Image forming apparatus

Abstract

To solve the problem in which: an impact when bringing a cleaning device into contact with an intermediate transfer body causes a toner discharged from the cleaning device to be scattered in an apparatus, which may cause an image defect.SOLUTION: An image forming apparatus has: an image carrier that carries a toner image; secondary transfer means that includes a secondary transfer roller and secondarily transfers the toner image primarily transferred from the image carrier to an intermediate transfer body from the intermediate transfer body to a recording medium; and a cleaning unit that can be brought into contact with and separated from the intermediate transfer body and is to remove toner remaining on the intermediate transfer body after the secondary transfer. The intermediate transfer body is inclined so that, in a contact area where the cleaning unit and the intermediate transfer body are in contact with each other, the upstream side in a conveyance direction of the intermediate transfer body is lower than the downstream side in the conveyance direction of the intermediate transfer body in the direction of gravity.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus that forms an image on a recording medium. [Background technology]

[0002] In an electrophotographic image forming apparatus, a toner image formed on an electrophotographic photosensitive member is first transferred onto an intermediate transfer member (primary transfer), and then the toner image transferred onto the intermediate transfer member is transferred to a recording medium by a transfer member that comes into contact with the recording medium and transfers the toner image to form an image. By using such an electrophotographic image forming apparatus, a color image with little physical misalignment (color shift) in the superimposition positions of the component color images can be obtained.

[0003] In image forming apparatuses using the above-mentioned intermediate transfer body, it is important to remove (clean) any toner remaining on the intermediate transfer body after the secondary transfer, which transfers an image from the intermediate transfer body to a recording medium such as paper, in order to obtain a good image. For this reason, a conventional method has been to provide a cleaning blade after the secondary transfer position to scrape off any remaining toner remaining on the intermediate transfer body after the secondary transfer (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5574924 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the cleaning unit including the cleaning blade is brought into contact with the intermediate transfer body, the impact can cause toner to be expelled from the cleaning unit and scattered inside the machine, resulting in poor image quality.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a technique for preventing toner, which is expelled due to the impact when the cleaning section contacts the intermediate transfer body, from scattering inside the machine. [Means for solving the problem]

[0007] In order to achieve the above object, an image forming apparatus according to one aspect of the present invention has the following configuration: an image carrier that carries a toner image; a secondary transfer means including a secondary transfer roller for secondarily transferring the toner image, which has been primarily transferred from the image carrier to an intermediate transfer medium, from the intermediate transfer medium to a recording medium; a cleaning unit that can be brought into contact with and separated from the intermediate transfer body and that cleans the toner remaining on the intermediate transfer body after the secondary transfer; In the contact area where the cleaning section and the intermediate transfer body contact each other, the upstream side of the intermediate transfer body in the transport direction is inclined so as to be lower in the direction of gravity than the downstream side of the intermediate transfer body in the transport direction. [Effects of the Invention]

[0008] According to the present invention, it is possible to prevent toner that is expelled due to the impact when the cleaning section contacts the intermediate transfer body from scattering inside the machine.

[0009] Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which the same or similar elements are designated by the same reference numerals. [Brief explanation of the drawings]

[0010] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating a schematic cross-sectional configuration of an image forming apparatus according to a first embodiment. [Figure 2]FIG. 2 is a schematic diagram showing a schematic configuration of a cleaning device for an intermediate transfer belt according to the first embodiment. [Figure 3] 5A and 5B are schematic diagrams illustrating a state in which the cleaning device for the intermediate transfer belt according to the first embodiment is in contact with and separated from the intermediate transfer belt. [Figure 4] FIG. 2 is a diagram illustrating a configuration for controlling contact / separation of an ICL brush in the image forming apparatus according to the first embodiment. [Figure 5] A cross-sectional schematic diagram showing the configuration of a typical intermediate transfer belt and ICL brush. [Figure 6] 5A and 5B are cross-sectional views illustrating the positional relationship between the intermediate transfer belt and the cleaning device for the intermediate transfer belt in the image forming apparatus according to the first embodiment, using modified examples and comparative examples. [Figure 7] FIG. 10 is a schematic diagram illustrating a cleaning device for an intermediate transfer belt according to a second embodiment. [Figure 8] 10A and 10B are diagrams showing evaluation results of occurrence of density unevenness according to the first and second embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention claimed. Although multiple features are described in the embodiments, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0012] [Embodiment 1] First, an image forming apparatus 1 according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 4. In the following description and in each drawing, the vertical direction when the image forming apparatus 1 is installed on a horizontal surface is referred to as the Z direction. The direction that intersects with the Z direction and is the direction of a rotation axis 90C (FIG. 1) of a rotary main body 90 (described later) (the direction of the rotary's rotation axis) is referred to as the Y direction. The direction that intersects with both the Z direction and the Y direction is referred to as the X direction. The X direction and the Y direction are preferably horizontal. The X direction, Y direction, and Z direction are preferably perpendicular to each other. Furthermore, as necessary, the directions of the arrows X, Y, and Z shown in each drawing will be referred to as the +X side, +Y side, and +Z side, respectively, and the opposite sides will be referred to as the -X side, -Y side, and -Z side, respectively.

[0013] FIG. 1 is a schematic cross-sectional view illustrating a schematic cross-sectional configuration of an image forming apparatus 1 according to the first embodiment.

[0014] The image forming apparatus 1 is a laser beam printer that forms an image on a sheet S by electrophotography. More specifically, the image forming apparatus 1 is a color laser beam printer equipped with four development units 50y, 50m, 50c, and 50k. As the sheet S, which is the recording material (recording medium), a variety of sheet materials of different sizes and materials can be used, including paper such as plain paper and cardboard, surface-treated sheet materials such as plastic film, cloth, and coated paper, and sheet materials of special shapes such as envelopes and index paper.

