Image forming apparatus

Abstract

The present disclosure relates to an image forming apparatus. An image forming apparatus includes a photosensitive member, a charging member, an exposure unit, a developing member, an intermediate transfer member, and a voltage application portion. A controller controls a primary transfer contrast, which is a difference between a transfer voltage applied by the voltage application portion in a nip and a potential of a portion on the photosensitive member exposed by the exposure unit. The controller transfers a toner image from the photosensitive member to the intermediate transfer member by flowing a current in a circumferential direction by applying a transfer voltage to the intermediate transfer member. The controller controls the primary transfer contrast by controlling the transfer voltage based on information on a usage state of toner related to a number of print sheets. The controller controls so that the transfer voltage becomes lower as the number of print sheets increases.

Description

Technical Field

[0001] This invention relates to image forming apparatuses, such as laser printers, copiers, and fax machines having an electrophotographic method. Background Technology

[0002] Image forming apparatuses, including those using intermediate transfer members, are generally well-known. In a primary transfer process, such an image forming apparatus transfers a toner image formed on the surface of a photosensitive drum to a primary transfer member provided in the portion facing the photosensitive drum (the first transfer portion) by applying voltage (hereinafter referred to as primary transfer). Furthermore, by repeating the primary transfer process with several colors of toner, a multi-tone toner image is formed on the surface of the intermediate transfer member. In a secondary transfer process, the multi-tone toner image formed on the surface of the intermediate transfer member is jointly transferred to the surface of a recording material (such as a sheet of paper) by applying voltage to the secondary transfer member (hereinafter referred to as secondary transfer). The toner image transferred to the surface of the recording material (such as a sheet of paper) is fixed onto the recording material by a fixing member, thus forming a multi-tone image. For example, Japanese Patent Application Publication No. 2018-036624 discloses a technique for improving transfer by forming a low-resistance conductive layer on the inner side of the outer surface of the base layer of the intermediate transfer belt, and applying a primary transfer voltage when current flows from a primary transfer current supply member not directly below the photosensitive drum to the circumferential direction of the intermediate transfer belt. Furthermore, Japanese Patent Application Publication No. 2012-150137 discloses a technique for adjusting the primary transfer voltage according to the ratio of deteriorating toner.

[0003] In structures using an intermediate transfer belt that includes a conventional inner conductive layer, the potential inside the intermediate transfer belt tends to be essentially constant. Therefore, it is even possible for the rotation direction of the intermediate transfer belt to have a potential close to the primary transfer voltage relative to the upstream portion of the primary transfer roller gap, which serves as the contact point between the photosensitive drum and the intermediate transfer belt. Consequently, a discharge current may occur upstream of the primary transfer roller gap relative to the rotation direction of the intermediate transfer belt, and pre-transfer may occur where the toner formed on the photosensitive drum before the primary transfer has already been transferred before reaching the primary transfer roller gap. Pre-transfer is particularly prone to occur when the toner charge is low.

[0004] Furthermore, conventional techniques for determining the primary transfer voltage based on toner degradation detection results require balancing not only pre-transfer but also primary transfer defects caused by insufficient primary transfer current. To determine the primary transfer voltage while considering the balance between pre-transfer and primary transfer defects, it is necessary to configure a primary transfer contrast that includes the potential on the photosensitive drum and the primary transfer voltage. Therefore, even for image forming apparatuses with an intermediate transfer belt including a low-resistance inner layer, excellent primary transfer performance is required. Summary of the Invention

[0005] The present invention was developed under the above circumstances. The object of the present invention is to obtain excellent single-pass transfer performance even when using an image forming apparatus having an intermediate transfer belt including a low-resistance inner layer.

[0006] To address the above problems, the present invention provides the following:

[0007] (1) An image forming apparatus for forming an image on a recording material, the image forming apparatus comprising: a photosensitive member; a charging member configured to charge the photosensitive member; an exposure unit configured to form an electrostatic latent image by exposing the photosensitive member according to an image signal; a developing member configured to form a toner image by developing the electrostatic latent image with a toner; an intermediate transfer member having a first conductive layer and a second conductive layer having a resistance value lower than that of the first layer, wherein the toner image is transferred to the intermediate transfer member at a gap between the intermediate transfer member and the photosensitive member; and a voltage applying member configured to apply a transfer voltage to the intermediate transfer member; The control section is configured to control the primary transfer contrast, which is the difference between the transfer voltage applied by the voltage application section in the roller gap section and the potential of the portion of the photosensitive member exposed by the exposure unit. The control section transfers the toner image from the photosensitive member to the intermediate transfer member by causing current to flow in the circumferential direction, and controls the primary transfer contrast by controlling the transfer voltage based on information about the toner usage status related to the number of printing sheets of the recording material. The control section also controls the transfer voltage to make it lower as the number of printing sheets increases.

[0008] (2) An image forming apparatus for forming an image on a recording material, the image forming apparatus comprising: a photosensitive member; a charging member configured to charge the photosensitive member; an exposure unit configured to form an electrostatic latent image by exposing the photosensitive member according to an image signal; a rotating member provided with a plurality of developing devices, each developing device including a developing member and a receiving portion, the developing member being configured to form a toner image by developing the electrostatic latent image with a toner through contact with the photosensitive member, the receiving portion being configured to receive a toner, and the rotating member being configured to be able to switch the developing member in contact with the photosensitive member by rotation; an intermediate transfer member provided with a first layer having conductivity and a second layer having conductivity and a resistance value lower than that of the first layer, and the toner image being on a roller between the intermediate transfer member and the photosensitive member. The gap portion is transferred to the intermediate transfer member; a voltage application portion is configured to apply a transfer voltage to the intermediate transfer member; and a control portion is configured to control the primary transfer contrast, which is the difference between the transfer voltage applied by the voltage application portion in the gap portion and the potential of the portion exposed by the exposure unit on the photosensitive member. The control portion transfers the toner image from the photosensitive member to the intermediate transfer member by causing current to flow in the circumferential direction, and controls the primary transfer contrast by controlling the transfer voltage based on information about the toner usage status related to the number of printing sheets of the recording material. The control portion also controls the transfer voltage to decrease as the number of printing sheets increases.

[0009] Further features of the invention will become clear from the following description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0010] Figure 1 This is a cross-sectional schematic diagram explaining the structure of the image forming apparatus in Embodiments 1 and 2.

[0011] Figure 2 This is a schematic diagram explaining the control block of the image forming apparatus in Embodiments 1 and 2.

[0012] Figure 3 Parts (a) and (b) are schematic diagrams showing the structure near the primary transfer roller gap portion and the cross-sectional schematic diagram of the structure of the intermediate transfer belt in Examples 1 and 2.

[0013] Figure 4 This is a schematic diagram showing the potential state of the internal conductive layer in Examples 1 and 2.

[0014] Figure 5Parts (a) and (b) are graphs showing the relationship between the number of printed sheets and the amount of toner charged in Examples 1 and 2, and a graph showing the relationship between the number of printed sheets and the single transfer voltage in Example 1.

[0015] Figure 6 This is a graph illustrating the adjustment control of the contrast during a single transfer in Example 1.

[0016] Figure 7 It is a graph showing the relationship between the number of printing sheets of the main component in Embodiment 1 and the single transfer voltage.

[0017] Figure 8 This is a cross-sectional schematic diagram explaining other structures of the image forming apparatus in Embodiments 1 and 2.

[0018] Figure 9 Parts (a) and (b) are graphs illustrating the adjustment control of the contrast for a single transfer in Example 2.

[0019] Figure 10 This is a schematic diagram illustrating the potential relationship in Example 2.

[0020] Figure 11 Parts (a) and (b) are graphs showing the relationship between exposure and the potential of the photosensitive drum in Example 2, and graphs showing the relationship between the number of printed sheets and the contrast of a single transfer in Examples 1, 2 and 3.

[0021] Figure 12 This is a graph showing the adjustment control of the contrast for a single transfer in Example 2.

[0022] Figure 13 This is a cross-sectional schematic diagram explaining the structure of the image forming apparatus in Embodiment 3.

[0023] Figure 14 This is a schematic diagram of the potential relationship in Example 3. Detailed Implementation

[0024] The invention will now be described by way of example with reference to the accompanying drawings. It should be noted that the dimensions, materials, shapes, and relative positions of the components described in these embodiments may be modified to correspond to the structure or variable conditions of the apparatus to which the invention is applied, and the scope of the invention is not limited to these disclosed embodiments.

[0025] [1. Image forming apparatus]

[0026] Figure 1This is a cross-sectional schematic diagram showing the structure of the image forming apparatus 100 in Embodiment 1. It should be noted that the image forming apparatus 100 is a so-called tandem image forming apparatus, which has multiple image forming sections (a), (b), (c), and (d). The first image forming section (a) (hereinafter simply referred to as image forming section (a)) forms an image using a yellow toner (Y), the second image forming section (b) (hereinafter simply referred to as image forming section (b)) forms an image using a magenta toner (M), the third image forming section (c) (hereinafter simply referred to as image forming section (c)) forms an image using a cyan toner (C), and the fourth image forming section (d) (hereinafter simply referred to as image forming section (d)) forms an image using a black toner (Bk). These four image forming sections (a), (b), (c), and (d) are arranged in a row at a certain constant interval, and their structures are basically similar except for the color of the toner they contain. Therefore, the image forming apparatus 100 in Embodiment 1 will be described below using image forming section (a).

[0027] The image forming section (a) includes a photosensitive drum 1a as a drum-shaped photosensitive component, a charging roller 2a as a charging component, a developing unit 4a as a developing component, and a drum cleaning device 5a. In Embodiment 1, the photosensitive drum 1a, charging roller 2a, developing roller 4a, and drum cleaning device 5a are integrated into a replaceable toner cartridge. It should be noted that the replaceable toner cartridge may have a structure that includes at least the photosensitive drum 1a and the developing unit 4a, or a structure that provides several cartridges for each color.

