Image forming apparatus and lubricant amount control method

Abstract

To provide an image forming apparatus and a lubricant amount control method that can prevent the occurrence of cleaning failure resulting from lubricant transferred onto an image carrier.SOLUTION: An image forming apparatus comprises: an image carrier that can carry a toner image; a transfer unit that performs transfer of the toner image to the image carrier; and a control unit that executes control of reducing the amount of lubricant on the image carrier according to a transfer pressure when the transfer is performed. For example, the control unit executes the control of reducing the amount of lubricant on the image carrier according to the transfer pressure and the amount of toner images on a recording medium formed by the image forming apparatus.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus and a method for controlling the amount of lubricant. [Background technology]

[0002] There is known an image forming apparatus that includes a photosensitive drum on which a toner image is formed by electrophotography, a primary transfer unit that transfers the toner image formed on the photosensitive drum to an intermediate transfer belt, a secondary transfer unit that transfers the toner image transferred to the intermediate transfer belt to paper (recording medium), and a fixing unit that fixes the toner image transferred to the paper.

[0003] The image forming apparatus is also equipped with a cleaning blade for cleaning residual toner remaining on the surface of the photosensitive drum, and a lubricant application unit for actively applying lubricant to the surface of the photosensitive drum to ensure stable cleaning performance.

[0004] For example, Patent Document 1 discloses a removal means for removing the lubricant remaining on the image carrier by charging the image carrier with an AC voltage in accordance with parameters such as coverage distribution.

[0005] Furthermore, for example, Patent Document 2 discloses a charging means that increases the charge amount of toner that reaches the cleaning means, thereby improving the performance of removing lubricant from the image carrier. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-159051 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-114915 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the amount of lubricant (lubricant film amount) actively applied to the surface of the photosensitive drum by the lubricant applicator may be transferred to the intermediate transfer belt located downstream of the photosensitive drum, causing adverse effects. For example, in the case of an intermediate transfer belt that does not inherently require the application of lubricant, there is no mechanism for controlling the amount of lubricant transferred from the photosensitive drum. Therefore, for example, if the amount of lubricant on the intermediate transfer belt is uneven, the friction force between the intermediate transfer belt and the cleaning blade may become uneven, resulting in poor cleaning. Also, if the amount of lubricant on the intermediate transfer belt becomes too large, the lubricant may accumulate at the contact point (edge) between the intermediate transfer belt and the cleaning blade, causing poor cleaning due to jamming.

[0008] SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus and an image forming method that can prevent the occurrence of cleaning defects caused by lubricant transferred to an image carrier. [Means for solving the problem]

[0009] The image forming apparatus according to the present invention comprises: an image carrier capable of carrying a toner image; a transfer unit that transfers a toner image between the image carrier and the transfer unit; Transfer pressure when the toner image is transferred to the image carrier an amount of lubricant on the image carrier based on a transfer pressure when the toner image carried on the image carrier is transferred to a recording medium and an amount of toner image formed on the recording medium; and a determination is made as to whether or not the estimated amount of lubricant exceeds a predetermined threshold value; and a control unit that executes control to reduce the amount of lubricant on the image carrier; Equipped with.

[0010] The lubricant amount control method of the present invention comprises the steps of: A toner image is transferred between the image carrier and the image carrier, and Transfer pressure when the toner image is transferred to the image carrier an amount of lubricant on the image carrier based on a transfer pressure when the toner image carried on the image carrier is transferred to a recording medium and an amount of the toner image formed on the recording medium; determining whether the estimated amount of lubricant exceeds a predetermined threshold, and based on the result of the determination, Control is performed to reduce the amount of lubricant on the image carrier. [Effects of the Invention]

[0011] According to the present invention, it is possible to prevent the occurrence of poor cleaning caused by the lubricant transferred to the image bearing member. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram illustrating a main part of a control system of the image forming apparatus according to the present embodiment. [Figure 3] FIG. 10 is a diagram showing an example of the relationship between the amount of lubricant on the intermediate transfer belt and cleaning failure. [Figure 4A] 10 is a diagram illustrating an example of the relationship between the secondary transfer pressure and the amount of lubricant transferred to the intermediate transfer belt. [Figure 4B] FIG. 10 is a diagram showing an example of the relationship between the secondary transfer pressure and the amount of lubricant remaining on the photosensitive drum. [Figure 5] FIG. 4 is a diagram illustrating an example of a secondary transfer pressure adjusting unit. [Figure 6A] 10A and 10B are diagrams illustrating an example of a paper ejection direction when the secondary transfer pressure is weak. [Figure 6B] 10A and 10B are diagrams illustrating an example of a paper ejection direction when the secondary transfer pressure is strong. [Figure 7] 10A and 10B are diagrams illustrating an example of the amount of lubricant on the intermediate transfer belt relative to the magnitude of the primary transfer pressure or the magnitude of the secondary transfer pressure. [Figure 8] FIG. 10 is a diagram showing an example of how to determine the slope of the amount of lubricant relative to the number of prints. [Figure 9] 5 is a flowchart showing an example of an operation of the image forming apparatus according to the present embodiment. [Figure 10] FIG. 2 is a diagram illustrating a part of an intermediate transfer unit. [Figure 11] 10A and 10B are diagrams illustrating the relationship between the hardness of the secondary transfer roller and the opposing roller and cleaning defects. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present embodiment will be described in detail below with reference to the drawings. FIG. 1 is a diagram schematically illustrating the overall configuration of an image forming apparatus 1 according to the embodiment of the present invention. FIG. 2 is a diagram illustrating the main components of a control system of the image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 is an intermediate transfer color image forming apparatus that utilizes electrophotographic process technology. That is, the image forming apparatus 1 performs primary transfer of toner images of each color (Yellow (Y), Magenta (M), C (Cyan), and K (K)) formed on a photosensitive drum 413 onto an intermediate transfer belt 421, and then superimposes the four color toner images on the intermediate transfer belt 421, performing secondary transfer onto paper S (a recording medium) to form a toner image.

