Image forming device

Abstract

To prevent filming at the ends of an intermediate transfer body at a lower cost than before and with reduced toner consumption.SOLUTION: An image forming apparatus has: an image carrier 2; a lubricant application device 20 that applies lubricant to a surface of the image carrier 2; an intermediate transfer body 3 that is arranged opposite to the image carrier 2; and a developing device 11 that is arranged between the lubricant application device 20 and a transfer nip in the direction of rotation of the image carrier and includes a developer carrier 51 carrying a two-component developer consisting of toner and carrier. The amount of developer drawn up at the ends in a longitudinal direction of the developer carrier 51 is larger than the amount of developer drawn up at the center in the longitudinal direction.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] Conventionally, in electrophotographic image formation, a latent image is formed by electrostatic charge on an image carrier such as a photoconductive material, and a visible image is formed by attaching charged toner particles to this electrostatic latent image. The visible image formed by the toner is finally transferred to a transfer medium such as paper, and then fixed to the transfer medium by heat, pressure, solvent gas, etc., to become an output image.

[0003] These electrophotographic image forming devices generally rotate a drum- or belt-shaped image carrier, generally a photosensitive member, while uniformly charging it, form a latent image pattern on the image carrier using laser light or the like, visualize this with a developing device, and transfer it onto a transfer medium.

[0004] Furthermore, after the toner image is transferred to the transfer medium, toner components that were not transferred remain on the image carrier. If these residues are transported to the charging step as they are, they may hinder uniform charging of the image carrier. Therefore, after the transfer step, the toner components remaining on the image carrier are generally removed in a cleaning step to ensure that the surface of the image carrier is sufficiently clean before charging the image carrier.

[0005] In this way, the surface of the image carrier is subjected to various physical and electrical stresses during each process such as charging, developing, transferring, and cleaning, and the surface condition changes with the passage of time during use. Among these stresses, the stress caused by friction during the cleaning process not only wears the image carrier, but also shortens the life of the cleaning member.

[0006] Extending the lifespan of image forming devices and the components used in them is of great interest in the market from the perspective of reducing running costs and waste, thereby protecting the global environment. Due to this trend, in recent years there has been a demand for extending the lifespan of not only image carriers but also peripheral components, and reducing stress during the cleaning process has become a major issue.

[0007] In recent years, contact charging and proximity charging have become more common with the aim of downsizing and reducing costs of devices. Of these, proximity charging makes it difficult to uniformly charge the surface of the image carrier due to slight unevenness in contact between the charging member and the surface of the image carrier, or, in the case of non-contact, due to fluctuations in the gap between the charging member and the surface of the image carrier, so in recent years, AC superimposed charging, in which an alternating current (AC) component is superimposed on a direct current (DC) component, has become more common.

[0008] The proximity charging method with superimposed AC components can realize a compact device and high image quality, and at the same time, by maintaining a uniform charge while keeping the charging member and image carrier in a non-contact state, it is possible to suppress deterioration of the charging member itself. Therefore, the proximity charging method is an extremely advantageous technology for compact device size, high image quality, and high durability.

[0009] However, when the image carrier is an organic photoconductor (OPC), it has become clear that the energy of AC superimposed charging breaks the resin chains on the surface of the image carrier, reducing its mechanical strength and significantly accelerating wear of the image carrier.

[0010] Furthermore, AC superimposed charging activates the surface of the image carrier, increasing the adhesive force between the surface of the image carrier and the toner, making it difficult to ensure high cleaning performance. Furthermore, in recent years, toner particles have been made smaller and more spherical in order to achieve high image quality, and high cleanability is being demanded.

[0011] To solve these problems, many proposals have been made to date regarding various lubricants (protective agents) and methods for supplying lubricating components and forming films, with the aim of reducing the friction between the image carrier and the cleaning member, protecting both the image carrier and the cleaning member, and improving cleaning performance.

[0012] For example, Patent Document 1 proposes that in order to extend the life of the photoreceptor and cleaning blade, a solid lubricant containing zinc stearate as a main component is supplied to the surface of the photoreceptor to form a lubricating film on the surface of the photoreceptor.

[0013] Furthermore, Patent Document 2 and the like propose supplying a protective agent (lubricant) containing a fatty acid metal salt and an inorganic lubricant to the surface of an image carrier. In this document, the cleaning performance is significantly improved compared to when zinc stearate is used alone, and the amount of toner that slips through the cleaning section is significantly reduced.

[0014] In the image density adjustment and color misregistration correction control used in electrophotographic image forming devices, the density and position of detection toner patterns created on a drum-shaped photosensitive member or an intermediate transfer belt are read and corrected using an optical sensor.

[0015] For example, in image density adjustment (process control), light emitted from the light-emitting element of a reflective optical sensor is reflected by the surface of the intermediate transfer belt where no toner is attached, and the reflected light is received by a light-receiving element, and the amount of light received corresponding to the reflected light is obtained, thereby calibrating the optical sensor.

