Image forming apparatus

Abstract

To reduce the occurrence of an image defect while preventing deterioration of an electrifying member.SOLUTION: During a non-image forming operation different from an image forming operation, a control unit 200 controls a common high voltage power supply so that a first voltage, which has a smaller absolute value than that of a discharge start voltage at which discharge is started between an electrifying roller 2K and a photoconductor drum 1K and has a normal polarity, is applied to the electrifying roller 2K, and controls the high voltage power supply so that a second voltage, which has a smaller absolute value than that of the first voltage and has a normal polarity, is applied to electrifying rollers 2Y, 2M, 2C or becomes 0 V.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an image forming apparatus, and more particularly to an electrophotographic apparatus such as a copying machine, a printer, a facsimile machine, and the like.

Background Art

[0002] Conventionally, there has been an electrophotographic image forming apparatus. A developing device that develops an image on a photosensitive drum includes a roller-shaped developer carrier that closes an opening of a developer container for storing a developer and is disposed with a part thereof exposed, and a developer regulating member that contacts the surface of the developer carrier and regulates the amount of the developer conveyed by the developer carrier to a certain amount. A flexible sealing sheet is used to close the opening of the developer container. When the developer adhering to the surface of the developer carrier passes through the developer regulating member as the developer carrier rotates, the excess amount is removed from the surface of the developer carrier and returned to the developer container. At the same time, a frictional charge is applied from the developer regulating member, and a thin layer is formed on the developer carrier. The developer having the frictional charge moves onto an electrostatic latent image previously formed on the surface of the photosensitive drum that rotates opposite to the developer carrier at a portion where the developer carrier is exposed from the developer container.

[0003] If the frictional charge of the thinned developer is insufficient, the frictional force with the sealing sheet may be stronger than the mirroring force (adhesion force) with the developer carrier, causing the developer to be scraped off the carrier and resulting in a phenomenon called "drip." When dripping occurs, the developer, which should be returned to the developing container, falls onto the photosensitive drum or recording material, which can cause image defects. Therefore, as a method to provide sufficient frictional charge to the developer, for example, Patent Document 1 describes a method of creating a potential difference between the developer regulating member and the developer carrier. When creating a potential difference between the developer regulating member and the developer carrier, if voltage is applied using independent high-voltage power supplies for each, the number of high-voltage power supplies increases, increasing the cost of the image forming apparatus. To solve this problem, for example, Patent Document 2 describes a technique for commonizing high-voltage power supplies in a high-voltage circuit that controls the potential difference between the developer regulating member and the developer carrier.

[0004] Furthermore, in order to further reduce costs, a configuration in which the power supply circuit that outputs the charging voltage applied to the charging member that charges the surface of the photosensitive drum and the voltage applied to the developer regulating member is common presents the following problems. When the developer carrier is rotating during non-image formation, if a charging voltage is not applied, a potential difference cannot be established between the developer regulating member and the developer carrier, resulting in dripping. On the other hand, if the same charging voltage as during image formation is continuously applied, the deterioration of the photosensitive drum, such as surface abrasion, is accelerated due to discharge to the surface of the photosensitive drum. As a technology to solve this problem, for example, a technology such as that disclosed in Patent Document 3 has been disclosed. Patent Document 3 uses a high-voltage configuration that generates the voltage applied to the developer carrier and the voltage applied to the developer regulating member by dividing the voltage from the output of the charging voltage with a Zener diode. With this configuration, by outputting a charging voltage above a certain level, it is possible to maintain the potential difference between the developer carrier and the developer regulating member at the potential difference necessary to suppress dripping. Furthermore, when the developer carrier is rotating during non-image formation, the potential difference between the developer carrier and the developer regulating member is maintained at a potential difference necessary to suppress dripping, and the voltage output is below the discharge threshold of the charged member. This suppresses both the deterioration of the photosensitive drum and the dripping. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 5007559 [Patent Document 2] Japanese Patent Publication No. 2014-032260 [Patent Document 3] Japanese Patent Publication No. 2020-101775 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, conventional technologies have the following problems: When a charging voltage is applied, the charged component deteriorates, and the higher the charging voltage, the more rapidly this deterioration progresses. For this reason, it is preferable to keep the voltage applied to the charged component as low as possible when not forming an image. However, there is an output value of the charging voltage required to maintain the potential difference between the developer carrier and the developer regulating member at the potential difference necessary to suppress dripping, and if the output value of the charging voltage is lowered below that voltage, dripping occurs. Therefore, in configurations that use the output of a charging voltage, there is a limit to how low the charging voltage can be when not forming an image, and consequently, there is a limit to how much deterioration of the charged component can be suppressed even when not forming an image. For this reason, there is a need to reduce the occurrence of image defects while suppressing the deterioration of the charged component.

[0007] This invention was made under these circumstances and aims to reduce the occurrence of image defects while suppressing the deterioration of the charged component. [Means for solving the problem]

[0008] To solve the above-mentioned problems, the present invention has the following configuration. (1) An image forming apparatus capable of performing an image forming operation, comprising: a first image forming unit having a rotatable first photoreceptor; a first charging means for charging the surface of the first photoreceptor to a predetermined potential; a first developer carrier for applying a first color developer charged with normal polarity to an electrostatic latent image formed on the first photoreceptor to form a developer image; and a first regulating member that contacts the first developer carrier and applies a predetermined charge to the first color developer and regulates the amount of the first color developer; a first image forming unit having a rotatable second photoreceptor; a second charging means for charging the surface of the second photoreceptor to a predetermined potential; and an electrostatic latent image formed on the second photoreceptor The aforementionedThe second image forming unit includes a second developer carrier that applies a second color developer charged to a normal polarity to form a developer image, and a second regulating member that contacts the second developer carrier and applies a predetermined charge to the second color developer and regulates the amount of the second color developer; a first power supply unit that applies voltage to the first charging means, the first developer carrier, the second developer carrier, the first regulating member and the second regulating member; a second power supply unit that applies voltage to the second charging means; and control means that control the first image forming unit, the second image forming unit, the first power supply unit and the second power supply unit. The first power supply unit is configured such that, during the image forming operation, it applies a fifth voltage of normal polarity to the first charging means, thereby applying a third voltage of normal polarity to the first regulating member and the second regulating member, and applies a fourth voltage of normal polarity to the first developer carrier and the second developer carrier, thereby forming a first potential difference between the first developer carrier and the first regulating member, and a second potential difference between the second developer carrier and the second regulating member. The control means, during non-image forming operations that are different from the image forming operations, i) The absolute value is smaller than the discharge initiation voltage at which discharge begins between the first charging means and the first photoreceptor. Furthermore, the above voltage has an absolute value smaller than the fifth voltage. A first voltage with normal polarity is applied to the first charging means. (ii) A sixth voltage, which is less than or equal to the absolute value of the third voltage, is applied to the first regulating member and the second regulating member, and a seventh voltage, which is less than or equal to the absolute value of the fourth voltage, is applied to the first developer carrier and the second developer carrier, thereby maintaining the first potential difference and the second potential difference from the image forming operation. Control the first power supply unit in such a manner. iii) The absolute value is smaller than the first voltage. i A second voltage of normal polarity is applied to the second charging means, or The voltage applied to the second charging means is The second power supply unit is controlled to become 0V. 、 An image forming apparatus characterized by the following features. (2) An image forming apparatus capable of performing an image forming operation, comprising: a first image forming unit having a rotatable first photoreceptor; a first charging means for charging the surface of the first photoreceptor to a predetermined potential; a first developer carrier for applying a first color developer charged with normal polarity to the electrostatic latent image formed on the first photoreceptor to form a developer image; a first regulating member that contacts the first developer carrier and applies a predetermined charge to the first color developer and regulates the amount of the first color developer; a first image forming unit having a rotatable second photoreceptor; a second charging means for charging the surface of the second photoreceptor to a predetermined potential; and a static latent image formed on the second photoreceptor. The second image forming unit includes a second developer carrier that applies a second color developer charged with the normal polarity to an electrolatent image to form a developer image, and a second regulating member that contacts the second developer carrier and applies a predetermined charge to the second color developer and regulates the amount of the second color developer; a first power supply unit that applies voltage to the first charging means, the first developer carrier, the second developer carrier, the first regulating member and the second regulating member; a second power supply unit that applies voltage to the second charging means; and control means that controls the first image forming unit, the second image forming unit, the first power supply unit and the second power supply unit, wherein the control means ,before Without using the second image forming unit Using the first image forming unit To recording material The aforementioned A first image forming operation performs an image forming operation, and the first image forming unit and the second image forming unit are used to form an image on a recording material. The aforementioned The second image formation operation, which performs the image formation operation, is controlled to be executable. The aforementioned first power supply unit is, The aforementioned 2 When performing an image forming operation, The first charging means is configured to apply the fifth voltage of the normal polarity, and the control means, when performing the first image forming operation, The absolute value is smaller than the discharge initiation voltage at which discharge begins between the second charging means and the second photoreceptor, and the first of the normal polarity 8 A voltage is applied to the second charging means, or The voltage applied to the second charging means is The second power supply unit is controlled to become 0V. 、 An image forming apparatus characterized by the following features. [Effects of the Invention]

