JP2012027282A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which can suppress image deletions due to discharge products and image defects such as a drum fusion, and disallow the fog density in a development area D to exceed a permissible value even if the fog density increases with the number of sheet outputs with use of toner 11 containing abrasive particles m.SOLUTION: As measures against fogging due to toner deterioration, an image forming device which controls switching of Vback during image formation according to the number of sheet outputs changes settings of developing bias during a non-image formation period in synchronization with timing of Vback switching, in order to increase supply of abrasive particles m onto a drum 1 during a non-image formation period.

Description

  The present invention relates to an image forming apparatus using an electrophotographic system and an electrostatic recording system in which an electrostatic latent image formed on an image carrier is developed with a developer.

  2. Description of the Related Art Conventionally, image forming apparatuses such as copying machines and laser beam printers generally employ an electrostatic transfer process. This apparatus supplies toner as a developer to an electrostatic latent image electrostatically formed on the surface of an image carrier and develops it as a toner image. The toner image is transferred onto a sheet (recording material) such as paper by a transfer member. Then, the unfixed toner image on the sheet is fixed on the sheet as a fixed image by the fixing unit. After the toner image is transferred to the sheet, the image carrier is repeatedly subjected to image formation after the residual adhering matter such as transfer residual toner is removed by the cleaning means.

  By the way, a discharge product generated due to the presence of a member to which a high voltage is applied such as a charging member or a transfer member in the image forming apparatus adheres to the surface of an image carrier (hereinafter referred to as a photoreceptor) as a foreign substance. Sometimes. In particular, it is known that, in a high-humidity environment, the adhered foreign matter is electrically reduced in resistance, preventing the formation of a clear electrostatic latent image and causing image flow or the like.

  As a method for preventing image defects due to discharge products such as image flow, Patent Document 1 discloses a method in which abrasive particles for polishing the surface of a photoreceptor are added to a developer in a developing unit. Has been proposed. In this method, abrasive particles are stored in a cleaning unit that is in contact with the photoconductor via the photoconductor from the developing unit, and the discharge product is removed by rubbing the surface of the photoconductor with the abrasive particles. Yes.

  The abrasive particles have a charge characteristic opposite to that of the toner. Then, in a white background portion (non-image portion) on the photosensitive member, a potential difference (hereinafter referred to as Vdev) between the dark portion potential (hereinafter referred to as Vd) of the photosensitive member and the voltage value (hereinafter referred to as Vdev) of the DC voltage component of the developing bias. , Expressed as Vback), the amount supplied from the developing means to the photoreceptor increases. For example, when the normal charging polarity of the toner is negative, the normal charging polarity of the abrasive particles is positive. Since the abrasive particles have a polarity opposite to that of the toner, the abrasive particles are collected by the cleaning means without being substantially transferred to the sheet at the transfer portion.

JP 2000-47545 A

  When a one-component developer is used, there is a problem that “toner deterioration” in which the toner is degenerated occurs and image defects such as low density and fog occur. This is because, as the number of print outputs increases, the toner is mechanically worn, the external additive is embedded in the toner, or the external addition state changes. Specifically, the developing means (developing apparatus) is used by pressing the developing blade against the developing sleeve with a high linear pressure in order to increase the charge amount of the toner. For this reason, the damage given to the toner due to pressure, heat, or the like is large at the contact portion between the developing sleeve and the developing blade.

  An image quality defect when the above “toner degradation” occurs will be described. FIG. 5A shows the relationship between Vback, which is the difference between Vd and Vdev, and the reflection density on the paper (so-called fog value) in a solid white image. As the total number of printed sheets (output number: cumulative number of printed sheets) increases, the toner deterioration is promoted, so that the fog value on the paper tends to increase even if Vback is the same value. That is, it is known that when toner deterioration is promoted, the proportion of toner charged to a reverse polarity increases, and as a result, fog tends to be detected.

  Further, when determining the design value of the developing bias, if the value of Vback is reduced, the amount of normal fog toner is greatly increased. In particular, it increases significantly at 100V or less. Therefore, when determining the development bias setting, Vback is set as large as possible in consideration of tolerances. Note that the intersection means the intersection of the developing bias and charging bias high voltage applying means. Therefore, as the number of output sheets increases as A → B → C in FIG. 5A, the Vback setting value (Vback setting range) is switched to a lower level such as RA → RB → RC. As a result, a control method is adopted in which the reflection density indicating fog is maintained within 3.0% as the average value on the paper, which is the upper limit of the allowable fog value.

  However, there are the following problems when the abrasive particles are supplied onto the photoreceptor by developing the white particles with the charging characteristics of the abrasive particles opposite to that of the toner as described above. Here, as an example, it is assumed that the normal charging polarity of the toner is negative and the normal charging polarity of the abrasive particles is positive.

  As shown in FIG. 5B, as shown in the conventional example, if Vback is reduced as the number of output sheets increases as a countermeasure against fogging due to toner deterioration, the amount of abrasive particles supplied onto the photoreceptor is reduced. Decreases and the abrasive particles present on the photoreceptor are insufficient. As a result, there is a problem that an image defect caused by a discharge product such as an image flow occurs. In addition, toner or an external additive is fixed on the photosensitive member and the exposure is blocked in the exposure portion, so that a phenomenon that white spots occur on the solid black image at the drum cycle may occur. Yes.