[0016] Next, a reference toner image (toner pattern for density adjustment) of a predetermined shape is formed on the surface of the photosensitive member, and the reference toner image is transferred onto an intermediate transfer belt. The light emitted from the light-emitting element is reflected by the reference toner image, and the reflected light is received by the light-receiving element, and the amount of light received corresponds to the reflected light.

[0017] The amount of light received on the background portion of the surface of the intermediate transfer belt is taken as a reference value, and this reference value is compared with the amount of light received on the reference toner image to determine the amount of toner adhesion per unit area of ​​the reference toner image.

[0018] Based on the determined toner adhesion amount, image forming conditions such as the charge potential of the photosensitive member, the development bias, the optical writing intensity to the photosensitive member, and the control target value of the toner concentration of the developer are adjusted so that the desired toner adhesion amount is achieved.

[0019] In color misregistration correction, toner patterns are formed at an angle to the main scanning direction, and positional deviations in the main scanning direction and sub-scanning direction are detected and corrected.

[0020] When adjusting density or correcting color misregistration, the output of the optical sensor is adjusted so that a predetermined amount of light is received on the background of the intermediate transfer belt surface. That is, the output (current value) of the light-emitting element is adjusted to calibrate the optical sensor so that a predetermined amount of light is received.

[0021] When a lubricant containing a fatty acid metal salt and an inorganic lubricant is applied to a photoreceptor, the lubricity is less likely to decrease even when subjected to discharge during the charging process, and stable cleaning performance can be maintained over a long period of time. However, there is a problem in that the inorganic lubricant is easily transferred to the surface of the intermediate transfer belt via the photoreceptor, which can easily cause filming.

[0022] When filming occurs, the glossiness of the belt decreases, and the amount of light received by the sensor at the background decreases. In such cases, calibration is performed to increase the output of the light-emitting element of the sensor so that the desired amount of light is received by adjusting the output (current value) of the light-emitting element.

[0023] In other words, because the amount of reflected light decreases due to filming, in order to obtain a predetermined amount of received light, the current value (forward current If) flowing through the light-emitting element such as an LED must be increased. The current value flowing through the light-emitting element becomes the output value of the sensor.

[0024] If the output value of the sensor's light emitting element exceeds the upper limit, the amount of received light is insufficient even if the amount of emitted light is increased, making it impossible to adjust density or correct color misregistration.

[0025] In particular, in the non-paper passing area (also called the non-paper passing area) located at the end of the intermediate transfer belt, the inorganic lubricant is not removed by the paper that passes through, so filming occurs more easily and accumulates, causing the end of the intermediate transfer belt to become cloudy, which causes the problem of being unable to properly detect the toner pattern.

[0026] In order to prevent belt filming at the end of the intermediate transfer belt, it has been proposed to write a toner discharge pattern at the end of the non-paper passing area and scrape off the filming material with toner. However, writing a toner pattern to suppress belt filming wastes toner and shortens toner yield.

[0027] Patent Document 3 discloses a technique for reducing the amount of lubricant applied to both longitudinal ends of a photoreceptor in order to suppress filming at the ends. Specifically, a flicking member is provided that strongly hits the center of the lubricant application member so that the amount of lubricant applied to both longitudinal ends of the photoreceptor is less than that to the center.

[0028] However, this configuration requires the provision of an additional member, the flicking member, which increases costs. In response to recent demands for cost reduction, there is a demand for a simpler method for suppressing belt filming. Summary of the Invention [Problem to be solved by the invention]

[0029] SUMMARY OF THE INVENTION It is therefore an object of the present invention to suppress filming at the end portions of an intermediate transfer body while reducing costs and reducing toner consumption compared to conventional methods. [Means for solving the problem]

[0030] This problem is solved by an image forming apparatus having an image carrier, a lubricant application device that applies a lubricant to the surface of the image carrier, an intermediate transfer body that is disposed opposite the image carrier, and a developing device that is disposed between the lubricant application device and a transfer nip in the rotation direction of the image carrier and that has a developer carrier that carries a two-component developer made of toner and carrier, the surface roughness of the developer carrier at the longitudinal end portion is greater than that of the longitudinal center portion, The aforementioned problem is solved by an image forming apparatus, wherein the amount of developer drawn up at the longitudinal end portions of the developer carrier is greater than the amount of developer drawn up at the longitudinal center portion. [Effects of the Invention]

[0031] This makes it possible to suppress filming at the end portions of the intermediate transfer body while reducing toner consumption at lower costs than before. [Brief explanation of the drawings]

