Image forming apparatus

Abstract

To provide an image forming apparatus that can prevent an image defect while achieving good primary transferability for an intermediate transfer belt having three or more layers.SOLUTION: An image forming apparatus has: an image carrier; an intermediate transfer belt that includes a base layer, a surface layer formed on an outer peripheral surface of the base layer, and an inner surface layer formed on an inner peripheral surface of the base layer, and has conductivity; and a current supply member that is arranged to sandwich the intermediate transfer belt with the image carrier, and has its center arranged on the downstream side in the direction of rotation of the intermediate transfer belt with respect to the center of the image carrier. When the volume resistance value in the thickness direction of the intermediate transfer belt is defined as Rv(Ω), a first surface resistance value in the surface direction on the inner surface layer as Rs1(Ω), and a second surface resistance value in the surface direction on the surface layer as Rs2(Ω), the relationships of Rv>Rs1, Rs2>Rs1, Rs2 / Rv≤40 are satisfied, and the second surface resistance value Rs2 is 3.00×107(Ω) or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to an image forming apparatus that uses an electrophotographic method, such as a laser printer, copier, or facsimile. [Background technology]

[0002] Image forming apparatuses that use an intermediate transfer medium have been known for some time.

[0003] In this type of image forming apparatus, during the primary transfer process, the toner image formed on the surface of the photosensitive drum is transferred onto an intermediate transfer body by applying a voltage to a primary transfer member located opposite the photosensitive drum (primary transfer section). Furthermore, by repeatedly performing the primary transfer process for multiple toner images, multiple toner images of different colors are formed on the surface of the intermediate transfer body.

[0004] Then, in the secondary transfer process, the toner images of multiple colors formed on the surface of the intermediate transfer body are transferred all at once to the surface of a recording material such as paper by applying a voltage to the secondary transfer member. The toner images transferred to the surface of the recording material are then fixed to the recording material by a fixing means, and a color image is formed.

[0005] Patent Document 1 proposes a configuration in an intermediate transfer belt consisting of a base layer and a surface layer in which the ratio of the surface resistances of the base layer and the surface layer is defined in order to suppress discharge upstream of the primary transfer section.

[0006] On the other hand, Patent Document 2 proposes a configuration in which a low-resistance layer is formed on the inner surface of the base layer of the intermediate transfer belt in order to improve transferability, and a primary transfer voltage is applied from a primary transfer current supply member so that current flows in the circumferential direction of the intermediate transfer belt. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2020-95227

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, regarding an intermediate transfer belt that performs "primary transfer" by a current flowing in the circumferential direction as in Patent Document 2, simply specifying the ratio of the resistance values of the base layer and the surface layer as in Patent Document 1 may not result in good primary transfer performance in some cases.

[0009] Specifically, in a belt having a three-layer structure with an "inner surface low-resistance layer" on the inner peripheral surface of the "base layer" and a "surface resistance layer" formed on the outer peripheral surface of the "base layer" as in Patent Document 2, when applying a configuration that specifies the ratio of the surface resistances of the "base layer" and the "surface layer" as in Patent Document 1, there is a possibility that the "surface resistance" may become too low or too high unintentionally.

[0010] When the "surface resistance" becomes too low, for example, when forming a discrete patch image, the primary transfer current flowing in the circumferential direction of the belt may not flow (pass through) on the patch image and may directly flow from the photosensitive drum to the intermediate transfer belt, which may lead to a decrease in primary transfer performance.

[0011] On the other hand, when the "surface resistance" becomes too high, for example, in the secondary transfer section, due to the current supply from the secondary transfer member, the surface of the intermediate transfer belt may be charged, and problems such as scattering in the primary transfer section and image defects caused by discharge may occur.

[0012] That is, in the conventional configuration such as Patent Document 1 or Patent Document 2, in the three-layer intermediate transfer belt, there is still room for improvement in maintaining primary transfer performance and suppressing image defects caused by scattering and discharge.

[0013] An object of the present invention is to provide an image forming apparatus that can suppress image defects while realizing good primary transfer performance with respect to an intermediate transfer belt having a structure of three or more layers.

Means for Solving the Problems

[0014] The present invention relates to an image forming apparatus comprising: an image carrier that carries a toner image; an intermediate transfer belt on which the toner image is transferred from the image carrier, the intermediate transfer belt comprising a base layer, a surface layer formed on the outer circumferential surface side of the base layer, and an inner surface layer formed on the inner circumferential surface side of the base layer, and having conductivity; and a current supply member disposed between the intermediate transfer belt and the image carrier, the current supply member having its center located downstream of the center of the image carrier in the rotational direction of the intermediate transfer belt, wherein when the volume resistivity of the intermediate transfer belt in the thickness direction is Rv(Ω), the first surface resistivity in the surface direction on the inner surface layer side is Rs1(Ω), and the second surface resistivity in the surface direction on the surface layer side is Rs2(Ω), then Rv>Rs1, Rs2>Rs1, 2.186≦ The relationship Rs2 / Rv ≤ 40 is satisfied, and the second surface resistance value Rs2 is 3.00 × 10⁻⁶. 7 It is characterized by being (Ω) or greater. [Effects of the Invention]

[0015] According to the image forming apparatus of the present invention, good primary transfer performance can be achieved with respect to an intermediate transfer belt having a structure of three or more layers, while suppressing image defects. [Brief explanation of the drawing]

[0016] [Figure 1] Cross-sectional conceptual diagram of an image forming apparatus according to Embodiment 1 of the present invention. [Figure 2] Control block diagram of an image forming apparatus according to Embodiment 1 of the present invention. [Figure 3] Cross-sectional conceptual diagram of the primary transfer section of the image forming apparatus according to Embodiment 1 of the present invention. [Figure 4] Cross-sectional conceptual diagram of the intermediate transfer belt of an image forming apparatus according to Embodiment 1 of the present invention. [Figure 5] (a)(b) Conceptual diagram showing the primary transfer current path a and current path b of the image forming apparatus according to Example 1 of the present invention. [Figure 6]A conceptual diagram showing the current path when measuring the surface resistivity of the surface layer of the intermediate transfer belt of the image forming apparatus according to Embodiment 1 of the present invention. [Figure 7] Conceptual diagram showing the primary transfer current path in Comparative Example 6 relative to Example 1 of the present invention. [Figure 8] Cross-sectional conceptual diagram of an image forming apparatus according to Embodiment 2 of the present invention. [Figure 9] Cross-sectional conceptual diagram of an image forming apparatus according to Embodiment 3 of the present invention. [Modes for carrying out the invention]

[0017] The embodiments of the present invention will be described below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the following embodiments should be appropriately changed depending on the configuration of the device to which the invention is applied and various conditions, and the scope of the present invention is not intended to be limited to the following embodiments.

[0018] (Example 1) 1. Image forming apparatus Figure 1 is a conceptual cross-sectional view of an image forming apparatus according to Embodiment 1 of the present invention.

[0019] Specifically, Figure 1 shows a longitudinal cross-section of the image forming apparatus 100 of this embodiment.

