishing also increases.
Japanese Patent Laid-Open No. 11-3014 JP-A-11-133462

  SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of removing impurities adhering to the surface of a photosensitive drum in a short time by efficiently supplying a developer to which an abrasive is added. To do.

To achieve the above object, the present invention provides a photosensitive drum, a developing unit for attaching a toner containing an abrasive to the surface of the photosensitive drum to form a toner image corresponding to an electrostatic latent image, and the photosensitive member. A toner supply step for supplying toner from the developing unit to the photosensitive drum side during non-image formation, and a polishing member that is pressed against the drum surface with a predetermined pressure and polishes the surface of the photosensitive drum. In the image forming apparatus capable of executing a refresh mode including a polishing step of supplying the toner discharged in the toner supply step to the polishing member and polishing the surface of the photosensitive drum one or more times, a unit in the toner supply step The toner supply amount per area is 0.2 mg / cm ² or more and 0.5 mg / cm ² or less, and the execution time of the toner supply step is the photosensitive drum. It is characterized by being more than the time required for one rotation.

  According to the present invention, in the image forming apparatus having the above-described configuration, the toner supplying step is executed by applying a developing bias to the developing unit in a state where the potential of the surface of the photosensitive drum is set to approximately zero. It is said.

  According to the present invention, in the image forming apparatus having the above-described configuration, the ratio between the rotation speed of the photosensitive drum in the toner supply process and the rotation speed of the photosensitive drum after completion of toner supply in the polishing process is 1: It is 1 or more and 1: 4 or less.

  According to the present invention, in the image forming apparatus having the above-described configuration, a humidity detection unit that detects humidity inside or outside the apparatus and a control unit that controls the toner supply amount according to the detection result of the humidity detection unit are provided. The control means increases the toner supply amount per unit area in the first toner supply step from the second time onward when the detection result of the humidity detection means is a predetermined value or more. .

  According to the first configuration of the present invention, since a toner layer close to a single layer is formed on the entire circumference of the photosensitive drum in the toner supplying step, all of the supplied toner can be used for polishing the photosensitive member, and a small amount of toner can be used. Efficient and non-uniform polishing is possible in a short time using toner.

  According to the second configuration of the present invention, in the image forming apparatus having the first configuration, the toner supply amount is determined by the developing bias value applied to the developing unit in a state where the surface potential of the photosensitive drum is close to zero. Therefore, the toner supply amount can be easily adjusted within a predetermined range.

  According to the third configuration of the present invention, in the image forming apparatus having the first or second configuration, the rotational speed of the photosensitive drum in the toner supply step and the photosensitive drum after completion of the toner supply in the polishing step. By setting the ratio to the preliminary rotational speed of 1: 1 to 1: 4, a necessary and sufficient polishing effect can be obtained in a short time without rubbing the resin component in the toner against the drum surface.

  According to the fourth configuration of the present invention, in the image forming apparatus having any one of the first to third configurations, in the first toner supply step, when the detection result of the humidity detection unit is a predetermined value or more. By increasing the toner supply amount per unit area from the second time onward, under conditions where the surface of the photosensitive drum is condensed, the toner on the surface of the photosensitive drum is surely absorbed by the toner immediately after the start of the refresh mode. After that, the photoconductor can be polished efficiently in a short time.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing the configuration of the image forming apparatus of the present invention, and FIG. 2 is a partial view showing in detail the periphery of the image forming unit in FIG. An image forming apparatus (here, a monochrome printer) 100 includes a photosensitive drum 1, a charging unit 2, an exposure unit 3, a developing unit 4, a transfer roller 5, a cleaning device 14, a toner storage unit 20, a sheet storage unit 21, and a conveyance unit 22. , A fixing unit 23, and a paper discharge unit 24.

  The photosensitive drum 1 is obtained by laminating a photosensitive layer made of a-Si or OPC (organic photosensitive layer) on an aluminum drum, and the surface of the photosensitive drum 1 is charged by a charging unit 2. Then, an electrostatic latent image in which charging is attenuated is formed on the surface that has received the laser beam from the exposure unit 3.