[0009] According to the present invention, it is possible to reduce the occurrence of image defects while suppressing the deterioration of the charged component.

Brief Description of the Drawings

[0010] [Figure 1] Schematic cross-sectional view showing the overall configuration of the image forming apparatuses of Examples 1 and 2 [Figure 2] Diagram showing the configuration of the high voltage power supplies of Examples 1 and 2 [Figure 3] Graph showing the relationship between the charging voltage and the developing blade voltage, and the developing roller voltage of Examples 1 and 2, and graph showing the relationship between the charging voltage and the surface potential [Figure 4] Graph showing the relationship between the laser light quantity and the drum potential of Examples 1 and 2, and diagram showing the relationship between the potentials during image formation [Figure 5] Diagram showing the configuration of a conventional high voltage power supply for a comparative example with Example 1

Best Mode for Carrying Out the Invention

Examples

[0012] Example 1 relates to an image forming apparatus that forms an image on a recording material (recording medium) using an electrophotographic method. Examples of the image forming apparatus include, for example, a copying machine, a printer (laser beam printer, LED printer, etc.), a facsimile apparatus, a word processor, and a multifunction machine (multifunction printer) thereof. Example 1 relates to a full-color image forming apparatus capable of forming images of multiple colors.

[0013] [Image forming apparatus] As an example of an image forming apparatus to which Example 1 can be applied, the overall configuration and operation of an electrophotographic image forming apparatus will be described. Figure 1 is a cross-sectional view showing the schematic configuration of the image forming apparatus 100 of Example 1. The image forming apparatus 100 is a full-color laser beam printer employing an in-line method and an intermediate transfer method, and can form a full-color image on a recording material (e.g., recording paper, plastic sheet, cloth, etc.) according to image information. The image information is input to the image forming apparatus 100 from an image reading device connected to the image forming apparatus 100 or from a host device such as a personal computer that is communicatively connected to the image forming apparatus 100.

[0014] The image forming apparatus 100 has a plurality of image forming sections, the first image forming section SY, the second image forming section SM, the third image forming section SC, and the fourth image forming section SK, each for forming images of yellow (Y), magenta (M), cyan (C), and black (K). In Embodiment 1, the first image forming section SY to the fourth image forming section SK are arranged in a line at regular intervals in a direction intersecting the vertical direction (up and down direction). In Embodiment 1, the configuration and operation of the first image forming section SY to the fourth image forming section SK are substantially the same except for the difference in the color of the image formed. Therefore, in the following description, unless otherwise specified, the subscripts Y, M, C, and K given to the symbols to indicate that an element is provided for one of the colors will be omitted, and a general description will be given. In Embodiment 1, the image forming apparatus 100 has four drum-type electrophotographic photoreceptors 1 arranged in parallel in a direction intersecting the vertical direction. The photoreceptor 1, which is the image carrier, will be referred to as the photosensitive drum 1 below.

[0015] The photosensitive drum 1 has a photoreceptor layer on an aluminum drum base (not shown) in which a functional film consisting of an undercoat layer, a carrier generation layer, and a carrier transfer layer is coated in that order. The drum is rotated in the direction of arrow a (clockwise direction) shown in Figure 1 at a predetermined peripheral speed (movement speed of the surface of the photosensitive drum 1) according to the image formation operation, etc., by the driving force of a drive motor (not shown), which is the driving means. In Example 1, the photosensitive drum 1 is a negatively charged organic photosensitive drum with a diameter of 20 mm and is rotated at a peripheral speed of 140 mm / sec.

[0016] A charging roller 2, an exposure device 3, and a developing device 4 are arranged around the photosensitive drum 1. The charging roller 2 is a contact charging means that uniformly charges the surface of the photosensitive drum 1 to a predetermined polarity potential. The charging roller 2 is in contact with the surface of the photosensitive drum 1 with a predetermined pressure and rotates driven by the friction with the surface of the photosensitive drum 1. In addition, a predetermined DC voltage is applied to the rotation axis of the charging roller 2 from a high-voltage power supply, which will be described later, according to the image forming operation. In Example 1, the charging roller 2 is mounted on a metal shaft with a diameter of 5.5 mm, has a thickness of 1.5 mm, and a volume resistivity of 1 × 10⁻¹⁶. 4 A base layer made of a conductive elastic material with a thickness of approximately Ωcm, and a volume resistivity of 1 × 10⁻¹⁵ μm. 10 A surface layer of approximately Ωcm is used. Then, in accordance with the image formation operation, a DC voltage is applied to the rotation axis of the charging roller 2 to charge the surface of the photosensitive drum 1. The exposure apparatus 3 is equipped with a laser driver, laser diode, rotating polyhedron mirror, optical lens system, etc., and is an exposure means that irradiates laser light based on image information input from a host computer (not shown) to form an electrostatic latent image on the uniformly charged surface of the photosensitive drum 1.

[0017] The developing device 4 comprises a non-magnetic one-component toner (hereinafter referred to as toner) as a developer, a developing roller 12 as a toner carrier, and a developing blade 13 as a toner regulating member, and is a developing means that develops an electrostatic latent image as a toner image (performs a developing operation on the photosensitive drum 1). The developing roller 12 contacts the photosensitive drum 1 with a predetermined contact width according to the image forming operation. The developing roller 12 is rotated at a peripheral speed faster than the peripheral speed of the photosensitive drum 1, so that the surface movement direction of the developing roller 12 is in the same direction as the surface movement direction of the photosensitive drum 1 at the part facing the photosensitive drum 1 (contact part). The driving means for driving the developing roller 12 may be the driving means for driving the photosensitive drum 1, or it may be provided independently. The developing blade 13 is positioned in contact with the surface of the developing roller 12 and regulates the amount of toner on the developing roller 12 and also applies an electric charge to the toner.

[0018] Here, the developing roller 12 is provided so as to be able to contact and separate from the photosensitive drum 1. That is, the developing device 4 and the main body of the image forming device 100 are equipped with a mechanism (not shown, hereinafter referred to as the contact / separation mechanism) that controls the contact and separation state between the developing roller 12 and the photosensitive drum 1. The developing roller 12 and the photosensitive drum 1 come into contact according to the image forming operation, etc., and separate when the operation stops. The contact / separation mechanism can individually control the timing of the contact and separation operation between the developing roller 12K and the photosensitive drum 1K, and the timing of the contact and separation between the developing rollers 12Y, 12M, 12C and the photosensitive drums 1Y, 1M, 1C.

