Transfer device and image forming apparatus

Abstract

To reduce a difference between pressure generated between one transfer roll and one image holding body in a center part in an axial direction and pressure generated between each of other transfer rolls and each of other image holding bodies, compared with a case where a shape of the one transfer roll and a shape of each of the other transfer rolls are the same as each other.SOLUTION: A transfer device comprises: an endless transfer belt; one image holding body that is in contact with the transfer belt from above; other image holding bodies that are in contact with the transfer belt from below; one transfer roll that sandwiches the transfer belt with the one image holding body, transfers an image held on the one image holding body to the transfer belt and has one cylindrical roll part; and other transfer rolls that are arranged on the opposite side of the transfer belt with respect to the other image holding bodies, sandwich the transfer belt with each of the other image holding bodies, transfer an image held on each of the other image holding bodies to the transfer belt, and have other roll parts in which an amount of projection of an axial center part with respect to a cylindrical contour at axial ends is made smaller than an amount of projection of the axial center part with respect to a contour at axial ends of the one roll part.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a transfer device and an image forming apparatus. [Background technology]

[0002] The image forming apparatus described in Patent Document 1 includes a plurality of image forming units that form a visible image by adhering a charged developer to an electrostatic latent image, a transfer belt member onto which the visible images formed by each of the plurality of image forming units are transferred, a plurality of tension members that suspend the transfer belt member, a primary transfer member that transfers the visible images formed by the plurality of image forming units to the transfer belt member, a secondary transfer member that transfers the visible images transferred to the transfer belt member to a recording medium, and a fixing unit that fixes the recording medium onto which the visible image has been transferred, and the image forming units are arranged in two or more transfer areas formed by dividing the transfer belt member with a plurality of tension members. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2009-80325 A Summary of the Invention [Problem to be solved by the invention]

[0004] The transfer device is provided with a plurality of image carriers arranged side by side in the rotation direction of the transfer belt, and transfer rolls arranged on the opposite sides of the image carriers across the transfer belt.

[0005] Here, one transfer roll may be provided that is arranged on the opposite side of one image carrier that contacts the outer peripheral surface of the transfer belt from above, with the transfer belt sandwiched therebetween, and another transfer roll may be provided that is arranged on the opposite side of another image carrier that contacts the outer peripheral surface of the transfer belt from below, with the transfer belt sandwiched therebetween.

[0006] In this configuration, when the shape of one transfer roll and the shape of the other transfer roll are the same, a difference occurs between the pressure at the axial center generated between one transfer roll and one image carrier and the pressure at the axial center generated between the other transfer roll and the other image carrier due to deflection of the transfer roll due to gravity.

[0007] The objective of the present disclosure is to reduce the difference between the pressure at the axial center generated between one transfer roll and one image carrier and the pressure at the axial center generated between another transfer roll and another image carrier, compared to when the shape of one transfer roll and the shape of another transfer roll are the same. [Means for solving the problem]

[0008] A transfer device according to a first aspect of the present disclosure is characterized in that it comprises a rotating, endless transfer belt onto which an image is transferred, one image holder that holds an image and contacts the outer peripheral surface of the transfer belt from above, another image holder that holds an image and contacts the outer peripheral surface of the transfer belt from below, one transfer roll that sandwiches the transfer belt between the one image holder and transfers the image held by the one image holder to the transfer belt and has a cylindrical one roll portion, and another transfer roll that sandwiches the transfer belt between the other image holder and transfers the image held by the other image holder to the transfer belt, and has another roll portion that is cylindrical and has a protrusion amount of the axial center relative to the outer shape of the axial end portions that is smaller than the protrusion amount of the axial center relative to the outer shape of the axial end portions of the one roll portion.

[0009] A transfer device according to a second aspect of the present disclosure is characterized in that, in the transfer device according to the first aspect, the outer peripheral surface of the one roll portion and the outer peripheral surface of the other roll portion are configured as curved surfaces.

