Transfer belt unit and image forming apparatus

Abstract

To reduce the likelihood of occurrence of turn-up at a leading end of a cleaning blade.SOLUTION: A transfer belt unit (30) has: an endless transfer belt (34) that is movable in a predetermined direction of movement (V); a cleaning blade (51) that is in contact with a surface (34a) of the transfer belt (34); and an opposing shaft (54) that is arranged opposite to the cleaning blade (51). The cleaning blade (51) includes a support member (52), and an elastic member (53) having a fixed end (531) supported by the support member (52) and a free end (532). The free end (532) includes a central region (R1), and end regions (R2) in contact with the opposing shaft (54, 54a). The cleaning blade (51) is configured such that the free length in the central region (R1) is shorter than the free length in the end regions (R2).SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a transfer belt unit to be mounted in an image forming apparatus, and the image forming apparatus. [Background technology]

[0002] Generally, in an image forming apparatus using an electrophotographic method, a developer image formed on a photosensitive drum serving as an image carrier is transferred to a printing medium on a transfer belt, or the developer image formed on the photosensitive drum is transferred (primary transfer) to the surface of a transfer belt (intermediate transfer belt), and the primary transferred developer image is then transferred (secondary transfer) to a printing medium (see, for example, Patent Document 1).

[0003] The developer remaining on the surface of the transfer belt after the developer image has been transferred to the print medium is removed by a belt cleaning unit having a cleaning blade arranged to contact the surface of the transfer belt and an opposing shaft arranged to face the cleaning blade across the transfer belt. In order to prevent the developer removed from the surface of the transfer belt by the cleaning blade from moving to the back side of the transfer belt, the width of the cleaning blade (i.e., the axial width of the opposing shaft) is made wider than the width of the transfer belt, and the width of the opposing shaft (i.e., the axial length of the surface in contact with the transfer belt and the cleaning blade) is also made wider than the width of the transfer belt. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-166115 Summary of the Invention [Problem to be solved by the invention]

[0005] However, there is an end region on the widthwise outside of the transfer belt where the elastic member at the tip of the cleaning blade comes into direct contact with the surface of the opposing shaft, which poses a problem that the elastic member of the cleaning blade is prone to curling in the end region.

[0006] An object of the present disclosure is to provide a transfer belt unit and an image forming apparatus in which curling of the elastic member of the cleaning blade is unlikely to occur in the end region on the outer side in the width direction of the transfer belt. [Means for solving the problem]

[0007] The transfer belt unit of the present disclosure comprises a plurality of rollers rotatably supported on a unit body, a transfer belt stretched across the plurality of rollers and movable in a predetermined movement direction, a cleaning blade that is wider than the transfer belt in a width direction perpendicular to the movement direction and that abuts against the surface of the transfer belt, and an opposing shaft that is rotatably supported on the unit body and positioned to face the cleaning blade across the transfer belt, wherein the cleaning blade comprises a support member supported on the unit body and an elastic member supported on the support member, wherein the elastic member comprises a fixed end supported on the support member and a free end opposite the fixed end, and wherein the free end comprises a first region that contacts the surface of the transfer belt and a second region that is outside the first region in the width direction and contacts the opposing shaft, and wherein the cleaning blade has a free length located in the first region that is shorter than that in the second region.

[0008] The image forming apparatus of the present disclosure includes an image forming unit that forms a developer image, a plurality of rollers rotatably supported on the device body, an endless transfer belt that is stretched over the plurality of rollers and is movable in a predetermined moving direction, a transfer section that transfers the developer image to the transfer belt or to a printing medium on the transfer belt, a cleaning blade that is wider than the transfer belt in a width direction perpendicular to the moving direction and that abuts against the surface of the transfer belt, and an opposing shaft that is rotatably supported on the device body and arranged to face the cleaning blade across the transfer belt, wherein the cleaning blade includes a support member supported on the device body and an elastic member supported on the support member, wherein the elastic member includes a fixed end supported on the support member and a free end opposite the fixed end, and the free end includes a first region that contacts the surface of the transfer belt and a second region that is outside the first region in the width direction and contacts the opposing shaft, and the cleaning blade has a free length located in the first region that is shorter than that in the second region. [Effects of the Invention]