[0032] [Figure 1] 1 is a schematic configuration diagram of a color printer as an image forming apparatus according to an embodiment of the present invention; [Figure 2] FIG. 2 is an enlarged view of the vicinity of the belt cleaning device 60. [Figure 3] FIG. 2 is a schematic configuration diagram of an optical sensor unit 30 according to the embodiment. [Figure 4] 2 is a cross-sectional view for explaining an outline of an example of the configuration of each imaging unit in the image forming apparatus of the present embodiment. FIG. [Figure 5] FIG. 2 is a schematic diagram showing the relationship between the lengths of the respective members in the longitudinal direction. [Figure 6] FIG. 2 is a schematic diagram illustrating a recess used in one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0033] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1 is a schematic diagram of a color printer as an image forming apparatus according to this embodiment. This color printer has a so-called tandem configuration in which four imaging units (process cartridges) each having photosensitive drums 2Y, 2C, 2M, and 2K as image carriers are arranged side by side within a device main body 1.

[0034] An intermediate transfer unit U is disposed opposite the photosensitive drums of each imaging unit. The intermediate transfer unit U has an intermediate transfer belt 3, which is an image carrier made of an endless belt and serves as an intermediate transfer body. The intermediate transfer belt 3 is rotatably wound around a plurality of support rollers 4, 5, 6, and 7. The support roller 4 serves as a drive roller and is driven counterclockwise, causing the intermediate transfer belt 3 to rotate in the direction of arrow L.

[0035] The intermediate transfer belt 3 has a multi-layer structure, with a base layer made of, for example, a low-stretch fluororesin, PVD sheet, or polyimide resin, and a surface covered with a smooth coating layer made of, for example, a fluororesin. Reference numeral 8 denotes a tension roller that presses against the surface of the intermediate transfer belt 3 to apply tension to the intermediate transfer belt 3. Hereinafter, the intermediate transfer belt 3 may be simply referred to as the belt.

[0036] In this embodiment, the number of photosensitive drums, i.e., the number of imaging units, is four, but this is not limited to four and may be five or more. The number of support rollers that support the intermediate transfer belt 3 may also be two or more, which is the minimum number required to rotate the intermediate transfer belt 3.

[0037] The photosensitive drums 2Y, 2C, 2M, and 2K are each driven to rotate clockwise while contacting the surface of the intermediate transfer belt 3. For example, the first photosensitive drum 2Y, which is located at the most upstream position, is charged to a predetermined polarity by a charging roller 9, and its charged surface is irradiated with a laser beam emitted from an optical writing unit 10 and optically modulated. This forms an electrostatic latent image on the first photosensitive drum 2Y, which is then visualized as a yellow toner image by a developing device 11. The image visualized by the toner from the electrostatic latent image is also referred to as a visible image, a toner image, etc.

[0038] A transfer voltage is applied to the primary transfer roller 12, which causes the toner image on the photosensitive drum 2Y to be primarily transferred onto the surface of the intermediate transfer belt 3, which is driven to rotate in the direction of arrow L. Residual toner remaining on the photosensitive drum 2Y after the toner image transfer is removed by a cleaning device 13.

[0039] In the same manner as above, a cyan toner image, a magenta toner image, and a black toner image are formed on the second to fourth photosensitive drums 2C, 2M, and 2K, respectively. Each toner image is transferred in order onto the intermediate transfer belt 3 onto which the yellow toner image has been transferred, so that a four-color superimposed toner image is carried on the intermediate transfer belt 3.

[0040] A paper feeder 14 is disposed at the bottom of the device main body 1, and paper S, which is a recording medium and a transfer object, fed from the paper feeder 14 is transported toward the secondary transfer section at a predetermined timing by the rotation of a pair of registration rollers provided within the image forming device.

[0041] The secondary transfer section is the area between the part of the intermediate transfer belt 3 supported by the support roller 4 and the secondary transfer roller 15 arranged opposite to it. A transfer voltage is applied to the secondary transfer roller 15, which causes the superimposed toner image on the intermediate transfer belt 3 to be secondarily transferred onto the paper S.

[0042] The secondary transfer roller 15 is pressed against the support roller 4 via the intermediate transfer belt 3 and is driven to rotate counterclockwise while being in contact with the surface of the intermediate transfer belt 3.

[0043] The paper S (recording medium) onto which the toner image has been transferred is sent to the fixing device 16, where the toner image is fixed to the paper S by the action of heat and pressure. The paper S that leaves the fixing device 16 is discharged onto a paper discharge tray 17 formed on the top surface of the device main body 1 and stacked there.

[0044] 1, reference numeral 18 denotes a toner bottle for replenishing toner to the developing device 11. Toner bottles are provided for each color (18Y, 18C, 18M, 18K).

[0045] After the secondary transfer, toner that was not completely transferred remains on the intermediate transfer belt 3. To clean this remaining toner, the intermediate transfer unit U is provided with a belt cleaning device 60 as cleaning means.

