Image forming apparatus and manufacturing method thereof

Abstract

To provide an image forming apparatus that lays an intermediate transfer belt in a tensioned state with tension rollers each having spiral groove parts formed along a roller circumferential direction to circulate in an axial direction of the roller, and execute polishing processing on ridge parts of the groove parts along a circumferential direction of the tension rollers to suppress occurrence of tension lines due to irregularities in the roller circumferential direction of the ridge parts.SOLUTION: On a longitudinal cross section of a tension roller 113, polishing processing is executed on ridge parts of a groove structure 31 along a circumferential direction of the tension roller 113.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus equipped with an intermediate transfer belt that carries a toner image and transfers the toner image to a recording material, and to an image forming apparatus having a spiral groove on the surface of a tension roller that tensions the intermediate transfer belt, and a manufacturing method thereof. [Background technology]

[0002] Conventionally, image forming apparatuses have been widely used in which a toner image formed on an image carrier is transferred to an intermediate transfer belt passing through a primary transfer section, conveyed to a secondary transfer section, and then collectively secondary-transferred to a recording material fed to the secondary transfer section. This intermediate transfer belt is usually formed in an endless shape, and is supported under tension by being stretched over one or more tension rollers (drive roller, tension roller, steering roller, support roller, etc.).

[0003] Foreign matter such as dirt and developer may get inside the intermediate transfer belt. If the foreign matter gets between the tension roller and the belt, the pressure applied to the belt increases locally depending on the height of the foreign matter. As a result, a streak-like deformation (tension line) may occur in the circumferential direction in part of the width direction of the belt.

[0004] Therefore, in Patent Document 1, a spiral groove is formed on the peripheral surface of the tension roller to prevent localized pressure buildup even if foreign matter adheres to the inner surface of the belt, thereby suppressing the occurrence of tension lines. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-169578 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in conventional image forming devices, if the ridges between the grooves of the tension roller have large unevenness (surface roughness) in the circumferential direction of the roller, the roller will have a locally pointed shape in the circumferential direction, and the contact pressure with the intermediate transfer belt will be locally large. As a result, there is a possibility that streak-like permanent deformation (hereinafter referred to as tension lines) will occur in the circumferential direction of the intermediate transfer belt.

[0007] In view of the problems existing in the conventional technology, the present invention aims to provide an image forming apparatus that can suppress the occurrence of tension lines due to unevenness of the ridges of the grooves in the circumferential direction of the roller while suppressing the occurrence of tension lines due to adhesion of foreign matter, etc., by forming a spiral groove on the circumferential surface of the tension roller. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides a printing apparatus comprising an image carrier, an image forming unit which forms a toner image on the image carrier, an endless belt member to which the toner image is transferred from the image carrier, and a tension roller which tensions the belt member, wherein the tension roller has a spiral groove formed on the peripheral surface of the tension roller so as to circle around the axial direction of the tension roller, the width of the groove is 100 μm or more and 500 μm or less, and the depth of the groove is 10 μm or more and 40 μm or less, and a ridge portion formed between the grooves has a flat portion which is polished along the circumferential direction of the tension roller, and the width of the flat portion is 30 μm or more and 150 μm or less, in the axial direction of the tension roller.

[0009] The present invention also provides a printing apparatus comprising an image carrier, an image forming unit which forms a toner image on the image carrier, an endless belt member onto which the toner image is transferred from the image carrier, and a tension roller which tensions the belt member, wherein the tension roller has a spiral groove formed on the circumferential surface of the tension roller so as to circle around the axial direction of the tension roller, the width of the groove being 100 μm or more and 500 μm or less, and the depth of the groove being 10 μm or more and 40 μm or less, and a ridge portion formed between the groove portions has a curved surface portion which is polished along the circumferential direction of the tension roller, and the width of the curved surface portion being 30 μm or more and 150 μm or less, in the axial direction of the tension roller.

