Image forming apparatus

Abstract

This disclosure relates to an image forming apparatus. The image forming apparatus includes an image carrier member comprising an intermediate transfer belt of a base layer, an inner surface layer, and a surface layer, and a contact member configured to contact the intermediate transfer belt. The image forming apparatus satisfies Rv>Rs1, Rs2>Rs1, and Rs2 / Rv≤40, where Rv(Ω) is the volume resistivity of the intermediate transfer belt in the thickness direction, Rs1(Ω) is a first surface resistance value in the surface direction on the inner surface layer side, and Rs2(Ω) is a second surface resistance value in the surface direction on the surface layer side.

Description

TECHNICAL FIELD

[0001] The present application relates to an image forming apparatus employing an electrophotographic method, such as a laser printer, a copier, and a facsimile. BACKGROUND

[0002] Hitherto, an image forming apparatus including an intermediate transfer member is known.

[0003] In such an image forming apparatus, in a primary transfer process, a toner image formed on the surface of a photosensitive drum is primary transferred onto an intermediate transfer member by applying a voltage to a primary transfer member (primary transfer portion) disposed facing the photosensitive drum. Further, by repeating the primary transfer process for toner images of a plurality of colors, toner images of the plurality of colors are formed on the surface of the intermediate transfer member.

[0004] Then, in a secondary transfer process, the toner images of the plurality of colors formed on the surface of the intermediate transfer member are collectively transferred onto the surface of a recording medium such as paper by applying a voltage to a secondary transfer member. Then, the toner images transferred onto the surface of the recording medium are fixed to the recording medium by a fixing unit to form a color image.

[0005] Japanese Patent Application Publication No. 2018-36624 discusses a configuration in which, in order to improve transferability, a low-resistance layer is formed on an inner circumferential surface of a base layer of an intermediate transfer belt, and a primary transfer voltage is applied to cause current to flow from a primary transfer member in the circumferential direction of the intermediate transfer belt. SUMMARY

[0006] The present application relates to an image forming apparatus capable of suppressing occurrence of image defects while achieving excellent primary transferability of an intermediate transfer belt including three or more layers.

[0007] According to an aspect of the present application, an image forming apparatus includes an image bearing member configured to bear a toner image; an endless conductive intermediate transfer belt configured to contact the image bearing member and to which the toner image is transferred from the image bearing member, the intermediate transfer belt including a base layer, a surface layer formed on an outer circumferential surface side of the base layer, and an inner surface layer formed on an inner circumferential surface side of the base layer; and a contact member configured to contact the intermediate transfer belt from an opposite side of the intermediate transfer belt to the image bearing member, wherein, from a direction of a rotation axis of the image bearing member, a position at which the contact member contacts the intermediate transfer belt is disposed on a downstream side of the intermediate transfer belt in a rotation direction of the intermediate transfer belt with respect to a rotation center of the image bearing member, and wherein Rv > Rs1 and Rs2 > Rs1 are satisfied, and Rs2 / Rv ≤ 40, where Rv (Ω) is a volume resistance value of the intermediate transfer belt in a thickness direction, Rs1 (Ω) is a first surface resistance value of the inner surface layer side in a surface direction, and Rs2 (Ω) is a second surface resistance value of the surface layer side in the surface direction.

[0008] Other features of the present application will become apparent from the following description of example embodiments thereof, taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 is a cross-sectional view schematically illustrating an image forming apparatus according to a first example embodiment of the present application.

[0010] Figure 2 is a control block diagram of the image forming apparatus according to the first example embodiment of the present application.

[0011] Figure 3 is a cross-sectional view schematically illustrating a primary transfer portion of the image forming apparatus according to the first example embodiment of the present application.

[0012] Figure 4 is a cross-sectional view schematically illustrating an intermediate transfer belt of the image forming apparatus according to the first example embodiment of the present application.

[0013] Figure 5A and Figure 5B are diagrams each schematically illustrating a primary transfer current path la and lb of the image forming apparatus according to the first example embodiment of the present application.

[0014] Figure 6 is a diagram schematically illustrating a current path when measuring a surface resistivity of a surface side of the intermediate transfer belt of the image forming apparatus according to the first example embodiment of the present application.

[0015] Figure 7 is a diagram schematically illustrating a primary transfer current path with respect to Comparative Example 6 of the first example embodiment of the present application.

[0016] Figure 8 is a schematic cross-sectional view illustrating an image forming apparatus according to a second exemplary embodiment of the present application.

[0017] Figure 9 is a schematic cross-sectional view illustrating an image forming apparatus according to a third exemplary embodiment of the present application. DETAILED DESCRIPTION

[0018] Exemplary embodiments of the present application will be described in detail with reference to the accompanying drawings. Note that the size, material, and shape of components described in the following exemplary embodiments, as well as their relative arrangement, are not intended to limit the scope of the present application, and can be appropriately changed depending on the configuration and various conditions of the apparatus to which the present application is applied.

[0019] 1. Image forming apparatus

[0020] Figure 1 is a schematic cross-sectional view illustrating an image forming apparatus according to a first exemplary embodiment.

[0021] More specifically, Figure 1 is a longitudinal cross section illustrating the configuration of the image forming apparatus 100 according to the present exemplary embodiment.

[0022] As Figure 1 illustrated, the image forming apparatus 100 is a so-called tandem type image forming apparatus including a plurality of image forming units (stations) Sa, Sb, Sc, and Sd. The first image forming unit Sa, the second image forming unit Sb, the third image forming unit Sc, and the fourth image forming unit Sd form respective images using yellow (Y) toner, magenta (M) toner, cyan (C) toner, and black (Bk) toner.

[0023] The four image forming units Sa, Sb, Sc, and Sd are arranged in a row at predetermined intervals, and the image forming units Sa, Sb, Sc, and Sd have substantially the same configuration except for the color of the toner stored therein. For this reason, the image forming apparatus 100 according to the first exemplary embodiment (as well as the second exemplary embodiment and the third exemplary embodiment) will be described mainly using the first image forming unit Sa.

[0024] The first image forming unit Sa includes a photosensitive drum 1a as a photosensitive member having a drum shape, a charging roller 2a as a charging member, a developing unit 4a, and a drum cleaning unit 5a.

[0025] The photosensitive drum 1a is an image bearing member for carrying a toner image, and is rotationally driven in the arrow R1 direction at a predetermined process speed (200 mm / s in the first exemplary embodiment). The developing unit 4a includes a developer container 41a for accommodating yellow toner, and a developing roller 42a serving as a developing member for carrying the yellow toner supplied from the developer container 41a to develop a yellow toner image on the photosensitive drum 1a.

[0026] The drum cleaning unit 5a is a unit for collecting toner adhering to the photosensitive drum 1a. The drum cleaning unit 5a includes a cleaning blade in contact with the photosensitive drum 1a, and a waste toner box for accommodating toner removed from the photosensitive drum 1a by the cleaning blade.

