Image carrier unit and image forming apparatus equipped therewith

Abstract

The present invention provides an image carrier unit and an image forming apparatus equipped therewith that can suppress damage to the edge portion of the cleaning blade and eliminate cleaning defects, even when the contact pressure of the cleaning blade fluctuates due to material tolerances or durable printing. [Solution] The image carrier unit comprises an image carrier and a cleaning device. The cleaning device has a cleaning blade made of a rectangular parallelepiped elastic material that makes line contact with the outer surface of the image carrier at a predetermined pressure to scrape off residual toner on the image carrier, and a support member to which the cleaning blade is fixed in a state that it protrudes upstream in the rotational direction of the image carrier. When the free length which is the protrusion length of the cleaning blade from the support member is L [mm], the thickness of the cleaning blade is t [mm], and the contact pressure of the cleaning blade against the image carrier is W [gf / cm], the following conditions are satisfied: 7.5 * (L / t) - 23.9 ≤ W ≤ 24 and 12 ≤ W.

Description

Technical Field

[0001] The present invention relates to a charging device used in an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine using an electrophotographic method, and an image forming apparatus including the same. In particular, the present invention relates to an image carrier unit including an image carrier and a cleaning device including a cleaning blade for removing residual toner on the image carrier, and an image forming apparatus including the same.

Background Art

[0002] In a conventional image forming apparatus, a powder developer is mainly used. An electrostatic latent image formed on an image carrier such as a photosensitive drum is visualized with toner in the developer, and after the visible image (toner image) is transferred onto a recording medium, a fixing process is generally performed. Toner remaining on the surface of the photosensitive drum is removed by a cleaning device including a cleaning blade pressed against the photosensitive drum, and a new toner image is formed.

[0003] In recent years, toner having a small particle size and high sphericity has been used, and the adhesion force of the toner to the photosensitive drum has increased. Therefore, in order to effectively remove the toner remaining on the surface of the photosensitive drum, it is necessary to increase the contact pressure of the cleaning blade. On the other hand, when the contact pressure of the cleaning blade is increased, the slipperiness of the surface of the photosensitive drum, particularly the slipperiness with respect to the cleaning blade, decreases. As a result, the cleaning blade is likely to make a rattling sound, curl, or the edge portion is likely to be damaged.

[0004] In addition, when toner having a small particle size and high sphericity is used, cleaning failure is likely to occur due to the toner and toner external additives attached to the surface of the photosensitive drum passing through the edge portion of the cleaning blade. Furthermore, when the edge portion of the cleaning blade is worn or damaged due to repeated use, cleaning failure is likely to occur.

[0005] Therefore, methods have been proposed to stabilize the cleaning performance of cleaning blades. For example, Patent Documents 1 and 2 disclose a cleaning member that suppresses noise, curling, and edge damage of the cleaning blade, while maintaining stable cleaning performance, by defining the relationship between the thickness and free length (protrusion length) of the cleaning blade. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2005-164774 [Patent Document 2] Japanese Patent Publication No. 2006-259402 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, even if the relationship between the thickness and free length of the cleaning blade is defined as in Patent Documents 1 and 2, cleaning failures can still occur depending on the setting of the contact pressure against the photoreceptor drum. Furthermore, the setting of these conditions does not take into account the material tolerances of the cleaning blade or the fluctuations in contact pressure during durable printing, making the design difficult.

[0008] In view of the above problems, the present invention aims to provide an image carrier unit and an image forming apparatus equipped therewith that can suppress damage to the edge portion of the cleaning blade and eliminate cleaning defects even when the contact pressure of the cleaning blade fluctuates due to material tolerances or durable printing. [Means for solving the problem]

[0009] To achieve the above objective, the first configuration of the present invention is an image carrier unit comprising an image carrier and a cleaning device. The image carrier is rotatable and has a toner image formed on its outer surface. The cleaning device has a cleaning blade made of a rectangular parallelepiped elastic material that makes line contact with the outer surface of the image carrier at a predetermined pressure to scrape off residual toner on the image carrier, and a support member to which the cleaning blade is fixed in a state that protrudes upstream in the rotational direction of the image carrier. When the free length of the cleaning blade, which is the length that protrudes from the support member, is L [mm], the thickness of the cleaning blade is t [mm], and the contact pressure of the cleaning blade against the image carrier is W [gf / cm], the following equations (1) and (2) are satisfied. 7.5*(L / t)-23.9≦W≦24 (1) 12 ≤ W ···(2)