  The present invention relates to an improvement in an image forming apparatus using a developer containing (added) abrasive particles as described above. The purpose is that even if the fog value increases as the number of output sheets increases, the fog value in the development area does not exceed the allowable value, and image flow caused by discharge products, drum fusion, etc. An object of the present invention is to provide an image forming apparatus capable of reducing image defects.

  In order to achieve the above object, a typical configuration of an image forming apparatus according to the present invention includes an image carrier on which an electrostatic latent image is formed, and the image carrier is charged in contact with the image carrier. A charging unit; a developing unit that develops the electrostatic latent image with a developer; a charging bias output unit that outputs a charging bias to the charging unit; and a development bias output that outputs a developing bias to the developing unit. And the developer contains abrasive particles for polishing the surface of the image carrier, and the abrasive particles are charged to a polarity opposite to the normal charging polarity of the developer. In the image forming apparatus, in order to increase the amount of the abrasive particles supplied to the image carrier, the setting condition of the developing bias output means according to the information related to the consumption amount of the developer During non-image formation and image formation Hey characterized by different things.

  According to the present invention, even when the number of output sheets is increased and toner deterioration is promoted, the fog value of the developing area does not exceed the allowable value, and an amount of abrasive particles sufficient for polishing the surface of the image carrier is provided. Can be supplied. As a result, image defects due to discharge products such as image flow can be reduced throughout the life of the image forming apparatus.

(A) is a longitudinal sectional view showing a schematic configuration of the image forming apparatus in Embodiment 1, and (b) is a block circuit diagram of a control system. FIG. 6 is an operation process diagram of the image forming apparatus. (A) is a figure which shows the effect of anti-fogging through durability, (b) is a figure which shows an example of the abrasive particle flying amount when Vpp of developing bias is changed. (A) is a figure which shows an example of the abrasive particle flying amount when the frequency of developing bias is changed, (b) is a figure which shows an example of the abrasive particle flying amount when changing Vback of developing bias. (A) is a relationship diagram between fog and Vback that changes in accordance with toner deterioration, and (b) is a diagram showing a relationship between abrasive particle flying amount and image adverse effect. It is a figure which shows the example measured with the hardness meter. It is explanatory drawing of a charge amount measuring apparatus.

[Example 1]
<Overall Configuration and Operation of Image Forming Apparatus>
FIG. 1A is a longitudinal sectional view showing a schematic configuration of the image forming apparatus 100 in this embodiment, and FIG. 1B is a block circuit diagram of a control system. The apparatus 100 of this embodiment is a laser printer using a transfer type electrophotographic process. That is, the apparatus 100 can form and output an image on the sheet-shaped recording material 13 based on electrical image information input to the control circuit unit (controller) 101 from an external host device 200 such as a personal computer. The control circuit unit 101 comprehensively controls the operation of the apparatus 100 and executes the image forming operation of the apparatus 100 according to a predetermined image forming sequence in response to a print command from the host device 200 or the operation unit 102.

  An apparatus 100 as a printer engine includes a drum-type electrophotographic photosensitive drum (hereinafter referred to as a drum) 1 as a rotatable image carrier. When the driving force is transmitted from the driving source M, the drum 1 is rotated at a predetermined process speed in the clockwise direction of the arrow R1 about the shaft 1a. In this embodiment, the process speed is 150 mm / sec.

  The surface of the rotating drum 1 is uniformly charged to a predetermined polarity and potential by a charging roller (contact charging member) 2 as a charging device (charging means). The charging roller 2 is disposed in contact with the surface of the drum 1 and rotates following the rotation of the drum 1. A predetermined charging bias output from a charging bias application power source (bias output means) E2 is applied to the charging roller 2 via a sliding contact. Thereby, the surface of the drum 1 is uniformly contact-charged to a predetermined polarity and a predetermined potential. In this embodiment, the power source E2 has an AC power source AC and a DC power source DC, and the charging roller 2 is superimposed with an AC voltage (AC voltage component) and a DC voltage (DC voltage component: DC component potential Vpre). A charging bias, which is an oscillating voltage, was applied. Specifically, an AC voltage that is a sine wave is applied to a peak to peak of 1600 V, a frequency of 620 Hz, and a DC voltage of −500 V, so that the surface of the drum 1 is uniformly at a potential around −500 V (dark part potential Vd). Charged. In this embodiment, the drum 1 is charged by an AC charging method in which an AC voltage and a DC voltage are applied to the contact charging roller 2 in a superimposed manner, but may be a DC charging method by applying only a DC voltage. . Further, other charging methods such as corona charging may be used.

  On the surface of the drum 1 after charging, an electrostatic latent image is formed by exposure L of image information by the exposure device 16. The exposure apparatus 16 in this embodiment is a laser exposure apparatus. It has a laser scanner 16a, a polygon mirror (not shown), a reflection lens 16b, and the like. The apparatus 16 irradiates the surface of the drum 1 with a laser beam L modulated based on image information (main scanning exposure) to remove charges on the irradiated portion, thereby forming an electrostatic latent image. In the present embodiment, the potential (light portion potential Vl) of the charge removal portion by the laser light L is about −150V. Thus, the electrostatic latent image (an electrostatic contrast image of the dark portion potential Vd and the bright portion potential Vl) formed on the surface of the drum 1 is developed with the developer (toner) in the developing device 4 by the developer image (toner image). As developed.