[0009] The transfer belt unit or image forming apparatus of the present disclosure has the effect that the elastic member of the cleaning blade is less likely to curl up in the end region on the outer side in the width direction of the transfer belt. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view schematically illustrating a configuration of an image forming apparatus according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view schematically illustrating a configuration of a transfer belt unit according to the embodiment. [Figure 3] (A) is a side view that schematically shows the configuration of the cleaning blade, transfer belt, and opposing shaft shown in Figures 1 and 2, (B) is a front view that schematically shows the cleaning blade of Figure 3(A), and (C) is a front view that schematically shows the opposing shaft of Figure 3(A). [Figure 4]FIG. 4 is a perspective view schematically illustrating the cleaning blade, transfer belt, and opposing shaft shown in FIGS. [Figure 5] 5 is a side view schematically showing a normal state of the elastic member and opposing shaft of the cleaning blade of portion B of FIG. 4. FIG. [Figure 6] 5 is a side view schematically showing an abnormal state (when curling occurs) of the elastic member and opposing shaft of the cleaning blade of part B in FIG. 4. FIG. [Figure 7] (A) is a side view that schematically shows another configuration of the cleaning blade, transfer belt, and opposing shaft shown in Figures 1 and 2, (B) is a front view that schematically shows the cleaning blade of Figure 7(A), and (C) is a front view that schematically shows the opposing shaft of Figure 7(A). [Figure 8] FIG. 8 is a perspective view schematically illustrating the cleaning blade, transfer belt, and opposing shaft shown in FIGS. 7(A) to 7(C). [Figure 9] FIG. 2 is a side view schematically showing a method for carrying out a performance test using a test piece (sample) made of the same material as the elastic member of the cleaning blade. [Figure 10] FIG. 10 is a side view schematically showing the state of curling that occurred in a performance test using a test piece formed from the same material as the elastic member of the cleaning blade. [Figure 11] FIG. 10 is a table showing the test results (evaluation of the presence or absence of chatter noise and curling) and the first overall evaluation of a performance test using a test piece formed from the same material as the elastic member of the cleaning blade. [Figure 12] This is a diagram showing the range in which the first overall evaluation is good, based on the test results of the performance test in Figure 11, on a two-dimensional coordinate system with the free length of the cleaning blade on the horizontal axis and the amount of deflection on the vertical axis. [Figure 13] FIG. 10 is a table showing the test results and the second overall evaluation of the performance test (evaluation of the presence or absence of chatter noise, curling, and toner passing through) using a test piece formed from the same material as the elastic member of the cleaning blade. [Figure 14]This is a diagram showing the range in which the second overall evaluation is good, based on the test results of the performance test in Figure 13, on a two-dimensional coordinate system with the free length of the cleaning blade on the horizontal axis and the amount of deflection on the vertical axis. DETAILED DESCRIPTION OF THE INVENTION

[0011] An image forming apparatus and a transfer belt unit detachably attached to the image forming apparatus according to an embodiment of the present disclosure will be described below with reference to the drawings. In the following embodiments, a device and a unit in which the image forming apparatus employs an intermediate transfer belt system (i.e., a system in which a developer image formed on a photosensitive drum is transferred to the intermediate transfer belt and then transferred from the intermediate transfer belt to a print medium) will be described in detail. However, the image forming apparatus and the transfer belt unit according to the embodiment of the present disclosure may also employ a direct transfer system (i.e., a system in which a developer image formed on a photosensitive drum is directly transferred to a print medium). Furthermore, the following embodiments are merely examples, and the embodiments can be modified as appropriate. In the drawings, identical components are designated by the same reference numerals.

[0012] <1> Image forming device 1 Fig. 1 is a cross-sectional view that schematically shows the configuration of an image forming apparatus 1 according to embodiment 1. As shown in Fig. 1, image forming apparatus 1 is a color printer that can print color images on a print medium P such as paper by an electrophotographic process using developers (i.e., toners) of four colors: yellow (Y), magenta (M), cyan (C), and black (K). Fig. 1 shows a case where print medium P is cut paper, but print medium P may also be a continuous medium such as roll paper.

[0013] As shown in FIG. 1, image forming apparatus 1 includes image forming units 10Y, 10M, 10C, and 10K (also referred to as "image forming units 10") that form developer images (i.e., toner images) made of developer on photosensitive drums 13Y, 13M, 13C, and 13K (also referred to as "photosensitive drums 13") as image carriers, and a transfer belt unit 30 that transfers (i.e., primary transfer) the developer images formed on photosensitive drums 13Y, 13M, 13C, and 13K onto a transfer belt (also referred to as an "intermediate transfer belt") 34. Image forming units 10Y, 10M, 10C, and 10K are detachably mounted in a housing 1a, which is the main body of image forming apparatus 1. Transfer belt unit 30 is also detachably mounted in a housing 1a, which is the main body of image forming apparatus 1.

[0014] The image forming device 1 has a secondary transfer roller 25 that transfers (i.e., secondary transfers) the developer image carried on the transfer belt 34 onto the printing medium P at the secondary transfer position, a medium supply and transport section 20 that supplies and transports the printing medium P, a fixing device 40, and a discharge roller 26 as a medium discharge section that discharges the printing medium P that has passed through the fixing device 40 to the outside.