[0027] When the DC controller 274 (see Figure 2 ) serving as a controller receives an image signal to start an image forming operation, the photosensitive drum 1a is rotationally driven. During the rotation of the photosensitive drum 1a, the photosensitive drum 1a is uniformly charged with a predetermined polarity (negative polarity in the first exemplary embodiment) at a predetermined potential (a dark portion potential Vd) by the charging roller 2a, and is exposed by the exposure unit 3a based on the image signal.

[0028] Thus, an electrostatic latent image corresponding to a yellow component image of a target color image is formed.

[0029] Next, the electrostatic latent image is developed by the developing roller 42a at a developing position, and is visualized as a yellow toner image (hereinafter simply referred to as a toner image). The developing roller 42a is rotated at a speed of 300 mm / s, which is 1.5 times the speed of the photosensitive drum 1a, in the same direction as the photosensitive drum 1a to stably develop the photosensitive drum 1a.

[0030] At this time, in the present exemplary embodiment, the normal charging polarity of the toner contained in the developing unit 4a is negative. The developing roller 42a performs reversal development of the electrostatic latent image by toner charged with the same polarity as the photosensitive drum 1a charged via the charging roller 2a. However, the present application is applicable to an image forming apparatus configured to perform normal development of the electrostatic latent image using toner charged with a polarity opposite to the charging polarity of the photosensitive drum 1a.

[0031] An annular movable intermediate transfer belt 10 serving as an intermediate transfer member is arranged at a position in contact with the photosensitive drums 1a to 1d of the image forming units Sa to Sd, and is stretched around three shafts including a drive roller 11, a stretching roller 12, and a secondary transfer opposing roller 13 each serving as a stretching member. The intermediate transfer belt 10 is stretched by the stretching roller 12 at a total tension of 60 N, and is moved in the arrow R2 direction via rotation of the secondary transfer opposing roller 13 which is rotated by receiving a driving force.

[0032] During transfer of the toner image through the primary transfer nip Nla of the photosensitive drum 1a and the intermediate transfer belt 10, the toner image formed on the photosensitive drum 1a is primary-transferred onto the intermediate transfer belt 10 by applying a voltage having a positive polarity from the primary transfer power source 23 to the primary transfer roller 6a. Then, the toner remaining on the photosensitive drum 1a without being primary-transferred onto the intermediate transfer belt 10 is collected by the drum cleaning unit 5a to be removed from the surface of the photosensitive drum 1a.

[0033] In the present exemplary embodiment, during primary transfer, a current is caused to flow from a contact member contacting the intermediate transfer belt 10 to the intermediate transfer belt 10. With this current, a primary transfer potential is formed at a primary transfer portion of each of the image forming units Sa to Sd (image forming stations) of the intermediate transfer belt 10.

[0034] In addition, a method of generating a primary transfer potential of the image forming apparatus 100 according to the present exemplary embodiment will be described in detail below.

[0035] Similarly to the yellow (first color) toner image, a magenta (second color) toner image, a cyan (third color) toner image, and a black (fourth color) toner image are formed and sequentially transferred in an overlapping manner onto the intermediate transfer belt 10. In this way, four-color toner images corresponding to a target color image are formed on the intermediate transfer belt 10. Then, the four-color toner images carried by the intermediate transfer belt 10 are secondary-transferred onto a transfer medium (recording medium) P such as a sheet or an overhead projector sheet fed from the paper feed unit 50 through the secondary transfer nip N2 formed by the secondary transfer roller 20 and the intermediate transfer belt 10 being in contact with each other.

[0036] The secondary transfer roller 20 is a roller having an outer diameter of 18 mm formed of a nickel-plated steel rod having an outer diameter of 8 mm covered with a foamed sponge material adjusted to have a 10 8The foamed sponge material has a volume resistivity of 1 Ω-cm and a thickness of 5 mm, and mainly includes nitrile rubber (NBR) and epoxide chloropropane rubber. In addition, the rubber hardness of the foamed sponge material was measured to be 30 degrees using an ASKER durometer C under a load of 500 grams. The secondary transfer roller 20 is in contact with the outer peripheral surface of the intermediate transfer belt 10, and a secondary transfer nip N2 is formed by the secondary transfer roller 20 being pressed against the secondary transfer counter roller 13 provided facing the secondary transfer roller 20 via the intermediate transfer belt 10 with a pressing force of 50 N.

[0037] The secondary transfer roller 20 is rotationally driven by the intermediate transfer belt 10, and is applied with a voltage from the secondary transfer power source 21. Thereby, a current flows from the secondary transfer roller 20 to the secondary transfer counter roller 13. In this way, the toner image carried by the intermediate transfer belt 10 is secondary transferred to the transfer medium P at the secondary transfer nip N2.

[0038] When the toner image on the intermediate transfer belt 10 is secondary transferred to the transfer medium P, the voltage applied to the secondary transfer roller 20 from the secondary transfer power source 21 is controlled so that a current constantly flows from the secondary transfer roller 20 to the secondary transfer counter roller 13 via the intermediate transfer belt 10. In addition, the magnitude of the current used to perform the secondary transfer is determined in advance based on the surrounding environment in which the image forming apparatus 100 is installed and the type of the transfer medium P.

[0039] The secondary transfer power source 21 is connected to the secondary transfer roller 20 to apply a transfer voltage to the secondary transfer roller 20. In addition, the secondary transfer power source 21 can output a voltage in a range from 100 V to 4000 V.

[0040] Then, the transfer medium P on which the toner images of the four colors are transferred by the secondary transfer is heated and pressed with the fixing unit 30. As a result, the toners of the four colors are melted and mixed to be fixed to the transfer medium P. On the other hand, the toner remaining on the intermediate transfer belt 10 after the secondary transfer is removed and cleaned by the belt cleaning unit 16 (collection unit) provided on the downstream side of the secondary transfer nip N2 in the moving direction of the intermediate transfer belt 10.

[0041] The belt cleaning unit 16 includes a cleaning blade 16a and a waste toner container 16b. The cleaning blade 16a serving as a contact member is in contact with the outer peripheral surface of the intermediate transfer belt 10 at a position facing the secondary transfer counter roller 13, and the waste toner container 16b accommodates the toner collected by the cleaning blade 16a. Hereinafter, the cleaning blade 16a will be simply referred to as the blade 16a.

[0042] In the image forming apparatus 100 according to the first example embodiment, a full-color print image is formed as described above.

[0043] 2. Control of image forming operation

[0044] Next, the control of the image forming operation according to the first exemplary embodiment will be described with reference to a control block diagram.

[0045] Figure 2 is a block diagram illustrating a control block of the image forming apparatus according to the first exemplary embodiment.

[0046] More specifically, Figure 2 A control block for controlling the operation of the image forming apparatus 100 is illustrated.

[0047] As Figure 2 shown, a personal computer (PC) 271 serving as a host computer issues a print instruction to a formatter 273 serving as a conversion unit included in the image forming apparatus 100 to transmit image data of a print image to the formatter 273.

[0048] The formatter 273 receives red / green / blue (RGB) image data or cyan / magenta / yellow / black (CMYK) image data from the PC 271 and converts the received image data into CMYK exposure data in a mode specified by the PC 271. The exposure data converted at this time has a resolution of 600 dots per inch (dpi). The mode specified from the PC 271 includes a mode related to image quality in addition to a paper type and a paper size.

