JP2016200680A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can effectively prevent contamination of a surface of an image carrier with a substance bled from a charging member in contact with the image carrier.SOLUTION: An image forming apparatus comprises: an image carrier; a charging member, a developing device, a transfer member, a cleaning device, a bias application device, and a control part. When a printing operation is not performed for a predetermined time period, the control part performs a bleed contamination prevention mode including an external additive discharge step of discharging only an external additive to a surface of the image carrier from a toner carrier, and an external additive adhesion step of causing the external additive discharged to the surface of the image carrier in the external additive discharge step to be adhered to the entire outer peripheral surface of the charging member, and subsequently makes a transition to a power saving mode of restricting a power to be supplied to the respective parts of the apparatus.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an image forming apparatus using electrophotography, and more particularly to an image forming apparatus provided with a charging member that charges a surface of a photosensitive drum in a contact state.

  Conventionally, in an image forming apparatus using an electrophotographic process, a charging device is used to charge the surface of a photosensitive drum (image carrier). As a charging device, a corotron (or scorotron) charging device that is disposed in non-contact with the photosensitive drum and charges the surface of the photosensitive drum by corona discharge, and is disposed in contact with the photosensitive drum to charge the photosensitive drum. A contact-type charging device using a charging member such as a charging roller is known. However, in recent years, in order to reduce the amount of ozone that is harmful to the human body, a contact-type charging device that uses a smaller amount of ozone has been increasingly employed.

  In the image forming apparatus using these photosensitive drums, a so-called image flow in which the image becomes faint or the periphery of the image becomes blurred depending on the use conditions occurs due to its characteristics. It is known to be easy. The cause of the image flow is that when the surface of the photosensitive drum is charged using a charging device, ozone is generated by discharging of the charging device. 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, a lateral flow of potential occurs at the edge portion of the electrostatic latent image formed on the surface of the photosensitive drum, and as a result, an image flow may occur. This phenomenon is particularly remarkable in an amorphous silicon (hereinafter abbreviated as a-Si) photosensitive drum in which the surface wear due to a blade or the like is small and the molecular structure of the photosensitive member surface easily adsorbs moisture.

  In addition, the image flow described above is caused by bleeding of the conductive agent in a rubber member such as a charging roller that is in contact with the surface of the photosensitive drum or the process oil (plasticizer) added when the rubber member is molded. This can also occur when moving to a photosensitive drum. In particular, it is known that process oil tends to bleed on the surface of the charging roller when the apparatus is stopped in a high temperature and high humidity environment.

  Therefore, a method for preventing bleeding of process oil from the charging roller has been proposed. For example, Patent Document 1 discloses a developer layer (charge roller) at a contact position between a photosensitive member and a contact member (charging roller) during non-image formation. A technique for preventing contamination of the surface of the photosensitive member by a bleed from the contact member by stopping the rotation of the photosensitive member with a toner layer interposed therebetween is disclosed.

JP 2007-199570 A

  In the method of Patent Document 1, toner is interposed only in the nip portion between the photosensitive member and the contact member. However, since the process oil bleeds from the entire outer peripheral surface of the charging roller, it is not sufficient to interpose toner in the nip portion as in Patent Document 1. Furthermore, the method of Patent Document 1 has a problem that the control is complicated because the bleed contamination prevention mode is executed based on the average printing rate.

  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 effectively preventing contamination of the surface of an image carrier due to a bleed from a charging member that contacts the image carrier.

  In order to achieve the above object, a first configuration of the present invention includes an image carrier, a charging member, a developing device, a transfer member, a cleaning device, a bias applying device, and a control unit. Forming device. The image carrier can be rotated in a predetermined rotation direction at the time of image formation, and an electrostatic latent image is formed. The charging member contacts the image carrier and charges the image carrier. The developing device has a toner carrier disposed opposite to the surface of the image carrier, and supplies toner containing one or more external additives from the toner carrier to the surface of the image carrier. The transfer member transfers the toner image formed by the developing device to a recording medium. The cleaning device collects residual toner on the surface of the image carrier after the toner image is transferred to the recording medium by the transfer member. The bias applying device applies a predetermined bias to the charging member, the toner carrier, and the transfer member. The control unit controls the operation of each unit including an image carrier, a charging member, a developing device, a cleaning device, and a bias applying device. When the printing operation has not been performed for a predetermined time, the control unit discharges only the external additive from the toner carrier onto the surface of the image carrier, and the image carrier is subjected to the external additive ejection step. And a bleed contamination prevention mode including an external additive attaching step for attaching the external additive discharged on the surface to the entire outer peripheral surface of the charging member, and then shifting to a power saving mode for restricting power supply to each part of the apparatus To do.

  According to the first configuration of the present invention, the bleed contamination prevention mode in which the external additive is attached to the entire outer peripheral surface of the charging member at the time of shifting to the power saving mode is executed. As a result, bleeding from the charging member is absorbed by the external additive and can be prevented from adhering to the surface of the image carrier. Therefore, it is possible to suppress the occurrence of an image flow due to a bleeding object from the charging member.

1 is a schematic diagram illustrating an overall configuration of an image forming apparatus 100 according to an embodiment of the present invention. 1 is a schematic enlarged cross-sectional view around the photosensitive drum 2 in FIG. 1 is a block diagram showing an example of a control path used in the image forming apparatus 100 of the present invention. FIG. 6 is a diagram illustrating rotation of the photosensitive drum 2, the charging roller 30, and the developing roller 5a in a bleed contamination prevention mode executed in the image forming apparatus 100 of the first embodiment. FIG. 6 is a diagram illustrating rotation of the photosensitive drum 2, the charging roller 30, and the developing roller 5a in a drum refresh mode executed in the image forming apparatus 100 according to the first embodiment. 6 is a flowchart illustrating an example of a control procedure of the image forming apparatus according to the first embodiment. Timing chart of control procedure of FIG. The figure which shows rotation of the photosensitive drum 2, the charging roller 30, and the developing roller 5a in the bleed contamination prevention mode performed in the image forming apparatus 100 of 2nd Embodiment. The figure which shows rotation of the photoconductive drum 2, the charging roller 30, and the developing roller 5a in the toner collection | recovery mode performed in the image forming apparatus 100 of 2nd Embodiment. The figure which shows rotation of the photosensitive drum 2, the charging roller 30, and the developing roller 5a in the drum refresh mode performed in the image forming apparatus 100 of the second embodiment. 8 is a flowchart illustrating an example of a control procedure of the image forming apparatus according to the second embodiment. FIG. 11 is a timing chart of the control procedure.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an image forming apparatus 100 according to an embodiment of the present invention. An image forming unit P is disposed in the image forming apparatus 100. The image forming unit P forms a predetermined image through each process of charging, exposure, development, and transfer.

  The image forming portion P is provided with a photosensitive drum 2 that carries a visible image (toner image), and the toner image formed on the photosensitive drum 2 is transferred onto a sheet (recording medium) 6. In addition, after fixing on the sheet 6 in the fixing device 7, it is discharged from the apparatus main body. The image forming process for the photosensitive drum 2 is executed while rotating the photosensitive drum 2 in the clockwise direction in FIG. 1 (forward rotation).