[0015] Each image forming unit 10 is also called an "image drum (ID) unit." The number of image forming units 10 installed in the image forming apparatus 1 may be three or less. The number of image forming units installed in the image forming apparatus 1 may be five or more. The image forming apparatus 1 may also be a monochrome printer that prints monochrome images by an electrophotographic process.

[0016] As shown in Figure 1, the media supply and transport section 20 has a media cassette 21, a hopping roller 22 that feeds out the printing media P loaded in the media cassette 21 one sheet at a time, a registration roller 23 that transports the printing media P fed out from the media cassette 21, and a roller pair 24 that transports the printing media P.

[0017] Image forming units 10Y, 10M, 10C, and 10K are arranged in a row in the movement direction (i.e., running direction) above transfer belt 34. Image forming units 10Y, 10M, 10C, and 10K, which are formed so as to be detachable from the apparatus main body, have the same structure except for the toner colors they use. However, image forming units 10Y, 10M, 10C, and 10K may have different structures.

[0018] Optical print heads 11Y, 11M, 11C, and 11K (also referred to as "optical print heads 11") are provided above the image forming units 10Y, 10M, 10C, and 10K, respectively, as exposure units for the respective colors. Each of the optical print heads 11Y, 11M, 11C, and 11K includes a light-emitting element array in which a plurality of light-emitting elements are arranged in the axial direction of the photosensitive drums 13Y, 13M, 13C, and 13K (the direction perpendicular to the paper on which FIG. 1 is drawn). The light-emitting elements are, for example, light-emitting diodes (LEDs) or light-emitting thyristors. Exposure by each of the optical print heads 11Y, 11M, 11C, and 11K is performed on the uniformly charged surfaces of the photosensitive drums 13Y, 13M, 13C, and 13K based on image data for printing. The exposure units may also be configured with a laser optical system.

[0019] Each of the image forming units 10Y, 10M, 10C, and 10K has a rotatably supported photosensitive drum 13Y, 13M, 13C, and 13K, a charging roller 14Y, 14M, 14C, and 14K (also referred to as "charging roller 14") as a charging member that uniformly charges the surface of the photosensitive drum 13Y, 13M, 13C, and 13K, and a developing device 15Y, 15M, 15C, and 15K (also referred to as "developing device 15") as a developing unit that forms an electrostatic latent image on the surface of the photosensitive drum 13Y, 13M, 13C, and 13K by exposure with the optical print head 11Y, 11M, 11C, and 11K, and then supplies toner to the surface of the photosensitive drum 13Y, 13M, 13C, and 13K to form a developer image corresponding to the electrostatic latent image. The photoreceptor drums 13Y, 13M, 13C, and 13K each include, for example, a cylindrical conductive support and a photosensitive layer coated on its surface. The photosensitive layer has a structure in which a blocking layer, a charge generation layer, and a charge transport layer are laminated in this order from the surface of the conductive support.

[0020] The developing devices 15Y, 15M, 15C, and 15K each have a developer storage section which is a container for storing developer, developing rollers 16Y, 16M, 16C, and 16K (also referred to as "developing rollers 16") as developer carriers that supply developer to the surfaces of the photosensitive drums 13Y, 13M, 13C, and 13K, supply rollers 17Y, 17M, 17C, and 17K (also referred to as "supply rollers 17") as developer supply bodies that supply the developer stored in the developer storage section to the developing rollers 16Y, 16M, 16C, and 16K, and layer forming blades 18Y, 18M, 18C, and 18K (also referred to as "layer forming blade 18") as developer regulating members that regulate the thickness of the developer layer on the surfaces of the developing rollers 16Y, 16M, 16C, and 16K.

[0021] As shown in FIG. 1, the transfer belt unit 30 has an endless transfer belt 34 for transferring a developer image onto a print medium P, a plurality of rollers (in the example of FIG. 1, a drive roller 31, a driven roller 32, and a backup roller 33 for secondary transfer) that are rotating bodies around which the transfer belt 34 is stretched, and transfer rollers 35Y, 35M, 35C, and 35K that serve as transfer members. The drive roller 31 is rotated by a driving force from a drive mechanism such as a motor, causing the transfer belt 34 to travel. The driven roller 32 is rotated in accordance with the travel of the transfer belt 34.