[0019] In other words, the image forming apparatus 100 includes a first contact / separation mechanism that brings the developing roller 12K into contact with or separates the photosensitive drum 1K, and a second contact / separation mechanism that brings the developing rollers 12Y, 12M, 12C into contact with or separates the photosensitive drums 1Y, 1M, 1C. The control unit 200, which will be described later, controls the apparatus as follows when using the first image forming unit SY to the fourth image forming unit SK, i.e., when performing a full-color image forming operation. Specifically, the control unit 200 brings the developing roller 12K into contact with the photosensitive drum 1K using the first contact / separation mechanism, and brings the developing rollers 12Y, 12M, 12C into contact with the photosensitive drums 1Y, 1M, 1C using the second contact / separation mechanism. Furthermore, the control unit 200 controls the apparatus as follows when using the fourth image forming unit SK, i.e., when performing a monochrome image forming operation. Specifically, the control unit 200 brings the developing roller 12K into contact with the photosensitive drum 1K using the first contact-separation mechanism, and separates the developing rollers 12Y, 12M, and 12C from the photosensitive drums 1Y, 1M, and 1C using the second contact-separation mechanism. Furthermore, after the image forming operation is completed, i.e., during the post-rotation operation described later, the control unit 200 controls as follows: Specifically, the control unit 200 separates the developing roller 12K from the photosensitive drum 1K using the first contact-separation mechanism, and separates the developing rollers 12Y, 12M, and 12C from the photosensitive drums 1Y, 1M, and 1C using the second contact-separation mechanism.

[0020] Furthermore, a predetermined DC voltage is applied to the core metal of the developing roller 12 from a high-voltage power supply described later, in accordance with the image formation operation. In Example 1, the developing roller 12 is driven to rotate at a peripheral speed of 180 mm / sec in accordance with the image formation operation, and a DC voltage of -350V is applied to the core metal of the developing roller 12. Similarly, a predetermined DC voltage is applied to the developing blade 13 from a high-voltage power supply described later, in accordance with the image formation operation. The voltage applied to the developing blade 13 has the same polarity as the voltage applied to the developing roller 12, but its absolute value is set to be larger, and in Example 1, a DC voltage of -450V is applied. By creating a potential difference between the developing roller 12 and the developing blade 13 in this way, it is possible to suppress the transfer of charge to the toner and the adhesion of toner to the developing blade 13.

[0021] The toner in Example 1 is a negatively charged, non-magnetic toner manufactured by suspension polymerization, with a volume-average particle size of approximately 6.5 μm. In addition, to modify the surface properties, silicon oxide particles with a volume-average particle size of approximately 20 nm are uniformly attached to the toner surface at a concentration of approximately 1.5% of the toner weight. However, although Example 1 uses toner manufactured by suspension polymerization, it is not limited to this method, and toners manufactured using other polymerization methods such as pulverization or emulsion polymerization may also be used. Furthermore, in Example 1, the developing units 4Y, 4M, 4C, and 4K contain yellow toner, magenta toner, cyan toner, and black toner, respectively.

[0022] In other words, in Example 1, the developing device 4 performs so-called inversion development, which involves depositing toner charged with the same polarity (normal polarity) (negative polarity in Example 1) as the charge of the photosensitive drum 1 onto the portion of the surface of the photosensitive drum 1 where the charge has been attenuated by exposure (exposed area). As a result, the electrostatic latent image on the photosensitive drum 1 (on the photoreceptor) is developed, and a toner image is formed.

[0023] The toner image on the photosensitive drum 1 is sequentially transferred to the intermediate transfer belt 5, which is an intermediate transfer body positioned opposite the photosensitive drum 1, with the toner images of each color superimposed, resulting in a full-color toner image (primary transfer). In the rotational direction of the photosensitive drum 1, the charging position by the charging roller 2, the exposure position by the exposure device 3, the development position by the developing device 4, and the transfer position of the toner image to the intermediate transfer belt 5 are arranged in this order.

[0024] The cleaning blade 14 is positioned in contact with the photosensitive drum 1 and removes the toner remaining on the photosensitive drum 1 after the toner image has been transferred to the intermediate transfer belt 5 (hereinafter referred to as residual toner). The residual toner removed from the photosensitive drum 1 by the cleaning blade 14 is stored in the storage container 15.

[0025] In Example 1, the photosensitive drum 1, the charging roller 2, the developing device 4, the cleaning blade 14, and the storage container 15 are integrated into a single cartridge to form a process cartridge 7. The process cartridge 7 is detachable from the image forming apparatus 100 via mounting means (not shown), such as mounting guides and positioning members, provided on the main body of the image forming apparatus 100. In Example 1, all process cartridges 7 for each color have the same shape, and each process cartridge 7 contains toner for yellow (Y), magenta (M), cyan (C), and black (K), respectively. However, while Example 1 describes the process cartridge 7, it is not limited to this. For example, the developing device 4 may be fixed to the main body of the image forming apparatus 100, and only toner may be supplied to the developing device 4, or the developing device 4 may be a separate cartridge that is detachable from the main body of the image forming apparatus 100.

[0026] Here, the photosensitive drum 1K corresponds to the first photoreceptor. The charging roller 2K corresponds to the first charging means that charges the surface of the photosensitive drum 1K to a predetermined potential. The developing roller 12K corresponds to the first developer carrier that applies black toner, which is the first color developer, to the electrostatic latent image formed on the photosensitive drum 1K to form a developer image. The developing blade 13K corresponds to the first regulating member that contacts the developing roller 12K and applies a predetermined charge to the black toner while also regulating the amount of black toner. The photosensitive drums 1Y, 1M, and 1C correspond to the second photoreceptor. The charging rollers 2Y, 2M, and 2C correspond to the second charging means that charges the surface of the photosensitive drums 1Y, 1M, and 1C to a predetermined potential. The developing rollers 12Y, 12M, and 12C correspond to the second developer carrier, which applies yellow toner, magenta toner, and cyan toner, which are the second color developers, to the electrostatic latent image formed on the photosensitive drums 1Y, 1M, and 1C, thereby forming a developer image. The developing blades 13Y, 13M, and 13C are in contact with the developing rollers 12Y, 12M, and 12C. The developing blades 13Y, 13M, and 13C correspond to the second regulating members, which apply a predetermined charge to the yellow toner, magenta toner, and cyan toner, and regulate the amount of yellow toner, magenta toner, and cyan toner. Furthermore, the fourth image forming unit SK corresponds to the first image forming unit, and the first image forming unit SY, the second image forming unit SM, and the third image forming unit SC correspond to the second image forming unit. Hereafter, black may be referred to as K, yellow as Y, magenta as M, and cyan as C.

[0027] The intermediate transfer belt 5 is formed of an endless, rotatable belt and is stretched between the drive roller 51, the secondary transfer opposing roller 52, and the tension roller 53 (hereinafter, the three together may be referred to as the tension rollers). Here, the drive roller 51, the secondary transfer opposing roller 52, and the tension roller 53 correspond to tension members. The intermediate transfer belt 5 contacts all of the photosensitive drums 1 on its outer surface and moves in a circulating motion (rotation or rotation) at a predetermined speed in the direction of arrow b in the figure (counterclockwise direction) by the drive of the drive roller 51 to which a drive motor (not shown) is connected. In Embodiment 1, the intermediate transfer belt 5 moves in a circulating motion (rotates) at 140 mm / sec, the same as the peripheral speed of the photosensitive drum 1.

[0028] On the inner circumferential surface of the intermediate transfer belt 5, four primary transfer rollers 8 are arranged in parallel, facing each photosensitive drum 1, as primary transfer means. The primary transfer rollers 8 press the intermediate transfer belt 5 toward the photosensitive drum 1, forming a nip portion (primary transfer nip portion) in the primary transfer portion where the intermediate transfer belt 5 and the photosensitive drum 1 come into contact. In addition, on the outer circumferential surface of the intermediate transfer belt 5, a secondary transfer roller 9, which constitutes a secondary transfer means, is positioned in contact with the intermediate transfer belt 5 at a location facing the secondary transfer opposing roller 52.