[0046] 2, the belt cleaning device 60 has a cleaning blade 62 that comes into contact with the surface of the intermediate transfer belt 3, and a transport screw 64 that transports the toner scraped off by the cleaning blade 62 to the outside. A backup roller 66 is disposed on the opposite side of the part where the cleaning blade 62 comes into contact with the intermediate transfer belt 3.

[0047] An optical sensor unit 30 serving as a toner image detection means is disposed downstream of the secondary transfer unit in the rotation direction of the intermediate transfer belt 3. The optical sensor unit 30 is disposed so as to face the front surface of the intermediate transfer belt 3 at the location where the intermediate transfer belt 3 is wound around the support roller 4, with a predetermined gap therebetween.

[0048] 3, the optical sensor unit 30 is configured with a plurality of optical sensors (hereinafter simply referred to as "sensors") 32, each of which is made up of a light-emitting element and a light-receiving element. That is, a plurality of optical sensors 32 are provided corresponding to the imaging units of each color.

[0049] Optical sensors 32Y, 32C, 32M, and 32K for each color are arranged along the belt width direction (main scanning direction) of the intermediate transfer belt 3 so that detection toner images (toner patterns for density adjustment) for each color of Y, C, M, and K can be detected in as short a time as possible.

[0050] A light-emitting diode (LED) can be used as the light-emitting element. The amount of light emitted by an LED can be adjusted by the forward current If passed through the LED, but the adjustment parameter for the amount of light emitted is not limited to the forward current If, and any equivalent adjustment parameter can be used. A photodiode (PD), phototransistor (PTr), photo IC, etc. can be used as the light-receiving element.

[0051] Light emitted from the light-emitting element is reflected by the surface of the intermediate transfer belt, and the light-receiving element receives the reflected light and outputs a light-receiving signal (amount of received light). The light-receiving signal is converted into an electrical signal and input to the control means provided in the image forming apparatus as a sensor measurement value.

[0052] The color printer according to this embodiment has an image density adjustment mode and a color misregistration correction mode. In the image density adjustment mode (process control), apart from the normal image forming operation, density adjustment toner patterns Yp, Cp, Mp, and Kp are formed as detection toner images and transferred onto the intermediate transfer belt 3. The density adjustment toner patterns are detected by the respective sensors, and the density adjustment as described above is performed based on the detection results.

[0053] In the color misregistration correction mode, apart from the normal image forming operation, a color misregistration correction toner pattern is formed as a detection toner image tilted in the main scanning direction and transferred onto the intermediate transfer belt 3. The color misregistration correction toner pattern is detected by each sensor, and positional deviations in the main scanning direction and sub-scanning direction are corrected based on the detection results. A system may be used in which each sensor detects the color misregistration correction toner patterns of all colors formed in series in the movement direction of the intermediate transfer belt.

[0054] Generally, such toner patterns are often formed at both ends and the center of the transfer belt. In this embodiment, it is preferable that at least one of such toner patterns is formed in an off-paper area (non-paper passing area) at the end of the intermediate transfer belt. In other words, in this embodiment, when the maximum area in the rotational axis direction of the photosensitive member through which the recording medium is transported is defined as the maximum paper passing width and the area outside the maximum paper passing width is defined as the non-paper passing area, it is preferable that a toner pattern for density adjustment or color misregistration correction is transferred to the intermediate transfer belt 3 in the non-paper passing area. In this case, image density adjustment and color misregistration correction can be performed without interfering with image formation on the recording medium.

[0055] FIG. 4 is a cross-sectional view for explaining an outline of an example of the configuration of each imaging unit in the image forming apparatus of this embodiment.

[0056] Around the photosensitive drum 2, a charging roller 9, a developing device 11, a cleaning mechanism 40, a lubricant applying device 20, etc. are arranged, and these constitute an image forming unit (process cartridge).

[0057] The lubricant application device 20, arranged opposite the photosensitive drum 2, is a device that applies lubricant to the surface of the photosensitive drum 2, and is mainly composed of a lubricant section 21, a lubricant supply member 22 consisting of a foam roller, a pressing force applying mechanism 23, a lubricant layer forming mechanism 24, etc.

[0058] The lubricant portion 21 comes into contact with the lubricant supplying member 22 due to the pressing force from the pressing force applying mechanism 23. The lubricant supplying member 22 rotates and rubs against the photosensitive drum 2 at a linear speed difference, supplying the lubricant held on the surface of the lubricant supplying member 22 to the photosensitive drum surface. Since the longitudinal density of the lubricant supplying member 22 can be uniform, the manufacture of the lubricant supplying member 22 is simplified, enabling cost reduction.

[0059] The cleaning mechanism 40 is mainly composed of a cleaning member 41 and a pressing means 42 that presses the cleaning member against the photosensitive drum 2. Since partially deteriorated lubricant and toner components remain on the surface of the photosensitive drum 2 after the transfer process, the cleaning member 41 cleans off the surface residue. In Figure 4, the cleaning member 41 is in contact with the photosensitive drum 2 at an angle similar to that of a so-called counter type (leading type).