[0022] Transfer rollers 35Y, 35M, 35C, and 35K (also referred to as "transfer rollers 35") are disposed opposite photoreceptor drums 13Y, 13M, 13C, and 13K, respectively, with transfer belt 34 sandwiched therebetween. The developer images formed on the surfaces of photoreceptor drums 13Y, 13M, 13C, and 13K are transferred sequentially onto transfer belt 34 by transfer rollers 35K, 35C, 35M, and 35Y, forming a color image in which multiple developer images are superimposed. Any developer remaining on photoreceptor drums 13Y, 13M, 13C, and 13K after transfer is removed by a cleaning blade. Examples of resin materials that may be used to form transfer belt 34 include polyimide (PI), polyvinylidene fluoride (PVDF), and polyamide-imide (PAI).

[0023] The transfer belt 34 is further arranged to pass through a secondary transfer section installed below the transfer belt unit 30. The secondary transfer section is composed of a secondary transfer roller 25 and a backup roller 33, and the backup roller 33 is arranged so that it suspends the transfer belt 34. The secondary transfer roller 25 forms a transfer electric field for transferring the developer image on the transfer belt 34 to the print medium P. The driven roller 32 and the backup roller 33 rotate together with the transfer belt 34, which is moved in the moving direction V by the drive roller 31.

[0024] A fuser 40 is disposed downstream of the secondary transfer roller 25 to fix the developer image on the print medium P to the print medium P by applying heat and pressure. The fuser 40 has a pair of rollers, a heating roller 41 and a pressure roller 42, which are in pressure contact with each other. The heating roller 41 has a built-in heater. The pressure roller 42 is pressed against the heating roller 41. The print medium P having an unfixed developer image thereon passes between the heating roller 41 and the pressure roller 42. At this time, the unfixed developer image is fixed onto the print medium P by applying heat and pressure.

[0025] A discharge path and discharge rollers 26 for discharging the print medium P to the outside are provided downstream of the fixing unit 40, and the discharged print medium P is discharged into a stacker on the housing.

[0026] <2> Transfer belt unit 30 FIG. 2 is a cross-sectional view schematically illustrating the configuration of a transfer belt unit 30 according to an embodiment. The transfer belt unit 30 in FIG. 2 is configured to be detachable from the image forming apparatus 1 in FIG. 1. The transfer belt unit 30 has a unit main body 36, such as a housing or frame structure of the transfer belt unit 30, and a drive roller 31, a driven roller 32, and a backup roller 33, which are rotatably supported by the unit main body 36. The unit main body 36 of the transfer belt unit 30 is configured to be detachable from the image forming apparatus 1 in FIG. 1. However, the unit main body 36 can also be part of the housing 1a of the image forming apparatus 1 in FIG. 1, in which case the components of the transfer belt unit 30 are attached to the housing 1a of the image forming apparatus 1.

[0027] The unit also includes an endless transfer belt 34 that is stretched across a transfer belt unit 30, a drive roller 31, a driven roller 32, and a backup roller 33 and is movable in a predetermined movement direction V; a cleaning blade (also referred to as a "belt cleaning blade") 51 that is wider than the transfer belt 34 in a width direction W perpendicular to the movement direction V and that abuts against a surface 34a of the transfer belt 34; and an opposing shaft 54 ​​that is rotatably supported by the unit body 36 and disposed opposite the cleaning blade 51 with the transfer belt 34 sandwiched between them. The cleaning blade 51 has the function of removing (i.e., scraping off) deposits (e.g., residual toner) on the transfer belt 34. The cleaning blade 51, the opposing shaft 54, and a waste toner box 55 that serves as a waste developer storage unit constitute a belt cleaning unit 50.

[0028] <3> Belt cleaning unit 50 Fig. 3(A) is a side view that schematically illustrates the configuration of the cleaning blade 51, transfer belt 34, and opposing shaft 54 ​​shown in Figs. 1 and 2, Fig. 3(B) is a front view that schematically illustrates the cleaning blade 51 of Fig. 3(A), and Fig. 3(C) is a front view that schematically illustrates the opposing shaft 54 ​​of Fig. 3(A). Fig. 3(B) shows the shape of the cleaning blade 51 as viewed in direction A in Fig. 3(A). Fig. 3(C) shows the shape of the opposing shaft 54 ​​as viewed in direction A in Fig. 3(A). Fig. 4 is a perspective view that schematically illustrates the cleaning blade 51, transfer belt 34, and opposing shaft 54 ​​shown in Figs. 3(A) to (C).

[0029] The cleaning blade 51 is wider than the transfer belt 34 in a width direction W perpendicular to the moving direction V of the transfer belt 34. In other words, the width W51 of the cleaning blade 51 (FIG. 3B) is wider than the width W34 of the transfer belt 34 (FIG. 4). The opposing shaft 54 ​​is also wider than the transfer belt 34 in the width direction W. In other words, the width W54 of the opposing shaft 54 ​​(FIG. 3C) is wider than the width W34 of the transfer belt 34.