[0010] The present invention also relates to a method for manufacturing an image forming apparatus having a tension roller for tensioning an endless belt member on which a toner image is transferred, the method comprising the steps of: cutting a peripheral surface of the tension roller to form a spiral groove around the axial direction of the tension roller; and forming a ridge line formed between the grooves in a cross section of the tension roller parallel to the axial direction of the tension roller along the circumferential direction of the tension roller. In the grinding direction and a polishing step of performing a polishing treatment. Effect of the Invention

[0011] According to the present invention, by forming a spiral groove on the peripheral surface of a tension roller, it is possible to provide an image forming device that can suppress the occurrence of tension lines due to the adhesion of foreign matter, while also suppressing the occurrence of tension lines due to unevenness in the circumferential direction of the roller at the ridge line of the groove. [Brief description of the drawings]

[0012] [Figure 1] Cross-sectional view of an image forming apparatus [Diagram 2] FIG. 1 is a perspective view of a support roller according to a first embodiment; [Diagram 3] FIG. 1 is a partial cross-sectional view in the longitudinal direction of a support roller according to a first embodiment; [Figure 4] FIG. 11 is a partial longitudinal cross-sectional view of a support roller according to a second embodiment of the present invention; [Diagram 5]A diagram showing belt deflection due to groove structure [Figure 6] Diagram showing belt waving caused by groove structure DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative positions, and the like of the components described in the embodiments are not intended to limit the scope of the present invention. EXAMPLES

[0014] (Image forming device) Fig. 1 is an explanatory diagram of the configuration of an image forming apparatus in this embodiment. As shown in Fig. 1, an image forming apparatus 100 has image forming units 109Y, 109M, 109C, and 109Bk for yellow, magenta, cyan, and black arranged along an intermediate transfer belt 101 as a belt member. In other words, the image forming apparatus in this embodiment is a full-color printer of a so-called tandem type intermediate transfer system.

[0015] In the image forming station 109Y, a yellow toner image is formed on the photosensitive drum 103Y and transferred to the intermediate transfer belt 101. In the image forming station 109M, a magenta toner image is formed in the same manner as in the image forming station 109Y and transferred and superimposed on the yellow toner image on the intermediate transfer belt 101. In the image forming stations 109C and 109Bk, a cyan toner image and a black toner image are formed in the same manner as in the image forming station 109M and transferred and superimposed in order onto the intermediate transfer belt 101.

[0016] The four-color toner images carried on the intermediate transfer belt 101 are transported to a secondary transfer section T2 and collectively secondarily transferred onto a recording material P. The recording material P taken out of a recording material cassette 120 is separated one by one by a separation roller 121 and transported to a registration roller 122. The registration roller 122 feeds the recording material P to the secondary transfer section T2 in synchronization with the toner images on the intermediate transfer belt 101.

[0017] The secondary transfer roller 111 comes into contact with the intermediate transfer belt 101 on the drive roller 110 to form a secondary transfer portion T2. ​​The recording material P onto which the four-color toner image has been secondarily transferred by passing through the secondary transfer portion T2 is separated from the intermediate transfer belt 101 by curvature and sent to a fixing device 112. The fixing device 112 heats and presses the recording material P at a nip portion between a fixing roller 112a and a pressure roller 112b to fix the image onto the recording material P. The recording material P onto which the image has been fixed by the fixing device 112 is discharged outside the apparatus body.

[0018] (Image forming section) The image forming units 109Y, 109M, 109C, and 109Bk are substantially identical in configuration, except that the colors of toner used in the respective developing devices are different: yellow, magenta, cyan, and black. In the following, the toner image forming process of the yellow image forming unit 109Y will be described, and duplicated descriptions of the other image forming units 109M, 109C, and 109Bk will be omitted.

[0019] The image forming unit 109Y has a charging roller 104, an exposure device 105, a developing device 106, a primary transfer roller 107Y, and a drum cleaning device 108 arranged around a photosensitive drum 103Y as an image carrier. The photosensitive drum 103Y has a photosensitive layer formed on its surface and rotates in the direction of the arrow at a predetermined process speed. The charging roller 104 charges the surface of the photosensitive drum 103Y to a uniform potential. The exposure device 105 scans a laser beam with a rotating mirror to write an electrostatic image of an image on the surface of the photosensitive drum 103Y. The developing device 106 transfers toner to the photosensitive drum 103Y to develop the electrostatic image into a toner image. The primary transfer roller 107Y transfers the toner image carried by the photosensitive drum 103Y to the intermediate transfer belt 101 when a voltage is applied. The drum cleaning device 108 rubs a cleaning blade against the photosensitive drum 103Y to collect the transfer residual toner remaining on the photosensitive drum 103Y.