  There are toners that are easily charged positively and those that are easily charged negatively (hereinafter referred to as “positive toner” and “negative toner”, respectively). On the developing sleeve and the developing roller, toner is applied, and a bias in which a DC component (developing DC bias) and an AC component (developing AC bias) are superimposed is applied. From the developing sleeve and the developing roller, toner is attached to the charge eliminating portion in the case of an image forming apparatus using negative toner, and to the non-charge removing portion in the case of an image forming apparatus using positive toner. In this manner, the electrostatic latent image on the photosensitive drum 1 is developed at the development position by the developing device 4, and a toner image is formed on the photosensitive drum 1. The developing device 4 will be described in detail later.

  The toner image formed on the surface of the drum 1 is transferred onto the sheet 13 by a transfer roller 5 as a transfer device. The sheets 13 are stacked and stored in the paper feed cassette 14. The sheet feeding roller 12 is driven at a predetermined control timing, whereby the sheet 13 in the cassette 14 is separated and fed one by one and reaches the registration roller 15 through the sheet path a. Then, the sheet 13 is introduced into a transfer nip portion N which is a pressure contact portion between the drum 1 and the roller 5 in synchronization with the toner image on the drum 1 by the roller 15 and is nipped and conveyed. While the sheet 13 is nipped and conveyed to the roller 5, a transfer bias, which is a DC voltage having a predetermined potential opposite to the charging polarity of the toner, is applied via a sliding contact from the transfer bias application power source E 5. Is done. As a result, the toner image on the drum 1 is electrostatically transferred onto the sheet 13 sequentially. The sheet 13 exiting the nip portion N is separated from the drum 1 and conveyed to the fixing device 8. Further, the drum 1 after separation of the sheet is cleaned by removing residuals such as toner and paper dust remaining on the surface by the cleaning device 6, and is repeatedly used for image formation. In this embodiment, the cleaning device 6 is of a blade type and includes a cleaning blade 7 as a cleaning member. The blade 7 is disposed such that the tip edge portion is in contact with the rotation direction R1 of the drum 1 in the counter direction. A contact portion between the blade 7 and the drum 1 is a cleaning portion b. The surface of the rotating drum 1 is rubbed at the blade edge portion in the cleaning portion b. As a result, adhesion residues such as transfer residual toner on the drum surface are scraped off and removed from the drum surface. The sheet 13 conveyed to the fixing device 8 is heated and pressed at a fixing nip portion that is a pressure contact portion between the fixing roller 8a and the pressure roller 8b, and the unfixed toner image is fixed as a fixed image. The sheet 13 after fixing the toner image is discharged as an image formed product (print, copy) by a discharge roller 17 to a discharge tray 18 outside the apparatus main body.

  In the apparatus 100 of the present embodiment, among the members that perform the image forming process, the drum 1, the charging roller 2, the developing device 4, and the cleaning device 6 are a process cartridge (hereinafter referred to as a cartridge) 20. In the cartridge 20, the above-described members 1, 2, 4, and 6 are integrally assembled to the cartridge frame 20a with a predetermined arrangement relationship, and in a predetermined manner with respect to a cartridge mounting mechanism (not shown) of the apparatus main body 100A. And is detachably mounted.

  Further, the cartridge 20 is provided with a storage means (memory) 21 as means for instructing information related to the consumption amount of the developer. As the memory 21, a normal semiconductor electronic memory can be used without any particular limitation. For example, any form such as a contact nonvolatile memory, a contactless nonvolatile memory, and a volatile memory having a power source can be used. In this embodiment, the non-contact nonvolatile memory 21 is mounted on the cartridge 3. The memory 21 has an antenna (not shown) which is information transmission means on the memory 21 side, and communicates with the main body side information transmission means 103 provided in the apparatus main body 100A wirelessly. In a state where the cartridge 20 is mounted on the apparatus main body 100A in a predetermined manner, the memory 21 is in a state facing the main body side information transmission means 103 in a predetermined manner. As a result, electrical information can be exchanged between the control circuit unit 101 and the memory 21 (reading and writing of information). In this embodiment, the control circuit unit 101 includes a control unit, a calculation unit, a storage unit (ROM), a clock function unit, and the like, and further has a function for reading and writing information to the memory 21 via the main body side information transmission means 103. I have. In the present embodiment, at least information related to the drive time of the drum 1 (the accumulated rotation time of the drum 1) is input from the control circuit unit 101 and stored (held) in the memory 21. The stored information is updated.

<Operation Process of Device 100>
FIG. 2 shows an operation process diagram of the apparatus 100.

  1) Pre-multi-rotation step: a start (start) operation period (warming period) of the image forming apparatus. The main motor of the image forming apparatus is activated by turning on the main power switch of the image forming apparatus, and a preparation operation for a required process device is executed.

  2) Standby: After the predetermined start operation period, the main motor is stopped and the image forming apparatus is kept in a standby (standby) state until a print job start signal is input.

  3) Pre-rotation step: This is a period in which the main motor is re-driven based on the input of the print job start signal and the pre-print job operation of the required process equipment is executed. More practically, a: the image forming apparatus receives a print job start signal, b: the image is developed by the formatter (the development time varies depending on the image data amount and the formatter processing speed), and c: the pre-rotation process starts. Order.

  If a print job start signal is input during the previous multi-rotation process of 1), the process proceeds to the pre-rotation process without standby of 2) after the completion of the pre-multi-rotation process.