  For example, in the case of an a-Si photosensitive layer containing carbon (C) and silicon (Si), a layer having a high carbon content layer (0.80 ≦ C / C + Si ≦ 0.94) exceeds about 35% of the surface layer ( 1000-2000 cm), and the carbon content ratio gradually decreases toward the inner surface side. Such an a-Si photosensitive layer is formed by a method that mainly uses a DC component during film formation.

  The charging unit 2 charges the surface of the photosensitive drum 1 by discharging (for example, corona discharge). For example, the charging unit 2 is discharged by applying a high voltage using a thin wire or the like as an electrode. .

  The exposure unit 3 irradiates the photosensitive drum 1 with a light beam (for example, a laser beam) based on the image data, and forms an electrostatic latent image on the surface of the photosensitive drum 1. The developing unit 4 includes a developing roller 4a disposed opposite to the photosensitive drum 1, and a developer image contained therein is attached to the electrostatic latent image on the photosensitive drum 1 by the developing sleeve 4a to form a toner image. It is something to be made.

  The cleaning device 14 includes a rubbing roller 6 which is a polishing system for polishing the photoconductor drum 1 and a cleaning blade 9. The rubbing roller 6 is pressed against the surface of the photoconductor drum 1 with a certain pressure by a spring (not shown). Has been.

  As is well known, an electrostatic latent image is recorded by the exposure unit 3 on the photosensitive drum 1 uniformly charged by the charging unit 2 after being neutralized by a static eliminating device (not shown), and the electrostatic latent image is inverted and developed. The developing unit 4 develops the toner image into a toner image, and the toner image is transferred onto the recording medium by the transfer roller 5. Untransferred toner that has not been transferred by the transfer roller 5 is removed as residual toner from the surface of the photosensitive drum 1 by the rubbing roller 6 and the cleaning blade 9, and the removed residual toner is discharged to a waste bottle (not shown) by the toner recovery device. Be transported.

  The toner storage unit (hopper) 20 supplies the developer to the developing unit 4 and stores the developer when the developer (toner) in the developing unit 4 becomes insufficient. The sheet storage unit 21 stores a sheet (paper, OHP, or the like) as a recording medium on which an image (toner image) is finally printed, and sends the sheet to the conveyance unit 22.

  The conveyance unit 22 is a sheet path from the sheet storage unit 21 to the paper discharge unit 24. The fixing unit 23 converts the toner image transferred onto the sheet into a stable permanent image. For example, the fixing unit 23 melts the toner image in a powder state by applying energy such as heat and pressure. The paper discharge unit 24 accommodates a sheet that has passed through the fixing unit 23, that is, a sheet on which a permanent image is printed and discharged to the outside of the apparatus.

  In addition, the image forming apparatus of the present invention develops in the developing unit 4 when the image forming apparatus is not transferred to a recording medium, for example, when the image forming apparatus is started up from a power-off state or a sleep (power saving) mode to a copy start state. A step of conveying the toner on the roller 4a to the photosensitive drum 1 side (hereinafter referred to as a toner supply step), and a toner conveyed to the photosensitive drum 1 side by the toner supply step is supplied to the rubbing roller 6 to supply the photosensitive member. A refresh mode including a step of polishing the surface of the drum 1 (hereinafter referred to as a polishing step) at least once each is configured to be executable.

    FIG. 3 is an enlarged view of the vicinity of the photosensitive drum in FIG. Around the photosensitive drum 1, along the rotation direction (clockwise in FIG. 3), the charging unit 2, the exposure unit 3 (see FIG. 2), the developing roller 4a, the transfer roller 5, the rubbing roller 6, and the cleaning blade 9 are arranged. Is arranged. The rubbing roller 6 is in pressure contact with the photosensitive drum 1 at a predetermined pressure, and is driven to rotate in the same direction on the contact surface with the photosensitive drum 1 by a driving means (not shown). It is controlled to 1.2 times the peripheral speed. Examples of the rubbing roller 6 include a structure in which a foam layer made of EPDM rubber and having an Asuka C hardness of 55 ° is formed as a roller body around a metal shaft. The material of the roller body is not limited to EPDM rubber, but may be rubber or foam rubber body of other materials, and those having an Asuka C hardness in the range of 10 to 90 ° are preferably used.