[0020] As shown in Figure 1, the image forming apparatus 100 is a so-called tandem type image forming apparatus equipped with multiple image forming sections Sa to Sd. The first image forming section Sa forms an image using yellow (Y) toner, the second image forming section Sb uses magenta (M) toner, the third image forming section Sc uses cyan (C) toner, and the fourth image forming section Sd uses black (Bk) toner to form an image.

[0021] These four image forming units are arranged in a line at regular intervals, and the configuration of each image forming unit is substantially the same in many ways, except for the color of the toner it contains. Therefore, the image forming apparatus 100 of Example 1 will be described below using the first image forming unit Sa.

[0022] The first image forming unit Sa includes a photosensitive drum 1a which is a drum-shaped photosensitive element, a charging roller 2a which is a charging member, a developing unit 4a which is a developing means, and a drum cleaning means 5a.

[0023] The photosensitive drum 1a is an image carrier that holds a toner image and is rotated at a predetermined process speed (200 mm / sec in Example 1) in the direction of the arrow R1 shown in the figure. The developing means 4a includes a developing container 41a that contains yellow toner and a developing roller 42a that holds the yellow toner contained in the developing container 41a and acts as a developing member for developing a yellow toner image on the photosensitive drum 1a.

[0024] The drum cleaning means 5a is a means for recovering toner adhering to the photosensitive drum 1a. The drum cleaning means 5a includes a cleaning blade that contacts the photosensitive drum 1a and a waste toner box that contains toner and other materials removed from the photosensitive drum 1a by the cleaning blade.

[0025] When the DC controller 274, acting as the control unit, receives an image signal and starts the image forming operation, the photosensitive drum 1a is driven to rotate. During the rotation process, the photosensitive drum 1a is uniformly charged by the charging roller 2a to a predetermined potential (dark area potential Vd) with a predetermined polarity (negative polarity in Embodiment 1), and is exposed by the exposure means 3a according to the image signal.

[0026] This creates an electrostatic latent image corresponding to the yellow component image of the target color image. Next, this electrostatic latent image is developed by the developing roller 4a at the development position and visualized as a yellow toner image (hereinafter simply referred to as the toner image). The developing roller 4a rotates at 300 mm / sec in the same direction as the photosensitive drum 1a at 1.5 times the speed to ensure stable development onto the photosensitive drum 1a.

[0027] In this embodiment, the normal charge polarity of the toner contained in the developing roller 4a is negative. The electrostatic latent image is reversed and developed by toner charged with the same polarity as the charge polarity of the photosensitive drum 1a by the charging roller 2a. However, the present invention can also be applied to an image forming apparatus in which the electrostatic latent image is positively developed by toner charged with the opposite polarity to the charge polarity of the photosensitive drum 1a.

[0028] The intermediate transfer belt 10, which is an endless and movable intermediate transfer body, is positioned in contact with each of the photosensitive drums 1a to 1d in each image forming section Sa to Sd, and is stretched by three axes: a drive roller 11, a tension roller 12, and a secondary transfer opposing roller 13, which are tensioning members. The intermediate transfer belt 10 is stretched by the tension roller 12 with a total tension of 60 N, and moves in the direction of arrow R2 shown in the figure by the rotation of the opposing roller 13, which rotates under the driving force.

[0029] The toner image formed on the photosensitive drum 1a is first transferred to the intermediate transfer belt 10 by applying a positive voltage from the primary transfer power supply 23 to the primary transfer roller 6a as it passes through the primary transfer nip N1a where the photosensitive drum 1a and the intermediate transfer belt 10 come into contact. Subsequently, any toner remaining on the photosensitive drum 1a that is not first transferred to the intermediate transfer belt 10 is collected by the drum cleaning means 5a and removed from the surface of the photosensitive drum 1a.

[0030] In this embodiment, during primary transfer, a current is supplied to the intermediate transfer belt 10 from a current supply member that contacts the intermediate transfer belt 10, and this current forms a primary transfer potential in the primary transfer section of each image forming station S(a~b) of the intermediate transfer belt 10.

[0031] The detailed method for generating the primary transfer potential in the image forming apparatus of this embodiment will be described later.

[0032] Similar to the first color, the second color magenta toner image, the third color cyan toner image, and the fourth color black toner image are formed and sequentially transferred onto the intermediate transfer belt 10. As a result, four toner images corresponding to the desired color image are formed on the intermediate transfer belt 10. Subsequently, the four toner images supported on the intermediate transfer belt 10 pass through a secondary transfer nip N2 formed by the contact between the secondary transfer roller 20 and the intermediate transfer belt 10. During this process, they are simultaneously transferred to the surface of the transfer material (recording material) P, such as paper or an OHP sheet, fed by the paper feeding means 50.

[0033] The secondary transfer roller 20 is made of a nickel-plated steel rod with an outer diameter of 8 mm and a volume resistivity of 10 8 A foamed sponge body with an outer diameter of 18 mm is used, which is mainly composed of NBR and epichlorohydrin rubber, adjusted to Ω·cm and 5 mm thick. The rubber hardness of the foamed sponge body was measured using an Asker hardness tester type C, and the hardness was 30° under a 500g load. The secondary transfer roller 20 is in contact with the outer surface of the intermediate transfer belt 10 and is pressed with a force of 50N against the secondary transfer opposing roller 13, which is positioned opposite the secondary transfer roller 20 via the intermediate transfer belt 10, forming a secondary transfer nip N2.

[0034] The secondary transfer roller 20 rotates in a driven manner relative to the intermediate transfer belt 10, and when a voltage is applied from the secondary transfer power supply 21, current flows from the secondary transfer roller 20 to the secondary transfer opposing roller 13. As a result, the toner image supported on the intermediate transfer belt 10 is transferred to the transfer material P at the secondary transfer nip N2.

[0035] When the toner image on the intermediate transfer belt 10 is transferred to the transfer material P, the voltage applied from the secondary transfer power supply 21 to the secondary transfer roller 20 is controlled so that the current flowing from the secondary transfer roller 20 to the secondary transfer opposing roller 13 via the intermediate transfer belt 10 remains constant. Furthermore, the magnitude of the current required for secondary transfer is predetermined based on the surrounding environment in which the image forming apparatus 100 is installed and the type of transfer material P.

[0036] The secondary transfer power supply 21 is connected to the secondary transfer roller 20 and applies the transfer voltage to the secondary transfer roller 20. The secondary transfer power supply 21 is capable of outputting voltages in the range of 100V to 4000V.

[0037] The transfer material P onto which the four toner images have been transferred by secondary transfer is then heated and pressurized in the fixing means 30, where the four toners melt and mix, fixing them to the transfer material P. Meanwhile, the toner remaining on the intermediate transfer belt 10 after secondary transfer is cleaned and removed by the belt cleaning means 16 (recovery means) located downstream of the secondary transfer nip N2 in the direction of movement of the intermediate transfer belt 10.

[0038] The belt cleaning means 16 includes a cleaning blade 16a as a contact member that contacts the outer circumferential surface of the intermediate transfer belt 10 at a position opposite to the opposing roller 13, and a waste toner container 16b that contains the toner collected by the cleaning blade 16a. In the following description, the cleaning blade 16a will be simply referred to as the blade 16a.

