Image forming apparatus

Abstract

To provide an image forming apparatus that is configured such that a free length at the ends in a longitudinal direction of a cleaning blade is made longer than a free length in a center part, and that can prevent charging failure.SOLUTION: The length from a fixation surface of an elastic part and a support part to a free end of the elastic part (free length) at the ends in a longitudinal direction of a cleaning blade, is longer than the free length in a center part in the longitudinal direction of the cleaning blade. The length in the longitudinal direction of a charging roller is longer than the length in the longitudinal direction of a developer coat area. The length in the longitudinal direction of a cleaning roller is longer than the length in the longitudinal direction of the charging roller. An elastic layer is provided in a portion of the cleaning roller in contact with the charging roller. In the portion of the cleaning roller provided with the elastic layer, the outer diameter of the cleaning roller at the ends in the longitudinal direction of the cleaning roller is larger than the outer diameter of the cleaning roller in a center part in the longitudinal direction of the cleaning roller.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus equipped with a cleaning blade. [Background technology]

[0002] Image forming apparatuses equipped with a photoconductor cleaning device that removes residual toner remaining on the photoconductor drum after primary transfer are known. A cleaning blade made of an elastic material such as rubber bonded to a supporting metal plate is widely used as a photoconductor cleaning device. In particular, the counter type, in which the cleaning blade is brought into contact with the photoconductor drum or intermediate transfer belt so as to face the driving direction of the photoconductor drum or intermediate transfer belt, is generally adopted because of its high cleaning performance.

[0003] However, in this counter-type blade cleaning, it is known that problems such as blade curling can occur when the frictional force between the cleaning blade and the photosensitive drum or intermediate transfer belt becomes large. Therefore, Patent Document 1 describes a configuration in which the free length at the longitudinal ends of the cleaning blade is made longer than the free length at the center. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2006-259394 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the configuration of Patent Document 1, the frictional force between the photosensitive drum and the cleaning blade is reduced in an area (hereinafter referred to as a high μ area) where the toner or developer acting as a lubricant at the end of the cleaning blade is hardly supplied. Specifically, the width of the area where the free length of the cleaning blade is set long is set to be larger than the width of the high μ area.

[0006] On the other hand, if the free length is set long, the contact pressure of the cleaning blade decreases, which may result in poor cleaning. Therefore, the width of the region where the free length is set long is set so as not to overlap with the toner image forming region.

[0007] However, even outside the toner image forming area, minute fog toner continues to be supplied onto the photosensitive drum at a position facing the developer coated area where the developing roller is coated with toner. If the free length of the cleaning blade in this area is long, the minute fog toner is not sufficiently collected by the cleaning blade and adheres to the charging roller located downstream of the cleaning blade. If such fog toner continues to be supplied to the charging roller for a long period of time, the accumulated toner becomes a resistor, causing charging failure and causing vertical streaks on the edge of the paper.

[0008] In particular, in recent years, the types of paper used have become more diverse, and there are more and more cases where images are formed on so-called 13-inch paper, up to the full image formable area of ​​the conventional design value in the longitudinal direction of the image forming device. For this reason, there has been a growing need in recent years to improve image defects such as vertical streaks appearing on the edges of the paper.

[0009] The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of suppressing charging defects in a configuration in which the free length at the longitudinal ends of the cleaning blade is longer than the free length at the central portion. [Means for solving the problem]

[0010] In order to achieve the above object, an image forming apparatus according to one aspect of the present invention has the following configuration: That is, the image forming apparatus includes a developing device having an image carrier on which an electrostatic latent image is formed, a developing container that contains a developer, and a developing roller that carries the developer to develop the electrostatic latent image formed on the image carrier, a transfer member to which a toner image formed on the image carrier is transferred, an elastic portion, and a support portion to which the elastic portion is fixed and that supports the elastic portion, and the image forming apparatus includes a cleaning blade that scrapes off residual developer on the image carrier after the toner image is transferred to the transfer member, a charging roller that contacts the image carrier to charge the image carrier, and a cleaning roller that contacts the charging roller to clean the surface of the charging roller, and the elastic portion is fixed to the cleaning blade from a fixed surface between the elastic portion and the support portion at an end of the cleaning blade in the longitudinal direction. the length of the charging roller is longer than the length of the developer coated area where the developer is coated on the developing roller; the length of the cleaning roller is longer than the length of the charging roller in the longitudinal direction; an elastic layer is provided on a portion of the cleaning roller that abuts against the charging roller; and in the portion of the cleaning roller where the elastic layer is provided, the outer diameter of the cleaning roller at the longitudinal end of the cleaning roller is larger than the outer diameter of the cleaning roller at the longitudinal center of the cleaning roller. Effect of the Invention

