Image forming apparatus

Abstract

To provide an image forming apparatus that, when not transferring toner images for control formed on a photoconductor drum to an intermediate transfer belt, can prevent a recording material from becoming dirty by a reversely polarized toner carried on the intermediate transfer belt.SOLUTION: When an image forming apparatus forms toner images for control such as a toner image for toner deterioration prevention and a toner image for blade supply that are not transferred to a recording material, the image forming apparatus causes a primary transfer power supply to apply, to primary transfer rollers, primary transfer voltage (-500 V) having a polarity opposite to that during image formation. The image forming apparatus causes a secondary transfer power supply to apply, to a secondary transfer inner roller, secondary transfer voltage (-3500 V) having the same polarity as that during image formation and a larger absolute value. With this, a reversely polarized toner transferred from the toner images for control formed on a photoconductor drum to the intermediate transfer belt hardly adheres to a secondary transfer outer roller that is in contact with an outer peripheral surface of the intermediate transfer belt during secondary transfer, and thereby the recording material can be prevented from becoming dirty.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to an image forming apparatus using electrophotographic technology, such as a printer, a copier, a facsimile machine, or a multifunction peripheral.

Background Art

[0002] As an image forming apparatus using the electrophotographic method, for example, there is an image forming apparatus using an intermediate transfer belt. In this image forming apparatus, the toner image formed on the photosensitive drum is primarily transferred from the photosensitive drum to the intermediate transfer belt at the primary transfer nip portion. The primary transfer residual toner remaining on the photosensitive drum after the primary transfer is removed by a drum cleaning blade that rubs the surface of the photosensitive drum. Then, the toner image primarily transferred to the intermediate transfer belt is secondarily transferred from the intermediate transfer belt to the recording material at the secondary transfer nip portion.

[0003] In an image forming apparatus, in order to forcibly discharge deteriorated toner from the developing container or to supply toner to maintain the rubbing property of the drum cleaning blade, a toner image (referred to as a control toner image) may be formed on the photosensitive drum but not transferred to the recording material. When a control toner image is formed on the photosensitive drum, a voltage of the opposite polarity (opposite to the normal toner charging polarity) to that during image formation in which a toner image is formed on the recording material is applied to the primary transfer roller that contacts the inner peripheral surface of the intermediate transfer belt at the primary transfer nip portion (Patent Document 1). By doing so, the control toner image formed on the photosensitive drum passes through the primary transfer nip portion without being transferred to the intermediate transfer belt and reaches the drum cleaning blade to be removed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, if a voltage with the opposite polarity to the normal toner charging polarity is applied to the primary transfer roller, a reverse-polarity toner, with the opposite polarity to the normal toner charging polarity, may be transferred to the intermediate transfer belt from the control toner image formed on the photosensitive drum. Conventionally, this reverse-polarity toner could adhere to the secondary transfer outer roller, which contacts the outer surface of the intermediate transfer belt during secondary transfer, potentially causing "backside staining" where toner adheres to the back of the recording material, or "edge staining" where toner adheres to the leading edge of the recording material.

[0006] The present invention aims to provide an image forming apparatus that can suppress contamination of the recording material by reverse polarity toner, even if, when the control toner image formed on the photosensitive drum is not transferred to the intermediate transfer belt, reverse polarity toner, which has the opposite polarity to the normal toner charge polarity, is carried on the intermediate transfer belt. [Means for solving the problem]

[0007] An image forming apparatus according to one embodiment of the present invention comprises a rotating photoreceptor, a charging member for charging the photoreceptor, an exposure apparatus for exposing the charged photoreceptor to light to form an electrostatic latent image, a developing apparatus for developing the electrostatic latent image formed on the photoreceptor into a toner image using a developer, an intermediate transfer body that rotates in contact with the photoreceptor, a primary transfer member for forming a primary transfer portion of the toner image from the photoreceptor to the intermediate transfer body, a secondary transfer member for forming a secondary transfer portion of the toner image from the intermediate transfer body to a recording material, a primary transfer power supply for applying a voltage to the primary transfer member, a secondary transfer power supply for applying a voltage to the secondary transfer member, and the photoreceptor into a toner The device includes a control means capable of performing a first mode in which an image is formed, a voltage of first polarity is applied to the primary transfer member to primary transfer the toner image formed on the photoreceptor to the intermediate transfer member, and a first voltage is applied to the secondary transfer member to secondary transfer the toner image primary transferred to the intermediate transfer member to the recording material, and a second mode in which a control toner image is formed on the photoreceptor, and a voltage of second polarity opposite to the first polarity is applied to the primary transfer member when the control toner image passes through the primary transfer section, wherein the control means ensures that when the control toner image passes through the primary transfer section, the region of the intermediate transfer member passing through the primary transfer section isfirst time When passing through the secondary transfer section, Without applying a voltage with the opposite polarity to the first voltage to the secondary transfer member, The secondary transfer member is the first Voltage and of the same polarity and with a greater absolute value than the first voltage but It is characterized by applying a large second voltage. [Effects of the Invention]