[0020] (Intermediate transfer unit) 1, the drive roller 110 stretches and drives the intermediate transfer belt 101, which is an example of an endless intermediate transfer belt. The frame 8 (not shown) is a frame member that rotatably supports the drive roller 110. The intermediate transfer unit 124 is an integral assembly of the frame 8, the intermediate transfer belt 101, the drive roller 110, the steering roller 1, the support rollers 113 and 114 as stretching rollers, and the primary transfer rollers 107Y, 107M, 107C, and 107Bk. The intermediate transfer unit 124 as a replacement unit can be removed as a unit from the housing structure of the image forming apparatus 100.

[0021] The intermediate transfer belt 101 is stretched around a driving roller 110, a steering roller 1, support rollers 113 and 114, and primary transfer rollers 107Y, 107M, 107C, and 107Bk. The secondary transfer roller 111 as a secondary transfer outer roller abuts against the outer surface of the intermediate transfer belt 101 and forms a secondary transfer portion T2 (transfer nip) where a toner image is transferred to a recording material between the driving roller 110 and the secondary transfer roller 110. That is, the driving roller 110 forms the secondary transfer portion T2 by sandwiching the intermediate transfer belt 101 between the secondary transfer roller 111 and the driving roller 110. Here, the driving roller 110 also functions as a secondary transfer inner roller as an opposing roller opposing the secondary transfer roller 111 through the intermediate transfer belt 101. The supporting roller 114 has a crown shape in which the outer diameter is maximum at the approximate center in the axial direction and gradually decreases toward both ends. This is to prevent the support roller 114 from bending at the center due to the tension of the intermediate transfer belt 101, causing wrinkles in the center of the intermediate transfer belt 101. The primary transfer rollers 107Y, 107M, 107C, and 107Bk are made of metal rollers (metal rollers), and are pressed against the inner surface of the intermediate transfer belt 101 by a pressing structure (not shown). Here, in this embodiment, the primary transfer rollers 107Y, 107M, 107C, and 107Bk are made of metal. In this case, if the intermediate transfer belt 101 is nipped by the photosensitive drum, which is a rigid body, and the primary transfer roller, which is a rigid body, there is a risk that the photosensitive drum will be damaged. Therefore, the position of the primary transfer roller is offset with respect to the rotation direction of the intermediate transfer belt so as not to face the photosensitive drums 103Y, 103M, 103C, and 103Bk. As a result, the pressure applied to the intermediate transfer belt 101 is set to be smaller than when the primary transfer roller is a general sponge roller. The steering roller 1 is connected to a tension spring 21 that applies a predetermined tension to the intermediate transfer belt 101, and also functions as a tension roller. The steering roller 1 is tiltable about a tilt axis that intersects with the rotation axis of the steering roller. The steering roller 1 is configured to tilt about the tilt axis so that the intermediate transfer belt 101 is positioned within a predetermined range in the width direction.

[0022] The intermediate transfer belt 101 is made of a resin belt with a base layer of polyimide (PI), and has a tensile elastic modulus E=18000N / cm2 and a thickness of 0.08mm. The intermediate transfer belt 101 is preferably made of a resin with high rigidity, such as polyvinylidene fluoride (PVDF), polyamide, polyimide resin (PI), polyethylene terephthalate (PET), polycarbonate (PC), etc. The thickness of the intermediate transfer belt 101 is preferably in the range of 0.02mm to 0.50mm. If the intermediate transfer belt 101 is too thin, it will not be able to obtain sufficient durability against wear, and if it is too thick, it will be difficult to bend around the drive roller 110, steering roller 1, and support rollers 113 and 114, resulting in deformation or folding.