[0011] According to the present invention, in a configuration in which the free length at the ends in the longitudinal direction of the cleaning blade is longer than the free length at the central portion, it is possible to suppress poor charging. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram illustrating a configuration of an image forming apparatus according to a first embodiment. [Diagram 2] FIG. 2 is a diagram illustrating a configuration of an image forming station according to the first embodiment. [Diagram 3] FIG. 2 is a diagram illustrating the configuration of a charging roller according to the first embodiment. [Figure 4] FIG. 2 is a diagram illustrating a configuration of a cleaning roller according to the first embodiment. [Diagram 5] FIG. 2 is a diagram illustrating a configuration of a cleaning blade according to the first embodiment. [Figure 6] FIG. 2 is a diagram for explaining the arrangement relationship of parts in the longitudinal direction according to the first embodiment. [Figure 7] FIG. 4 is a diagram illustrating an effect of the first embodiment. [Figure 8] 10A and 10B are diagrams illustrating a configuration of a cleaning roller according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the present invention, and not all of the combinations of features described in the embodiments are necessarily essential to the solution of the present invention. The present invention can be implemented in various applications, such as printers, various printing machines, copiers, FAX machines, and multifunction machines.

[0014] [First embodiment] (Configuration of Image Forming Apparatus) 1 is a diagram illustrating the configuration of an image forming apparatus according to a first embodiment of the present invention. The image forming apparatus 100 is a full-color printer of a tandem intermediate transfer type in which yellow, magenta, cyan, and black image forming stations PY, PM, PC, and PK are arranged along an intermediate transfer belt 90.

[0015] In the image forming station PY, a yellow toner image is formed on the photosensitive drum 1Y as an image carrier and transferred to the intermediate transfer belt 90 (transfer member). Similarly, in the image forming stations PM, PC, and PK, a magenta toner image, a cyan toner image, and a black toner image are formed on the photosensitive drums 1M, 1C, and 1K, respectively, and transferred to the intermediate transfer belt 90.

[0016] The full-color toner image formed by superimposing the four color toner images is conveyed to the secondary transfer section 11 as the intermediate transfer belt 90 rotates, and is secondarily transferred onto the recording material 13 .

[0017] The recording material 13 taken out from the recording material cassette is separated one by one by the secondary transfer section 11 and conveyed to the registration rollers 12 .

[0018] The registration rollers 12 feed the recording material 13 to the secondary transfer section 11 in synchronization with the toner image on the intermediate transfer belt 90 .

[0019] The recording material 13 onto which the full-color toner image has been secondarily transferred in the secondary transfer section 11 is heated and pressurized in a fixing device to fix the image on its surface, and then discharged outside the apparatus.

[0020] The image forming stations PY, PM, PC, and PK are configured almost identically, except that the colors of toner used in the developing devices 4Y, 4M, 4C, and 4K are different. In the following, the image forming station PY will be described, and the image forming stations PM, PC, and PK will be described by replacing the Y at the end of the reference numerals of the components of the image forming station PY with M, C, and K.

[0021] (Image forming station configuration) 2 is a diagram illustrating the configuration of the image forming station (PY). The image forming station PY has a charging roller 2Y, a cleaning roller 8Y (charging roller cleaning member), an exposure device 3Y (laser scanner), a developing device 4Y, a cleaning blade 7Y, and a primary transfer roller 9Y arranged around a photosensitive drum 1Y. Note that the other image forming stations have the same configuration as the image forming station PY, so their descriptions are omitted.

[0022] The material for the outer peripheral surface of the photosensitive drum 1Y may be phenol resin, acrylic resin, methacrylic resin, or the like.

[0023] The charging roller 2Y has a rotating shaft (core metal) supported by a bearing member, and is brought into contact with the photosensitive drum 1Y by the bearing member being biased. The charging roller 2Y is rotated in conjunction with the rotation of the photosensitive drum 1Y, and the photosensitive drum 1Y is charged by applying a voltage thereto.

[0024] The cleaning roller 8Y is in contact with the charging roller 2Y and rotates with the rotation of the charging roller 2Y to clean off any deposits adhering to the charging roller 2Y. The toner consumed by the developing device 4Y is appropriately replenished from a toner replenishing device 5Y.

[0025] The developing device 4Y includes a developer container that contains a developer, and a developing roller 41Y as a developer carrier that carries the developer to develop the electrostatic latent image formed on the photosensitive drum 1Y.

[0026] (Configuration of the charging roller) 3 shows the layer configuration of the charging roller 2. The charging roller 2 has a conductive base such as a metal as a core 2a, and a conductive rubber layer 2d on the conductive base, and the conductive rubber layer 2d has, in that order from the bottom (from the core 2a side), an elastic layer 2d1, a conductive layer 2d2, and a resistive layer 2d3.

[0027] The core bar 2a is a shaft made of stainless steel and has a radius of 4 mm.