[0028] The photosensitive drum 1a is an image-carrying member that carries the toner image and is driven to rotate at a predetermined processing speed (e.g., 200 mm / s in Example 1) in the direction of arrow R1 (counterclockwise) in the figure. The developing unit 4a includes a developing container 41a as a receiving portion for containing yellow toner, and a developing roller 42a as a developing member that carries the yellow toner contained in the developing container 41a and develops the yellow image on the photosensitive drum 1a. The developing roller 42a rotates while in contact with the photosensitive drum 1a. The toner is a powder whose abrasive material is a thermoplastic resin and includes pigments that form the color, release agents, charge control agents, etc. Moreover, the photosensitive drum 1a is made of a conductive hollow tube such as SUS (stainless steel) coated with a photosensitive layer. The drum cleaning device 5a is a component that collects the toner deposited on the photosensitive drum 1a. The drum cleaning device 5a includes a cleaning scraper that contacts the photosensitive drum 1a and a waste toner box that holds toner and the like removed from the photosensitive drum 1a by the cleaning scraper.

[0029] When an image forming operation is initiated by receiving an image signal via a control unit 274, such as a DC controller, the photosensitive drum 1a is driven to rotate. During rotation, the photosensitive drum 1a is uniformly charged by the charging roller 2a at a predetermined potential (dark component potential Vd) with a predetermined polarity (negative polarity in Embodiment 1), and receives exposure from the exposure device 3a of the exposure unit corresponding to the image signal. This forms an electrostatic latent image (bright component potential VL) corresponding to the yellow component of the target multicolor image. Next, the electrostatic latent image is developed by the developing roller 42a and visualized at the developed position as a yellow toner image (hereinafter simply referred to as the toner image). The developing roller 42a is stably developed by rotating in the same direction at a speed 1.5 times faster than the photosensitive drum 1a (e.g., 300 mm / s). In Embodiment 1, a voltage is applied to the charging roller 2a such that the dark component potential Vd is -600V, and the exposure amount of the exposure device 3a is determined such that the bright component potential VL is -150V. Furthermore, the developing roller 42a is subjected to, for example, a developing voltage Vdc of -350V. The absolute value of the difference between the bright portion potential VL and the developing voltage Vdc is called the developing contrast. It should be noted that, in Example 1, the emission intensity of the laser emitted from the exposure device 3a to the photosensitive drum 1a is, for example, a maximum of 0.5 μJ / cm². 2 ).

[0030] Here, the normal polarity of the toner deposited on the surface of the developing roller 42a is negative. Toner is supplied to the surface of the developing roller 42a from a toner supply roller (not shown) that rotates in contact with the developing roller 42a, and the supplied toner is deposited on the surface of the developing roller 42a. The toner deposited on the surface of the developing roller 42a is leveled to a predetermined thickness by an adjusting scraper (not shown) that contacts the surface of the developing roller 42a, and becomes negatively polarized through friction between the adjusting scrapers.

[0031] Although in Example 1 the electrostatic latent image is developed by reversing the polarity of the toner charged with the same polarity as the charged photosensitive drum 1a by the charging roller 2a, it is not limited to this. For example, it is applicable to image forming apparatuses that develop electrostatic latent images with toners charged with the opposite polarity to the charged photosensitive drum 1a. In Example 1, when the surface of the photosensitive drum 1a is at a bright portion potential VL, a voltage greater than 150V is required as development contrast in order to develop 100% of the toner on the developing roller 42a onto the photosensitive drum 1a.

[0032] The intermediate transfer belt 10 is an annular and movable intermediate transfer member, provided at a position in contact with each image forming portion a, b, c, and d of each photosensitive drum 1a, 1b, 1c, and 1d, and is stretched along three axes of rollers serving as stretching members: a drive roller 11, a stretching roller 12, and a secondary transfer blocking roller 13. The intermediate transfer belt 10 is stretched by the stretching roller 12 with a tension of, for example, 60 N, and moves in the direction of arrow R2 (clockwise) in the figure by the secondary transfer blocking roller 13, which rotates via a driving force.

[0033] The toner image formed on the photosensitive drum 1a is transferred to the intermediate transfer belt 10 during the primary transfer roller gap N1a where the photosensitive drum 1a contacts the intermediate transfer belt 10, by applying a positive voltage from the primary transfer power source 23 to the primary transfer roller 6a (primary transfer). The primary transfer power source 23 acts as a primary application component, applying a primary transfer voltage, which is the transfer voltage, to the primary transfer roller 6a, which is the transfer component. Afterwards, residual toner remaining on the photosensitive drum 1a that was not transferred to the intermediate transfer belt 10 is collected by the drum cleaning device 5a. Similarly, a magenta toner image (second color), a cyan toner image (third color), and a black toner image (fourth color) are formed and sequentially transferred to the intermediate transfer belt 10. Therefore, a toner image with four colors corresponding to the target multicolor image is formed on the intermediate transfer belt 10.

[0034] In Example 1, the primary transfer roller 6 in contact with the intermediate transfer belt 10 is energized during the primary transfer. Therefore, current flows on the inner circumferential surface of the intermediate transfer belt 10, and this current creates a primary transfer potential at the primary transfer roller gap portions N1a, N1b, N1c, and N1d in each image forming portion a, b, c, and d. Thus, the primary transfer rollers 6a, 6b, 6c, and 6d are all energized with the same primary transfer voltage. After the primary transfer, the toner image with four colors carried by the intermediate transfer belt 10 passes through the secondary transfer roller gap portion N2 formed by their contact between the secondary transfer roller 20 and the intermediate transfer belt 10. In this process, the toner image with four colors is transferred together onto the surface of the transfer material (recording material) P, such as a printing sheet or OHP sheet fed from the sheet feed roller 50 (secondary transfer).

[0035] The secondary transfer roller 20 is made of an 8mm outer diameter nickel-plated steel rod covered with, for example, a foamed sponge with an outer diameter of 18mm. Here, the foamed sponge is adjusted to 10... 8It is made of NBR (nitrile butadiene rubber) and epichlorohydrin rubber with a volume resistivity of Ω·cm and a thickness of 5mm. It should be noted that the rubber hardness of the foamed sponge is 30° hardness under a 500g load when measured using Asker hardness measurement type C. The secondary transfer roller 20 contacts the outer circumferential surface of the intermediate transfer belt 10, and is pressed against the secondary transfer blocking roller 13 located facing the secondary transfer blocking roller 20 by the intermediate transfer belt 10 with a pressure of 50N, forming the secondary transfer roller gap portion N2.

[0036] The secondary transfer roller 20 rotates following the intermediate transfer belt 10, and current flows down from the secondary transfer roller 20 to the secondary transfer blocking roller 13 by applying voltage from the secondary transfer power supply 21. Therefore, the toner image carried by the intermediate transfer belt 10 is transferred a second time onto the transfer material P at the secondary transfer roller gap portion N2. It should be noted that the toner image is transferred a second time onto the transfer material P via the intermediate transfer belt 10 as follows. The voltage applied from the secondary transfer power supply 21 to the secondary transfer roller 20 is controlled so that the current flowing down from the secondary transfer roller 20 through the intermediate transfer belt 10 to the secondary transfer blocking roller 13 is constant. Furthermore, the magnitude of the current performing the secondary transfer is predetermined depending on the environment providing the image forming apparatus or the type of transfer material P. The secondary transfer power supply 21 is connected to the secondary transfer roller 20 and applies a secondary transfer voltage to the secondary transfer roller 20. Moreover, the secondary transfer power supply 21 is capable of outputting a voltage between 100V and 4000V.

[0037] After the image of four colors of toner is transferred onto the transfer material P in the secondary transfer process, the transfer material P is heated and pressurized in the fixing device 30, which serves as a fixing component. The four colors of toner are melted, mixed, and then fixed onto the transfer material P. On the other hand, the toner remaining on the intermediate transfer belt 10 after the secondary transfer is cleaned and removed by a belt cleaning device 16 (collection component) provided downstream of the secondary transfer roller gap portion N2 relative to the direction of movement (rotation). The belt cleaning device 16 includes a cleaning blade 16a as a contact member and a waste toner container 16b. The cleaning blade 16a, as a contact member, contacts the outer circumferential surface of the intermediate transfer belt 10 at a position facing the secondary transfer blocking roller 13. The waste toner container 16b contains the toner collected by the cleaning blade 16a. It should be noted that the cleaning blade 16a is referred to as blade 16a in the following explanation. When adjustment control is performed to adjust the position or density of the image formed in the image forming apparatus 100, an optical sensor 60, which serves as a detection component, is used. Through the above operation, a full-color printed image is formed in the image forming apparatus 100 of Embodiment 1.

[0038] [2. Explanation of Control Block View]

[0039] Next, a control block diagram will be used to describe the control in Example 1. Figure 2 This is a control block diagram that controls the operation of the image forming apparatus 100. The PC 271, acting as a host computer, commands the formatter 273, a conversion unit, to print, and sends the image data of the printed image to the formatter 27. The formatter 273 receives RGB or CMYK image data from the PC 271 and converts it into CMYK exposure data according to a specified mode. Here, the converted exposure data is, for example, 600 dpi. The mode specified by the PC 271 is a mode for type, print sheet size, or image quality.

[0040] The formatter 273 forwards the converted exposure data to the exposure control device 277 provided in the control section 274. The exposure control device 277 controls the exposure device 3 via commands from the CPU 276. Figure 2 In the image forming apparatus 100, halftone control is achieved by adjusting the occupied area of ​​exposure data. In Embodiment 1, as halftone control, a predetermined halftone control image is formed by adjusting the size of the toner dots, for example, using a dither matrix method. The CPU 276 begins the image forming sequence upon receiving a print command from the formatter 273.

[0041] The control unit 274 is equipped with a CPU 276, a memory 275, etc., and is pre-programmed for operation. The CPU 276 performs the formation of an electrostatic latent image by controlling the charging power supply 281, the developing power supply 280, the primary power supply 23, and the secondary power supply 21, and performs image formation by controlling the transfer of the developed toner image, etc. Moreover, when performing correction control to correct the position and density of the image formed in the image forming apparatus 100, the CPU 276 performs the process of receiving signals from the optical sensor 60. It should be noted that the CPU 276, as a control unit, controls the primary transfer contrast corresponding to the toner usage conditions described below. Primary transfer contrast is the difference between the potential at the primary transfer roller gap portion N1 when the primary transfer voltage is applied to the transfer roller 6 by the primary transfer power supply 23 and the potential at the portion of the photosensitive drum 1 (on the photosensitive member) exposed by the exposure device 3.