  Next, the image forming unit P will be described in detail. Around and above the rotatable photoconductor drum 2, there are a charging device 3 for charging the photoconductor drum 2, an exposure device 4 for exposing image information to the photoconductor drum 2, and the photoconductor drum 2. Are provided with a developing device 5 that forms a toner image, a cleaning device 9 that collects the developer (toner) remaining on the photosensitive drum 2, and a static elimination device 10 that removes residual charges on the photosensitive drum 2. It has been.

  First, the surface of the photosensitive drum 2 is uniformly charged by the charging device 3, and then light is irradiated by the exposure device 4 to form an electrostatic latent image corresponding to the image signal on the photosensitive drum 2. The developing device 5 includes a developing roller 5a disposed so as to face the photosensitive drum 2, and the developing device 5 includes a magnetic two-component developer containing a magnetic carrier and toner (hereinafter also simply referred to as a developer). Is filled with a predetermined amount. In addition, when the ratio of the toner in the developer filled in the developing device 5 falls below a specified value due to the formation of a toner image described later, the toner is supplied from the toner container 11 to the developing device 5. This toner is supplied to the surface of the photosensitive drum 2 by the developing roller 5a to which a predetermined developing bias is applied, and adheres electrostatically. Thereby, a toner image corresponding to the electrostatic latent image formed by exposure from the exposure device 4 is formed.

  The sheet 6 on which the toner image is transferred is accommodated in a plurality of paper feed cassettes 12a, 12b, and 12c that accommodate the sheet 6, and a stack bypass (manual feed tray) 12d provided above the sheet cassettes. The sheet 6 is conveyed toward the photosensitive drum 2 on which the toner image is formed via the paper feed roller 13 and the registration roller pair 14.

  At this time, the image writing signal is turned on, and the image is formed on the photosensitive drum 2 so that the toner image is transferred to a predetermined position on the sheet 6. A toner image on the photosensitive drum 2 is transferred onto the sheet 6 by applying an electric field to the lower portion of the photosensitive drum 2 with a transfer roller 17 to which a predetermined transfer bias is applied.

  The sheet 6 on which the toner image is transferred is conveyed to the fixing device 7. In addition, the photosensitive drum 2 after the toner image is transferred is collected by the cleaning device 9 in preparation for a new electrostatic latent image to be subsequently formed. Further, the residual charge on the surface of the photosensitive drum 2 is removed by the static eliminator 10. The sheet 6 conveyed to the fixing device 7 is heated and pressed by the fixing roller pair 7a, and the toner image is fixed on the surface of the sheet 6 to form a predetermined image. The sheet 6 on which the image is formed is then discharged to the discharge tray 19 by the discharge roller pair 18.

  FIG. 2 is a schematic enlarged cross-sectional view around the photosensitive drum 2 in FIG. In FIG. 2, the direction of the straight arrow indicates the conveyance direction of the sheet 6. Portions common to those in FIG. 1 are denoted by common reference numerals and description thereof is omitted. As the photosensitive drum 2, an amorphous silicon drum in which a positively chargeable amorphous silicon (a-Si) layer is formed as a photosensitive layer on the surface of a cylindrical metal base made of, for example, an aluminum tube can be used. In this embodiment, the photosensitive drum 2 in which an amorphous silicon layer having a thickness of 20 μm is formed on the outer peripheral surface of an aluminum base tube having a diameter of 30 mm is used. Further, the photosensitive drum 2 is connected to the main motor 45 via a drive gear (not shown), and thus rotates in the forward direction (clockwise direction in FIG. 2) and the reverse direction (counterclockwise direction in FIG. 2). It rotates in the forward direction (forward rotation) during image formation.

  A charging device 3 is disposed above the photosensitive drum 2. The charging device 3 rotates in contact with the photosensitive drum 2 and is driven to rotate. The charging roller 30 charges the surface of the photosensitive drum 2 and is rotated in contact with the charging roller 30 to clean the outer peripheral surface of the charging roller 30. And a cleaning brush 31.

The charging roller 30 has an elastic layer (rubber layer) 30b formed of a semiconductive elastic material on the outer peripheral surface of a metal core 30a. In this embodiment, an epichlorohydrin rubber layer having a volume resistance of 3 × 10 ⁷ Ω and a rubber hardness (JIS hardness) of 40 on the outer peripheral surface of a core metal 30a having a diameter of 6 mm, and a polyamide resin laminated on the surface of the epichlorohydrin rubber layer A conductive rubber roller having an elastic layer 30b having a surface hardness (JIS hardness) of 41, which is composed of a coating film having a thickness of 5 μm, is used. The charging roller 30 is rotatably supported by the casing of the charging device 3. The charging roller 30 is pressed against the photosensitive drum 2 with a predetermined nip pressure, and is rotated by being driven by the photosensitive drum 2.

  Further, at the time of image formation, a charging bias having the same polarity (positive polarity) as that of the toner is applied to the charging roller 30. Specifically, the cored bar 3a of the charging roller 3 is electrically connected to the charging bias power source 42 via the bias control circuit 41 (see FIG. 3), and an AC voltage is applied from the charging bias power source 42 to the charging roller 30. A charging bias composed of a DC voltage superimposed with is applied. By applying the charging bias, the surface of the photosensitive drum 2 can be charged by a current that flows according to the resistance of the elastic layer 30b of the charging roller 30. Here, the charging bias is set to a DC voltage Vdc = 650 V, an AC voltage Vpp superimposed on the DC voltage = 1.2 kV, and a frequency Vf = 1.5 kHz. As a result, the surface of the photosensitive drum 2 is charged to a positive polarity (300 V).

  The cleaning brush 31 has a brush portion formed of a resin such as conductive nylon protruding on the outer peripheral surface of the rotating shaft, and the charging roller is rotated by rotating the brush portion in contact with the outer peripheral surface of the charging roller 30. Toner, paper dust and the like adhering to 30 are removed. An input gear (not shown) connected to an output gear (not shown) provided on the rotating shaft of the photosensitive drum 2 is fixed to one end of the rotating shaft of the cleaning brush 31. By the rotational driving force, the charging roller 30 rotates (with rotation) in the same direction on the surface facing the charging roller 30 with a predetermined linear velocity difference. In place of the cleaning brush 31, a cleaning roller made of a sponge roller made of rubber or resin may be used.

  The developing device 5 includes a developing roller 5a disposed opposite to the photosensitive drum 2, a magnetic roller 5b disposed adjacent to the developing roller 5a, and toner supplied from a toner container 11 (see FIG. 1). Agitating / conveying members 5c for mixing (positively charged toner) with a magnetic carrier, agitating, conveying, and charging are rotatably disposed. The developing roller 5a and the magnetic roller 5b rotate in the counterclockwise direction in FIG. 2 with respect to the respective rotation axes.