[0010] A transfer device according to a third aspect of the present disclosure is characterized in that, in the transfer device according to the second aspect, the protrusion amount of the one roll portion is positive and the protrusion amount of the other roll portion is negative.

[0011] A transfer device according to a fourth aspect of the present disclosure is characterized in that, in the transfer device according to the first aspect, the outer diameter of the one image carrier and the outer diameter of the other image carrier are similar.

[0012] A transfer device according to a fifth aspect of the present disclosure is characterized in that, in the transfer device according to the fourth aspect, the one transfer roll has one shaft member that is inserted into the one roll portion and protrudes from both sides of the one roll portion, and the other transfer roll has another shaft member that is inserted into the other roll portion and protrudes from both sides of the other roll portion, and the distance between the center of the one shaft member at a portion where the one shaft member is supported and the axis of the one image carrier is shorter than the distance between the center of the other shaft member at a portion where the other shaft member is supported and the axis of the other image carrier.

[0013] An image forming apparatus according to a sixth aspect of the present disclosure is characterized in that it comprises a transfer device according to any one of claims 1 to 5, and a fixing section which fixes an image transferred to a recording medium by the transfer device onto the recording medium. Effect of the Invention

[0014] According to the transfer device of the first aspect of the present disclosure, the difference between the pressure at the axial center generated between one transfer roll and one image carrier and the pressure at the axial center generated between the other transfer roll and the other image carrier can be made smaller compared to when the shape of one transfer roll and the shape of another transfer roll are the same.

[0015] According to the transfer device of the second aspect of the present disclosure, compared to a case in which the outer peripheral surface of one roll portion and the outer peripheral surface of the other roll portion include a step portion, the change in pressure generated between one transfer roll and one image carrier in the axial direction, and the pressure generated between the other transfer roll and the other image carrier in the axial direction, change gradually.

[0016] According to the transfer device of the third aspect of the present disclosure, the difference between the pressure at the axial center generated between one transfer roll and one image carrier and the pressure at the axial center generated between another transfer roll and another image carrier can be made smaller compared to when the protrusion amounts of both roll portions are positive or when the protrusion amounts of both roll portions are negative.

[0017] According to the transfer device according to the fourth aspect of the present disclosure, an increase in the number of parts can be suppressed compared to a case in which the outer diameter of one image carrier is different from the outer diameter of another image carrier.

[0018] According to the transfer device of the fifth aspect of the present disclosure, the difference between the axial center pressure generated between one transfer roll and one image holder and the axial center pressure generated between another transfer roll and another image holder can be made smaller than when the distances between the center of the shaft member and the axis of the image holder at the portion where the shaft member is supported are all the same.

[0019] According to the image forming apparatus according to the sixth aspect of the present disclosure, degradation in quality of the output image can be suppressed compared to a case in which a transfer device in which one roll portion and another roll portion have the same shape is provided. [Brief description of the drawings]

[0020] [Figure 1] 1 is a schematic configuration diagram illustrating an image forming apparatus according to an embodiment of the present disclosure. [Diagram 2] 1 is a schematic configuration diagram illustrating a transfer device according to an embodiment of the present disclosure. [Diagram 3] 1 is a schematic configuration diagram illustrating a transfer device according to an embodiment of the present disclosure. [Figure 4] FIG. 2 is a schematic configuration diagram illustrating a photoconductor and a primary transfer roll in a transfer device according to an embodiment of the present disclosure. [Diagram 5] FIG. 2 is a schematic configuration diagram illustrating a photoconductor and a primary transfer roll in a transfer device according to an embodiment of the present disclosure. [Figure 6] 4A and 4B are diagrams illustrating a roll unit and the like of a transfer device according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] An example of a transfer device and an image forming device according to an embodiment of the present disclosure will be described with reference to Figures 1 to 6. Note that, in the drawings, arrow H indicates the up-down direction (vertical direction) of the device, arrow W indicates the width direction (horizontal direction) of the device, and arrow D indicates the depth direction (horizontal direction) of the device.