[0042] [3. The stretching structure of the intermediate transfer belt]

[0043] The intermediate transfer belt 10, its stretching members (drive roller 11, stretch roller 12, and secondary transfer blocking roller 13), and primary transfer roller 6 will be described below. The intermediate transfer belt 10 is provided at positions facing each image forming section a, b, c, and d. The intermediate transfer belt 10 is an annular belt in which a conductive agent is added to its resin material to impart conductivity, and it is stretched by three axes—drive roller 11, stretch roller 12, and secondary transfer blocking roller 13—as stretching members, with a total tension of 60 N by stretch roller 12.

[0044] like Figure 1 As shown, primary transfer rollers 6a, 6b, 6c and 6d, which serve as contact members for contacting the inner circumferential surface of the intermediate transfer belt 10, are provided downstream of the photosensitive drums 1a, 1b, 1c and 1d in the rotation direction of the intermediate transfer belt 10. Figure 3 Part (a) is a diagram showing the relative positions between the photosensitive drum 1 and the primary transfer roller 6, and arrow R2 is also shown. Figure 1 The rotation direction is shown. Each primary transfer roller 6 is provided downstream of the vertical line L1 from the center of the photosensitive drum 1 to the primary transfer belt 10 in the rotation direction of the photosensitive drum 1. Each primary transfer roller 6a, 6b, 6c and 6d is positioned to enter the surface of the intermediate belt 10 to ensure that there is a sufficient amount of intermediate transfer belt 10 wrapped around the photosensitive drums 1a, 1b, 1c and 1d in the corresponding image forming portions a, b, c and d.

[0045] A straight primary transfer roller 6, made of a nickel-plated SUS bar with an outer diameter of 6 mm and including a metal roller, is driven to rotate along with the rotation of the intermediate transfer belt 10. In Embodiment 1, the outer diameter of the photosensitive drum 1 is, for example, 24 mm. The primary transfer roller 6 contacts a predetermined area on its longitudinal side orthogonal to the moving direction (arrow R2) of the intermediate transfer belt 10. Here, the distance between the perpendicular line L1 from the center of the photosensitive drum 1 toward the intermediate transfer belt 10 and the perpendicular line L2 from the center of the primary transfer roller 6 toward the intermediate transfer belt 10 is referred to as W. Here, the line connecting the predetermined point of contact between the photosensitive drum 1 and the point of contact between the adjacent photosensitive drum 1 and the intermediate transfer belt 10 is... Figure 3In the cross-sectional view of part (a), it is referred to as virtual line S1. Additionally, a line parallel to virtual line S1, including the point where the primary transfer roller 6 contacts the intermediate transfer belt 10, is referred to as virtual line S2. The distance between virtual line S1 and virtual line S2 in the direction perpendicular to line L2 is the amount by which the primary transfer roller 6 enters the area of ​​the intermediate transfer belt 10, or in other words, the height by which the primary transfer roller 6 lifts the intermediate transfer belt 10 (hereinafter referred to as the lifting height). The lifting height of the primary transfer roller 6 lifting the intermediate transfer belt 10 is defined as H1. In Embodiment 1, W = 10 mm and H1 = 2 mm are defined. It should be noted that a primary transfer voltage is applied to the primary transfer roller 6 from the primary transfer power supply 23, and a primary transfer current is supplied through the interior of the inner circumferential layer of the intermediate transfer belt 10.

[0046] [4. Intermediate transfer belt]

[0047] Next, the intermediate transfer belt 10 will be described. The intermediate transfer belt 10 includes a base layer 10a that serves as the first layer in contact with the photosensitive drum 1, and an inner layer 10b that serves as the second layer in contact with the primary transfer roller 6 and has a lower resistance value than the base layer 10a. Figure 3 Part (b) is a schematic diagram showing a cross-sectional view of the intermediate transfer belt 10 used in Example 1. The intermediate transfer belt 10 has a circumference of 700 mm and a thickness of 90 μm, and is composed of a base layer 10a and an inner layer 10b. The base layer 10a is made of cyclic polyethylene naphthalate (PEN) mixed with an ionic conductive material as a conductive agent, and the inner layer 10b is made of acrylic resin mixed with carbon as a conductive agent. The inner layer 10b is formed inside the base layer 10a (stretch axial side). When the thickness of the polyvinylidene fluoride layer of the base layer 10a is referred to as t1 and the thickness of the acrylic resin layer of the inner layer 10b is referred to as t2, t1 = 87 μm and t2 = 2 μm. Although polyethylene naphthalate (PEN) is used as the material of the base layer 10a of the intermediate transfer belt 10, other materials, such as copolymers of polyesters, acrylonitrile, butadiene and styrene (ASB), or resins of these materials, can also be used. For the material of the inner layer 10b of the intermediate transfer belt 10, other materials besides acrylic resin, such as polyester, can be used.

[0048] In Example 1, the volume resistivity measured from the base layer 10a side and the surface resistivity measured from the inner layer 10b side were used as the resistance values ​​of the intermediate transfer tape 10. The volume resistivity was measured using a Mitsubishi Chemical Corporation Hiresta-UP (MCT-HT450) with a UR-type ring probe (MCP-HTP12 model). The metal surface of the UFL registration meter was used as the opposing probe electrode. The surface resistivity was measured using the same resistivity meter with a UR 100-type ring probe (MCP-HTP16 model). The Teflon (R: registered trademark) surface of the UFL registration meter was used as the opposing probe electrode.

[0049] The volume resistivity of the intermediate transfer belt 10 was measured by pressing the probe with 1 kg of pressure under a 250 V voltage for 10 seconds. The volume resistivity of the intermediate transfer belt 10 in Example 1 was 3.55 × 10⁻⁶. 10 (Ω·cm). The surface resistivity of the inner layer 10b was measured from the inner surface by pressing the probe with a pressure of 1 kg under an applied voltage of 10 V and measuring for 10 seconds. The surface resistivity of the inner layer 10b of the intermediate transfer tape 10 in Example 1 is 1.00 × 10⁻⁶. 6 (Ω·cm). These resistivity values ​​were measured in an environment with a room temperature of 23°C and an indoor humidity of 50%.

[0050] [5. Primary Transfer Voltage Control]

[0051] Next, the primary transfer voltage control, a feature of Example 1, will be described. The CPU 276 controls the primary transfer contrast by controlling the primary transfer voltage. The toner consumption is indicated by the amount of printing sheet, and the CPU 276 controls the primary transfer voltage to decrease as the amount of printing sheet increases.

[0052] Figure 4 This is a view showing the state of the potential formed in the inner surface layer 10b when a positive voltage is applied to the primary transfer roller 6. The inner surface layer 10b has a low surface resistivity. Therefore, in the portion from the primary transfer roller 6 to the primary transfer roller gap portion N1, which serves as the contact point between the photosensitive drum 1 and the intermediate transfer belt 10, the surface potential of the inner surface layer 10b hardly decreases and forms a surface potential almost similar to the voltage applied to the primary transfer roller 6 (primary transfer voltage). Furthermore, in the region of the inner surface layer 10b upstream of the primary transfer roller gap portion N1 in the rotational direction (arrow R2) from the intermediate transfer belt 10, a potential identical to the voltage applied to the primary transfer roller 6 is formed. In Embodiment 1, the width of the primary transfer roller gap portion N1 (its length in the moving direction of the intermediate transfer belt 10) is 4 mm.

[0053] In the following text, in Embodiment 1, each item on the line L3 (or virtual line L3) that is orthogonal to the intermediate transfer belt 10 and is tangent to the photosensitive drum 1 as described above is defined as follows. The contact point between the virtual line L3 and the photosensitive drum 1 is called Cd, the intersection point between the virtual line L3 and the surface of the base layer 10a of the intermediate transfer belt 10 is called Ca, and the region along the intermediate transfer belt 10 from Ca to the surface of the base layer 10a of the primary transfer roll gap portion N1 is called the upstream roll gap region Un.

[0054] When a positive voltage is applied to the primary transfer roller 6, the upstream region of the roll gap also exhibits a positive polarity because the potential of the inner surface layer 10b is almost similar to the voltage applied to the primary transfer roller 6. The toner image formed by the surface of the photosensitive drum 1 (hereinafter referred to as the image forming region) is charged with the bright portion potential VI, and the toner is also charged with a negative polarity. Therefore, a potential difference appears between the base layer 10a and the surface of the photosensitive drum 1 in the upstream region Un of the roll gap. In addition, as the distance between the surface of the photosensitive drum 1 and the base layer 10a increases from... Figure 4 The gap between the contact point Cd and the primary transfer rollers narrows at the initial contact point Cd. The positive discharge current flowing from the base layer 10a to the photosensitive drum 1 in this region exceeds the discharge threshold according to Paschen's law. When the positive discharge current flows out, the toner on the photosensitive drum 1 is transferred to the intermediate transfer belt 10 via the discharge current. This situation is referred to below as pre-transfer.

[0055] (Evaluation of poor first-pass transfer and pre-transfer)

[0056] Table 1 shows the results of evaluating primary transfer defects and pre-transfer images when the primary transfer voltage in the yellow image forming section a is varied according to the grade and the amount of printing sheet. The results are similar to those for magenta, cyan, and black.

[0057] [Table 1]

[0058]

[0059] Table 1 shows the initial transfer voltage (V) in the first column, the highlight potential VL (-V) in the second column, and the initial transfer contrast (V) in the third column. The fourth column of Table 1 shows the number of printing sheets (print count) and the grades of transfer defects and pre-transfers (A, B, C, and D) when printing 0, 1000, 2000, 3000, 4000, and 5000 sheets. In Example 1, the toner usage is indicated by the number of printing sheets.

[0060] First, the definitions of different levels of poor transfer will be described. Level A is a state where a single transfer defect can only be slightly detected, even on the photosensitive drum 1. Level B is a state where toner residue remains on the photosensitive drum 1 after passing through the transfer roller gap section N1 and cannot be transferred in one pass. Level C is a state where defects in the image caused by a single transfer defect can be slightly detected. Level D is a state where defects in the image caused by a single transfer defect can be clearly detected.

[0061] Next, the definition of pre-transfer will be described. Level A is a state where pre-transfer occurs almost entirely. Level B is a state where toner dispersion can be observed when the toner printed on the sheet is examined under a microscope. Level C is a state where slight concentration differences can be identified in the image. Level D is a state where concentration differences can be clearly identified in the image.