[0015] Next, a description will be given of the schematic configuration and image forming operation of the image forming apparatus 1 with reference to Fig. 1. As shown in Fig. 1, the image forming apparatus 1 has an image forming apparatus main body (hereinafter referred to as apparatus main body) 1A and toner cartridges 70y, 70m, 70c, and 70k that are detachably attached to the apparatus main body 1A. The apparatus main body 1A according to the first embodiment is the portion of the image forming apparatus 1 excluding the toner cartridges 70y, 70m, 70c, and 70k.

[0016] The apparatus main body 1A of the image forming apparatus 1 has a drum-shaped (cylindrical) electrophotographic photosensitive member (hereinafter referred to as photosensitive drum) 2 as an image carrier that carries an electrostatic latent image. Around the photosensitive drum 2, a charging roller 3, a scanner 4 as an exposure device, and a cleaning unit 6 for the photosensitive drum 2 are arranged.

[0017] The charging roller 3 is an example of a charging means for uniformly charging the photosensitive drum 2. The scanner 4 is an example of an exposure means for irradiating the photosensitive drum 2 with laser light according to image information to expose it. By irradiating the charged photosensitive drum 2 with laser light from the scanner 4, an electrostatic latent image according to the image information is formed on the surface of the photosensitive drum 2. The photosensitive drum cleaning unit 6 is an example of a cleaning means for removing toner remaining on the surface of the photosensitive drum 2.

[0018] The apparatus main body 1A also has a rotary main body (rotary, rotating body) 90 having development units 50y, 50m, 50c, and 50k. In the first embodiment, trays 80y, 80m, 80c, and 80k are attached to the rotary main body 90. Toner cartridges 70y, 70m, 70c, and 70k are removably attached to the trays 80y, 80m, 80c, and 80k.

[0019] The developing units 50y, 50m, 50c, and 50k are examples of developing means that develop (visualize) the electrostatic latent image formed on the photosensitive drum 2 into a toner image using toner of the corresponding color. The developing units 50y, 50m, 50c, and 50k develop the electrostatic latent image formed on the photosensitive drum 2 using yellow toner, magenta toner, cyan toner, or black toner, respectively.

[0020] The developing unit 50y has a developing roller 51y, a supply roller 52y, and a developing blade (not shown). The developing roller 51y is a developer carrier that carries toner as a developer and rotates to supply yellow toner to the photosensitive drum 2. The supply roller 52y is disposed in contact with the developing roller 51y and is a supply member that supplies yellow toner to the developing roller 51y. The developing blade is a regulating member that regulates the thickness of the yellow toner layer carried by the developing roller 51y. The other developing units 50m, 50c, and 50k each have similar developing rollers 51m, 51c, and 51k, supply rollers 52m, 52c, and 52k, and a developing blade.

[0021] Toner cartridges 70y, 70m, 70c, and 70k corresponding to the developing units 50y, 50m, 50c, and 50k are attached to the rotary body 90. The toner cartridges 70y, 70m, 70c, and 70k contain yellow toner, magenta toner, cyan toner, and black toner, respectively, to be supplied to the developing units 50y, 50m, 50c, and 50k.

[0022] The rotary body 90 is rotatable around a rotation axis (rotation center) 90C. The rotation axis 90C is substantially parallel to the rotation axis (rotation center) of the photosensitive drum 2. By rotating around the rotation axis 90C, the rotary body 90 can assume a development posture in which any one of the developing rollers 51y, 51m, 51c, and 51k faces the photosensitive drum 2. The posture in which the developing roller 51y faces the photosensitive drum 2 is called a yellow development posture. The posture in which the developing roller 51m faces the photosensitive drum 2 is called a magenta development posture. The posture in which the developing roller 51c faces the photosensitive drum 2 is called a cyan development posture. The posture in which the developing roller 51k faces the photosensitive drum 2 is called a black development posture. In other words, the rotary body 90 can rotate around the rotation axis 90C so that the positions of the developing rollers 51y, 51m, 51c, and 51k relative to the photosensitive drum 2 change.

[0023] The apparatus main body 1A has motors M1 (not shown), M2 (not shown), and M3 as drive sources. The motor M1 supplies a drive force for rotating the rotary main body 90 about the rotation axis 90C. The motor M2 moves the trays 80y, 80m, 80c, and 80k relative to the rotary main body 90.

[0024] Motor M3 (FIG. 4) drives components other than those driven by motors M1 and M2. For example, motor M3 drives the photosensitive drum 2, developing units 50y, 50m, 50c, and 50k, pickup roller 310, feed roller 311, conveying roller pair 320, secondary transfer roller 12, belt drive roller 10b, and fixing device 40. It is also used to drive the secondary transfer roller 12 and intermediate transfer belt cleaning device (cleaning unit) 13 to contact and separate from the intermediate transfer belt 20a. The components driven by motors M1, M2, and M3 can be changed as appropriate. Alternatively, any two or all three of the functions of motors M1, M2, and M3 can be combined into a single motor. Alternatively, additional drive sources other than motors M1, M2, and M3 may be added.

[0025] The subscripts y, m, c, and k of the reference symbols for the development units 50y, 50m, 50c, and 50k, the toner cartridges 70y, 70m, 70c, and 70k, and the trays 80y, 80m, 80c, and 80k indicate the toner colors corresponding to the corresponding units and components. Here, they represent yellow, magenta, cyan, and black, respectively. The development units 50y, 50m, 50c, and 50k share the same basic configuration and function. The toner cartridges 70y, 70m, 70c, and 70k also share the same basic configuration and function. The trays 80y, 80m, 80c, and 80k also share the same basic configuration and function. Therefore, when it is not necessary to distinguish between them, the subscripts y, m, c, and k are omitted, and the description will be given assuming that each unit is any one of the four units, cartridges, and trays.