[0014] In addition, the image forming apparatus 1 employs a tandem system in which photosensitive drums 413 corresponding to the four colors YMCK are arranged in series in the running direction of the intermediate transfer belt 421, and each color toner image is transferred sequentially to the intermediate transfer belt 421 in a single step.

[0015] As shown in FIG. 2, the image forming apparatus 1 includes an image reading unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a paper conveying unit 50, a fixing unit 60, a control unit 101, and the like.

[0016] The control unit 101 includes a CPU (Central Processing Unit) 102, a ROM (Read Only Memory) 103, a RAM (Random Access Memory) 104, etc. The CPU 102 reads a program corresponding to the processing content from the ROM 103, loads it into the RAM 104, and centrally controls the operation of each block of the image forming apparatus 1 in cooperation with the loaded program. At this time, various data stored in the storage unit 72 is referenced. The storage unit 72 is configured, for example, with a non-volatile semiconductor memory (so-called flash memory) or a hard disk drive.

[0017] The control unit 101 transmits and receives various data to and from an external device (for example, a personal computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 71. The control unit 101 receives, for example, image data transmitted from an external device, and forms a toner image on the paper S based on this image data (input image data). The communication unit 71 is configured, for example, by a communication control card such as a LAN card.

[0018] The image reading unit 10 is configured to include an automatic document feeder 11 called an ADF (Auto Document Feeder), an original image scanning device 12 (scanner), and the like.

[0019] The automatic document feeder 11 transports the document D placed on the document tray using a transport mechanism and sends it to the document image scanning device 12. The automatic document feeder 11 can continuously read images (including both sides) of multiple documents placed on the document tray all at once.

[0020] The document image scanning device 12 optically scans a document transported onto the contact glass from the automatic document feeder 11 or a document placed on the contact glass, and forms an image of the light reflected from the document on the light receiving surface of a CCD (Charge Coupled Device) sensor 12a to read the document image. The image reading unit 10 generates input image data based on the reading result by the document image scanning device 12. This input image data is subjected to predetermined image processing in the image processing unit 30.

[0021] The operation display unit 20 is composed of, for example, a liquid crystal display (LCD) with a touch panel, and functions as a display unit 21 and an operation unit 22. The display unit 21 displays various operation screens, image status indications, and the operating status of each function in accordance with a display control signal input from the control unit 101. The operation unit 22 has various operation keys such as a numeric keypad and a start key, accepts various input operations by the user, and outputs operation signals to the control unit 101. The input operations include an operation to select one of the normal mode, a low gloss mode in which the gloss level is lower than a predetermined value (the normal mode value), and a high gloss mode in which the gloss level is higher than a predetermined value.

[0022] The image processing unit 30 includes a circuit for performing digital image processing on input image data according to initial settings or user settings. For example, under the control of the control unit 101, the image processing unit 30 performs gradation correction based on gradation correction data (gradation correction table). In addition to gradation correction, the image processing unit 30 also performs various correction processes such as color correction and shading correction, as well as compression, on the input image data. The image forming unit 40 is controlled based on the image data that has undergone these processes.

[0023] The image forming section 40 includes image forming units 41Y, 41M, 41C, and 41K for forming images with color toners of Y, M, C, and K components based on input image data, an intermediate transfer unit 42, and the like.

[0024] The image forming units 41Y, 41M, 41C, and 41K for the Y, M, C, and K components have the same configuration. For ease of illustration and explanation, common components are denoted by the same reference numerals, and when distinguishing between them, the reference numerals are suffixed with Y, M, C, or K. In Figure 1, only the components of the image forming unit 41Y for the Y component are denoted by reference numerals, and the components of the other image forming units 41M, 41C, and 41K are not denoted by reference numerals.

[0025] The image forming unit 41 includes an exposure device 411, a developing device 412, a photosensitive drum 413, a charging device 414, a drum cleaning device 415, and the like.

[0026] The photoconductor drum 413 is a negatively charged organic photoconductor (OPC) in which an undercoat layer (UCL), a charge generation layer (CGL), and a charge transport layer (CTL) are sequentially laminated on the circumferential surface of an aluminum conductive cylinder (aluminum tube). The charge generation layer is made of an organic semiconductor in which a charge generation material (e.g., a phthalocyanine pigment) is dispersed in a resin binder (e.g., polycarbonate), and generates pairs of positive and negative charges upon exposure to light by an exposure device. The charge transport layer is made of a hole transport material (an electron-donating nitrogen-containing compound) dispersed in a resin binder (e.g., polycarbonate resin), and transports the positive charges generated in the charge generation layer to the surface of the charge transport layer.