[0010] According to the first configuration of the present invention, the amplitude due to the stick-slip motion of the cleaning blade can be reduced, and the dynamic linear pressure can be maintained above a certain level. As a result, the passage of external additive aggregates at the edge of the cleaning blade can be reduced, and damage to the edge can be suppressed. [Brief explanation of the drawing]

[0011] [Figure 1] A schematic cross-sectional view showing the overall configuration of the image forming apparatus 1 equipped with the drum unit 50 of the present invention. [Figure 2] Side cross-sectional view showing the configuration of a drum unit 50 and the vicinity of a toner transport device 60 connected thereto according to one embodiment of the present invention. [Figure 3] Perspective view of the cleaning blade 53 and support member 55 used in the drum unit 50 of this embodiment. [Figure 4] Enlarged perspective view of the area around the end of the cleaning blade 53 and support member 55 in Figure 3. [Figure 5] Enlarged view of the contact area between the cleaning blade 53 and the photoreceptor drums 1a-1d in Figure 2. [Figure 6]Conceptual diagram illustrating the damage to the edge portion 53a of the cleaning blade 53. [Figure 7] Conceptual diagram showing the fluctuation of the dynamic linear pressure of the cleaning blade 53 when the photoreceptor drums 1a to 1d are rotated. [Figure 8] Graph showing the designable range of the cleaning blade 53 used in the drum units 50a to 50d of this embodiment. [Figure 9] Graph showing the relationship between the allowable range and tolerance range of contact pressure variation of the cleaning blade 53. [Figure 10] The graph shows the relationship between L / t and contact pressure W for the drum unit 40a in the embodiment, as well as the evaluation results of noise and curling of the cleaning blade 53, damage to the edge portion 53a, and poor cleaning. [Modes for carrying out the invention]

[0012] [1. Configuration of the image forming apparatus] Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a schematic cross-sectional view showing the internal structure of an image forming apparatus 100 equipped with drum units 50a to 50d according to one embodiment of the present invention. The image forming apparatus 100 shown in Figure 1 is a so-called tandem color printer.

[0013] Inside the main body 7 of the image forming apparatus 100, image forming sections Pa to Pd are arranged horizontally. Each image forming section Pa to Pd sequentially forms yellow, magenta, cyan, and black images through the processes of charging, exposure, development, and transfer, respectively. Each image forming section Pa to Pd is provided to correspond to the image of each color. Below, only the image forming section Pa will be described, but the image forming sections Pb to Pd have basically the same configuration and will therefore not be described.

[0014] The image forming unit Pa is provided with a photosensitive drum 1a that carries a visible image (toner image). Above the image forming unit Pa, an exposure device 5 is arranged. The exposure device 5 emits a light beam toward the surfaces of the photosensitive drums 1a to 1d to draw an electrostatic latent image. Around the photosensitive drum 1a, a charging device 2a, a developing device 3a, and a cleaning device 23a are arranged along the drum rotation direction (clockwise direction in FIG. 1). A unit composed of the photosensitive drums 1a to 1d, the charging devices 2a to 2d, and the cleaning devices 23a to 23d is hereinafter referred to as drum units 50a to 50d (see FIG. 2).

[0015] The charging device 2a is arranged to face the photosensitive drum 1a and can charge the surface of the photosensitive drum 1a. The developing device 3a includes a developing container 4a, a developing roller 21a, and a supply roller 24a. The developing container 4a is filled with a predetermined amount of toner. The toner filled in the developing containers 4a to 4d is either yellow, magenta, cyan, or black for each of the developing devices 3a to 3d. The developing roller 21a is arranged to face the photosensitive drum 1a. The supply roller 24a supplies the toner in the developing container 4a to the outer peripheral surface of the developing roller 21a. The developing roller 21a can supply the toner supplied to its outer peripheral surface to the photosensitive drum 1a.

[0016] Below the photosensitive drums 1a to 1d, an intermediate transfer unit 31 is provided. The intermediate transfer unit 31 includes a frame 30, a driving roller 10, a tension roller 11, an intermediate transfer belt 8, and primary transfer rollers 6a to 6d. The driving roller 10 and the tension roller 11 are rotatably supported at both ends in the longitudinal direction of the frame 30.