  A DC voltage and an AC voltage are superimposed and applied to the developing roller 5a, and a DC voltage is applied to the magnetic roller 5b. These DC voltage and AC voltage are applied from the developing bias power source 43 to the developing roller 5a and the magnetic roller 5b via the bias control circuit 41. In this embodiment, a 150 V DC voltage and a rectangular wave AC voltage having a peak-to-peak value of 1.5 to 2.0 kV, a frequency of 4.5 kHz, and a duty ratio of 43% are applied to the developing roller 5a as a developing bias. Is done. In addition, a DC voltage of 200 to 400 V is applied to the magnetic roller 5b.

  The operation of the developing device 5 will be described. The developer is transported in the axial direction (direction perpendicular to the paper surface of FIG. 2) while being stirred by the stirring and transporting member 5c, and circulates in the developing device 5. Thereby, the toner in the developing device 5 is charged. The charged developer is conveyed to the magnetic roller 5b and forms a magnetic brush (not shown) on the magnetic roller 5b. After the thickness of the magnetic brush on the magnetic roller 5b is regulated by the earbrushing blade 5d, the magnetic brush is conveyed to the opposite portion between the magnetic roller 5b and the developing roller 5a, and is applied to the DC voltage applied to the magnetic roller 5b and the developing roller 5a. A toner thin layer is formed on the developing roller 5a by the potential difference ΔV from the direct current voltage and the magnetic field.

  The toner layer thickness on the developing roller 5a varies depending on the resistance of the developer and the difference in rotational speed between the magnetic roller 5b and the developing roller 5a, but can be controlled by ΔV. When ΔV is increased, the toner layer on the developing roller 5a is thickened, and when ΔV is decreased, the toner layer is thinned. The range of ΔV at the time of development is generally about 100V to 350V.

  The toner in the developer is obtained by adding one or more external additives to the toner base particles. The toner base particles contain a binder resin and a colorant, and are produced by a known method such as a pulverization classification method, a melt granulation method, a spray granulation method, or a polymerization method. Examples of the external additive include inorganic oxides such as silica, titanium oxide, and alumina, and metal soaps such as calcium stearate. The addition amount of the external additive is usually 0.1 to 5 parts by weight with respect to 100 parts by weight of the toner base particles.

  The core 17a of the transfer roller 17 is electrically connected to the transfer bias power source 44 via the bias control circuit 41, and has a polarity opposite to that of the toner from the transfer bias power source 44 to the transfer roller 17 during image formation. A certain negative transfer bias is applied. In a bleed contamination prevention mode and a drum refresh mode described later, a positive polarity bias (transfer reverse bias) having a polarity opposite to the transfer bias is applied to the transfer roller 17.

  The cleaning device 9 includes a cleaning blade 22 for removing residual toner and external additives on the surface of the photosensitive drum 2, and removing residual toner on the surface of the photosensitive drum 2 and rubbing the surface of the photosensitive drum 2. A cleaning roller 23 for polishing and a recovery screw 24 for discharging the toner removed from the surface of the photosensitive drum 2 by the cleaning blade 22 and the cleaning roller 23 to the outside of the cleaning device 9 are provided.

  The cleaning blade 22 is disposed so that the tip end that comes into contact with the surface of the photosensitive drum 2 is directed upstream (to be a counter) with respect to the positive rotation direction (clockwise direction in FIG. 2) of the photosensitive drum 2. ing. As the cleaning blade 22, for example, a polyurethane rubber blade having a JIS hardness of 78 ° and a thickness of 1.2 mm is used, and is attached at a predetermined angle with respect to the tangential direction of the photosensitive drum 2 at the contact point. The material, hardness, dimensions, the amount of biting into the photosensitive drum 2 and the pressure contact force of the cleaning blade 22 are appropriately set according to the specifications of the photosensitive drum 2.

  The cleaning roller 23 is in pressure contact with the photosensitive drum 2 at a predetermined pressure upstream of the cleaning blade 22 with respect to the positive rotation direction of the photosensitive drum, and a contact surface with the photosensitive drum 2 by a driving unit (not shown). Rotate in the same direction (with rotation). The linear velocity of the cleaning roller 23 is set to be faster (here, 1.2 times) than the linear velocity of the photosensitive drum 1a. Examples of the cleaning roller 23 include a structure in which a foam layer made of EPDM rubber and having an Asker 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 a rubber or foamed rubber body of another material, and those having an Asker C hardness of 10 to 90 ° are preferably used.

  Although not shown in FIG. 2, the cleaning device 9 has a scraper for setting the toner on the surface of the cleaning roller 23 to a predetermined layer thickness and prevents waste toner in the cleaning device 9 from leaking outside. Urethane seals are also provided.

  FIG. 3 is a block diagram illustrating an example of a control path used in the image forming apparatus 100 of the present invention. It should be noted that since various control of each part of the apparatus is performed when the image forming apparatus 100 is used, the control path of the entire image forming apparatus 100 becomes complicated. Therefore, here, a portion of the control path that is necessary for the implementation of the present invention will be mainly described.

  The image input unit 40 is a receiving unit that receives image data transmitted from the personal computer or the like to the image forming apparatus 100. The image signal input from the image input unit 40 is converted into a digital signal and then sent to the temporary storage unit 94.

  The bias control circuit 41 is connected to the charging bias power source 42, the developing bias power source 43, and the transfer bias power source 44, and operates each of these power sources in accordance with an output signal from the control unit 90. In accordance with control signals from the control circuit 41, the charging bias power source 42 is applied to the charging roller 30 in the charging device 3, the developing bias power source 43 is applied to the developing roller 5a and the magnetic roller 5b in the developing device 5, and the transfer bias power source 44 is transferred to the transfer roller. A predetermined bias is applied to 17 respectively.

  The main motor 45 is connected to the photosensitive drum 2, the developing device 5, the transfer roller 17, the fixing device 7, the conveyance roller of each part of the device through a gear train, and the device based on a control signal from the control unit 90. Each part is driven.

  The in-machine temperature / humidity sensor 47 constantly detects the temperature and humidity inside the image forming apparatus 100. The detection result is transmitted to the control unit 90 via an I / F 96 described later.

  The operation unit 50 is provided with a liquid crystal display unit 51 and LEDs 52 that indicate various states, and displays the state of the image forming apparatus 100 and displays the image forming status and the number of copies to be printed. Various settings of the image forming apparatus 100 are performed from a printer driver of a personal computer.

  In addition, the operation unit 50 includes a start button that the user instructs to start image formation, a stop / clear button that is used when image formation is stopped, and various settings of the image forming apparatus 100 that are in a default state. A reset button or the like is provided for use.

  The control unit 90 includes a central processing unit (CPU) 91 as a central processing unit, a read only memory (ROM) 92 that is a read-only storage unit, a random access memory (RAM) 93 that is a read / write storage unit, A plurality of (two in this case) that transmit a control signal to each device in the temporary storage unit 94, the counter 95, and the image forming apparatus 100 for storing image data and the like, and receive an input signal from the operation unit 50. The I / F (interface) 96 is provided. Further, the control unit 90 can be arranged at an arbitrary location inside the apparatus main body.