[0049] On the other hand, the formatter 273 transmits the converted exposure data to an exposure control unit 277 serving as an exposure control device included in a DC controller 274. The exposure control unit 277 controls the exposure units 3a to 3d in accordance with an instruction from a central processing unit (CPU) 276.

[0050] In the image forming apparatus 100 shown in Figure 2 , halftone control is performed by adjusting the on and off areas of the exposure data. The CPU 276 starts an image forming sequence upon receiving a print instruction from the formatter 273.

[0051] The DC controller 274 includes the CPU 276, a memory 275, and the like, and performs a pre-programmed operation. The CPU 276 controls a charging high voltage (charging power supply 281), a developing high voltage (developing power supply 280), and a transfer high voltage (primary transfer power supply 23 and secondary transfer power supply 21) to form an electrostatic latent image, and also controls a transferred toner image after development and the like to form an image.

[0052] Furthermore, the CPU 276 also processes signals received from the optical sensor 60, which acts as a detection unit used in performing correction control to correct the position and density of the image to be formed by the image forming apparatus 100. In image correction control, the optical sensor 60 measures the amount of reflected light reflected from a test patch (for detection of the toner image) formed on the outer peripheral surface of the intermediate transfer belt 10 at a position facing the optical sensor 60.

[0053] In addition, the detection signal detected by the optical sensor 60 is converted from analog to digital (AD) by the CPU 276 and then stored in the memory 275. The DC controller 274 uses the detection results from the optical sensor 60 to perform calculations and various corrections.

[0054] 3. Stretching configuration of the intermediate transfer belt

[0055] Next, the intermediate transfer belt 10 used in the image forming apparatus 100 according to this exemplary embodiment will be described, as well as the drive roller 11, the stretching roller 12 and the secondary transfer opposing roller 13, which are stretching members of the intermediate transfer belt 10, and the primary transfer rollers 6a to 6d.

[0056] like Figure 1 As shown, the intermediate transfer belt 10 is arranged as an intermediate transfer component at positions facing each image forming unit Sa to Sd. The intermediate transfer belt 10 is an annular belt formed by adding a conductive agent to the resin material to increase its conductivity. The intermediate transfer belt 10 is stretched by three axes, which include a drive roller 11, a stretching roller 12, and a secondary transfer opposing roller 13, which serve as stretching components. Thus, the intermediate transfer belt 10 is stretched by the stretching roller 12 with a total tension of 60 N.

[0057] In addition, such as Figure 1 As shown, primary transfer rollers 6a to 6d are disposed downstream of the photosensitive drums 1a, 1b, 1c, and 1d respectively, along the moving direction of the intermediate transfer belt 10. Primary transfer rollers 6a to 6d are contact members that contact the inner circumferential surface of the intermediate transfer belt 10.

[0058] Figure 3 This is a cross-sectional view schematically illustrating a primary transfer portion of the image forming apparatus 100 according to this exemplary embodiment. Since the image forming units Sa, Sb, Sc, and Sd have substantially the same configuration, the image forming apparatus 100 according to the first exemplary embodiment will be described primarily using the first image forming unit Sa.

[0059] More specifically, Figure 3 The arrangement between the photosensitive drum 1a and the primary transfer roller 6a is illustrated.

[0060] likeFigure 3 As shown, in the image forming unit Sa, the primary transfer roller 6a is disposed at the downstream side of the photosensitive drum la along the rotation direction R2 of the intermediate transfer belt 10. More specifically, a perpendicular line L04 to the intermediate transfer belt 10 is located at the downstream side of a perpendicular line L03 to the intermediate transfer belt 10 along the rotation direction R2 of the intermediate transfer belt 10. The perpendicular line L04 passes through the rotation center C02 of the primary transfer roller 6a, and the perpendicular line L03 passes through the rotation center C01 of the photosensitive drum la.

[0061] Further, the primary transfer roller 6a is arranged at a position where it enters the surface of the intermediate transfer belt 10, so that a "winding amount" of the intermediate transfer belt 10 around the photosensitive drum la can be ensured in the image forming unit Sa. In addition, Figure 3 The broken line L01 in FIG. 10 illustrates a position of the surface of the intermediate transfer belt 10 before the primary transfer roller 6a enters the surface of the intermediate transfer belt 10. On the other hand, Figure 3 The broken line L02 in FIG. 10 illustrates a position of the vertex 10cl of the surface of the intermediate transfer belt 10 after the primary transfer roller 6a enters the surface of the intermediate transfer belt 10. In the present exemplary embodiment, the vertex 10cl is a position where the intermediate transfer belt 10 and the primary transfer roller 6a contact.

[0062] In the present exemplary embodiment, the primary transfer roller 6a is a metal roller composed of a straight nickel-plated round bar having a diameter of 6 mm formed of Steel User Stainless (SUS). The primary transfer roller 6a rotates along with the rotation of the intermediate transfer belt 10. On the other hand, in the first exemplary embodiment, the photosensitive drum la has an outer diameter of 24 mm. The primary transfer roller 6a contacts the intermediate transfer belt 10 over a predetermined region in the length direction (width direction) orthogonal to the moving direction of the intermediate transfer belt 10.

[0063] Further, a distance between a perpendicular line L03 drawn from the rotation center C01 of the photosensitive drum la and a perpendicular line L04 drawn from the rotation center C02 of the primary transfer roller 6a is defined as W, and a height of the intermediate transfer belt 10 lifted by the primary transfer roller 6a (i.e., a distance between the broken lines L01 and L02) is defined as Hl. At this time, in the first exemplary embodiment, W = 10 mm, and Hl = 2 mm.

[0064] In addition, a voltage is applied to the primary transfer roller 6a from the primary transfer power source 23, and a primary transfer current (described below) is supplied through the inner peripheral surface conductive layer of the intermediate transfer belt 10. In the first exemplary embodiment, 300 V is applied as the primary transfer voltage.

[0065] 4. Intermediate transfer belt

[0066] Next, the intermediate transfer belt 10 as a feature of the first example embodiment will be described.

[0067] Figure 4 is a schematic cross-sectional view illustrating the intermediate transfer belt 10 of the image forming apparatus 100 according to the first example embodiment.

[0068] More specifically, Figure 4 A vertical cross-sectional view in the thickness direction of the intermediate transfer belt 10 used in the first example embodiment is illustrated.

[0069] In the present example embodiment, the intermediate transfer belt 10 has a circumference of 700 mm and a thickness of 90 μm, and has a three-layer configuration including a base layer 10a, an inner surface layer 10b formed on the inner circumferential surface of the base layer 10a, and a surface layer 10c formed on the outer circumferential surface of the base layer 10a.

[0070] The base layer 10a is a ring-shaped layer formed of polyethylene naphthalate (PEN) mixed with an ion conductive material as a conductive agent. Further, the inner surface layer 10b is a layer formed of an acrylic resin mixed with carbon as a conductive agent. The surface layer 10c is a layer formed of an acrylic resin mixed with a metal oxide as a conductive agent.