[0027] The control unit 101 controls the drive current supplied to a drive motor (not shown) that rotates the photosensitive drum 413, thereby rotating the photosensitive drum 413 at a constant peripheral speed.

[0028] The charging device 414 uniformly charges the surface of the photoconductive photosensitive drum 413 to a negative polarity. The exposure device is composed of, for example, a semiconductor laser, and irradiates the photosensitive drum 413 with laser light corresponding to an image of each color component. Positive charges are generated in the charge generation layer of the photosensitive drum 413 and transported to the surface of the charge transport layer, thereby neutralizing the surface charge (negative charge) of the photosensitive drum 413. An electrostatic latent image of each color component is formed on the surface of the photosensitive drum 413 due to the potential difference with the surrounding area.

[0029] The developing device 412 is, for example, a two-component developing device, and visualizes the electrostatic latent image by attaching toner of each color component to the surface of the photosensitive drum 413, thereby forming a toner image.

[0030] Drum cleaning device 415 has a drum cleaning blade or the like that is in sliding contact with the surface of photosensitive drum 413, and cleans the residual toner remaining on the surface of photosensitive drum 413 after the primary transfer. In order to ensure stable cleaning performance, a lubricant application unit that actively applies lubricant to photosensitive drum 413 is provided.

[0031] The intermediate transfer unit 42 includes an intermediate transfer belt 421, a primary transfer roller 422, a plurality of support rollers 423, 423A, a secondary transfer roller 424, a belt cleaning device 426, a primary transfer pressure adjusting unit 427, and a secondary transfer pressure adjusting unit 428 (see FIG. 5).

[0032] The intermediate transfer belt 421 is an endless belt that is stretched around a plurality of support rollers 423, 423A in a loop shape. At least one of the support rollers 423, 423A is a drive roller, and the others are driven rollers. For example, it is preferable that the roller disposed downstream of the primary transfer roller 422 for the K component in the belt running direction be the drive roller. This makes it easier to maintain a constant running speed of the intermediate transfer belt 421. As the drive roller rotates, the intermediate transfer belt 421 runs at a constant speed in the direction of arrow A.

[0033] Primary transfer roller 422 is disposed on the inner circumferential surface side of intermediate transfer belt 421, facing photosensitive drum 413 for each color component. Primary transfer roller 422 is pressed against photosensitive drum 413 with intermediate transfer belt 421 sandwiched therebetween, thereby forming a primary transfer nip for transferring a toner image from photosensitive drum 413 to intermediate transfer belt 421. Primary transfer pressure adjustment unit 427 adjusts the transfer pressure (primary transfer pressure) of the primary transfer nip. Photosensitive drum 413, intermediate transfer belt 421, and primary transfer roller 422 form a primary transfer unit.

[0034] Secondary transfer roller 424 is disposed on the outer peripheral surface side of intermediate transfer belt 421, facing opposing roller 423B, which is disposed downstream of the drive roller in the belt running direction. Secondary transfer roller 424 is pressed against opposing roller 423B with intermediate transfer belt 421 sandwiched therebetween, thereby forming a secondary transfer nip for transferring a toner image from intermediate transfer belt 421 to paper S. Secondary transfer pressure adjustment unit 428 adjusts the transfer pressure (secondary transfer pressure) of the secondary transfer nip. The opposing roller 423B, intermediate transfer belt 421, and secondary transfer roller 424 together form a secondary transfer unit.

[0035] When intermediate transfer belt 421 passes through the primary transfer nip, the toner images on photosensitive drum 413 are sequentially superimposed and primarily transferred onto intermediate transfer belt 421. Specifically, a primary transfer bias is applied to the primary transfer roller, and a charge of the opposite polarity to the toner is applied to the back side of intermediate transfer belt 421 (the side that contacts the primary transfer roller), so that the toner images are electrostatically transferred onto intermediate transfer belt 421.

[0036] Thereafter, when the paper S passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is secondarily transferred onto the paper S. Specifically, a secondary transfer bias is applied to the secondary transfer roller 424, and a charge of the opposite polarity to the toner is applied to the back side of the paper S (the side that abuts the secondary transfer roller 424), so that the toner image is electrostatically transferred onto the paper S. The paper S onto which the toner image has been transferred is transported towards the fixing unit 60.

[0037] Belt cleaning device 426 has a belt cleaning blade or the like that slides against the surface of intermediate transfer belt 421, and removes residual toner remaining on the surface of intermediate transfer belt 421 after secondary transfer. Note that instead of secondary transfer roller 424, a configuration in which the secondary transfer belt is stretched in a loop shape around a plurality of support rollers including a secondary transfer roller (a so-called belt-type secondary transfer unit) may be employed.

[0038] Fixing section 60 includes upper fixing section 60A having a fixing surface side member arranged on the fixing surface side of paper S (surface on which a toner image is formed), lower fixing section 60B having a back surface side support member arranged on the back surface side of paper S (surface opposite to the fixing surface), and heating sources 60C, 60D, etc. Fixing section 60 is arranged as a unit in a fuser, i.e., a housing.