[0028] The hardness of the elastic layer 2d1 is preferably 30° or less in terms of rubber hardness based on JIS AGS-706 from the viewpoint of adhesion to the photosensitive drum 1 due to flexibility. The layer thickness of the elastic layer is preferably 2 mm or more. With the above-mentioned rubber hardness and layer thickness, it is possible to sufficiently ensure adhesion to the photosensitive drum 1 and the charging roller 2. Therefore, it is possible to suppress the contact state between the photosensitive drum 1 and the charging roller 2 from varying in the longitudinal direction due to manufacturing tolerances of the crown amount and outer diameter of the photosensitive drum 1 and the charging roller 2.

[0029] The conductive layer 2d2 preferably has a volume resistivity of 10^7 Ω·cm or less. If the volume resistivity exceeds the above-mentioned value, a voltage drop occurs in the conductive layer when a charging bias consisting of a DC component and an AC component is applied from a charging bias power supply, and the potential of the photosensitive drum surface that should be formed equivalent to the applied DC bias decreases. In addition, the conductive layer 2d2 may be made of a metal deposition film, a conductive particle dispersion resin, a conductive resin, or the like.

[0030] The resistive layer 2d3 is configured to have a volume resistivity of about 10^7 to 10^12 Ω·cm, which is higher than that of the conductive layer 2d2, when a DC bias of -200 V is applied, and is made of an insulating layer with conductive particles dispersed therein. The thickness of the resistive layer 2d3 is preferably 500 μm or less from the viewpoint of electrostatic chargeability.

[0031] As described later, these conductive particles are gradually lost when the surface of the charging roller 2 is destroyed by friction with the photosensitive drum 1, and as a result, the absolute value of the surface potential of the photosensitive drum 1 may also decrease relative to its target potential.

[0032] (Configuration of the charging roller cleaning member) 4 shows the layer structure of the cleaning roller 8 serving as a charge roller cleaning member, and FIG. 4(A) is a schematic cross-sectional view of the cleaning roller 8 in a state where it is not in contact with the charge roller 2. FIG.

[0033] The cleaning roller 8 is a sponge roller having a metal core 8a as a support shaft and a sponge layer 8d formed on the circumferential surface of the metal core 8a. The metal core 8a is a shaft made of SUS and has a diameter of 4 mm.

[0034] The sponge layer 8d is a continuous-foam sponge layer in which the wall surfaces of the bubble parts communicate with each other. In the first embodiment, a polyurethane sponge is assumed. However, as will be described later, if the apparent density, 25% compression load, etc. are equivalent, a porous material such as a polystyrene-based elastomer, a polyolefin-based elastomer, or a polyurethane-based elastomer may be used. The sponge layer 8d is provided substantially concentrically around the rotation central axis of the core metal 8a, and has a configuration with a radial thickness of 3 mm and a diameter D1 = 10 mm.

[0035] Further, FIG. 4(B) is a schematic view in the longitudinal direction of the cleaning roller 8. In the first embodiment, the relationship between the outer diameter D2 of the end portion of the portion made of the same sponge and the diameter D1 of the central portion of the portion made of the sponge is D1 < D2. The specific numerical value of D2 in the first embodiment will be described later. Also, the longitudinal length Ws in the region of the outer diameter D2 of the sponge end portion in the first embodiment will be described later.

[0036] Further, so as not to impair the function of the charging roller 2 for charging the photosensitive drum 1, the cleaning roller 8 is made of a non-conductive material, and its resistance value may be as large as possible, but is usually about 10^13 Ω or less for manufacturing reasons or the like.

[0037] Also, the apparent density of the sponge material of the cleaning roller 8 is about 0.2 [g / cm^3], and the 25% compression load is about 0.057 [kgf / cm^2]. Generally, at this density, the relationship between compression from 0 to about 50% and the force required for compression can be approximately linear and estimated.

[0038] Here, the ranges of the apparent density and the 25% compression load in the first embodiment were selected based on the following judgment.

[0039] The lower the apparent density of the sponge, the better the conformability of the sponge surface to the surface of the charging roller 2. However, if the apparent density of the sponge is too low, it will conform too closely to the shape of the charging roller 2, resulting in loss of driven rotation, and driving parts such as gears will be required, making the structure, including assembly, more complicated. Generally, if the indentation is not less than half the radius, it will be difficult for the force in the rotational driving direction on the surface to act.

[0040] On the other hand, if a sponge with a higher compression load is used, that is, if a harder sponge is used, the conductive particles on the surface of the charging roller 2 are pressed against the sponge and slide in contact, which increases the degree to which they fall off. As a result, the function of maintaining the charging ability of the charging roller 2 by cleaning the surface of the charging roller 2 is lost.

[0041] In the first embodiment, the charging roller 2 and the cleaning roller 8 are fixed to bearings biased by springs at both longitudinal ends, and the spring pressure is 500 gf on each side.