[0071] More specifically, the inner surface layer 10b is a layer formed on the inner side (stretching axis side) of the base layer 10a. Assuming that the thickness of the polyvinylidene fluoride layer as the base layer 10a is tl, the thickness of the acrylic resin layer as the inner surface layer 10b is t2, and the thickness of the acrylic resin layer as the surface layer 10c is t3, tl = 87 μm, t2 = 2 μm, and t3 = 3 μm.

[0072] Further, in the present example embodiment, PEN is used as the material of the base layer 10a of the intermediate transfer belt 10. However, other materials can be used. For example, materials such as polyester or acrylonitrile-butadiene-styrene (ABS) copolymer or a mixed resin thereof can be used.

[0073] Further, in the present example embodiment, an acrylic resin is used as the material of the inner surface layer 10b of the intermediate transfer belt 10. However, other materials can be used. For example, materials such as polyester can be used.

[0074] Further, in the present example embodiment, an acrylic resin is used as the material of the surface layer 10c of the intermediate transfer belt 10. However, other materials can be used. For example, materials such as polyester can be used.

[0075] In the present example embodiment (Experiment Examples 1 to 9), the preferable resistance value of the intermediate transfer belt 10 was set as the resistance value of the intermediate transfer belt 10 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 surface layer 10b side.

[0076] Further, the volume resistivity was measured using a UR type ring probe (MCP-HTP12) attached to a Hiresta-UP (MCP-HT450) of Mitsubishi Chemical Corporation. As a probe opposing electrode, a metal surface of a Register table UFL was used.

[0077] On the other hand, the surface resistivity was measured using a UR 100 type ring probe (MCP-HTP16) attached to the same measuring device as that used for the measurement of the volume resistivity. As a probe opposing electrode, a metal surface of a Register table UFL was used.

[0078] Further, the measurement of the volume resistivity was performed under conditions in which the probe was pressed from the front surface side of the intermediate transfer belt 10 at a pressing force of 1 kg, the applied voltage was 250 V, and the measurement time was 10 s. The measurement of the volume resistivity is the measurement of the resistance value in the thickness direction of the intermediate transfer belt 10, and corresponds to the measurement of the resistance value of the base layer 10a. If the applied voltage is too high, it is difficult to detect the change in the volume resistivity. On the other hand, if the applied voltage is too low, the repeatability of the measurement value is reduced due to the influence of the surface shape of the surface layer 10c or the influence of foreign matter attached to the probe. In view of these conditions, in the first example embodiment, the applied voltage was determined to be 250 V.

[0079] The measurement of the surface resistivity of the inner surface layer 10b was performed under conditions in which the probe was pressed from the inner surface side of the intermediate transfer belt 10 at a pressing force of 1 kg, the applied voltage was 10 V, and the measurement time was 10 s.

[0080] Further, the measurement of the surface resistivity of the surface layer 10c was performed under conditions in which the probe was pressed from the inner surface side of the intermediate transfer belt 10 at a pressing force of 1 kg, the applied voltage was 100 V, and the measurement time was 10 s.

[0081] ​The measurement of the surface resistivity of the surface layer 10c corresponds to the measurement of the resistance value of the surface layer 10c. If the applied voltage is too high, the amount of current passing through the base layer 10a and the inner surface layer 10b increases. On the other hand, if the applied voltage is too low, a case where the resistance value cannot be measured because no current flows between the probe electrodes, or a case where the repeatability of the measured value is reduced due to the influence of the surface shape of the surface layer 10c or the influence of foreign matter attached to the probe, can occur. For this reason, the applied voltage is determined to be 100 V in the first example embodiment in consideration of these conditions.

[0082] In addition, in the present example embodiment, as the measurement environment of the resistance value, the indoor temperature is set to 23°C and the indoor humidity is set to 50%.

[0083] The above-described "volume resistivity" and "surface resistivity" are defined by Japanese Industrial Standards (JIS) K 6911 and are represented by the following equations (1) and (2).

[0084] Volume resistivity pv (Ω-cm) = R (Ω) x RCFv x t (cm)... (1)

[0085] Surface resistivity ps (Ω / D) = R (Ω) x RCFs... (2)

[0086] RCFv in equation (1) and RCFs in equation (2) are resistivity correction coefficients and are constants set for each probe used for measurement.

[0087] In the present example embodiment, a UR-type ring probe (MCP-HTP12) is used to measure the "volume resistivity", and RCFv is 2.011 in this case.

[0088] Further, a UR 100-type ring probe (MCP-HTP16) is used to measure the "surface resistivity", and RCFs is 100 in this case.

[0089] Further, "t" in equation (1) is the thickness of the intermediate transfer belt 10.

[0090] In the present example embodiment, the resistance values calculated according to equation (1) and equation (2) will be described to compare the resistance values (R) in the thickness direction and in the surface direction.

[0091] In the following description, the resistance value obtained by converting the volume resistivity (pv) using equation (1) is referred to as the "volume resistance value (Rv)", and the resistance value obtained by converting the surface resistivity (ps) using equation (2) is referred to as the surface resistance value (Rs). In Experimental Example 1 of the first example embodiment, as described in Table 1 below, the intermediate transfer belt 10 has a volume resistivity (pv) of 1.62 x 1010Ω-cm and a surface resistivity (ps) of 1.62 x 1011Ω / D. 7The volume resistivity (Ω) is 1.10 × 10⁻⁶. 5 The surface resistivity of the inner surface layer 10b (Ω) and 3.55 × 10 7 The surface resistance value of surface layer 10c is (Ω). Therefore, in "Experimental Example 1", assuming the volume resistivity is Rv, the surface resistance of inner surface layer 10b is Rs1, and the surface resistance of surface layer 10c is Rs2, the value of Rs1 is lower than the values ​​of Rv and Rs2, and Rs2 / Rv is 2.19.

[0092] Next, refer to Figure 5A and Figure 5B The reason why the surface resistance value Rs1 of the inner surface layer 10b is set to be lower than, for example, the surface resistance value Rs2 of the surface layer 10c will be described in this exemplary embodiment.

[0093] Figure 5A and Figure 5B These are schematic diagrams illustrating the primary transfer current path Ia and primary transfer current path Ib of the image forming apparatus 100 according to a first exemplary embodiment of the present invention.

[0094] More specifically, Figure 5A and Figure 5B The illustration shows the state in which the current supplied from the primary transfer roller 6 flows in two different current paths, including current path Ia and current path Ib.

[0095] like Figure 5A As shown, in the current path Ia, the primary transfer current supplied from the primary transfer roller 6 flows mainly in the inner surface layer 10b in the direction opposite to the rotation direction R2 of the intermediate transfer belt 10. Furthermore, the primary transfer current reaches the primary transfer roller gap N1, which serves as the contact point between the photosensitive drum 1 and the intermediate transfer belt 10, and flows towards the photosensitive drum 1.

[0096] On the other hand, such as Figure 5B As shown, for current path Ib, the primary transfer current mainly flows in surface layer 10c. More specifically, when the inner surface layer 10b, base layer 10a, and surface layer 10c have similar resistance values, the primary transfer current passes through the base layer 10a or surface layer 10c, which serves as the current path from primary transfer roller 6 to primary transfer roller gap N1.

