Image forming device

Abstract

To provide an image forming apparatus that prevents filming on an intermediate transfer body while greatly improving performance of cleaning an image carrier, thereby preventing poor cleaning and abnormal image density for a long period.SOLUTION: An image forming apparatus has: image carriers 2; lubricant application devices 20 that apply lubricant 21 to surfaces of the image carriers 2; and an intermediate transfer body 3 that is arranged opposite to the image carriers 2. The lubricant 21 contains at least a fatty acid metal salt (A), inorganic lubricant (B), and inorganic fine particles (C). The content of the inorganic fine particles (C) in the lubricant 21 at the ends in a longitudinal direction is larger than the content of the inorganic fine particles (C) 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 over time. 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] Patent Document 3 discloses the use of an image carrier protective agent containing a hydrophobic organic compound, inorganic fine particles, and an inorganic lubricant to suppress abrasion and filming of a photoreceptor, which is an image carrier, contamination of a charging member, and toner slip-through. However, filming tends to accumulate at the edge of an intermediate transfer belt. Summary of the Invention [Problem to be solved by the invention]

[0027] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an image forming apparatus that improves the cleaning performance of the image carrier while suppressing filming on the intermediate transfer body, thereby suppressing poor cleaning and abnormal image density over a long period of time. [Means for solving the problem]

[0028] 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, and an intermediate transfer body that is disposed opposite the image carrier, wherein the lubricant contains at least a fatty acid metal salt (A), an inorganic lubricant (B), and inorganic fine particles (C), and the lubricant is applied to the longitudinal end of the image carrier. and in the non-paper passing area outside the maximum paper passing width The aforementioned problems are solved by an image-forming apparatus, characterized in that the content of the inorganic fine particles (C) in the longitudinal center portion is larger than the content of the inorganic fine particles (C) in the longitudinal center portion. [Effects of the Invention]

[0029] According to the present invention, an image forming apparatus is provided in which the cleaning performance of the image carrier is improved while filming on the intermediate transfer member is suppressed, and cleaning defects and abnormal image density are suppressed for a long period of time. [Brief explanation of the drawings]

[0030] [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] 1 is a schematic view showing a lubricant portion 21 according to an embodiment of the present invention. [Figure 6] 1 is a schematic view showing a lubricant portion 21 according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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).

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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 (photosensitive unit).

[0055] 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 as a lubricant, a lubricant supply member 22 consisting of a foam roller, a pressing force applying mechanism 23, a lubricant layer forming mechanism 24, etc.

[0056] 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.

[0057] 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).

[0058] 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.

[0059] 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 photoreceptor unit.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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 particularly excellent film-forming properties on the photoreceptor. That is, it is preferable that the fatty acid metal salt (A) in the lubricant contains zinc stearate, which enhances the belt filming suppression effect. Note that, in this embodiment, the "main component" refers to a component that accounts for more than 50% by weight of the entire lubricant.

[0067] 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.

[0068] For the above reasons, in this embodiment, the fatty acid metal salt (A) and the inorganic lubricant (B) are used in combination.

[0069] 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, tabular alumina, sericite, and synthetic mica. Among these, boron nitride is the most preferred in this embodiment because its hexagonal mesh of tightly interlocking atoms overlaps at wide intervals, and the only interlayer force is weak van der Waals force, allowing for easy cleavage and lubrication. In other words, it is preferable for the inorganic lubricant (B) in the lubricant to contain boron nitride, which improves photoreceptor cleaning performance. These inorganic lubricants may be surface-treated as needed to impart hydrophobicity or the like.

[0070] Such lubricants are applied to the photoreceptor surface, but it is known that they are transferred in small amounts from the photoreceptor surface to the intermediate transfer belt 3 during the image creation process. Furthermore, when a lubricant containing a fatty acid metal salt (A) and an inorganic lubricant (B) is applied to the photoreceptor surface, the lubricity is less likely to decrease even when affected by discharge during the charging process, and stable cleaning performance can be maintained over the long term. However, the inorganic lubricant (B) in particular is easily transferred to the intermediate transfer belt 3 via the photoreceptor drum 2 and is difficult to remove, which increases belt filming over time.

[0071] 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.