  4) Print job execution: When a predetermined pre-rotation process is completed, the image forming process (mono print or multi print) is subsequently executed, and an image-formed recording material is output. In the case of multi-printing (continuous print job), the above-described image forming process is repeated, and a predetermined number of image-formed recording materials are sequentially output.

  5) Inter-sheet process: In the case of a continuous print job, this is an interval process between the trailing edge of one recording material P and the leading edge of the next recording material P, and is a non-paper-passing period in the transfer unit and the fixing device. .

  6) Post-rotation process: After the recording material with the image formed thereon is output in the case of a mono print job of only one sheet, or after the recording material with the final image formation is output in the case of multi-printing The motor is continuously driven for a predetermined time. This is a period during which the post-print job operation of the required process device is executed.

  7) Standby: After completion of the predetermined post-rotation process, the driving of the main motor is stopped, and the image forming apparatus is kept in a standby state until the next print job start signal is input.

  In the above, the execution time of the print job of 4) is the time of image formation, the time of 1) the pre-multi-rotation process, 3) the pre-rotation process, 5) the inter-sheet process, 6) the post-rotation process It is during non-image formation. The non-image forming time is at least one of the above-mentioned pre-multi-rotation process, the pre-rotation process, the inter-sheet process, the post-rotation process, and at least a predetermined time within the process. .

<Developing device>
The developing device 4 of this embodiment is a developing device using a magnetic one-component toner as a developer. The apparatus 4 is supported by a toner container 4a for storing toner 11, a stirring member 3 for transporting the toner 11 stored in the container 4a while loosening, a developing sleeve 10 for supporting and transporting the transported toner 11, and a sleeve 10. And a developing blade 9 for regulating the toner layer thickness.

  The stirring member 3 is rotationally driven by the drive source M at a rotational speed of 30 rpm in the clockwise direction of the arrow R3. The stirring member 3 has a mounting shaft 3a rotatably supported by a container 4a and a stirring sheet made of polyphenyl sulfide having a thickness of 50 μm. The stirring member 3 is driven by the same drive system as the sleeve 10.

  The sleeve 10 is a nonmagnetic sleeve formed of an aluminum or stainless steel pipe, and is supported by the container 4a so as to be rotatable in the counterclockwise direction of the arrow R2. In this embodiment, a hollow cylindrical tube made of aluminum and having a diameter of 16.0 mm is used for the sleeve 10. Rollers (not shown) are fixed to both ends of the sleeve 10 in the axial direction. The sleeve 10 has a predetermined gap (gap) α: 320 μm secured between the sleeve 10 and the drum surface by abutting the outer peripheral surface of the roller against the opposing drum 1. The surface of the sleeve 10 was coated with a phenol resin and a solvent in which carbon, a charge control agent, and fine particles for roughening the surface were dispersed so that an appropriate charge was applied when a desired amount of toner was carried. Further, the surface of the sleeve 10 has a roughness due to the paint coating, and in this embodiment, an arithmetic average roughness Ra: 1.2 μm was used. A magnet (not shown) is disposed inside the sleeve 10. The magnet is formed in a cylindrical shape, and a plurality of N poles and S poles are alternately formed in the circumferential direction. Unlike the sleeve 10 rotating in the direction of the arrow R <b> 2, the magnet is fixedly disposed inside the sleeve 10.

  The blade 9 includes a support member and an elastic blade, and is provided so that the elastic blade contacts the surface of the sleeve 10. The elastic blade is made of, for example, urethane rubber formed into a plate shape, and its base end is fixed to the support sheet metal, and its distal end is brought into contact with the surface of the sleeve 10 with a predetermined pressure to be elastically deformed. is doing. The elastic blade regulates the layer thickness of the toner 11 attracted to the surface of the sleeve 10 by the magnetic force of the magnet.

  The toner carried on the surface of the sleeve 10 is frictionally charged with the toner by being conveyed by the rotation of the sleeve 10 and the friction between the sleeve 10 and the elastic blade when the layer thickness is regulated by the blade 9. An appropriate charge is imparted by triboelectric charging. Then, the sleeve 10 is conveyed to the developing area D facing the surface of the drum 1 by the subsequent rotation of the sleeve 10. At this time, a predetermined developing bias output from a developing bias application power source (bias output means) E10 is applied to the sleeve 10 via a sliding contact. In this embodiment, the power supply E10 has an AC power supply unit AC and a DC power supply unit DC, and has a predetermined developing bias that is an oscillating voltage in which an AC voltage (AC voltage component) and a DC voltage (DC voltage component) are superimposed. Applied. As a result, the toner on the sleeve 10 flies to the drum 1 in the developing region D and electrostatically adheres to the electrostatic latent image. Thereby, the electrostatic latent image on the drum surface is visualized (developed) as a toner image.

<Toner and external additives>
The toner 11 used in this example is a negatively chargeable one-component magnetic toner produced by a suspension polymerization method, and has a volume average particle diameter of 6.5 μm. In addition, the toner 11 in the container 4a contains abrasive particles m having a property of being charged with a polarity opposite to the normal charging polarity of the toner 11. In this embodiment, since the normal charging polarity of the toner 11 is a negative charging polarity, the normal charging polarity of the abrasive particles m is positive. In particular, in this example, strontium titanate having a positively charged polarity was used as the abrasive particle m.