[0030] The cleaning blade 51 includes a metal plate 52 serving as a support member supported by the unit body 36 of the transfer belt unit 30, and an elastic member 53 having a fixed end 531 fixed to the metal plate 52 and a movable free end 532. The metal plate 52 is formed, for example, from a plate-shaped metal material, and the fixed end side of the elastic member 53 is fixed to the metal plate 52. The material of the elastic member 53 is, for example, urethane rubber.

[0031] As shown in FIG. 3B , the free end 532, which is the tip side portion of the elastic member 53 of the cleaning blade 51, includes a central region (first region) R1 that contacts the surface 34a of the transfer belt 34 and an end region (second region) R2 that is located outside (on both sides) of the central region R1 in the width direction W and contacts the opposing shaft 54. The cleaning blade 51 has a shorter free length in the central region (first region) R1 than in the end region (second region) R2. It is desirable to configure the metal plate 52 serving as the support member and the elastic member 53 so that the free length L, which is the length from the fixed end 531 to the free end 532, becomes shorter as it approaches the end of the elastic member 53 in the width direction W in the end region R2. The free end 532 has a linear shape extending in the width direction W.

[0032] 3B, the length Q2 of the metal plate 52 of the cleaning blade 51 corresponding to the edge region R2 is longer than the length Q1 of the metal plate 52 corresponding to the central region R1. Also, in the example of FIG. 3B, the length Q2 of the metal plate 52 corresponding to the edge region R2 is formed to become longer as it approaches the edge of the cleaning blade 51 in the width direction W, so that the free length L becomes shorter as it approaches the edge of the elastic member 53 in the width direction W in the edge region R2.

[0033] 5 is a side view schematically illustrating a normal state of the elastic member 53 of the cleaning blade 51 and the opposing shaft 54 ​​in part B (end region R2) of FIG. 4. As shown in FIG. 5, in the end region R2, the free end 532 of the elastic member 53 of the cleaning blade 51 is in direct contact with the surface of the opposing shaft 54. In the end region R2, the surface of the opposing shaft 54, which rotates as the transfer belt 34 moves in the movement direction V, remains in contact with the free end 532 of the elastic member 53, preventing toner scraped off from the surface 34a of the transfer belt 34 in the central region R1 from entering the back surface 34b of the transfer belt 34 via the end region R2.

[0034] 6 is a side view schematically illustrating an abnormal state (when curling occurs) of the elastic member 53 of the cleaning blade 51 and the opposing shaft 54 ​​in part B (end region R2) of FIG. 4. As shown in FIG. 6, in end region R2, the tip portion near the free end 532 of the elastic member 53 of the cleaning blade 51 is bent and strongly presses against the surface of the opposing shaft 54. This can occur because the surface roughness of the metal opposing shaft 54 ​​is greater than the surface roughness of the surface 34a of the transfer belt 34, resulting in large frictional resistance between the surface of the opposing shaft 54 ​​and the free end 532 of the elastic member 53. In such a situation, the opposing shaft 54 ​​becomes unable to rotate, which may result in the transfer belt 34 stopping movement in the movement direction V.

[0035] To prevent the situation shown in FIG. 6 from occurring, in this embodiment, the cleaning blade 51 is formed so that the free length in the central region (first region) R1 is shorter than the free length in the end region (second region) R2, as shown in FIG. 3B. Also, as shown in FIG. 3B, the metal plate 52 and the elastic member 53 are configured so that the free length L of the elastic member becomes shorter in the end region R2 as it approaches the end of the elastic member 53 in the width direction W. By making the free length L in the end region R2, where a relatively large frictional force is applied to the free end 532 of the elastic member 53, shorter than the free length in the central region R1, the line pressure is prevented from becoming too large, and curling of the elastic member 53 in the end region R2 is prevented. To prevent curling due to an increase in the coefficient of friction caused by a step, it is desirable to have no step between the slope of the end region R2 of the metal plate 52 of the cleaning blade 51 and the slope near the end of the opposing shaft 54 ​​(a continuous linear or gently curved slope).

[0036] In addition, the free length L in the end region R2 of the elastic member 53 is configured to gradually decrease as it approaches the widthwise end of the elastic member 53, making it less likely for toner to slip through near the boundary between the central region R1 and the end region R2, and making it less likely for toner to enter the back surface 34b of the transfer belt 34.