[0062] (Evaluation results of a single poor transfer)

[0063] Next, Table 1 will be used to describe the evaluation results of a single transfer defect. A single transfer defect is a defective image that occurs because the toner is not transferred from the photosensitive drum 1 to the intermediate transfer belt, and it has the characteristic of appearing as if the toner is missing at different locations on the image. Moreover, a single transfer defect has the characteristic of the defective image suddenly becoming prominent when the voltage becomes less than a predetermined threshold. A solid image is formed as the image to be evaluated.

[0064] (Inspection results of one transfer failure when 0 sheets were printed)

[0065] In Table 1, when printing with a sheet quantity close to zero, the result is Grade A when printing with a primary transfer voltage of 350V or higher. The result is Grade B when printing with a primary transfer voltage of 300V. The result is Grade D when printing with a primary transfer voltage of 250V or lower.

[0066] (Inspection results of a single poor transfer when printing 1000 copies)

[0067] When printing close to 1000 sheets, the result is Grade A when printing with a primary transfer voltage of 300V or higher. The result is Grade B when printing with primary transfer voltages of 150V, 200V, and 250V. The result is Grade D when printing with a primary transfer voltage of 100V or lower.

[0068] (Inspection results of a single transfer failure when printing 2000 copies)

[0069] When printing approximately 2000 sheets, the result is Grade A when printing with a primary transfer voltage of 250V or higher. The result is Grade B when printing with a primary transfer voltage of 150V and 200V. The result is Grade D when printing with a primary transfer voltage of 100V or lower.

[0070] (Inspection results of a single transfer failure when printing 3000 copies)

[0071] When printing approximately 3000 sheets, the result is Grade A when printing with a primary transfer voltage of 200V or higher. The result is Grade B when printing with a primary transfer voltage of 150V. The result is Grade D when printing with a primary transfer voltage of 100V or lower.

[0072] (Inspection results of a single transfer failure when printing 4000 copies)

[0073] When printing on approximately 4000 sheets, a grade A result is achieved when printing with a primary transfer voltage of 200V or higher. A grade B result is achieved when printing with primary transfer voltages of 100V and 150V.

[0074] (Inspection results of a single transfer failure when printing 5000 copies)

[0075] When printing at a rate of approximately 5000 sheets, a grade A result is achieved when printing with a primary transfer voltage of 150V or higher. A grade B result is achieved when printing with a primary transfer voltage of 100V or lower.

[0076] The results in Table 1 show that the first transfer voltage at which a transfer defect occurs tends to decrease as the number of printed sheets increases. Even with a first transfer voltage of 100V, no transfer defects were observed in the images when printing nearly 5000 sheets.

[0077] (Evaluation results of pre-transfer printing)

[0078] Next, the tendency of pre-transfer will be described. Pre-transfer is a defective image that appears by transferring the toner on the photosensitive drum 1 to the intermediate transfer belt 10 in the upstream area Un of the roll gap, and is also a defective image with density differences due to the dispersion of dots in the image position. A 50% halftone image is used as the image to be evaluated.

[0079] (Pre-transfer check results when 0 sheets were printed)

[0080] In Table 1, when printing with a sheet quantity close to zero, the result is Grade A when printing with a single transfer voltage of 350V or less. The result is Grade B when printing with a single transfer voltage of 400V. The result is Grade C when printing with a single transfer voltage of 450V or greater.

[0081] (Inspection results of a single poor transfer when printing 1000 copies)

[0082] Next, when printing approximately 1000 sheets, the results were grade A when printing with a primary transfer voltage of 300V or less. Grade B was achieved when printing with a primary transfer voltage of 350V. Grade C was achieved when printing with primary transfer voltages of 400V and 450V. Grade D was achieved when printing with a primary transfer voltage of 500V or greater.

[0083] (Inspection results of a single transfer failure when printing 2000 copies)

[0084] Next, when printing approximately 2000 sheets, the results were grade A when printing with a primary transfer voltage of 250V or less. The result was grade B when printing with a primary transfer voltage of 300V. The results were grade C when printing with primary transfer voltages of 350V, 400V, and 450V. The result was grade D when printing with a primary transfer voltage of 500V or greater.

[0085] (Inspection results of a single transfer failure when printing 3000 copies)

[0086] Next, with printing quantities approaching 3000 sheets, the results were grade A when printing with a primary transfer voltage of 200V or less. Grade B was achieved when printing with primary transfer voltages of 250V and 300V. Grade C was achieved when printing with primary transfer voltages of 350V, 400V, and 450V. Grade D was achieved when printing with a primary transfer voltage of 500V or greater.

[0087] (Inspection results of a single transfer failure when printing 4000 copies)

[0088] Next, with approximately 4000 sheets printed, the results were grade A when printing with a primary transfer voltage of 200V or less. Grade B was achieved when printing with primary transfer voltages of 250V and 300V. Grade C was achieved when printing with primary transfer voltages of 350V and 400V. Grade D was achieved when printing with primary transfer voltages of 450V or greater.

[0089] (Inspection results of a single transfer failure when printing 5000 copies)

[0090] Next, with printing on approximately 5000 sheets, the results were grade A when printing with a primary transfer voltage of 150V or less. Grade B was achieved when printing with primary transfer voltages of 200V, 250V, and 300V. Grade C was achieved when printing with primary transfer voltages of 350V and 400V. Grade D was achieved when printing with a primary transfer voltage of 450V or greater. These results show that the primary transfer voltage at which pre-transfer occurs tends to decrease as the number of sheets printed increases.

[0091] (The relationship between the quantity of printing sheets and the charge on the toner)

[0092] Next, we will describe the reasons why the primary transfer defects and the reduction of the primary transfer voltage during pre-transfer occur as the number of printing sheets increases. Figure 5 Part (a) is a graph showing the correlation between the amount of printed sheet and the charge of the negative polarity toner. Figure 5 In section (a), the vertical axis shows the negative charge of the toner formed on the photosensitive drum 1, and the horizontal axis shows the quantity of the printing sheet. For example... Figure 5 As shown in section (a), the charge of the toner (hereinafter referred to as toner charge) tends to decrease as the number of printing sheets increases. Regarding the toner charge, the slope of the decrease in toner charge is shown to be steeper when the number of printing sheets is low, and becomes gentler as the number of printing sheets increases. Some of the reasons for the decrease in toner charge in Example 1 include: the toner being clamped between the developing roller 42a and the supply roller, or the voltage control agent controlling the toner charge being excessively consumed due to friction between the toner and the adjusting scraper when the printing tensor is initially low.

[0093] (The relationship between the number of printed sheets and the voltage of a single transfer)

[0094] Next, the relationship between the amount of printing sheet and the primary transfer voltage will be described. As shown in Table 1, when the primary transfer voltage decreases, primary transfer defects tend to increase. This is because when the primary transfer current decreases, the amount of toner moving from the photosensitive drum 1 to the intermediate transfer belt 10 in the primary transfer roller gap section N1 decreases. In other words, a higher primary transfer voltage is required because the more charge the toner carries, the greater the amount of toner moving current required. Figure 5 As described in part (a), a higher primary transfer voltage is required because, in Example 1, the negative polarity toner carries a large charge when the number of printed sheets is small. On the other hand, it is preferable to reduce the primary transfer voltage because the required current decreases as the toner charge decreases with the increase in the number of printed sheets.

[0095] The relationship between toner charge and pre-transfer will be described next. In the image forming apparatus of Example 1, because the base layer 10a of the intermediate transfer belt is charged with positive polarity, a discharge current is also generated in the upstream region Un of the roll gap. As the discharge current flows through the toner image on the photosensitive drum 1, the negative polarity of the toner charge decreases or reverses to positive polarity. Therefore, the phenomenon that a portion of the toner image on the photosensitive drum 1 is transferred to the upstream region Un of the roll gap on the intermediate transfer belt 10 is pre-transfer. As the negative charge of the toner image on the photosensitive drum 1 increases, if the discharge current passes through and pre-transfer occurs almost no more, the negative charge remains at a high ratio. This characteristic means that when the amount of printed sheet is low and the negative charge is high, the primary transfer voltage resulting in pre-transfer is high.

[0096] As mentioned above, the primary transfer voltage that causes poor primary transfer and pre-transfer depends on the negative charge of the toner. Given the trends in Table 1, a control method is needed to balance the primary transfer voltage without causing these image defects. Specifically, the primary transfer voltage is controlled to decrease in proportion to the amount of printing sheet.

[0097] (Control the primary transfer voltage)

[0098] Figure 5Part (b) is a graph reflecting the control method of the primary transfer voltage as found by the results in Table 1, with the number of printing sheets shown on the horizontal axis and the primary transfer voltage (V) shown on the vertical axis. A primary transfer voltage of 350V is selected when the number of printing sheets is low and the sheets are brand new, while a primary transfer voltage of 200V is selected when the number of printing sheets is 3000. Furthermore, between the new state and 3000 sheets, the primary transfer voltage is controlled to decrease linearly with the number of printing sheets, corresponding to 200V at 3000 sheets. Additionally, a primary transfer voltage of 200V is set as a predetermined value after 3000 sheets. As described above, in Embodiment 1, the CPU 276 controls the primary transfer voltage to decrease linearly with the number of printing sheets from an initial value (e.g., 350V) until the number of printing sheets reaches a predetermined number (e.g., 3000 sheets), the initial value being the primary transfer voltage when the number of printing sheets is 0. After the number of printed sheets reaches a predetermined quantity (e.g., 3000 sheets), the CPU 276 maintains the transfer voltage at a predetermined value.

[0099] exist Figure 5 In the example of part (b), the transfer voltage is controlled to decrease linearly in response to the number of printing sheets until 3000 sheets are printed, and a predetermined value is selected after 3000 sheets are printed. However, in the case of an image forming apparatus where the change in toner charge is different from that in Example 1, appropriate control can be performed in response to its trend. For example, when the toner charge decreases linearly in response to the number of printing sheets, the transfer voltage can decrease continuously at a constant and determined slope in response to the number of printing sheets without providing a point of change (the point of change at 3000 sheets), such as... Figure 5 The point of change in part (b).