[0042] (Cleaning blade configuration) 5 is a diagram illustrating the configuration of the cleaning blade 7. The cleaning blade 7 plays a role of scraping off residual developer on the photosensitive drum 1 (image carrier) after the toner image is transferred to the intermediate transfer belt 90.

[0043] 5(A) and 5(B), the cleaning blade 7 is composed of an elastic member 7a (elastic portion) and a supporting metal plate 7b (support portion). The elastic member 7a is fixed to the supporting metal plate 7b and supports the elastic member 7a.

[0044] Also, the free length is changed in the longitudinal direction depending on the shape of the support sheet metal 7b. The free length refers to the length from the adhesion surface (fixed surface) of the elastic member 7a and the support sheet metal 7b to the free end of the elastic member 7a. Specifically, the free length L1 at the central portion in the longitudinal direction of the elastic member 7a and the free length L2 in the region of the width w at the longitudinal end of the cleaning blade 7 satisfy the relationship L1 < L2. Specific numerical values of the width w at the longitudinal end of the cleaning blade 7 will be described later.

[0045] At the longitudinal ends of the cleaning blade 7, even in the region where charging is performed on the photosensitive drum 1 by the charging roller 2, there is a region (hereinafter referred to as the non-image forming region) where toner and external additives are not actively supplied by the developing roller 41.

[0046] In this non-image forming region, although the electrostatic adhesion force on the surface of the photosensitive drum 1 is high, since the supply of toner and external additives is small, the frictional force between the photosensitive drum 1 and the cleaning blade 7 becomes high, and so-called blade streaks are likely to occur. Also, even if blade streaks do not occur, due to the high frictional force, the surface of the photosensitive drum 1 is likely to be scratched, and the life of the photosensitive drum 1 tends to be shortened.

[0047] On the other hand, when the free length described above is set to be uniformly long in the longitudinal direction to weaken the frictional force, in the image forming region where the developing roller 41 faces the photosensitive drum 1, the cleaning ability of the cleaning blade 7 to scrape off toner and external additives tends to be insufficient. As a result, potential unevenness on the surface of the photosensitive drum 1 caused by the adhesion of toner and external additives to the surface of the charging roller 2 may occur, leading to uneven image density and becoming apparent.

[0048] Therefore, in the image forming area where the developing roller 41 faces the photosensitive drum 1, the developing roller 41 has a sufficient frictional force to prevent poor image quality, and in the non-image forming area, the developing roller 41 is required to have the above-mentioned configuration in order to suppress curling and drum scraping. Also, the cleaning blade 7 needs to have a frictional force that can scrape off only the minimum amount of toner and external additives that does not cause fogged images.

[0049] Next, a description will be given of design values ​​required in the longitudinal direction when the above-described configuration of the cleaning blade 7 is adopted, and problems associated with this configuration.

[0050] (Longitudinal arrangement of cleaning blades) 6 is a diagram for explaining the longitudinal arrangement of the main elements of the image forming apparatus 100. For simplicity, the explanation will be given using the width measured from the center of the image toward the end, rather than the overall width in the longitudinal direction.

[0051] Each roller is installed with its shaft fitting into the bearing hole, but the diameter of the shaft is larger than that of the bearing hole on the inside in the longitudinal direction from the bearing, and the position is determined because the shaft cannot enter. The positional deviation of the developing roller 41, charging roller 2, and cleaning roller 8 from the target position has an error of less than ±1 mm.

[0052] In consideration of development stability at the longitudinal ends, the developable area (401) in the developing device 4 is set to be larger than the exposable area (402) which is an area where the charging roller 2 can charge the opposing photosensitive drum 1 and where the exposure device 3 can expose. The developable area (401) corresponds to a developer coated area where the developing roller 41 is coated with developer.

[0053] Also, within the exposure range, taking into consideration longitudinal positional deviation and the like, an area where the amount of exposure to the photosensitive drum 1 and the amount of toner to be developed are guaranteed (hereinafter referred to as image guarantee area) is designated as 403. Here, longitudinal positional deviation refers to deviations caused by positional accuracy such as the longitudinal position of the charging roller 2, the exposure range of the exposure device 3, and the guaranteed area of ​​the magnetic force of the magnet fixedly disposed inside the developing roller 41.

[0054] The specific longitudinal positions are as follows: At the end of the image guaranteed area (403), it is 150 mm from the center of the image; at the end of the exposable area (402), it is 152 mm from the center of the image; and at the end of the developable area (401), it is 157 mm from the center of the image. As mentioned above, there is a longitudinal positional deviation of less than ±1 mm for each.

[0055] Next, the length (201) of the charging roller 2 in the longitudinal direction must be longer than the developable area (401). If the length (201) of the charging roller 2 in the longitudinal direction is shorter than the developable area (401), a larger contrast potential than that required to draw a so-called solid image will be formed between the zero charging potential and the development potential. As a result, not only the toner but also the carrier component of the developer will be attracted to the drum side due to the strong electrostatic force.