[0097] In this case, in such Figure 5BIn the case of the "current path Ib" shown, the surface layer 10c has a positive polarity, and there is a possibility that a discharge current can be generated between the intermediate transfer belt 10 and the photosensitive drum 1 disposed on the downstream side of the primary transfer nip Nl in the direction R2. As a result, there is a possibility that an image defect having a discharge pattern can occur in the corresponding image forming unit at the time of transfer, or so-called "re-transfer" can occur. Re-transfer is a phenomenon in which toner once transferred to the intermediate transfer belt 10 is transferred to the photosensitive drum 1 disposed at a station on the downstream side of the intermediate transfer belt 10 in the direction of rotation R2.

[0098] Therefore, it is necessary to bypass the "current path Ib" shown to suppress a discharge current generated on the downstream side of the primary transfer nip Nl in the direction R2, and prevent re-transfer. Therefore, in the present exemplary embodiment, the resistance value of the inner surface layer 10b is made sufficiently smaller than the resistance values of the base layer 10a and the surface layer 10c to achieve a configuration in which the primary transfer current reaches the primary transfer nip Nl mainly through the inner surface layer 10b. In other words, the "current path Ia" shown is achieved. Figure 5B Figure 5A The "current path Ia" shown.

[0099] Next, a preferred relationship between the volume resistance value Rv and the surface resistance value Rs2 on the surface layer 10c side will be described.

[0100] Figure 6 is a diagram schematically illustrating a current path at the time of measuring the surface resistance value Rs2 on the surface layer 10c side of the intermediate transfer belt 10 of the image forming apparatus 100 according to the first exemplary embodiment.

[0101] As shown in Figure 6 The surface resistance value Rs2 on the surface layer 10c side is obtained by measuring the current flowing from the positive electrode to the negative electrode that contacts the surface layer 10c.

[0102] Since the thickness "t3" of the surface layer 10c is thin (3 μm), the current flowing between the electrodes of the probe passes through the base layer 10a in addition to the surface layer 10c to reach the negative electrode from the positive electrode at the time of measuring the surface resistance value Rs2 of the surface layer 10c. Further, since the intermediate transfer belt 10 according to the first exemplary embodiment includes the inner surface layer 10b, a portion of the current flowing between the electrodes of the probe passes through the inner surface layer 10b. As a result, the surface resistance value Rs2 of the surface layer 10c is measured as if it is lower than the actual resistance value.

[0103] ​In a case where the surface resistance value Rs2 of the surface layer 10c is high, for example, at the time when a voltage is applied to the secondary transfer roller 20, a discharge current can be generated between the secondary transfer roller 20 and the intermediate transfer belt 10, affected by the pattern of the toner image or unevenness of the paper. With this discharge current, electric charges are accumulated on the surface layer 10c of the intermediate transfer belt 10 to form a potential as a potential memory. In this way, the potential can be maintained on the surface layer 10c. If primary transfer is performed in this state, a discharge current is generated between the photosensitive drum 1 on the upstream side of the primary transfer nip Nl in the rotation direction R2 of the intermediate transfer belt 10 and the intermediate transfer belt 10.

[0104] With this discharge current, a phenomenon called pre-transfer occurs. This phenomenon is a phenomenon in which the primary transfer toner on the photosensitive drum 1 is transferred to the intermediate transfer belt 10 at a gap between the photosensitive drum 1 on the upstream side of the primary transfer nip Nl and the intermediate transfer belt 10. Due to this primary transfer failure, an image defect in which the quality of the formed image is deteriorated or a discharge trace is formed as a toner image can occur.

[0105] In the present exemplary embodiment, in order to prevent such a primary transfer failure, the surface resistance value Rs2 of the surface layer 10c of the intermediate transfer belt 10 is investigated so as to have a preferable surface resistance value, in consideration of the amount of passage current into the inner surface layer 10b. Further, since the preferable primary transfer voltage varies depending on the volume resistance value, the surface resistance value Rs2 of the surface layer 10c is set to be able to suppress an image defect caused by the above-described discharge current, in consideration of the volume resistance value.

[0106] <Evaluation>

[0107] Next, an evaluation regarding the first exemplary embodiment will be described.

[0108] Table 1 describes the comparison results of Experimental Examples 1 to 9 according to the first exemplary embodiment and Comparative Examples 1 to 6 of the first exemplary embodiment obtained by changing the volume resistance value Rv of the intermediate transfer belt 10 and the surface resistance value Rs2 of the surface layer 10c used in the first exemplary embodiment.

[0109] More specifically, Table 1 includes the volume resistance value Rv, the surface resistance value Rs1 on the inner surface layer side, the surface resistance value Rs2 on the surface layer side, Rs2 / Rv, and the image evaluation results (A) to (F) for each intermediate transfer belt 10 of Experimental Examples 1 to 9 and Comparative Examples 1 to 6.

[0110] In addition, Comparative Examples 1 to 6 and Experimental Examples 1 to 9 differ only in the resistance value of the intermediate transfer belt 10 of the first exemplary embodiment, and the other configurations are the same as those of Experimental Examples 1 to 9.

[0111] The intermediate transfer belts 10 in Experimental Examples 1 to 9 and Comparative Examples 1 to 6 of the first exemplary embodiment have the same materials and shapes in the base layer 10a, the inner surface layer 10b, and the surface layer 10c. The resistance values thereof are adjusted by adjusting the amount of the electrically conductive agent to be added to the respective layers.

[0112] Next, with reference to Table 1, the evaluation of the “image quality” of each of the evaluation images (A) to (F) according to the first exemplary embodiment will be described.

[0113] Table 1 includes the resistance values of the intermediate transfer belts 10 in Experimental Examples 1 to 9 and Comparative Examples 1 to 6 according to the first exemplary embodiment measured at an ambient temperature of 23°C and a humidity of 50%, and the transferability of the images formed at the primary transfer portions of the respective intermediate transfer belts 10 at an ambient temperature of 23°C and a humidity of 50%.

[0114] Further, for the “evaluation images (A) to (E)” shown in Table 1, an A4-size sheet GF-C081 (produced by CANON) having a grammage of 81.4 g / m 2 was used.

[0115] More specifically, as the evaluation image (E), a full-page solid color (solid color in Table 1) image having an average density of 100% of yellow, magenta, cyan, and black was printed and evaluated.

[0116] Further, as the evaluation image (D), a solid color patch image having 10 mm x 10 mm square color patches for various colors arranged discretely was printed and evaluated.

[0117] Further, as the evaluation images (B) and (C), full-page half-tone (HT in Table 1) images having average densities of 20% and 50%, respectively, were printed and evaluated.

[0118] Further, as the evaluation image (F), a full-page sum (secondary) color (Ary color in Table 1) image of red, green, and blue having an average density of 200% was printed and evaluated.

[0119] Further, as the evaluation image (A), a text image including yellow, magenta, cyan, and black texts each having an average density of 100% was printed and evaluated.

[0120] First, the evaluation results of Experimental Examples 1 to 9 of the intermediate transfer belt 10 according to the first exemplary embodiment will be described.