[0100] It should be noted that, although in Figure 5 In section (b), the transfer voltage is selected in relation to the amount of printing sheet. However, the transfer voltage can also be selected relative to other parameters corresponding to changes in toner charge. For example, it is possible to select the transfer voltage in relation to the amount of toner consumed (hereinafter referred to as toner consumption) as the toner dosage consumed during printing is counted. In other words, the toner usage status is indicated by the toner consumption, and the CPU 276 can control the transfer contrast in relation to the toner consumption. Furthermore, in cases where toner degradation (hereinafter referred to as toner degradation) caused by sliding on the developing member becomes dominant as the toner charge decreases, the transfer voltage can be selected using the number of rotations of the developing member as a parameter. In other words, the toner usage status can be indicated by the cumulative number of rotations of the developing roller 42, and the CPU 276 can control the transfer contrast in relation to the cumulative number of rotations.

[0101] Furthermore, the value of multiplying the rotation number of the developing member by the amount of toner consumed is defined as the toner degradation index, and a primary transfer voltage corresponding to the toner degradation index can be selected. Moreover, when the outer diameter of the photosensitive drum 1 changes, the distance between the surface of the photosensitive drum 1 in the upstream region Un of the roller gap and the surface of the base layer 10a of the intermediate transfer belt 10 changes. Therefore, the appropriate value of the primary transfer voltage changes correspondingly to the characteristics of the image forming apparatus, because the threshold for the discharge current changes and the primary transfer voltage, which causes a concentration difference due to pre-transfer, also changes.

[0102] Next, we will describe how to select an optimal primary transfer voltage for all image forming sections a, b, c, and d. In Example 1, the same primary transfer voltage is applied to all primary transfer rollers 6a, 6b, 6c, and 6d; therefore, a primary transfer voltage cannot be selected for each image forming section a, b, c, and d. Therefore, considering the expected amount of printing sheet from each image forming section a, b, c, and d, the anticipated primary transfer defects, and the primary transfer voltage occurring during pre-transfer, a primary transfer voltage needs to be selected based on a balance of these factors.

[0103] As described above, image defects tend to become more prominent when the primary transfer voltage is less than the threshold for primary transfer defects. Therefore, in Example 1, primary transfer control is performed on the image forming section, which has the smallest number of printing sheets, to prevent primary transfer defects from occurring. To perform this control, the process begins with changing any color toner cartridge, based on... Figure 5 Part (b) performs a transfer voltage control corresponding to the number of printing sheets.

[0104] (The process of determining the primary transfer voltage)

[0105] Figure 6 It's like a process Figure 1 A diagram illustrating the process of determining the transfer voltage is provided. Separately, the CPU 276 controls the transfer voltage at... Figure 6 The left side shows the box replacement operation, and the right side shows it. (See diagram below.) Figure 5 As described in section (b), in step (hereinafter referred to as S)1, CPU 276 sets the initial transfer voltage to a value of 350V. In S2, CPU 276 performs the printing operation. It should be noted that CPU 276 is considered to include a counter (not shown in the figure) that counts the number of printed sheets, and counts the total number of printed sheets since the initial transfer voltage was set to 350V in S1.

[0106] In S3, a primary transfer voltage corresponding to the number of printing sheets is set. For each defined number of printing sheets, the primary transfer voltage is set to a target voltage, and the relationship between the number of printing sheets and the primary transfer voltage is a linear function until the predetermined number of printing sheets is reached. Figure 5 In part (b), the target voltage is 350V for 0 sheets and 200V after 3000 sheets. When the number of sheets printed in S3 is between 0 and 3000, the transfer voltage is set as a linear interpolation between 0 sheets and 3000 sheets (350V and 200V).

[0107] Moreover, regardless Figure 6 The status of the single-transfer voltage control operation on the left side, and the replacement of any color box at any time shown in S4. With the execution of S4, CPU 276 executes... Figure 6 In the S1 process on the left, the transfer voltage is set to 350V. As described above, the transfer voltage returns to the initial value of 350V and the counter that counts the number of printed sheets is initialized to 0 corresponding to the replacement of the new cartridge.

[0108] (Transition of the first transfer voltage in Example 1)

[0109] Figure 7 Based on Figure 6 The flowchart illustrates an example of primary transfer voltage control, and shows a control method for primary transfer voltage control relative to the number of printing sheets in the main component of the image forming apparatus 100. Figure 7 In the image forming apparatus 100, the horizontal axis shows the number of printing sheets of the main component (number of printing sheets of the main component), and the vertical axis shows... Figure 7 The primary transfer voltage (V) is determined by the primary transfer voltage control. Figure 7 Points Ta, Tb, Tc, and Td in the diagram represent the timing for changing the toner cartridges. The cyan cartridge (third image forming part c) is changed at point Ta, the black cartridge (fourth image forming part d) is changed at point Tb, the yellow cartridge (first image forming part a) is changed at point Td, and the magenta cartridge (fourth image forming part e) is changed at point Te.

[0110] When the main component prints zero sheets, all color cartridges are new and all color toners have the highest charge. Therefore, a primary transfer voltage of 350V is chosen as the initial value. This is consistent with... Figure 6 This corresponds to the operation in S1. As the number of sheets printed by the main component increases, the applied primary transfer voltage decreases as the toner charge decreases. This is consistent with... Figure 6The operations in S2, S3, and S4 correspond to these. At point Ta, as the cyan box is replaced, the charge on the cyan toner increases. If the same primary transfer voltage as before replacing the cyan box is selected in this state, there is a risk of a poor primary transfer of cyan. Therefore, a primary transfer voltage of 350V (returning to the initial value) is selected to prevent the poor primary transfer that occurred in Example 1. This is consistent with... Figure 6 The operations in S4 to S1 correspond.

[0111] Then, at point Ta, which serves as the starting point, a lower primary transfer voltage is selected and applied, corresponding to the number of sheets printed by the main component. At point Tb, the timing for changing the black box, a primary transfer voltage of 350V is selected again to prevent primary transfer defects. Additionally, at point Tb, which also serves as the starting point, a lower primary transfer voltage is selected and applied, corresponding to the number of sheets printed by the main component; at point Tc, the primary transfer voltage is 200V. Because... Figure 5 In section (b), the minimum single transfer voltage selected is 200V, therefore the single transfer voltage selected from point Tc to point Td is fixed at 200V. Point Td is the timing for changing the yellow box, and then the single transfer voltage is 350V again. Then, until point Te, the timing for changing the magenta box, the selected single transfer voltage is reduced according to the number of sheets printed by the main component.

[0112] In the following description, the CPU 276 selects 350V for the primary transfer voltage when changing any color cartridge at any time, and selects a lower primary transfer voltage corresponding to the number of sheets printed by the main component starting from the cartridge change timing. By performing these controls, it is possible to select a primary transfer voltage that suppresses poor primary transfer and pre-transfer, regardless of the number of each color or each type of sheet. As described above, with cartridge change, the CPU 276 restores the primary transfer voltage to its initial value, regardless of the print quantity, and controls the primary transfer voltage corresponding to the number of sheets printed after restoring the initial value.

[0113] exist Figure 7 In the example, although a 350V primary transfer voltage is selected for timing the replacement of any toner cartridge in yellow, magenta, cyan, and black, it's possible to switch the primary transfer voltage for a different color, considering the impact on image quality. For instance, yellow images are less prone to showing defects even if the primary transfer is flawed or the pre-transfer is at the same level as other colors. Therefore, it's possible to execute the timing for timing the replacement of any toner cartridge in magenta, cyan, and black other than yellow, as follows: Figure 7 The transfer voltage is controlled in one step.

[0114] In Example 1, in an image forming apparatus using an intermediate transfer belt including an inner surface conductive layer, a method for suppressing primary transfer defects and pre-transfer caused by discharge current in the upstream region of the roll gap has been described above. To supply excellent primary transfer images, Example 1 describes a control method for applying a lower primary transfer voltage when the toner charge is low. Furthermore, a control method has been described above that selects the primary transfer voltage corresponding to the toner cartridge replacement timing, taking into account the characteristic that all image forming sections have the same primary transfer voltage.

[0115] [Other structures of the image forming apparatus]

[0116] like Figure 1 As shown, although the image forming apparatus 100 in Embodiment 1 is described as including a plurality of photosensitive drums 1 in a series system, the control method in the embodiment is applicable not only to systems with a series connection but also to systems with a series connection. Figure 8 The image forming apparatus of the rotating system shown is effective. Figure 8 In the process, the control section 1274 controls the transfer contrast in accordance with the usage status of the toner.

[0117] Figure 8 The image forming apparatus includes a single photosensitive drum 1100 rotatable in direction R1. A rotating member 400 can switch the developing element 420 in contact with the photosensitive drum 1100 by rotation. By rotating the rotating member 400 in direction R0, one of the developing elements 420a, 420b, 420c, and 420d, consisting of yellow (a), magenta (b), cyan (c), and black (d), contacts the photosensitive drum 1100. Each developing element 420a, 420b, 420c, or 420d rotates by contact with the photosensitive drum 1100. In the following text, the following reference letters indicating colors are sometimes omitted except to explain specific colors. An image of each color is transferred to an intermediate transfer belt 110 by forming a toner image on the photosensitive drum 1100. Figure 8 In the image forming apparatus, besides Figure 1 Apart from the inner surface layer 110b, which serves as a conductive layer, the dimensions of the components used in the image forming apparatus and the intermediate transfer belt 110 moving in the direction R2 are the same.

[0118] The toner image formed on the photosensitive drum 1100 (to which the primary transfer roller 260 applies a positive voltage) is transferred to the intermediate transfer belt 110. The toner image is conveyed on the intermediate transfer belt 110 and again reaches the primary transfer roller gap section for... Figure 8A multicolor image is formed in the image forming apparatus. At the timing when the image from the previous transfer reaches the gap of the primary transfer rollers, the rotating member 400 rotates approximately 90° in direction R0, and the next color is developed to perform a transfer while overlapping the intermediate transfer belt 110. It should be noted that during repeated primary transfers, the secondary transfer roller 210 and the toner charging roller 160 are separated from the intermediate transfer belt 110. When a four-color toner image is formed on the intermediate transfer belt 110, the secondary transfer roller 210 contacts the intermediate transfer belt 110, applies a predetermined voltage, and the multicolor toner image is transferred a second time onto the recording material P.