[0029] The secondary transfer roller 9 presses against the secondary transfer opposing roller 52 via the intermediate transfer belt 5, forming a nip portion (secondary transfer nip portion) in the secondary transfer section N where the intermediate transfer belt 5 and the secondary transfer roller 9 come into contact. The recording material P, which has been transported to the secondary transfer section N, has a full-color toner image transferred onto it by the secondary transfer roller 9 in the secondary transfer section N (secondary transfer). A predetermined DC voltage is then applied to the secondary transfer roller 9 from the secondary transfer voltage power supply 6. Furthermore, an intermediate transfer belt cleaning device 11, which serves as a recovery means (intermediate transfer body cleaning means), is provided on the outer circumferential surface side of the intermediate transfer belt 5 near the secondary transfer opposing roller 52. Here, the secondary transfer voltage power supply 6 applies voltage to the secondary transfer roller 9 and also applies voltage to the intermediate transfer belt 5 which is in contact with the secondary transfer roller 9. The secondary transfer roller 9 and the secondary transfer voltage power supply 6 constitute the secondary transfer means.

[0030] The intermediate transfer belt cleaning device 11 has a cleaning blade that contacts the outer surface of the intermediate transfer belt 5 to scrape off toner on the intermediate transfer belt 5 and collect it inside the intermediate transfer belt cleaning device 11. The intermediate transfer belt cleaning device 11 is positioned downstream of the secondary transfer section N in the rotational direction of the intermediate transfer belt 5 to collect toner adhering to the intermediate transfer belt 5 (on the intermediate transfer body). Furthermore, a fixing device 10, which has a fixing roller and a pressure roller, is provided downstream of the secondary transfer section N in the transport direction of the recording material P. The fixing device 10 fixes the unfixed toner image transferred to the recording material P.

[0031] The image forming apparatus 100 includes a control unit 200 that controls the entire image forming apparatus 100, including the image forming operation, the transport operation of the recording material P, and each power supply (common high-voltage power supply 74, high-voltage power supply 75, which will be described later), by controlling each of the above-mentioned parts. The control unit 200 also controls the rotational drive of the photosensitive drum 1 and the developing roller 12, and the contact and separation between the photosensitive drum 1 and the developing roller 12. The control unit 200 has, for example, a CPU 200a, which executes a program stored in ROM 200b while controlling the timing with a timer 200d and using RAM 200c as a temporary work area.

[0032] [power supply] The image forming apparatus 100 has a common high-voltage power supply 74 and a high-voltage power supply 75 as shown in Figure 2. The common high-voltage power supply 74 functions as a first power supply unit that applies voltage to the charging roller 2K, the developing rollers 12Y, 12M, 12C, 12K, and the developing blades 13Y, 13M, 13C, 13K. The high-voltage power supply 75 functions as a second power supply unit that applies voltage to the charging rollers 2Y, 2M, 2C. The common high-voltage power supply 74 has a charging voltage 74a connected to a resistor R, a Zener diode ZD1, and a Zener diode ZD2 as voltage maintenance elements. The charging voltage 74a is connected to the charging roller 2K, the developing blade voltage 74b is connected to the developing blades 13Y, 13M, 13C, 13K, and the developing voltage 74c is connected to the developing rollers 12Y, 12M, 12C, 12K. In other words, the developing blade voltage 74b is the voltage at the connection point between resistor R and Zener diode ZD1, and the developing voltage 74c is the voltage at the connection point between Zener diode ZD1 and Zener diode ZD2. The high-voltage power supply 75 is connected to the charging rollers 2Y, 2M, and 2C.

[0033] Thus, in Embodiment 1, the common high-voltage power supply 74 includes a power supply 74d, a resistor R, a Zener diode ZD1, and a Zener diode ZD2. The power supply 74d is a first output means that outputs a voltage. The resistor R is a resistor with one end connected to the power supply 74d. The Zener diode ZD1 is a first constant voltage element with one end (anode terminal) connected to the other end of the resistor R. The Zener diode ZD2 is a second constant voltage element with one end (anode terminal) connected to the other end (cathode terminal) of the Zener diode ZD1 and the other end (cathode terminal) grounded. The power supply 74d applies a voltage to the charging roller 2K. The connection point between the resistor R and the Zener diode ZD1 is connected to the developing blades 13Y, 13M, 13C, and 13K. The connection point between the Zener diode ZD1 and the Zener diode ZD2 is connected to the developing rollers 12Y, 12M, 12C, and 12K. Furthermore, the high-voltage power supply 75 has a second output means, power supply 75a, which applies voltage to the charging rollers 2Y, 2M, and 2C.

[0034] [Common high-voltage power supply] The voltage output characteristics of the common high-voltage power supply 74 will be explained using Figure 3(a). Figure 3(a) shows the changes in the developing blade voltage and developing voltage when the charging voltage is changed in the common high-voltage power supply 74. The horizontal axis shows the charging voltage (-V), and the vertical axis shows the voltage (-V). Black circles indicate the developing blade voltage, white circles indicate the developing roller voltage, and white squares indicate the potential difference between the developing blade voltage and the developing roller voltage (developing blade voltage - developing roller voltage). In the common high-voltage power supply 74 of Example 1, Zener diodes ZD1 and ZD2 can clamp a predetermined voltage when the charging voltage is higher than -725V. As a result, when the charging voltage is higher than -725V, the developing blade voltage can be maintained at -450V and the developing voltage at -350V. Also, when the charging voltage is higher than -400V, the potential difference between the developing blade voltage and the developing roller voltage can be maintained at 100V. This is because, due to the presence of high-resistance toner between the developing blade 13 and the developing roller 12, almost no current flows, allowing the Zener diode ZD2 to maintain a predetermined Zener voltage.

[0035] During image formation, a charging voltage of -1100V is applied, resulting in a developer blade voltage of -450V and a developer voltage of -350V. At this time, the developer blade voltage is 100V higher than the developer roller voltage, which is a predetermined potential difference, thus enabling charge transfer from the developer blade 13 to the toner.

[0036] [Operation during full-color image formation] The following describes the operation during full-color image formation. Upon receiving an image formation command from the host computer, the drive motor is driven and the common high-voltage power supply 74 and high-voltage power supply 75 are output approximately simultaneously. Here, "approximately simultaneously" includes cases where it is exactly simultaneous, and also includes time intervals that are considered substantially the same as simultaneous. As a result, the photosensitive drum 1, developing roller 12, and developing blade 13 are subjected to voltage, and the photosensitive drum 1 and developing roller 12 are rotated. At this point, a charging voltage of -1100V is applied to the charging roller 2, causing the surface of the photosensitive drum 1 to be charged to a voltage of -600V. The potential of the surface of the photosensitive drum 1 is also called the surface potential or drum potential.

[0037] Figure 3(b) shows the relationship between the charging voltage and surface potential of the photosensitive drum 1 in Example 1, with the charging voltage (-V) on the horizontal axis and the surface potential (-V) on the vertical axis. When the absolute value of the charging voltage is increased, the charging voltage at which discharge begins between the charging roller 2 and the surface of the photosensitive drum 1 (hereinafter referred to as the discharge initiation voltage) is -500V. At charging voltages with a lower absolute value than this, the surface potential of the photosensitive drum 1 is 0V. Also, since a charging voltage of -1100V is applied, the surface potential is -600V, -350V is applied to the developing roller 12, and -450V is applied to the developing blade 13 (see also Figure 3(a)). Subsequently, the photosensitive drum 1 and the developing roller 12 come into contact with each other by the contact-separation mechanism.