[0023] The belt cleaning device 102 collects the residual toner by rubbing the cleaning blade 102b against the intermediate transfer belt 101. The cleaning blade 102b is in contact with the winding region where the intermediate transfer belt 101 is wound around the steering roller 1. The tip of the cleaning blade 102b is disposed in a counter direction to the moving direction V of the intermediate transfer belt 101. The belt cleaning device 102 collects the residual toner and the like that is not transferred to the recording material P and remains on the intermediate transfer belt 101 by contacting the tip of the cleaning blade 102b with the outer surface of the intermediate transfer belt 101. The cleaning blade 102b is made of urethane rubber. The urethane rubber has a JIS-A hardness of 75 degrees and a thickness of 2 mm. The contact angle of the cleaning blade 102b is 25° and the contact pressure is 3 N / m (30 gf / cm). However, the present invention is not limited thereto.

[0024] (Tension Line) When the intermediate transfer belt 101, which is supported by multiple tension rollers, is rotated, stripe-like unevenness (tension lines) may occur on the intermediate transfer belt 101 along the conveying direction of the intermediate transfer belt 101. These tension lines may be formed when the tension applied to the intermediate transfer belt 101 becomes uneven, causing localized stress, or when the surface of the intermediate transfer belt is scratched by a sharp object such as a foreign object.

[0025] The reason for the uneven tension is that when dirt or carrier gets on the back surface of the intermediate transfer belt, the dirt or carrier adheres to the tension roller, causing a localized increase in pressure at the contact point between the intermediate transfer belt 101 and the tension roller.

[0026] If a soft material such as rubber is used for the tension roller, the tension roller will collapse and no large pressure will be applied locally even if dust or carrier gets into the contact area between the tension roller and the intermediate transfer belt 101. However, it is difficult to make all the tension rollers out of rubber because of the high cost.

[0027] These tension lines gradually deteriorate as the rotational drive is repeated, causing the size of the unevenness to increase and the number of such lines to increase.

[0028] When tension lines occur, the unevenness and microscopic deterioration of the intermediate transfer belt cause uneven transferability, resulting in images with vertical streaks being output.

[0029] Next, the groove structure 31 of the support rollers 113 and 114, which is a feature of this embodiment, will be described.

[0030] FIG. 2 is a perspective view of the support rollers 113 and 114, and FIG. 3 is a partial cross-sectional view of the support rollers 113 and 114 in the longitudinal direction.

[0031] 2, the support rollers 113 and 114 as tension rollers in this embodiment have a groove structure 31 as a spiral groove portion formed on the peripheral surface so as to go around the axial direction of each support roller. By providing such a groove structure 31, even if foreign matter, carrier, etc. adheres to the back surface of the intermediate transfer belt 101 or the surfaces of the support rollers 113 and 114, these foreign matter can be made to enter the groove portion of the groove structure 31. As a result, it is possible to prevent the contact pressure against the back surface of the intermediate transfer belt from being locally increased due to the dirt or carrier adhered to the surfaces of the support rollers 113 and 114, and to prevent the occurrence of tension lines.

[0032] The support rollers 113 and 114 have a spiral groove structure 31 as a surface structure. The spiral groove structure 31 is almost parallel to the circumferential direction, but has a slight inclination with respect to the tangential direction of the cylindrical surface of the support rollers 113 and 114, so that the contact position with the intermediate transfer belt 101 moves with rotation. By forming the support rollers 113 and 114 with the spiral groove structure 31, the ease of processing is improved, and the outer diameter runout and straightness of the roller surface can be improved. Note that the angle formed by the spiral groove portion of the groove structure 31 in this embodiment and the circumferential direction (tangential direction) of the support rollers 113 and 114 is greater than 0 degrees and less than 10 degrees. More preferably, it is greater than 0 degrees and 5 degrees or less.