[0119] Because the discharge current occurs in the upstream region of the roll gap and the pre-transfer printing also occurs... Figure 8 In an image forming apparatus, it is therefore necessary to select a primary transfer voltage to obtain an excellent primary transfer image that balances poor primary transfer performance. Furthermore, since the toner charge decreases as the amount of printing sheet increases, the appropriate primary transfer voltage for obtaining an excellent primary transfer image needs to be changed. In an image forming apparatus with a rotating system, it is possible to select an appropriate primary transfer voltage corresponding to the timing of the next color being developed as the rotating element 400 rotates.

[0120] It should be noted that the image forming apparatus with a rotating system includes developing units 40a, 40b, 40c, and 40d for each color, a charging roller 200, a drum cleaning device 150, a drive roller 120, a pair of secondary transfer rollers 130, a primary transfer power supply 230, and a secondary transfer power supply 220. The rotating component 400 includes multiple developing units, each developing unit comprising a developing member 420 and a toner-containing container, and... Figure 8 In the image forming apparatus, each control is performed by the control section 1274. Furthermore, each developing unit 40a, 40b, 40c, and 40d can be detached from and replaced from the main assembly of the image forming apparatus. In the following text, developing units 40a, 40b, 40c, and 40d are sometimes referred to as cartridges.

[0121] (The process of determining the transfer voltage)

[0122] Figure 9 Part (a) is a flowchart-like diagram showing when Figure 8 The process of determining the primary transfer voltage for each developing color when the image forming apparatus forms a multicolor image in the order of Y, M, C, and K. The control unit 1274 can also control the primary transfer contrast by controlling the primary transfer voltage in the image forming apparatus with a rotation system. The toner usage status is indicated by the amount of printing sheet, and the control unit 1274 controls the primary transfer voltage to decrease as the amount of printing sheet increases. For example, as... Figure 5As shown, the control unit 1274 can control the primary transfer voltage to decrease linearly with the number of printing sheets, from a threshold voltage when the number of printing sheets is 0 until the number of printing sheets reaches a predetermined number. After the number of printing sheets reaches the predetermined number, the control unit 1274 can maintain the primary transfer voltage at a predetermined value. It should be noted that the control unit 1274 controls the primary transfer voltage each time the developing unit 40 switches.

[0123] exist Figure 9 In part (a), the primary transfer voltage control is shown on the left and the operation of the rotating member 400 is shown on the right. In S21, the control unit 1274 controls the Y developing unit 40a to move to the image forming position by rotating the rotating member 400. Again, the image forming position is the position where the Y developing unit 40 contacts the photosensitive drum 1100. In S22, the control unit 1274 sets the primary transfer voltage for Y. Next, in S23, when the formation of image Y is finished, the control unit 1274 controls the M developing unit 40b to move to the image forming position by rotating the rotating member 400. In S24, the control unit 1274 sets the primary transfer voltage for M.

[0124] Next, in S25, when image M is formed, the control unit 1274 controls the C developing unit 40c to move to the image forming position by rotating the rotating member 400. In S26, the control unit 1274 sets the primary transfer voltage for C. Next, in S27, when image C is formed, the control unit 1274 controls the K developing unit 40d to move to the image forming position by rotating the rotating member 400. In S28, the control unit 1274 sets the primary transfer voltage for K. When image K is formed, the process returns to S21, and the control unit 1274 again controls the Y developing unit 40a to move to the image forming position by rotating the rotating member 400 to form the next image.

[0125] Figure 9 Part (b) is a flowchart explaining the method for controlling the transfer voltage for each color. That is, Figure 9 Part (b) indicates Figure 9 The processes S22, S24, S26, or S28 in part (a). It is important to note that in... Figure 9 In part (b), although process Y as S22 is used as an example for explanation, the same control is performed in process M as S24, process C as S26, and process K as S28. Furthermore, Figure 9In part (b), the left side shows the primary transfer voltage control, and the right side shows the cartridge replacement operation. In an image forming apparatus with a rotating system, when the developing unit 40 (or cartridge) is replaced, the CPU 276 controls the primary transfer voltage to its initial value regardless of the number of printing sheets, and controls it in accordance with the number of printing sheets after the primary transfer voltage returns to its initial value.

[0126] It is important to note that Figure 9 The processes in S31, S32, S33, and S34 of part (b) are the same as those in S1, S2, S3, and S4. In other words, when the Y developing unit 40a is new, the control unit 1274 sets the primary transfer voltage to 350V as an initial value in S31. As shown in S32 and S33, the control unit 1274 sets the primary transfer voltage to decrease as the amount of printed sheet increases. Figure 9 In the example of part (b), after the primary transfer voltage becomes 200V, the primary transfer voltage does not decrease, but remains at 200V or even continues printing. For example, when the Y cartridge is replaced in S34, the control part 1274 sets the primary transfer voltage to 350V (initial value) and returns to S31, then repeats S32, S33, and S34. As described above, in an image forming apparatus with a rotation system, when the timing of changing the color of the formed image by the rotation of the rotating member 400 is such that the appropriate primary transfer voltage can be selected corresponding to the degree of deterioration of the toner for each color.

[0127] In addition, Figure 8 In image forming apparatuses, when the voltage cannot be switched before image forming timing due to long primary transfer voltage start-up time or excessively fast processing speed, the primary transfer voltage can be controlled as follows. In other words, even image forming apparatuses with rotation systems can be controlled as follows. Figure 6 It is controlled as shown. More specifically, when changing any color cartridge, the transfer voltage can be set accordingly to that cartridge and is set to decrease as the number of printing sheets decreases.

[0128] As described above, according to Embodiment 1, excellent single-pass transfer performance can be obtained even in an image forming apparatus having an intermediate transfer belt including an internal low-resistance layer.

[0129] The primary transfer contrast, which is the difference between the primary transfer voltage and the potential of the surface of the photosensitive drum 1 (hereinafter referred to as surface potential), contributes to the primary transfer performance. In Example 1, a method for obtaining excellent primary transfer performance by controlling the primary transfer voltage was described. In Example 2, regarding primary transfer contrast, as a method to form an appropriate primary transfer contrast by considering the balance between poor primary transfer and pre-transfer, a method of adjusting the surface potential of the photosensitive drum 1 in addition to the primary transfer voltage will be described. The image forming apparatus in Example 2 and... Figure 1 The image forming apparatus is the same as in Example 1, except that the primary transfer voltage control method and the exposure control method for forming the surface potential of the photosensitive drum 1 through the exposure device 3 differ from those in Example 1. In Example 2, the CPU 276 controls the primary transfer contrast by controlling the primary transfer voltage and the surface potential of the photosensitive drum 1.

[0130] [One-time transfer contrast]

[0131] First, we will describe the first transfer contrast using image forming part a as an example. Figure 10 This is a schematic diagram used to explain the relationship between the primary transfer voltage and the surface of the photosensitive drum 1a, and the potential (-V) is shown on the vertical axis. Figure 10 The dark portion potential (Vd) is the surface potential of the photosensitive drum 1 after being charged by the charging roller 2a. Immediately after the photosensitive drum 1a passes through the charging roller 2a with applied voltage, the surface potential of the photosensitive drum 1a is uniformly charged to Vd. Then, the photosensitive drum 1a receives exposure corresponding to the image signal at the exposure position via the exposure device 3a. Therefore, a bright portion potential VL corresponding to the yellow component image in the target multicolor image is formed. Moreover, a developing voltage (Vdc) is applied to the developing roller 42a, and the toner on the developing roller 42a is developed on the surface of the photosensitive drum 1a through the potential difference between the developing voltage Vdc and the bright portion potential VL. Therefore, a toner image is formed on the bright portion potential VL on the surface of the photosensitive drum 1a. The potential difference between the developing voltage Vdc and the bright portion potential VL is the developing contrast.

[0132] In the upstream region Un of the roll gap described in Example 1, a discharge current occurs due to the difference between the bright portion potential VL and the potential of the intermediate transfer belt 10. The potential of the intermediate transfer belt 10 is almost similar to that of the inner surface layer 10b upstream and downstream of the primary transfer roll gap portion N1 relative to the rotation direction of the intermediate transfer belt 10. In Example 2, the absolute value of the difference between the bright portion potential VL and the primary transfer voltage (Vt1), |VL-Vt1|, is defined as the primary transfer contrast. The larger the primary transfer contrast, the more frequently the discharge current appears in the upstream region Un of the roll gap. Example 2 is characterized in that, in addition to the primary transfer voltage, the primary transfer contrast is adjusted by adjusting the bright portion potential VL using the exposure device 3a.

[0133] Figure 11 Part (a) is a graph showing the relationship between the exposure amount of the laser emitted by the exposure device 3a and the surface potential of the photosensitive drum 1a. Figure 11 The horizontal axis in section (a) shows the exposure amount (μJ / cm). 2 The vertical axis shows the surface potential (negative potential) (-V) of the photosensitive drum 1a. Figure 11 As shown in part (a), the absolute value of the surface potential of the photosensitive drum 1a decreases with increasing exposure. However, the change in surface potential of the photosensitive drum 1a relative to the exposure decreases with increasing exposure, and tends to be approximately 0.5 μJ / cm² at 100V. 2 Saturation. Furthermore, when adjusting the transfer contrast once via the surface potential of the photosensitive drum 1a, it is necessary to adjust within a range that satisfies the development contrast. Therefore, the adjustment range is smaller compared to adjusting the transfer voltage once.

[0134] On the other hand, Figure 1 In the image forming apparatus, it is possible to set the exposure amount for each image forming section a, b, c, and d. Therefore, in Embodiment 2, the characteristic is that the exposure amount is adjusted for each image forming section, and an appropriate primary transfer contrast is set for each image forming section, so that an excellent primary transfer voltage is obtained by adjusting the primary transfer voltage after using a basic primary transfer contrast. As an example, a method for setting the primary transfer contrast when the number of printing sheets for Y, M, and C is 0 and the number of printing sheets for K is 5000 will be described below. The method for controlling the primary transfer voltage is the same as in Embodiment 1, and for each color in Table 1, the occurrence level of primary transfer defects and pre-transfers is the same for each number of printing sheets.

[0135] (Evaluation of poor first-pass transfer and pre-transfer)

[0136] Since the number of printing sheets for Y, M, and C is 0, the transfer voltage is set to an initial value of 350V. Figure 6 As shown in Table 2, the levels of first-pass defects or pre-transfers for each color are indicated when the first-pass transfer voltage is set to 350V. Since the highlight potential VL is -150V, the first-pass contrast is 500V (=|-150V-350V|).