  Further, a scraper 10 is pressed against the rotational direction in the counter direction on the surface of the rubbing roller 6 on the downstream side in the rotational direction from the contact surface with the photosensitive drum 1. As the scraper 10, for example, an elastic plate made of SUS304 having a thickness of 0.02 to 2.0 mm is used, and its fixed end is attached to the mounting stay 11a. The free end of the scraper 10 pressed against the rubbing roller 6 is positioned below the fixed end, and the toner scraped off from the rubbing roller 6 by the scraper 10 falls to the recovery screw 13 side. Yes.

  Here, the attachment direction of the scraper 10 is the tangential direction at the pressure contact on the surface of the rubbing roller 6, but the present invention is not limited to this, and the pressure contact may have a predetermined angle with respect to the tangent. The material of the scraper 10 is not limited to weak magnetic SUS304, and nonmagnetic SUS plates, various resin, metal blade plates, rubber blade plates, and the like can be used.

  A cleaning blade 9 is fixed to the mounting stay 11b in a state where the cleaning blade 9 is in contact with the photosensitive drum 1 on the downstream side in the rotation direction from the contact surface with the rubbing roller 6 on the surface of the photosensitive drum 1. As the cleaning blade 9, for example, a polyurethane rubber blade having a JIS hardness of 78 ° is used, and is attached at a predetermined angle with respect to the tangential direction of the photosensitive member at the contact point. Note that the material, hardness, dimensions, the amount of biting into the photosensitive drum 1, the pressure contact force, and the like of the cleaning blade 9 are appropriately set according to the specifications of the photosensitive drum 1.

  Residual toner removed from the surface of the photosensitive drum 1 by the rubbing roller 6 and the cleaning blade 9 moves upward and is discharged to the outside of the cleaning device 14 (see FIG. 2) as the recovery screw 13 rotates. As the toner used in the present invention, silica, titanium oxide, strontium titanate, alumina or the like is embedded in the toner particle surface as an abrasive and held so as to partially protrude on the surface. Those that are electrostatically attached to the surface are used.

  FIG. 4 is a schematic diagram illustrating a state in which the image forming unit of the image forming apparatus of the present invention is in each process during the refresh mode. Here, a case where positively charged toner is used is described, and description of the charging unit 2 and the exposure unit 3 is omitted. FIG. 4A shows a state where the image forming unit is in the toner supply process. In the toner supply step, a developing bias having the same polarity (positive) as that of the toner is applied to the developing roller 4a in the developing unit 4 so that the toner used for polishing the surface of the photosensitive drum 1 is transferred from the developing unit 4 to the photosensitive drum 1. Supply to the side.

  In the present invention, the toner supply amount per unit area in the toner supply step (hereinafter simply referred to as toner supply amount) is limited, and the toner supply step is continued for one or more revolutions of the photosensitive drum. As a result, the toner layer T supplied onto the photosensitive drum 1 becomes a thin layer (preferably a single layer), and slipping between the toner layers in the gap between the surface of the photosensitive drum 1 and the rubbing roller 6 is suppressed. All of the supplied toner can be used for polishing the surface of the photoconductor, so that the polishing efficiency can be improved and the amount of toner supply can be minimized.

Here, when the toner supply amount exceeds 0.5 mg / cm ² , the toner layer T becomes multi-layered and slips between the layers, and the polishing efficiency of the drum surface is lowered. On the other hand, when the toner supply amount is less than 0.2 mg / cm ² , it is difficult to form a uniform toner layer T on the drum surface. Therefore, in the present invention, the toner supply amount is 0.2 mg / cm ² or more and 0.5 mg / cm ² or less.