[0039] In the image forming apparatus 100 of Example 1, a full-color print image is formed by the above operation.

[0040] 2. Control of image formation operations Next, the control of the image formation operation in Example 1 will be explained using a control block diagram.

[0041] Figure 2 is a control block diagram of an image forming apparatus according to Embodiment 1 of the present invention.

[0042] Specifically, Figure 2 shows the control blocks for controlling the operation of the image forming apparatus 100.

[0043] As shown in Figure 2, the host computer PC271 issues a print command to the formatter 273, which is a conversion means located inside the image forming apparatus 100, and transmits the image data of the print image to the formatter 273.

[0044] The formatter 273 receives RGB or CMYK image data from the PC271 and converts it to CMYK exposure data according to the mode specified by the PC271. The exposure data converted at this time is 600 dpi. Among the modes specified by the PC271 are modes related to paper type, size, and image quality.

[0045] Meanwhile, the formatter 273 transfers the converted exposure data to the exposure control unit 277, which is an exposure control device located within the DC controller 274. The exposure control unit 277 controls the exposure means 3 based on instructions from the CPU 276.

[0046] In the image forming apparatus 100 shown in Figure 2, halftone control is controlled by adjusting the on / off area of ​​the exposure data. When the CPU 276 receives a print command from the formatter 273, it starts the image forming sequence.

[0047] The DC controller 274 is equipped with a CPU 276, memory 275, etc., and performs pre-programmed operations. The CPU 276 controls the charging high voltage (charging power supply 281), the developing high voltage (developing power supply 280), and the transfer high voltage (primary transfer power supply 23, secondary transfer power supply 21) to form an image by controlling the formation of an electrostatic latent image and the transfer of the developed toner image.

[0048] Furthermore, the CPU 276 also performs processing to receive signals from the optical sensor 60, which is a detection means, when performing correction control to correct the position and density of the image formed in the image forming apparatus 100. In image correction control, the amount of reflected light from a test patch (detection toner image) formed on the outer surface of the intermediate transfer belt 10 at a position opposite the optical sensor 60 is measured by the optical sensor 60.

[0049] The detection signal from the optical sensor 60 is converted via AD conversion through the CPU 276 and then stored in the memory 275. The controller 274 performs calculations using the detection result from the optical sensor 60 and makes various corrections.

[0050] 3. Tension configuration of the intermediate transfer belt Next, we will describe the intermediate transfer belt 10 used in the image forming apparatus of this embodiment, the tensioning members 11, 12, and 13 which are tensioning members of the intermediate transfer belt 10, and the primary transfer roller 6.

[0051] As shown in Figure 1, an intermediate transfer belt 10 is positioned opposite each image forming station S(a, b, c, d) as an intermediate transfer body. The intermediate transfer belt 10 is an endless belt made of a resin material to which a conductive agent has been added to impart conductivity. It is stretched by three axes consisting of a drive roller 11, a tension roller 12, and a secondary transfer opposing roller 13, and is stretched by the tension roller 12 with a total tension of 60 N.

[0052] Furthermore, as shown in Figure 1, in the direction of movement of the intermediate transfer belt 10, primary transfer rollers 6a to 6d, which are contact members that contact the inner circumferential surface of the intermediate transfer belt 10, are arranged downstream of the photosensitive drums 1a, 1b, 1c, and 1d.

[0053] Figure 3 is a conceptual cross-sectional view of the primary transfer section of an image forming apparatus according to Embodiment 1 of the present invention.

[0054] Specifically, Figure 3 shows the arrangement of the photosensitive drum 1 and the primary transfer roller 6.

[0055] As shown in Figure 3, in each image forming station S, the primary transfer roller 6 is positioned downstream of the intermediate transfer belt 10 in the rotational direction R2 relative to the photosensitive drum 1. More specifically, the perpendicular L04 that passes through the rotational center C02 of the primary transfer roller 6 to the intermediate transfer belt 10 is located downstream of the perpendicular L03 that passes through the rotational center C01 of the photosensitive drum 1 to the intermediate transfer belt 10 in the rotational direction R2.

[0056] Furthermore, the primary transfer roller 6 is positioned to penetrate the intermediate transfer belt surface (10) so as to ensure the "amount of wrapping" of the intermediate transfer belt 10 around the photosensitive drum 1 in each image forming section (Sa to Sd) corresponding to the image. The dotted line L01 in Figure 3 indicates the position of the intermediate transfer belt surface (10) before the primary transfer roller 6 penetrates. On the other hand, the dotted line L02 in Figure 3 indicates the position of the apex 10c1 of the intermediate transfer belt surface (10) after penetration.

[0057] In this embodiment, the primary transfer roller 6 is a metal roller, consisting of a straight, nickel-plated SUS round bar with an outer diameter of 6 mm, and rotates in conjunction with the rotation of the intermediate transfer belt 10. In contrast, in Embodiment 1, the outer diameter of the photosensitive drum 1 is 24 mm. The primary transfer roller 6 is in contact with the intermediate transfer belt 10 over a predetermined area in the longitudinal direction (width direction) perpendicular to the direction of movement of the intermediate transfer belt 10.

[0058] Furthermore, W is defined as the distance between the perpendicular line L03 drawn from the center C01 of the photosensitive drum 1 and the perpendicular line L04 drawn from the center C02 of the primary transfer roller 6, and H1 is defined as the lift height of the primary transfer roller 6 relative to the intermediate transfer belt 10 (i.e., the distance between the dotted lines L01 and L02). In this example, W = 10 mm and H1 = 2 mm.

[0059] Furthermore, a voltage is applied to the primary transfer roller 6 from the primary transfer power supply 23, and this is supplied as the primary transfer current that passes through the conductive layer on the inner surface of the intermediate transfer belt 10, which will be described later. In Example 1, 300V is applied as the primary transfer voltage.

[0060] 4. Intermediate transfer belt Next, we will describe the intermediate transfer belt 10, which is a feature of Example 1.

[0061] Figure 4 is a conceptual cross-sectional view of the intermediate transfer belt of an image forming apparatus according to Embodiment 1 of the present invention.

[0062] Specifically, Figure 4 shows a longitudinal cross-section in the thickness direction of the intermediate transfer belt 10 used in Example 1.

[0063] In this embodiment, the intermediate transfer belt 10 has a circumference of 700 mm and a thickness of 90 μm, and consists of three layers: a base layer 10a, an inner layer 10b formed on the inner surface of the base layer 10a, and a surface layer 10c formed on the outer surface of the base layer 10a.

[0064] The base layer 10a is a layer made of endless polyethylene naphthalate (PEN) mixed with an ionic conductive material as a conductive agent. The inner layer 10b is a layer made of acrylic resin mixed with carbon as a conductive agent. The surface layer 10c is a layer made of acrylic resin mixed with a metal oxide as a conductive agent.

[0065] More specifically, the inner layer 10b is a layer formed on the inside (tension axis side) of the base layer 10a. When the thickness of the polyvinylidene fluoride layer, which is the base layer 10a, is t1, the thickness of the acrylic resin layer, which is the inner layer 10b, is t2, and the thickness of the acrylic resin layer, which is the surface layer 10c, is t3, then t1 = 87 μm, t2 = 2 μm, and t3 = 3 μm.