[0121] As shown in Table 1, in the present exemplary embodiment, the volume resistivity value Rv of the intermediate transfer belt 10 in each of Experimental Examples 1 to 9 was in the range from 2.60 x 10 6 (Ω) to 3.51 x 10 7 (Ω), and the surface resistivity value Rs1 of the inner surface layer 10b was in the range from 1.10 x 10 3 (Ω) to 1.10 x 10 5 (Ω).

[0122] In the present exemplary embodiment, the surface resistivity value Rs2 of the surface layer 10c of the intermediate transfer belt 10 in each of Experimental Examples 1 to 9 was in the range from 3.55 x 10 7 (Ω) to 6.41 x 10 8 (Ω), and Rs2 / Rv was in the range from 2.186 to 38.740.

[0123] On the other hand, the volume resistivity value Rv of the intermediate transfer belt 10 in each of Comparative Examples 1 to 5 was in the range from 1.56 x 10 6 (Ω) to 1.42 x 10 8 (Ω), and the surface resistivity value Rs1 of the inner surface layer 10b was 1.10 x 10 5 (Ω). The surface resistivity value Rs2 of the surface layer 10c of the intermediate transfer belt 10 in each of Comparative Examples 1 to 5 was in the range from 1.23 x 10 8 (Ω) to 6.04 x 10 10 (Ω), and Rs2 / Rv was in the range from 53.564 to 424.523.

[0124] Further, in the intermediate transfer belt 10 of Comparative Example 6, the volume resistivity value Rv was 1.98 x 10 6 (Ω), the surface resistivity value Rs1 of the inner surface layer 10b was 1.10 x 10 5 (Ω), the surface resistivity value Rs2 of the surface layer 10c was 2.18 x 10 6 (Ω), and Rs2 / Rv was 1.103.

[0125] As shown in Table 1, for each of the evaluation images (A) to (F) of Experimental Examples 1 to 9 according to the first exemplary embodiment, no image defects were observed (evaluation result “AA”). In Table 1, “AA” means excellent, “A” means good, “B” means small image defects, and “NG” means image defects.

[0126] Next, the reason why excellent images can be obtained in the intermediate transfer belts 10 of Experimental Examples 1 to 9 according to the first exemplary embodiment will be described.

[0127] First, in view of the fact that the inner surface layer 10b is formed, since the intermediate transfer belt 10 is configured not to have excessively high surface resistance values on the surface layer 10c side, excellent images are obtained even for the full-page halftone 20% image (B) and the full-page halftone 50% image (C), which are images in which discharge images are easily noticeable.

[0128] On the other hand, by setting the volume resistance value Rv and the surface resistance value Rs2 of the surface layer 10c to have close values, even if a primary transfer voltage sufficient to obtain a required primary transfer current is applied, a potential memory phenomenon of the surface layer 10c does not occur, and a discharge current on the upstream side of the primary transfer nip N1 is suppressed. More specifically, if Rs2 / Rv ≤ 40 is satisfied, the volume resistance value Rv and the surface resistance value Rs2 of the surface layer 10c become close to each other, thereby effectively suppressing the discharge current. Furthermore, since the surface resistance value Rs1 on the inner surface layer 10b side is set to be sufficiently small, the primary transfer voltage applied to the primary transfer roller 6 hardly attenuates before reaching the primary transfer nip N1. Therefore, even for images that require a sufficient transfer current, such as the full-page solid color image (E) and the full-page secondary color image (F), excellent transfer properties are obtained.

[0129] Furthermore, since the surface resistance value Rs2 of the surface layer 10c is high, occurrence of a transfer failure due to a reason that a primary transfer current does not pass through a solid color patch image, which will be described below, can also be limited in the solid color patch image (D).

[0130] In addition, since the potential memory phenomenon of the surface layer 10c generally tends to easily occur as the surface resistance value Rs2 of the surface layer 10c becomes larger, in the present exemplary embodiment, it is preferable to set the surface resistance value Rs2 to 1.00 x 10 9 (Ω) or less. Furthermore, more preferably, the surface resistance value Rs2 of the surface layer 10c is set to 6.41 x 10 8 (Ω) or less to reduce the influence of the potential memory phenomenon.

[0131] Next, evaluation results of the intermediate transfer belts 10 in Comparative Examples 1 to 5 will be described.

[0132] The intermediate transfer belt 10 of Comparative Example 1 has a surface resistance value Rs2 of the surface layer 10c that is relatively high with respect to the volume resistance value Rv, and the value of Rs2 / Rv is 53.564. For the intermediate transfer belt 10 of Comparative Example 1, slight discharge traces were observed on each of the full-page halftone 20% image (B) and the full-page halftone 50% image (C), which are images in which discharge traces are easily noticeable, as a result of a potential memory phenomenon of the surface layer 10c occurring.

[0133] Further, the Rs2 / Rv value of the intermediate transfer belt 10 of each of Comparative Example 2 and Comparative Example 3 is in a range from 120.001 to 195.914 and is larger than the Rs2 / Rv value of Comparative Example 1, and the potential memory phenomenon of the surface layer 10c can be more likely to occur.

[0134] As a result, the discharge trace was more easily noticeable in Comparative Example 2 and Comparative Example 3, a slight discharge trace was observed on the solid halftone 20% image (B), and a clear discharge trace was observed on the solid halftone 50% image (C).

[0135] Further, each of the intermediate transfer belts 10 in Comparative Example 4 and Comparative Example 5 has an Rs2 / Rv value in a range from 408.413 to 424.523, which is larger than the Rs2 / Rv values of Comparative Example 2 and Comparative Example 3, a slight discharge trace was observed on the solid halftone 20% image (B), and a clear discharge trace was observed on the solid halftone 50% image (C) and the solid color image (E).

[0136] On the other hand, for the intermediate transfer belt 10 of Comparative Example 6, a transfer failure occurred on the solid color patch image (D), which was caused by the toner image on the photosensitive drum 1 not being sufficiently transferred to the intermediate transfer belt 10 because of the lack of the primary transfer current.

[0137] More specifically, the Rs2 / Rv value of the intermediate transfer belt 10 of Comparative Example 6 is 1.103, the surface resistance value Rs2 on the surface layer 10c side is almost equal to the volume resistance value Rv, and even if the potential memory phenomenon of the surface layer 10c does not occur, the surface resistance value Rs2 on the surface layer 10c side is as low as 2.18 x 10 6 (Ω). In comparison with Comparative Example 6, any one of Experimental Example 1 to Experimental Example 9 according to the first exemplary embodiment has a surface resistance value Rs2 of 3.00 x 10 7 (Ω) or more. Thus, without the lack of the primary transfer current, no image defects were observed on the solid color patch image (D).

[0138] Next, in the intermediate transfer belt 10 of Comparative Example 6, a mechanism in which a transfer failure occurs on the solid color patch image (D) in a case where the surface resistance value Rs2 on the surface layer 10c side is small will be described.

[0139] Figure 7 is a diagram schematically illustrating a primary transfer current path in Comparative Example 6 according to the first exemplary embodiment of the present invention.

[0140] More specifically, Figure 7 the state of the current at the primary transfer in the configuration of Comparative Example 6 is illustrated.