[0026] Furthermore, the apparatus main body 1A has a sheet storage section 300, a pickup roller 310, a feed roller 311, a separation roller 312, a pair of conveying rollers 320, a secondary transfer roller 12, a fixing device 40, and an intermediate transfer unit 10. The pickup roller 310 is an example of a feeding means that feeds the sheet S. The feed roller 311 and the separation roller 312 are examples of a separation conveying unit that separates and conveys the sheets S one by one by frictional force. The secondary transfer roller 12 is an example of a transfer means that transfers an image from the intermediate transfer belt 10a to the sheet S.

[0027] The intermediate transfer unit 10 has an intermediate transfer belt 10a, a belt drive roller 10b, a tension roller 10c, an intermediate transfer belt cleaning device 13, and a primary transfer roller 11. The intermediate transfer belt 10a is an example of an intermediate transfer body that carries an image transferred (primary transfer) from the photosensitive drum 2 and transports the image to transfer (secondary transfer) onto a sheet S. The intermediate transfer belt 10a is stretched over the belt drive roller 10b and the tension roller 10c. The belt drive roller 10b is a drive member that is rotationally driven by a motor M3, which is a drive source, to transport the intermediate transfer belt 10a.

[0028] FIG. 2 is a schematic diagram showing a schematic configuration of the cleaning device 13 for the intermediate transfer belt 10a according to the first embodiment.

[0029] 2A is a cross-sectional view of the intermediate transfer belt cleaning device 13 in a contact state as viewed from the Y-axis direction. The intermediate transfer belt cleaning device 13 has an ICL brush 13a on the outer peripheral side of the intermediate transfer belt 10a and an ICL opposing member (backup member) 13b on the inner peripheral side thereof. The ICL brush 13a and the intermediate transfer belt 10a form a nip portion (N1-N2), and the ICL opposing member 13b and the intermediate transfer belt 10a form a nip portion (N3-N4). In the first embodiment, the nip portion (N1-N2) includes areas (N1-N3) and (N4-N2) without the ICL opposing member 13b (areas not backed up by the ICL opposing member 13b). However, the present invention is not limited to such a configuration. The area of ​​the intermediate transfer belt 10a without the ICL facing member 13b deforms slightly when the ICL brush 13a contacts it, thereby reducing the impact when the ICL brush 13a contacts the intermediate transfer belt 10a. Therefore, this configuration reduces the scattering distance of the toner held by the ICL brush 13a. Note that the ICL facing member 13b is not necessary.

[0030] The ICL brush 13a has a support and brush bristles. Its functions are to charge the residual toner to a potential opposite to that of the photosensitive drum 2 and to entangle and temporarily hold a portion of the residual toner. Therefore, the bristles of the ICL brush 13a according to the first embodiment are made of conductive resin, such as nylon or rayon, and are woven onto the support at a predetermined density. Specifically, brush bristles made of conductive nylon resin, each 5 mm long and having a single filament fineness of 5 dtex, are woven into the support at a density of 100 kF / inch2. The ICL opposing member 13b is a cylindrical roller member made of aluminum and is arranged to rotate in response to the transport of the intermediate transfer belt 10a.

[0031] FIG. 2(b) is a longitudinal schematic diagram of the cleaning device 13 for the intermediate transfer belt as viewed from the X-axis direction.

[0032] The length of the ICL brush 13a in the axial direction (Y-axis direction) is long enough to cover the area where toner is transferred to the surface of the intermediate transfer belt 10a. Specifically, the length of the intermediate transfer belt 10a in the Y-axis direction is 236 mm, the length of the ICL brush 13a in the Y-axis direction is 224 mm, and the length of the toner transfer area in the Y-axis direction is 220 mm. The ICL brush 13a can be brought into contact with and separated from the intermediate transfer belt 10a.

[0033] FIG. 3 is a schematic diagram illustrating the contact / separation states of the intermediate transfer belt cleaning device 13 with respect to the intermediate transfer belt 10a according to the first embodiment.

[0034] FIG. 3(a) is a cross-sectional view of the ICL brush 13a in contact with the intermediate transfer belt 10a, and FIG. 3(b) is a cross-sectional view of the ICL brush 13a separated from the intermediate transfer belt 10a. The ICL brush 13a is held by a lever 201, which is rotatable around the Y axis. A spring 202 is disposed at the end of the lever 201 opposite the portion holding the ICL brush 13a. The spring 202 presses the lever 201 in a direction that brings the ICL brush 13a into contact with the intermediate transfer belt 10a. Supporting the ICL brush 13a with the pressure of the spring 202 allows the ICL brush 13a to be in stable contact with the intermediate transfer belt 10a. Furthermore, adjusting the contact pressure of the ICL brush 13a against the intermediate transfer belt 10a using the spring 202 can prevent deformation of the bristles of the ICL brush 13a due to the contact.

[0035] Then, as shown in FIG. 3(b), the cam member 203 as a switching member rotates in the direction of the arrow (clockwise), pressing the lever 201 together with the spring 202, and the ICL brush 13a is moved to a position separated from the intermediate transfer belt 10a.