  The ROM 92 stores a control program for the image forming apparatus 100, data necessary for control, and the like that are not changed during use of the image forming apparatus 100. The RAM 93 stores necessary data generated during the control of the image forming apparatus 100, data temporarily required for controlling the image forming apparatus 100, and the like.

  Further, the RAM 93 (or ROM 92) stores a temperature / humidity threshold for determining whether or not to execute a bleed contamination prevention mode and a drum refresh mode, which will be described later, timings and lines of reverse rotation and forward rotation of the photosensitive drum 2. A program for controlling the speed, a developing bias value for supplying an external additive or toner from the developing roller 5a to the surface of the photosensitive drum 2 as will be described later, a timing for applying and stopping the application of the developing bias, and a charging roller 30 The charging bias, the charging reverse bias, the application and application stop timing thereof, the transfer bias applied to the transfer roller 17, the transfer reverse bias, the application and application stop timing, and the like are also stored.

  The temporary storage unit 94 temporarily stores the image signal input from the image input unit 40 and converted into a digital signal. The counter 95 counts the accumulated number of printed sheets.

  In addition, the control unit 90 transmits a control signal from the CPU 91 to the respective units and apparatuses in the image forming apparatus 100 through the I / F 96. In addition, a signal indicating the state and an input signal are transmitted from each part or device to the CPU 91 through the I / F 96. Examples of each part and device controlled by the control unit 90 include the image forming unit P, the exposure device 4, the fixing device 7, the transfer roller 17, the in-machine temperature / humidity sensor 47, the bias control circuit 41, and the operation unit 50. .

  As described above, the elastic layer 30b of the charging roller 30 contains a bleed material such as a conductive agent or process oil added during molding. When the image forming apparatus 100 is stopped in a high-temperature and high-humidity environment, these bleed materials bleed on the surface of the elastic layer 30b and move to the surface of the photosensitive drum 2 to cause problems such as image flow. May cause this.

  Therefore, in the image forming apparatus 100 of the present invention, when the image forming apparatus 100 does not perform the printing operation for a predetermined time, the temperature inside the apparatus is changed before the shift to the power saving mode (sleep mode) for restricting the power supply to each part of the apparatus. The humidity sensor 47 detects the temperature and humidity inside the image forming apparatus 100. When the detected temperature and humidity are equal to or higher than a predetermined value, the contamination of the photosensitive drum 2 due to the bleeding material from the charging roller 30 is prevented. The mode is going to be executed. Hereinafter, the bleed contamination prevention mode, which is a characteristic part of the present invention, will be described in detail.

<First Embodiment>
In the bleed contamination prevention mode of the present embodiment, when the temperature and humidity detected by the in-machine temperature / humidity sensor 47 when the image forming apparatus 100 shifts to the power saving mode is equal to or higher than a predetermined value, the developing roller 5a to the photosensitive drum. 2 includes an external additive discharge step of discharging the external additive onto the surface 2 and an external additive attachment step of attaching the discharged external additive to the outer peripheral surface of the charging roller 30.

  During non-image formation, the application of the charging bias to the charging roller 30, the application of the developing bias to the developing roller 5a, the application of the transfer bias to the transfer roller 17, and the rotation of the photosensitive drum 2 are stopped.

  From this state, the photosensitive drum 2 is rotated (forward rotation) in the same direction as the image formation (clockwise direction in FIG. 4). Almost simultaneously with the start of rotation of the photosensitive drum 2, a charging bias is applied to the charging roller 30 and the developing bias described above is applied to the developing roller 5a. At this time, the DC component of the developing bias applied to the developing roller 5a is lower than the DC component (150V) applied at the time of development, and is slightly higher than the bias value at which the toner starts to fly toward the drum surface ( About 50V).

  As a result, after the toner T comes into contact with the photosensitive drum 2, it is pulled back to the developing roller 5a side by the minus part of the AC waveform of the developing bias. On the other hand, the external additive G in the toner T remains on the photosensitive drum 2 because it is not easily affected by the electric field between the developing roller 5 a and the photosensitive drum 2. As a result, as shown in FIG. 4A, only the external additive G is discharged onto the photosensitive drum 2 (external additive discharge step). In this embodiment, by setting at least one of the external additives G contained in the toner to have a volume resistance value of 1 kΩ or less, only the external additive G can be easily discharged onto the photosensitive drum 2.

  At this time, the discharge length of the external additive G in the circumferential direction of the photosensitive drum 2 is set to be equal to or longer than the outer peripheral length (one turn) of the charging roller 30. The linear velocity of the photosensitive drum 2 when discharging the external additive G is set to a linear velocity (for example, 100 mm / sec) slower than the linear velocity (for example, 300 mm / sec) during image formation.

  Next, the application of the charging bias to the charging roller 30 is stopped, and as shown in FIG. 4B, the photosensitive drum 2 is rotated (reversely rotated in the counterclockwise direction in FIG. 4) in the reverse direction to the image formation. Rotate). As a result, the external additive G discharged onto the photosensitive drum 2 reaches the nip between the photosensitive drum 2 and the charging roller 30. When the external additive G enters the nip between the charging roller 30 and the photosensitive drum 2, the external additive G moves from the photosensitive drum 2 to the charging roller 30 due to a physical action by the nip pressure. .

  The reverse rotation of the photosensitive drum 2 is continued until the discharge region of the external additive G completely passes through the nip between the photosensitive drum 2 and the charging roller 30. As a result, as shown in FIG. 4C, the external additive G on the surface of the photosensitive drum 2 can be attached substantially uniformly to the entire outer peripheral surface of the charging roller 30 (external additive attaching step). When the external additive G is adhered, the linear speed of the photosensitive drum 2 is set to a lower speed (for example, 100 mm / sec) than the time of image formation following the discharge of the external additive, thereby charging the external additive more reliably. It can be attached to the roller 30.

  Further, when the image forming apparatus 100 returns from the power saving mode, a drum refresh mode for removing moisture and contaminants on the surface of the photosensitive drum 2 according to the temperature and humidity detected by the in-machine temperature / humidity sensor 47 is executed. To do. When the temperature and humidity detected by the in-machine temperature / humidity sensor 47 are equal to or higher than a predetermined value, the photosensitive drum 2 is rotated forward without applying a charging bias to the charging roller 30 as shown in FIG. At substantially the same time, a developing bias similar to that at the time of image formation is applied to the developing roller 5a. As a result, the toner T is discharged onto the photosensitive drum 2. The discharged toner T absorbs moisture and contaminants on the surface of the photosensitive drum 2. A part of the external additive G adhering to the charging roller 30 also moves to the photosensitive drum 2.