[0060] Residual toner and degraded lubricant are removed from the surface by a cleaning mechanism 40, and a lubricant is supplied to the surface of the photoreceptor from a lubricant supplying member 22. The lubricant is supplied to the surface of the photoreceptor, and a film-like lubricant layer is formed by a lubricant layer forming mechanism 24.

[0061] After the photoreceptor on which the lubricating layer has been formed is charged, an electrostatic latent image is formed by exposure to a laser L or the like. The image is then developed into a visible image by a developing device 11 and transferred to an intermediate transfer belt 3 by a primary transfer roller 12 or the like outside the process cartridge.

[0062] 4, the developing device 11 includes a developing roller 51 disposed adjacent to and facing the photosensitive drum 2, and a doctor blade 54 serving as a developer regulating member for regulating the developer on the developing roller 51 to a constant height. The developing device 11 also includes a first transport screw 52 and a second transport screw 53 disposed facing each other for agitating the developer and supplying the developer to the developing roller 51, and a partition wall 55 disposed between the first transport screw 52 and the second transport screw 53. The developing device 11 also includes toner bottles 56 containing toner of each color, bias application means for applying a DC component developing bias to the developing roller 51, and the like. The developing device 11 is disposed between the lubricant applicator 20 and the transfer nip (primary transfer nip) in the rotational direction of the photosensitive drum 2, and includes the developing roller 51 carrying a two-component developer consisting of toner and carrier.

[0063] The developing roller 51 has a developer carrier (developing sleeve) that carries the developer on its surface. The bias applying means applies a developing bias to the developing sleeve, the bias being of an appropriate magnitude between the exposed and non-exposed portions of the photosensitive drum 2.

[0064] Next, the lubricant portion 21 in this embodiment will be described. This embodiment is premised on the use of a lubricant to improve the cleaning properties of the photoreceptor surface. The lubricant portion 21 in this embodiment is made of or contains a lubricant, has a block shape, and extends in the direction of the rotation axis of the photoreceptor.

[0065] The material of the lubricant portion 21 is preferably one that spreads evenly and quickly over the surface of the photoreceptor, coating the surface of the photoreceptor while providing lubrication to protect the blade. Specific examples include inorganic lubricants, fatty acid metal salts, waxes, oils, and fluororesins. In this embodiment, the lubricant portion 21 contains a fatty acid metal salt (A) and an inorganic lubricant (B), and the fatty acid metal salt (A) and the inorganic lubricant (B) are used in combination.

[0066] In this embodiment, the lubricant portion 21 is formed in a block shape because it allows for easy adjustment of the supply amount and allows for miniaturization of the device. The lubricant portion 21 in this embodiment may also be referred to as a lubricant bar, lubricant block, etc. An example of the shape of the lubricant portion 21 is shown in, for example, FIG. 4.

[0067] As a molding method for the lubricant portion 21, known methods can be used, such as melt molding, in which the material is melted and poured into a mold, and then cooled and solidified, or compression molding, in which the powder material is compressed as is to obtain a molded product.However, in this embodiment, compression molding is preferably used because the hardness can be easily adjusted, so it can be ground with less force and can be supplied onto the photosensitive member.

[0068] Examples of fatty acid metal salts (A) in this embodiment include, but are not limited to, barium stearate, lead stearate, iron stearate, nickel stearate, cobalt stearate, copper stearate, strontium stearate, calcium stearate, cadmium stearate, magnesium stearate, zinc stearate, zinc oleate, magnesium oleate, iron oleate, cobalt oleate, copper oleate, lead oleate, manganese oleate, zinc palmitate, cobalt palmitate, lead palmitate, magnesium palmitate, aluminum palmitate, calcium palmitate, lead caprylate, lead caprate, zinc linoleate, cobalt linoleate, calcium linoleate, zinc ricinoleate, cadmium ricinoleate, barium laurate, lithium laurate, calcium laurate, and zinc laurate. Mixtures of these may also be used. In this embodiment, zinc stearate is preferably used as the main component of the lubricant because it has excellent film-forming properties on the photoreceptor. Note that the term "main component" as used in this embodiment means a component that accounts for more than 50% by weight of the entire lubricant.

[0069] However, while zinc stearate excels at forming a uniform film, it is susceptible to deterioration due to charging stress. In typical image creation processes, blade cleaning is used to remove residual toner from the photoreceptor after transfer. However, when zinc stearate is used, the zinc stearate deteriorates when subjected to a charging hazard, reducing its lubricity and making it easier for the toner to slip through the blade. If toner slips through the cleaning blade 62, it can appear directly on the image or further accelerate contamination of the charging roller 9. This toner slip-through is more pronounced the smaller the toner particle size and the stronger the charging hazard. At the same time, excessive toner and other particles slipping through can wear out the cleaning blade 62 and shorten the life of the imaging unit.