[0037] <4> Belt cleaning unit 50a Fig. 7(A) is a side view that schematically illustrates another configuration of the cleaning blade 51, transfer belt 34, and opposing shaft 54a shown in Figs. 1 and 2, Fig. 7(B) is a front view that schematically illustrates the cleaning blade 51 of Fig. 7(A), and Fig. 7(C) is a front view that schematically illustrates the opposing shaft 54a of Fig. 7(A). Fig. 7(B) shows the shape of the cleaning blade 51 as viewed in the direction A in Fig. 7(A). Fig. 7(C) shows the shape of the opposing shaft 54a as viewed in the direction A in Fig. 7(A). Fig. 8 is a perspective view that schematically illustrates the cleaning blade 51, transfer belt 34, and opposing shaft 54a shown in Figs. 7(A) to (C).

[0038] The cleaning blade 51 is wider than the transfer belt 34 in the width direction W of the transfer belt 34. In other words, the width W51 of the cleaning blade 51 (FIG. 7B) is wider than the width W34 of the transfer belt 34 (FIG. 4). Furthermore, the opposing shaft 54 ​​is wider than the transfer belt 34 in the width direction W. In other words, the width W54a of the opposing shaft 54 ​​(FIG. 7C) is wider than the width W34 of the transfer belt 34.

[0039] The cleaning blade 51 is the same as that shown in Figures 3A and 3B. As shown in Figures 7A and 7C and 8, the shape of the opposing shaft 54a of the belt cleaning unit 50a is different from that of the belt cleaning unit 50 shown in Figures 3A and 3C and 4. In the belt cleaning unit 50a, the opposing shaft 54a is configured so that the diameter D of the opposing shaft 54a becomes smaller as it approaches the end of the opposing shaft 54a in the width direction W in the region facing the end region R2.

[0040] 7(B), the length Q2 of the metal plate 52 of the cleaning blade 51 corresponding to the edge region R2 is longer than the length Q1 of the metal plate 52 corresponding to the central region R1. Also, in the example of Fig. 7(B), the length Q2 of the metal plate 52 corresponding to the edge region R2 is formed to become longer as it approaches the edge of the cleaning blade 51 in the width direction W, so that the free length L becomes shorter as it approaches the edge of the elastic member 53 in the width direction W in the edge region R2.

[0041] 6 does not occur, in this embodiment, as shown in FIG. 7B, the metal plate 52 and the elastic member 53 are configured so that the free length L of the elastic member becomes shorter in the end region R2 as it approaches the end of the elastic member 53 in the width direction W. Additionally, in the belt cleaning unit 50a, the opposing shaft 54a is configured so that the diameter of the opposing shaft 54a in the region facing the end region (second region) R2 is smaller than the diameter of the opposing shaft 54a in the region facing the central region (first region) R1. In the example of FIG. 7C, in the belt cleaning unit 50a, the opposing shaft 54a is configured so that the diameter D of the opposing shaft 54a in the region facing the end region R2 becomes smaller as it approaches the end of the opposing shaft 54a in the width direction W. In this way, by making the free length L in the end region R2, where a relatively large frictional force is applied to the free end 532 of the elastic member 53, shorter than the free length in the central region R1 and by making the diameter D of the opposing shaft 54a smaller in the region opposing the end region R2 as it approaches the end of the opposing shaft 54a in the width direction W, the linear pressure in the end region R2 is prevented from becoming too large, and curling up of the elastic member 53 is prevented. Note that, in order to prevent curling up due to an increase in the coefficient of friction caused by a step, it is desirable that there be no step between the slope of the end region R2 of the metal plate 52 of the cleaning blade 51 and the slope near the end of the opposing shaft 54 ​​(a continuous linear or gently curved slope).

[0042] In addition, by configuring the free length L in the end region R2 of the elastic member 53 to gradually decrease as it approaches the widthwise end of the elastic member 53 and by configuring the diameter D of the opposing shaft 54a to decrease as it approaches the widthwise end W of the opposing shaft 54a in the region opposite the end region R2, toner is less likely to slip through near the boundary between the central region R1 and the end region R2, making it less likely that toner will enter the back surface 34b of the transfer belt 34.

[0043] <5> Performance test and first comprehensive evaluation 9 is a side view schematically showing a method for conducting a performance test using a test piece (sample) 71 made of the same material as the elastic member 53 of the cleaning blade 51. FIG. 10 is a side view schematically showing a state of curling up that occurred in a performance test using the test piece 71 made of the same material as the elastic member 53 of the cleaning blade 51.

[0044] In the performance test, the test piece of the elastic member 53 was made of urethane rubber, had a thickness of 2 mm, a width of 147 mm, and a free length L in the range of 5 mm to 11 mm. In the performance test, a friction and wear tester was used to measure the free length L [mm] and deflection amount Y [mm] of the elastic member 53 of the cleaning blade 51 to determine what values ​​would be suitable for actual use.