  The toner is supplied to the photosensitive drum 1 by exposing the entire drum surface uniformly charged by the charging unit 2 by the exposure unit 3 and applying a developing bias having the same polarity (positive) as the toner to the developing roller 4a. Although it is possible to carry out by a normal image forming process in which toner is ejected onto the drum surface, this method increases the amount of toner supplied per unit area and makes it difficult to make the toner layer T a thin layer close to a single layer. It is.

  Therefore, it is preferable to use a method in which toner is supplied to the surface of the drum by applying a developing bias to the developing roller 4a in a state where the surface potential of the photosensitive drum 1 is near 0V (ground) without charging by the charging unit 2. . At this time, the developing bias applied to the developing roller 4a is set to a value (approximately 30 to 50 V) slightly higher than the bias value at which the toner starts to fly toward the drum surface.

  FIG. 4B shows a state where the toner supplied to the drum surface in the toner supply process reaches the rubbing roller 6 and the polishing process is started. In the polishing step, after supplying toner onto the photosensitive drum 1 in the toner supply step, the surface of the photosensitive drum 1 is polished by rotating the rubbing roller 6 with respect to the photosensitive drum 1 with a speed difference. This is a process for removing moisture and contaminants on the drum surface together with the toner. In addition, while supplying toner to the rubbing roller 6, a bias voltage having the same polarity (positive) as that of the toner is applied to the transfer roller 5 so that the toner does not adhere to the transfer roller 5.

  The toner that has passed through the contact portion between the photosensitive drum 1 and the rubbing roller 6 adheres to the rubbing roller 6 and is used again for polishing the drum surface during the next rotation. Most of the toner is slid by the scraper 10 (see FIG. 3). It is scraped off from the rubbing roller 6. Therefore, the duration of one toner supply step is set to be longer than the time required for one rotation of the photosensitive drum 1, and the toner surface can be uniformly polished by attaching the toner to the entire surface of the photosensitive drum 1.

  FIG. 4C shows a state where the toner supply process is completed during the polishing process. In the polishing process, even after the supply of toner from the developing roller 4a is stopped, the photosensitive drum 1 and the rubbing roller 6 continue to rotate for a while. In the present invention, since the toner layer T close to a single layer is formed on the entire circumference of the photosensitive drum 1 in the toner supply step, efficient polishing is possible. Further, when the toner supply is stopped, if the preliminary rotation is increased, the resin component in the toner is rubbed against the drum surface.

  Therefore, in the present invention, it is preferable to suppress the preliminary rotation number of the photosensitive drum as compared with the conventional case, and specifically, it is preferable to set the rotation number of the photosensitive drum in the toner supply process to be four times or less. On the other hand, in order to remove the deposits on the drum surface without unevenness, the preliminary rotation number of the photosensitive drum needs to be at least equal to or higher (one rotation or more) than the rotation number of the photosensitive drum in the toner supply process.

  Impurities on the surface of the photosensitive drum 1 can be removed in a short time by repeating the toner supply process and the polishing process shown in FIG. Thus, an effective polishing system can be obtained which can effectively prevent the image flow and can also make the polishing amount of the photosensitive layer on the drum surface constant. The number of executions and the execution time of each process are appropriately set according to the configuration of the photosensitive layer to be used, the usage environment of the apparatus, the execution interval of the refresh mode, and the like.

  FIG. 5 is a block diagram showing an example of a control path in the image forming apparatus of the present invention. The image forming apparatus 100 includes an image forming unit 15, an image input unit 31, a control unit 32, an operation panel 33, a humidity sensor 34, and a storage unit 35.

  When the image forming apparatus 100 is a copying machine, the image input unit 31 includes a scanning optical system equipped with a scanner lamp that illuminates the document during copying and a mirror that changes the optical path of reflected light from the document, and reflected light from the document. 1 is a printer such as that shown in FIG. 1, in which the image forming apparatus 100 includes a condensing lens that collects and forms an image and a CCD that converts the imaged image light into an electrical signal. In this case, the receiving unit receives image data transmitted from a personal computer or the like.