[0070] For the above reasons, in this embodiment, the fatty acid metal salt (A) and the inorganic lubricant (B) are used in combination.

[0071] In this embodiment, the inorganic lubricant (B) refers to an inorganic compound that cleaves to lubricate or causes internal sliding. Specific examples of such materials include, but are not limited to, talc, mica, boron nitride, molybdenum disulfide, tungsten disulfide, kaolin, smectite, hydrotalcite compounds, calcium fluoride, graphite, plate-like alumina, sericite, and synthetic mica. Among these, boron nitride is the most preferred in this embodiment because it easily cleaves and lubricates the surface, with its hexagonal mesh of tightly interlocking atoms overlapping at wide intervals, and the only interlayer force is a weak van der Waals force. These inorganic lubricants may be surface-treated as needed to impart hydrophobicity or the like.

[0072] Such lubricants are applied to the surface of the photoreceptor, but it has been found that they are transferred little by little from the surface of the photoreceptor to the intermediate transfer belt 3 during the image formation process. When a mixture of fatty acid metal salt (A) and inorganic lubricant (B) is used as in this embodiment, it has been found that the inorganic lubricant (B) in particular is easily transferred onto the belt and is difficult to remove, which increases belt filming over time.

[0073] This phenomenon is particularly noticeable in the non-paper passing areas at both ends of the intermediate transfer belt 3. The reason is that the paper S has the effect of removing the inorganic lubricant in the paper passing areas, but this effect is not obtained in the non-paper passing areas. If such filming worsens, the glossiness of the intermediate transfer belt 3 decreases, making it impossible to properly detect the toner pattern, and making it impossible to adjust the density or correct the color misregistration.

[0074] Therefore, in this embodiment, the amount of developer drawn up at the longitudinal ends of the developing roller 51 is made greater than the amount of developer drawn up at the longitudinal center, so that in the development area, more of the lubricant applied to the photosensitive drum 2 by the lubricant supply member 22 is scraped off at the longitudinal ends by the magnetic brushes of the developer drawn up onto the developing roller 51 than at the center. This reduces the amount of lubricant at the longitudinal ends that wraps around to the intermediate transfer belt 3, and in particular reduces the amount of lubricant applied to the adjustment pattern writing section in the non-paper passing area, suppressing belt filming at the longitudinal ends and eliminating erroneous detection of the process control pattern.

[0075] Here, FIG. 5 is a schematic diagram showing the relationship between the lengths of the respective members in the longitudinal direction. In this embodiment, the lubricant (lubricant portion 21) has a length that covers the entire surface of the intermediate transfer belt relative to the width of the belt. On the other hand, the developing opening width is narrower than that, but wider than the paper passing width of a commonly used paper S. Furthermore, the longitudinal ends of the developing opening width, i.e., the longitudinal ends of the developing roller 51, are located in the non-paper passing area. The longitudinal center of the developing opening width, i.e., the longitudinal center of the developing roller 51, is located in the paper passing area.

[0076] In addition, adjustment patterns such as process control patterns are often formed in this non-paper passing area (outside the paper passing width), and since this area is outside the width of paper that is generally passed through, such as A4-sized paper, it is difficult to remove filming substances.

[0077] Therefore, as described above, in this embodiment, by increasing the amount of developer drawn up at both ends of the developing opening width compared to the center, the lubricant that wraps around to the intermediate transfer belt 3 is scraped off in the developing area upstream of the transfer nip in the rotation direction, thereby reducing the amount of lubricant that wraps around and reducing belt filming. This suppresses filming in the non-paper passing area where the adjustment pattern is written, while also making it possible to prevent abnormal images due to contamination of the charging roller 9 or poor cleaning in the paper passing area containing inorganic lubricant. Preventing filming on the intermediate transfer belt 3 also prevents erroneous detection of the adjustment pattern.

[0078] Furthermore, a method is known in which a toner ejection pattern is written at the end of a non-paper passing area and the toner is used to scrape off filming material. However, in this embodiment, a toner pattern for suppressing filming is not formed at the longitudinal end of the intermediate transfer belt 3, particularly in the non-paper passing area. This makes it possible to suppress toner consumption.

[0079] In order to increase the amount of developer drawn up at both longitudinal ends of the developing opening width compared to the center, the doctor gap (the gap between the surface of the developing roller 51 and the doctor blade 54) of the doctor blade 54, which is a developer regulating member, is changed. In other words, the doctor blade 54 is configured so that the doctor gap between the doctor blade 54 and the surface of the developing roller 51 at the longitudinal ends is wider than at the longitudinal center. By making the doctor gap at the longitudinal ends wider than the doctor gap at the longitudinal center, the amount of developer drawn up at the longitudinal ends of the developing roller 51 is increased, and the ability to scrape off lubricant from the photosensitive drum 2 can be strengthened.