[0137] [Table 2]

[0138]

[0139] Table 2 shows the primary transfer voltage (V) in the first column, the highlight potential (-V) in the second column, and the primary transfer contrast (V) in the third column. Table 2 also shows the grade (A, B, C, or D) of a primary transfer defect or pre-transfer when the number of printed sheets in columns Y (fourth), M (fifth), and C (sixth) is 0. The seventh column of Table 2 shows the grade (A, B, C, or D) of a primary transfer defect or pre-transfer when the number of printed sheets in column K is 5000.

[0140] In row 'a' of Table 2, the evaluation results are shown when the highlight potential VL is set to -150V, the same as in Example 1. The primary transfer contrast is 500V. The primary transfer failure and pre-transfer grades for Y, M, and C are both Grade A because the number of print sheets for Y, M, and C is 0 and the primary transfer voltage is an appropriate setting for 0 sheets. On the other hand, regarding K, although the primary transfer failure is Grade A, the pre-transfer is Grade C. This is because the number of print sheets for K is 5000 and the toner charge is reduced due to toner deterioration.

[0141] Row 'b' in the table shows the evaluation results of setting the bright portion potential VL to -100V when the exposure is stronger than in row 'a', and the primary transfer contrast is 450V. For Y, M, and C, the primary transfer failure is grade B, and the pre-transfer is grade C. On the other hand, for K, the primary transfer failure is grade A, the same as in 'a', and the pre-transfer is grade B, better than 'a'. Based on these results, for a primary transfer voltage of 350V, a bright portion potential VL of -150V for Y, M, and C, and a bright portion potential VL of -100V for K, a more suitable primary transfer can be obtained by adjusting the laser exposure.

[0142] In Example 2, the use of toner is also indicated by the number of print sheets. CPU 276 controls the primary transfer voltage to decrease and the exposure to increase as the number of print sheets increases. CPU 276 controls the primary transfer voltage corresponding to the number of print sheets (e.g., 0) in a predetermined cartridge (e.g., Y, M, or C), which is the cartridge with the fewest print sheets among multiple cartridges. For another cartridge (e.g., K), which is different from the predetermined cartridge, CPU 276 controls the exposure corresponding to the number of print sheets (e.g., 5000 sheets) in that other cartridge.

[0143] Figure 11 Part (b) is a graph showing the relationship between the amount of printing sheet and the optimal single-pass transfer contrast. Figure 11In section (b), the horizontal axis shows the number of prints (sheets), and the vertical axis shows the first-pass contrast. As the number of print sheets increases, the optimal first-pass contrast tends to decrease. As described in Example 1, the first-pass voltage is set corresponding to the color cartridge with the minimum number of print sheets. Therefore, the exposure can be set within the range of maximum light intensity to obtain a predetermined first-pass voltage relative to other color cartridges. Figure 11 The first transfer contrast in part (b).

[0144] (The process of determining the transfer voltage and exposure amount)

[0145] Figure 12 It is a diagram that shows the above control process as a flowchart. Figure 12 Is Figure 6 A new line of diagrams for laser exposure control has been added. Therefore, explanations of the processes in S1, S2, and S3 for single-transfer voltage control and S4 for cartridge replacement are omitted. Figure 12 In the flowchart, after determining the transfer voltage in S1 or S3, processes S5, S6, and S7 are executed, and the exposure amount for boxes other than those with the minimum number of printing sheets is determined. More specifically, after S1, proceeding to S2, the CPU 276 also executes process S5 for laser exposure control. Moreover, as it proceeds from S2 to S3 and then back to S2 after S3, the CPU 276 executes process S5.

[0146] In S5, the CPU 276 detects the number of printed sheets at a time when determining the transfer voltage. It's important to note that the CPU 276 is considered to be counting the printed sheets as described above. In S6, the CPU 276 determines the appropriate transfer contrast based on the number of printed sheets detected in S5. For example, based on... Figure 11 Based on the relationship in part (b), CPU 276 can determine the primary transfer contrast. In S6, based on the primary transfer voltage determined in S8 for the appropriate primary transfer contrast, CPU 276 determines the laser exposure to obtain the appropriate bright part potential VL.

[0147] As described above, in Embodiment 2, each image forming portion a, b, c, or d obtains appropriate primary transfer contrast in the same image forming apparatus as in Embodiment 1. In Embodiment 2, a method for adjusting the laser exposure and fine-tuning the bright portion potential VL based on a predetermined primary transfer voltage is described.

[0148] Example 2 describes a trend where the primary transfer contrast has the same tendency for the number of printed sheets in all image forming sections a, b, c, and d. However, when each image forming section a, b, c, or d has a different appropriate primary transfer contrast, the laser exposure can be determined as the bright portion potential VL corresponding to each image forming section. Furthermore, although Example 2 describes a control process for determining the laser exposure after determining the primary transfer voltage, it is not limited to this process; the primary transfer voltage can be determined after determining the laser exposure. Additionally, the description in Example 2 is for... Figure 8 The image forming apparatus with a rotating system shown is effective and is expected to have the same effect as in Embodiment 1, especially when the same primary transfer voltage is applied to each image forming section. Furthermore, when different primary transfer voltages are set for each image forming section, for example, even when there is not a sufficient range for setting the primary transfer voltage, a more appropriate primary transfer contrast can be set by slightly adjusting the laser exposure.

[0149] As described above, according to Embodiment 2, it is also possible to obtain excellent primary transfer performance in an image forming apparatus having an intermediate transfer belt with an inner surface including a low-resistivity layer.

[0150] In Example 3, a method for forming a primary transfer contrast by applying a voltage to a photosensitive drum will be described. Figure 13 This is a cross-sectional schematic diagram showing the structure of the image forming apparatus 300 in Embodiment 3. Figure 1 Compared to the image forming apparatus 100 described herein, the primary transfer rollers 6a, 6b, 6c, and 6d are grounded, and there is no primary transfer power supply 23. Instead, a drum power supply 24, which serves as a negative power supply, is provided and is shared by the photosensitive drums 1a, 1b, 1c, and 1d. The drum power supply 24 acts as a secondary application component, applying voltage to the photosensitive drums 1a, 1b, 1c, and 1d. The drum power supply 24 is connected to apply voltage (hereinafter referred to as drum voltage) to the carrier tube of each photosensitive drum 1a, 1b, 1c, or 1d. In Embodiment 3, the CPU 276 is controlled by the drum power supply 24 to apply voltage to the photosensitive drum 1 and controls the primary transfer contrast by controlling the surface potential of the photosensitive drum 1. The process other than forming the primary transfer contrast by the drum voltage is the same as in Embodiments 1 and 2. Figure 1 In structures identical to those described herein, the same reference numerals are given and descriptions are omitted. The following description, using image forming part a as an example, illustrates the single-transfer contrast achieved by applying a drum voltage.

[0151] [One-time transfer contrast]

[0152] Figure 14 This is a schematic diagram illustrating the relationship between the primary transfer potential and the surface potential of the photosensitive drum 1a. Figure 14 The diagram illustrates the formation of the drum base potential Vdr obtained by applying a drum voltage. A net dark portion potential Vd' or net bright portion potential VL' is formed by superimposing the surface potential of the photosensitive drum 1a onto the drum base potential Vdr. Both the net dark portion potential Vd' and the net bright portion potential VL' are the sum of the drum base potential Vdr and the dark portion potential Vd or bright portion potential VL when the drum base potential Vdr is 0V. Furthermore, the net developing potential Vdc' is the sum of the drum base potential Vdr and the developing potential Vdc when the drum base potential Vdr is 0V. In Example 3, since the primary transfer roller 6a is grounded, the primary transfer potential is 0V.

[0153] (Evaluation of poor first-pass transfer and pre-transfer)

[0154] In Example 3, the toner usage is also represented by the number of printing sheets. The CPU276 controls the surface potential of the photosensitive drum 1a to decrease as the number of printing sheets increases. Table 3 shows the evaluation results of primary transfer defects and pre-transfers, which are changed by adjusting the drum voltage for each number of printing sheets. Table 3 shows the evaluation results under the condition that the bright part potential VL obtained by laser exposure is fixed at -150V and the net bright part potential VL' is changed by adjusting the drum potential Vdr. Since the primary transfer potential is 0V, the absolute value of the net bright part potential VL' is the primary transfer contrast. Figure 3 The same evaluation results of the transfer contrast in the middle are as follows: Figure 1 same.

[0155] [Table 3]

[0156]

[0157] Table 3 shows the primary transfer voltage (V) in the first column, the drum potential (-V) in the second column, the net bright portion potential VL' (-V) in the third column, and the primary transfer contrast (V) in the fourth column. The fifth column of Table 1 shows the number of sheets printed (print count) and the grades of poor transfer and pre-transfer (A, B, C, and D) when printing 0, 1000, 2000, 3000, 4000, and 5000 sheets.

[0158] (Evaluation results of a single poor transfer)

[0159] Next, Table 3 will describe the results of a single poor transfer.

[0160] (Inspection results of one transfer failure when 0 sheets were printed)

[0161] In Table 3, when printing with almost zero sheet material, the result is Grade A when printing with a drum potential of 350V or higher. The result is Grade B when printing with a drum potential of 300V. The result is Grade D when printing with a drum potential of 250V or lower.

[0162] (Inspection results of a single poor transfer when printing 1000 copies)

[0163] When printing close to 1000 sheets, the result is Grade A when printing with a drum potential of 300V or higher. The result is Grade B when printing with drum potentials of 150V, 200V, and 250V. The result is Grade D when printing with a drum potential of 100V.

[0164] (Inspection results of a single transfer failure when printing 2000 copies)

[0165] When printing approximately 2000 sheets, the result is Grade A when printing with a drum potential of 250V or higher. The result is Grade B when printing with drum potentials of 150V and 200V. The result is Grade D when printing with a drum potential of 100V.

[0166] (Inspection results of a single transfer failure when printing 3000 copies)

[0167] When printing approximately 3000 sheets, the result is Grade A when printing with a drum voltage of 200V or higher. The result is Grade B when printing with a drum voltage of 150V. The result is Grade D when printing with a drum voltage of 100V.