[0008] According to the present invention, even if a reverse-polarity toner, which has the opposite polarity to the normal toner charge polarity, is supported on the intermediate transfer medium when the control toner image formed on the photoreceptor is not transferred to the intermediate transfer medium, contamination of the recording material by the reverse-polarity toner can be suppressed. [Brief explanation of the drawing]

[0009] [Figure 1] A schematic diagram showing the image forming apparatus of this embodiment. [Figure 2] A schematic diagram showing the configuration of the image forming unit. [Figure 3] A schematic diagram showing the structure near the secondary transfer nip. [Figure 4] A control block diagram illustrating the control unit. [Figure 5] (a) Diagram showing toner image for toner degradation prevention, (b) Diagram showing toner image for blade supply. [Figure 6] This figure illustrates the transfer voltage control of this embodiment, showing (a) primary transfer voltage and (b) secondary transfer voltage. [Figure 7] A schematic diagram showing the configuration near the secondary transfer nip when using the gravity transfer method. [Modes for carrying out the invention]

[0010] <Image forming apparatus> Hereinafter, this embodiment will be described. First, the image forming apparatus of this embodiment will be described using FIGS. 1 to 3. FIG. 1 is a schematic diagram showing the image forming apparatus of this embodiment. As shown in FIG. 1, the image forming apparatus 100 is a tandem type intermediate transfer type image forming apparatus in which image forming units Pa, Pb, Pc, and Pd are arranged along an intermediate transfer belt 7.

[0011] The image forming unit Pa forms a yellow toner image on the photosensitive drum 1a and transfers it to the intermediate transfer belt 7. The image forming unit Pb forms a magenta toner image on the photosensitive drum 1b and transfers it to the intermediate transfer belt 7. The image forming units Pc and Pd form a cyan toner image and a black toner image on the photosensitive drums 1c and 1d, respectively, and transfer them to the intermediate transfer belt 7. The four-color toner images transferred and overlapped on the intermediate transfer belt 7 are collectively transferred to the recording material S at the secondary transfer nip portion N2 as a secondary transfer unit.

[0012] The recording material S is loaded in the cassette 10, pulled out from the cassette 10, separated one by one by the separation roller 9, and waits at the registration roller 15. The registration roller 15 feeds the recording material S to the secondary transfer nip portion N2 in synchronization with the toner image on the intermediate transfer belt 7. Examples of the recording material S include various types of sheet materials such as plain paper, thick paper, rough paper, embossed paper, coated paper, plastic film, and cloth.

[0013] The recording material S onto which the toner image has been transferred at the secondary transfer nip portion N2 is conveyed to the fixing device 20. The fixing device 20 sandwiches the recording material S at the fixing nip portion N3 formed by the fixing roller and the pressure roller, and heats and presses it to fix the toner image on the recording material S.

[0014] The intermediate transfer belt 7 as an intermediate transfer member is stretched over the driving roller 11, the tension roller 12, and the secondary transfer inner roller 13, and is driven by the driving roller 11 to be movably provided in a predetermined moving direction (direction of arrow R2).

[0015] The belt cleaning device 17 is disposed downstream of the secondary transfer nip portion N2 in the moving direction of the intermediate transfer belt 7 and upstream of the image forming units Pa, Pb, Pc, Pd, and removes the toner on the intermediate transfer belt 7 that has passed through the secondary transfer nip portion N2. In the present embodiment, the belt cleaning device 17 electrostatically collects and cleans the secondary transfer residual toner and the like on the intermediate transfer belt 7 (on the intermediate transfer member).

[0016] In the present embodiment, an intermediate transfer belt unit 50 is constituted by an intermediate transfer belt 7 stretched over a plurality of rollers, primary transfer rollers 5a to 5d, a belt cleaning device 17, a frame for supporting these, and the like. The intermediate transfer belt unit 50 is detachably provided with respect to the apparatus main body 120 for maintenance or replacement.