[0066] In this embodiment, polyethylene naphthalate (PEN) is used as the material for the base layer 10a of the intermediate transfer belt 10, but other materials may be used. For example, materials such as polyester, acrylonitrile-butadiene-styrene copolymer (ABS), and mixed resins thereof may be used.

[0067] In this embodiment, acrylic resin was used as the material for the inner layer 10b of the intermediate transfer belt 10, but other materials may also be used. For example, materials such as polyester may be used.

[0068] Furthermore, although acrylic resin was used as the material for the surface layer 10c of the intermediate transfer belt 10 in this embodiment, other materials may also be used. For example, materials such as polyester may be used.

[0069] In this embodiment (Experimental Examples 1-14), a suitable resistance value for the intermediate transfer belt 10 is set using the volume resistivity measured from the surface layer 10c side, the surface resistivity measured from the surface layer 10c side, and the surface resistivity measured from the inner layer 10b side.

[0070] The volume resistivity will be measured using Mitsubishi Chemical Corporation's Hiresta-UP (MCP-HT450) with a ring probe of type UR (model MCP-HTP12). The metal surface of the UFL register table will be used as the probe's counter electrode.

[0071] On the other hand, for measuring surface resistivity, the same measuring instrument as for volume resistivity is used, but with a ring probe of type UR100 (model MCP-HTP16). The Teflon® surface of the UFL register table is used as the probe's counter electrode.

[0072] Furthermore, the volume resistivity was measured by applying a probe to the surface side of the intermediate transfer belt 10 with a pressure of 1 kg, using an applied voltage of 250 V and a measurement time of 10 seconds. Volume resistivity is a measurement of the resistance value in the thickness direction of the intermediate transfer belt 10, and mainly corresponds to measuring the resistance value of the base layer 10a. If the applied voltage is too high, it becomes difficult to capture changes in volume resistivity, while if it is too low, the repeatability of the measurement value decreases due to the influence of the surface shape of the surface layer 10c and foreign matter adhering to the probe. Considering this, the applied voltage was set to 250 V in Example 1.

[0073] The surface resistivity of the inner layer 10b was measured by applying a probe to the inner surface of the intermediate transfer belt 10 with a pressure of 1 kg, using an applied voltage of 10 V and a measurement time of 10 seconds.

[0074] Furthermore, the surface resistivity of the surface layer 10c was measured by applying a probe to the inner surface of the intermediate transfer belt 10 with a pressure of 1 kg, using an applied voltage of 100 V and a measurement time of 10 seconds.

[0075] Measuring the surface resistivity of the surface layer 10c is equivalent to measuring the resistance of the surface layer 10c. If the applied voltage is too high, the current flow through the base layer 10a and inner layer 10b increases. On the other hand, if the applied voltage is too low, current may not flow between the probe electrodes, making it impossible to measure the resistance, or the repeatability of the measurement may decrease due to the surface shape of the surface layer 10c or foreign matter adhering to the probe. For these reasons, in this embodiment 1, the applied voltage was set to 100V.

[0076] In this embodiment, the resistance measurement environment was set to an indoor temperature of 23°C and an indoor humidity of 50%.

[0077] The aforementioned "volume resistivity" and "surface resistivity" are defined in JIS K 6911 and are expressed by the following equations (1) and (2). Volume resistivity ρv(Ω cm)=R(Ω)×RCFv×t(cm) Formula (1) Surface resistivity ρs(Ω / □)=R(Ω)×RCFs Formula (2) In equation (1), RCFv, and in equation (2), RCFs are resistivity correction coefficients, which are constants set for each probe used in the measurement.

[0078] In this example, a ring probe of type UR (model MCP-HTP12) was used to measure the "volume resistivity," and the RCFv was 2.011.

[0079] Furthermore, a ring probe type UR100 (model MCP-HTP16) was used to measure "surface resistivity," and the RCFs were 100.

[0080] Furthermore, in equation (1), t is the thickness of the intermediate transfer belt.

[0081] In this embodiment, in order to compare the resistance values ​​(R) in the thickness direction and the surface direction, the resistance values ​​calculated from equations (1) and (2) will be explained.

[0082] In the following explanation, the resistance value obtained by converting the volume resistivity (ρv) using equation (1) will be called the "volume resistivity (Rv)," and the resistance value obtained by converting the surface resistivity (ρs) using equation (2) will be called the "surface resistivity (Rs)." In "Experimental Example 1" of this Example 1, as shown in Table 1 below, the intermediate transfer belt 10 has a volume resistivity of 1.62 × 10⁻⁶. 7 (Ω), the surface resistance of the inner layer 10b is 1.10 × 10 5 (Ω), the surface resistance of the surface layer 10c is 3.55 × 10 7 (Ω). That is, in "Experimental Example 1", when the volume resistivity is Rv, the surface resistivity of the inner layer 10b is Rs1, and the surface resistivity of the outer layer 10c is Rs2, the value of Rs1 is lower than Rv and Rs2, and Rs2 / Rv is 2.19.

[0083] Next, using Figure 5, we will explain the reason why, in this embodiment, the surface resistance value Rs1 of the inner layer 10b is set lower (for example, lower than the surface resistance value Rs2 of the outer layer 10c).

[0084] Figure 5(a,b) is a conceptual diagram showing the primary transfer current path a and current path b of the image forming apparatus according to Embodiment 1 of the present invention.

[0085] Specifically, Figure 5 conceptually illustrates how the current supplied from the primary transfer roller 6 flows through two different current paths, current path a and current path b.

[0086] As shown in Figure 5(a), in current path a, the primary transfer current supplied from the primary transfer roller 6 flows mainly through the inner layer 10b in the opposite direction to the rotational direction R2 of the intermediate transfer belt 10. The primary transfer current also reaches the primary transfer nip N1, which is the contact point between the photosensitive drum 1 and the intermediate transfer belt, and then proceeds to the photosensitive drum 1.

[0087] On the other hand, as shown in Figure 5(b), in current path b, the primary transfer current mainly flows through the surface layer 10c. That is, when the resistance values ​​of the inner layer 10b and the base layer 10a or surface layer 10c are close, the current path from the primary transfer roller 6 to the primary transfer nip N1 will pass through the base layer 10a or surface layer 10c.

[0088] In the case of "current path b" as shown in Figure 5(b), the surface layer 10c has a positive potential, and a discharge current may be generated between the intermediate transfer belt 10 and the photosensitive drum 1 downstream of the primary transfer nip N1 (direction R2). As a result, during transfer, image defects of the discharge pattern may occur at the station in question, or so-called "re-transfer" may occur at a station downstream in the rotational direction of the intermediate transfer belt 10, in which the toner that was primarily transferred onto the intermediate transfer belt 10 is reverse-transferred to the photosensitive drum 1.