[0036] FIG. 3(c) shows a cross-sectional view of the intermediate transfer belt cleaning device 13 when the ICL brush 13a and the intermediate transfer belt 10a are in a separated state, as viewed from the Y-axis direction. Arrow 13A indicates the path along which the center position of the nip portion (N1-N2) of the ICL brush 13a moves as the ICL brush 13a transitions from the separated state to the contact state. Dashed line 13B indicates a perpendicular line to the surface of the intermediate transfer belt 10a at the center position of the nip portion (N1-N2) of the ICL brush 13a in the contact state. Just before the contact state is reached, arrow 13A is positioned downstream of dashed line 13B in the transport direction of the intermediate transfer belt 10a. This facilitates scattering of toner when the ICL brush 13a contacts the intermediate transfer belt 10a toward the upstream side in the transport direction. The reason for this is that when the ICL brush 13a collides with the intermediate transfer belt 10a and decelerates, the toner held by the ICL brush 13a is more likely to scatter due to inertial force in the direction of arrow 13A, i.e., upstream in the transport direction of the intermediate transfer belt 10a.

[0037] FIG. 4 is a diagram illustrating a configuration for controlling contact / separation of the ICL brush 13a in the image forming apparatus 1 according to the first embodiment.

[0038] The cam member 203 is connected to a drive source via a gear train. The final end gear 204, which transmits drive to the cam member 203, disengages its claws when a solenoid 205 performs an attraction operation for a certain period of time, and rotates once by driving a motor M3 serving as a drive source. In the first embodiment, the cam member 203 is configured to rotate one-third of the way when the final end gear 204 rotates once. Therefore, the contact / separation state of the ICL brush 13a transitions depending on the drive of the solenoid 205, and the solenoid 205 is driven via a solenoid drive circuit 206 by a signal output from a CPU 207, which serves as a control unit.

[0039] Furthermore, the cleaning device 13 for the intermediate transfer belt is disposed downstream of the secondary transfer nip (contact portion with the secondary transfer roller 12) in the transport direction of the intermediate transfer belt 10a. In the first embodiment, it is disposed downstream of the intermediate position between the belt drive roller 10b and the tension roller 10c.

[0040] Next, an image forming operation in embodiment 1 will be described. First, the photosensitive drum 2 is rotated in the direction of the arrow (counterclockwise) in Fig. 1 in synchronization with the rotation of the intermediate transfer belt 10a. Then, the surface of the photosensitive drum 2 is uniformly charged by the charging roller 3.

[0041] When a color image is formed on the sheet S, the rotary body 90 rotates in the direction of the arrow in Figure 1 (clockwise) while supporting the developing units 50y, 50m, 50c, and 50k. Then, the electrophotographic process is repeatedly performed while the developing rollers 51y, 51m, 51c, and 51k are moved one by one to the developing position.

[0042] First, the scanner 4 irradiates the photosensitive drum 2 with laser light based on image data corresponding to a yellow image, forming an electrostatic latent image corresponding to the yellow image on the surface of the photosensitive drum 2. In parallel with the formation of this electrostatic latent image, the motor M1 rotates the rotary body 90, causing the rotary body 90 to assume a yellow developing position. When the rotary body 90 is in the yellow developing position, the developing roller 51y is in the developing position and develops the electrostatic latent image formed on the photosensitive drum 2 with yellow toner. A developing voltage of opposite polarity to the charging polarity of the photosensitive drum 2 is applied to the developing roller 51y so that the toner adheres to the latent image on the photosensitive drum 2.

[0043] In the first embodiment, each of the developing rollers 51y, 51m, 51c, and 51k is an elastic roller having a metal shaft coated with rubber. At the developing position, each of the developing rollers 51y, 51m, 51c, and 51k develops an electrostatic latent image while in contact with the photosensitive drum 2. In other words, the image forming apparatus 1 according to the first embodiment employs a contact development method. However, each of the developing rollers 51y, 51m, 51c, and 51k may also develop an electrostatic latent image while a gap is provided between the developing rollers 51y, 51m, 51c, and 51k and the photosensitive drum 2 at the developing position. In other words, the image forming apparatus 1 may employ a non-contact development method.

[0044] Once the yellow toner image is developed, the yellow toner image on the photosensitive drum 2 is primarily transferred onto the intermediate transfer belt 10a by the primary transfer roller 11 arranged inside the intermediate transfer belt 10a. At this time, a primary transfer voltage of the opposite polarity to that of the toner image formed on the photosensitive drum 2 is applied to the primary transfer roller 11.

[0045] Thereafter, the rotary body 90 is rotated to move the developing rollers 51m, 51c, and 51k to the developing positions in order, thereby sequentially forming toner images of each color on the photosensitive drum 2. That is, after a yellow toner image is formed on the intermediate transfer belt 10a, the rotary body 90 assumes the magenta developing position, and a magenta toner image is formed on the intermediate transfer belt 10a. After the magenta toner image is formed on the intermediate transfer belt 10a, the rotary body 90 assumes the cyan developing position, and a cyan toner image is formed on the intermediate transfer belt 10a. After the cyan toner image is formed on the intermediate transfer belt 10a, the rotary body 90 assumes the black developing position, and formation of a black toner image on the intermediate transfer belt 10a begins. Until the yellow, magenta, and cyan toner images formed on the intermediate transfer belt 10a pass through the secondary transfer section and the cleaning device, the secondary transfer roller 12 and the cleaning device 13 are separated from the intermediate transfer belt 10a. The secondary transfer roller 12 is brought into contact with the intermediate transfer belt 10a after the yellow, magenta, and cyan toner images formed on the intermediate transfer belt 10a have passed through the secondary transfer section and before the leading edge of the color toner image on the intermediate transfer belt 10a, on which the fourth color, black toner image, has been formed, reaches the secondary transfer section again.