[0017] <Image forming unit> The image forming units Pa, Pb, Pc, Pd will be described using FIG. 2. FIG. 2 is a schematic diagram showing the configuration of the image forming unit. Since the image forming units Pa, Pb, Pc, Pd are configured identically except that the colors of the toner used in the developing devices 4a, 4b, 4c, 4d are different, the image forming unit Pa will be described below, and redundant descriptions regarding the image forming units Pb, Pc, Pd will be omitted. Further, in order to facilitate understanding of the description below, the case where toner having a normal toner charging polarity of negative (-) is used will be described as an example, and the "toner charging polarity" refers to the normal toner charging polarity.

[0018] As shown in FIG. 2, the image forming unit Pa arranges a charging roller 2a, an exposure device 3a, a developing device 4a, a primary transfer roller 5a, and a drum cleaning device 6a around a photosensitive drum 1a. The photosensitive drum 1a, the charging roller 2a, the developing device 4a, and the drum cleaning device 6a are assembled in a process cartridge 8a that is detachable from the apparatus main body of the image forming apparatus 100.

[0019] The photosensitive drum 1a, acting as a photoreceptor, has a photosensitive layer formed on the circumferential surface of an aluminum cylinder and is rotated by a motor (not shown) in the direction of arrow R1 at a peripheral speed of, for example, "100 mm / sec". The charging roller 2a, acting as a charging member, is charged with a superimposed voltage obtained by superimposing an AC voltage on a DC voltage by a charging power supply (not shown), thereby charging the photosensitive drum 1a to a uniform negative potential.

[0020] The exposure device 3a scans the surface of the photosensitive drum 1a with a laser beam that is ON / OFF modulated from the scan line signal, which is obtained by unfolding the yellow separated image along the scan line, thereby lowering the absolute value of the potential of the exposed area and forming an electrostatic latent image of a negative potential. The developing device 4a supplies toner to the photosensitive drum 1a and develops the electrostatic latent image into a toner image.

[0021] The primary transfer roller 5a, acting as a primary transfer member, contacts the inner circumferential surface of the intermediate transfer belt 7 and, in response to the voltage applied by the primary transfer power supply 82, transfers the toner image from the photosensitive drum 1a, which passes through the primary transfer nip section N1, acting as the primary transfer section, to the intermediate transfer belt 7. The primary transfer roller 5a is constructed by providing an elastic layer made of ion-conductive foamed rubber on the outer circumference of a metal core (core material). For example, the primary transfer roller 5a has an outer diameter of 15-20 mm, and its electrical resistance is measured at 23°C and 50% RH with a voltage of 2 kV applied, resulting in an electrical resistance of 1 × 10⁻¹⁰. 5 ~1 × 10 8 It is Omega.

[0022] The drum cleaning device 6a uses a drum cleaning blade 62, which acts as a cleaning element, to rub against the photosensitive drum 1a, thereby recovering the toner on the photosensitive drum 1a that has passed through the primary transfer nip section N1. The toner that falls into the cleaning container 61 is collected at one end of the cleaning container 61 by a transport screw 63 and discharged into a toner recovery container (not shown).

[0023] The developing device 4a houses a developer (two-component developer) containing toner and carrier in a developing container 41. Inside the developing container 41, the developer is circulated and agitated by transport screws 42 and 43, which serve as transport means, thereby negatively charging the toner and positively charging the carrier. The developing sleeve 45 carries the charged two-component developer and rotates in the direction of arrow R4. Due to the magnetic field of a magnet (not shown) placed inside the developing sleeve 45, the two-component developer rises at the point opposite the photosensitive drum 1a and rubs against the photosensitive drum 1a. A superimposed voltage, obtained by superimposing an AC voltage on a DC voltage by a developing power supply (not shown), is applied to the developing sleeve 45 as the developing voltage, causing the toner to transfer to the electrostatic latent image on the photosensitive drum 1a.

[0024] <Configuration near the secondary transfer nip area> Next, the configuration near the secondary transfer nip will be explained using Figure 3. Figure 3 is a schematic diagram showing the configuration near the secondary transfer nip. As shown in Figure 3, in this embodiment, the secondary transfer inner roller 13 abuts against the inner circumferential surface of the intermediate transfer belt 7, and the secondary transfer outer roller 14 abuts against the outer circumferential surface of the intermediate transfer belt 7, forming a secondary transfer nip N2 between the secondary transfer outer roller 14 and the intermediate transfer belt 7.