[0089] Therefore, it is necessary to avoid "current path b" as shown in Figure 5(b), suppress the discharge current generated downstream of the primary transfer nip N1 (direction R2), and suppress re-transfer. For this reason, in this embodiment, the resistance value of the inner layer 10b is set to a value that is sufficiently small compared to the resistance value of the base layer 10a and the resistance value of the surface layer 10c, thereby realizing a configuration in which the primary transfer current mainly passes through the inner layer 10b to reach the primary transfer nip N1 (i.e., "current path a" as shown in Figure 5a).

[0090] Next, we will explain the preferred relationship between the volume resistivity Rv and the surface resistivity Rs2 on the surface layer 10c.

[0091] Figure 6 is a conceptual diagram showing the current path when measuring the surface resistance on the surface side of the intermediate transfer belt of the image forming apparatus according to Embodiment 1 of the present invention.

[0092] As shown in Figure 6, the surface resistance of the surface layer can be obtained by measuring the current flowing from the positive electrode to the negative electrode in contact with the surface layer 10c.

[0093] Because the surface layer 10c has a thin thickness t3 of 3 μm, when measuring the surface resistance of the surface layer 10c, the current flowing between the probe electrodes passes not only through the surface layer 10c but also through the base layer 10a, from the positive electrode to the negative electrode. Furthermore, since the intermediate transfer belt of Example 1 has an inner conductive layer 10b, a portion of the current flowing between the probe electrodes passes through the inner layer 10b. For this reason, the surface resistance of the surface layer 10c is measured to be seemingly lower than the actual resistance.

[0094] If the surface resistance of the surface layer 10c is high, a discharge current is generated between the secondary transfer roller 20 and the intermediate transfer belt 10, for example, when a voltage is applied to the secondary transfer roller 20, due to the influence of the toner image pattern and the unevenness of the paper. As a result, charges may accumulate on the surface layer 10c of the intermediate transfer belt 10, forming a potential as a potential memory, and the potential may be retained on the surface layer 10c. When primary transfer is performed in this state, a discharge current is generated between the photosensitive drum 1 and the intermediate transfer belt 10 upstream of the primary transfer nip N1 with respect to the rotation direction R2 of the intermediate transfer belt 10.

[0095] As a result, a phenomenon called pre-transfer occurs upstream of the primary transfer nip N1, where the primary transfer toner on the photosensitive drum 1 is transferred onto the intermediate transfer belt 10 in the gap between the photosensitive drum 1 and the intermediate transfer belt 10. Due to such primary transfer defects, image defects may occur, such as distorted image images or the formation of discharge marks as toner images.

[0096] To suppress such primary transfer defects, in this embodiment, the resistance value of the intermediate belt was considered to be suitable for the surface resistance value of the surface layer 10c, taking into account the current passing through the inner layer 10b. Furthermore, since the suitable primary transfer voltage also changes depending on the volume resistance, the surface resistance value of the surface layer 10c was set to suppress the image defects caused by the discharge current as described above, while also taking the volume resistance value into consideration.

[0097] (evaluation) Next, we will describe the evaluation of Example 1.

[0098] Table 1 shows the results of comparing Experimental Examples 1 to 9, which constitute Example 1, with Comparative Examples 1 to 6 of Example 1, by changing the volume resistivity Rv and surface resistivity Rs2 of the surface layer 10c for the intermediate transfer belt 10 used in Embodiment 1 of the present invention.

[0099] Specifically, Table 1 summarizes the volume resistivity Rv, surface resistivity Rs1 on the inner layer side, surface resistivity Rs2 on the outer layer side, Rs2 / Rv, and the image evaluation results for each of the (A) to (F) intermediate transfer belts in Experimental Examples 1 to 9 and Comparative Examples 1 to 6.

[0100] For Comparative Examples 1 to 6, the only difference from the intermediate transfer belts of Experimental Examples 1 to 9 in Example 1 is the resistance value; the other configurations are the same as those of Experimental Examples 1 to 9.

[0101] The intermediate transfer belts in Experimental Examples 1-9 of Example 1 and Comparative Examples 1-6 are identical in material and shape to the base layer 10a, inner layer 10b, and surface layer 10c, and the resistance value is adjusted by adjusting the amount of conductive agent added to each layer.

[0102] Next, using Table 1, we will explain the evaluation of the "image quality" for each of the evaluation images (A) to (F) in Example 1.

[0103] Table 1 shows the resistance values ​​of the intermediate transfer belts for Experimental Examples 1-9 of Example 1 and Comparative Examples 1-6, measured in an ambient temperature and humidity of 23°C and 50%, and the transferability of the primary transfer portion of the image formed on each intermediate transfer belt in an ambient temperature and humidity of 23°C and 50%.

[0104] Note that each of the "evaluation images (A) to (E)" shown in Table 1 is A4 size GF-C081 (basis weight: 81.4 g / m²). 2 I used a Canon camera (manufacturer).

[0105] Specifically, the evaluation image (E) was a full-bleed image with an average density of 100% for yellow, magenta, cyan, and black, which was then printed and evaluated.

[0106] Furthermore, as evaluation image (D), a solid patch image was printed using discretely arranged 10mm x 10mm squares of each color, and the evaluation was performed.

[0107] In addition, as evaluation images (B, C), full-surface halftone images with average densities of 20% and 50% were printed and evaluated.

[0108] In addition, as evaluation image (F), a full-surface secondary color image with an average density of 200% for red, green, and blue was printed and evaluated.

[0109] In addition, as evaluation image (A), a text image formed with an average density of 100% for each of yellow, magenta, cyan, and black was printed and evaluated.

[0110] First, the evaluation results of the intermediate transfer belt in Experimental Examples 1 to 9 of Example 1 will be described.

[0111] As shown in Table 1, in this example, for the intermediate transfer belts of Experimental Examples 1 to 9, the volume resistivity Rv is 2.60×10 6 (Ω) to 3.51×10 7 (Ω), and the surface resistivity Rs1 of the inner layer 10b is 1.10×10 3 (Ω) to 1.10×10 5 (Ω).

[0112] And, in this example, the surface resistivity Rs2 of the surface layer 10c of the intermediate transfer belts of Experimental Examples 1 to 9 is 3.55×10 7 (Ω) to 6.41×10 8 (Ω), and Rs2 / Rv is 2.186 to 38.740.

[0113] On the other hand, for the intermediate transfer belts of Comparative Examples ₁ to 5, the volume resistivity Rv is ₁.56×10 6 (Ω) to 1.42× 8 (Ω), and the surface resistivity Rs1 of the inner layer 10b is 1.10×10 5 (Ω). And, the surface resistivity Rs2 of the surface layer 10c of the intermediate transfer belts of Comparative Examples ₁ to 5 is 1.23×10 8 (Ω) to 6.04×10 10 (Ω), and Rs2 / Rv is 53.564 to 424.523.

[0114] Furthermore, the belt in Comparative Example 6 has a volume resistivity Rv of 1.98 × 10⁻⁶. 6 (Ω), the surface resistance Rs1 of the inner layer 10b is 1.10 × 10 5 (Ω), the surface resistance value Rs2 of the surface layer 10c is 2.18 × 10 6 (Ω) and Rs² / Rv is 1.103.