[0022] (Image forming apparatus 10) The image forming apparatus 10 according to the present embodiment is an electrophotographic image forming apparatus that forms a toner image on a sheet member P as a recording medium. As shown in FIG. 1, the image forming apparatus 10 includes a storage section 20, a conveying section 30, an image forming section 40, and a fixing device 50.

[0023] [Storage section 20, conveying section 30] The storage section 20 includes a storage member 22 that stores the sheet material P, and a delivery roll 24 that delivers the sheet material P stored in the storage member 22 to a transport path 32 for the sheet material P. In addition, the transport section 30 includes a plurality of transport rolls 34 that transport the sheet material P along the transport path 32.

[0024] [Image forming unit 40] The image forming section 40 includes a toner image forming section 60 that forms a toner image, and a transfer device 70 that transfers the toner image formed in the toner image forming section 60 onto a sheet member P.

[0025] -Toner image forming unit 60- The toner image forming unit 60 includes toner image forming units 60Y, 60M, 60C, and 60K for a total of four colors: yellow (Y), magenta (M), cyan (C), and black (K). Note that the alphabets at the end of the reference numerals may be omitted when there is no need to distinguish between Y, M, C, and K.

[0026] Toner image forming units 60Y and 60M are basically configured in the same way except for the toner they use, whereas toner image forming units 60C and 60K are basically configured in the same way except for the toner they use.

[0027] 1 and 2, the toner image forming units 60Y and 60M are aligned along a horizontal portion of a transfer belt 71 provided in the transfer device 70. Also, the toner image forming units 60C and 60K are aligned along an inclined portion of the transfer belt 71 provided in the transfer device 70, as shown in FIGS.

[0028] As shown in FIG. 2, the toner image forming units 60Y and 60M are equipped with photoconductors 61Y and 61M which rotate in the direction of the arrow A01 in the figure and contact the outer peripheral surface of the transfer belt 71 from above, and charging devices 62Y and 62M which charge the photoconductors 61Y and 61M.

[0029] Furthermore, the toner image forming units 60Y, 60M are equipped with exposure devices 63Y, 63M that expose the photoconductors 61Y, 61M charged by the charging devices 62Y, 62M to form electrostatic latent images, and developing devices 64Y, 64M that develop the electrostatic latent images using toner to form toner images.

[0030] As shown in FIG. 3, the toner image forming units 60C and 60K include photoconductors 61C and 61K which rotate in the direction of the arrow A02 in the figure and contact the outer peripheral surface of the transfer belt 71 from below, and charging devices 62C and 62K which charge the photoconductors 61C and 61K.

[0031] Furthermore, the toner image forming units 60C, 60K are equipped with exposure devices 63C, 63K that expose the photoconductors 61C, 61K charged by the charging devices 62C, 62K to form electrostatic latent images, and developing devices 64C, 64K that develop the electrostatic latent images using toner to form toner images.

[0032] -Transfer device 70- 1, the transfer device 70 includes photoconductors 61Y, 61M, 61C, and 61K, a transfer belt 71, a plurality of rolls 72, primary transfer rolls 73Y, 73M, 73C, and 73K, a secondary transfer roll 76, and a removal blade 78. In this manner, the photoconductors 61Y, 61M, 61C, and 61K are members that constitute the transfer device 70 and also members that constitute the toner image forming section 60.

[0033] In this configuration, the primary transfer rolls 73Y, 73M, 73C, and 73K transfer the toner images held on the photoconductors 61Y, 61M, 61C, and 61K to the rotating transfer belt 71. Furthermore, the secondary transfer roll 76 transfers the toner images transferred to the transfer belt 71 to the conveyed sheet member P. The transfer device 70 will be described in detail later.

[0034] [Fixing device 50] 1, the fixing device 50 includes a rotating heating roll 50a and a pressure roll 50b that rotates following the heating roll 50a, sandwiches a sheet member P between the heating roll 50a, and presses the sheet member P against the heating roll 50a. The fixing device 50 is an example of a fixing section.