[0025] The secondary transfer roller 13, which serves as a secondary transfer member, is constructed by providing an elastic layer of electronically conductive rubber on the outer circumference of a metal core. The electronically conductive rubber material of the elastic layer is such as neoprene rubber with dispersed carbon. In this embodiment, the secondary transfer roller 13 has an outer diameter of 20 to 22 mm, and its electrical resistance is 1 × 10⁻¹⁶ when measured with a voltage of 50V applied in an environment of 23°C and 50% RH. 5 ~1 × 10 8 It is Ω. For example, the secondary transfer roller 13 has an elastic layer of conductive rubber material with a thickness of 0.5 mm on the circumferential surface of an aluminum cylindrical material with a diameter of 12 mm.

[0026] On the other hand, the secondary transfer outer roller 14 is constructed by providing an elastic layer of ion-conductive foamed rubber on the outer circumference of a metal core (core material). In this embodiment, the secondary transfer outer roller 14 has an outer diameter of 20 to 25 mm, and its electrical resistance is 1 × 10 when measured with a voltage of 2 kV applied in an environment of 23°C and 50% RH. 5 ~1 × 10 8 It is Ω. For example, the secondary transfer outer roller 14 has an elastic layer of conductive rubber material with a thickness of 2.0 mm on the circumferential surface of a cylindrical aluminum material with a diameter of 16 mm, and a release layer coated with fluororesin material on the surface of the elastic layer. The conductive rubber material of the elastic layer is ethylene-propylene-butadiene rubber containing an ionic conductive agent. The fluororesin material of the release layer is polytetrafluoroethylene.

[0027] In this embodiment, a secondary transfer power supply 16 is connected to the secondary transfer inner roller 13, and the secondary transfer outer roller 14 is grounded. The secondary transfer power supply 16 applies a secondary transfer voltage, which is a DC voltage with the same polarity (negative) as the toner charge polarity, to the secondary transfer inner roller 13 when the recording material S passes through the secondary transfer nip section N2, for example, superimposed on the intermediate transfer belt 7 carrying the toner image. As a result, the toner image carried on the intermediate transfer belt 7 is secondary transferred from the intermediate transfer belt 7 to the recording material S.

[0028] <Department Head> As shown in Figure 1, the image forming apparatus 100 is equipped with a control unit 500. The control unit 500 will be described using Figure 4 with reference to Figures 2 and 3. In addition to what is shown in Figure 4, the control unit 500 is also connected to various other devices, such as motors that rotate the photosensitive drums 1a to 1d, the drive roller 11, etc., as well as a charging power supply and a developing power supply. However, since these are not the main focus of the invention, their illustration and description are omitted here.

[0029] The control unit 500, acting as a control means, controls various operations of the image forming apparatus 100, such as image forming operations, and includes, for example, a CPU (Central Processing Unit) 501 and a memory 502. The memory 502 is composed of ROM (Read Only Memory) and RAM (Random Access Memory), and stores various programs and data for controlling the image forming apparatus 100. The CPU 501 can execute various programs, such as image forming jobs, stored in the memory 502. The memory 502 can also temporarily store calculation results and other data associated with the execution of various programs.

[0030] In this embodiment, the control unit 500 applies a primary transfer voltage with the opposite polarity (first polarity, in this case positive) to the primary transfer roller 5a using the primary transfer power supply 82 for the primary transfer of the toner image from the photosensitive drum 1a to the intermediate transfer belt 7. For example, the control unit 500 applies a positive DC voltage (e.g., +1000V) to the primary transfer roller 5a using the primary transfer power supply 82. In response to the application of this primary transfer voltage, the toner image on the photosensitive drum 1a passing through the primary transfer nip section N1 is primary transferred to the intermediate transfer belt 7.

[0031] Furthermore, the control unit 500 applies a constant voltage controlled secondary transfer voltage with the same polarity (negative) as the toner charge polarity to the secondary transfer roller 13 using the secondary transfer power supply 16 for secondary transfer of the toner image to the recording material S. For example, the control unit 500 applies a DC voltage of "-1 to -7KV" to the secondary transfer roller 13 using the secondary transfer power supply 16. In response to the application of this secondary transfer voltage, a secondary transfer current of "-40 to -120μA" flows between the secondary transfer roller 13 and the secondary transfer outer roller 14, and the toner image on the intermediate transfer belt 7 passing through the secondary transfer nip section N2 is secondary transferred to the recording material S.