[0038] Next, laser light based on image information is sequentially irradiated from the exposure apparatus 3 onto the surfaces of the photosensitive drums 1Y, 1M, 1C, and 1K, forming an electrostatic latent image. In the formation of the electrostatic latent image, the laser light is directed at the image forming area (printing area, exposure area) of the image region at a rate of 0.3 μJ / cm². 2 The light intensity is irradiated at 0.05 μJ / cm², and non-image areas (non-printed areas, non-exposed areas) receive 0.05 μJ / cm². 2 The laser is irradiated with a light intensity of [μJ / cm²]. Figure 4(a) shows the relationship between the laser light intensity and the drum potential in the photosensitive drum 1, with the horizontal axis representing the laser light intensity [μJ / cm²]. 2 The diagram shows the voltage and the drum potential (-V) on the vertical axis. From Figure 4(a), the potential of the printed area (light area potential) is -150V, and the potential of the non-printed area (dark area potential) is -500V.

[0039] The purpose of exposure to non-printed areas (background exposure) is to arbitrarily control the difference between the development voltage and the dark area potential (back contrast) even when the charging voltage and development voltage are common for multiple colors. In Example 1, the charging voltage and development voltage are common for YMC, but the back contrast of YMC can be arbitrarily set by performing background exposure. The back contrast has an appropriate value depending on the characteristics of the toner, and if it is too large or too small, it will result in image defects such as background smudges. In Example 1, the back contrast of all colors is common at -150V, but if you want to change the back contrast for each color, you can change the amount of light to the non-printed areas for each color.

[0040] As described above, the exposure apparatus 3 is an exposure means that irradiates photosensitive drums 1Y, 1M, 1C, and 1K with laser light to form an electrostatic latent image. When performing the image formation operation, the control unit 200 controls as follows: The control unit 200 controls the laser light so that the second light intensity of the laser light irradiated to the second region on the photosensitive drum 1K where K-colored toner is not applied is less than the first light intensity of the laser light irradiated to the first region on the photosensitive drum 1K where K-colored toner is applied. The first region corresponds to the printing area, and the second region corresponds to the non-printing area. And / or, the control unit 200 controls the laser light so that the fourth light intensity of the laser light irradiated to the fourth region where these toners are not applied is less than the third light intensity of the laser light irradiated to the third region on the photosensitive drums 1Y to 1C where Y-colored, M-colored, and C-colored toners are applied. The third region corresponds to the printing area, and the fourth region corresponds to the non-printing area.

[0041] (Relationship between drum potential and each voltage) Figure 4(b) shows the relationship of drum potential in Example 1, with the horizontal axis showing the unprinted area, printed area, and unprinted area of ​​the surface of the photosensitive drum 1. In Figure 4(b), (i) shows the drum potential, (ii) shows the dark area potential (potential of the unprinted area), (iii) shows the development voltage, and (iv) shows the bright area potential (potential of the printed area). When a charging voltage of -1100V is applied during image formation, the drum potential becomes -600V. At this time, the dark area potential becomes -500V in the unprinted area, and the bright area potential becomes -150V in the printed area. At this time, the back contrast is the difference between the dark area potential and the development voltage (dark area potential - development voltage), and the latent image contrast is the difference between the development voltage and the bright area potential (development voltage - bright area potential).

[0042] In other words, the potential in the first region is less in absolute value than the voltage applied to the developing roller 12K, and the potential in the second region is greater in absolute value than the voltage applied to the developing roller 12K. And / or, the potential in the third region is less in absolute value than the voltage applied to the developing rollers 12Y, 12M, and 12C, and the potential in the fourth region is greater in absolute value than the voltage applied to the developing rollers 12Y, 12M, and 12C.

[0043] Next, when the electrostatic latent image unit rotates to a position opposite the developing roller 12, it is developed by the force of the electric field, and a toner image is formed on the photosensitive drum 1. When the toner image on the photosensitive drum 1 rotates to a position opposite the primary transfer roller 8, it is primary transferred to the intermediate transfer belt 5 in the order of YMCK, and a full-color toner image is formed on the intermediate transfer belt 5 by superimposing the toner images of each color. After the transfer to the intermediate transfer belt 5 is complete, the surface of the photosensitive drum 1 rotates and reaches the cleaning blade 14, where any remaining toner on its surface is cleaned. After all the toner images on the photosensitive drum 1 have been transferred to the intermediate transfer belt 5, the photosensitive drum 1 and the developing roller 12 are separated by the contact-separation mechanism, and the photosensitive drum 1 and the developing roller 12 continue to rotate until the image formation operation is complete (hereinafter referred to as the post-rotation operation).

[0044] The full-color toner image on the intermediate transfer belt 5 is transported to the secondary transfer nip section N by the rotation of the intermediate transfer belt 5, and is secondaryly transferred to the recording material P, which is transported in sync with the movement of the intermediate transfer belt 5, by the force of an electric field. The recording material P on which the unfixed toner image has been transferred is transported to the fixing device 10, where heat and pressure are applied to fix the toner image. The recording material P on which the toner image has been fixed is discharged to the outside of the image forming apparatus 100. Meanwhile, the surface of the intermediate transfer belt 5, on which the transfer to the recording material P has been completed, is cleaned of any remaining toner by the intermediate transfer belt cleaning device 11. After the above series of operations are completed, the drive motor is stopped, and the image forming apparatus 100 stops operating.

[0045] [Voltage control] The voltage applied during the post-rotation operation in Example 1 is described below. Post-rotation refers to the various post-processing steps performed to put the image forming apparatus 100 into a standby or stopped state after image formation is complete. During post-rotation, the photosensitive drum 1 and the developing roller 12 continue to rotate, so a potential difference of 100V must be maintained between the developing roller 12 and the developing blade 13 to prevent dripping. For this reason, as explained in Figure 3(a), the charging voltage 74a needs to output a voltage of -400V or higher. On the other hand, in order to suppress the deterioration of the photosensitive drum 1K, the charging voltage 74a needs to output less than -500V (in absolute value), which is the discharge start voltage. Furthermore, in order to suppress deterioration due to voltage supply to the charging roller 2K, it is desirable to reduce the output of the charging voltage 74a. For these reasons, the output of the charging voltage 74a during post-rotation is -400V. The output of the high-voltage power supply 75 is unrestricted, making it possible to reduce the output to suppress degradation of the charging rollers 2Y, 2M, and 2C due to voltage supply (hereinafter referred to as current degradation).

[0046] In other words, in Embodiment 1, the control unit 200 performs the following control during the post-rotation operation (post-processing) after the image formation operation on the recording material P has been completed. The control unit 200 controls the common high-voltage power supply 74 so that a first voltage (e.g., -400V) with an absolute value smaller than the discharge start voltage at which discharge begins between the charging roller 2K and the photosensitive drum 1K is applied to the charging roller 2K. The control unit 200 controls the high-voltage power supply 75 so that a second voltage (0V, -200V) with an absolute value smaller than the first voltage (-400V) is applied to the charging rollers 2Y, 2M, and 2C.

[0047] Table 1 shows the experimental results when the output of the high-voltage power supply 75 was changed during the reverse rotation operation. [Table 1]

[0048] Table 1 shows the high-voltage configuration, high-voltage output for YMC, high-voltage output for K, and effects for each example. The examples are Example 1-1, Example 1-2, Comparative Example 1, Comparative Example 2, and Comparative Example 3. For the high-voltage output, the charging voltage, developing blade voltage, developing voltage (developing roller voltage), and the difference between the developing blade voltage and the developing voltage are shown. For the effects, for YMC, the presence or absence of droplet drop (none, occurred) and the presence or absence of black spots (○, △, ×) due to charging failure caused by the deterioration of the charging roller 2's current supply are shown. ○ indicates that no black spots occurred in the solid white image after 5000 prints. △ indicates that slight black spots occurred in the halftone image after 5000 prints. × indicates that black spots occurred in the solid white image after 5000 prints.