[0035] As a result, the fixing device 50 heats and pressurizes the sheet member P onto which the toner image has been transferred, thereby fixing the toner image onto the sheet member P. Then, the sheet member P onto which the toner image has been fixed is discharged to the outside of the housing 10a of the image forming apparatus 10.

[0036] (Main part configuration) Next, the transfer device 70 will be described. As described above, the transfer device 70 includes the photoconductors 61Y, 61M, 61C, and 61K, the transfer belt 71, a plurality of rolls 72, the primary transfer rolls 73Y, 73M, 73C, and 73K, the secondary transfer roll 76, and the removal blade 78. The photoconductors 61Y and 61M are an example of one image carrier, and the photoconductors 61C and 61K are an example of another image carrier. The primary transfer rolls 73Y and 73M are an example of one transfer roll, and the primary transfer rolls 73C and 73K are an example of another transfer roll.

[0037] [Photoreceptor 61] Photoconductors 61Y, 61M, 61C, and 61K have a circular cross section, and all of photoconductors 61Y, 61M, 61C, and 61K have the same outer diameter. In other words, photoconductors 61Y, 61M, 61C, and 61K all have the same shape.

[0038] 2, the photoconductors 61Y and 61M are in contact with the outer circumferential surface of the transfer belt 71 from above. Also, the photoconductors 61C and 61K are in contact with the outer circumferential surface of the transfer belt 71 from below.

[0039] [Transfer belt 71, roll 72, secondary transfer roll 76, removal blade 78] 1, the transfer belt 71 is endless and wound around a plurality of rolls 72 so as to assume an inverted triangular posture. The toner image forming units 60Y and 60M are aligned along an upper horizontal portion of the transfer belt 71, and the toner image forming units 60C and 60K are aligned along an inclined portion of the transfer belt 71 on one side in the device width direction (the right side in the figure). The transfer belt 71 rotates in the direction of arrow B when at least one of the plurality of rolls 72 is driven to rotate.

[0040] Among the multiple rolls 72, a secondary transfer roll 76 is disposed on the opposite side of the transfer belt 71 to the roll 72 (roll 72a in the figure) that is disposed so as to push out the inclined portion of the transfer belt 71 on the other side in the device width direction (left side in the figure). The secondary transfer roll 76 transfers the toner image transferred to the transfer belt 71 at a transfer position NT to the sheet member P being transported.

[0041] Furthermore, a removing blade 78 is disposed on the opposite side of the transfer belt 71 with respect to the roll 72 (roll 72b in the drawing) around which the other side of the transfer belt 71 in the device width direction is wound. The removing blade 78 is configured to remove any deposits adhering to the transfer belt 71 from the transfer belt 71.

[0042] [Primary transfer roll 73] As shown in FIG. 2, the primary transfer rolls 73Y and 73M are disposed on the opposite side of the transfer belt 71 with respect to the photoconductors 61Y and 61M, and sandwich the transfer belt 71 between the lower side of the transfer belt 71 and the photoconductors 61Y and 61M.

[0043] Here, the fact that the primary transfer rolls 73Y, 73M sandwich the transfer belt 71 between the photoconductors 61Y, 61M and the lower side of the transfer belt 71 means that the primary transfer rolls 73Y, 73M are disposed below the photoconductors 61Y, 61M as viewed from the device depth direction. Specifically, the primary transfer rolls 73Y, 73M are disposed below the photoconductors 61Y, 61M in a state in which a line segment L1 connecting the center C of the primary transfer rolls 73Y, 73M and the center C of the photoconductors 61Y, 61M is inclined by 15 degrees or more with respect to the horizontal direction. In this embodiment, as an example, the line segment L1 is inclined by 90 degrees with respect to the horizontal direction.

[0044] As shown in FIG. 4, the primary transfer rolls 73Y, 73M are configured to include roll portions 80Y, 80M that are cylindrical and made of an elastic material, and shaft members 82Y, 82M that are inserted into the roll portions 80Y, 80M and are made of stainless steel and protrude from both sides of the roll portions 80Y, 80M.