  The image signal read by the image input unit 31 is sent to the control unit 32, and image processing such as gradation processing is appropriately performed to convert the image signal into image data. The image forming unit 15 includes a photosensitive drum 1, a charging unit 2, an exposure unit 3, a developing unit 4, a transfer roller 5, a cleaning device 14, and the like, and is based on image data converted by the control unit 32. A latent image is formed on the drum 1, and after development, the toner image is transferred onto the sheet. The control unit 32 also controls each part of the image forming apparatus such as the image input unit 31 and the image forming unit 15 according to the set program.

  The operation panel 33 includes operation keys for the user to set device functions, printing conditions, and the like, and a display unit (none of which is shown) that displays the setting conditions, device states, and the like. The humidity sensor 34 constantly detects the humidity inside the apparatus every predetermined time, and the detected humidity is sent to the control unit 32. The controller 32 controls the refresh mode by changing the bias voltage applied to the developing roller 4a (see FIG. 3) and the transfer roller 5 in the developing unit 4 based on the humidity detected by the humidity sensor 34.

  The refresh mode control is preferably performed using the detection value immediately before, but may be controlled using humidity detected at another timing. It is also possible to detect the humidity a predetermined number of times and use the average value of the detected values. The humidity sensor 34 is installed, for example, in the vicinity of the transfer roller 5, the rubbing roller 6, and the photosensitive drum 1, but may be installed in other places where the humidity inside the apparatus can be accurately detected.

  The storage unit 35 stores a control program for each unit used by the control unit 32. As will be described later, when the toner supply amount immediately after the start of the refresh mode is changed according to the humidity detected by the humidity sensor 34, a developing bias value corresponding to the humidity is also stored.

Next, a refresh mode execution procedure in the image forming apparatus according to the present embodiment will be described with reference to FIGS. When the image forming apparatus is turned on, in the sleep (power saving) mode, or when the refresh mode is started by setting by the user, the humidity inside the apparatus detected by the humidity sensor 34 when the main motor is started is controlled. Is sent out. Next, the toner supply amount immediately after the start of the refresh mode (first toner supply step) is set based on the humidity inside the apparatus. Here, the toner supply amount is determined by the amount of water vapor per 1 m ^{3 of} air (hereinafter referred to as HUMID).

  Then, the toner supply onto the photosensitive drum 1 is started by applying a developing bias corresponding to the toner supply amount to the developing roller 4a with a slight delay from the start of driving of the main motor, and at the same time, the transfer roller 5 is supplied with the same toner as the toner. A polar bias voltage is applied (see FIG. 4A). As a result, toner does not adhere to the transfer roller 5, and sufficient toner used in the polishing process is supplied to the rubbing roller 6. This toner supply process is continuously performed for a time required for one rotation of the photosensitive drum 1.

  Thereafter, the polishing process is started when the toner reaches the rubbing roller 6 (see FIG. 4B). The polishing process continues after the toner supply process is completed, and the photosensitive drum 1 and the rubbing roller 6 are preliminarily rotated by a predetermined number of rotations (see FIG. 4C). The start-up of the apparatus is completed by repeating the toner supply process and the polishing process once or a plurality of times. When the humidity (HUMID) is high, only the toner supply amount in the first toner supply step is increased, and the toner supply amount is returned to the normal after the second time.

  According to the above procedure, when the moisture amount on the surface of the photosensitive drum increases as the humidity increases, an amount of toner that can adsorb moisture is supplied at the start of the refresh mode, and then the toner supply amount is decreased. Thus, a toner thin layer can be formed. Accordingly, it is possible to efficiently polish the surface of the photoreceptor simultaneously with moisture adsorption, and it is possible to effectively prevent the occurrence of image flow while suppressing the execution time of the refresh mode in a short time. Note that the refresh mode may be automatically started in accordance with the humidity detected by the humidity sensor 34 or the number of printed sheets from the previous refresh mode execution.

  In addition, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, the toner supply amount immediately after the start of the toner supply process is changed based on the humidity inside the apparatus detected by the humidity sensor 34. However, the humidity outside the apparatus is detected, and the toner is detected based on the detected humidity. The supply amount may be changed.