[0017] The intermediate transfer belt 8 is an endless belt (preferably a seamless belt without joints). The intermediate transfer belt 8 is wound around the drive roller 10 from the tension roller 11 so as to be rotatable in the circumferential direction. When the drive roller 10 rotates by the rotational driving force of a belt drive motor (not shown), the rotational driving force is transmitted to the intermediate transfer belt 8 by frictional force. Thereby, the intermediate transfer belt 8 rotates in the same direction as the rotational direction of the drive roller 10. The primary transfer rollers 6a to 6d are rotatably and movably supported by the frame 30 at positions facing the photosensitive drums 1a to 1d with the intermediate transfer belt 8 interposed therebetween.

[0018] The secondary transfer roller 9 is provided so as to face the drive roller 10 with the intermediate transfer belt 8 interposed therebetween. The secondary transfer roller 9 is pressed against the intermediate transfer belt 8 to form a secondary transfer nip N. The secondary transfer roller 9 secondarily transfers the toner image formed on the intermediate transfer belt 8 onto the sheets S1 and S2 passing through the secondary transfer nip N.

[0019] Inside the image forming apparatus 100, at positions on the sides of the image forming units Pa to Pd and the intermediate transfer belt 8, there are arranged a sheet conveyance path 20, a registration roller pair 12, a sheet cassette 16, a sheet feeding unit 25, and a manual paper feeding unit 26.

[0020] The sheet conveyance path 20 is configured to include a main conveyance path 28 and a duplex conveyance path 18. The main conveyance path 28 extends in the vertical direction. At an intermediate position of the main conveyance path 28, the registration roller pair 12, the secondary transfer roller 9, and the fixing device 13 are arranged. The main conveyance path 28 conveys the sheet S1 or the sheet S2 so as to pass through the manual paper feeding unit 26 and the sheet cassette 16 described later in this order: the registration roller pair 12, the secondary transfer nip N, and the fixing device 13.

[0021] The registration roller pair 12 aligns the conveyance directions of the sheets S1 and S2 so that the leading ends (the downstream ends with respect to the sheet conveyance direction) of the sheets S1 and S2 are orthogonal to the sheet conveyance direction, and corrects skew conveyance.

[0022] A sheet discharge port 15 leading to the outside of the image forming apparatus 100 is provided at the downstream end of the main transport path 28 in the direction of sheet transport. A pair of discharge rollers 22 is provided at the sheet discharge port 15.

[0023] A branching section 14 is provided between the discharge roller pair 22 and the fixing device 13 in the sheet conveying direction. The double-sided conveying path 18 branches off from the main conveying path 28 at a position that coincides with the branching section 14 of the main conveying path 28 in the sheet conveying direction, and rejoins the main conveying path 28 upstream of the resist roller pair 12. The branching section 14 can distribute the sheets S1 and S2 that have passed through the fixing device 13 to the sheet discharge port 15 or the double-sided conveying path 18.

[0024] The sheet cassette 16 and the manual feed unit 26 are located upstream of the main transport path 28 with respect to the sheet transport direction. Sheet S1 can be loaded into the sheet cassette 16, and sheet S2 can be loaded into the manual feed unit 26. The sheet feeding unit 25 is positioned between the main transport path 28 and the sheet cassette 16 and manual feed unit 26, and feeds sheets S1 and S2 to the main transport path 28.

[0025] The sheet cassette 16 is detachable from the main unit 7 of the device. Specifically, it can be pulled out from the main unit 7 of the device when it is inserted to the deepest part of the cassette housing in the horizontal direction (attached state).

[0026] The manual feed section 26 is mounted on the side of the main body 7, between the loading entrance 38 and the opening edge of the cassette storage section 29 in the vertical direction. The manual feed section 26 can feed sheets S2 (sheets used as recording media, including special-sized paper, cardboard, envelopes, OHP sheets, etc.) onto its upper surface. The loading entrance 38 is provided with a loading roller pair 40 and a sheet feeding roller 41. The sheet feeding roller 41 and the loading roller pair 40 rotate to load the sheets S2 into the manual feed path 39. The sheets S2 loaded into the manual feed path 39 are then transported toward the pickup roller 42 by a transport roller pair 47.

[0027] The sheet feeding unit 25 includes a pickup roller 42 and a pair of feeding rollers 43. The pickup roller 42 rotates in contact with the upper surface of the sheet S1 loaded on the sheet stacking plate 37 in the sheet cassette 16 and the sheet S2 that is fed from the manual feed unit 26 into the manual feed path 39. As a result, the sheets S1 and S2 are fed in the feeding direction and handed over to the pair of feeding rollers 43.