[0072] Therefore, in the image forming apparatus according to the present invention, the lubricant contains inorganic fine particles (C) in addition to the fatty acid metal salt (A) and the inorganic lubricant (B). The content of inorganic fine particles (C) at the longitudinal ends of the lubricant is greater than the content of inorganic fine particles (C) at the longitudinal center. While the inorganic lubricant (B) easily transfers to the intermediate transfer belt 3 via the photosensitive drum 2, the inorganic fine particles (C) have the effect of abrading the inorganic lubricant (B). Therefore, the higher the inorganic lubricant content, the less the inorganic lubricant (B) accumulates on the belt. This improves the cleaning performance of the photosensitive drum 2 while suppressing filming at the longitudinal ends of the belt, thereby preventing poor cleaning and false detection of toner patterns (pro-control patterns) over a long period of time.

[0073] Furthermore, the content of inorganic fine particles (C) in the non-paper passing regions of the lubricant at the longitudinal ends, which are outside the maximum paper passing width, is higher than the content of inorganic fine particles (C) in the longitudinal center portion (see FIG. 5). By making the content of inorganic fine particles (C) higher only in the non-paper passing regions than in the center portion, it is possible to suppress filming and false detection of the toner pattern, as well as reduce contamination of the ends of the charging roller 9.

[0074] In this embodiment, the inorganic fine particles (C) refer to particles that act as rollers sandwiched between objects but do not undergo internal sliding or cleavage. Specific examples of inorganic fine particles (C) include, but are not limited to, metal oxides such as silica, tin oxide, zinc oxide, titanium oxide, alumina, zirconium oxide, indium oxide, antimony oxide, bismuth oxide, calcium oxide, antimony-doped tin oxide, and tin-doped indium oxide; metal fluorides such as tin fluoride, calcium fluoride, and aluminum fluoride; and potassium titanate. Among these, alumina is particularly preferred in this embodiment because of its excellent abrasive properties, and the inorganic fine particles (C) contain alumina. Using alumina as the inorganic fine particles (C) in the lubricant enhances the belt filming suppression effect. In this embodiment, these materials may be used in combination.

[0075] The preferred range of the content of inorganic fine particles (C) varies slightly depending on the type of inorganic fine particles (C) and the process conditions of the image forming apparatus, but is generally about 1 to 10 parts by weight, and particularly about 2 to 8 parts by weight, per 100 parts by weight of the lubricant before addition of the inorganic fine particles (C). In this embodiment, it is preferable that the content of inorganic fine particles (C) in the longitudinal center and end portions of the lubricant be within this range. If it is less than 1 part by weight, the polishing action of the inorganic fine particles (C) may be insufficient, and if it is more than 10 parts by weight, scratches may be generated on the surface of the photoreceptor, slightly deteriorating the cleaning ability of the photoreceptor.

[0076] Furthermore, in this embodiment, the content of inorganic fine particles (C) in the block-shaped lubricant in the non-paper-passing region outside the maximum paper-passing width is 1.2 to 2.0 times, particularly 1.4 to 1.8 times, the content of inorganic fine particles (C) in the longitudinal center. This significantly suppresses filming in the non-paper-passing region where the toner pattern (process control pattern) is written. At the same time, by containing inorganic lubricant (B) and inorganic fine particles (C) in an appropriate range even in the paper-passing region, sufficient cleaning performance on the photoreceptor is ensured, making it possible to prevent contamination of the charging roller 9 and abnormal images due to poor cleaning without side effects such as photoreceptor damage. In other words, belt filming, photoreceptor cleanability, and charging roller edge contamination can all be improved with minimal side effects.

[0077] The effects of the present invention can be obtained even outside the above range, but if it is more than 2.0 times, the amount of lubricant consumed at the longitudinal ends will be greater than that at the longitudinal center, resulting in slightly worse end contamination of the charging roller 9. Also, if it is less than 1.2 times, the effect of suppressing filming at the longitudinal ends of the intermediate transfer belt 3 will be slightly weaker, and the effects of the present invention may not be fully obtained.

[0078] 5 and 6 are schematic diagrams showing the lubricant portion 21 according to the embodiment of the present invention. As shown in Fig. 5, the width of the secondary transfer belt 3 is 347 mm, while the maximum paper passing width is 329 mm (A3+). For this reason, the content of inorganic fine particles (C) in the lubricant applied to the photosensitive drum 2 over a width of 348 mm is varied at least in 9.5 mm sections on both sides, which are non-paper passing regions outside the maximum paper passing width. In addition, in the embodiment of Fig. 6, the content of inorganic fine particles (C) in the lubricant applied to the photosensitive drum 2 over a width of 348 mm is varied in 12.5 mm sections on both sides of the longitudinal ends of the lubricant. In other words, the content of inorganic fine particles (C) at the longitudinal ends of the lubricant is greater than the content of inorganic fine particles (C) in the longitudinal center portion.