[0033] As shown in FIG. 3, the longitudinal cross section of the groove structure 31 (the cross section of the support rollers 113 and 114 parallel to the axial direction of the support rollers 113 and 114) is composed of a large number of grooves. The grooves of the groove structure 31 are formed by V-shaped inclined surfaces 32 in the groove. That is, the groove structure 31 has a first inclined flat surface portion arranged on one side and a second inclined flat surface portion arranged on the other side facing the first inclined surface. Between adjacent groove structures 31, flat portions W1 are formed adjacent to the inclined surfaces 32 in the groove structure. That is, in this embodiment, in the longitudinal cross section of the support rollers 113 and 114, the ridges formed between the groove structures 31 have a flat shape. This allows the ridges of the groove structure 31 to have a gentler inclination angle than the inclined surfaces 32 in the groove (including zero inclination angle). As a result, the stress concentration on the intermediate transfer belt at the ridges of the groove structure 31 can be reduced.

[0034] A method for manufacturing the groove structure 31 in this embodiment will be described.

[0035] In this embodiment, the groove structure 31 is formed by cutting using a lathe. (Cutting process) It is preferable that the groove width L is 100 μm or more and 500 μm or less, and the groove depth D is 10 μm or more and 40 μm or less. In this embodiment, when cutting, the groove pitch is set so that no gaps are generated between adjacent grooves.

[0036] If the groove width L is less than 100 μm, the dirt and carrier will not enter the groove. As a result, the contact pressure against the back surface of the intermediate transfer belt may become locally large due to the dirt and carrier adhering to the surface of the support rollers 113 and 114, and tension lines may occur. The longitudinal width of the region in which the groove structure 31 is formed is at least larger than the width of the maximum image forming region. In addition, both ends of the region in which the groove structure 31 is formed are formed so as to be outside both ends of the maximum image forming region. In this embodiment, the groove structure 31 is formed over almost the entire longitudinal region (the entire region of the large diameter portion) of the support rollers 113 and 114.

[0037] As described above, the thickness of the intermediate transfer belt 101 is preferably 0.02 mm or more and 0.50 mm or less. If the groove width L is greater than 500 μm, the bent intermediate transfer belt 101 will excessively intrude into the groove structure 31 as shown in FIG. 5. As a result, as shown in FIG. 6, waving may occur in the tensioned portion of the support rollers 113 and 114.

[0038] In this embodiment, the flat portion W1 is polished (mirror-finished) on the outer diameter of the support rollers 113 and 114 to remove the sharp groove ridge tips after forming the groove inclined surface 32. (Polishing step) Specifically, a polishing cloth having a predetermined roughness is brought into contact with the peripheral surface of the support rollers 113 and 114 in the longitudinal direction of the support rollers. By rotating the support rollers 113 and 114 in this state, polishing (mirror-finished) is performed on the ridges of the groove structure 31 along the circumferential direction of the support rollers 113 and 114. As a result, the ridges (groove ridge tips) of the groove structure 31 are polished along the roller circumferential direction, and the height (unevenness) of the ridges of the groove structure 31 can be made approximately the same in the roller circumferential direction. As a result, the unevenness (surface roughness) of the ridges of the groove structure 31 in the roller circumferential direction is configured to be smaller than the surface roughness of the valley side of the side of the groove structure 31. Alternatively, the peripheral surface of the support roller may be ground in the circumferential direction in advance to form the flat portion W1, and the groove pitch X may be widened so that the flat portion W1 remains when the in-groove slope 32 is formed.

[0039] The width of the flat portion W1 is preferably 30 μm or more and 150 μm or less.

[0040] If the flat portion W1 is less than 30 μm, the unevenness of the ridge line in the circumferential direction of the roller may not be sufficiently reduced. In addition, the contact pressure on the back surface of the intermediate transfer belt 101 may become locally large at the contact portion between the support rollers 113 and 114 and the intermediate transfer belt 101, which may cause tension lines.

[0041] If the flat portion W1 is larger than 150 μm, there is a possibility that dirt or carrier particles of a size that can cause tension lines may adhere to the flat portion W1, which may result in localized contact pressure between the dirt or carrier particles and the back surface of the intermediate transfer belt, causing tension lines to form.

[0042] In addition, the ratio of the flat portion W1 to the groove pitch X is preferably 5% or more and 30% or less. If this ratio is less than 5%, it becomes difficult to reduce the surface roughness of the ridge line. If this ratio is more than 30%, the proportion of the flat portion increases, and the effect of suppressing the tension line may decrease.