[0028] An operation panel 101 is located at the front of the image forming apparatus 100. The operation panel 101 is an operating unit for receiving various setting inputs. A control unit 102 is located inside the image forming apparatus 100. The control unit 102 oversees the operation of the entire image forming apparatus 100 and controls each part of the image forming apparatus 100.

[0029] Next, the image formation procedure in the image forming apparatus 100 will be described. When the user inputs the start of image formation, first, the photoreceptor drum 1a is rotated while the charging devices 2a to 2d uniformly charge the surfaces of the photoreceptor drums 1a to 1d. Then, the exposure device 5 irradiates the surfaces of the photoreceptor drums 1a to 1d with light, forming an electrostatic latent image on the photoreceptor drums 1a to 1d corresponding to the image signal.

[0030] Then, the toner in the developer of the developing devices 3a to 3d is supplied onto the photoreceptor drums 1a to 1d by the developing rollers 21a to 21d and adheres to them electrostatically. As a result, a toner image corresponding to the electrostatic latent image is formed on the photoreceptor drums 1a to 1d.

[0031] In this state, the drive roller 10 is rotated to start the counterclockwise rotation of the intermediate transfer belt 8. Then, the toner images of each color formed on the photoreceptor drums 1a to 1d are sequentially transferred onto the intermediate transfer belt 8. After the primary transfer is complete, any toner remaining on the photoreceptor drums 1a to 1d is removed by the cleaning devices 23a to 23d in preparation for the formation of a new electrostatic latent image. In addition, any residual charge remaining on the photoreceptor drums 1a to 1d is removed by a static eliminator (not shown).

[0032] Subsequently, at a predetermined timing, sheets S1 and S2 are fed from the sheet cassette 16 or manual feed section 26 to the main transport path 28, pass through the registration roller pair 12, and are then transported to the secondary transfer nip N. At this point, the toner image on the intermediate transfer belt 8 is secondarily transferred to sheets S1 and S2. Then, sheets S1 and S2 are transported to the fuser unit 13, where they are heated and pressurized by the fuser roller pair 13a of the fuser unit 13, fixing the toner image to the surface of sheets S1 and S2.

[0033] When printing on one side of sheets S1 and S2, the branching section 14 distributes sheets S1 and S2 that have passed through the fuser 13 to the sheet discharge port 15. Sheets S1 and S2 that reach the sheet discharge port 15 are discharged onto the sheet discharge tray 17 by the discharge roller pair 22.

[0034] When performing double-sided printing on sheets S1 and S2, the branching unit 14 distributes sheets S1 and S2, which have passed through the fuser unit 13, to the double-sided transport path 18. The double-sided transport path 18 then transports sheets S1 and S2 again to the registration roller pair 12, while reversing their front and back sides. Sheets S1 and S2 then pass through the secondary transfer nip N and fuser unit 13 again, and after the toner image is fixed to the back side, they are distributed to the sheet discharge port 15 by the branching unit 14.

[0035] [2. Configuration of the drum unit and toner transport device] Figure 2 is a cross-sectional view of the main components of a drum unit 50a and the toner transport device 60 connected thereto, according to one embodiment of the present invention. The cleaning device 23a includes a friction roller 51 that makes linear contact with the photoreceptor drums 1a to 1d in the longitudinal direction, a cleaning blade 53, and a recovery screw 57. The drum units 50b to 50d have a similar configuration, so their description is omitted.

[0036] The friction roller 51 is pressed against the photoreceptor drum 1a at a predetermined pressure by a coil spring (not shown), and rotates in the same direction (forward rotation) at the contact surface with the photoreceptor drum 1a by a driving means (not shown). The peripheral speed of the friction roller 51 is controlled to be faster than the peripheral speed of the photoreceptor drum 1a (here, 1.2 times). An example of the friction roller 51 is a structure in which a foam layer made of EPDM rubber with an Asker C hardness of 55° is formed as a roller body around a metal shaft. The material of the roller body is not limited to EPDM rubber, but may be other rubber materials or foamed rubber materials, and those with an Asker C hardness in the range of 10 to 90° are preferably used.