  Further, the present invention is not limited to the monochrome printer as shown in FIG. 1, and includes a photosensitive drum such as a tandem or rotary color copier and printer, a monochrome copier, a digital multifunction machine, a facsimile machine, or the like. Of course, the present invention can be applied to various image forming apparatuses.

The polishing performance in the refresh mode executed in the image forming apparatus of the present invention was evaluated. In the present invention 1, the toner supply amount in the toner supply step is 0.2 mg / cm ² and the development bias application time (toner supply time) to the developing roller 4a is 1 sec. On the other hand, a case where the toner supply amount in the toner supply step is 0.8 mg / cm ² and the development bias application time (toner supply time) to the developing roller 4a is 1 sec is a comparative example.

As an evaluation method, the refresh mode was executed after printing 100,000 test images under normal humidity conditions (23 ° C., 55%, HUMID 120 mg) under the conditions of the present invention 1 and the comparative example. Further, the toner supply amount in the first toner supply step is 0.4 mg / cm ² under high humidity conditions (35 ° C., 80%, HUMID 335 mg), and the toner supply amount in the subsequent toner supply step is 0.2 mg / cm ^2. In this case, the present invention 2 was used, and the refresh mode was executed in the same manner. In the present inventions 1 and 2 and the comparative example, the polishing performance was evaluated by comparing the time required for polishing the photoreceptor (refresh mode time).

  As test conditions, an a-Si photosensitive drum having a diameter of 30 mm was used, and the drum rotation speed was set to 100 mm / sec (about one second in one round of the drum). Further, a positively chargeable magnetic one-component toner having an average particle size of 7.3 μm and containing 0.6% by weight of silica and 1.4% by weight of titanium oxide was used as an abrasive. In the toner supply step, the surface potential of the photosensitive drum was set to about 0 V, and a positive bias of 50 V was applied to the developing roller to supply toner to the drum surface. The results are shown in Table 1.

As shown in Table 1, when the toner supply time per one toner supply step is 1 second (≈one round of the photosensitive drum), the toner supply amount is as low as 0.2 mg / cm ² in the present invention 1, and polishing is performed. The preliminary rotation time required after the toner supply is stopped in the process is 3.75 seconds (approximately 3.75 revolutions of the photosensitive drum), and the number of repetitions of the toner supply process and the polishing process necessary for polishing the photosensitive member is 8, The refresh mode execution time was 38 seconds.

On the other hand, in the comparative example in which the toner supply amount is 0.8 mg / cm ² , the preliminary rotation time required after the toner supply is stopped is 60 seconds (≈60 photosensitive drums), which is necessary for polishing the photosensitive member. Each process was repeated twice and the refresh mode execution time was 122 seconds.

On the other hand, under high humidity conditions, as in the present invention 2, the toner supply amount in the first toner supply step is 0.4 mg / cm ² , and the preliminary rotation time in the subsequent first polishing step is 7.5 seconds. In addition to the double of the invention 1, thereafter, the toner supply amount is set to 0.2 mg / cm ² , the preliminary rotation time is returned to 3.75 seconds and each process is repeated 6 times in the same manner as in the invention 1. The photosensitive drum could be polished in an execution time of 37 seconds.

  From this result, it was confirmed that the refresh mode execution time can be greatly shortened in the present invention because the supplied toner adheres as a thin layer on the entire drum surface and improves the polishing efficiency. In addition, by increasing the amount of toner supplied in the first toner supply step under high humidity conditions, moisture on the surface of the photoreceptor can be adsorbed at one time, and then sufficient polishing can be performed in a short time. .

The present invention includes a photosensitive drum, a developing unit that forms a toner image corresponding to an electrostatic latent image by attaching a toner containing an abrasive to the surface of the photosensitive drum, and a pressure contact with the surface of the photosensitive drum at a predetermined pressure. And a polishing member for polishing the surface of the photosensitive drum, and a toner supply step for supplying toner from the developing unit to the photosensitive drum side during non-image formation, and a toner discharged from the toner supply step for polishing the toner In the image forming apparatus capable of executing a refresh mode including at least one polishing process for polishing the surface of the photosensitive drum by supplying to the toner, the toner supply amount per unit area in the toner supply process is 0.2 mg / cm ² or more It is 0.5 mg / cm ² or less, and the execution time of the toner supply process is set to be longer than the time required for one rotation of the photosensitive drum.