[0045] The primary transfer rolls 73Y and 73M are rotatably supported by support members 98 disposed on both ends of the shaft members 82Y and 82M. As a result, the primary transfer rolls 73Y and 73M are rotated by being driven by the moving transfer belt 71.

[0046] On the other hand, as shown in FIG. 3, the primary transfer rolls 73C and 73K are disposed on the opposite side of the transfer belt 71 from the photoconductors 61C and 61K, and sandwich the transfer belt 71 between them from above the transfer belt 71.

[0047] Here, the fact that the primary transfer rolls 73C, 73K sandwich the transfer belt 71 between the photoconductors 61C, 61K and the upper side of the transfer belt 71 means that the primary transfer rolls 73C, 73K are disposed above the photoconductors 61C, 61K as viewed from the device depth direction. Specifically, the primary transfer rolls 73C, 73K are disposed above the photoconductors 61C, 61K in a state in which the line segment L2 connecting the center C of the primary transfer rolls 73C, 73K and the center C of the photoconductors 61C, 61K is inclined by 15 degrees or more with respect to the horizontal direction. In this embodiment, as an example, the line segment L2 is inclined by 65 degrees with respect to the horizontal direction.

[0048] As shown in FIG. 5, the primary transfer rolls 73C, 73K are configured to include roll portions 80C, 80K that are cylindrical and made of an elastic material, and shaft members 82C, 82K that are inserted into the roll portions 80C, 80K and protrude from both sides of the roll portions 80C, 80K and are made of stainless steel.

[0049] The primary transfer rolls 73C and 73K are rotatably supported by support members 98 disposed on both ends of the shaft members 82C and 82K. As a result, the primary transfer rolls 73C and 73K are rotated by being driven by the moving transfer belt 71.

[0050] Here, the primary transfer rolls 73Y and 73M are deflected by gravity with the support member 98 as a support point, as shown by the two-dot chain line in FIG. 4. Therefore, the distance between the primary transfer rolls 73Y and 73M and the photoconductors 61Y and 61M at the axial center becomes longer than when the primary transfer rolls are not deflected. In contrast, the primary transfer rolls 73C and 73K are deflected by gravity with the support member 98 as a support point, as shown by the two-dot chain line in FIG. 5. Therefore, the distance between the primary transfer rolls 73C and 73K and the photoconductors 61C and 61K at the axial center becomes shorter than when the primary transfer rolls are not deflected.

[0051] It should be noted that the two-dot chain lines in Figs. 4 and 5 indicating the bending are exaggerated so that the bending state can be easily understood.

[0052] For the above reasons, it is considered that the pressure generated between the primary transfer rolls 73Y, 73M and the photoconductors 61Y, 61M at the axial center is weaker than the pressure generated between the primary transfer rolls 73C, 73K and the photoconductors 61C, 61K at the axial center.

[0053] However, as shown in FIG. 6A, the outer diameter of the axial center of the roll parts 80Y, 80M of the primary transfer rolls 73Y, 73M is larger than the outer diameter of the axial end of the roll parts 80Y, 80M. The outer peripheral surface of the roll parts 80Y, 80M is formed by one convex curved surface. In this way, the outer peripheral surface of the roll parts 80Y, 80M is formed into a positive crown shape. Here, the axial end of the roll part 80 is the axial end of the outer peripheral surface of the roll part 80. Also, the axial center of the roll part 80 is a portion that is the same distance from one axial end and the same distance from the other axial end.

[0054] In contrast, as shown in FIG. 6B, the outer diameter of the axial center of the roll parts 80C and 80K of the primary transfer rolls 73C and 73K is smaller than the outer diameter of the axial end parts of the roll parts 80C and 80K. The outer peripheral surfaces of the roll parts 80C and 80K are formed by a single concave curved surface. In this manner, the outer peripheral surfaces of the roll parts 80C and 80K are negatively crowned. The outer diameters of the axial end parts of the roll parts 80C and 80K are the same as the outer diameters of the axial end parts of the roll parts 80Y and 80M. The degree of the crown shape shown in FIG. 6A and FIG. 6B is exaggerated so that the crown shape can be easily understood.