[0037] The cleaning blade 53 makes line contact with the photoreceptor drum 1a on the surface of the photoreceptor drum 1a, downstream in the rotational direction from the contact surface with the friction roller 51. The cleaning blade 53 is supported by a support member 55 fixed within the housing of the cleaning device 23a. For example, the cleaning blade 53 is made of polyurethane rubber with a JIS hardness of 78° and is mounted at a predetermined angle with respect to the tangential direction of the photoreceptor drum 1a at the contact point on the surface of the photoreceptor drum 1a. The material, hardness, dimensions, and amount of penetration into the photoreceptor drum 1a of the cleaning blade 53 are appropriately set according to the specifications of the photoreceptor drum 1a.

[0038] Residual toner scraped off the surface of the photoreceptor drum 1a by the scraping roller 51 or cleaning blade 53 falls due to gravity and gradually accumulates inside the housing of the cleaning device 23a. Then, as the recovery screw 57 rotates, the toner inside the housing is sequentially transported in the longitudinal direction of the housing (the direction perpendicular to the plane of the paper in Figure 2) and discharged to the outside of the cleaning device 23a from the toner discharge section 59 provided at one end of the bottom surface of the housing.

[0039] The toner transport device 60 comprises a toner transport pipe 61 and a transport screw 65. Toner inlet 62 and toner outlet 63 are formed at both ends of the toner transport pipe 61. The toner inlet 62 is connected to the toner outlet 25 of the cleaning device 23a, and the toner outlet 63 is connected to the waste toner bottle 37. The transport screw 65 consists of a transport blade (spiral blade) 65a and a rotating shaft 65b passing through its center, and is rotatably supported within the toner transport pipe 61. One end of the rotating shaft 65b extends outside the toner transport pipe 61, and a drive input gear 69 is attached to its tip. The drive input gear 69 is connected to a drive motor (not shown), and the transport screw 65 is rotated at a predetermined speed. Toner transported from the cleaning device 23a through the toner inlet 62 into the toner transport pipe 61 is sequentially transported through the toner transport pipe 61 in the direction of arrow B by a transport screw 65 that rotates in the direction of arrow A in Figure 2, and is stored in the waste toner bottle 37 through the toner discharge port 63.

[0040] Figure 3 is a perspective view of the cleaning blade 53 and support member 55 used in the drum units 50a to 50d of this embodiment, and Figure 4 is an enlarged perspective view of the area around the ends of the cleaning blade 53 and support member 55 (within the dashed circle S in Figure 3).

[0041] The support member 55 is formed by bending a sheet metal such as stainless steel into an L-shape when viewed from the side, and has sufficient rigidity. The cleaning blade 53 is adhesively fixed along the outside of one side of the L-shape of the support member 55 (the bottom side in Figure 3). In other words, the contact surface between the support member 55 and the cleaning blade 53 becomes the adhesive region R (see Figure 4).

[0042] As shown in Figure 4, the cleaning blade 53 is adhesively fixed to the support member 55 so that its tip protrudes from it. The edge portion 53a of the tip of the cleaning blade 53, on the side furthest from the support member 55, contacts the surfaces of the photoreceptor drums 1a to 1d.

[0043] Furthermore, the direction of one side of the cleaning blade 53 parallel to the rotation axis of the photoreceptor drums 1a to 1d (the X direction in Figure 4) is defined as the longitudinal direction of the cleaning blade 53, and the direction of one side of the cleaning blade 53 perpendicular to the longitudinal direction and extending in the direction of movement of the outer peripheral surface of the photoreceptor drums 1a to 1d (the Y direction in Figure 4) is defined as the width direction of the cleaning blade 53, and the direction of one side of the cleaning blade 53 perpendicular to the longitudinal direction and the width direction (the Z direction in Figure 4) is defined as the thickness direction of the cleaning blade 53.

[0044] Figure 5 is an enlarged view of the contact area between the cleaning blade 53 and the photoreceptor drums 1a to 1d in Figure 2. As shown in Figure 5, the cleaning blade 53 has its tip facing upstream with respect to the rotational direction of the photoreceptor drums 1a to 1d (clockwise direction in Figure 5), and its edge portion 53a is in contact with the surface of the photoreceptor drums 1a to 1d.