[0141] In addition, Figure 7 The direction from the front side to the rear side corresponds to the direction of rotation R2 of the intermediate transfer belt 10.

[0142] As Figure 7 indicated, for the intermediate transfer belt 10 of Comparative Example 6, the surface resistance value Rs2 of the surface layer 10c is small, and the primary transfer current easily bypasses the toner image to flow to the photosensitive drum 1.

[0143] More specifically, as a current path of the primary transfer current, there is a path through which the primary transfer current flows from the intermediate transfer belt 10 to the photosensitive drum 1 through the toner image. On the other hand, as Figure 7 indicated, there is another path through which the primary transfer current flows from the intermediate transfer belt 10 to the photosensitive drum 1 directly without passing through the toner image. In the configuration shown in Figure 7 indicated, the path through which the current flows through (passes through) the toner image generally has a greater resistance value than the path that does not pass through the toner image.

[0144] However, in the case where the surface resistance value Rs2 of the surface layer 10c is small, the difference in resistance value between the current path through the toner image and the current path not passing through the toner image becomes large. For this reason, as Figure 7 indicated, in Comparative Example 6, a large amount of the primary transfer current flows from the intermediate transfer belt 10 to the photosensitive drum 1 directly without passing through the toner image.

[0145] Therefore, since the primary transfer is performed by moving the toner image on the current passing path, for the configuration shown in Comparative Example 6, if the ratio of the current flowing through the path not passing through the toner image increases, it is not possible to supply a sufficient amount of transfer current to the toner image, which can result in a transfer failure.

[0146] In addition, for the text image (A), no image defects were observed in any of the intermediate transfer belts 10 of Comparative Examples 1 to 6 and Experimental Examples 1 to 9 according to the first exemplary embodiment.

[0147] As described above, for the intermediate transfer belt 10 composed of three layers including the base layer 10a, the inner surface layer 10b, and the surface layer 10c, in order to obtain good transferability, the primary transfer current supplied from the primary transfer roller 6 needs to pass through the inner surface layer 10b to reach the primary transfer nip N1. In addition, it is necessary to adjust the resistance values of the base layer 10a and the surface layer 10c to have a certain relationship, thereby limiting the discharge marks and the pre-transfer to obtain good transferability.

[0148] More specifically, in the present exemplary embodiment, the volume resistivity value Rv of the base layer 10a of the intermediate transfer belt 10 and the surface resistivity value (second surface resistivity value) Rs2 of the surface layer 10c need to be greater than the surface resistivity value (first surface resistivity value) Rs1 of the inner surface layer 10b. In addition, Rs2 / Rv ≤ 40 needs to be satisfied, and the surface resistivity value (second surface resistivity value) Rs2 needs to be 3.00 x 10 7 (Ω) or more.

[0149] In the present exemplary embodiment, as the resistivity values of the intermediate transfer belts 10 of Experimental Examples 1 to 9 according to the first exemplary embodiment, each volume resistivity value Rv is set to a value within a range from 2.60 x 10 6 (Ω) to 3.51 x 10 7 (Ω). In other words, it is preferable to set the volume resistivity value Rv within this range. In addition, it is more preferable to set the volume resistivity value Rv to a value within a range from 4.57 x 10 6 (Ω) to 1.83 x 10 7 (Ω).

[0150] Further, in the present exemplary embodiment, the surface resistivity value Rs1 of the inner surface layer 10b is set to a value within a range from 1.10 x 10 3 (Ω) to 1.10 x 10 5 (Ω). In other words, it is desirable to set the surface resistivity value Rs1 of the inner surface layer 10b within this range.

[0151] Therefore, in the present exemplary embodiment, the surface resistivity value Rs2 of the surface layer 10c is set to a value within a range from 3.55 x 10 7 (Ω) to 6.41 x 10 8 (Ω). In other words, it is desirable to set the surface resistivity value Rs2 of the surface layer 10c to 3.55 x 10 7 (Ω) or more. On the other hand, considering the influence of potential memory, it is desirable to set the surface resistivity value Rs2 of the surface layer 10c to 6.41 x 10 8 (Ω) or less.

[0152] Further, in the present exemplary embodiment, Rs2 / Rv is set to a value within a range from 2.186 to 38.740. Therefore, Rs2 / Rv ≤ 40 is satisfied.

[0153] Thus, according to the present exemplary embodiment, by setting Rv, Rs1, and Rs2 as described above, it is possible to limit the potential memory phenomenon of the surface layer 10c while applying a sufficient primary transfer voltage for primary transfer, to obtain an intermediate transfer belt 10 for obtaining a good image quality in which the concentration unevenness and the discharge trace caused by the pre-transfer are suppressed.

[0154] On the other hand, for the intermediate transfer belt 10 of each of Comparative Examples 1 to 6, Rs2 / Rv was 53.564 or more, and image defects caused by the discharge trace of the intermediate transfer belt 10 were observed.

[0155] In order to limit the potential memory phenomenon of the surface layer 10c, it is desirable that the surface resistivity ps2 on the surface layer 10c side be smaller than the surface resistivity of the other layers, and Rs2 / Rv needs to be 40 or less. In addition, in order to effectively limit the occurrence of image defects under conditions in which image defects due to the discharge trace are likely to occur (for example, when the use environment at the time of image formation is low temperature and low humidity, or when the toner is deteriorated), it is preferable to set Rs2 / Rv to be 21.859 or less. The reason for this is that the larger Rs2 / Rv is, the more likely the potential memory phenomenon of the surface layer 10c is to occur.

[0156] In addition, as is clear from Comparative Example 6, in order to effectively limit the occurrence of primary transfer failure of the solid color patch image (D), it is necessary to reduce the resistance value difference between the resistance value of the current path formed from the intermediate transfer belt 10 to the photosensitive drum 1 and the resistance value of the current path formed from the intermediate transfer belt 10 via the toner image to the photosensitive drum 1. Therefore, in the present exemplary embodiment, the surface resistance value Rs2 on the surface layer 10c side is set to be 3.00 x 10 7 (Ω) or more.

[0157] [Table 1]

[0158]

[0159] The image forming apparatus according to the second exemplary embodiment of the present application is basically similar to the image forming apparatus according to the first exemplary embodiment, and thus only different parts will be described.

[0160] Figure 8 is a schematic cross-sectional view illustrating an image forming apparatus 200 according to the second exemplary embodiment of the present application.

[0161] As Figure 8In the configuration of the second exemplary embodiment, the driving roller 11 and the primary transfer rollers 6a, 6b, 6c, and 6d are electrically connected to the secondary transfer opposing roller 13 to be the same potential, as shown. Since the image forming units Sa, Sb, Sc, and Sd have substantially the same configuration, the image forming apparatus 200 according to the second exemplary embodiment will be mainly described using the first image forming unit Sa.

[0162] More specifically, the secondary transfer opposing roller 13, the primary transfer rollers 6a, 6b, 6c, and 6d are grounded via a Zener diode 24 as a voltage support element. In this way, a voltage is supplied to the primary transfer roller 6a by a Zener voltage generated at the cathode of the Zener diode 24 by a current supplied from the secondary transfer roller 20 as a current supply member.