[0045] The test equipment used was a rotating drum / reciprocating sliding motion combined friction and wear tester, "TRIBOGEAR TYPE:34," manufactured by Shinto Scientific Co., Ltd. The test was carried out at a temperature of 23°C and a humidity of 50%.

[0046] As shown in Figure 9, a blade test piece, a fragment of the cleaning blade 51 (approximately 2 cm wide), was attached to the testing machine at a 20° angle relative to the surface of a horizontal base 61. The free lengths L (mm) of the blade test pieces were set to 5 mm, 6 mm, 7 mm, 8 mm, 8.8 mm, 10 mm, and 11 mm when attached to the metal plate 72. A part 62, a piece of the transfer belt 34 cut to an appropriate size, was attached to the base 61 of the testing machine with mending tape. The testing machine allows the blade test piece to be moved up and down, and the deflection amount Y (mm) can be freely adjusted by changing the length of contact with the part 62 fixed to the base 61. The blade test piece is brought into contact with the part 62 on the base 61, and the base 61 is moved in the direction of arrow T at a speed of 2 ips while the blade test piece is deflected. The tester evaluates whether the blade test piece curls up and whether chatter noise (vibration noise caused by the blade) is generated.

[0047] 11 is a table showing the test results (evaluation of the presence or absence of chatter noise and curling up) and the first overall evaluation of a performance test using a blade test piece formed from the same material as the elastic member 53 of the cleaning blade 51. The evaluation items were the presence or absence of chatter noise (vibration noise caused by the blade) and the presence or absence of curling up. Good results (no problems) are indicated by a circle "◯", and bad results (problems) are indicated by a cross "×".

[0048] Fig. 12 is a diagram showing the range where the first overall evaluation is good (circle "O") based on the test results of the performance test in Fig. 11, on a two-dimensional coordinate system with the free length L [mm] of the cleaning blade 51 on the horizontal axis and the deflection Y [mm] on the vertical axis. From Fig. 12 showing the first overall evaluation, if the area is within the shaded area surrounded by straight lines, it is evaluated whether or not the blade test piece is curled up and whether or not chatter noise (vibration noise caused by the blade) is generated.

[0049] From FIG. 12 showing the first comprehensive evaluation, when the free length is L [mm] and the deflection amount of the elastic member 53 is Y [mm], the free length L [mm] is within the range of 5 [mm] to 10 [mm], and the elastic member 53 is

number

[0050] By satisfying condition 1, the free length L in the end region R2, where a relatively large frictional force is applied to the free end 532 of the elastic member 53, can be made smaller than the free length in the central region R1, thereby preventing the line pressure from becoming too large and preventing curling of the elastic member 53 in the end region R2.

[0051] (6) Performance test and second comprehensive evaluation In the second performance test for comprehensive evaluation, in addition to the first performance test for comprehensive evaluation, whether or not the toner slipped through was evaluated.

[0052] In the second performance test for the overall evaluation, toner was applied to a part 62 on a base 61, and the blade test piece was brought into contact with the base 61, and the base was moved in a bending state at a speed of 2 ips in the moving direction V. At this time, it was checked whether the blade test piece could remove all of the toner and whether any toner slipped through.

[0053] 13 is a table showing the test results (evaluation of the presence or absence of chatter noise, the presence or absence of curling, and the presence or absence of toner passing through) and the second overall evaluation of the performance test using a blade test piece formed from the same material as the elastic member 53 of the cleaning blade 51. The evaluation items were the presence or absence of chatter noise (vibration noise caused by the blade), the presence or absence of curling, and the presence or absence of toner passing through. With regard to the presence or absence of chatter noise (vibration noise caused by the blade) and the presence or absence of curling, good (no problem occurred) is represented by a circle "O" and bad (problem occurred) is represented by a cross "X". With regard to the presence or absence of toner passing through, good (no slip-through occurred) is represented by a circle "O" and bad (slip-through occurred) is represented by a triangle "△".

[0054] Fig. 14 is a diagram showing the range where the second overall evaluation is good (circle "O") based on the test results of the performance test in Fig. 13, on a two-dimensional coordinate system with the free length L [mm] of the cleaning blade 51 on the horizontal axis and the deflection Y [mm] on the vertical axis. From Fig. 14 showing the second overall evaluation, if the area is within the shaded area surrounded by straight lines, it is evaluated whether or not the blade test piece is curled up and whether or not chatter noise (vibration noise caused by the blade) is generated.