[0049] We checked whether or not ink droplets occurred during post-rotation printing (image formation) when the voltage applied to the charging rollers 2Y, 2M, and 2C during post-rotation was changed, and also checked the level of black dot-like image defects (hereinafter referred to as "black dots") that occurred due to electrical degradation after 5000 prints. The black dots occur due to electrical degradation of the charging roller 2. When the electrical degradation occurs, the charging performance to the photosensitive drum 1 becomes insufficient, and the background contrast narrows at the point of insufficient charging, causing black dots to appear on the image. As the electrical degradation progresses, the black dot images worsen from being slightly visible in halftones to appearing on white backgrounds.

[0050] (Example 1-1) Example 1-1 is the case where the voltage applied to the charged rollers 2Y, 2M, and 2C by the high-voltage power supply 75 is set to 0V. In Example 1-1, there was no dripping during the reverse rotation, and no black spots were produced.

[0051] (Examples 1-2) Examples 1-2 involve applying a voltage of -200V to the charged rollers 2Y, 2M, and 2C using a high-voltage power supply 75. In Examples 1-2, there was no dripping during the subsequent rotation, and black spots were only slightly visible in halftone.

[0052] (Comparative Example 1) Comparative Example 1 is the case where the voltage applied to the charged rollers 2Y, 2M, and 2C by the high-voltage power supply 75 was set to -400V. In Comparative Example 1, there was no dripping during the reverse rotation, but black spots appeared on the white areas as well. From the above, it can be seen that the smaller the voltage applied to the charged rollers 2Y, 2M, and 2C during the reverse rotation operation, the more effective it is in suppressing the appearance of black spots.

[0053] (Comparative Example 2, Comparative Example 3) As another comparative example, experiments were also conducted with a conventional configuration. When the conventional configuration is applied to a full-color image forming apparatus, a power supply with the same configuration as the common high-voltage power supply 74 will be provided for each color, as shown in Figure 5. Figure 5 shows the conventional high-voltage power supplies 170Y, 170M, 170C, and 170K. Since the high-voltage power supplies 170Y to 170K all have the same configuration, we will explain the high-voltage power supply 170Y. In the high-voltage power supply 170Y, the charging voltage 170a(Y) is connected to a resistor R(Y), a Zener diode ZD1(Y), and a Zener diode ZD2(Y). The charging voltage 170a(Y) is connected to the charging roller 2Y, the developing blade voltage 170b(Y) is connected to the developing blade 13Y, and the developing voltage 170c(Y) is connected to the developing roller 12Y. In other words, the developing blade voltage 170b(Y) is the voltage at the connection point between resistor R(Y) and Zener diode ZD1(Y), and the developing voltage 170c(Y) is the voltage at the connection point between Zener diode ZD1(Y) and Zener diode ZD2(Y). For high-voltage power supplies 170M to 170K, Y should be read as M, C, and K respectively.

[0054] Comparative Example 2 is the case where the voltage applied to the charging rollers 2Y, 2M, and 2C during the reverse rotation is set to 0V in the configuration shown in Figure 5. In Comparative Example 2, no black spots occurred, but dripping occurred. In Comparative Example 2, the output of the charging voltages 170a(Y), 170a(M), and 170a(C) for YMC was set to 0V. As a result, the potential difference between the developing rollers 12Y, 12M, and 12C and the developing blades 13Y, 13M, and 13C became 0V, and the 100V potential difference necessary to suppress dripping could not be maintained.

[0055] Comparative Example 3 is the case where the voltage applied to the charging rollers 2Y, 2M, and 2C during the reverse rotation is set to -200V in the configuration shown in Figure 5. In Comparative Example 3, black spots occurred at a level that could be slightly confirmed in halftone, and dripping also occurred. In Comparative Example 3, the output of the charging voltages 170a(Y), 170a(M), and 170a(C) for YMC was set to -200V. As a result, the potential difference between the developing rollers 12Y, 12M, and 12C and the developing blades 13Y, 13M, and 13C became 75V, which was not possible to maintain the 100V potential difference necessary to suppress dripping.

[0056] In the high-voltage configuration shown in Figure 5, if the voltage applied to the charging rollers 2Y, 2M, and 2C during re-rotation is lowered below -400V, the potential difference between the developing rollers 12Y, 12M, and 12C and the developing blades 13Y, 13M, and 13C cannot be maintained at 100V, resulting in dripping. If the voltage applied to the charging rollers 2Y, 2M, and 2C is raised above -400V to suppress dripping, then the degradation of the electrical conductivity of the charging rollers 2Y, 2M, and 2C cannot be suppressed.

[0057] As explained above, by using the configuration of Example 1, the voltage applied to the charging rollers 2Y, 2M, and 2C can be reduced compared to the conventional technology while suppressing the occurrence of droplet dripping during post-rotation. This makes it possible to suppress the deterioration of the electrical conductivity of the charging rollers 2Y, 2M, and 2C. In Example 1, examples were shown in which the output of the high-voltage power supply 75 during post-rotation was set to 0V or -200V, but the value is not limited to these values. A smaller output is desirable, but it may be set appropriately within that range depending on the specifications of the image forming apparatus used. In Example 1, the above-mentioned voltage control was performed during the post-processing operation, but it is not limited to this. That is, the above-mentioned voltage control may be performed during non-image forming operations, such as during preparatory operations before starting the image forming operation (pre-rotation operation) or between recording materials (between papers) when image forming is performed continuously.

[0058] According to the above Example 1, it is possible to reduce the occurrence of image defects while suppressing the deterioration of the charged component. [Examples]

[0059] Example 2 demonstrates a different image forming operation from Example 1, specifically the so-called mono-mode operation, where image formation is performed using only black toner. Mono-mode is implemented to suppress the degradation of the YMC image forming section, which is not necessary for image formation. The configuration of the image forming apparatus 100 is the same as in Example 1, so its explanation will be omitted, and only the image forming operation specific to Example 2 will be described.

[0060] [Operation during image formation in mono mode] When the control unit 200 receives an image forming operation command from the host computer, it drives the drive motor and outputs the common high-voltage power supply 74. As a result, the photosensitive drum 1K and the developing roller 12K are rotated with voltage applied to them. At this point, a charging voltage of -1100V is applied to the charging roller 2K, causing the surface of the photosensitive drum 1K to be charged to a voltage of -600V. In addition, -350V is applied to the developing roller 12K and -450V to the developing blade 13K. Since the high-voltage power supply 75 is not output, no voltage is applied to the charging rollers 2Y, 2M, and 2C during monocolor image formation, thus suppressing the degradation of the electrical conductivity of the charging rollers 2Y, 2M, and 2C. Furthermore, since there is no discharge from the charging rollers 2Y, 2M, and 2C, surface abrasion of the photosensitive drums 1Y, 1M, and 1C can also be suppressed. On the other hand, since the high-voltage power supply 74 is outputting power, a potential difference is created between the developing rollers 12Y, 12M, 12C and the developing blades 13Y, 13M, 13C, preventing toner from dripping due to insufficient charge transfer. Subsequently, the contact-separation mechanism brings only the photosensitive drum 1K and the developing roller 12K into contact.

[0061] Next, laser light based on image information is sequentially irradiated from the exposure apparatus 3 onto the surface of the photosensitive drum 1K, forming an electrostatic latent image. In the formation of the electrostatic latent image, 0.3 μJ / cm² is applied to the printed area of ​​the image region. 2 The light intensity is irradiated at 0.05 μJ / cm² to the non-printed area. 2The light intensity is used for illumination. As shown in Figure 4(b) described in Example 1, the potential of the printed area (bright area potential) is -150V, and the potential of the non-printed area (dark area potential) is -500V.