  Accordingly, since a toner layer close to a single layer is formed on the entire circumference of the photosensitive drum in the toner supply process in the refresh mode, all of the supplied toner can be used for polishing in the polishing process. Accordingly, it is possible to provide an image forming apparatus capable of efficient and uniform polishing in a short time in the refresh mode.

  In addition, since the toner supplying process is executed by applying a developing bias to the developing unit with the electric potential of the surface of the photosensitive drum being close to 0, image formation capable of easily forming a thin toner layer on the surface of the photosensitive drum It becomes a device.

  Further, since the ratio of the rotational speed of the photosensitive drum in the toner supply process and the preliminary rotational speed of the photosensitive drum after completion of the toner supply in the polishing process is set to 1: 1 or more and 1: 4 or less, the resin component in the toner Thus, a necessary and sufficient polishing effect can be obtained in a short time without rubbing the surface of the drum, and the printing waiting time can be shortened while reliably preventing the image flow.

  In addition, in a high humidity condition where the surface of the photosensitive drum is dewed, the toner supply amount per unit area in the first toner supply step is increased from the second time onward, so that the moisture on the surface of the photosensitive drum is removed. In this state, the photoconductor can be polished efficiently in a short time, and the refresh mode time can be shortened regardless of the use environment.

FIG. 1 is a schematic cross-sectional view showing an overall configuration of an image forming apparatus of the present invention. FIG. 2 is a partially enlarged view around the image forming unit in FIG. 1. FIG. 3 is a partially enlarged view around the photosensitive drum in FIG. 2. FIGS. 4A and 4B show the periphery of the photosensitive drum showing the toner supply process (FIG. 4A), the polishing process (FIG. 4B), and the polishing process (FIG. 4C) after the toner supply process is completed in the refresh mode. FIG. FIG. 3 is a block diagram showing a control path of the image forming apparatus of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging unit 3 Exposure unit 4 Developing unit 4a Developing roller 5 Transfer roller 6 Sliding roller 9 Cleaning blade 10 Scraper 11a, 11b Mounting stay 13 Collecting screw 14 Cleaning device 15 Image forming part 31 Image input part 32 Control part 34 Humidity sensor 35 Storage unit 100 Image forming apparatus T Toner layer

Claims (3)

A photosensitive drum, a developing unit that forms a toner image corresponding to the electrostatic latent image by attaching a toner containing an abrasive to the surface of the photosensitive drum, and is pressed against the surface of the photosensitive drum with a predetermined pressure. A polishing member for polishing the surface of the photosensitive drum,
A toner supplying step for supplying toner from the developing unit to the photosensitive drum side during non-image formation, and a polishing step for polishing the surface of the photosensitive drum by supplying the toner discharged in the toner supplying step to the polishing member In an image forming apparatus capable of executing a refresh mode including two or more times,
The toner supply amount per unit area in the toner supply process is 0.2 mg / cm ² or more and 0.5 mg / cm ² or less, and the execution time of the toner supply process is more than the time required for one rotation of the photosensitive drum. Yes,
Humidity detection means for detecting the humidity inside or outside the apparatus and control means for controlling the toner supply amount according to the detection result of the humidity detection means are provided. An image forming apparatus, wherein when the detection result is equal to or greater than a predetermined value, the toner supply amount per unit area in the first toner supply step is increased from the second time onward.   2. The image forming apparatus according to claim 1, wherein the toner supplying step is executed by applying a developing bias to the developing unit in a state in which a potential of the surface of the photosensitive drum is close to 0. 3.   The ratio between the rotation speed of the photosensitive drum in the toner supply step and the rotation speed of the photosensitive drum after completion of toner supply in the polishing step is 1: 1 to 1: 4. The image forming apparatus according to claim 1.

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