[0055] Furthermore, the distance (D1 shown in FIG. 4) between the center of the portion where the shaft members 82Y, 82M are supported by the support member 98 and the axis of the photoconductors 61Y, 61M is shorter than the distance (D2 shown in FIG. 5) between the center of the portion where the shaft members 82C, 82K are supported by the support member 98 and the axis of the photoconductors 61C, 61K. Note that the distances D1 and D2 can be measured, for example, by using a three-dimensional measuring device.

[0056] (summary) As described above, in the transfer device 70, the outer diameter of the axial center portion of the roll portion 80Y, 80M of the primary transfer roll 73Y, 73M is larger than the outer diameter of the axial end portion of the roll portion 80Y, 80M. Furthermore, the outer diameter of the axial center portion of the roll portion 80C, 80K of the primary transfer roll 73C, 73K is smaller than the outer diameter of the axial end portion of the roll portion 80C, 80K. Therefore, compared to the case where the shape of the roll portion 80Y, 80M of the primary transfer roll 73Y, 73M is the same as the shape of the roll portion 80C, 80K of the primary transfer roll 73C, 73K, the difference between the pressure of the axial center portion generated between the primary transfer roll 73Y, 73M and the photoconductor 61Y, 61M and the pressure of the axial center portion generated between the primary transfer roll 73C, 73K and the photoconductor 61C, 61K becomes smaller.

[0057] In the transfer device 70, the outer circumferential surfaces of the roll parts 80Y and 80M and the outer circumferential surfaces of the roll parts 80C and 80K are curved surfaces. As a result, the pressure generated between the primary transfer roll 73 and the photoreceptor 61 in the axial direction gradually changes, compared to when the roll parts are configured to include a step portion.

[0058] In addition, in the transfer device 70, the outer peripheral surfaces of the roll parts 80Y and 80M have a positive crown shape, and the outer peripheral surfaces of the roll parts 80C and 80K have a negative crown shape. In other words, the protrusion amount of the roll parts 80Y and 80M is positive, and the protrusion amount of the roll parts 80C and 80K is negative. Therefore, compared to when the protrusion amounts of both roll parts are positive or when the protrusion amounts of both roll parts are negative, the difference between the pressure at the axial center generated between the primary transfer rolls 73Y and 73M and the photoconductors 61Y and 61M and the pressure at the axial center generated between the primary transfer rolls 73C and 73K and the photoconductors 61C and 61K becomes smaller. Here, the magnitude of the protrusion amount does not refer to the magnitude of the absolute value, but refers to the magnitude taking into account the positive and negative values.

[0059] Furthermore, in the transfer device 70, the outer diameter of the photoconductors 61Y and 61M is the same as the outer diameter of the photoconductors 61C and 61K. This suppresses an increase in the number of parts compared to a case in which the outer diameter of the photoconductors 61Y and 61M is different from the outer diameter of the photoconductors 61C and 61K.

[0060] In the transfer device 70, the distance (D1 shown in FIG. 4) between the center of the portion where the shaft members 82Y, 82M are supported by the support member 98 and the axis of the photoconductors 61Y, 61M is shorter than the distance (D2 shown in FIG. 5) between the center of the portion where the shaft members 82C, 82K are supported by the support member 98 and the axis of the photoconductors 61C, 61K. As a result, compared to a case where the distances between the centers of the shaft members at the portions where the shaft members are supported and the axis of the photoconductors are all the same, the displacement of the shaft member 82 caused by the reaction force of the roll portion 80 is corrected, and the difference between the pressure at the axial center generated between the primary transfer rolls 73Y, 73M and the photoconductors 61Y, 61M and the pressure at the axial center generated between the primary transfer rolls 73C, 73K and the photoconductors 61C, 61K is reduced.

[0061] The image forming apparatus 10 is also provided with a transfer device 70. This reduces the difference in pressure generated between the primary transfer roll 73 and the photoconductor 61 at the axial center compared to a case where a transfer device is provided in which the roll portions 80Y and 80M have the same shape as the roll portions 80C and 80K, thereby suppressing deterioration in the quality of the output image.