[0045] In this embodiment, when the free length (protrusion length from the support member 55) of the cleaning blade 53 is L [mm], its thickness is t [mm], and the contact pressure of the cleaning blade 53 against the photoreceptor drums 1a to 1d is W [gf / cm], the following equations (1) and (2) are satisfied. Here, the contact pressure W of the cleaning blade 53 is the pressure force directed toward the center of rotation of the photoreceptor drums 1a to 1d along a straight line O passing through the center of rotation of the photoreceptor drums 1a to 1d and the edge portion 53a. 7.5*(L / t)-23.9≦W≦24 (1) 12 ≤ W ···(2)

[0046] By designing the cleaning blade to satisfy equations (1) and (2) above, it is possible to suppress damage to the edge portion 53a of the cleaning blade, thereby eliminating cleaning failures caused by toner and external additives seeping through, and the resulting image defects. The reason why damage to the edge portion 53a of the cleaning blade 53 is suppressed will be explained below in this embodiment.

[0047] Figure 6 is a conceptual diagram illustrating the defects in the edge portion 53a of the cleaning blade 53. As shown in Figure 6, most of the defects D in the edge portion 53a of the cleaning blade 53 are thought to be caused by the stress generated when external additive aggregates G attached to the surface of the photoreceptor drums 1a to 1d pass through the edge portion 53a. In other words, in order to suppress defects in the edge portion 53a, it is necessary to reduce the amount of external additive aggregates G that remain on the edge portion 53a, or to suppress the passage of external additive aggregates G by suppressing the local decrease in the dynamic linear pressure F of the cleaning blade 53.

[0048] The amount of external additive aggregates G that remain at the edge portion 53a varies greatly depending on the operating conditions and system of the image forming apparatus 1. For example, in areas with a small amount of printing, the amount of residual toner on the surface of the photoreceptor drums 1a to 1d is small, so the replacement of external additives at the edge portion 53a is reduced, and external additive aggregates G are more likely to form.

[0049] Furthermore, when the intermediate transfer belt 8 (see Figure 1) is a resin belt, the external additive recovery capacity from the surface of the photoreceptor drums 1a to 1d is lower compared to when the intermediate transfer belt 8 is an elastic belt, and the amount of external additive aggregates G that remain at the edge portion 53a tends to be larger. In addition, the amount of external additive aggregates G also changes depending on the amount and type of toner external additive added. Considering that these factors are necessary to ensure each function in the image forming operation, it is considered effective to suppress the local decrease in the dynamic linear pressure F of the cleaning blade 53.

[0050] Next, a means for suppressing the localized decrease in the dynamic linear pressure F of the cleaning blade 53 will be described. Figure 7 is a conceptual diagram showing the fluctuation of the dynamic linear pressure of the cleaning blade 53 when the photoreceptor drums 1a to 1d are rotated. As shown by the solid line A in Figure 7, when the photoreceptor drums 1a to 1d are rotated, the dynamic linear pressure of the cleaning blade 53 relative to the photoreceptor drums 1a to 1d fluctuates with a constant period of time due to the stick-slip motion of the cleaning blade 53. During this fluctuation, when the dynamic linear pressure falls below a certain pressure, the external additive aggregates G slip through.

[0051] In order to prevent the dynamic linear pressure from falling below a certain pressure, it is effective to increase the contact pressure W of the cleaning blade 53 with respect to the photoreceptor drums 1a to 1d (dashed line B in Figure 7), or to reduce the amplitude due to stick-slip motion (dashed line C in Figure 7). As shown in equation (a) below, the amplitude A [gf / cm] due to stick-slip motion is proportional to the cube of the ratio of the free length L to the thickness t of the cleaning blade 53 (L / t). A∝W(L / t) 3 ...(a)

[0052] In other words, by increasing the contact pressure W or decreasing L / t, the amplitude A due to stick-slip motion can be reduced, and the dynamic linear pressure can be maintained above a certain level. As a result, the slippage of external additive aggregates G at the edge portion 53a can be reduced, and damage to the edge portion 53a can be suppressed.

[0053] Furthermore, the relationship shown in equation (a) is determined solely by the free length L [mm], thickness t [mm], and contact pressure W [gf / cm] of the cleaning blade 53, regardless of the rebound elasticity [%], hardness [°], and Young's modulus [MPa] of the cleaning blade 53. In other words, by designing to satisfy equations (1) and (2), chipping of the edge portion 53a can be suppressed regardless of the material of the cleaning blade 53. However, the cleaning blade 53 must be made of an elastic material.