[0039] The upper fixing unit 60A has an endless fixing belt 61, which is a fixing surface side member, a heating roller 62, and an upper pressure roller 63 (belt heating system). The fixing belt 61 is stretched between the heating roller 62 and the upper pressure roller 63 with a predetermined tension applied.

[0040] The lower fixing section 60B has a lower pressure roller 64 that constitutes a back-side support member (roller pressure system). The lower pressure roller 64 is pressed against the upper pressure roller 63 via the fixing belt 61 with a predetermined fixing load. In this way, a fixing nip NP that holds and transports the paper S is formed between the upper pressure roller 63, the fixing belt 61, and the lower pressure roller 64. In the fixing section 60, the upper fixing section 60A, the lower fixing section 60B, and the heating sources 60C and 60D fix the unfixed toner image to the paper S by heating and pressurizing the paper S at the fixing nip NP while transporting it.

[0041] The paper transport section 50 includes a paper feed section 51, a paper discharge section 52, and a transport path section 53. The three paper feed tray units 51a to 51c that make up the paper feed section 51 store paper S (standard paper, special paper) identified based on basis weight, size, etc., by pre-set type. The transport path section 53 has a plurality of transport roller pairs, such as a registration roller pair 53a.

[0042] The sheets S stored in the sheet feed tray units 51a to 51c are fed out one by one from the top, and are transported to the image forming unit 40 by the transport path unit 53. At this time, a registration roller unit having a registration roller pair 53a corrects the skew of the fed sheets S and adjusts the transport timing. Then, in the image forming unit 40, the toner image on the intermediate transfer belt 421 is secondarily transferred all at once onto one side of the sheets S, and a fixing process is performed in the fixing unit 60. The sheets S with the image formed thereon are discharged outside the apparatus by the sheet discharge unit 52 having a sheet discharge roller 52a.

[0043] However, the lubricant actively applied to the photosensitive drum 413 to ensure stable cleaning performance can adversely affect the intermediate transfer belt 421 and the fixing unit 60, which are located downstream of the photosensitive drum 413. For example, cleaning defects can occur due to uneven friction between the intermediate transfer belt 421 and a belt cleaning blade that slides against the surface of the intermediate transfer belt 421. When the amount of lubricant on the intermediate transfer belt 421 becomes too large, the lubricant accumulates on the edge of the belt cleaning blade, causing jamming and resulting in poor cleaning. Furthermore, if the amount of lubricant on the intermediate transfer belt is uneven, the toner adhesion to the intermediate transfer belt will differ in the areas where the unevenness exists, resulting in uneven transfer efficiency when the toner image is transferred to paper. Therefore, with coated paper, for example, the difference in transfer efficiency can directly lead to uneven image density.

[0044] FIG. 3 is a diagram showing an example of the relationship between the amount of lubricant on the intermediate transfer belt 421 and cleaning defects. As shown in FIG. 3, when the amount of lubricant on the intermediate transfer belt 421 (amount of lubricant on the belt) is 2 nm or 4 nm, no cleaning defects (CL defects) occur on the belt ("◯" in FIG. 3). When the amount of lubricant on the belt is 6 nm, very slight CL defects occur on the belt. No transfer occurs to the paper ("◯△" in FIG. 3). When the amount of lubricant on the belt is 8 nm, moderate CL defects occur on the belt. A small amount of transfer occurs to the paper, which is visible under magnification ("△" in FIG. 3). When the amount of lubricant on the belt is 10 nm, severe CL defects occur on the belt. Transfer also occurs to the paper, which is visible to the naked eye ("X" in FIG. 3). As described above, as the amount of lubricant on the belt increases, CL defects become more apparent. In order to prevent the problem of CL defects from becoming apparent, it is necessary to maintain an appropriate amount of lubricant on the intermediate transfer belt 421.

[0045] FIG. 4A is a diagram showing an example of the relationship between the secondary transfer pressure and the amount of lubricant transferred to the intermediate transfer belt 421. The horizontal axis of FIG. 4A represents the secondary transfer pressure, and the vertical axis represents the converted value of the amount of lubricant transferred. As shown in FIG. 4A, when the secondary transfer pressure is low (30 N), the amount of transfer is approximately 3.37. When the secondary transfer pressure is medium (55 N), the amount of transfer is approximately 3.63. When the secondary transfer pressure is high (80 N), the amount of transfer is approximately 3.73.

[0046] FIG. 4B is a diagram showing an example of the relationship between secondary transfer pressure and the amount of residual lubricant on photosensitive drum 413. The horizontal axis of FIG. 4B shows the secondary transfer pressure, and the vertical axis shows the converted value of the residual amount. As shown in FIG. 4B, when the secondary transfer pressure is low (30 N), the residual amount is approximately 2.5. When the secondary transfer pressure is medium (55 N), the residual amount is approximately 2.3. When the secondary transfer pressure is high (80 N), the residual amount is approximately 2.1.