[0046] Meanwhile, a sheet S is fed by a pickup roller 310 from a sheet storage unit 300 provided at the bottom of the apparatus main body 1A. The sheets S are separated into individual sheets by a feed roller 311 and a separation roller 312 and then fed to a pair of conveying rollers 320. The sheet S fed to the pair of conveying rollers 320 waits until a toner image is formed on the intermediate transfer belt 10a. After the toner image is formed on the intermediate transfer belt 10a, the sheet S that has been waiting by the pair of conveying rollers 320 is conveyed and sent to a transfer unit (secondary transfer unit), which is a nip between the intermediate transfer belt 10a and a secondary transfer roller 12. In this way, the color image on the intermediate transfer belt 10a is transferred (secondary transfer) onto the surface of the conveyed sheet S. At this time, a secondary transfer voltage of a polarity opposite to the charge polarity of the toner image is applied to the secondary transfer roller 11.

[0047] The sheet S onto which the color image has been transferred in this manner is sent to the fixing device 40. In the fixing device 40, the sheet S is heated and pressurized, and the image is fixed onto the sheet S. After passing through the fixing device 40, the sheet S is discharged outside the image forming apparatus 1 as a finished product.

[0048] Residual toner remaining on the surface of the intermediate transfer belt 10a after the secondary transfer is cleaned by the cleaning device 13 for the intermediate transfer belt as follows.

[0049] The ICL brush 13a serves to charge the transfer residual toner on the intermediate transfer belt 10a to a potential opposite to the charge potential of the photosensitive drum 2 and to temporarily hold the transfer residual toner by entangling it in the brush. The transfer residual toner on the intermediate transfer belt 10a is charged to a potential opposite to the charge potential of the photosensitive drum 2 as it passes through the ICL brush 13a. In the first embodiment, the photosensitive drum 2 is negatively charged, and a positive (plus) voltage is applied to the ICL brush 13a. Therefore, the transfer residual toner that passes through the ICL brush 13a is positively charged. The positively charged transfer residual toner is transferred to the negatively charged surface of the photosensitive drum 2 at the primary transfer nip and collected by the cleaning unit 6 for the photosensitive drum 2. At the same time that the transfer residual toner is transferred to the negatively charged surface of the photosensitive drum 2 at the primary transfer nip, the toner image carried on the photosensitive drum 2 may be primarily transferred to the intermediate transfer belt 10a.

[0050] On the other hand, the transfer residual toner that does not pass through the ICL brush 13a and is temporarily held by the ICL brush 13a is discharged from the ICL brush 13a onto the intermediate transfer belt 10a again in the operation after image formation. It is then transferred to the surface of the photosensitive drum 2 at the primary transfer nip and collected by the photosensitive drum cleaning unit 6. However, not all of the toner temporarily held by the ICL brush 13a is discharged onto the intermediate transfer belt 10a, and a certain amount of the residual toner after the secondary transfer is still held by the ICL brush 13a.

[0051] While toner is held by the ICL brush 13a, it is possible that the ICL brush 13a may transition from a spaced state to a contact state with the intermediate transfer belt 10a. In such a case, the shock of the contact causes the toner held by the ICL brush 13a to be ejected from the ICL brush 13a. This ejected toner may scatter into the interior of the machine, move due to gravity or the movement of air within the machine, and adhere to components other than the intermediate transfer belt 10a, potentially causing problems such as image defects. For example, scattered toner adhering to the surface of the secondary transfer roller 12 may adhere to the back surface of the sheet S, causing staining, a problem known as backside contamination. Furthermore, scattered toner adhering to the scanner 4 may block a portion of the laser light in the Y-axis direction, resulting in a decrease in image density at that position and vertical streaks of uneven density, a problem known as uneven density.

[0052] Next, a general example will be used to explain the mechanism by which toner discharged from the ICL brush scatters into the interior of the machine when the cleaning device comes into contact with the intermediate transfer belt.

[0053] FIG. 5 is a cross-sectional view showing the configuration of a general intermediate transfer belt 510a and an ICL brush 513a.

[0054] 5, the intermediate transfer belt 510a is horizontal at the contact position of the ICL brush 513a. When the ICL brush 513a contacts the intermediate transfer belt 510a in this state, the scattered toner ejected from the ICL brush 513a scatters on both the upstream and downstream sides of the transport direction of the intermediate transfer belt 510a.

[0055] Of this, the toner that has scattered downstream (the right side in FIG. 5) winds around tension roller 510c as intermediate transfer belt 510a is transported, and when it moves onto the curved intermediate transfer belt 510a, some of it may scatter into the interior of the machine. The reason that scattered toner on the curved surface of intermediate transfer belt 510a scatters into the interior of the machine is because the polarity of the scattered toner cannot be controlled. In addition, the curved surface of intermediate transfer belt 510a undergoes slight expansion and contraction due to fluctuations in tension and curvature of intermediate transfer belt 510a, making it difficult to retain scattered toner on intermediate transfer belt 510a.

[0056] On the other hand, toner scattered upstream (left side in FIG. 5) is less likely to diffuse into the interior of the machine. The toner scattered upstream reaches the ICL brush 513a again as it is transported by the intermediate transfer belt 510a, where it is charged and passes through the ICL brush 513a or is held by the ICL brush 513a again. The scattered toner that has been charged and passed through the ICL brush 513a remains on the intermediate transfer belt 510a due to electrostatic adhesion, even on the curved surface of the intermediate transfer belt 510a, without scattering into the interior of the machine, and is transferred to the surface of the photosensitive drum 502 and collected by the cleaning unit 506.

[0057] Therefore, in embodiment 1, in order to prevent toner from scattering inside the machine, the intermediate transfer belt 10a at the contact position of the intermediate transfer belt cleaning device 13 is inclined so that the upstream side of the conveying direction of the intermediate transfer belt 10a is downward in the direction of gravity.

[0058] FIG. 6 is a cross-sectional view illustrating the positional relationship between the intermediate transfer belt 10a and the cleaning device 13 for the intermediate transfer belt in the image forming apparatus 1 according to the first embodiment, using a modified example and a comparative example.