[0056] Therefore, in the first embodiment, when a toner image is not formed on the surface of the photosensitive drum 1 facing the developing roller 41, the potential difference is set so that a so-called fog removal potential of 180 V is formed.

[0057] In addition, the length (801) of the cleaning roller 8 in the longitudinal direction must be longer than the developable area (401). This is because, if the length (801) of the cleaning roller 8 in the longitudinal direction is shorter than the developable area (401), depending on the deviation in the longitudinal positional deviation between the charging roller 2 and the cleaning roller 8, an area where the cleaning roller 8 does not fully contact the surface of the charging roller 2 may occur.

[0058] The specific longitudinal positions are as follows: The longitudinal ends of the charging roller 2 are 159 mm from the center of the image. The longitudinal ends of the cleaning roller 8 are 163 mm from the center of the image. As described above, there is a longitudinal positional deviation of less than ±1 mm.

[0059] Next, the length (701) of the cleaning blade 7 in the longitudinal direction must be at least longer than the length of the region where the charging roller 2 faces the photosensitive drum 1. This is because, even at the longitudinal ends of the charging roller 2, the opportunity for the toner and external additives adhering to the surface of the photosensitive drum 1 to come into contact with the cleaning roller 7 is suppressed, and the fog removal potential on the photosensitive drum 1 is maintained in the region adjacent to the developable region (401). This makes it possible to suppress the generation of a large contrast potential that would cause the toner and carrier to adhere, even if there is a longitudinal positional deviation between the charging roller 2 and the cleaning roller 8.

[0060] Next, a region (hereinafter, referred to as the UP free length portion) (702) of the cleaning blade 7, which has a longer free length than the image forming region, will be described. The UP free length portion (702) must be located at least outside the image guaranteed region (403). This is because the frictional force of the cleaning blade 7 in the UP free length portion (702) is lower than that in the image region, so that toner and external additives tend to slip through, and there is a risk that the level of contamination of the external additives on the charging roller 2 will not reach the target value required for the image region.

[0061] In the first embodiment, the cleaning blade 7 is not a bearing but is attached to a container that houses the photosensitive drum 1 and the cleaning blade 7 together, and the positional deviation in the longitudinal direction is less than ±0.2 mm. The free length UP portion (702) of the cleaning blade 7 also depends on the bonding position of the cleaning blade 7 to the supporting metal plate 7b, and the positional deviation in the longitudinal direction is less than ±0.2 mm.

[0062] Therefore, as a specific longitudinal arrangement, the longitudinal end of the cleaning blade 7 is 162 mm from the center of the image. Also, the starting position on the central side of the free length UP portion (702) must not be inside the maximum value of 151 mm of the image guarantee area (403), and the design value can be calculated as 151.2 mm.

[0063] Next, the length (101) of the photosensitive drum 1 in the longitudinal direction is, naturally, longer than the length (701) of the cleaning blade 7 in the longitudinal direction. In terms of the specific longitudinal arrangement, the end of the photosensitive drum 1 in the longitudinal direction is 178 mm from the center of the image.

[0064] In the first embodiment, in the image forming apparatus 100, the cleaning ability is improved and the potential drop is suppressed by making the outer diameter of the sponge of the cleaning roller 8 larger in the portion where the slip-through is deteriorated due to the free length UP portion (702). The details are described below.

[0065] (Position where the outer diameter of the cleaning roller is increased) As described above, the starting position of the central part of the free length UP part (702) must not be inside the maximum value 151 mm of the image guarantee area (403), and the design value is calculated to be 151.0 + 0.2 mm. The width w of the free length UP part (702) at the end of the longitudinal direction of the cleaning blade 7 described above is w = 9.8 mm in the first embodiment.

[0066] On the other hand, the part where the sponge outer diameter of the cleaning roller 8 is thickened (hereinafter referred to as the outer diameter UP part of the cleaning roller 8) must not be inside the maximum value of 151 mm of the image guarantee area (403). This is because, in the image area, cleaning the charging roller 2 with strong pressure causes the conductive particles on the surface of the charging roller 2 to fall off from the charging roller 2, causing a drop in potential. Therefore, considering a positional deviation of ±1 mm in the longitudinal direction of the cleaning roller 8, in the first embodiment, 152.0 mm is the limit position on the central position side. Therefore, the longitudinal length of the part where the sponge outer diameter of the cleaning roller 8 is thickened (the outer diameter UP part of the cleaning roller 8) is Ws = 11.0 mm at one of the longitudinal ends.

[0067] (Maximum outer diameter and load of cleaning roller) In the first embodiment, the outer diameter of the cleaning roller 8 is set to be approximately 1.33 times the thickness of the sponge at the image position in the 11 mm range from the non-image forming position, i.e., the position 152 mm from the center position to the end 163 mm in the longitudinal direction, i.e., 4.0 mm in radial thickness of the sponge.