  Here, the strontium titanate used in this example will be described more specifically. That is, the strontium titanate used in this example has an average primary particle size in the range of 30 nm to 300 nm, has a cubic or cuboid particle shape, and has a perovskite crystal. It has a structure. When such strontium titanate is used, discharge products can be effectively removed even in an image forming apparatus that does not have a member that strongly rubs the drum 1 such as the cleaning blade 7. The amount of the abrasive particles m added to the toner 11 is preferably 0.1 wt% or more and 2.0 wt% or less with respect to the toner 11. In this embodiment, the amount of the abrasive particles m added is 0.3% by weight with respect to the toner 11.

  More specifically, the abrasive particles m are inorganic fine powder, and have a function of scraping off the low electrical resistance substance such as paper powder and the toner 11 adhering to the drum surface. It also has an effect of assisting charging of the developer. The inorganic fine powder has a weight average diameter of primary particles (particles in a state of being separated into individual unit particles) or secondary particles (in a state where primary particles are aggregated), 0.1 to 5.0 μm, preferably 0. .5 to 5.0 μm, more preferably 1.0 to 5.0 μm. When the weight average diameter of the inorganic fine powder is larger than the above range, it remains in the developing device 4 without being developed, which accumulates and causes image deterioration. When the weight average diameter is smaller than the above range, the polishing effect of the inorganic fine powder on the photosensitive drum 1 decreases, or “cleaning failure”, which is a phenomenon in which the cleaning blade 7 cannot scrape off the transfer residual toner, occurs. Cause image deterioration.

  Examples of other abrasive particles m that can be used in this example are given below. Examples of the inorganic fine powder include metal oxides such as magnesium, aluminum, titanium, iron, zirconium, and cerium, and composite metal oxides such as calcium titanate, magnesium titanate, strontium titanate, and barium titanate. Among these, carbides such as aluminum oxide, cerium oxide, titanium oxide, strontium titanate, magnesium titanate, silicon carbide, and titanium carbide, and nitrides such as silicon nitride and germanium nitride are often used.

<Method for measuring charge amount of toner and external additive>
Hereinafter, a method for measuring the charge amount of the toner and the external additive will be described. For the measurement, a charge amount measuring apparatus shown in FIG. 7 is used. The temperature is 23 ° C. and the relative humidity is 60%. As an iron powder carrier, an iron powder carrier having a distribution of 50% to 70% by weight in a particle size range of 106 μm to 150 μm and a distribution of 20% to less than 50% by weight in a particle size range of 75 μm to less than 106 μm (for example, DSP138 (manufactured by Dowa Iron Powder Co., Ltd.)) is used. A mixture obtained by adding 1.0 g of an external additive as an inorganic fine powder or 1.0 g of toner particles to 9.0 g of an iron powder carrier is placed in a polyethylene bottle having a capacity of 50 to 100 ml and shaken by hand 50 times.

  Next, 1.0 to 1.2 g of the mixture is put into a metal measuring container 72 having a 500-mesh screen 73 at the bottom, and a metal lid 74 is formed. The total weight of the measurement container 72 at this time is weighed and is defined as W1 (g). Next, in the suction machine 71 (at least the part in contact with the measurement container 72 is suctioned), the pressure of the vacuum gauge 75 is set to 2 kPa by suctioning from the suction port 77 and adjusting the air volume control valve 76.

  In this state, suction is performed for 1 minute to remove the developer by suction. The potential of the electrometer 79 at this time is set to V (volt). Here, 78 is a capacitor, and the capacity is C (μF). Moreover, the mass of the whole measuring machine after suction is weighed and is defined as W2 (g). The triboelectric charge quantity Q (μC / g) of the inorganic fine powder or toner particles is calculated as follows.

Q = CV / (W1-W2)
Further, it is more preferable to use a characteristic higher than the hardness of the surface layer of the photosensitive drum 1 as well as the charging polarity as characteristics required for the external additive.

  The reason is as follows. First, the photosensitive drum 1 used in the image forming apparatus of the present embodiment will be described. The ease of shaving of the photosensitive drum 1 correlates with the hardness of the drum, and can be expressed by universal hardness. The photosensitive drum 1 used in this embodiment has a universal hardness (Hu) of 235. Also, other photosensitive drums can be applied.

  Universal hardness (Hu) was measured using a hardness meter (H100VP-HCU) manufactured by Fischer Co., Ltd., Germany. Hereinafter, this is called a Fisher hardness meter. The measurement environment was all 23 ° C./55% RH. The Fischer hardness tester is not a method of obtaining hardness by measuring the residual indentation after unloading (after removing the load) with a microscope, as in the conventional micro Vickers method, by pushing the indenter into the sample surface. In this method, a continuous load is applied to the indenter and the indentation depth under the load is directly read to obtain the continuous hardness.

Universal hardness (Hu) is defined as follows. As the indenter, a diamond indenter (Vickers indenter) having a facing angle (136 °) at the tip of the quadrangular pyramid is used, and the indentation depth under a test load is measured. The universal hardness (Hu) is expressed as a ratio obtained by dividing the test load by the surface area of the indentation (calculated from the geometry of the indenter) generated by the test load, and is represented by the following formula (1). That is,
Hu = (test load (N)) / (surface area of the Vickers indenter under the test load (mm ² ))
= F / (26.43 × h2) (N / mm ² ) (1)
Here, Hu: universal hardness (N / mm ² ), F: test load (N), h: indentation depth under test load (mm).