  When the photosensitive drum 2 continues to rotate forward, the toner T discharged onto the surface of the photosensitive drum 2 passes through the nip between the photosensitive drum 2 and the transfer roller 17. At this time, since a transfer reverse bias having a reverse polarity (same polarity as the toner) applied to the transfer roller 17 during image formation is applied to the transfer roller 17, the toner T is as shown in FIG. Then, it passes through the nip without adhering to the transfer roller 17, reaches the cleaning device 9, and is collected by the cleaning blade 22 of the cleaning device 9. The external additive G that has moved from the charging roller 30 to the photosensitive drum 2 is also collected by the cleaning blade 22 together with the toner T.

  At this time, in order to absorb moisture in the entire outer peripheral surface of the photosensitive drum 2, the discharge length of the toner T in the circumferential direction of the photosensitive drum 2 is set to be equal to or longer than the outer peripheral length (one turn) of the photosensitive drum 2. It is preferable. Further, the linear velocity of the photosensitive drum 2 is returned to the linear velocity (300 mm / sec) at the time of image formation. As a result, since the toner adhesion area per unit time is widened, the time required to remove the moisture on the surface of the photosensitive drum 2, that is, the execution time of the drum refresh mode can be shortened.

  Next, a description will be given of control when shifting to the power saving mode and returning from the power saving mode in the image forming apparatus 100 according to the present embodiment. FIG. 6 is a flowchart illustrating an example of a control procedure of the image forming apparatus 100 according to the present embodiment, and FIG. 7 is a timing chart of the control procedure of FIG. This control example will be described along the steps of FIG. 6 with reference to FIGS. 1 to 5 and 7 as necessary.

  After the image formation (printing) is finished, the application of the charging bias to the charging roller 30, the operation of the developing device 5, the application of the bias to the transfer roller 17, and the rotation of the photosensitive drum 2 are stopped (OFF). Then, the control unit 90 determines whether or not to shift the image forming apparatus 100 to the power saving mode based on whether or not the printing stop state has continued for a predetermined time (step S1).

  When the predetermined time has elapsed since the previous printing operation and the mode is shifted to the power saving mode (YES in step S1), whether the internal temperature T detected by the internal temperature / humidity sensor 47 is equal to or higher than the predetermined temperature T1, and the internal humidity It is determined whether or not H is equal to or higher than a predetermined humidity H1 (step S2). If T ≧ T1 and H ≧ H1 (YES in step S2), the control unit 90 executes the bleed contamination prevention mode.

  Specifically, as shown in FIG. 4A, a control signal is transmitted to the main motor 45 to rotate the photosensitive drum 2 in the forward direction, and the charging roller 30 is rotated by being driven by the photosensitive drum 2. Immediately after the charging bias is applied, the developing bias is applied to the developing roller 5a, and the external additive for the outer peripheral length of the charging roller 30 is discharged onto the surface of the photosensitive drum 2. Then, as shown in FIGS. 4B and 4C, the photosensitive drum 2 is rotated in the reverse direction so that the external additive on the photosensitive drum 2 adheres to the entire outer peripheral surface of the charging roller 30 (step S3). ). Thereafter, the image forming apparatus 100 shifts to the power saving mode. On the other hand, if T <T1 or H <H1 (NO in step S2), the process proceeds to the power saving mode without executing the bleed contamination prevention mode.

  Next, the control unit 90 determines whether or not a print command is input from a personal computer or the like (step S4). When a print command is input (YES in step S4), the controller 90 determines whether the in-machine temperature T detected by the in-machine temperature / humidity sensor 47 is equal to or higher than the predetermined temperature T1, and the in-machine humidity H is equal to or higher than the predetermined humidity H1. It is determined whether or not there is (step S5). If T ≧ T1 and H ≧ H1 (YES in step S5), the control unit 90 executes the drum refresh mode when returning from the power saving mode.

  Specifically, the control unit 90 transmits a control signal to the bias control circuit 41 and the main motor 45 to rotate the photosensitive drum 2 in the forward direction, and follows the photosensitive drum 2 without applying a charging bias to the charging roller 30. Then, a reverse transfer bias is applied to the transfer roller 17 while rotating (step S6). Next, as shown in FIG. 5A, a developing bias is applied to the developing roller 5a to discharge the toner for the outer peripheral length of the photosensitive drum 2 onto the surface of the photosensitive drum 2 (step S7). Then, as shown in FIG. 5B, the photosensitive drum 2 is continuously rotated in the forward direction, and the toner that has absorbed moisture and contaminants on the surface of the photosensitive drum 2 is collected by the cleaning blade 22 (step S8).

  On the other hand, if T <T1 or H <H1 (NO in step S5), the drum refresh mode is not executed and the power saving mode is resumed. Note that when the photosensitive drum 2 is rotated in the reverse direction in the external additive discharging step described above, there is a possibility that the toner collected by the cleaning device 9 at the time of image formation reaches the transfer roller 17 and adheres thereto. Therefore, in order to prevent the toner adhering to the transfer roller 17 from contaminating the back surface of the sheet 6, a transfer reverse bias is applied to the transfer roller 17 while the photosensitive drum 2 is rotated forward (step S9). Then, the toner adhering to the transfer roller 17 is returned onto the photosensitive drum 2 (transfer member cleaning operation).

  Thereafter, the printing operation is started (step S10), and it is determined whether or not the printing operation is completed (step S11). When the printing operation is completed, the process returns to step S1 and the same processing is repeated (steps S1 to S11).

  According to the above control, the bleed contamination prevention mode in which the external additive is attached to the charging roller 30 is executed in the case of a high temperature and high humidity environment when shifting to the power saving mode. As a result, the bleed material that bleeds from the charging roller 30 during the power saving mode is absorbed by the external additive and can be prevented from adhering to the surface of the photosensitive drum 2. Therefore, it is possible to suppress the occurrence of an image flow due to a bleeding object from the charging roller 30.

  If the environment is a high temperature and high humidity environment when returning from the power saving mode, a drum refresh mode is performed in which toner is discharged onto the photosensitive drum 2 to absorb moisture and contaminants on the surface of the photosensitive drum 2. As a result, it is possible to suppress the occurrence of image flow due to moisture adhering to the surface of the photosensitive drum 2 during the power saving mode. Therefore, it is possible to effectively suppress the occurrence of image flow over a long period of time and to obtain stable image quality.

  On the other hand, if the environment is not high-temperature and high-humidity when returning from the power saving mode, the drum refresh mode is not executed and the printing operation is started. Therefore, unnecessary drum refresh mode is not executed and unnecessary toner consumption is suppressed. And the waiting time of the user can be shortened.

  When the drum refresh mode is not executed when returning from the power saving mode, the printing operation is performed with the external additive attached to the charging roller 30, but the external additive has a lower resistance than the toner. For this reason, even if it is attached to the charging roller 30, the image formation is not affected. In particular, by using an external additive having a volume resistance value of 1 kΩ or less, the influence on image formation can be further reduced. However, when the toner collected by the cleaning device 9 in the external additive discharging step contaminates the transfer roller 17, it is desirable to perform the printing operation after the cleaning operation of the transfer roller 17 as described above.