[0047] 4A and 4B show that increasing the secondary transfer pressure reduces the amount of lubricant remaining on photosensitive drum 413 and increases the amount transferred onto intermediate transfer belt 421. In other words, it can be seen that the amount of lubricant transferred from photosensitive drum 413 to intermediate transfer belt 421 increases. The mechanism behind this is presumed to be that increasing the secondary transfer pressure changes the state of the primary transfer nip, making it easier to scrape off the lubricant on photosensitive drum 413 toward intermediate transfer belt 421. Note that while FIGS. 4A and 4B show that the amount of lubricant transferred onto intermediate transfer belt 421 increases depending on the magnitude of the secondary transfer pressure, it is presumed that the amount of lubricant transferred onto intermediate transfer belt 421 similarly increases depending on the magnitude of the primary transfer pressure.

[0048] That is, the amount of lubricant transferred onto intermediate transfer belt 421 increases depending on the magnitude of the primary transfer pressure or the magnitude of the secondary transfer pressure. As a result, if the amount of lubricant on intermediate transfer belt 421 is reduced depending on the magnitude of the primary transfer pressure or the secondary transfer pressure, it becomes possible to maintain an appropriate amount of lubricant on intermediate transfer belt 421. Below, we will explain, as a representative example, how to reduce the amount of lubricant on intermediate transfer belt 421 depending on the magnitude of the secondary transfer pressure.

[0049] Next, the primary transfer pressure adjusting unit 427 and the secondary transfer pressure adjusting unit 428 will be described with reference to FIG. 5. The primary transfer pressure adjusting unit 427 and the secondary transfer pressure adjusting unit 428 have the same configuration. The secondary transfer pressure adjusting unit 428 will be described below as a representative example. FIG. 5 is a diagram showing an example of the secondary transfer pressure adjusting unit 428. The intermediate transfer belt 421 is omitted from FIG. 5.

[0050] The secondary transfer pressure adjusting unit 428 includes a secondary transfer pressure adjusting cam 428A, a biasing member 429 such as a spring member, a gripping portion 429A, and a driving portion (not shown). The secondary transfer pressure adjusting cam 428A is configured using an eccentric cam in which the distance (diameter) between a rotation shaft 428B and an outer circumferential surface 428C continuously increases with rotation in the forward direction (clockwise direction in FIG. 5).

[0051] The urging member 429 is disposed in a compressed state between the outer peripheral surface 428C and the gripping portion 429A. The gripping portion 429A rotatably grips the rotation shaft 424C of the secondary transfer roller 424. The restoring force of the urging member 429 presses the opposing roller 423B against the secondary transfer roller 424 via the intermediate transfer belt (not shown). This forms a secondary transfer nip. The secondary transfer pressure of the secondary transfer nip increases according to the distortion of the urging member 429. The distortion of the urging member 429 corresponds to the rotation angle θ of the secondary transfer pressure adjusting cam 428A. This makes it possible to determine the secondary transfer pressure based on the rotation angle θ of the secondary transfer pressure adjusting cam 428A. When the rotation angle θ is small, the secondary transfer pressure becomes low (low pressure). When the rotation angle θ is large, the secondary transfer pressure becomes high (high pressure). The relationship between the rotation angle θ and the magnitude of the secondary transfer pressure (high pressure, medium pressure, constant pressure) is preset. The relationship between the rotation angle of the primary transfer pressure adjusting cam and the magnitude of the primary transfer pressure (high pressure, medium pressure, low pressure) is set in advance.

[0052] FIG. 6A is a diagram showing an example of the paper ejection direction when the secondary transfer pressure is weak. FIG. 6B is a diagram showing an example of the paper ejection direction when the secondary transfer pressure is strong. The secondary transfer pressure is set according to the stiffness of the paper. For example, if the paper is thin, the paper is weak and difficult to separate from intermediate transfer belt 421. To make it easier to separate the paper from intermediate transfer belt 421, the secondary transfer pressure is set high. When the secondary transfer pressure is set high, the opposing roller 423B side is recessed, so the paper ejection direction is downward. This allows the leading edge of the ejected paper to be directed away from intermediate transfer belt 421, making it easier to separate the paper from intermediate transfer belt 421.

[0053] Next, a lubricant removal unit that removes lubricant from intermediate transfer belt 421 will be described. Even when the secondary transfer pressure is set high, it is necessary to reduce the amount of lubricant on intermediate transfer belt 421 in order to maintain an appropriate amount of lubricant on intermediate transfer belt 421. A belt cleaning blade that comes into sliding contact with the surface of intermediate transfer belt 421 can be used as the lubricant removal unit. For example, by sending a toner band to the belt cleaning blade when no image is being formed, it is possible to remove the lubricant from intermediate transfer belt 421. In this embodiment, a belt cleaning device 426 having a belt cleaning blade is used as the lubricant removal unit.

[0054] Another example of a lubricant removal unit is a charging electrode for charging the toner. For example, by increasing the amount of charge on the toner using a charging electrode, the adhesion of the toner to the intermediate transfer belt 421 increases, and the amount of lubricant that can be removed when scraped off by the belt cleaning blade increases. This makes it possible to improve the performance of removing lubricant from the intermediate transfer belt 421.