[0032] There are two methods for secondary transfer of the toner image from the intermediate transfer belt 7 to the recording material S: a repulsive transfer method and an attractive transfer method. In the repulsive transfer method, the secondary transfer outer roller 14 is grounded, and a voltage with the same polarity as the toner charge polarity is applied to the secondary transfer inner roller 13 to form a secondary transfer electric field. On the other hand, in the attractive transfer method, the secondary transfer inner roller 13 is grounded, and a voltage with the opposite polarity to the toner charge polarity is applied to the secondary transfer outer roller 14 to form a secondary transfer electric field. In this embodiment, the repulsive transfer method is employed.

[0033] Incidentally, the control unit 500 may form toner images on the photosensitive drum 1a even if they are not formed on the recording material S, in addition to the toner images formed on the recording material S. Examples of toner images not formed on the recording material S include control toner images such as a toner image for preventing toner degradation, which is used to forcibly discharge deteriorated toner from the developing container 41, or a blade supply toner image, which is used to supply toner to maintain the frictional properties of the drum cleaning blade 62. These toner images for preventing toner degradation and blade supply are formed on the photosensitive drum 1a by applying the same charging voltage as when a toner image is formed on the recording material S (referred to as the first mode, or image formation mode), but they are not transferred from the photosensitive drum 1a to the intermediate transfer belt 7. Thus, in addition to the normal image formation mode (first mode) in which the toner image formed on the photosensitive drum 1a is transferred to the intermediate transfer belt 7 to form an image on the recording material S, the control unit 500 can also execute a non-transfer mode (second mode) in which the control toner image formed on the photosensitive drum 1a is not transferred to the intermediate transfer belt 7.

[0034] <Image of toner for preventing toner degradation> Figure 5(a) shows an example of a toner image for control, which is a toner image for preventing toner degradation. As shown in Figure 2, in the developing device 4a, the developer is circulated while being agitated by the transport screws 42 and 43. Therefore, if images with low toner consumption, such as characters, are continuously formed on the recording material S, the agitation time becomes excessive and the toner deteriorates. For this reason, if images with low toner consumption are continuously formed, the control unit 500 temporarily interrupts the job, even if an image is being formed on the recording material S, and forms the toner image Ga for preventing toner degradation shown in Figure 5(a) on the photosensitive drum 1a.

[0035] The control unit 500 determines the amount of toner consumption deficit over the period each time it forms a predetermined number of images (e.g., 100 images) on the recording material S, and forms a toner degradation prevention toner image Ga on the photosensitive drum 1a with a toner amount corresponding to the toner consumption deficit. The amount of toner consumption deficit over the period of continuous image formation is determined by calculating the density integrated value of the image data for each toner image and accumulating the difference with the reference density integrated value (e.g., 5% of the maximum density across the entire surface).

[0036] Then, when the cumulative difference from the standard density cumulative value reaches a value equivalent to the toner consumption required to form a toner image (solid image) with 100% area gradation across the entire area where an image can be formed in landscape orientation of A4 size paper, a toner degradation prevention toner image Ga is formed on the photosensitive drum 1a. The toner degradation prevention toner image Ga is formed to the size of the area where an image can be formed in landscape orientation of A4 size paper. In this way, a portion of the toner in the developing device 4a is forcibly discharged to the photosensitive drum 1a as a toner degradation prevention toner image Ga.

[0037] Unlike during image formation, the toner image Ga for preventing toner degradation is not transferred to the intermediate transfer belt 7 by applying a voltage with the same polarity as the toner's charging polarity (second polarity, negative in this case) to the primary transfer roller 5a. Instead, it passes straight through the primary transfer nip section N1 and is collected by the drum cleaning blade 62. In this way, the toner in the developing unit 4a is forcibly consumed, thereby suppressing the degradation of the toner in the developing unit 4a.

[0038] It is also conceivable that the toner image Ga for preventing toner degradation could be transferred to the intermediate transfer belt 7 by applying a voltage with the opposite polarity (positive) to the toner charge polarity to the primary transfer roller 5a and then collected by the belt cleaning device 17. However, the toner image Ga for preventing toner degradation is often formed at a high density in front of the image-forming area (i.e., a large amount of toner). Therefore, when it is primary transferred to the intermediate transfer belt 7 and a voltage with the opposite polarity (positive) to the toner charge polarity (positive) is applied to the secondary transfer inner roller 13 to allow it to pass through the secondary transfer nip section N2, there is a greater possibility that some of the toner will adhere to the secondary transfer outer roller 14 compared to this embodiment. For this reason, it is preferable to have the toner image Ga for preventing toner degradation collected by the drum cleaning blade 62.