[0059] FIG. 6A is a schematic cross-sectional view showing the positional relationship between the intermediate transfer belt 10a and the cleaning device 13 for the intermediate transfer belt according to the first embodiment.

[0060] The intermediate transfer belt 10a at the contact nip (N1-N2) is tilted upward in the direction of gravity and with its upstream side in the conveying direction tilted downward in the direction of gravity. Furthermore, tensioning surfaces (A-N1) and (N2-B) facing upward in the direction of gravity are provided on the upstream and downstream sides of the contact nip (N1-N2). The inclination of these tensioning surfaces (A-N1) and (N2-B) with respect to the horizontal plane is set to an angle equal to or less than the angle of repose of the toner. Specifically, the angle of repose of the toner in the first embodiment is 45°, and the intermediate transfer belt 10a at the contact nip (N1-N2) and the tensioning surfaces (A-N1) and (N2-B) are arranged so that their upstream sides are tilted downward by 27° in the direction of gravity. The method for measuring the angle of repose will be described later. The relationship in length between the tension surface (A-N1) and the tension surface (N2-B) is set to satisfy (A-N1)>(N2-B).

[0061] In this embodiment, the angle of repose of the toner is determined by the following method.

[0062] Measuring device: Powder tester PT-N type (Hosokawa Micron Corporation) Measurement method: Follow the angle of repose measurement instructions in the instruction manual for the Powder Tester PT-N (sieve opening 710 μm, vibration time 180 s, amplitude 2 mm or less). However, after leaving the sample overnight at 23°C and 60% RH, the angle of repose was measured using a measuring device in an environment of 23°C and 60% RH, and the measurement was repeated five times to obtain the average value.

[0063] Next, the effect of suppressing toner scattering inside the machine at the moment when the ICL brush 13a according to the first embodiment comes into contact with the ICL will be described.

[0064] As described above, the intermediate transfer belt 10a is inclined at the contact nip (N1-N2). Therefore, when the ICL brush 13a vibrates finely due to the shock of contact and the toner held by the ICL brush 13a is expelled, the toner is likely to scatter downward in the direction of gravity due to the influence of gravity. Thus, in the first embodiment, the amount of toner scattered into the machine is suppressed by reducing the amount of toner scattered downstream (upward in FIG. 6A), where it is more likely to scatter into the machine, and increasing the amount of toner scattered upstream (downward in FIG. 6A), where it is less likely to scatter into the machine.

[0065] In addition, in the first embodiment, the angle of the tension surface (A-N1) is set to be equal to or less than the angle of repose of the toner, thereby more effectively preventing the scattered toner from scattering inside the machine. This prevents the scattered toner to the upstream side (the downward direction in FIG. 6(a)) from rolling down the tension surface (A-N1) and scattering inside the machine, and makes it easier to transport it back to the position of the ICL brush 13a.

[0066] The position of the contact nip (N1-N2) may be anywhere as long as there are tension surfaces facing upward in the direction of gravity on the upstream and downstream sides. For example, as shown in the modified example of FIG. 6(b), the distance between the tension surfaces (A-N1) may be less than the distance between the tension surfaces (N2-B). However, it is more preferable to position the ICL brush 13a so that the distance between the tension surfaces (A-N1) is greater than the distance between the tension surfaces (N2-B), as shown in FIG. 6(a) of the first embodiment.

[0067] The inclination of the intermediate transfer belt 10a at the contact nip (N1-N2) position increases the scattering distance of scattered toner upstream in the transport direction and decreases the scattering distance of scattered toner downstream in the transport direction compared to when the contact nip is not inclined. If the distance between the tensioning surfaces (A-N1) is shorter than the scattering distance of scattered toner, the toner scattered upstream in the transport direction may scatter into the machine without being transported back to the ICL brush 13a. Therefore, the distance between the tensioning surfaces (A-N1) is made longer than the distance between the tensioning surfaces (N2-B).

[0068] On the other hand, if there is no tension surface facing upward in the direction of gravity on the upstream or downstream side of the contact nip (N1-N2), more toner will be scattered into the machine. For example, in a configuration in which the ICL brush 13a is placed on the intermediate transfer belt 10a facing the belt drive roller 10b, as in Comparative Example 1 shown in Figure 6(c), the toner scattered upstream will be scattered onto the curved surface of the intermediate transfer belt 10a.

[0069] In a configuration in which the ICL brush 13a is disposed on the intermediate transfer belt 10a facing the tension roller 10c, as in Comparative Example 2 shown in Figure 6(d), toner scattered downstream is scattered onto the curved surface of the intermediate transfer belt 10a. Because the toner scattered on the curved surface of the intermediate transfer belt 10a is unstable, it tends to roll down the curved surface and then scatter into the interior of the machine. Therefore, the arrangement of the ICL brush 13a shown in Figures 6(c) and 6(d) is not preferable.

[0070] Next, for the first embodiment, an image evaluation test was carried out after paper feeding durability.

[0071] Two types of image forming apparatus configurations were prepared for the evaluation test: the first embodiment and a conventional example.

[0072] The image evaluation method was performed in an N / N environment (temperature 23°C, humidity 50%) by printing evaluation images on evaluation paper using an image forming apparatus after 50,000 sheets had been passed through. Specifically, 50,000 sheets of letter-size plain paper (basis weight 75 g / m²) were printed on one side with an 8% coverage image (an image with 2% coverage of horizontal lines of yellow, magenta, cyan, or black toner). Then, a full-page halftone image with a 50% coverage of black toner was printed on one side as the evaluation image. Density unevenness was evaluated as "OK" if the density unevenness of the halftone image of the evaluation image was not visible to the naked eye, and "NG" if it was visible to the naked eye. The evaluation results are shown in Figure 8(a).