[0043] As described above, by providing the flat portion W1 having a thickness of 30 μm or more and 150 μm or less in the groove structure 31, it is possible to reduce localized stress concentration on the intermediate transfer belt 101 and suppress the occurrence of tension lines. This makes it possible to provide an image forming apparatus capable of outputting stable image quality. EXAMPLES

[0044] 4 is a partial longitudinal cross-sectional view of the support rollers 113 and 114 of the second embodiment. In the second embodiment, the shape of the tip of the groove structure 31 is different from that of the first embodiment. In the first embodiment, the ridge of the groove structure 31 is flat in the longitudinal cross-section of the groove structure 31, but in the present embodiment, it is curved (arc-shaped). This allows the inclination angle of the ridge of the groove structure 31 to be gentler than the inclination angle of the in-groove inclined surface 32. As a result, it is possible to reduce local stress concentration on the intermediate transfer belt 101 due to the ridge of the groove structure 31.

[0045] The longitudinal cross section of the groove structure 31 is made up of a large number of grooves, and adjacent groove structures 31 in the axial direction of the cylindrical surface are formed with an inner groove inclined surface 32 and an arc portion W2 as a curved surface portion adjacent to each other.

[0046] It is preferable that the groove width L of the groove structure 31 is 100 μm or more and 500 μm or less, and the groove depth D is 10 μm or more and 40 μm or less.

[0047] If the groove width L is less than 100 μm, the dirt and carrier will not enter the grooves. As a result, the contact pressure with the back surface of the intermediate transfer belt may become locally large due to the dirt and carrier adhering to the surfaces of the support rollers 113 and 114, which may cause tension lines.

[0048] As described above, the intermediate transfer belt 101 desirably has a thickness of 0.02 mm or more and 0.50 mm or less, and if the groove width L is greater than 500 μm, the bent intermediate transfer belt 101 will excessively intrude into the groove structure 31 as shown in Fig. 5. As a result, as shown in Fig. 6, there is a possibility that waving will occur in the tensioned portion of the support rollers 113 and 114.

[0049] The width of the arc portion W2 is preferably 30 μm or more and 150 μm or less. If the arc portion W2 is less than 30 μm, the contact pressure on the back surface of the intermediate transfer belt 101 may become locally large at the contact portion between the support rollers 113 and 114 and the intermediate transfer belt 101, and tension lines may occur.

[0050] If the arc portion W2 is larger than 150 μm, there is a possibility that dust or carrier of a size that can cause a tension line will adhere to the arc portion W2. As a result, the contact pressure of the dust or carrier and the back surface of the intermediate transfer belt may become locally large, and a tension line may occur. As described above, by providing an arc portion W2 of 30 μm or more and 150 μm or less between the groove structures 31, it is possible to reduce local stress concentration on the intermediate transfer belt 101 and suppress the occurrence of tension lines. Also, as in the first embodiment, the ratio of the arc portion W2 to the groove pitch X is preferably 5% or more and 30% or less. This makes it possible to provide an image forming apparatus that can output stable image quality.

[0051] In addition, the arc portion W2 is polished in the circumferential direction of the roller, as in Example 1. That is, after the roller is cut to form the groove inner slope 32, the sharpened groove ridge tip is polished in the circumferential direction of the roller. In this way, the surface roughness of the ridge portion of the groove structure 31 can be made smaller than the surface roughness of the valley portion side of the groove structure 31. In this example, the groove ridge tip of the groove structure 31 is polished to have an arc shape by placing an abrasive cloth opposite the roller circumferential surface while rotating the support rollers 113 and 114 and polishing for a predetermined time.

[0052] In this embodiment, in the longitudinal cross section of the support rollers 113 and 114, the shape between the groove structures 31 is the arc portion 2, but is not limited to this. For example, the shape between adjacent groove structures 31 may be an arc. For example, the shape between the groove structures 31 may be a part of an ellipse.

[0053] When the side surface of the groove structure 31 is curved, the ridge portion (upwardly convex region) sandwiched between the positions where the groove inclination angle 32 of the groove structure 31 is maximum is defined as the curved portion W2.