Second Embodiment
In the bleed contamination prevention mode of the present embodiment, when the temperature and humidity detected by the in-machine temperature / humidity sensor 47 when the image forming apparatus 100 shifts to the power saving mode is equal to or higher than a predetermined value, the developing roller 5a to the photosensitive drum. 2 includes a toner discharge step of discharging toner onto the surface 2 and a toner attachment step of attaching the discharged toner to the outer peripheral surface of the charging roller 30.

  From the state where the printing operation is stopped, as shown in FIG. 8A, the photosensitive drum 2 is rotated (forward rotation) in the same direction as the image formation (clockwise direction in FIG. 8). Almost simultaneously with the start of rotation of the photosensitive drum 2, the above-described developing bias is applied to the developing roller 5a without applying a charging bias to the charging roller 30. At this time, the DC component of the developing bias applied to the developing roller 5a is set to a value (about 150V) sufficiently higher than the bias value at which the toner starts to fly toward the drum surface. Thereby, the toner T is discharged onto the photosensitive drum 2 (toner discharge step).

  At this time, the discharge length of the toner T in the circumferential direction of the photosensitive drum 2 is set to be equal to or longer than the outer peripheral length (one turn) of the charging roller 30. The linear velocity of the photosensitive drum 2 is set to a linear velocity (for example, 100 mm / sec) that is slower than the linear velocity (for example, 300 mm / sec) during image formation.

  Next, as shown in FIG. 8B, a charging reverse bias having a reverse polarity (a reverse polarity to the toner) applied to the charging roller 30 at the time of image formation is applied to the charging roller 30 to form an image on the photosensitive drum 2. It is rotated (reversely rotated) in the opposite direction (counterclockwise direction in FIG. 8). As a result, the toner T discharged onto the photosensitive drum 2 reaches the nip between the photosensitive drum 2 and the charging roller 30. When the toner T enters the nip between the charging roller 30 and the photosensitive drum 2, the toner T is caused by a physical action due to the nip pressure and an electric action due to a potential difference between the charging roller 30 and the photosensitive drum 2. Moves from the photosensitive drum 2 to the charging roller 30.

  The reverse rotation of the photosensitive drum 2 is continued until the discharge area of the toner T completely passes through the nip between the photosensitive drum 2 and the charging roller 30. As a result, as shown in FIG. 8C, the toner T on the surface of the photosensitive drum 2 can be adhered substantially uniformly to the entire outer peripheral surface of the charging roller 30 (toner adhesion step). By setting the linear velocity of the photosensitive drum 2 to a lower speed (for example, 100 mm / sec) than the time of image formation following the toner discharge step, the toner T can be more reliably attached to the charging roller 30.

  Further, by applying a charging reverse bias having a polarity opposite to that of the toner to the charging roller 30, the toner T can be reliably attached by the charging roller 30. Note that the toner T can be attached to the charging roller 30 only by a physical action by the nip pressure without applying a reverse charging bias to the charging roller 30.

  Further, the reverse charging bias may be applied to the charging roller 30 from the start of the reverse rotation of the photosensitive drum 2, or the timing at which the discharge area of the toner T on the photosensitive drum 2 arrives at the charging roller 3. It is also possible to apply in accordance with.

  Further, when the image forming apparatus 100 returns from the power saving mode, a toner recovery mode is executed in which the toner attached to the charging roller 30 is moved onto the photosensitive drum 2. As shown in FIG. 9A, by rotating the photosensitive drum 2 forward and applying a charging bias having the same polarity as the toner to the charging roller 30, the toner T adhering to the charging roller 30 is removed from the photosensitive member. Move onto drum 2. The moved toner T passes through the nip between the photosensitive drum 2 and the transfer roller 17. At this time, since the transfer reverse bias having the same polarity as the toner is applied to the transfer roller 17, the toner T passes through the nip without being attached to the transfer roller 17 for cleaning as shown in FIG. 9B. It reaches the device 9 and is collected by the cleaning blade 22. A part of the toner T adheres to the cleaning roller 23.

  Further, similarly to the first embodiment, the drum refresh mode for removing moisture and contaminants on the surface of the photosensitive drum 2 is executed according to the temperature and humidity detected by the in-machine temperature / humidity sensor 47.

  When the temperature and humidity detected by the in-machine temperature / humidity sensor 47 are equal to or higher than a predetermined value, the photosensitive drum 2 is rotated forward without applying a charging bias to the charging roller 30 as shown in FIG. At substantially the same time, the developing bias described above is applied to the developing roller 5a. As a result, the toner T is discharged onto the photosensitive drum 2. The discharged toner T absorbs moisture and contaminants on the surface of the photosensitive drum 2.

  When the photosensitive drum 2 continues to rotate forward, the toner T discharged from the developing roller 5a and the toner T moved from the charging roller 30 pass through the transfer roller 17 as shown in FIG. At this time, since a transfer reverse bias having a reverse polarity (same polarity as the toner) applied to the transfer roller 17 during image formation is applied to the transfer roller 17, the toner T passes without adhering to the transfer roller 17. Then, it reaches the cleaning device 9 and is collected by the cleaning blade 22 of the cleaning device 9.

  Here, in order to absorb moisture in the entire outer peripheral surface of the photosensitive drum 2, the discharge length of the toner T in the circumferential direction of the photosensitive drum 2 is set to be equal to or longer than the outer peripheral length (one turn) of the photosensitive drum 2. It is preferable. Further, the linear velocity of the photosensitive drum 2 is returned to the linear velocity (300 mm / sec) at the time of image formation. As a result, since the toner adhesion area per unit time is widened, the time required to remove the moisture on the surface of the photosensitive drum 2, that is, the execution time of the drum refresh mode can be shortened.

  In this embodiment, the toner including the bleed material attached to the charging roller 30 at the time of executing the toner recovery mode adheres to the outer peripheral surface of the cleaning roller 23, but adheres to the cleaning roller 23 by the execution of the drum refresh mode. The toner containing the bleed material can be replaced with a new toner. In order to replace the toner adhering to the cleaning roller 23, the discharge length of the toner T in the drum refresh mode needs to be equal to or longer than the outer peripheral length (one turn) of the cleaning roller 23. By setting the discharge length to be equal to or longer than the outer peripheral length (one turn) of the photosensitive drum 2, toner equal to or longer than the outer peripheral length of the cleaning roller 23 is discharged. Therefore, the toner attached to the cleaning roller 23 is surely replaced. Can do.

  Next, an example of control of the image forming apparatus according to the present embodiment will be described. FIG. 11 is a flowchart illustrating an example of a control procedure of the image forming apparatus 100 according to the present embodiment, and FIG. 12 is a timing chart of the control procedure of FIG. This control example will be described along the steps of FIG. 11 with reference to FIGS. 8 to 10 and FIG. 12 as necessary.

  After the image formation (printing) is finished, the application of the charging bias to the charging roller 30, the operation of the developing device 5, the application of the bias to the transfer roller 17, and the rotation of the photosensitive drum 2 are stopped (OFF). Then, the control unit 90 determines whether or not to shift the image forming apparatus 100 to the power saving mode based on whether or not the printing stop state has continued for a predetermined time (step S1).