[0079] In addition, the toner pattern (process control pattern) is written in an area 9 mm from both ends of the belt, which is a non-paper passing area outside the maximum paper passing width, and density adjustment and color misalignment correction are performed by reading this pattern with a sensor.

[0080] <Lubricant formulation example> Table 1 shows various compositions of lubricants having a fatty acid metal salt (A), an inorganic lubricant (B) and inorganic particulates (C). The compositions shown in Formulations 1 to 14 were mixed according to the mixing ratios (by weight) shown in the table. A Wonder Blender WB-1 (Osaka Chemical Co., Ltd.) was used for mixing, and mixing was carried out twice for 10 seconds at a rotation speed of 25,000 rpm to obtain the powder mixture sample. A Ricoh MPC5503 copier was used as the image forming apparatus.

[0081] [Table 1]

[0082] <Examples 1 to 11 and Comparative Examples 1 to 3> Next, the mixture was poured into an aluminum mold measuring 20 mm deep, 9 mm wide, and 348 mm long using the lubricant formulation combination shown in Table 2. In Examples 1 to 9, a region 9.5 mm from each longitudinal end (see FIG. 5) was separated from the longitudinal center, while in Examples 10 and 11, a region 12.5 mm from each longitudinal end (see FIG. 6) was separated from the longitudinal center. A partition member was used to separate the region, and compositions with different formulations were poured into the mold at the center and both ends, as shown in Table 2. For example, in Example 1, Formulation 1 was used for the center and Formulation 2 was used for the both ends. Therefore, the inorganic fine particle (C) content was 5 parts by weight in the center and 9 parts by weight at the ends, resulting in a total inorganic fine particle (C) content (both ends / center) of 1.8 parts by weight. After pouring these compositions, the partition member was removed, and the mixture was compressed in a press to a height of 8 mm to form a powder compact. In Comparative Example 1, the same formulation was used throughout the longitudinal direction without a partition member.

[0083] The weight of the powder charged into the mold was adjusted so that the filling rate of the powder compact would be 90%. That is, the weight of the powder charged = the volume of the mold × the true specific gravity of the powder × 0.9.

[0084] [Table 2]

[0085] After molding, the solid was removed from the mold and attached to a metal support with double-sided tape to prepare lubricant bars for Examples 1 to 11 and Comparative Examples 1 to 3. These lubricant bars, which are the lubricant section 21, were installed on the photosensitive unit of all stations of a Ricoh copier MPC5503, and the pressing force of the pressing force applying mechanism 23 was adjusted so that the consumption of the lubricant section 21 was twice that under standard conditions for the purpose of accelerated evaluation, and then the following evaluation was carried out. The photosensitive unit of this copying machine has a configuration similar to that shown in FIG.

[0086] <Evaluation> 1. Intermediate transfer belt filming Using the copier configured as described above, 120,000 sheets were continuously printed in A4 size, full-color mode, under normal temperature and humidity conditions, using a chart with a 5% image area ratio for each color. The gloss (20°) was measured in the non-paper-passing area of ​​the intermediate transfer belt 3 at 60,000 and 120,000 sheets. When filming occurs on the intermediate transfer belt 3, the belt becomes cloudy and the gloss value decreases. The initial gloss value of the belt was approximately 160, and if it falls below approximately 80, process control will be impaired. A PG-1 gloss meter manufactured by Nippon Denshoku Co., Ltd. was used.

[0087] 2. Dirt on the charging roller After 120,000 sheets had been continuously fed, the photosensitive unit was removed and the edge staining of the charging roller 9 was visually inspected, and the edge staining was ranked on a 5-point scale from 5 to 1 in ascending order of edge staining (best to worst). As can be seen from Table 2, the edge staining ranks for Examples 1 to 11 were classified into 3 to 5, and no defects in the image due to the edge staining of the charging roller 9 occurred in any of the cases.

[0088] 3. Photoconductor cleaning ability After the intermediate transfer belt filming evaluation in 1 was performed, the pressure of the pressure applying mechanism 23 was returned to normal so that the consumption of the lubricant section 21 was at the standard condition, and the copier was placed in a low-temperature, low-humidity environment of 10°C and 15% RH. With the transfer current turned off, 100 sheets of A4 size vertical stripe chart were input consecutively to check for cleaning defects on the photoreceptor. If cleaning defects occurred, vertical stripes would appear on the image, so the number of sheets at which vertical stripes were first visually observed was recorded.