[0054] [others] In this embodiment, in the longitudinal cross section of the support roller, the shape between the groove structures 31 is an arc portion W2 (curved surface portion W2) or a flat portion W1. However, the shape between the groove structures 31 is not limited to the above shape. For example, the shape between the groove structures 31 may be a shape that combines both the flat portion W1 and the arc portion W2. For example, the boundary (corner portion) between the flat portion W1 and the groove inclination 32 in Example 1 may be polished to connect the groove inclination 32 and the flat portion W1 with a smooth curve, and a gentle slope may be formed by both the flat portion W1 and the curved portion W2. In this case, it is sufficient that the longitudinal width of the flat portion W1 and the curved portion W2 added together is 30 μm or more and 150 μm or less.

[0055] Further, in the cross section of the longitudinal direction of the support roller, the groove structure 31 is formed in a V-shape in the above embodiment, but the groove shape may be a U-shape, a trapezoidal shape, a sinusoidal shape, a rectangular shape, or the like. [Explanation of symbols]

[0056] 1 Steering roller 8 Frames 21 Tension spring 31 Groove structure 32 Groove slope 100 Image forming device 101 intermediate transfer belt, 102 Belt cleaning device 102b Cleaning blade 103Y, 103M, 103C, 103Bk Photosensitive drum 104 Charging roller 105 Exposure equipment 106 Developing device 107Y, 107M, 107C, 107Bk Primary transfer roller 108 Drum cleaning device 109Y, 109M, 109C, 109Bk Image forming unit 110 Drive roller 111 Secondary transfer roller 112 Fixing device 113, 114 Support roller 120 Recording material cassette 121 Separation roller 122 Registration roller 124 Intermediate transfer unit 300 Sensor Unit D Groove Depth L groove width W1 flat part W2 Arc section X Groove Pitch

Claims

1. An image carrier; an image forming unit for forming a toner image on the image carrier; an endless belt member onto which a toner image is transferred from the image carrier; a tension roller for tensioning the belt member, The tension roller has a spiral groove formed on a peripheral surface of the tension roller so as to go around an axial direction of the tension roller, In the axial direction of the tension roller, the width of the groove is 100 μm or more and 500 μm or less, and the depth of the groove is 10 μm or more and 40 μm or less, An image forming apparatus characterized in that a ridge portion formed between the groove portions has a flat portion polished along the circumferential direction of the tension roller, and the width of the flat portion in the axial direction of the tension roller is 30 μm or more and 150 μm or less.

2. An image carrier; an image forming unit for forming a toner image on the image carrier; an endless belt member onto which a toner image is transferred from the image carrier; a tension roller for tensioning the belt member, The tension roller has a spiral groove formed on a peripheral surface of the tension roller so as to go around an axial direction of the tension roller, In the axial direction of the tension roller, the width of the groove is 100 μm or more and 500 μm or less, and the depth of the groove is 10 μm or more and 40 μm or less, An image forming apparatus characterized in that a ridge portion formed between the groove portions has a curved surface portion polished along the circumferential direction of the tension roller, and the width of the curved surface portion in the axial direction of the tension roller is 30 μm or more and 150 μm or less.

3. 3. The image forming apparatus according to claim 1, wherein the groove portion is formed by a first flat portion disposed on one side surface and a second flat portion disposed on the other side surface.

4. 4. The image forming apparatus according to claim 1, wherein a width of the region in which the groove is formed in the axial direction of the tension roller is larger than a width of a maximum image forming region.

5. 5. The image forming apparatus according to claim 1, wherein the belt member has a thickness of 0.02 mm or more and 0.50 mm or less.

6. A method for manufacturing an image forming apparatus having a tension roller that tensions an endless belt member onto which a toner image is transferred, comprising the steps of: a cutting step of forming a spiral groove on the peripheral surface of the tension roller so as to go around the axial direction of the tension roller; a polishing process for polishing ridge portions formed between the groove portions in a cross section of the tension roller parallel to the axial direction of the tension roller in a polishing direction along the circumferential direction of the tension roller.

Images