[0039] <Image of toner for blade supply> Figure 5(b) shows an example of a control toner image, which is a blade supply toner image. In the case of the drum cleaning device 6a shown in Figure 2, it is desirable that a certain amount of toner be present in the friction area between the drum cleaning blade 62 and the photosensitive drum 1a. If a certain amount of toner is not present in the friction area, self-excited vibration (stick-slip) that causes abnormal noise may occur in the drum cleaning blade 62, or the frictional resistance force may increase (torque increase) that hinders the rotation of the photosensitive drum 1a. Therefore, the control unit 500 forms a blade supply toner image Gb on the photosensitive drum 1a in order to supply toner to the friction area.

[0040] The control unit 500 forms a blade supply toner image Gb on the photosensitive drum 1a, for example, with a length of 1 mm and a width of 290 mm in the rotation direction of the photosensitive drum 1a (arrow R1 direction), each time the cumulative number of images formed on the recording material S reaches a predetermined number (for example, 100 images). The blade supply toner image Gb is formed in a strip shape and has a smaller toner quantity compared to the toner degradation prevention toner image Ga.

[0041] Unlike during image formation, the toner image Gb for blade supply is not transferred to the intermediate transfer belt 7 by applying a voltage with the same polarity as the toner charge polarity (second polarity, negative in this case) to the primary transfer roller 5a. Instead, it passes straight through the primary transfer nip section N1 and reaches the drum cleaning blade 62. In this way, toner is forcibly discharged from the developing device 4a and supplied to the friction area between the drum cleaning blade 62 and the photosensitive drum 1a.

[0042] <Transfer voltage control in non-transfer mode> The transfer voltage control process of this embodiment during the execution of the non-transfer mode, when forming the toner image Ga for toner degradation prevention or the toner image Gb for blade supply, will be explained below with reference to Figures 2, 3, and 4, and using Figures 6(a) and 6(b). Since the transfer voltage control is the same when forming the toner image Ga for toner degradation prevention and the toner image Gb for blade supply, the case of forming the toner image Ga for toner degradation prevention will be used as a representative example below.

[0043] As shown in Figure 6(a), when the control unit 500 forms a toner image on the recording material S, it applies a primary transfer voltage (+1000V) with the opposite polarity to the charging polarity of the toner to the primary transfer roller 5a using the primary transfer power supply 82. As a result, the toner image formed on the photosensitive drum 1a is primary transferred from the photosensitive drum 1a to the intermediate transfer belt 7 as it passes through the primary transfer nip section N1.

[0044] Then, as shown in Figure 6(b), during image formation, the control unit 500 applies a secondary transfer voltage (first voltage, -3000V) with the same polarity as the charge polarity of the toner to the secondary transfer roller 13 using the secondary transfer power supply 16. As a result, the toner image supported on the intermediate transfer belt 7 is secondary transferred from the intermediate transfer belt 7 to the recording material S as it passes through the secondary transfer nip section N2.

[0045] On the other hand, when the control unit 500 forms a toner image Ga for toner degradation prevention on the recording material S (in non-transfer mode), it applies a primary transfer voltage (-500V) with the opposite polarity to the voltage applied during image formation (+1000V) as the primary transfer voltage applied by the primary transfer power supply 82. This voltage with the opposite polarity is smaller in absolute value than the voltage applied during image formation. As a result, the toner image Ga for toner degradation prevention formed on the photosensitive drum 1a is not primary transferred from the photosensitive drum 1a to the intermediate transfer belt 7, but passes through the primary transfer nip section N1 while still supported on the photosensitive drum 1a.

[0046] However, when the toner degradation prevention toner image Ga passes through the primary transfer nip section N1, the reverse polarity toner contained in the toner degradation prevention toner image Ga is easily transferred from the photosensitive drum 1a to the intermediate transfer belt 7. The reverse polarity toner is toner whose polarity is reversed from that of the normal toner when the toner degradation prevention toner image Ga is developed by the developer (in this embodiment, it is positive polarity toner).

[0047] In this embodiment, as shown in Figure 6(b), when in non-transfer mode, the control unit 500 applies a secondary transfer voltage (second voltage, -3500V) to the secondary transfer inner roller 13 using the secondary transfer power supply 16, which has the same polarity as during image formation but a larger absolute value than during image formation. As a result, even if reverse polarity toner is supported on the intermediate transfer belt 7, it will not be transferred from the intermediate transfer belt 7 to the secondary transfer outer roller 14 when passing through the secondary transfer nip section N2. The reverse polarity toner that remains supported on the intermediate transfer belt 7 and passes through the secondary transfer nip section N2 is then removed by the belt cleaning device 17. The period during which the secondary transfer voltage (second voltage) is applied includes at least the period during which the region of the intermediate transfer belt 7 on which the reverse polarity toner included in the control toner image is transferred first passes through the secondary transfer nip section N2. In other words, when the control toner image passes through the primary transfer nip section N1, the system is configured to apply a secondary transfer voltage (second voltage) during the period when the region of the intermediate transfer belt 7 passing through the primary transfer nip section N1 first passes through the secondary transfer nip section N2.