[0080] If the doctor gap is displaced stepwise in the longitudinal direction, density differences in the image may occur at the boundary, so it is desirable for the doctor gap to have a gradual change.

[0081] In another embodiment, the developing roller 51 is configured so that the surface roughness of the longitudinal ends of the developing roller 51 is greater than that of the longitudinal center, in order to increase the amount of two-component developer drawn up at both longitudinal ends of the developing opening width compared to the longitudinal center. This makes it easier for the longitudinal ends of the developing roller 51 to draw up two-component developer than the longitudinal center, and the amount drawn up at the ends increases. This strengthens the ability of the longitudinal ends to scrape off the lubricant on the photosensitive drum 2, thereby suppressing filming.

[0082] In yet another embodiment, the developing roller 51 has a plurality of grooves on its surface, and is configured so that the groove shape at the longitudinal ends of the developing roller 51 is different from the groove shape at the longitudinal center of the developing roller 51. Specifically, the central portion of the developing roller 51 is configured as a sandblasted sleeve, and the ends are configured as V-groove sleeves. By making the surface shape of the longitudinal ends of the developing roller 51 different from that of the longitudinal center (fleur-de-lis shape, V-groove, or other various groove shapes), the developer transport force at the longitudinal ends can be strengthened, the amount of developer drawn up can be increased, and the ability to scrape off lubricant from the photosensitive drum 2 can be improved.

[0083] Here, the V-groove sleeve has a higher developer transporting capacity than the sandblast sleeve, and can pick up a larger amount of lubricant, so that more of the lubricant on the photosensitive drum 2 can be scraped off from the center portion than from the center portion.

[0084] The types of groove shapes are not limited to the above combinations, and any sleeve shapes with different conveying capacities may be used. It is possible to freely combine V-grooves, DA sleeves, fleur-de-lis shapes, sandblasting, etc.

[0085] Here, the DA sleeve is a groove-shaped sleeve as shown in FIG. As shown in Fig. 6(a), the outer surface of the developing sleeve 132 is provided with a number of grooves 139 that are elliptical in plan view. These grooves 139 are formed by cutting using a rotary tool that rotates about its axis and has cutting blades spaced apart in the circumferential direction at its tip. The developing sleeve is arranged so as to intersect with the axis of the rotary tool, and while the rotary tool and the developing sleeve are rotated about that axis, the grooves 139 are formed by moving relatively in the longitudinal direction of the developing sleeve. This processing is called DA processing, and a developing sleeve formed by DA processing is called a DA sleeve.

[0086] As shown in Figure 6(b), the cross-sectional shape of the groove 139 in its width direction (circumferential direction of the developing sleeve 132) is V-shaped, and as shown in Figure 6(c), the cross-sectional shape in its length direction (longitudinal direction of the developing sleeve 132) is formed as an arc-shaped curved surface.

[0087] Furthermore, the developing roller 51 has a plurality of grooves on its surface, and by making the number (density) of grooves at the longitudinal ends of the developing roller 51 greater than at the longitudinal center, it is also possible to increase the amount of developer drawn up at the longitudinal ends compared to at the longitudinal center. This increases the amount of developer drawn up at the longitudinal ends, and strengthens the ability to scrape off lubricant from the photosensitive drum 2, even if the grooves formed at the longitudinal ends and the longitudinal center are the same type. Note that the grooves formed at the ends and the center may be different types, and the number (density) of grooves at the longitudinal ends of the developing roller 51 may be greater than at the longitudinal center.

[0088] Alternatively, the developing roller 51 may have a plurality of grooves on its surface, and the depth of the grooves at the longitudinal ends of the developing roller 51 may be greater than the depth of the grooves at the longitudinal center, thereby increasing the amount of developer drawn up at the longitudinal ends compared to the longitudinal center. This increases the amount of developer drawn up at the longitudinal ends, even if the grooves formed at the longitudinal ends and the longitudinal center are the same type, thereby enhancing the ability to scrape off lubricant from the photosensitive drum 2. Note that the grooves formed at the ends and the center may be different types, and the depth of the grooves at the longitudinal ends of the developing roller 51 may be greater than the depth of the grooves at the longitudinal center.