[0163] Further, a primary transfer current supplied from the primary transfer roller 6a passes through the inner surface layer 10b and reaches the primary transfer nip Nla, and is then supplied to the photosensitive drum la. In order to obtain a desired primary transfer property, the Zener voltage is set to "300 V" in the present exemplary embodiment.

[0164] In the second exemplary embodiment, similarly to the first exemplary embodiment, a preferred primary transfer property can be obtained in the intermediate transfer belt 10 composed of three layers of a base layer, an inner surface layer, and a surface layer.

[0165] Further, in the second exemplary embodiment, instead of Figure 1 The Zener diode 24 connected to the secondary transfer opposing roller 13 and the primary transfer roller 6a is used to generate a primary transfer voltage, instead of the primary transfer power supply 23 in the first exemplary embodiment shown. In this way, the second exemplary embodiment has an advantage that good primary transfer property can be obtained with a simpler configuration, compared to the first exemplary embodiment.

[0166] The image forming apparatus according to the third exemplary embodiment of the present application is substantially similar to the image forming apparatus of the first exemplary embodiment or the second exemplary embodiment, and thus only different parts will be described below.

[0167] Figure 9 is a schematic cross-sectional view illustrating an image forming apparatus 300 according to the third exemplary embodiment of the present application.

[0168] In the first exemplary embodiment and the second exemplary embodiment described above, toner on the surface of the photosensitive drum la is primary transferred to the intermediate transfer belt 10 by applying a primary transfer voltage to form a potential difference between the surface potential of the photosensitive drum la and the potential of the intermediate transfer belt 10. The third exemplary embodiment is characterized in that the primary transfer rollers 6a to 6d are grounded and a drum power supply 25 as a negative power supply common to the photosensitive drums la to Id is provided.

[0169] More specifically, in the third exemplary embodiment, a drum power supply 25 is connected to supply a voltage to each of the drum element tubes of the photosensitive drums la to Id. Hereinafter, the voltage applied by the drum power supply 25 to the drum element tubes is referred to as "drum voltage".

[0170] In the third exemplary embodiment, the potential difference between the surface potential of the photosensitive drum la and the surface potential of the intermediate transfer belt 10 is formed by adjusting the drum voltage. The configuration other than the configuration for performing the primary transfer is the same as that of the first exemplary embodiment and the second exemplary embodiment.

[0171] In the third exemplary embodiment, similarly to the first exemplary embodiment and the second exemplary embodiment, good primary transfer performance can be obtained in the intermediate transfer belt 10 composed of three layers including a base layer, an inner surface layer, and a surface layer.

[0172] In addition, in the third exemplary embodiment, the primary transfer rollers 6a to 6d can be grounded instead of arranging the drum power supply 25 connected to the drum element tubes of the photosensitive drums la to Id. In this way, the third exemplary embodiment has an advantage that, while good primary transfer performance is obtained, a stretching unit having a simpler configuration for stretching the intermediate transfer belt 10 can be obtained, compared to the first exemplary embodiment and the second exemplary embodiment.

[0173] While the present application has been described with reference to exemplary embodiments, it is to be understood that the application is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the widest interpretation so as to embrace all such modifications and equivalent structures and functions.

Claims

1. An image forming apparatus comprising: an image bearing member configured to bear a toner image; a loop-shaped conductive intermediate transfer belt configured to contact the image bearing member, and to which the toner image is transferred from the image bearing member, the intermediate transfer belt including a base layer, a surface layer formed on an outer peripheral surface side of the base layer, and an inner surface layer formed on an inner peripheral surface side of the base layer; and a contact member configured to contact the intermediate transfer belt from an opposite side of the intermediate transfer belt to the image bearing member, wherein, from a direction of an axis of rotation of the image bearing member, a position at which the contact member contacts the intermediate transfer belt is disposed on a downstream side of the intermediate transfer belt in a direction of rotation of the intermediate transfer belt with respect to a center of rotation of the image bearing member, wherein Rv > Rs1 and Rs2 > Rs1 are satisfied, and Rs2 / Rv ≤ 40, where Rv (Ω) is a volume resistivity value of the intermediate transfer belt in a thickness direction, Rs1 (Ω) is a first surface resistivity value of the inner surface layer side in a surface direction, Rs2 (Ω) is a second surface resistivity value of the surface layer side in the surface direction, and the volume resistivity value Rv and the second surface resistivity value Rs2 satisfy Rs2 / Rv ≤ 22. wherein the volume resistivity Rv is a value in the range from 2.60 x 10 6 (Ω) to 3.51 x 10 7 (Ω).

2. The image forming apparatus according to claim 1, wherein The second surface resistance value Rs2 is 3.00 x 10 7 (Ω) or more.

3. The image forming apparatus according to claim 1, wherein the base layer is a layer that is thickest in the thickness direction among a plurality of layers included in the intermediate transfer belt.

4. The image forming apparatus according to claim 1, wherein The second surface resistance value Rs2 is 7.00 x 10 7 (Ω) or more.

5. The image forming apparatus according to claim 1, wherein The volume resistance value Rv is a value in the range from 4.57 x 1010 6 (Ω) to 1.83 x 1010 7 (Ω).

6. The image forming apparatus according to claim 1, wherein The second surface resistance value Rs2 is 6.41 x 10 8 (Ω) or less.

7. The image forming apparatus according to claim 1, wherein the surface layer is provided in contact with a surface of the base layer on the outer peripheral surface side.

8. The image forming apparatus of claim 1, wherein, a surface of the surface layer opposite to the surface contacting the base layer is configured to contact the image bearing member.

9. The image forming apparatus according to claim 8, wherein the inner surface layer is provided in contact with a surface of the base layer on the inner peripheral surface side.

10. The image forming apparatus of claim 1, wherein, a surface of the inner surface layer opposite to the surface contacting the base layer is in contact with the contact member.

11. The image forming apparatus according to claim 10, wherein the contact member presses the intermediate transfer belt in a thickness direction of the intermediate transfer belt from a side on which the contact member is located to a side on which the image bearing member is located, to cause the intermediate transfer belt to wrap around a surface of the image bearing member.

12. The image forming apparatus according to any one of claims 1 to 11, wherein 13. The image forming apparatus according to claim 12, further comprising a power source connected to the contact member, by the power source applying a voltage of an opposite polarity to a normal charge polarity of the toner to the contact member, the toner image borne by the image bearing member is transferred to the intermediate transfer belt. wherein the contact member is a rotatable metal roller.

14. The image forming apparatus according to claim 13, wherein by the power source applying a voltage to the contact member, a current flows from the contact member to the image bearing member, and the current flows from the inner surface layer to the image bearing member in a thickness direction of the intermediate transfer belt via the base layer and the surface layer after flowing through the inner surface layer in a circumferential direction. 15.The image forming apparatus according to claim 13, wherein 16. The image forming apparatus according to claim 1, further comprising a power source connected to the image bearing member, by the power source applying a voltage of a same polarity as a normal charge polarity of the toner to the image bearing member, the toner image borne by the image bearing member is transferred to the intermediate transfer belt. wherein ​

Images