[0115] As shown in Table 1, no image defects ("×" rating) were observed for the evaluation images "(A)~(F)" of Experimental Examples 1 in Example 1. In Table 1, "◎" means "very good," "〇" means "good," "△" means "minor image defect," and "×" means "image defect."

[0116] Next, we will explain why good image quality was obtained in the intermediate transfer belts of Experimental Examples 1 to 9 of Example 1.

[0117] First, the reason why good images were obtained even in the full-surface halftone 20% (B) and full-surface halftone 50% (C) settings, where discharge images are easily noticeable, is that the surface resistance value of the surface layer 10c was not made too high, considering that the inner layer 10b is formed.

[0118] On the other hand, by setting the resistance values ​​such that the volume resistance Rv and the surface resistance Rs2 of the surface layer 10c are close, even when a primary transfer voltage is applied that yields the desired primary transfer current, a potential memory is not generated in the surface layer 10c, and the discharge current upstream of the primary transfer nip N1 is suppressed. That is, if the relationship Rs2 / Rv ≤ 40 is satisfied, the resistance values ​​of the two become close, and the discharge current is effectively suppressed. In addition, by setting the surface resistance Rs1 on the inner layer 10b side to be sufficiently small, the primary transfer voltage applied to the primary transfer roller 6 hardly attenuates before reaching the primary transfer nip N1. That is, good transfer performance can be obtained even for images that require a sufficient transfer current, such as a solid color (E) or a secondary color image (F).

[0119] Furthermore, the high surface resistance Rs2 of the surface layer 10c suppresses the occurrence of transfer defects in the solid patch image (D), which are caused by the primary transfer current not passing through the solid patch image described later.

[0120] Generally, the larger the surface resistance Rs2 of the surface layer 10c, the more likely potential memory is to occur in the surface layer 10c. Therefore, in this embodiment, Rs2 is set to 1.00 × 10⁻⁶. 9 It is preferable to keep the resistance value Rs2 of the surface layer 10c to 6.41 × 10⁻¹⁰. 8 Setting it to (Ω) or less is preferable, as it further reduces the influence of potential memory.

[0121] Next, we will explain the evaluation results of the intermediate transfer belts for Comparative Examples 1 to 5.

[0122] In Comparative Example 1, the intermediate transfer belt had a surface resistance Rs2 of the surface layer 10c that was higher than the volume resistance Rv, with an Rs2 / Rv value of 53.564. As a result of potential memory forming in the surface layer 10c of the intermediate transfer belt in Comparative Example 1, slight discharge marks were observed on the image in images where discharge marks are easily noticeable, such as full halftone 20% (B) and full halftone 50% (C).

[0123] Furthermore, the intermediate transfer belts of Comparative Examples 2 and 3 had Rs2 / Rv values ​​ranging from 120.001 to 195.914, which were larger than those of Comparative Example 1, indicating that potential memory is more likely to occur in the surface layer 10c.

[0124] As a result, in Comparative Examples 2 and 3, discharge marks were more noticeable, with minor discharge marks observed in the 20% full-surface halftone (B) and prominent discharge marks in the 50% full-surface halftone (C).

[0125] Furthermore, the intermediate transfer belts of Comparative Examples 4 and 5 had Rs2 / Rv values ​​of 408.413 to 424.523, which were higher than those of Comparative Examples 2 and 3. Minor discharge marks were observed with a full 20% halftone (B), and significant discharge marks were observed with a full 50% halftone (C) and a full solid image (E).

[0126] On the other hand, in Comparative Example 6, the intermediate transfer belt experienced transfer defects in the solid patch image (D) due to insufficient primary transfer current, which prevented the toner image on the photosensitive drum 1 from being sufficiently transferred to the intermediate transfer belt 10.

[0127] Specifically, in Comparative Example 6, the intermediate transfer belt had an Rs2 / Rv value of 1.103, and the surface resistance value Rs2 on the surface layer 10c side was almost equal to the volume resistance value Rv. Although no potential memory was generated on the surface layer 10c, the surface resistance value Rs2 on the surface layer 10c side was 2.18 × 10⁻⁶. 6 (Ω) is low. Compared to Comparative Example 6, in all of these cases (Experimental Examples 1-9), Rs2 was 3.00 × 10⁻⁶. 7 The value was above (Ω), there was no shortage of primary transfer current, and no image defects were observed in the beta-patch image (D).

[0128] Next, we will explain the mechanism by which transfer defects occur in the solid patch image (D) when the surface resistance value Rs2 on the surface layer 10c side is small in the intermediate transfer belt of Comparative Example 6.

[0129] Figure 7 is a conceptual diagram showing the primary transfer current path in Comparative Example 6 compared to Example 1 of the present invention.

[0130] Specifically, Figure 7 shows the current during primary transfer in the configuration of Comparative Example 6. Note that in Figure 7, the direction from the front to the back of the drawing is the rotational direction R2 of the intermediate transfer belt.

[0131] As shown in Figure 7, in the intermediate transfer belt of Comparative Example 6, the surface resistance Rs2 of the surface layer 10c is small, making it easier for the primary transfer current to bypass the patch image and flow to the photosensitive drum 1.

[0132] In other words, one current path for the primary transfer current is one that flows from the intermediate transfer belt 10 through the toner image to the photosensitive drum 1. On the other hand, as shown in Figure 7, there is also a path in which the primary transfer current flows directly from the intermediate transfer belt 10 to the photosensitive drum 1 without going through the toner image. In the configuration shown in Figure 7, it can be assumed that the path through which the current passes the toner image usually has a higher resistance than the path that does not.

[0133] However, when the surface resistance Rs2 of the surface layer 10c is small, the "difference" in resistance between the current path that goes through the toner image and the current path that does not go through the toner image becomes large. For this reason, as shown in Figure 7, in Comparative Example 6, most of the primary transfer current flows directly from the intermediate transfer belt 10 to the photosensitive drum 1 without going through the toner image.

[0134] Therefore, since primary transfer is achieved by the movement of the toner image along the current path, in a configuration like Comparative Example 6, if the proportion of current flowing through paths that do not involve the toner image increases, sufficient transfer current cannot be supplied to the toner image, leading to transfer failure.

[0135] Furthermore, regarding the text image (A), no image defects were observed in any of the intermediate transfer belts in Experimental Examples 1-9 of Example 1 or Comparative Examples 1-6.

[0136] As explained above, in an intermediate transfer belt consisting of three layers: a base layer 10a, an inner layer 10b, and a surface layer 10c, in order to obtain good primary transfer performance, the primary transfer current supplied from the primary transfer roller 6 must pass through the inner layer 10b and reach the primary transfer nip N1. Furthermore, in order to suppress discharge marks and pre-transfer and obtain good transfer performance, the resistance values ​​of the base layer 10a and the surface layer 10c must be adjusted to a predetermined relationship.

[0137] In other words, in this embodiment, the volume resistivity Rv of the base layer 10a (intermediate transfer belt 10) and the surface resistivity (second surface resistivity) Rs2 of the surface layer 10c must be greater than the surface resistivity (first surface resistivity) Rs1 of the inner layer 10b. Furthermore, the relationship Rs2 / Rv ≤ 40 must be satisfied, and the surface resistivity (second surface resistivity) Rs2 of the surface layer must be 3.00 × 10⁻⁶. 7 It must be (Ω) or greater.