[0068] At this time, the charging roller 2 and the cleaning roller 8 are in pressure contact with each other by a spring biased by a bearing, and are pressed against the cleaning roller 8 with a total load of 1000 gf as described above.

[0069] At this time, the 25% compression load of the sponge in the first embodiment is about 0.057 [kgf / cm^2]. In addition, if a force of 1000 g is received by the sponge length (total 326 mm) and the free length UP part (702) (total 22 mm) at the inner end, the longitudinal end is compressed by about 45%.

[0070] This configuration can suppress density fluctuation caused by toner fine powder and external additives detached from the toner surface adhering to the surface of the charging roller 2 in the image area, resulting in a decrease in the charging potential of the photosensitive drum 1. This configuration can also suppress the occurrence of fogged images at the longitudinal ends of paper with a large longitudinal width, such as 13-inch paper.

[0071] Next, for the cleaning roller 8, in the conventional configuration, as described above, the sponge thickness was set to a constant 3.0 mm over a total of 326 mm, 163 mm from the center position toward both ends.

[0072] On the other hand, in the configuration according to the first embodiment, the thickness is constant at 3.0 mm over 152 mm from the center position toward both ends, totaling 304 mm. In addition, the thickness of the sponge is 4.0 mm over 11 mm from the center position toward both ends, from 152 mm to 163 mm.

[0073] As bias conditions during paper passage, the bias applied to the developing roller 41 is 520 V, the DC bias component applied to the charging roller 2, i.e., the charging potential on the photosensitive drum 1, is 700 V, and the difference therebetween, the so-called fog removal bias, is 180 V. Hereinafter, the fog removal bias is referred to as Vback.

[0074] Here, the target value of Vback will be described.

[0075] In the first embodiment, in the image area, the permissible potential difference deviation of the charged potential on the photosensitive drum 1 is within Δ25 V. This is because if there is a difference in the charged potential between adjacent charged potentials on the surface of the photosensitive drum 1 that is greater than this, a potential difference of several to several tens of volts remains even in the potential after exposure, which is recognized by the user as density unevenness.

[0076] Moreover, the potential difference deviation in the non-image portion is within Δ40 V. This is because, in the first embodiment, when Vback is less than 140 V on the surface of the photosensitive drum 1, the electrostatic force that repels the weakly charged toner present on the developing roller 41 due to the potential difference between the developing roller 41 and the photosensitive drum 1 weakens. As a result, the amount of fogging toner on the photosensitive drum 1 increases.

[0077] In the first embodiment, since the cleaning blade 7 is provided with a free length UP portion 702w, the opportunity for the toner to slip through and adhere to the end of the charging roller 2 increases, and the potential of the photosensitive drum 1 at the longitudinal position is further lost.

[0078] Here, the dirt on the surface of the charging roller 2 and the drop in the charging potential on the photosensitive drum 1 will be described. As described above, the dirt on the surface of the charging roller 2 mainly consists of toner fine powder and toner external additives. The external additives are generally made of metals such as silica (Si) and titanium (Ti), so the amount of the additives can be quantified by a so-called fluorescent X-ray analyzer. The inventors quantified the relationship between the amount of dirt and the drop in the charging potential using an XGT-9000 (manufactured by HORIBA) as a measuring device. As a result, a drop in the charging potential of approximately Δ40V occurs for a silica (Si) detection value of Δ120 [cps / mA].

[0079] Next, we will explain the extent to which the conductive particles on the surface of the charging roller 2 fall off depending on the pressure at which the surface of the charging roller 2 is contacted, and the degree to which the charged potential decreases depending on the amount of the conductive particles. As described above, when the surface conductive particles fall off the charging roller 2 due to the sliding action between the charging roller 2 and the cleaning roller 8, the charged potential gradually decreases.

[0080] Image forming operations were performed on 200,000 sheets of A4 paper using the image forming apparatus 100. As a result, when the cleaning roller 8 had a conventional uniform thickness of 3.0 mm over the entire area, the frictional force between the charging roller 2 and the cleaning roller 8 was small, and the drop in surface potential of the photosensitive drum 1 due to the sliding operation was about 5 V.

[0081] On the other hand, in the configuration in which the thickness of the cleaning roller 8 at the longitudinal end is 4.0 mm as in the first embodiment, the frictional force between the charging roller 2 and the cleaning roller 8 is small, and the decrease in the surface potential of the photosensitive drum 1 due to the sliding action is approximately 8.9 V.

[0082] In order to confirm the effects of the present invention, a configuration according to the present invention was mounted on image forming apparatus 100, and a continuous paper feed test was carried out with the following configurations for comparison.

[0083] 7(A), the sponge thickness at the longitudinal end of the cleaning roller 8, i.e., the position corresponding to the non-image area, is X mm. At this time, the sponge thickness at the longitudinal center of the cleaning roller 8, i.e., the image area, is 3.0 mm.