[0062] Next, when the electrostatic latent image unit rotates to a position opposite the developing roller 12, it is developed by the force of the electric field, and a toner image is formed on the photosensitive drum 1K. When the toner image on the photosensitive drum 1K rotates to a position opposite the primary transfer roller 8K, it is primary transferred to the intermediate transfer belt 5, and a black toner image is formed on the intermediate transfer belt 5. After the transfer to the intermediate transfer belt 5 is complete, the surface of the photosensitive drum 1K rotates and reaches the cleaning blade 14K, where any remaining toner on its surface is cleaned. After all the toner image on the photosensitive drum 1 has been transferred to the intermediate transfer belt 5, the photosensitive drum 1K and the developing roller 12K are separated by the contact-separation mechanism, and the photosensitive drum 1K continues to rotate until the image formation operation is complete.

[0063] The black toner image on the intermediate transfer belt 5 is transported to the secondary transfer nip section N by the rotation of the intermediate transfer belt 5, and is secondaryly transferred to the recording material P, which is transported in sync with the movement of the intermediate transfer belt 5, by the force of an electric field. The recording material P on which the unfixed black toner image has been transferred is transported to the fixing device 10, where heat and pressure are applied to fix the black toner image. The recording material P on which the black toner image has been fixed is discharged to the outside of the image forming apparatus 100. Meanwhile, the surface of the intermediate transfer belt 5, on which the transfer to the recording material P has been completed, is cleaned of any remaining toner by the intermediate transfer belt cleaning device 11. After the above series of operations are completed, the output of the drive motor and the high-voltage power supply 74 is stopped, and the image forming apparatus 100 stops operating.

[0064] [Voltage control] The voltage applied in mono mode in Example 2 is described below. In mono mode, the photosensitive drum 1 and the developing roller 12 continue to rotate. Also, since the charging voltage 74a outputs a voltage of -1100V for image formation, a potential difference of 100V is maintained between the developing blade 13 and the developing roller 12. On the other hand, since the high-voltage power supply 75 does not need to output, it is possible to reduce the output of the high-voltage power supply 75 in order to suppress the deterioration of the electrical conductivity of the charging rollers 2Y, 2M, and 2C.

[0065] In other words, in Embodiment 2, the control unit 200 controls the first image forming operation, which is mono mode, in which the image forming operation on the recording material P is performed using the fourth image forming unit SK, which is the first image forming unit, without using the first to third image forming units SY to SC, which are the second image forming units, as follows: The control unit 200 controls the first image forming operation when performing the image forming operation 5 The common high-voltage power supply 74 is controlled so that a voltage (-1100V) is applied to the charging roller 2K. The control unit 200 controls a voltage that is smaller in absolute value than the discharge initiation voltage at which discharge begins between the charging rollers 2Y, 2M, 2C and the photosensitive drums 1Y, 1M, 1C. 8 The high-voltage power supply 75 is controlled so that voltages (0V, -200V) are applied to the charging rollers 2Y, 2M, and 2C. In contrast to the mono mode, which is the first image forming operation, the full-color mode, in which an image is formed on the recording material using the first to fourth image forming units SY to SK, corresponds to the second image forming operation. The image forming apparatus of Example 2 is capable of performing both mono mode and full-color mode.

[0066] Table 2 shows the experimental results when the output of the high-voltage power supply 75 in mono-mode was changed. [Table 2]

[0067] Table 2 shows the high-voltage configuration, high-voltage output for YMC, high-voltage output for K, and effects for each example. The examples are Example 2-1, Example 2-2, Comparative Example 4, Comparative Example 5, and Comparative Example 6. For the high-voltage output, it shows the charging voltage, developing blade voltage, developing voltage (developing roller voltage), and the difference between the developing blade voltage and the developing voltage. For the effects, for YMC, it shows whether or not blotting occurred (none, occurred) and whether or not there were black spots (○, △, ×) due to poor charging caused by the deterioration of the charging roller 2's current. ○ indicates that no black spots occurred in the solid white image after 10,000 mono-mode prints. △ indicates that black spots occurred in the halftone image after 10,000 mono-mode prints. × indicates that black spots occurred in the solid white image after 10,000 mono-mode prints. We checked whether or not streaking occurred in mono mode when printing with different voltages applied to the 2Y, 2M, and 2C charging rollers, and also checked the level of black spots caused by power degradation when printing in full color after 10,000 prints.

[0068] (Example 2-1) Example 2-1 is the case where the applied voltage to the charging rollers 2Y, 2M, and 2C is set to 0V. In Example 2-1, there was no dripping after monomode, and no black spots were observed.

[0069] (Example 2-2) Example 2-2 is the case where the applied voltage to the charging rollers 2Y, 2M, and 2C was set to -200V. In Example 2-2, there was no drop-off after mono-mode, and black spots occurred at a level that could only be slightly confirmed in halftone.

[0070] (Comparative Example 4 to Comparative Example 6) Comparative Example 4 involved applying a voltage of -400V to the charged rollers 2Y, 2M, and 2C. In Comparative Example 4, there was no dripping after monomode, but black spots appeared on the white areas as well. From the above, it can be seen that the smaller the voltage applied to the charged rollers 2Y, 2M, and 2C during monomode, the more effective it is in suppressing black spots.

[0071] In addition, experiments were conducted with a conventional configuration as another comparative example. When the conventional configuration is applied to a full-color image forming apparatus, a power supply with the same configuration as the common high-voltage power supply 74 is provided for each color, as shown in Figure 5. Comparative Example 5 is the case where the voltage applied to the charging rollers 2Y, 2M, and 2C in mono mode is set to 0V in the configuration shown in Figure 5. In Comparative Example 5, no black spots occurred, but dripping occurred. In Comparative Example 5, the output of the charging voltages 170a(Y), 170a(M), and 170a(C) was set to 0V. As a result, the potential difference between the developing rollers 12Y, 12M, and 12C and the developing blades 13Y, 13M, and 13C became 0V, and the 100V potential difference necessary to suppress dripping could not be maintained.

[0072] Comparative Example 6 is the case where the voltage applied to the charging rollers 2Y, 2M, and 2C in mono mode is -200V. In Comparative Example 6, black spots occurred at a level that could be slightly confirmed in halftone, and blotting also occurred. In Comparative Example 6, the output of the charging voltages 170a(Y), 170a(M), and 170a(C) was set to -200V. As a result, from the output characteristics shown in Figure 3(a), the potential difference between the developing rollers 12Y, 12M, and 12C and the developing blades 13Y, 13M, and 13C became 75V, and the 100V potential difference necessary to suppress blotting could not be maintained. In the configuration shown in Figure 5, if the voltage applied to the charging rollers 2Y, 2M, and 2C in mono mode is lowered to below -400V, the potential difference between the developing rollers 12Y, 12M, and 12C and the developing blades 13Y, 13M, and 13C cannot be maintained at 100V, and blotting occurs. If the voltage applied to the charged rollers 2Y, 2M, and 2C is set to -400V or higher to suppress dripping, the deterioration of the electrical conductivity of the charged rollers 2Y, 2M, and 2C cannot be suppressed.

[0073] As explained above, by using the configuration of Example 2, the voltage applied to the charging rollers 2Y, 2M, and 2C can be reduced compared to the conventional technology while suppressing the occurrence of droplet dripping in mono-mode. This makes it possible to suppress the degradation of the electrical conductivity of the charging rollers 2Y, 2M, and 2C. In Example 2, examples were shown in which the output of the high-voltage power supply 75 in mono-mode was set to 0V or -200V, but it is not limited to these values. A smaller output is desirable, but it may be set appropriately within that range depending on the specifications of the image forming apparatus used.

[0074] As described above, according to Example 2, it is possible to reduce the occurrence of image defects while suppressing the deterioration of the charged component.