[0048] As described above, in this embodiment, when forming a toner image Ga for preventing toner degradation and a toner image Gb for blade supply that are not transferred to the recording material, the primary transfer power supply 82 applies a primary transfer voltage with the opposite polarity to that used during image formation to the primary transfer roller 5a. Then, the secondary transfer power supply 16 applies a secondary transfer voltage with the same polarity as during image formation but with a larger absolute value to the secondary transfer inner roller 13. This makes it difficult for the reverse-polarity toner transferred from the control toner image formed on the photosensitive drum 1a to the intermediate transfer belt 7 to adhere to the secondary transfer outer roller 14 that contacts the outer surface of the intermediate transfer belt 7 during secondary transfer. Therefore, "backside staining" where toner adheres to the back surface of the recording material S and "edge staining" where toner adheres to the leading edge of the recording material S do not occur.

[0049] [Other embodiments] As shown in Figure 4, a temperature and humidity sensor 510 is connected to the control unit 500. The temperature and humidity sensor 510, which acts as a humidity detection means, is located inside the main body 120 of the device (see Figure 1) and detects the temperature and humidity inside the main body 120. The control unit 500 can control the voltage value applied to the secondary transfer roller 13 by the secondary transfer power supply 16 described above, according to the detection result of the temperature and humidity sensor. In this embodiment, when the humidity is low (first humidity, for example, less than 40%), the control unit 500 sets the secondary transfer voltage to "-3200V" (first setting value) and applies it. On the other hand, when the humidity is higher than the first humidity (second humidity, for example, 40% or more), the control unit 500 sets the secondary transfer voltage to "-3500V" (second setting value), which has a larger absolute value than when the humidity is low, and applies it. [Table 1]

[0050] This is because, in a dry environment with low humidity, it is more difficult for reverse-polarity toner, which has the opposite polarity (positive polarity) to the normal toner charging polarity, to be electrically transferred from the intermediate transfer belt 7 to the secondary transfer outer roller 14 than in a high-humidity environment. Therefore, in the case of a second humidity level with high humidity (e.g., 40% or higher), it is preferable to apply a second voltage value (second setting value, -3500V) that is larger in absolute value than the first voltage value (first setting value, -3200V) applied in the case of a first humidity level lower than the second humidity level (e.g., less than 40%), for the purpose of saving power.

[0051] In the above-described embodiment, the case using a repulsive transfer method was explained as an example, but the transfer voltage control of this embodiment can also be adopted when using an attractive transfer method. Figure 7 shows the configuration near the secondary transfer nip when using an attractive transfer method. As shown in Figure 7, in this case, a secondary transfer voltage is applied from the secondary transfer power supply 16 to the secondary transfer outer roller 14. In the case of an attractive transfer method, the control unit 500 applies a secondary transfer voltage with the opposite polarity (positive) to the toner charge polarity to the secondary transfer outer roller 14 from the secondary transfer power supply 16 for secondary transfer of the toner image. On the other hand, when forming the toner image Ga for toner degradation prevention or the toner image Gb for blade supply on the photosensitive drum 1a, a secondary transfer voltage with the same polarity (negative) as the toner charge polarity is applied from the secondary transfer power supply 16 to the secondary transfer outer roller 14.

[0052] Furthermore, it is preferable that the transfer voltage control in this embodiment described above be repeated even after the portion of the intermediate transfer belt 7 that came into contact with the control toner image as the control toner image passed through the primary transfer nip section N1 has passed through the belt cleaning device 17. This ensures that even when a control toner image is formed that tends to have a large amount of reverse polarity toner, such as the toner degradation prevention toner image Ga, the belt cleaning device 17 can reliably remove the reverse polarity toner. This is particularly effective when the belt cleaning device 17 is of the type that electrically removes toner using an electrostatic brush.