  When the predetermined time has elapsed since the previous printing operation and the mode is shifted to the power saving mode (YES in step S1), whether the internal temperature T detected by the internal temperature / humidity sensor 47 is equal to or higher than the predetermined temperature T1, and the internal humidity It is determined whether or not H is equal to or higher than a predetermined humidity H1 (step S2). If T ≧ T1 and H ≧ H1 (YES in step S2), the control unit 90 executes the bleed contamination prevention mode.

  Specifically, a control signal is transmitted to the main motor 45 to rotate the photosensitive drum 2 forward, and the charging roller 30 is driven and rotated by the photosensitive drum 2 without applying a charging bias. As shown in a), a developing bias is applied to the developing roller 5a to discharge the toner for the outer peripheral length of the charging roller 30 onto the surface of the photosensitive drum 2. Then, as shown in FIGS. 8B and 8C, the photosensitive drum 2 is rotated in the reverse direction so that the toner on the photosensitive drum 2 adheres to the entire outer peripheral surface of the charging roller 30 (step S3). Thereafter, the image forming apparatus 100 shifts to the power saving mode. On the other hand, if T <T1 or H <H1 (NO in step S2), the process proceeds to the power saving mode without executing the bleed contamination prevention mode.

  Next, the control unit 90 determines whether or not a print command is input from a personal computer or the like (step S4). When a print command is input (YES in step S4), the controller 90 determines whether the in-machine temperature T detected by the in-machine temperature / humidity sensor 47 is equal to or higher than the predetermined temperature T1, and the in-machine humidity H is equal to or higher than the predetermined humidity H1. It is determined whether or not there is (step S5). If T ≧ T1 and H ≧ H1 (YES in step S5), the control unit 90 executes the toner recovery mode and the drum refresh mode when returning from the power saving mode.

  Specifically, a transfer signal is generated while transmitting a control signal to the main motor 45 to rotate the photosensitive drum 2 forward and rotating the charging roller 30 following the photosensitive drum 2 in a state where a charging reverse bias is applied. A reverse transfer bias is applied to 17. As a result, as shown in FIG. 9A, the toner including the bleed material adhering to the charging roller 30 moves to the surface of the photosensitive drum 2 (step S6). Then, as shown in FIG. 9B. As described above, the forward rotation of the photosensitive drum 2 is continued, and the toner including the bleed material that has moved to the surface of the photosensitive drum 2 is collected by the cleaning blade 22. Further, a part of the toner including the bleed material adheres to the cleaning roller 23.

  Subsequently, the control unit 90 transmits a control signal to the bias control circuit 41 and the main motor 45 to rotate the photosensitive drum 2 in the forward direction, and follows the photosensitive drum 2 without applying a charging bias to the charging roller 30. While rotating, a transfer reverse bias is applied to the transfer roller 17. Next, as shown in FIG. 10A, a developing bias is applied to the developing roller 5a to discharge the toner for the outer peripheral length of the photosensitive drum 2 onto the surface of the photosensitive drum 2 (step S7). Then, as shown in FIG. 10B, the photosensitive drum 2 continues to rotate forward, and the toner that has absorbed moisture and contaminants on the surface of the photosensitive drum 2 is collected by the cleaning blade 22. Further, the toner including the bleed material adhering to the cleaning roller 23 is replaced.

  On the other hand, if T <T1 or H <H1 (NO in step S5), only the toner recovery mode is executed (step S8), and the process returns to the power saving mode without executing the drum refresh mode.

  Thereafter, the printing operation is started (step S9), and it is determined whether or not the printing operation is finished (step S10). When the printing operation is completed, the process returns to step S1 and the same processing is repeated (steps S1 to S10).

  According to the above control example, the bleed contamination prevention mode in which the toner is attached to the charging roller 30 is executed in the high temperature and high humidity environment when shifting to the power saving mode. As a result, the bleed material that bleeds from the charging roller 30 during the power saving mode is absorbed by the toner and can be prevented from adhering to the surface of the photosensitive drum 2. Therefore, it is possible to suppress the occurrence of an image flow due to a bleeding object from the charging roller 30.

  Further, in a high temperature and high humidity environment when returning from the power saving mode, a toner collection mode in which the toner including the bleed material adhering to the charging roller 30 is moved onto the photosensitive drum 2 and then collected by the cleaning blade 22. Then, a drum refresh mode is executed in which toner is discharged onto the photosensitive drum 2 to absorb moisture and contaminants on the surface of the photosensitive drum 2. As a result, it is possible to suppress the occurrence of image flow due to moisture adhering to the surface of the photosensitive drum 2 during the power saving mode. Therefore, it is possible to effectively suppress the occurrence of image flow over a long period of time and to obtain stable image quality.

  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, the material, outer diameter, linear velocity, and the like of the photosensitive drum 2 and the charging roller 30 are not particularly limited, and can be appropriately set according to the apparatus configuration and the like. In each of the above embodiments, the present invention is applied to a positively charged toner. However, the present invention can also be applied to a negatively charged toner. The charging bias, the developing bias, and the transfer bias can be positive or negative depending on the polarity of the toner. What is necessary is just to set to a negative polarity bias.

  In each of the above embodiments, the magnetic roller 5b (toner supply member) on which the developer is carried and the development roller 5a (toner carrier) to which only the toner is supplied from the magnetic roller are provided. The image forming apparatus including the developing device 5 that causes only the toner to fly to the body drum 2 has been described. However, an image forming apparatus including a one-component developing type developing device that uses a magnetic one-component developer, or a two-component developer may be used. In the case of an image forming apparatus that includes only a magnetic roller 5b (toner supply member) to be carried and includes a two-component developing type developing device in which a magnetic brush of a two-component developer comes into contact with the photosensitive drum 2 during development. Even so, the bleed contamination prevention mode, toner recovery mode, and drum refresh mode described above can be executed by appropriately setting development conditions and the like.

  Further, the present invention is not limited to the monochrome printer as shown in FIG. 1, and is a contact type such as a digital multifunction peripheral, a tandem type color copying machine, a copying machine such as an analog monochrome copying machine, a facsimile, a laser printer, or the like. The present invention can be applied to various image forming apparatuses having the above charging device. EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to a present Example.

  With the control as shown in FIG. 6, the bleed contamination prevention mode is executed according to the temperature / humidity condition when shifting to the power saving mode, and the drum refresh mode is executed according to the temperature / humidity condition when returning from the power saving mode. Using the image forming apparatus 100 of the first embodiment, 20K (20,000) images are continuously printed in a high temperature and high humidity environment (32.5 ° C., 80%), and then left for 8 hours. Then, the procedure for evaluating the image flow was repeated for 3 days. The process speed during image formation was 160 mm / sec.