[0055] Even when the amount of lubricant on intermediate transfer belt 421 increases depending on the magnitude of the primary transfer pressure or the magnitude of the secondary transfer pressure, the amount of lubricant on intermediate transfer belt 421 can be reduced by the lubricant removal unit described above. FIG. 7 is a diagram showing an example of the amount of lubricant on intermediate transfer belt 421 relative to the magnitude of the primary transfer pressure or the magnitude of the secondary transfer pressure. The horizontal axis of FIG. 7 shows the number of prints (corresponding to the "amount of toner image formation" in this disclosure), and the vertical axis shows the amount of lubricant on intermediate transfer belt 421. The lubricant amounts shown in FIG. 7 are mapped and registered in a mapping table. In addition, for the lubricant amounts shown in FIG. 7, CL defect occurrence lines, which are lines at which CL defects can be visually recognized ("△" or "X" shown in FIG. 3), are predetermined.

[0056] FIG. 7 illustrates the amount of lubricant on intermediate transfer belt 421 for each magnitude of primary transfer pressure and secondary transfer pressure. For example, the amount of lubricant on intermediate transfer belt 421 when the secondary transfer pressure is high and the primary transfer pressure is high is shown by a dashed line in FIG. 7. The amount of lubricant on intermediate transfer belt 421 when the secondary transfer pressure is high and the primary transfer pressure is medium is shown by a dashed line in FIG. 7. The amount of lubricant on intermediate transfer belt 421 when the secondary transfer pressure is high and the primary transfer pressure is medium is shown by a solid line in FIG. The amount of lubricant on intermediate transfer belt 421 when the secondary transfer pressure is medium and the primary transfer pressure is medium is shown by a two-dot chain line in FIG. The amount of lubricant on intermediate transfer belt 421 when the secondary transfer pressure is low and the primary transfer pressure is medium is shown by a dotted line in FIG. 7.

[0057] The control unit 101 acquires the rotation angle of the primary transfer pressure adjusting cam and the rotation angle θ of the secondary transfer pressure adjusting cam 428A. The control unit 101 estimates the amount of lubricant on the intermediate transfer belt 421 by referencing a predetermined mapping table based on the magnitude of the primary transfer pressure (high, medium, low) corresponding to the rotation angle of the primary transfer pressure adjusting cam and the magnitude of the secondary transfer pressure (high, medium, low) corresponding to the rotation angle θ of the secondary transfer pressure adjusting cam 428A. The mapping table defines the slope of the lubricant amount versus the number of prints. As shown in FIG. 7, the number of prints is divided into sections: 0 to 50 kp, 50 kp to 100 kp, 100 kp to 200 kp, and 200 kp to 300 kp. The slope of the lubricant amount versus the number of prints is defined for each section. The control unit 101 acquires the number of prints from the storage unit 72.

[0058] Next, an example of how to determine the slope of the lubricant amount versus the number of prints will be described with reference to FIG. 8. As shown in FIG. 8, the slope A of the lubricant amount in the section from 0 to 50 kp is represented by the slope of a line connecting the lubricant amount at 0 kp to the lubricant amount at 50 kp. The slope B of the lubricant amount in the section from 50 kp to 100 kp is represented by the slope of a line connecting the lubricant amount at 50 kp to the lubricant amount at 100 kp. The slope C of the lubricant amount in the section from 100 kp to 200 kp is represented by the slope of a line connecting the lubricant amount at 100 kp to the lubricant amount at 200 kp. The slope D of the lubricant amount in the section from 200 kp to 300 kp is represented by the slope of a line connecting the lubricant amount at 200 kp to the lubricant amount at 300 kp.

[0059] The control unit 101 estimates the amount of lubricant on the intermediate transfer belt 421 based on the slope of the lubricant amount for each section as follows. For example, when the secondary transfer pressure is high and the primary transfer pressure is medium in the section from 0 to 100 kp, the control unit 101 estimates the amount of lubricant based on slopes A and B of the dashed line shown in FIG. 8. When the secondary transfer pressure is high and the primary transfer pressure is high in the section from 100 kp to 200 kp, the control unit 101 estimates the amount of lubricant based on slope C of the dashed line shown in FIG. 8. When the secondary transfer pressure is medium and the primary transfer pressure is medium in the section from 200 kp to 300 kp, the control unit 101 estimates the amount of lubricant based on slope D of the two-dot chain line shown in FIG. 8. The control unit 101 then integrates the amount of lubricant estimated based on slopes A and B, the amount of lubricant estimated based on slope C, and the amount of lubricant estimated based on slope D. When the integrated amount of lubricant exceeds the CL defect occurrence line, the control unit 101 controls the belt cleaning device 426 (lubricant removal unit) so as to reduce the amount of lubricant on the intermediate transfer belt 421.

[0060] As shown in Figure 8, it is predicted that the accumulated amount of lubricant will exceed the CL defect occurrence line at around 250 kp. Therefore, the control unit 101 stops image formation at 250 kp (shown by the dashed line in Figure 8) and executes control to reduce the amount of lubricant on the intermediate transfer belt 421. Note that if the print job is forcibly stopped when the accumulated amount of lubricant exceeds the CL defect occurrence line, downtime will occur, so the control unit 101 may execute control to reduce the amount of lubricant on the intermediate transfer belt 421 between the print job in question and the print job immediately before it.