[0084] Here, the contact area between the charging roller 2 and the cleaning roller 8 increases in proportion to the outer diameter of the cleaning roller 8, thereby reducing the amount of dirt on the surface of the charging roller 2. In other words, the thickness of the sponge part of the cleaning roller 8 in the non-image area and the potential drop due to dirt on the charging roller 2 are inversely proportional to each other, as shown in FIG.

[0085] Furthermore, the contact pressure between the charging roller 2 and the cleaning roller 8 increases in proportion to the outer diameter of the cleaning roller 8, which increases the number of conductive particles that fall off the surface of the charging roller 2. Here, since the conductive particles are spherical, the potential drop of the photosensitive drum 1 due to the falling off of the conductive particles tends to be approximated by a square. Therefore, the thickness of the sponge part of the cleaning roller 8 in the non-image area and the potential drop due to the falling off of the conductive particles of the charging roller 2 are in an approximately square proportional relationship, as shown in FIG. 7(A).

[0086] Figure 7(B) is a graph showing the relationship between the thickness of the sponge part of the cleaning roller in the non-image area, as mentioned above, and (x): potential drop due to contamination of the charging roller, (y): potential drop due to conductive particles falling off the charging roller, and (z): potential drop of the photosensitive drum.

[0087] The sum of [(x): potential drop due to charging roller contamination] and [(y): potential drop due to conductive particles falling off the charging roller] may be in the following cases: In other words, it may be within the allowable range of Vback drop in the non-image area described above (indicated by a circle for [Non-image area judgment] in Fig. 7(A)) or outside the range (indicated by a circle for [Non-image area judgment] in Fig. 7(A)).

[0088] Therefore, in the first embodiment, the outer diameter of the non-image area of ​​the cleaning roller 8 is preferably about 4.0 mm at minimum and about 6.0 mm at maximum.

[0089] From the above results, it has been demonstrated that the configuration of the first embodiment can suppress image defects such as fogging caused by the accumulation of dirt on the charging roller 2 in the non-image area.

[0090] According to the first embodiment, even if the free length at the ends in the longitudinal direction of the cleaning blade 7 is made longer than the free length at the central portion, it is possible to suppress charging defects.

[0091] [Second embodiment] In the configuration of the second embodiment, the description of the same parts as those in the first embodiment will be omitted. In the second embodiment, the configuration of the cleaning roller is different from that in the first embodiment.

[0092] The cleaning roller 80 according to the second embodiment has a configuration in which a sponge is wound in a spiral shape around a core metal 80a, as shown in Fig. 8. Also, in the second embodiment, unlike the first embodiment, the entire area of ​​the cleaning roller 80 is not covered with a sponge layer.

[0093] However, from the viewpoint of uniform contact, the sponge layer wound spirally around the core 80a contacts the cleaning roller with higher pressure over a smaller area than if the sponge layer were to cover the entire longitudinal area of ​​the cleaning roller. Therefore, the cleaning ability of the second embodiment is not necessarily inferior to that of the first embodiment.

[0094] In the second embodiment, the ratio of the sponge member per revolution of the cleaning roller 80 is 90[° / 360°] at the center in the longitudinal direction, i.e., the area ratio is 25%. Also, the sponge member is wound around the core metal 80a at least three revolutions within a width of 304 mm in the central region in the longitudinal direction of the cleaning roller 80. In the second embodiment, the number of sponges per 360° in the circumferential direction at one point on the longitudinal direction of the cleaning roller 80 is one, but there may be multiple spiral windings.

[0095] In the second embodiment, the position of the cleaning roller 80 corresponding to the free length UP portion (702) of the cleaning blade 7 corresponds to the width Ws in the longitudinal direction of the cleaning roller 80 shown in FIG. 8. For this width Ws=11 mm, the width Ws is 120[° / 360°] on the longitudinal center side, i.e., the area ratio is 33.3%. In this configuration, the outer diameter D2 of the longitudinal end portion of the cleaning roller 80 is 3.0 mm, which is equivalent to the outer diameter D1 of the longitudinal center portion of the cleaning roller 80.

[0096] In the second embodiment, the upper and lower limits of the area ratio of the longitudinal end of the cleaning roller 80 that are effective are 1.33 to 2.0 times, similar to the first embodiment. This is because, in the first embodiment, the outer diameter of the charging roller 2 and the outer circumferential length of the cleaning roller 8 are in a proportional relationship. In other words, just as the cleaning ability is improved by increasing the contact distance of the cleaning roller 8 with the charging roller 2, in the second embodiment, increasing the density of the cleaning roller 80 is equivalent to increasing the number of contacts of the non-porous parts in the sponge structure. Therefore, the second embodiment can obtain the same effect as the first embodiment.

[0097] [Third embodiment] In the configuration of the third embodiment, the description of the same parts as those of the first embodiment will be omitted. In the third embodiment, the positional relationship in the longitudinal direction is the same as that in the first embodiment, and the density of the cleaning roller 8 at the longitudinal end portion is higher than that at the center portion.