[0054] Figure 8 is a graph showing the designable range of the cleaning blade 53 used in the drum units 50a to 50d of this embodiment. As shown in Figure 8, it has been confirmed that the smaller L / t is, the less damage occurs to the edge portion 53a even in the region where the contact pressure W is small (the region above the straight line y = 7.5x - 23.9 in Figure 8). On the other hand, if the contact pressure W is higher than 24 [gf / cm], the wear of the photosensitive layer of the photosensitive drums 1a to 1d is accelerated, shortening the lifespan (service life) of the drum unit 40. In addition, the increased frictional force with the photosensitive drums 1a to 1d can cause squeaking and curling of the cleaning blade 53.

[0055] Furthermore, if the contact pressure W is lower than 12 [gf / cm], problems such as poor cleaning due to the external additive passing through and the occurrence of dash marks may occur. Therefore, as shown in Figure 8, it is preferable to set the blade contact pressure W of the cleaning blade 53 to a range OW (operation window, hatched area in Figure 8) that satisfies 7.5*(L / t)-23.9≦W≦24 and 12≦W. In addition, the above-mentioned range of contact pressure W must be maintained through the material tolerances of the cleaning blade 53 and through durable printing.

[0056] Figure 9 is a graph showing the relationship between the allowable range and tolerance range of contact pressure fluctuation of the cleaning blade 53. In Figure 9, the allowable range of contact pressure fluctuation is shown by a dashed line, and the tolerance range is shown by a solid line. The allowable range is calculated from OW shown in Figure 8. More specifically, when L / t is 4.8 or less, the upper limit of the contact pressure W is 24 [gf / cm] and the lower limit is 12 [gf / cm], so the allowable range of contact pressure fluctuation is 12 [gf / cm]. When L / t is 4.8 or more, the lower limit of the contact pressure W increases along the line y = 7.5x - 23.9, so the allowable range of contact pressure fluctuation gradually narrows from 12 [gf / cm].

[0057] The tolerance range was calculated by performing durable printing while keeping the distance between the cleaning blade 53 and the photoreceptor drums 1a to 1d constant (using a constant displacement method), taking into account the material tolerance of the cleaning blade 53 and the amount of wear on the cleaning blade 53 during durable printing.

[0058] As shown in Figure 9, the larger L / t is, the narrower the allowable range of contact pressure that can be designed, and the smaller L / t is, the more strongly it is affected by tolerances, making design difficult. Therefore, it is necessary to set L / t within an appropriate range, and it is desirable to set it within the range that satisfies equation (3) as shown in Figure 9 (hatched area in Figure 9). 4.5 ≤ L / t ≤ 5.3 ···(3)

[0059] Furthermore, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. For example, although the above embodiments described cleaning devices 23a to 23d equipped with a friction roller 51 and a cleaning blade 53, the present invention can also be applied to cleaning devices 23a to 23d equipped with, for example, only a cleaning blade 53.

[0060] Furthermore, although the above embodiment described an intermediate transfer type image forming apparatus 100 that first transfers the toner images formed on the photoreceptor drums 1a to 1d to an intermediate transfer belt 8, the same method is applicable to a direct transfer type image forming apparatus that directly transfers the toner images formed on the photoreceptor drum to a recording medium. The effects of the present invention will be described in more detail below with reference to examples. [Examples]

[0061] The effectiveness of varying the free length L, thickness t, and contact pressure W with respect to the photoreceptor drums 1a-1d of the cleaning blade 53 in suppressing noise, curling, edge damage 22a, and cleaning defects of the cleaning blade 53 was investigated. As the test machine, an image forming apparatus 100 (a modified ECOSYS PA2100 manufactured by Kyocera Document Solutions Corporation) as shown in Figure 1 was used, with a system linear velocity of 165 mm / sec.

[0062] The photoreceptor drums 1a to 1d were 30 mm in diameter, positively charged single-layer OPC (organic photosensitive layer) drums, with a photosensitive layer thickness of 30 μm. The charging roller 21 was made of epichlorohydrin rubber with a diameter of 9.5 mm and a thickness of 1.75 mm, and a constant DC voltage was applied as the charging voltage. The developing devices 3a to 3d used a two-component developing method with a two-component developer containing toner and a magnetic carrier. The intermediate transfer belt 8 was a resin belt.