  The measurement condition of the hardness tester is a square pyramid with a diamond indenter with a facing angle of 136 ° at the tip. . An example measured with a hardness meter is shown in FIG. The horizontal axis is the indentation depth 3 (μm), and the vertical axis is the load L (mN). Universal hardness is calculated | required by putting the load L and indentation depth which were obtained here in Formula (1).

  As described above, if the external additive has a charge polarity opposite to that of the toner as a characteristic of the external additive, the external additive is positively applied to the photosensitive drum 1 during non-image formation in which the toner does not adhere to the photosensitive drum 1. Let's fly to. This external additive can be supplied to the contact portion between the cleaning blade 7 and the photosensitive drum 1 and used as an abrasive on the surface of the photosensitive drum.

  Further, when the photosensitive drum 1 is charged by the charging member, an “image flow” that is a phenomenon in which a discharge product adheres to the surface of the photosensitive drum 1 and the latent image on the surface of the photosensitive drum 1 is disturbed easily occurs. Therefore, if the hardness of the external additive is equal to or greater than the hardness of the surface layer of the photosensitive drum 1 (the hardness of the abrasive particles is higher than the hardness of the surface layer of the image carrier), the discharge product adhered to the surface of the photosensitive drum 1 is removed. It can be scraped off with an external additive together with one surface layer. Therefore, it is more preferable that the external additive has a charge polarity opposite to the charge polarity of the toner and has a hardness equal to or higher than the hardness of the surface of the photosensitive drum (universal hardness).

  The abrasive particles m contained in the toner 11 are transported from the developing device 4 to the cleaning unit b via the drum 1 photoreceptor and stored. The abrasive particles m rub the surface of the drum 1 to remove discharge products. The abrasive particles m have a charging property opposite to that of the toner. Then, in the white background portion (non-image portion) on the drum 1, the developing device 4 supplies the drum 1 with the difference potential Vback between the dark portion potential Vd of the drum 1 and the voltage value Vdev of the DC voltage component of the developing bias. The amount increases. Since the abrasive particles m have a polarity opposite to that of the toner 11, the abrasive particles m are collected by the cleaning unit b without being substantially transferred to the sheet 13 in the transfer unit.

<Control of supply amount of abrasive particles to drum>
In this embodiment, the electrostatic latent image on the drum surface is developed by the developing device 4 by applying the following developing bias to the sleeve 10 from the power source E10 to realize jumping development.

Development bias: DC component (DC component potential Vdev)-350 V, AC component 1400 Vpp (Vpp: AC component potential amplitude), frequency 2000 Hz, 50% Duty, rectangular wave AC voltage superimposed In this embodiment, a horizontal line image with a printing rate of 2% is performed at 2 sheets / 18 seconds in a high temperature and high humidity environment with a temperature of 30 ° C. and a humidity of 90%, and intermittent durability is performed up to 6000 sheets, which is the nominal life. Then, the reflection density average value of the solid white image output every 500 sheets was measured. The result is shown in “Anti-fogging measure” in FIG. Further, as a countermeasure against fogging caused by toner deterioration, when Vback is switched as in the table shown in Table 1, as shown in “Vback change” in FIG. Compared with, fog is improved.

  When the “fogging prevention” control is performed, image flow, drum fusion, and the like occur in the second half of the durability after 4000 sheets. This is considered to be because, after 3000 sheets, Vback is reduced, the flying amount of the abrasive particles m is reduced, and the amount of abrasion by the abrasive particles m in the cleaning part b on the drum surface in the latter half of the durability is reduced. . Here, the flying amount of the abrasive particles m is the flying amount (mg / min) of the abrasive particles m from the sleeve 10 to the drum 1 in the development region D. In this embodiment, Vback is switched twice, but it is preferable to set the number of switching and the switching timing optimally according to the change of the fog value.

  Therefore, in this embodiment, the AC component of the developing bias at the time of non-image formation is set larger than that at the time of image formation so as not to reduce the flying amount of the abrasive particles m while performing the above-described “fogging prevention” control. The method of increasing the flying amount of the abrasive m during non-image formation was used.

  Here, the time of non-image formation is a timing other than the time of image formation in which an image formation operation for transferring and outputting to the sheet 13 is performed. Examples of the non-image formation include a pre-rotation that is a preparatory operation before the image forming operation and a post-rotation that is a rearranging operation after the image forming operation. Further, there is a time between sheets corresponding to the interval between the preceding sheet 13 and the next succeeding sheet 13 during a series of image forming operations (during a continuous image forming operation) for a plurality of sheets 13.

  As described above, by increasing the AC component Vpp of the developing bias during non-image formation, the flying amount of the abrasive particles m can be increased, and the abrasive particles m can be efficiently supplied to the cleaning unit b in a short time.

  In the present embodiment, the above-described development bias switching control is performed by the control circuit unit 101. The timing for changing Vback or Vpp is determined by the control circuit unit 101 using the non-volatile storage memory 21 of the cartridge 20 that stores information on the drum driving time. Here, as a result of examining how the flying amount of the abrasive particles m changes onto the drum by changing the peak-to-peak voltage Vpp of the AC component of the developing bias while the Vback potential is fixed at 150 V, This is shown in FIG. The abrasive particles m are supplied to the drum 1 by the action of setting the developing bias at the time of image formation to 1400 Vpp and the developing bias at the time of non-image formation to 3000 Vpp. In particular, when the peak-to-peak voltage Vpp of the AC component of the developing bias is increased to 3000 Vpp, it is possible to obtain a flying amount that is approximately twice that at 1400 Vpp.