[0138] In this embodiment, as shown in Table 1, the volume resistivity Rv is set to 2.60 × 10⁻⁶ as the resistance value of the intermediate transfer belt 10 in Experimental Examples 1 to 9 of Example 1. 6 (Ω) ~ 3.51 × 10 7 It is set to (Ω). That is, it is preferable to set the volume resistivity Rv within this range. A more preferable range for Rv is 4.57 × 10 6 (Ω) ~ 1.83 × 10 7 It is (Ω).

[0139] Furthermore, in this embodiment, the surface resistance value Rs1 of the inner layer 10b is set to 1.10 × 10 3 (Ω) ~ 1.10 × 10 5 It is preferable to set the surface resistance value Rs1 of the inner layer 10a to (Ω), i.e., to be within this range.

[0140] In this embodiment, the surface resistance value Rs2 of the surface layer 10c is set to 3.55 × 10 7 (Ω) ~ 6.41 × 10 8 It is set to (Ω). That is, the surface resistance value Rs2 of the surface layer 10c is 3.55 × 10 7 (Ω) or higher is preferable. On the other hand, when considering the effect of potential memory, Rs2 is 6.41 × 10 8 It is preferable that the value is less than or equal to (Ω).

[0141] Furthermore, in this embodiment, Rs2 / Rv is set to 2.186 to 38.740. That is, the relationship Rs2 / Rv ≤ 40 is satisfied.

[0142] Thus, in this embodiment, by setting Rv, Rs1, and Rs2 to the above relationship, a good quality intermediate transfer belt is obtained that suppresses potential memory on the surface layer 10c while applying a sufficient primary transfer voltage for primary transfer, thereby suppressing discharge marks and density unevenness due to pre-transfer.

[0143] On the other hand, in the intermediate transfer belts of Comparative Examples 1 to 6, the Rs2 / Rv ratio was 53.564 or higher, indicating image defects due to discharge marks on the intermediate transfer belt.

[0144] This is because, in order to suppress potential memory in the surface layer 10c, the surface resistivity ρs2 of the surface layer 10c should be smaller than that of other layers, and Rs2 / Rv should be 40 or less. Furthermore, even under conditions where image formation is performed in an environment of low temperature and low humidity, or under conditions where toner degradation makes image defects due to discharge marks more severe, it is preferable to set Rs2 / Rv to 21.859 or less in order to more effectively suppress the occurrence of image defects. This is because the larger Rs2 / Rv, the more likely potential memory is to occur in the surface layer 10c.

[0145] Furthermore, as can be seen from Comparative Example 6, in order to effectively suppress the occurrence of primary transfer defects in the solid patch image (D), it is necessary to reduce the "difference" between the resistance value of the current path flowing between the intermediate transfer belt 10 and the photosensitive drum 1 and the resistance value of the current path flowing from the intermediate transfer belt 10 through the toner image to the photosensitive drum 1. For this reason, in this embodiment, the surface resistance value Rs2 on the surface layer 10c side is set to 3.00 × 10⁻⁶. 7 It must be (Ω) or greater.

[0146] [Table 1]

[0147] (Example 2) The image forming apparatus of Example 2 of the present invention is basically the same as that of Example 1, and the differences will be explained below.

[0148] Figure 8 is a conceptual cross-sectional view of an image forming apparatus according to Embodiment 2 of the present invention.

[0149] As shown in Figure 8, in the configuration of Embodiment 2, the drive roller 11 and the primary transfer roller 6 are electrically connected to the secondary transfer opposing roller 13 and are at the same potential.

[0150] In other words, the secondary transfer opposing roller 13 and the primary transfer roller 6 are grounded via a Zener diode 24, which is a voltage maintenance element. As a result, a voltage is applied to the primary transfer roller 6 by the Zener voltage generated at the cathode of the Zener diode 15 by the current applied from the secondary transfer roller 20, which acts as a current supply member.

[0151] Furthermore, the primary transfer current supplied from the primary transfer roller 6 passes through the inner layer 10b to the primary transfer nip N1, and the current is supplied to the photosensitive drum 1. In this embodiment, the Zener voltage is set to "300V" in order to obtain the desired primary transfer performance.

[0152] Example 2, similar to Example 1, can obtain good primary transfer performance in an intermediate transfer belt consisting of three layers: a base layer, an inner layer, and a surface layer.

[0153] Furthermore, in Example 2, instead of the primary transfer power supply 23 in Example 1 (shown in Figure 1), the primary transfer voltage is generated by a Zener diode 24 electrically connected to the secondary transfer opposing roller 13 and the primary transfer roller 6. As a result, Example 2 has the advantage of obtaining good primary transfer performance with a simpler configuration compared to Example 1.

[0154] (Example 3) The image forming apparatus of Example 3 of the present invention is basically the same as that of Example 1 or Example 2, and the differences will be explained below.

[0155] Figure 9 is a conceptual cross-sectional view of an image forming apparatus according to Embodiment 3 of the present invention.

[0156] In the aforementioned Examples 1 and 2, a primary transfer voltage was applied to create a potential difference between the potential of the surface of the photosensitive drum 1 and the potential of the intermediate transfer belt 10, thereby performing primary transfer of toner from the surface of the photosensitive drum 1 to the intermediate transfer belt 10. Example 3 is characterized by grounding the primary transfer members 6a to 6d and providing a drum power supply 24, which is a common negative power supply for the photosensitive drums 1a to 1d.

[0157] Specifically, in Example 3, the drum power supply 24 is connected to apply voltage to each of the photosensitive drum tubes 1a to 1d. Hereinafter, the voltage applied to the drum tubes by the drum power supply 24 will be referred to as the "drum voltage".

[0158] In Example 3, the configuration is the same as in Examples 1 and 2, except that the drum voltage is adjusted to create a potential difference between the surface potential of the photosensitive drum 1a and the surface potential of the intermediate transfer belt 10, thereby performing primary transfer.

[0159] Furthermore, Example 3, like Examples 1 and 2, can obtain good primary transfer performance in an intermediate transfer belt consisting of three layers: a base layer, an inner layer, and a surface layer.

[0160] In Example 3, instead of arranging drum power supplies 24 connected to each of the photosensitive drums 1a to 1d, the primary transfer rollers 6a to 6d can be grounded. This has the advantage that, compared to Examples 1 and 2, Example 3 allows for a simpler configuration of the tensioning unit that tensions the intermediate transfer belt 10, while still achieving good primary transfer performance.

[0161] The present invention can be summarized as follows.

[0162] (1) The image forming apparatus (100) of the present invention is An image carrier (1) that holds the toner image, An intermediate transfer belt (10) on which a toner image is transferred from an image carrier comprises a base layer (10a), a surface layer (10c) formed on the outer circumferential surface side of the base layer, and an inner surface layer (10b) formed on the inner circumferential surface side of the base layer, and is conductive, The current supply member (6) is positioned so as to sandwich the intermediate transfer belt between the image carrier, and the current supply member (6) has its center (C02) positioned downstream of the center (C01) of the image carrier in the rotational direction (R2) of the intermediate transfer belt.