[0075] Furthermore, while embodiments describing the execution of this control during non-image forming operations, as in Example 1, and during mono mode, as in Example 2, are described, the invention is not limited to these embodiments. Specifically, the invention is not limited to the above embodiments as long as a charging voltage is applied to the black element and the developing roller of the color cartridge is separated from the photosensitive drum. Furthermore, the above-mentioned control is performed from before the secondary transfer begins after the primary black transfer is complete, but is not limited to this. For example, the primary transfer, secondary transfer, and fixing process are also included in the image formation operation. [Explanation of symbols]

[0076] 1 Photosensitive drum 2 Charging rollers 12 Developing roller 13 Developing blades 74 Common High Voltage Power Supply 75 High-voltage power supply 200 Control Unit

Claims

1. An image forming apparatus capable of performing an image forming operation, A first image forming unit comprising: a rotatable first photoreceptor; a first charging means for charging the surface of the first photoreceptor to a predetermined potential; a first developer carrier for applying a first color developer charged with normal polarity to the electrostatic latent image formed on the first photoreceptor to form a developer image; and a first regulating member that contacts the first developer carrier and applies a predetermined charge to the first color developer while regulating the amount of the first color developer; A second image forming unit comprising: a rotatable second photoreceptor; a second charging means for charging the surface of the second photoreceptor to a predetermined potential; a second developer carrier for applying a second color developer charged with the normal polarity to the electrostatic latent image formed on the second photoreceptor to form a developer image; and a second regulating member that contacts the second developer carrier and applies a predetermined charge to the second color developer while regulating the amount of the second color developer. The first charging means, the first developer carrier, the second developer carrier, the first regulating member, and the first power supply unit that applies voltage to the second regulating member, A second power supply unit that applies voltage to the second charging means, Control means for controlling the first image forming unit, the second image forming unit, the first power supply unit, and the second power supply unit, Equipped with, The first power supply unit is configured such that, during the image forming operation, it applies a fifth voltage of normal polarity to the first charging means, thereby applying a third voltage of normal polarity to the first regulating member and the second regulating member, and applies a fourth voltage of normal polarity to the first developer carrier and the second developer carrier, thereby forming a first potential difference between the first developer carrier and the first regulating member, and a second potential difference between the second developer carrier and the second regulating member. The control means, during non-image forming operations that are different from the image forming operations, i) The first voltage of normal polarity is applied to the first charging means, which has an absolute value smaller than the discharge initiation voltage at which discharge is initiated between the first charging means and the first photoreceptor, and also has an absolute value smaller than the fifth voltage. ii) A sixth voltage, which is less than or equal to the absolute value of the third voltage, is applied to the first regulating member and the second regulating member, and a seventh voltage, which is less than or equal to the absolute value of the fourth voltage, is applied to the first developer carrier and the second developer carrier, thereby maintaining the first potential difference and the second potential difference from the image forming operation. The first power supply unit is controlled in such a way. iii) The second voltage of normal polarity, which has an absolute value smaller than the first voltage, is applied to the second charging means, or the second power supply is controlled so that the voltage applied to the second charging means becomes 0V. An image forming apparatus characterized by the following features.

2. The image forming apparatus according to claim 1, characterized in that the non-image forming operation includes a post-processing operation after the completion of the image forming operation.

3. An image forming apparatus capable of performing an image forming operation, A first image forming unit comprising: a rotatable first photoreceptor; a first charging means for charging the surface of the first photoreceptor to a predetermined potential; a first developer carrier for applying a first color developer charged with normal polarity to the electrostatic latent image formed on the first photoreceptor to form a developer image; and a first regulating member that contacts the first developer carrier and applies a predetermined charge to the first color developer while regulating the amount of the first color developer; A second image forming unit comprising: a rotatable second photoreceptor; a second charging means for charging the surface of the second photoreceptor to a predetermined potential; a second developer carrier for applying a second color developer charged with the normal polarity to the electrostatic latent image formed on the second photoreceptor to form a developer image; and a second regulating member that contacts the second developer carrier and applies a predetermined charge to the second color developer while regulating the amount of the second color developer. The first charging means, the first developer carrier, the second developer carrier, the first regulating member, and the first power supply unit that applies voltage to the second regulating member, A second power supply unit that applies voltage to the second charging means, Control means for controlling the first image forming unit, the second image forming unit, the first power supply unit, and the second power supply unit, Equipped with, The control means controls the execution of a first image forming operation, in which the image forming operation is performed on the recording material using the first image forming unit without using the second image forming unit, and a second image forming operation, in which the image forming operation is performed on the recording material using the first image forming unit and the second image forming unit. The first power supply unit is configured to apply the fifth voltage of the normal polarity to the first charging means when performing the second image forming operation. When the control means performs the first image forming operation, The second power supply unit is controlled such that the eighth voltage, which has a normal polarity and whose absolute value is smaller than the discharge initiation voltage at which discharge begins between the second charging means and the second photoreceptor, is applied to the second charging means, or the voltage applied to the second charging means becomes 0V. An image forming apparatus characterized by the following features.

4. The first power supply unit is, A first output means that outputs voltage, A resistor with one end connected to the first output means, A first constant voltage element, one end of which is connected to the other end of the resistor, A second constant voltage element, one end of which is connected to the other end of the first constant voltage element and the other end of which is grounded, It has, The first output means applies a voltage to the first charging means, The connection point between the resistor and the first constant voltage element is connected to the first regulating member and the second regulating member. The image forming apparatus according to any one of claims 1 to 3, characterized in that the connection point between the first constant voltage element and the second constant voltage element is connected to the first developer carrier and the second developer carrier.

5. The first constant voltage element and the second constant voltage element are Zener diodes, One end of the first constant voltage element and one end of the second constant voltage element are the anode terminals of the Zener diode. The image forming apparatus according to claim 4, characterized in that the other end of the first constant voltage element and the other end of the second constant voltage element are the cathode terminals of the Zener diode.

6. A first contact-separation mechanism for bringing the first developer carrier and the first photoreceptor into contact or separating, A second contact-separation mechanism for bringing the second developer carrier and the second photoreceptor into contact or separating, Equipped with, The control means is When performing an image forming operation using the first image forming unit and the second image forming unit, the first contact-separation mechanism brings the first developer carrier into contact with the first photoreceptor, and the second contact-separation mechanism brings the second developer carrier into contact with the second photoreceptor. When performing an image forming operation using the first image forming unit, the first contact-separation mechanism brings the first developer carrier into contact with the first photoreceptor, and the second contact-separation mechanism separates the second developer carrier from the second photoreceptor. The image forming apparatus according to any one of claims 1 to 5, characterized in that, after the image forming operation is completed, the first contact-separation mechanism separates the first developer carrier from the first photoreceptor and the second contact-separation mechanism separates the second developer carrier from the second photoreceptor.

7. The image forming apparatus according to any one of claims 1 to 6, further comprising a driving means for driving the rotation of the first photoreceptor, the second photoreceptor, the first developer carrier, and the second developer carrier.

8. The system includes an exposure means for irradiating the first photoreceptor and the second photoreceptor with laser light to form an electrostatic latent image, The control means, when performing the image forming operation, The second light intensity of the laser light irradiated onto a second region on the first photoreceptor where the first color developer is not applied is less than the first light intensity of the laser light irradiated onto a first region on the first photoreceptor where the first color developer is applied. and / or, The amount of laser light irradiated onto a fourth region on the second photoreceptor where the second color developer is not applied is less than the amount of laser light irradiated onto a third region on the second photoreceptor where the second color developer is applied. The image forming apparatus according to any one of claims 1 to 7, characterized in that it controls the exposure means.

9. The potential in the first region is less in absolute value than the voltage applied to the first developer carrier, and the potential in the second region is greater in absolute value than the voltage applied to the first developer carrier. and / or, The image forming apparatus according to claim 8, characterized in that the potential of the third region is less in absolute value than the voltage applied to the second developer carrier, and the potential of the fourth region is greater in absolute value than the voltage applied to the second developer carrier.

10. The first color developer is a black toner. The image forming apparatus according to any one of claims 1 to 9, characterized in that the second color developer includes a yellow toner, a magenta toner, and a cyan toner.

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