  In this example, the flying amount of the abrasive particles m (the unit is mg / min) was measured as follows. The bias condition at the time of image formation or non-image formation is set, for example, the apparatus is continuously operated for 5 minutes, and the toner is collected by the cleaning device 6 during that time. Thereafter, the toner in the cleaning device 6 is collected, the abrasive particles m are separated from the toner, the weight mg is measured, and divided by 5 to calculate the recovered amount mg / min per minute.

  As described above, in this embodiment, the abrasive particles m are supplied to the cleaning unit b which is a contact portion between the blade 7 and the drum 1 via the drum 1 during image formation, and at the time of non-image formation, Vpp is increased. The amount of abrasive particles supplied to the drum 1 per unit time is increased. And the quantity of the abrasive particle m supplied to the cleaning part b via the drum 1 is increased.

  Depending on the configuration of the image forming apparatus 100, the amount of discharge products adhering to the drum 1 is different, and the desired supply amount of abrasive particles to the cleaning unit b is different. Therefore, although it can be changed according to the configuration of the image forming apparatus, according to the study of the present inventor, the flying amount of the abrasive particles m measured by the above measuring method is 1.5 mg at the time of non-image formation. / Min. To 6.0 mg / min. If the flying amount of the abrasive particles m is smaller than this range, it may take too much time to obtain a desired supply amount of the abrasive particles m, or a sufficient amount of the abrasive particles m may not be supplied. On the other hand, when the flying amount of the abrasive particles m is larger than this range, the abrasive particles are excessively removed from the developer of the developing device 4, and the developing ability of the developing device 4 may be greatly changed.

  As described above, by increasing the peak-to-peak voltage of the AC component of the developing bias, the flying amount of the abrasive particles m increases. From the viewpoint of leakage, the peak-to-peak interval may be 4.0 KV or less. preferable. That is, when supplying abrasive particles during non-image formation, the peak-to-peak voltage of the alternating current component of the developing bias is preferably not less than the peak-to-peak voltage of the alternating current component of the developing bias during image formation and not more than 4.0 KV. .

  As described above, in this embodiment, as a countermeasure against fogging, control is performed to increase the peak-to-peak voltage Vpp of the developing bias at the time of non-image formation compared to that at the time of image formation in accordance with the timing at which the Vback setting is switched. Specifically, as shown in Table 2, the developing bias AC component during non-image formation was changed to 2200 Vpp when outputting 3001 to 5000 sheets and 3000 Vpp when outputting 5001 to 6000 sheets. Thereby, it is possible to effectively increase the flying amount of the abrasive particles m to the drum 1 without lowering the fog value of the developing region D which is a cause of toner deterioration in the second half of the endurance.

  In addition, even when Vback is reduced as a countermeasure against fogging in the second half of the endurance, the amount of abrasive particles supplied to the contact portion b of the cleaning blade 7 and the drum 1 can always be maintained above a certain amount. Therefore, it is possible to reduce the occurrence of image defects such as image flow due to discharge products and drum fusion while suppressing fogging over long-term durability.

  The apparatus 100 of the first embodiment is summarized as follows. An image carrier 1 on which an electrostatic latent image is formed, a charging unit 2 that contacts the image carrier 1 and charges the image carrier 1, and a developing unit 4 that develops the electrostatic latent image with a developer 11. Have In addition, a charging bias output unit E2 that outputs a charging bias to the charging unit 2 and a developing bias output unit E10 that outputs a developing bias to the developing unit 4 are provided. The developer 11 contains abrasive particles m for polishing the surface of the image carrier 1, and the abrasive particles m have a property of being charged with a polarity opposite to the normal charge polarity of the developer 11. Then, in order to increase the amount of abrasive particles m supplied to the image carrier 1, the setting condition of the developing bias output means is set at the time of non-image formation and at the time of image formation according to information related to the consumption amount of the developer 11. Different.

  The developer 11 is a one-component magnetic toner. The development bias is an oscillating voltage in which a DC voltage component and an AC voltage component are superimposed. The setting condition of the developing bias output means is the AC component potential amplitude Vpp or the DC component potential Vdev. A memory 21 is mounted as means for instructing information related to the consumption amount of the developer, and the memory 21 holds information related to the driving time of the image carrier.

[Example 2]
In the second embodiment, as in the first embodiment, the frequency of the developing bias AC component at the time of non-image formation is changed as means for increasing the supply amount of the abrasive particles m onto the drum 1 at the timing of switching the Vback in the latter half of the durability. How to do it. That is, in this embodiment, the setting condition of the developing bias output means is the frequency.

  Specifically, control is performed to increase the frequency of the developing bias AC component during non-image formation. Thereby, it is possible to effectively increase the flying amount of the abrasive particles m to the drum 1 in a shorter time. FIG. 4A shows the result of investigating the relationship between the flying amount of the abrasive particles m and the frequency of the developing bias AC component by the same measurement method as in Example 1. If the frequency is increased, a tendency of increasing the amount of abrasive supplied onto the drum 1 can be confirmed.