[0061] Next, an example of the operation of the image forming apparatus 1 according to this embodiment will be described with reference to Fig. 9. Fig. 9 is a flowchart showing an example of the operation of the image forming apparatus 1 according to this embodiment. This flow is started by an image formation instruction input to the image forming apparatus 1. The operation shown in this flow is a process that is repeatedly performed during the image formation process.

[0062] First, in step 100, the control unit 101 acquires the number of prints.

[0063] Next, in step 110, the control unit 101 acquires the rotation angle of the primary transfer pressure adjusting cam and the rotation angle θ of the secondary transfer pressure adjusting cam 428A.

[0064] Next, in step S120, the control unit 101 estimates the amount of lubricant by referring to a predetermined mapping table based on the number of prints, the magnitude of the primary transfer pressure corresponding to the rotation angle of the primary transfer pressure adjusting cam, and the magnitude of the secondary transfer pressure corresponding to the rotation angle θ of the secondary transfer pressure adjusting cam 428A.

[0065] Next, in step S130, the control unit 101 integrates the estimated amount of lubricant.

[0066] In step S140, the control unit 101 determines whether the estimated lubricant amount exceeds the CL malfunction occurrence line. If the lubricant amount exceeds the CL malfunction occurrence line (step S140: YES), the process proceeds to step S150. If the lubricant amount does not exceed the CL malfunction occurrence line (step S140: NO), the flow shown in FIG. 9 ends.

[0067] In step S150, the control unit 101 executes control to reduce the amount of lubricant on the intermediate transfer belt 421. After that, the flow shown in FIG. 9 ends.

[0068] The image forming apparatus 1 according to the above embodiment includes an intermediate transfer belt 421 that carries a toner image, a primary transfer unit that transfers the toner image from the photosensitive drum 413 to the intermediate transfer belt 421, a secondary transfer unit that transfers the toner image on the intermediate transfer belt 421 to paper, and a control unit 101 that executes control to reduce the amount of lubricant on the intermediate transfer belt 421 depending on the transfer pressure and the number of prints related to the primary transfer unit and the secondary transfer unit.

[0069] The above configuration allows the amount of lubricant on the intermediate transfer belt 421 to be estimated based on the transfer pressures and the number of prints at the primary and secondary transfer units. Therefore, by reducing the amount of lubricant on the intermediate transfer belt 421 before a problem occurs, it is possible to significantly reduce problems caused by the lubricant on the intermediate transfer belt 421, such as slippage due to uneven application of the lubricant itself or clumping due to lubricant-derived aggregates. Furthermore, because there is no unevenness in the amount of lubricant on the intermediate transfer belt, there is no difference in the adhesion force of the toner to the intermediate transfer belt, and no uneven transfer efficiency occurs when the toner image is transferred to paper. This makes it possible to prevent uneven image density, even on coated paper, for example, where uneven transfer efficiency directly leads to uneven image density.

[0070] In the image forming apparatus 1 according to the above embodiment, the parameters for the conditions for executing control to reduce the amount of lubricant on the intermediate transfer belt 421 are the transfer pressure for the primary transfer unit and the secondary transfer unit and the number of prints, but the present invention is not limited to this, and the parameters may be the transfer pressure for the primary transfer unit and the secondary transfer unit, or the transfer pressure for the primary transfer unit.

[0071] In addition, in the image forming apparatus 1 according to the above embodiment, the condition for executing control to reduce the amount of lubricant on the intermediate transfer belt 421 is the number of prints to form toner images, but the present invention is not limited to this and may also be the print time.

[0072] Furthermore, in the image forming apparatus 1 according to the above embodiment, the intermediate transfer belt 421 is used as the image carrier, but the present invention is not limited to this, and an intermediate transfer roller may also be used, for example.

[0073] <Modification> Next, a modified example of the image forming apparatus 1 according to the present embodiment will be described with reference to Fig. 10. Fig. 10 is a diagram showing a part of the intermediate transfer unit 42.

[0074] In the above embodiment, the relationship between the hardness of opposing roller 423B and secondary transfer roller 424 is not limited. Furthermore, the materials of the opposing rollers are not limited. In contrast, in a modified example, the hardness of opposing roller 423B is lower than that of secondary transfer roller 424. Furthermore, opposing roller 423B has a sponge rubber layer. Furthermore, secondary transfer roller 424 has a solid rubber layer. As a result, when secondary transfer roller 424 presses opposing roller 423B, opposing roller 423B is crushed, the tension of intermediate transfer belt 421 increases, and the amount of lubricant transferred from photosensitive drum 413 to intermediate transfer belt 421 at the primary transfer nip increases. Therefore, when the hardness of opposing roller 423B is lower than that of secondary transfer roller 424, it is necessary to perform control to remove the amount of lubricant on intermediate transfer belt 421 (lubricant removal mode control) more than when the hardness of opposing roller 423B is equal to or greater than that of secondary transfer roller 424.