[0089] Table 3 shows the results of Examples 1 to 11 and Comparative Examples 1 to 3.

[0090] [Table 3]

[0091] As can be seen from Table 3, in Examples 1 to 11, filming did not worsen even in the non-paper passing areas of the intermediate transfer belt 3, and good levels of photosensitive member cleaning performance and edge contamination of the charging roller were maintained.

[0092] In particular, a comparison between Examples 1-2 and Examples 10-11 revealed that by increasing the content of inorganic fine particles (C) only in the non-paper passing areas outside the maximum paper passing width compared to the longitudinal center, both belt filming and charging roller end contamination can be particularly improved.

[0093] Furthermore, a comparison of Examples 1 to 3 with Examples 4 to 6 revealed that by setting the content of inorganic fine particles (C) in the lubricant in the non-paper passing area outside the maximum paper passing width to 1.2 to 2.0 times the content of inorganic fine particles (C) in the longitudinal center, it is possible to maintain good levels of belt filming, photosensitive body cleaning performance, and charging roller end contamination.

[0094] Furthermore, a comparison of Example 1 with Examples 7 to 9 revealed that the effects of the present invention are enhanced by using zinc stearate as the fatty acid metal salt (A) in the lubricant, boron nitride as the inorganic lubricant (B), and alumina as the inorganic microparticles (C).

[0095] In Comparative Example 1, the content of inorganic fine particles (C) in the longitudinal direction of the lubricant was the same, while in Comparative Example 2, the content of inorganic fine particles (C) at both ends was less than the content of inorganic fine particles (C) in the center, so the effect of suppressing belt filming in non-paper passing areas was not obtained.

[0096] In Comparative Example 3, the inorganic lubricant (B) was not contained in the entire region of the lubricant in the longitudinal direction, and therefore the effect of suppressing belt filming was good, but the photoreceptor cleaning ability and the rank of charging roller end contamination were poor.

[0097] In addition, in a comparison between Example 5 and Example 6, even though the contents of inorganic fine particles (C) in the lubricant are different, the belt filming suppression effect is determined by the content ratio of both ends / center. This is because changing the content of inorganic fine particles (C) changes the amount of lubricant consumed itself, and the pressing force is different between Example 5 and Example 6 to make the amount of lubricant consumed the same. Therefore, in the present invention, the important thing is not the absolute value of the content of inorganic fine particles (C), but the ratio of the content of inorganic fine particles (C) in the center and end parts in the longitudinal direction of the lubricant.

[0098] As described above, in an embodiment of the present invention, in an image forming apparatus having a photosensitive drum 2, a lubricant applicator 20 that applies a lubricant to the surface of the photosensitive drum 2, and an intermediate transfer belt 3 disposed opposite the photosensitive drum 2, the lubricant contains at least a fatty acid metal salt (A), an inorganic lubricant (B), and inorganic fine particles (C), and the content of inorganic fine particles (C) at the longitudinal ends of the lubricant is greater than the content of inorganic fine particles (C) at the longitudinal center. This results in an image forming apparatus that significantly improves the cleaning performance of the photosensitive drum 2 while suppressing filming on the intermediate transfer belt 3, thereby suppressing poor cleaning and abnormal image density over a long period of time. [Explanation of symbols]

[0099] 2Y, 2C, 2M, 2K photosensitive drum (image carrier) 3 Intermediate transfer belt (intermediate transfer body) 20 Lubricant application device 21 Lubricant section (lubricant) [Prior art documents] [Patent documents]

[0100] [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. 2009-186610

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; The lubricant contains at least a fatty acid metal salt (A), an inorganic lubricant (B), and inorganic fine particles (C), an inorganic fine particle (C) content in a non-paper passing region at a longitudinal end of the lubricant that is outside a maximum paper passing width is greater than an inorganic fine particle (C) content in a longitudinal center portion of the lubricant.

2. An image forming apparatus as described in Claim 1, characterized in that the content of the inorganic fine particles (C) of the lubricant in the non-paper passing area outside the maximum paper passing width is 1.2 to 2.0 times the content of the inorganic fine particles (C) in the longitudinal center portion.

3. 3. The image forming apparatus according to claim 1, wherein the inorganic fine particles (C) contain alumina.

4. 4. The image forming apparatus according to claim 1, wherein the fatty acid metal salt (A) contains zinc stearate.

5. 5. The image forming apparatus according to claim 1, wherein the inorganic lubricant (B) contains boron nitride.

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