  Therefore, in this embodiment, as shown in Table 3, control is performed to switch the frequency of the developing bias AC component to 2500 Hz at 3001 to 5000 sheets and 3000 Hz at 5001 to 6000 sheets with respect to 2000 Hz at the time of image formation. It was. As the effect, it was possible to reduce the occurrence of image problems such as image flow and drum fusion in the latter half of the durability.

[Example 3]
In the third embodiment, the development bias DC component (DC component potential Vdev) at the time of non-image formation is changed as means for increasing the supply amount of the abrasive particles m onto the drum 1 at the timing of switching Vback in the latter half of the durability. A method for changing Vback will be described.

  Specifically, it is a method of increasing the flying amount of abrasive particles by changing Vback by changing the developing bias DC component during non-image formation. In this embodiment, the charging bias is set to be the same as that at the time of image formation. In addition, it is possible to increase the amount of abrasive flying in the same way by changing the charging bias to change the charging potential on the photosensitive drum to change Vback. FIG. 4B shows the experimental results of examining the relationship between Vback and the flying amount of abrasive particles. It can be seen that the amount of abrasive particles flying to the photosensitive drum 1 can be increased by increasing Vback.

  Further, as a means for setting different Vback during image formation and during non-image formation, there is a means for changing Vback by changing the charging bias DC component during non-image formation. That is, in order to increase the amount of abrasive particles m supplied to the image carrier 1, the setting conditions of the charging bias output means E2 are set at the time of non-image formation and at the time of image formation according to information related to the consumption amount of the developer 11. It differs in. That is, regarding the charging bias output unit E2, the difference Vback between the voltage value Vd for uniformly charging the image carrier and the voltage value Vdev of the DC voltage component of the bias applied to the developing unit 4 is changed. Setting conditions differ between image formation and non-image formation. The setting condition of the charging bias output means E2 is the DC component potential Vpre. This also provides the same effect as when the setting conditions of the developing bias output means E10 are different between non-image formation and image formation.

  In order to increase the amount of abrasive particles m supplied to the image carrier 1, both the setting conditions of the developing bias output means E10 and the setting conditions of the charging bias output means E2 are made different during non-image formation and image formation. You can also.

  The apparatus 100 according to the embodiment is an electrophotographic apparatus using a photoconductor as an image carrier, but the apparatus 100 may be an electrostatic recording apparatus. This apparatus uses a non-photosensitive dielectric as an image carrier, uniformly charges the surface with a charging means, and selectively removes the charged surface with a discharging means such as a discharging needle array to obtain image information. A corresponding electrostatic latent image is formed. The electrostatic latent image is developed as a developer image (toner image) by developing means. Thereafter, similarly to the electrophotographic apparatus, an image formed product is output by a transfer process and a fixing process. The image carrier is cleaned by a cleaning unit and repeatedly used for image formation. The same effect can be obtained by applying the present invention to such an apparatus.

  DESCRIPTION OF SYMBOLS 1 ... Image carrier 2, ... Charging means 11, ... Developer 4, ... Developing means E2 .... Charging bias output means, E10 ... Developing bias output means, m ... Abrasive particles

Claims (9)

An image carrier on which an electrostatic latent image is formed; a charging unit that contacts the image carrier to charge the image carrier; a developing unit that develops the electrostatic latent image with a developer; A charging bias output unit that outputs a charging bias to the developing unit; and a developing bias output unit that outputs a developing bias to the developing unit. The developer polishes the surface of the image carrier. In the image forming apparatus, the abrasive particles have a property of being charged with a polarity opposite to the normal charging polarity of the developer.
In order to increase the amount of the abrasive particles supplied to the image carrier, the setting conditions of the developing bias output means differ between non-image formation and image formation according to information relating to the consumption amount of the developer. An image forming apparatus characterized by that. An image carrier on which an electrostatic latent image is formed; a charging unit that contacts the image carrier to charge the image carrier; a developing unit that develops the electrostatic latent image with a developer; A charging bias output unit that outputs a charging bias to the developing unit; and a developing bias output unit that outputs a developing bias to the developing unit. The developer polishes the surface of the image carrier. In the image forming apparatus, the abrasive particles have a property of being charged with a polarity opposite to the normal charging polarity of the developer.
In order to increase the amount of the abrasive particles supplied to the image carrier, the setting conditions of the charging bias output means differ between non-image formation and image formation according to information relating to the consumption amount of the developer. An image forming apparatus characterized by that.   The image forming apparatus according to claim 1, wherein the developer is a one-component magnetic toner.   The image forming apparatus according to claim 1, wherein the developing bias is an oscillating voltage in which a DC voltage component and an AC voltage component are superimposed.   2. The image forming apparatus according to claim 1, wherein the setting condition of the developing bias output means is an AC component potential amplitude Vpp, a DC component potential Vdev, or a frequency.   6. The image formation according to claim 1, wherein the charging bias is an oscillation voltage in which only a DC voltage component or a DC voltage component and an AC voltage component are superimposed. apparatus.   3. The image forming apparatus according to claim 2, wherein the setting condition of the charging bias output means is a DC component potential Vpre.   The storage means is mounted as means for instructing information relating to the consumption amount of the developer, and information relating to the drive time of the image carrier is held in the storage means. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein a hardness of the abrasive particles is higher than a hardness of a surface layer of the image carrier.