[0073] The above evaluation tests show that the first embodiment can suppress problems caused by toner scattered inside the machine.

[0074] Although the first embodiment has been described with reference to the example of color print image formation, the same effects can be obtained in monochrome print image formation, and this is not excluded from the scope of the invention.

[0075] In addition, the configuration in which the ICL brush is spaced apart from the intermediate transfer belt also has the effect of improving the durability of the intermediate transfer belt, and it is preferable to keep the ICL brush spaced apart as much as possible. Therefore, even in monochrome printing, there is the problem of unintended toner scattering onto the intermediate transfer belt due to the contact and separation of the ICL brush, and the configuration of the present invention provides the same effect.

[0076] In addition, in the first embodiment, an image forming apparatus that performs multiple development using one photosensitive drum has been described as an example, but the same effects can be obtained with a so-called inline type image forming apparatus that forms images using photosensitive drums of each color arranged side by side on an intermediate transfer belt, and these are not excluded from the scope of the invention.

[0077] Although the first embodiment employs a cleaning method using an ICL brush 13a as the intermediate transfer belt cleaning device 13, the present invention is not limited to this configuration. For example, a cleaning method using a roller-shaped charging member instead of the ICL brush 13a may be used. Alternatively, a method of collecting toner on the intermediate transfer belt 10a and storing it in a separately provided waste toner box may be used. In this method, the member for collecting toner on the intermediate transfer belt 10a may be a plate-shaped resin or metal, or a brush-shaped resin or metal. The present invention is also effective against toner held by these toner collecting members scattering into the machine. However, because a cleaning method using a charging member intentionally retains toner in the intermediate transfer belt cleaning device 13, the amount of scattered toner tends to be greater than the method of collecting toner and storing it in a separately provided waste toner box. Therefore, the configuration of the first embodiment is more effective in a cleaning method using a charging member.

[0078] Furthermore, when the intermediate transfer belt cleaning device 13 is made of a brush-shaped member that contacts the intermediate transfer belt 10a rather than a plate-shaped or roller-shaped member, the surface area is larger and the amount of toner that can be stored is larger, which tends to result in more scattered toner. Therefore, among cleaning methods that use a charging member, the configuration of embodiment 1 is more effective in a configuration that uses the ICL brush 13a.

[0079] As described above, according to the first embodiment, it is possible to expel more toner, which is expelled from the cleaning device due to the impact when the cleaning device contacts the intermediate transfer belt, upstream in the transport direction of the intermediate transfer belt. This makes it possible to collect the toner expelled onto the intermediate transfer belt after the cleaning device contacts the intermediate transfer belt, and has the effect of suppressing image defects caused by toner scattering inside the device.

[0080] [Embodiment 2] Next, a second embodiment of the present invention will be described. The second embodiment has the same configuration as the first embodiment, except that the ICL opposing member 13b is arranged in a tensioned state so as to wrap around a portion of the intermediate transfer belt 10a.

[0081] FIG. 7 is a schematic diagram illustrating a cleaning device for an intermediate transfer belt according to the second embodiment.

[0082] Fig. 7(a) is a schematic diagram illustrating the contact state of the intermediate transfer belt cleaning device 13 with the intermediate transfer belt 10a according to embodiment 2. Fig. 7(b) is an enlarged view of the contact portion between the ICL brush 13a and the intermediate transfer belt 10a in Fig. 7(a).

[0083] 7(a) and 7(b), the ICL opposing member (backup member) 13b is positioned higher in the direction of gravity than the configuration of FIG. 6(a) of embodiment 1. As a result, the intermediate transfer belt 10a is stretched not only by the belt drive roller 10b and tension roller 10c but also by the ICL opposing member 13b. This configuration allows a wider nip portion (N3-N4) to be formed between the ICL opposing member 13b and the intermediate transfer belt 10a, stabilizing the transport of the intermediate transfer belt 10a.

[0084] In the second embodiment, the intermediate transfer belt 10a at the contact nip (N1-N2) is also inclined so that the upstream side in the conveying direction is downward in the direction of gravity. Furthermore, tensioning surfaces (A-N1) and (N2-B) facing upward in the direction of gravity are provided on the upstream and downstream sides of the contact nip (N1-N2), respectively. The inclination of the tensioning surface (A-N1) is set to an angle equal to or less than the angle of repose of the toner; specifically, the inclination of the tensioning surface (A-N1) is 34°. Meanwhile, the inclination of the tensioning surface (N2-B) is 10°.

[0085] In this way, an experiment was conducted in the second embodiment to confirm the same effects as those in the first embodiment, and the results are shown in FIG. 8(b).

[0086] As shown in FIG. 8(b), it can be seen that the problems caused by toner scattered inside the machine can also be suppressed in the second embodiment.

[0087] In the second embodiment, the nip portion (N1-N2) includes areas (N1-N3) and (N4-N2) where the ICL facing member 13b is not present, but the present invention is not limited to this configuration. For example, the nip portion (N1-N2) may be included within the area of ​​the nip portion (N3-N4).

[0088] (Other embodiments) The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that realizes one or more functions.

[0089] The present specification and drawings disclose the following image forming apparatus.

[0090] (Item 1) an image carrier that carries a toner image; a secondary transfer means including a secondary transfer roller for secondarily transferring the toner image, which has been primarily transferred from the image carrier to an intermediate transfer medium, from the intermediate transfer medium to a recording medium; a cleaning unit that can be brought into contact with and separated from the intermediate transfer body and that cleans the toner remaining on the intermediate transfer body after the secondary transfer; an image forming apparatus characterized in that, in a contact area where the cleaning section and the intermediate transfer body contact each other, the upstream side of the intermediate transfer body in the transport direction is inclined so as to be lower in the direction of gravity than the downstream side of the intermediate transfer body in the transport direction.