[0053] Although the present invention has been described above in reference to specific embodiments, the present invention is not limited to the embodiments described above. The present invention can also be implemented in other embodiments in which some or all of the configurations of the above embodiments are replaced with alternative configurations. Therefore, it can be implemented in any image forming apparatus, regardless of whether it is a tandem type / single drum type, a charging method, an electrostatic image formation method, a developing method, a transfer method, or a fixing method. In the embodiments described above, the main parts related to the formation / transfer of toner images were described, but the present invention can be implemented in various applications such as printers, various printing machines, copiers, fax machines, and multifunction devices by adding necessary equipment, equipment, and housing structures. Furthermore, although an example of constant voltage control was shown in the above embodiments for transfer bias control, it can also be implemented without distinction using constant current control or other high-voltage control methods. [Explanation of symbols]

[0054] 1a(1b, 1c, 1d)...Photoreceptor (photosensitive drum), 2a(2b, 2c, 2d)...Charging member (charging roller), 3a(3b, 3c, 3d)...Exposure device, 4a(4b, 4c, 4d)...Developing device, 5a(5b, 5c, 5d)...Primary transfer member (primary transfer roller), 7...Intermediate transfer body (intermediate transfer belt), 13...Secondary transfer member (secondary transfer inner roller), 16...Secondary transfer power supply, 17...Belt cleaning device, 41...Developing container, 42(43)...Conveying means (conveying screw), 62...Cleaning blade (drum cleaning blade), 82...Primary transfer power supply, 100...Image forming apparatus, 500...Control means (control unit), 510...Humidity detection means (temperature and humidity sensor), N1...Primary transfer section (primary transfer nip section), N2...Secondary transfer section (secondary transfer nip section), S...Recording material

Claims

1. A rotating photoreceptor, A charging member that charges the photoreceptor, An exposure apparatus that exposes the charged photoreceptor to form an electrostatic latent image, A developing apparatus that develops an electrostatic latent image formed on the photoreceptor into a toner image using a developer, An intermediate transfer body that rotates in contact with the photosensitive element, A primary transfer member that forms the primary transfer portion of the toner image from the photoreceptor to the intermediate transfer body, A secondary transfer member that forms a secondary transfer portion of the toner image from the intermediate transfer body to the recording material, A primary transfer power supply that applies a voltage to the primary transfer member, A secondary transfer power supply that applies a voltage to the secondary transfer member, The system includes a control means capable of performing a first mode in which a toner image is formed on the photoreceptor, a voltage of first polarity is applied to the primary transfer member to primary transfer the toner image formed on the photoreceptor to the intermediate transfer member, and a first voltage is applied to the secondary transfer member to secondary transfer the toner image primary transferred to the intermediate transfer member to secondary transfer to a recording material, and a second mode in which a control toner image is formed on the photoreceptor, and a voltage of second polarity opposite to the first polarity is applied to the primary transfer member when the control toner image passes through the primary transfer section. The control means, when the toner image for control passes through the primary transfer section and the region of the intermediate transfer body that passes through the primary transfer section passes through the secondary transfer section for the first time, applies a second voltage to the secondary transfer member that has the same polarity as the first voltage and has a larger absolute value than the first voltage, without applying a voltage that has the opposite polarity to the first voltage to the secondary transfer member. An image forming apparatus characterized by the following:

2. The control means applies a third voltage to the primary transfer member when the toner image passes through the primary transfer section in the first mode, and applies a fourth voltage to the primary transfer member that is smaller than the absolute value of the third voltage when the control toner image passes through the primary transfer section in the second mode. The image forming apparatus according to feature 1.

3. The developing apparatus comprises a developing container for containing a developer and a conveying means for conveying the developer while stirring it within the developing container. The control toner image is a toner degradation prevention toner image for preventing the deterioration of the developer contained in the developing container. The image forming apparatus according to claim 1 or 2.

4. With respect to the rotation direction of the photoreceptor, it is positioned downstream of the primary transfer section and upstream of the charging member, and includes a cleaning blade that contacts the photoreceptor to remove toner adhering to it, The control toner image is a supply toner image for supplying toner to the cleaning blade. The image forming apparatus according to any one of claims 1 to 3.

5. With respect to the rotational direction of the intermediate transfer body, a cleaning device is provided which is located downstream of the secondary transfer unit and upstream of the primary transfer unit to remove toner adhering to the intermediate transfer body. The image forming apparatus according to any one of claims 1 to 4.

6. Equipped with a humidity detection means for detecting humidity, The control means sets the second voltage to a first set value when the humidity detected by the humidity detection means is a first humidity, and sets the second voltage to a second set value that is greater in absolute value than the first set value when the humidity detected by the humidity detection means is a second humidity that is higher than the first humidity. The image forming apparatus according to any one of claims 1 to 5.

Images