[0063] The cleaning blade 53 was made of urethane rubber with a JIS-A hardness of 72°, a rebound elasticity of 24% at 25°C, and a Young's modulus of 7.1 MPa. Drum units 50a to 50d were fabricated by varying the thickness t=1.6 to 2.0 mm, free length L=8 to 11 mm, and contact pressure W=11 to 25 [gf / cm] of the cleaning blade 53. Furthermore, when image output was performed using each drum unit 50a, the noise or curling of the cleaning blade 53, damage to the edge portion 53a, and cleaning failures were evaluated.

[0064] Figure 10 shows the relationship between L / t and contact pressure W for the fabricated drum units 50a to 50d, as well as the evaluation results for noise and curling of the cleaning blade 53, damage to the edge portion 53a, and cleaning failure. In Figure 10, L / t is plotted on the horizontal axis and the contact pressure W [gf / cm] of the cleaning blade 53 is plotted on the vertical axis, showing the contact pressure W as L / t is varied.

[0065] Furthermore, a circle (○) indicates that no squeaking or peeling of the cleaning blade 53, no damage to the edge portion 53a, or cleaning failure occurred; an asterisk (*) indicates that squeaking or peeling of the cleaning blade 53 occurred; a cross (×) indicates that vertical streaks occurred in the half-image due to damage to the edge portion 53a; and a plus (+) indicates that a hazy image occurred due to toner leakage.

[0066] As is clear from Figure 10, in regions where the contact pressure W is 24 [gf / cm] or higher, noise or peeling of the cleaning blade occurred (plot in Figure 10 *). Also, in regions where the contact pressure W is 7.5*(L / t)-23.9 [gf / cm] or lower, vertical streaks in the half-image occurred due to edge loss (plot in Figure 10 ×). Furthermore, even when the contact pressure W is 7.5*(L / t)-23.9 [gf / cm] or higher, in regions where the contact pressure W is 12 [gf / cm] or lower, a fogging image occurred due to toner leakage (plot in Figure 10 +).

[0067] On the other hand, in the region where the contact pressure W is 12 ≤ W and 7.5*(L / t)-23.9 ≤ W ≤ 24 [gf / cm] (hatched region in Figure 10), none of the following occurred: squeaking or curling of the cleaning blade 53, vertical streaks in the half-image due to defects in the edge portion 53a, or fogging due to toner leakage.

[0068] Based on the above results, it was confirmed that drum units 50a to 50d that satisfy equations (1) and (2) can be expected to prevent squeaking and curling of the cleaning blade 53, damage to the edge portion 53a, and cleaning failures. [Industrial applicability]

[0069] The present invention can be used in an image carrier unit that integrates an image carrier and a cleaning device equipped with a cleaning blade for removing residual toner from the image carrier. By using the present invention, it is possible to provide an image carrier unit and an image forming apparatus equipped therewith that can suppress edge damage of the cleaning blade and eliminate cleaning defects even when the contact pressure of the cleaning blade fluctuates due to material tolerances or durable printing. [Explanation of Symbols]

[0070] 1a~1d Photoreceptor drum (image carrier) 2a~2d Charging device 3a~3d developing device 5. Exposure apparatus 8. Intermediate transfer belt 23a~23d Cleaning device 50a~50d Drum unit (image carrier unit) 53 Cleaning Blade 55 Support member 53a Edge section 60 Toner transport device 100 Image forming apparatus Pa~Pd Image Forming Unit

Claims

1. A rotatable image carrier on which a toner image is formed on its outer surface, A cleaning blade, formed of a rectangular parallelepiped-shaped elastic material, makes line contact with the outer surface of the image carrier at a predetermined pressure and scrapes off residual toner on the image carrier, A support member to which the cleaning blade is fixed in a state protruding upstream in the rotational direction of the image carrier, A cleaning device having, In an image carrier unit equipped with, An image carrier unit characterized in that, when the free length of the cleaning blade, which is the length of the cleaning blade protruding from the support member, is L [mm], the thickness of the cleaning blade is t [mm], and the contact pressure of the cleaning blade against the image carrier is W [gf / cm], the unit satisfies the following equations (1) and (2). 7.5*(L / t)-23.9≦W≦24...(1) 12 ≤ W ... (2)

2. The image carrier unit according to claim 1, characterized in that the ratio L / t of the free length L [mm] to the thickness t [mm] satisfies the following formula (3). 4.5 ≤ L / t ≤ 5.3 ... (3)

3. An image forming apparatus comprising the image carrier unit according to claim 1 or claim 2.

Images