[0062] Although the present disclosure has been described in detail with respect to a specific embodiment, it is clear to those skilled in the art that the present disclosure is not limited to the embodiment, and various other embodiments are possible within the scope of the present disclosure. For example, in the embodiment, the outer peripheral surface of the roll part 80 is configured as a curved surface, but the roll part may be provided with corners, steps, etc. However, in this case, the effect of the outer peripheral surface of the roll part 80 being configured as a curved surface is not achieved.

[0063] Also, in the above embodiment, the protrusion amount of the roll parts 80Y, 80M is positive and the protrusion amount of the roll parts 80C, 80K is negative, but the protrusion amounts of both roll parts may be positive, or both roll parts may be negative, or one of the protrusion amounts may be 0. However, in this case, the effect of the protrusion amount of the roll parts 80Y, 80M being positive and the protrusion amount of the roll parts 80C, 80K being negative is not achieved.

[0064] In the above embodiment, the distance (D1 shown in FIG. 4) between the center of the portion where the shaft members 82Y, 82M are supported by the support member 98 and the axis of the photoconductors 61Y, 61M is shorter than the distance (D2 shown in FIG. 5) between the center of the portion where the shaft members 82C, 82K are supported by the support member 98 and the axis of the photoconductors 61C, 61K. However, the distance D1 and the distance D2 may be the same distance. In that case, however, the effect of making the distance D1 shorter than the distance D2 is not achieved.

[0065] In addition, although not specifically described in the above embodiment, the pressure generated between the secondary transfer roll 76 and the roll 72a is made higher than the pressure generated between the primary transfer roll 73 and the photoconductor 61.

[0066] (((1))) A transfer belt that rotates endlessly and onto which an image is transferred; an image carrier that carries an image and contacts the outer peripheral surface of the transfer belt from above; another image carrier that carries an image and is in contact with the outer peripheral surface of the transfer belt from below; a transfer roll having a cylindrical roll portion, the transfer roll sandwiching the transfer belt between the first image carrier and the first image carrier and transferring an image held by the first image carrier onto the transfer belt; another transfer roll, which sandwiches the transfer belt between itself and the other image carrier and transfers an image held by the other image carrier to the transfer belt, and which has a cylindrical other roll portion in which the amount of protrusion of the axial center portion relative to the outer shape of the axial end portions is smaller than the amount of protrusion of the axial center portion relative to the outer shape of the axial end portions of the one roll portion; A transfer device comprising:

[0067] (((2))) The outer circumferential surface of the one roll portion and the outer circumferential surface of the other roll portion are configured with curved surfaces. The transfer device according to (((1))).

[0068] (((3))) a protruding amount of the one roll portion is positive and a protruding amount of the other roll portion is negative; A transfer device according to (((1))) or (((2))).

[0069] (((4))) the outer diameter of the one image carrier is the same as the outer diameter of the other image carrier; The transfer device according to any one of (((1))) to (((3))).

[0070] (((5))) the first transfer roll has a shaft member that is inserted into the first roll portion and protrudes from both sides of the first roll portion, the other transfer roll has another shaft member that is inserted into the other roll portion and protrudes from both sides of the other roll portion, a distance between a center of the first shaft member at a portion where the first shaft member is supported and an axis of the first image carrier is shorter than a distance between a center of the second shaft member at a portion where the second shaft member is supported and an axis of the second image carrier; The transfer device according to any one of (((1))) to (((4))).

[0071] (((6))) A transfer device according to any one of (((1))) to (((5))), a fixing unit that fixes the image transferred onto the recording medium by the transfer device; An image forming apparatus comprising:

[0072] According to the transfer device of (((1))), the difference between the pressure at the axial center generated between one transfer roll and one image carrier and the pressure at the axial center generated between the other transfer roll and the other image carrier can be made smaller than when the shape of one transfer roll and the shape of another transfer roll are the same.