For evaluation of image flow, a 25% half image of 600 dpi, 1 × 1 dot was printed, and the density unevenness of the image was measured. For measurement of image unevenness, a transmission density measuring device (Model 310T) manufactured by X-rite was used, and dot reproducibility was lost (image density unevenness ΔT
When the D value was more than 0.1), the image was defective. As a result of the test, no image blur was observed after standing for 8 hours in all three days.

Comparative example

  Implementation is performed using the image forming apparatus 100 that does not execute the bleed contamination prevention mode according to the temperature / humidity condition when shifting to the power saving mode and performs the drum refresh mode according to the temperature / humidity condition when returning from the power saving mode. Image flow was evaluated by the same procedure and evaluation method as in the examples. As a result of the test, the occurrence of image blur was observed after standing for 8 hours on the third day.

  From the above results, it was confirmed that in the image forming apparatus 100 of the present invention that executes the bleed contamination prevention mode according to the temperature and humidity conditions when shifting to the power saving mode, it is possible to prevent deterioration in image quality due to image flow. Here, the image forming apparatus 100 according to the first embodiment in which the external additive is attached to the charging roller 30 in the bleed contamination prevention mode has been evaluated. However, in the second embodiment, the toner is attached to the charging roller 30 in the bleed contamination prevention mode. It has been confirmed that the same result can be obtained also in the image forming apparatus 100 of the embodiment.

  The present invention can be used in an image forming apparatus including a charging member that charges the surface of an image carrier in a contact state. By utilizing the present invention, it is possible to provide an image forming apparatus capable of effectively preventing contamination of the surface of the image carrier due to a bleed from a charging member that contacts the image carrier.

2 Photosensitive drum (image carrier)
3 Charging device 5 Developing device 5a Developing roller (toner carrier)
9 Cleaning device 17 Transfer roller (transfer member)
22 Cleaning blade 23 Rub roller 30 Charging roller (charging member)
30a Metal core 30b Elastic layer 41 Bias control circuit (bias application device)
42 Charging bias power supply (bias application device)
43 Development bias power supply (bias application device)
44 Transfer bias power supply (bias application device)
47 In-machine temperature / humidity sensor 90 Control unit 100 Image forming apparatus

Claims (12)

An image carrier capable of rotating in a predetermined rotation direction during image formation and forming an electrostatic latent image;
A charging member that contacts the image carrier and charges the image carrier;
A developing device having a toner carrier disposed opposite to the surface of the image carrier, and supplying toner containing one or more external additives from the toner carrier to the surface of the image carrier;
A transfer member for transferring a toner image formed by the developing device to a recording medium;
A cleaning device that collects residual toner on the surface of the image carrier after the toner image is transferred to a recording medium by the transfer member;
A bias applying device that applies a predetermined bias to the charging member, the toner carrier, and the transfer member;
A control unit for controlling the operation of each unit including the image carrier, the charging member, the developing device, the cleaning device, and the bias applying device;
In an image forming apparatus comprising:
The control unit includes an external additive discharge step of discharging only the external additive from the toner carrier onto the surface of the image carrier when the printing operation is not continuously performed for a predetermined time, and the external additive discharge Supplying a power to each part of the apparatus after executing a bleed contamination prevention mode including an external additive attaching step of attaching the external additive discharged on the surface of the image carrier to the entire outer peripheral surface of the charging member in a process An image forming apparatus that shifts to a power saving mode that restricts the image quality.   The controller rotates the image carrier in the same direction as when forming an image to execute the external additive discharging step, and then rotates the image carrier in the reverse direction to execute the external additive attaching step. The image forming apparatus according to claim 1. In-machine temperature and humidity detection sensor that detects the temperature and humidity inside the image forming device,
3. The image according to claim 1, wherein the control unit executes the bleed contamination prevention mode when the temperature and humidity detected by the in-machine temperature / humidity detection sensor are equal to or higher than a predetermined value. 4. Forming equipment.   When the temperature and humidity detected by the in-machine temperature / humidity detection sensor at the time of return from the power saving mode are equal to or higher than a predetermined value, the control unit transfers the image carrier 1 from the toner carrier to the surface of the image carrier. 4. The image forming apparatus according to claim 1, wherein a drum refresh mode is performed in which the toner exceeding the circumference is ejected and the ejected toner is collected by the cleaning device. 5.   When the temperature and humidity detected by the in-machine temperature / humidity detection sensor are less than predetermined values when returning from the power saving mode, the control unit applies the bias having the same polarity as the toner to the transfer member. 4. The image forming apparatus according to claim 1, wherein a printing operation is performed after a transfer member cleaning operation for rotating the transfer member.   The image forming apparatus according to claim 1, wherein at least one of the external additives has a volume resistance of 1 kΩ or less.   The image forming apparatus according to claim 1, wherein the bias applying device applies a developing bias including an AC bias to the toner carrier. An image carrier capable of rotating in a predetermined rotation direction during image formation and forming an electrostatic latent image;
A charging member that contacts the image carrier and charges the image carrier;
A developing device having a toner carrier disposed opposite to the surface of the image carrier, and supplying toner from the toner carrier to the surface of the image carrier;
A transfer member for transferring a toner image formed by the developing device to a recording medium;
A cleaning device for recovering toner remaining on the surface of the image carrier after the toner image is transferred to the recording medium by the transfer member;
A bias applying device that applies a predetermined bias to the charging member, the toner carrier, and the transfer member;
A control unit for controlling the operation of each unit including the image carrier, the charging member, the developing device, the cleaning device, and the bias applying device;
In an image forming apparatus comprising:
The control unit includes: a toner discharge step for discharging the toner from the toner carrier onto the surface of the image carrier when the printing operation has not been performed for a predetermined time; and the surface of the image carrier by the toner discharge step. A bleed contamination prevention mode including a toner adhesion step for adhering the toner discharged to the entire outer peripheral surface of the charging member, and then shifting to a power saving mode for restricting power supply to each part of the apparatus. An image forming apparatus.   The controller rotates the image carrier in the same direction as when forming an image and executes the toner discharge step, and then rotates the image carrier in the reverse direction to execute the toner attaching step. The image forming apparatus according to claim 8. In-machine temperature and humidity detection sensor that detects the temperature and humidity inside the image forming device,
10. The image according to claim 8, wherein the control unit executes the bleed contamination prevention mode when the temperature and humidity detected by the in-machine temperature / humidity detection sensor are equal to or higher than a predetermined value. Forming equipment.   The controller moves the toner adhering to the outer peripheral surface of the charging member to the surface of the image carrier when returning from the power saving mode, and performs a toner recovery mode in which the moved toner is recovered by the cleaning device. The image forming apparatus according to claim 8, wherein the image forming apparatus is executed.   When the temperature and humidity detected by the in-machine temperature / humidity detection sensor at the time of return from the power saving mode are equal to or higher than a predetermined value, the control unit performs from the toner carrier to the image carrier after execution of the toner recovery mode. 12. The image forming apparatus according to claim 11, wherein a drum refresh mode is executed in which a toner of one or more rotations of the image carrier is discharged to the surface, and the discharged toner is collected by the cleaning device.

Images