[0089] These measures allow the amount of lubricant drawn up at the longitudinal ends of the developing sleeve to be greater than at the center, allowing the magnetic brushes to scrape off more of the lubricant applied to the photosensitive drum 2 by the lubricant supply member 22 in the development area. This allows the amount of lubricant that wraps around the ends of the intermediate transfer belt 3 to be less than at the center, suppressing filming at the belt ends where the adjustment pattern is read and preventing abnormalities such as erroneous detection of the process control pattern over the long term. Furthermore, since there is no need to install additional components such as a flicking member, the device can be constructed at lower cost than conventional devices. Furthermore, there is no need to write toner discharge patterns at the belt ends, which are areas outside the paper feed area, resulting in less toner consumption than conventional devices. [Explanation of symbols]

[0090] 2Y, 2C, 2M, 2K photosensitive drum (image carrier) 3 Intermediate transfer belt (intermediate transfer body) 20 Lubricant application device 51 Developing roller (developer carrier) 54 Doctor blade (developer control member) [Prior art documents] [Patent documents]

[0091] [Patent Document 1] Special Publication No. 51-22380 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-282160 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-106004

Claims

1. Image carrier, a lubricant application device that applies a lubricant to the surface of the image carrier; an intermediate transfer member disposed opposite the image carrier; an image forming apparatus including a developing device disposed between the lubricant application device and a transfer nip in a rotation direction of the image carrier, the developing device including a developer carrier carrying a two-component developer composed of toner and carrier, the surface roughness of the developer carrier at the longitudinal end portion is greater than that of the longitudinal center portion; An image forming apparatus, wherein the developer carrying member has a larger amount of developer drawn up at its longitudinal ends than at its longitudinal center.

2. The developer carrier has a plurality of grooves on its surface, 2. The image forming apparatus according to claim 1, wherein the shape of the grooves at the longitudinal end portions of the developer carrier is different from the shape of the grooves at the longitudinal center portion.

3. the developer carrier has a plurality of grooves on its surface, 2. The image forming apparatus according to claim 1, wherein the groove density at the longitudinal end portions of the developer carrier is greater than the groove density at the longitudinal center portion.

4. the developer carrier has a plurality of grooves on its surface, 2. The image forming apparatus according to claim 1, wherein the developer carrier has a groove having a depth greater at its longitudinal end portions than at its longitudinal center portion.

5. An image carrier, a lubricant application device that applies a lubricant to the surface of the image carrier; an intermediate transfer member disposed opposite the image carrier; an image forming apparatus including a developing device disposed between the lubricant application device and a transfer nip in a rotation direction of the image carrier, the developing device including a developer carrier carrying a two-component developer composed of toner and carrier, the developer carrier has a plurality of grooves on its surface, the groove shape at the longitudinal end portion of the developer carrier is different from the groove shape at the longitudinal center portion, An image forming apparatus, wherein the developer carrying member has a larger amount of developer drawn up at its longitudinal ends than at its longitudinal center.

6. An image carrier, a lubricant application device that applies a lubricant to the surface of the image carrier; an intermediate transfer member disposed opposite the image carrier; an image forming apparatus including a developing device disposed between the lubricant application device and a transfer nip in a rotation direction of the image carrier, the developing device including a developer carrier carrying a two-component developer composed of toner and carrier, the developer carrier has a plurality of grooves on its surface, the groove density at the longitudinal end portion of the developer carrier is greater than the groove density at the longitudinal center portion, An image forming apparatus, wherein the developer carrying member has a larger amount of developer drawn up at its longitudinal ends than at its longitudinal center.

7. An image carrier, a lubricant application device that applies a lubricant to the surface of the image carrier; an intermediate transfer member disposed opposite the image carrier; an image forming apparatus including a developing device disposed between the lubricant application device and a transfer nip in a rotation direction of the image carrier, the developing device including a developer carrier carrying a two-component developer composed of toner and carrier, the developer carrier has a plurality of grooves on its surface, the groove density at the longitudinal end portion of the developer carrier is greater than the groove density at the longitudinal center portion, An image forming apparatus, wherein the developer carrying member has a larger amount of developer drawn up at its longitudinal ends than at its longitudinal center.

8. An image forming apparatus as described in any one of claims 1 to 7, characterized in that no toner pattern for suppressing filming is formed at the longitudinal end of the intermediate transfer body.

9. An image carrier, a lubricant application device that applies a lubricant to the surface of the image carrier; an intermediate transfer member disposed opposite the image carrier; an image forming apparatus including a developing device disposed between the lubricant application device and a transfer nip in a rotation direction of the image carrier, the developing device including a developer carrier carrying a two-component developer composed of toner and carrier, the amount of developer drawn up at the longitudinal end portions of the developer carrier is greater than the amount of developer drawn up at the longitudinal center portion, 10. An image forming apparatus, wherein a toner pattern for suppressing filming is not formed at the longitudinal end of the intermediate transfer member.

10. a developer regulating member that regulates the developer on the developer carrier; The image forming apparatus according to any one of claims 1 to 9, characterized in that the developer regulating member is formed so that a gap between the developer regulating member and the developer carrier at a longitudinal end portion is wider than a gap at a longitudinal center portion.

11. 11. The image forming apparatus according to claim 1, wherein an end portion in the longitudinal direction of the developer carrier is located in a non-paper passing area.

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