[0073] According to the transfer device of (((2))), compared to a case in which the outer peripheral surface of one roll portion and the outer peripheral surface of the other roll portion are configured to include a step portion, the change in pressure generated between one transfer roll and one image carrier in the axial direction, and the pressure generated between the other transfer roll and the other image carrier in the axial direction, change gradually.

[0074] According to the transfer device of (((3))), the difference in pressure at the axial center generated between one transfer roll and one image carrier and the pressure at the axial center generated between another transfer roll and another image carrier can be made smaller, compared to when the protrusion amounts of both roll portions are positive or when the protrusion amounts of both roll portions are negative.

[0075] According to the transfer device of (((4))), an increase in the number of parts can be suppressed compared to a case in which the outer diameter of one image carrier is different from the outer diameter of another image carrier.

[0076] According to the transfer device of (((5))), the difference in axial center pressure generated between one transfer roll and one image holder and the difference in axial center pressure generated between another transfer roll and another image holder can be made smaller, compared to a case in which the distances between the center of the shaft member and the axis of the image holder at the portion where the shaft member is supported are all the same.

[0077] According to the image forming apparatus of (((6))), deterioration in quality of the output image can be suppressed compared to a case in which a transfer device in which one roll portion and another roll portion have the same shape is provided. [Explanation of symbols]

[0078] 10 Image forming device 50 Fixing device (an example of a fixing section) 61C Photoconductor (an example of another image carrier) 61K Photoconductor (an example of another image carrier) 61M Photoconductor (an example of an image carrier) 61Y Photoconductor (an example of an image carrier) 70 Transcription device 71 Transfer belt 73C Primary transfer roll (an example of another transfer roll) 73Y Primary transfer roll (an example of another transfer roll) 73M Primary transfer roll (an example of a primary transfer roll) 73Y Primary transfer roll (an example of a primary transfer roll) 80C Roll section (an example of another roll section) 80K roll section (an example of another roll section) 80M Roll section (Example of one roll section) 80Y Roll section (an example of a roll section) 82C Shaft members (examples of other shaft members) 82K Shaft component (an example of another shaft component) 82M Shaft member (an example of a shaft member) 82Y Shaft member (an example of a shaft member) 98 Support member

Claims

1. A transfer belt that rotates endlessly and onto which an image is transferred; an image carrier that carries an image and contacts the outer peripheral surface of the transfer belt from above; another image carrier that carries an image and is in contact with the outer peripheral surface of the transfer belt from below; a transfer roll having a cylindrical roll portion, the transfer roll sandwiching the transfer belt between the first image carrier and the first image carrier and transferring an image held by the first image carrier onto the transfer belt; another transfer roll, which sandwiches the transfer belt between itself and the other image carrier and transfers an image held by the other image carrier to the transfer belt, and which has a cylindrical other roll portion in which the amount of protrusion of the axial center portion relative to the outer shape of the axial end portions is smaller than the amount of protrusion of the axial center portion relative to the outer shape of the axial end portions of the one roll portion; A transfer device comprising:

2. The outer circumferential surface of the one roll portion and the outer circumferential surface of the other roll portion are configured with curved surfaces. The transfer device according to claim 1 .

3. a protruding amount of the one roll portion is positive and a protruding amount of the other roll portion is negative; The transfer device according to claim 2 .

4. the outer diameter of the one image carrier is the same as the outer diameter of the other image carrier; The transfer device according to claim 1 .

5. the first transfer roll has a shaft member that is inserted into the first roll portion and protrudes from both sides of the first roll portion, the other transfer roll has another shaft member that is inserted into the other roll portion and protrudes from both sides of the other roll portion, a distance between a center of the first shaft member at a portion where the first shaft member is supported and an axis of the first image carrier is shorter than a distance between a center of the second shaft member at a portion where the second shaft member is supported and an axis of the second image carrier; The transfer device according to claim 4 .

6. A transfer device according to any one of claims 1 to 5, a fixing unit that fixes the image transferred onto the recording medium by the transfer device; An image forming apparatus comprising:

Images