[0163] When the volume resistivity of the intermediate transfer belt (10) in the thickness direction is Rv (Ω), the first surface resistivity in the surface direction on the inner layer (10b) side is Rs1 (Ω), and the second surface resistivity in the surface direction on the surface layer (10c) side is Rs2 (Ω), Rv>Rs1, Rs2 > Rs1, The relationship Rs² / Rv ≤ 40 is satisfied, and The second surface resistance value Rs2 is 3.00 × 10⁻⁶ 7 It is greater than or equal to (Ω).

[0164] (2) In the image forming apparatus of the present invention, the relationship Rs2 / Rv≦22 may be satisfied with respect to the volume resistivity Rv and the second surface resistivity Rs2.

[0165] This makes it possible to more effectively suppress the occurrence of image defects even under conditions where image formation is difficult due to discharge marks, such as low temperature and low humidity, or toner degradation.

[0166] (3) In the image forming apparatus of the present invention, the second surface resistance value Rs2 is set to 7.00 × 10 7 It can be (Ω) or greater.

[0167] This makes it possible to further suppress the flow of the primary transfer current supplied via the inner layer 10b to the photosensitive drum 1 without passing through the toner image during patch image formation. Therefore, the transferability of solid patch images can be further improved.

[0168] (4) In the image forming apparatus of the present invention, the volume resistivity Rv is set to 2.60 × 10 6 (Ω) ~ 3.51 × 10 7 It can be expressed as (Ω).

[0169] The primary transfer current supplied via the inner layer 10b flows in the primary transfer section in the thickness direction of the intermediate transfer belt 10 and reaches the photosensitive drum 1. By setting Rv within the above range, the resistance value of the current path can be stabilized.

[0170] That is, Rv = 2.60 × 10 6 By keeping the value below (Ω), the reduction in the primary transfer current can be effectively suppressed, further reducing transfer defects.

[0171] On the other hand, Rv is 3.51 × 10 7 By setting the value to (Ω) or higher, it is possible to effectively suppress the flow of the primary transfer current supplied via the inner layer 10b to the photosensitive drum 1 without passing through the toner image during patch image formation.

[0172] (5) In the image forming apparatus of the present invention, the volume resistivity Rv is further set to 4.57 × 10 6 (Ω) ~ 1.83 × 10 7 It can also be written as (Ω).

[0173] By setting Rv within the above range, the resistance value of the current path can be further stabilized.

[0174] That is, Rv = 1.83 × 10 7 By keeping the value below (Ω), the reduction in the primary transfer current can be more effectively suppressed, and transfer defects can be further reduced.

[0175] On the other hand, Rv is 4.57 × 10 6 By setting the value to (Ω) or higher, it is possible to further suppress the flow of the primary transfer current supplied via the inner layer 10b to the photosensitive drum 1 without passing through the toner image during patch image formation.

[0176] (6) In the image forming apparatus of the present invention, the second surface resistance value Rs2 is set to 6.41 × 10 8 It can be set to (Ω) or less. This further reduces the influence of surface potential memory.

[0177] (7) In the image forming apparatus of the present invention, the base layer (10a) can be the thickest layer in the thickness direction.

[0178] (8) In the image forming apparatus of the present invention, the surface layer (10c) may be provided in contact with the outer surface of the base layer (10a).

[0179] (9) In the image forming apparatus of the present invention, the inner layer (10b) may be provided in contact with the inner circumferential surface of the base layer (10a).

[0180] (10) In the image forming apparatus of the present invention, the current supply member (6) can be configured to press the intermediate transfer belt (10) from the side where the current supply member is located to the side where the image carrier (1) is located, thereby causing the intermediate transfer belt (10) to wrap around the surface of the image carrier (1). [Explanation of Symbols]

[0181] 1. Photosensitive drum (image carrier) 6. Primary transfer roller (current supply member) 10 Intermediate transfer belt 10a base layer 10b Inner layer 10c Surface layer (surface layer) 100 Image forming apparatus C01 Center of the photosensitive drum (image carrier) C02 Center of the primary transfer roller (current supply member) R2 Direction of movement (rotational direction) of the intermediate transfer belt surface Rv (volume resistivity) Rs1 Surface resistance value of the inner layer (first surface resistance value on the inner layer side) Rs2 Surface resistance value of the surface layer (second surface resistance value on the surface layer side)

Claims

1. An image carrier that holds the toner image, An intermediate transfer belt on which a toner image is transferred from the image carrier, comprising a base layer, a surface layer formed on the outer circumferential surface side of the base layer, and an inner surface layer formed on the inner circumferential surface side of the base layer, and having conductivity, An image forming apparatus having a current supply member positioned to sandwich the intermediate transfer belt between the image carrier and the current supply member, the current supply member having its center positioned downstream of the center of the image carrier in the rotational direction of the intermediate transfer belt, Let Rv (Ω) be the volume resistivity of the intermediate transfer belt in the thickness direction. Let Rs1 (Ω) be the first surface resistance value in the surface direction on the inner layer side. When the second surface resistance value in the surface direction on the surface layer side is Rs2 (Ω), Rv > Rs1, Rs2 > Rs1, 2. The relationship 186 ≤ Rs² / Rv ≤ 40 is satisfied, and The second surface resistance value Rs2 is 3.00 × 10 ７ An image forming apparatus characterized by being (Ω) or greater.

2. The volume resistance value Rv and the second surface resistance value Rs2 are, The image forming apparatus according to claim 1, characterized in that it satisfies the relationship Rs² / Rv ≤ 22.

3. The second surface resistance value Rs2 is 7.00 × 10 ７ The image forming apparatus according to claim 1 or 2, characterized in that it is (Ω) or greater.

4. The aforementioned volume resistivity Rv is 2.60 × 10 ６ (Ω) ~3.51×10 ７ The image forming apparatus according to any one of claims 1 to 3, characterized in that it is (Ω).

5. The aforementioned volume resistivity Rv is 4.57 × 10 ６ (Ω) ~1.83×10 ７ The image forming apparatus according to claim 4, characterized in that it is (Ω).

6. The second surface resistance value Rs2 is 6.41 × 10⁻⁶ ８ The image forming apparatus according to claim 4 or 5, characterized in that it is less than or equal to (Ω).

7. The image forming apparatus according to any one of claims 1 to 6, characterized in that the base layer is the thickest layer in the thickness direction.

8. The image forming apparatus according to any one of claims 1 to 7, characterized in that the surface layer is provided in contact with the outer surface of the base layer.

9. The image forming apparatus according to any one of claims 1 to 8, characterized in that the inner surface layer is provided in contact with the inner circumferential surface of the base layer.

10. The image forming apparatus according to any one of claims 1 to 9, characterized in that the current supply member is configured such that the intermediate transfer belt wraps around the surface of the image carrier by pressing the intermediate transfer belt from the side where the current supply member is located toward the side where the image carrier is located.

Images