[0055] From FIG. 14 showing the second comprehensive evaluation, when the free length is L [mm] and the deflection amount of the elastic member 53 is Y [mm], the free length L [mm] is within the range of 6 [mm] to 10 [mm], and the elastic member 53 is

number

[0056] By satisfying condition 2, the free length L in the end region R2, where a relatively large frictional force is applied to the free end 532 of the elastic member 53, is made smaller than the free length in the central region R1, thereby preventing the linear pressure from becoming too large and preventing curling of the elastic member 53 in the end region R2. Furthermore, by satisfying condition 2, it is possible to make it difficult for toner to slip through.

[0057] 7. Variations The transfer belt unit described above can also be applied to image forming apparatuses such as MFPs (multi-function peripherals), fax machines, and copiers. [Explanation of symbols]

[0058] 1 image forming apparatus, 1a apparatus main body, 10, 10Y, 10M, 10C, 10K image forming unit, 11, 11Y, 11M, 11C, 11K optical print head (exposure section), 13, 13Y, 13M, 13C, 13K photosensitive drum (image carrier), 14, 14Y, 14M, 14C, 14K charging roller (charging section), 15, 15Y, 15M, 15C, 15K developing device, 16, 16Y, 16M, 16C, 16K developing roller (developer carrier), 17, 17Y, 17M, 17C, 17K supply roller (developer supply body), 18, 18Y, 18M, 18C, 18K layer forming blade, 20 medium supply transport section, 30 Transfer belt unit, 31 drive roller, 32 driven roller, 33 tension roller, 34 transfer belt, 34a surface, 35, 35Y, 35M, 35C, 35K transfer rollers (transfer section), 36 unit body, 40 fuser, 41 heating roller, 42 pressure roller, 50, 50a belt cleaning section, 51 cleaning blade, 52 sheet metal (support member), 53 elastic member (urethane rubber), 531 fixed end, 532 free end, 54, 54a opposing shaft, 55 waste toner box (waste developer storage section), P printing medium, V movement direction, W width direction, R1 central region (first region), R2 end region (second region), L free length, D diameter.

Claims

1. a plurality of rollers rotatably supported on the unit body; a transfer belt that is stretched over the plurality of rollers and is movable in a predetermined direction; a cleaning blade that is wider than the transfer belt in a width direction perpendicular to the moving direction and that comes into contact with the surface of the transfer belt; an opposing shaft rotatably supported by the unit main body and disposed opposite the cleaning blade with the transfer belt interposed therebetween; and The cleaning blade is a support member supported by the unit body; an elastic member supported by the support member; Including, The elastic member is a fixed end supported by the support member, and a free end opposite to the fixed end; Including, The free end is a first area contacting the surface of the transfer belt; a second region that is outside the first region in the width direction and that contacts the opposing shaft; Including, The cleaning blade is The free length located in the first region is shorter than that located in the second region. A transfer belt unit characterized by:

2. The opposing shaft is configured so that a diameter of the opposing shaft in a region facing the second region is smaller than a diameter of the opposing shaft in a region facing the first region.

2. The transfer belt unit according to claim 1, wherein the transfer belt unit is a belt unit having a plurality of transfer rollers.

3. The free end has a linear shape extending in the width direction.

2. The transfer belt unit according to claim 1, wherein the transfer belt unit is a belt unit having a plurality of transfer rollers.

4. When the free length is L [mm] and the deflection amount of the elastic member is Y [mm], the free length L [mm] is within a range of 5 [mm] to 10 [mm], The elastic member is [Equation 3] It was configured as 4. The transfer belt unit according to claim 1, wherein the transfer belt unit is a transfer belt unit having a first surface and a second surface.

5. When the free length is L [mm] and the deflection amount of the elastic member is Y [mm], the free length L [mm] is within a range of 6 [mm] to 10 [mm], The elastic member is [Equation 4] It was configured as 4. The transfer belt unit according to claim 1, wherein the transfer belt unit is a transfer belt unit having a first surface and a second surface.

6. An image forming apparatus comprising the transfer belt unit according to claim 1 .

7. an image forming unit that forms a developer image; a plurality of rollers rotatably supported on the device body; an endless transfer belt that is stretched around the plurality of rollers and is movable in a predetermined direction; a transfer section that transfers the developer image to the transfer belt or to a print medium on the transfer belt; a cleaning blade that is wider than the transfer belt in a width direction perpendicular to the moving direction and that comes into contact with the surface of the transfer belt; an opposing shaft that is rotatably supported by the apparatus main body and is disposed opposite the cleaning blade across the transfer belt; and The cleaning blade is a support member supported by the device body; an elastic member supported by the support member; Including, The elastic member is a fixed end supported by the support member, and a free end opposite to the fixed end; Including, The free end is a first area contacting the surface of the transfer belt; a second region that is outside the first region in the width direction and that contacts the opposing shaft; Including, The cleaning blade is The free length located in the first region is shorter than that located in the second region. An image forming apparatus characterized by:

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