[0091] (Item 2) Item 1. The image forming apparatus according to item 1, wherein the length of the tension surface of the intermediate transfer body on the upstream side of the contacting nip in the transport direction is longer than the length of the tension surface of the intermediate transfer body on the downstream side of the contacting nip in the transport direction.

[0092] (Item 3) 3. The image forming apparatus according to item 1 or 2, wherein the inclination of the tension surface of the intermediate transfer body on the upstream side of the contact nip is equal to or smaller than the angle of repose.

[0093] (Item 4) The image forming apparatus according to any one of items 1 to 3, characterized in that the intermediate transfer body is stretched over a first roller that is close to the secondary transfer roller and a second roller that is farther from the secondary transfer roller than the first roller, and the position of the first roller in the direction of gravity is lower than the second roller.

[0094] (Item 5) 5. The image forming apparatus according to any one of items 1 to 4, further comprising a backup member that backs up the intermediate transfer body on the surface opposite to the surface of the intermediate transfer body that contacts the cleaning unit, wherein the backup member does not back up the intermediate transfer body at the upstream end and downstream end of the contacting nip.

[0095] (Item 6) Item 6. The image forming apparatus according to item 5, wherein the intermediate transfer body is stretched by the backup member in addition to a first roller that is close to the secondary transfer roller and a second roller that is farther from the secondary transfer roller than the first roller.

[0096] (Item 7) 7. The image forming apparatus according to item 6, wherein the distance between the first roller and the backup member is longer than the distance between the second roller and the backup member.

[0097] (Item 8) 8. The image forming apparatus according to any one of items 1 to 7, wherein a trajectory along which the cleaning unit moves immediately before the cleaning unit comes into contact with the intermediate transfer body is located downstream in the transport direction of the intermediate transfer body with respect to a perpendicular line to the surface of the intermediate transfer body at the center position of the nip where the cleaning unit comes into contact.

[0098] (Item 9) 9. The image forming apparatus according to any one of items 1 to 8, characterized in that the cleaning unit is applied with a voltage of a polarity opposite to the normal polarity of the toner, and charges a portion of the toner remaining on the intermediate transfer body with the opposite polarity, thereby retaining the portion of the toner remaining on the intermediate transfer body.

[0099] (Item 10) 10. The image forming apparatus according to any one of items 1 to 9, wherein the cleaning unit has a brush-like member, and the member is configured to contact the intermediate transfer body.

[0100] The present invention is not limited to the above-described embodiments, and various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the following claims are appended to apprise the public of the scope of the present invention. [Explanation of symbols]

[0101] 1...image forming apparatus, 2...photosensitive drum, 10...intermediate transfer unit, 10a...intermediate transfer belt, 12...secondary transfer roller, 13...cleaning device for intermediate transfer belt, 13a...ICL brush, 40...fixing device, 50...developing unit, S...sheet

Claims

1. an image carrier that carries a toner image; a secondary transfer means including a secondary transfer roller for secondarily transferring the toner image, which has been primarily transferred from the image carrier to an intermediate transfer medium, from the intermediate transfer medium to a recording medium; a cleaning unit that can be brought into contact with and separated from the intermediate transfer body and that cleans the toner remaining on the intermediate transfer body after the secondary transfer; an image forming apparatus characterized in that, in a contact area where the cleaning section and the intermediate transfer body contact each other, the upstream side of the intermediate transfer body in the transport direction is inclined so as to be lower in the direction of gravity than the downstream side of the intermediate transfer body in the transport direction.

2. 2. The image forming apparatus according to claim 1, wherein the length of the tension surface of the intermediate transfer body on the upstream side of the contact nip in the transport direction is longer than the length of the tension surface of the intermediate transfer body on the downstream side of the contact nip in the transport direction.

3. 2. The image forming apparatus according to claim 1, wherein an inclination of the tension surface of the intermediate transfer body on the upstream side of the contact nip is equal to or smaller than an angle of repose.

4. 2. The image forming apparatus according to claim 1, wherein the intermediate transfer member is stretched across a first roller that is closer to the secondary transfer roller and a second roller that is farther from the secondary transfer roller than the first roller, and the position of the first roller in the direction of gravity is lower than the second roller.

5. 5. An image forming apparatus according to claim 1, further comprising a backup member that backs up the intermediate transfer body on the side opposite to the surface of the intermediate transfer body that contacts the cleaning section, wherein the backup member does not back up the intermediate transfer body at the upstream end and downstream end of the contacting nip.

6. 6. The image forming apparatus according to claim 5, wherein the intermediate transfer body is stretched by the backup member in addition to a first roller that is closer to the secondary transfer roller and a second roller that is farther from the secondary transfer roller than the first roller.

7. 7. The image forming apparatus according to claim 6, wherein the distance between the first roller and the backup member is longer than the distance between the second roller and the backup member.

8. 2. The image forming apparatus according to claim 1, wherein the trajectory of movement of the cleaning unit just before the cleaning unit comes into contact with the intermediate transfer body is located downstream in the transport direction of the intermediate transfer body with respect to a line perpendicular to the surface of the intermediate transfer body at the center position of the contacting nip.

9. 2. The image forming apparatus according to claim 1, wherein the cleaning unit is applied with a voltage of a polarity opposite to the normal polarity of the toner, and charges a portion of the toner remaining on the intermediate transfer body with the opposite polarity to retain the portion of the toner remaining on the intermediate transfer body.

10. 2. The image forming apparatus according to claim 1, wherein the cleaning unit has a brush-like member, and the member is configured to contact the intermediate transfer body.

Images