[0098] Specifically, in the third embodiment, the density of the central portion in the longitudinal direction of the cleaning roller 8 is 0.2 [g / cm^3], whereas the density is 1.33 to 2.0 times that, that is, 0.27 to 0.40 [g / cm^3].

[0099] In the third embodiment, the upper and lower limits of the density at the longitudinal end of the cleaning roller 8 that are effective are 1.33 to 2.0 times, similar to the first embodiment. This is because, in the first embodiment, the outer diameter of the charging roller 2 and the outer circumferential length of the cleaning roller 8 are in a proportional relationship. In other words, just as the cleaning ability is improved by increasing the contact distance of the cleaning roller 8 with the charging roller 2, in the third embodiment, increasing the density of the cleaning roller 8 is equivalent to increasing the number of contacts of the non-porous parts in the sponge structure. Therefore, the third embodiment can obtain the same effect as the first embodiment.

[0100] [Fourth embodiment] In the configuration of the fourth embodiment, the description of the same parts as those of the first embodiment will be omitted. In the fourth embodiment, the positional relationship in the longitudinal direction is the same as that in the first embodiment, and the outer diameter of the end portion in the longitudinal direction of the cleaning roller 8 is larger than the outer diameter of the central portion, as in the first embodiment.

[0101] However, in the configuration of the fourth embodiment, the part with the outer diameter D1 in the center of the cleaning roller 8 in the longitudinal direction continues to the end, and the outer diameter D2 of the end of the cleaning roller 8 in the longitudinal direction is realized by fitting a hollow sponge with an inner diameter of D2 that is equal to or smaller than D1 to the end of the cleaning roller 8. In the fourth embodiment, the sponge is fixed in the longitudinal direction by adhesive. Alternatively, the sponge may be fitted with an inner diameter smaller than D1 so that no shift occurs in the longitudinal direction. Therefore, the fourth embodiment can obtain the same effect as the first embodiment.

[0102] (Other embodiments) The present invention is not limited to the above-described embodiments, and various modifications (including organic combinations of the respective embodiments) are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0103] In the above embodiment, as shown in Fig. 1, the image forming apparatus 100 is configured to use the intermediate transfer belt 90, but the present invention is not limited to this. It is also possible to apply the present invention to an image forming apparatus configured to directly contact the recording material 13 with the photosensitive drum 1 in sequence to perform transfer. [Explanation of symbols]

[0104] 1 Photosensitive drum 2. Charge roller 4. Developing device 7 Cleaning Blade 8 Cleaning roller 90 Intermediate transfer belt 100 Image forming device

Claims

1. an image carrier on which an electrostatic latent image is formed; a developing device including a developing container that contains a developer and a developing roller that carries the developer in order to develop an electrostatic latent image formed on the image carrier; a transfer member onto which a toner image formed on the image carrier is transferred; a cleaning blade having an elastic portion and a support portion to which the elastic portion is fixed and which supports the elastic portion, the cleaning blade scraping off residual developer on the image carrier after the toner image is transferred to the transfer member; a charging roller that contacts the image carrier and charges the image carrier; a cleaning roller that comes into contact with the charging roller and cleans the surface of the charging roller; Equipped with a length from a fixing surface between the elastic portion and the support portion to a free end of the elastic portion at an end portion in a longitudinal direction of the cleaning blade is longer than a length from a fixing surface between the elastic portion and the support portion to a free end of the elastic portion at a central portion in a longitudinal direction of the cleaning blade, a longitudinal length of the charging roller is longer than a longitudinal length of a developer coating area of ​​the developing roller where the developer is coated, The length of the cleaning roller in the longitudinal direction is longer than the length of the charging roller in the longitudinal direction, an elastic layer is provided on a portion of the cleaning roller that contacts the charging roller, In a portion of the cleaning roller where the elastic layer is provided, the outer diameter of the cleaning roller at the end portion in the longitudinal direction of the cleaning roller is larger than the outer diameter of the cleaning roller at the central portion in the longitudinal direction of the cleaning roller.

1. An image forming apparatus comprising:

2. The elastic layer is provided in a spiral shape on the rotation shaft of the cleaning roller, In a portion where the elastic layer is provided on the cleaning roller, the number of turns of the spiral elastic layer at the end portions in the longitudinal direction of the cleaning roller is greater than the number of turns of the spiral elastic layer at the central portion in the longitudinal direction of the cleaning roller.

2. The image forming apparatus according to claim 1,

3. In the portion where the elastic layer is provided on the cleaning roller, the density of the elastic layer at the end portions in the longitudinal direction of the cleaning roller is greater than the density of the elastic layer at the central portion in the longitudinal direction of the cleaning roller.

2. The image forming apparatus according to claim 1,

Images