[0168] (Inspection results of a single transfer failure when printing 4000 copies)

[0169] When printing on approximately 4000 sheets using a primary transfer voltage of 200V or higher, the result is Grade A. When printing with primary transfer voltages of 100V and 150V, the result is Grade B.

[0170] (Inspection results of a single transfer failure when printing 5000 copies)

[0171] When printing at a rate of approximately 5000 sheets, printing with a drum voltage of 150V or higher yields a grade A result. Printing with a drum voltage of 100V yields a grade B result.

[0172] The results in Table 3 show that as the number of printed sheets increases, the absolute value of the drum potential at which a single transfer defect occurs tends to decrease. Even when printing with a print run of nearly 5000 sheets, and the absolute value of the drum potential was 100V, no transfer defects were observed in the images.

[0173] (Evaluation results of pre-transfer printing)

[0174] Next, we will describe the trends in pre-transfer printing.

[0175] (Pre-transfer check results when 0 sheets were printed)

[0176] In Table 3, when printing with almost zero sheet material, the result is Grade A when printing with a drum potential of 350V or less. The result is Grade B when printing with a drum potential of 400V. The result is Grade C when printing with a drum potential of 450V or greater.

[0177] (Pre-transfer inspection results when printing 1000 copies)

[0178] Next, when printing approximately 1000 sheets, the results are as follows: Printing with a drum voltage of 300V or less yields Grade A; printing with a drum voltage of 350V yields Grade B; printing with drum voltages of 400V and 450V yields Grade C; and printing with a drum voltage of 500V or greater yields Grade D.

[0179] (Pre-transfer inspection results when printing 2000 copies)

[0180] Next, with printing quantities approaching 2000 sheets, the results were grade A when printing with a drum potential of 250V or less. Grade B was achieved when printing with a drum potential of 300V. Grade C was achieved when printing with drum potentials of 350V, 400V, and 450V. Grade D was achieved when printing with a drum potential of 500V or greater.

[0181] (Pre-transfer inspection results when printing 3000 copies)

[0182] Next, with printing quantities approaching 3000 sheets, the results were grade A when printing with a drum potential of 200V or less. Grade B was achieved when printing with drum potentials of 250V and 300V. Grade C was achieved when printing with drum potentials of 350V, 400V, and 450V. Grade D was achieved when printing with a drum potential of 500V or greater.

[0183] (Pre-transfer inspection results when printing 4000 copies)

[0184] Next, with printing quantities approaching 4000 sheets, the results were grade A when printing with a drum potential of 200V or less. Grade B was achieved when printing with drum potentials of 250V and 300V. Grade C was achieved when printing with drum potentials of 350V and 400V. Grade D was achieved when printing with a drum potential of 450V or greater.

[0185] (Pre-transfer inspection results when printing 5000 copies)

[0186] Next, with printing quantities approaching 5000 sheets, the results were grade A when printing with a drum potential of 150V or less. Grade B was achieved when printing with drum potentials of 200V, 250V, and 300V. Grade C was achieved when printing with drum potentials of 350V and 400V. Grade D was achieved when printing with a drum potential of 450V or greater.

[0187] The results show that as the amount of printing sheet increases, the absolute value of the drum potential during pre-transfer tends to decrease.

[0188] (The process of determining the primary transfer voltage and drum voltage)

[0189] The process for determining the primary transfer voltage and drum voltage in Example 3 can be referred to Figure 12 .exist Figure 12 In the image, the laser exposure control shown on the left is called drum potential control. Additionally, the CPU276 can be based on... Figure 11 In part (b), after obtaining the first transfer contrast corresponding to the amount of printing sheet in S8, the drum potential Vdr is determined in S9 to be the first transfer contrast obtained in S8. Furthermore, the CPU 276 can control the drum power supply 24 to apply the drum voltage.

[0190] In Example 3, although Figure 9 The image forming apparatus 300 with a series system described herein describes a method for adjusting the drum voltage as an adjustment means for primary transfer contrast, but the same adjustment may be performed in a rotating system. Furthermore, although the primary transfer voltage is described as being grounded in Embodiment 3, grounding is not always necessary. Additionally, the drum voltage may be adjusted to generate a fixed voltage by, for example, connecting a Zener diode. Moreover, both the primary transfer voltage and the drum voltage may be used to adjust the primary transfer contrast.

[0191] As described above, according to Embodiment 3, it is also possible to obtain excellent primary transfer performance in an image forming apparatus having an intermediate transfer belt with an inner surface including a low-resistivity layer.

[0192] According to the present invention, it is also possible to obtain excellent primary transfer performance in an image forming apparatus having an intermediate transfer belt having an inner surface including a low-resistivity layer.

[0193] While the invention has been described with reference to exemplary embodiments, it should be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the appended claims should be given the broadest interpretation to cover all such modifications and equivalent structures and functions.

Claims

1. An image forming apparatus for forming an image on a recording material, characterized in that, The image forming apparatus includes: Photosensitive components; The charging component is configured to charge the photosensitive component; The exposure unit is configured to form an electrostatic latent image by exposing a photosensitive component according to an image signal; The developing component is configured to form a toner image by developing an electrostatic latent image with toner; The intermediate transfer member has a first conductive layer and a second conductive layer with a lower resistance value than the first layer, and the toner image is transferred to the intermediate transfer member in the gap between the intermediate transfer member and the photosensitive member. The voltage application section is configured to apply a transfer voltage to the intermediate transfer member; and The control section is configured to control the primary transfer contrast, which is the difference between the transfer voltage applied by the voltage application section in the roll gap section and the potential of the portion exposed on the photosensitive element by the exposure unit. Specifically, by applying a transfer voltage from the voltage application section to the intermediate transfer member, the control section transfers the toner image from the photosensitive member to the intermediate transfer member by causing current to flow in the circumferential direction. Specifically, by applying a transfer voltage, a potential difference capable of inducing discharge is formed between the photosensitive component and the intermediate transfer component in the upstream region upstream of the upstream end of the gutter portion, along the moving direction of the surface of the intermediate transfer component. The control section controls the transfer voltage to control the primary transfer contrast based on information about the toner usage status related to the quantity of the printing sheet containing the recording material. The control section controls the transfer voltage to become lower as the number of printing sheets increases.

2. The image forming apparatus according to claim 1, wherein the control unit controls the transfer voltage to decrease linearly from an initial value when the number of printing sheets is zero as the number of printing sheets increases, until the number of printing sheets becomes a predetermined number, and maintains the transfer voltage at a constant value after the number of printing sheets reaches the predetermined number.

3. The image forming apparatus of claim 2, further comprising a plurality of replaceable cartridges, each cartridge including a receiving portion configured to receive toner and at least a photosensitive element and a developing element. in, When the cartridge is replaced, the control unit restores the transfer voltage to its initial value regardless of the number of printed sheets, and then controls the transfer voltage based on the number of printed sheets after restoring the number of printed sheets.

4. The image forming apparatus according to claim 1, wherein the control section controls the primary transfer contrast by controlling the surface potential of the photosensitive element.

5. The image forming apparatus according to claim 4, wherein the control section controls the surface potential of the photosensitive element by controlling the amount of exposure of the surface of the photosensitive element by the exposure unit.

6. The image forming apparatus according to claim 5, wherein the control section increases the exposure as the number of printing sheets increases.

7. The image forming apparatus of claim 6, further comprising a plurality of replaceable cartridges, each cartridge including a receiving portion configured to receive toner and at least a photosensitive element and a developing element. The control unit controls the transfer voltage based on the number of printing sheets in the first box, which has the smallest number of printing sheets among the plurality of boxes, and controls the exposure of the second box based on the number of printing sheets in the second box, the number of printing sheets in the second box being different from the number of printing sheets in the first box.

8. The image forming apparatus according to claim 1, wherein information regarding the usage status of the toner is represented by the cumulative revolutions of the developing member, and The control section controls the contrast of a single transfer based on the cumulative number of revolutions.

9. The image forming apparatus according to claim 1, wherein information on the usage status of the toner is represented by the amount of toner consumed, and The control section controls the contrast of a single transfer based on the amount of toner consumed.

10. An image forming apparatus for forming an image on a recording material, characterized in that, The image forming apparatus includes: Photosensitive components; The charging component is configured to charge the photosensitive component; The exposure unit is configured to form an electrostatic latent image by exposing a photosensitive element according to an image signal. The rotating component is provided with multiple developing devices, each developing device including a developing member and a receiving portion. The developing member is configured to form a toner image by developing an electrostatic latent image with toner through contact with a photosensitive member. The receiving portion is configured to contain toner, and the rotating component is configured to switch the developing member in contact with the photosensitive member by rotation. The intermediate transfer member has a first conductive layer and a second conductive layer with a lower resistance value than the first layer, and the toner image is transferred to the intermediate transfer member in the gap between the intermediate transfer member and the photosensitive member. The voltage application section is configured to apply a transfer voltage to the intermediate transfer member; and The control section is configured to control the primary transfer contrast, which is the difference between the transfer voltage applied by the voltage application section in the roll gap section and the potential of the portion exposed on the photosensitive element by the exposure unit. Specifically, by applying a transfer voltage from the voltage application section to the intermediate transfer member, the control section transfers the toner image from the photosensitive member to the intermediate transfer member by causing current to flow in the circumferential direction. Specifically, by applying a transfer voltage, a potential difference capable of inducing discharge is formed between the photosensitive component and the intermediate transfer component in the upstream region upstream of the upstream end of the gutter portion, along the moving direction of the surface of the intermediate transfer component. The control section controls the transfer voltage to control the primary transfer contrast based on information about the toner usage status related to the quantity of the printing sheet containing the recording material. The control section controls the transfer voltage to become lower as the number of printing sheets increases.

11. The image forming apparatus according to claim 10, wherein the control unit controls the transfer voltage to decrease linearly from an initial value when the number of printing sheets is zero as the number of printing sheets increases, until the number of printing sheets becomes a predetermined number, and maintains the transfer voltage at a constant value after the number of printing sheets reaches the predetermined number.

12. The image forming apparatus according to claim 11, wherein the control unit controls the transfer voltage whenever the developing device is switched.

13. The image forming apparatus according to claim 12, wherein when the developing equipment is replaced, the control unit restores the transfer voltage to its initial value regardless of the number of printing sheets, and controls the transfer voltage based on the number of printing sheets after restoring the number of printing sheets.

Images