[0075] <Example> Next, an example of lubricant removal mode control will be described with reference to FIG. 11. Lubricant removal mode control was performed using the following combination of types and hardness of opposing roller 423B and secondary transfer roller 424. Note that a comparative example was performed using the same combination but without lubricant removal mode control. Note that in FIG. 11, the sponge rubber layer is indicated by "sponge" and the solid rubber layer is indicated by "solid."

[0076] FIG. 11 shows an example in which the lubricant removal mode control was performed using the same combination configuration, and a comparative example in which it was not performed. In each of the configurations of Example 1 and Comparative Example 1, the type of opposing roller 423B was "sponge," the Asker C hardness was "40°," and the type of secondary transfer roller 424 was "solid," and the Asker C hardness was "70°." In addition, in each of the configurations of Example 2 and Comparative Example 2, the type of opposing roller 423B was "sponge," the Asker C hardness was "30°," the type of secondary transfer roller 424 was "solid," and the Asker C hardness was "75°." In addition, in each of the configurations of Example 3 and Comparative Example 3, the type of opposing roller 423B was "sponge," the Asker C hardness was "45°," the type of secondary transfer roller 424 was "solid," and the Asker C hardness was "60°."

[0077] In Comparative Examples 1 and 2, where lubricant removal mode control was "not performed," poor CL defects occurred on the paper ("X" in FIG. 11). In Comparative Example 3, moderate CL defects occurred on the belt, which was slightly transferred to the paper and was visible under magnification ("△" in FIG. 11). In contrast, in Examples 1 to 3, where lubricant removal mode control was "performed," CL was good, and the effect of lubricant removal mode control was significant ("◯" in FIG. 11).

[0078] In each of Example 4 and Comparative Example 4, the type of opposing roller 423B was "solid," the Asker C hardness was "70°," and the type of secondary transfer roller 424 was "sponge," and the Asker C hardness was "40°." In addition, in each of Example 5 and Comparative Example 5, the type of opposing roller 423B was "solid," the Asker C hardness was "70°," and the type of secondary transfer roller 424 was "solid," and the Asker C hardness was "70°." In addition, in each of Example 6 and Comparative Example 6, the type of opposing roller 423B was "sponge," the Asker C hardness was "40°," and the type of secondary transfer roller 424 was "sponge," and the Asker C hardness was "40°."

[0079] In Comparative Examples 4 to 6, where the lubricant removal mode control was "not performed," very slight CL defects occurred on the belt, but were at a level that did not transfer to the paper ("○△" in FIG. 11). In contrast, in Examples 4 to 6, where the lubricant removal mode control was "performed," the CL defect issue itself was slight, so the effect of the lubricant removal mode control was small, but it was effective in avoiding even slight transfer to the paper ("○" in FIG. 11).

[0080] Furthermore, the above-described embodiments are merely examples of specific embodiments for carrying out the present invention, and the technical scope of the present invention should not be construed as being limited by these embodiments. In other words, the present invention can be carried out in various forms without departing from the gist or main features thereof. [Industrial Applicability]

[0081] The present invention is suitably used in an image forming apparatus that is required to prevent the occurrence of cleaning defects caused by lubricant transferred onto an image bearing member. [Explanation of symbols]

[0082] 1. Image forming device 10 Image reading unit 20 Operation display section 30 Image processing section 40 Image forming unit 41 Image forming unit 413 Photosensitive drum 42 Intermediate transfer unit 421 Intermediate transfer belt 422 Primary transfer roller 424 Secondary transfer roller 426 Belt cleaning device (lubricant removal section) 427 Primary transfer pressure adjustment unit 428 Secondary transfer pressure adjustment unit 50 Paper transport section 51 Paper feed section 52 Paper output section 53 Conveying path section 60 Fixing unit 101 Control section

Claims

1. an image carrier capable of carrying a toner image; a transfer unit that transfers a toner image between the image carrier and the transfer unit; a control unit that estimates an amount of lubricant on the image carrier based on a transfer pressure when the toner image is transferred to the image carrier, a transfer pressure when the toner image carried on the image carrier is transferred to a recording medium, and an amount of toner image formed on the recording medium, determines whether the estimated amount of lubricant exceeds a predetermined threshold, and executes control to reduce the amount of lubricant on the image carrier based on the result of the determination; An image forming apparatus comprising:

2. the image carrier is an intermediate transfer belt; The image forming apparatus according to claim 1 .

3. The transfer unit includes: a transfer roller that contacts the recording medium; an opposing roller having a lower hardness than the transfer roller and facing the transfer roller across the intermediate transfer belt; having The image forming apparatus according to claim 2 .

4. The opposing roller has a sponge rubber layer. The image forming apparatus according to claim 3 .

5. The transfer roller has a solid rubber layer.

5. The image forming apparatus according to claim 3.

6. A toner image is transferred between the image carrier and the image carrier, and estimating an amount of lubricant on the image carrier based on a transfer pressure when the toner image is transferred to the image carrier, a transfer pressure when the toner image carried on the image carrier is transferred to a recording medium, and an amount of toner image formed on the recording medium; determining whether the estimated amount of lubricant exceeds a predetermined threshold, and based on the result of the determination, executing control to reduce the amount of lubricant on the image carrier; Lubricant amount control method.

Images