JP2019158915A - Fixing device and image forming apparatus - Google Patents

Abstract

To prevent wrinkles on a sheet and conveyance disturbance on the upstream side in a sheet conveyance direction of a pressure area.SOLUTION: A fixing device 1 comprises: a rotatable endless fixing belt 21; a pressure roller 23 that forms, with the fixing belt 21, a pressure area N through which a sheet is sandwiched and conveyed; and a pressing pad 27 that is in contact with an inner peripheral surface of the fixing belt 21 in the pressure area N and has a slide surface 41 sliding with respect to the rotating fixing belt 21. The slide surface 41 has an arc-shaped surface 43 that has a radius of curvature larger than the radius of curvature of the pressure roller 23 and is depressed on the opposite side of the pressure roller 23, and a first flat surface 45 that is formed on the upstream side in a sheet conveyance direction Y continuously from the arc-shaped surface 43. The boundary B1 between the arc-shaped surface 43 and first flat surface 45 corresponds to an upstream end Nx in the conveyance direction Y of the pressure area N.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a fixing device that fixes a toner image on a sheet and an image forming apparatus including the fixing device.

  A sliding belt fixing method is known as one method for widening the pressure region of the fixing device. The fixing device of the sliding belt fixing method is formed between a pressure roller by pressing a flexible endless fixing belt against a pressure roller by a pressing pad disposed inside the fixing belt. It is rotated by the frictional force in the pressure region. The sheet on which the toner image has been transferred is nipped and conveyed between the fixing belt and the pressure roller, and the toner image is fixed on the sheet.

  Conventionally, in the sliding belt fixing system, studies have been made to suppress the occurrence of paper wrinkles. For example, the fixing device described in Patent Document 1 locally increases the pressing pressure of the pressure pad on the upstream side in the paper conveyance direction and projects the central portion of the pressure area to the upstream side, thereby preventing the paper from being pressed. Reduces stress and suppresses wrinkles. Further, the fixing device described in Patent Document 2 suppresses the occurrence of paper wrinkles by forming both the upstream side and the downstream side of the pressing pad in the paper transport direction in a convex shape.

JP 2007-41288 A JP 2014-228762 A

  However, the configurations described in Patent Documents 1 and 2 are intended to improve the behavior of the paper after entering the pressurizing region, and are upstream of the pressurizing region in the paper transport direction. Whether paper is conveyed along the conveyance path without disturbing its behavior has not been studied. Therefore, with the configurations described in Patent Documents 1 and 2, it is not possible to suppress paper wrinkles and transport disturbances on the upstream side in the paper transport direction from the pressurization region.

  In view of the above circumstances, an object of the present invention is to suppress paper wrinkles and conveyance disturbance on the upstream side in the paper conveyance direction from the pressurization region.

  In order to solve the above problems, a fixing device of the present invention includes a rotatable endless fixing belt, a pressure roller that forms a pressure region in which a sheet is nipped and conveyed between the fixing belt, A pressure pad having a sliding surface that contacts the inner peripheral surface of the fixing belt in the pressure region and slides relative to the rotating fixing belt, and the sliding surface has a curvature of the pressure roller. An arcuate surface having a radius of curvature greater than the radius and recessed to the opposite side of the pressure roller; and a first flat surface formed continuously from the arcuate surface to the upstream side in the paper conveyance direction; The boundary between the arcuate surface and the first flat surface corresponds to the upstream end of the pressurizing region in the transport direction.

  In the fixing device according to the aspect of the invention, the upstream end portion of the first flat surface in the transport direction is located at the center in the width direction of the sheet on the upstream side of the transport direction from both ends in the width direction. It is good also as the characteristic.

  In the fixing device of the present invention, the first flat surface may be inclined to the pressure roller side with respect to an extended surface obtained by extending the arc-shaped surface to the upstream side in the transport direction.

  In the fixing device of the present invention, an end of the first flat surface on the upstream side in the transport direction may be located on the pressure roller side with respect to the extended surface.

  In the fixing device of the present invention, the sliding surface has a second flat surface formed continuously from the arc-shaped surface to the downstream side in the sheet conveyance direction, and the arc-shaped surface and the second flat surface. The boundary with the surface may correspond to the downstream end of the pressurizing region in the transport direction.

  In the fixing device of the present invention, the second flat surface may be inclined to the pressure roller side with respect to an extended surface obtained by extending the arc-shaped surface to the downstream side in the transport direction.

  The fixing device according to the present invention may include a sliding sheet that covers the sliding surface, and the pressing pad contacts an inner peripheral surface of the fixing belt via the sliding sheet.

  An image forming apparatus according to the present invention includes an image forming unit that forms a toner image on a sheet, and the fixing device described above that fixes the toner image on the sheet.

  According to the present invention, paper wrinkles and transport disturbance on the upstream side in the paper transport direction from the pressurizing region are suppressed.

1 is a front view schematically showing an internal configuration of a printer according to an embodiment of the present invention. 1 is a cross-sectional view illustrating a fixing device according to an embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating a pressing pad of a fixing device according to an embodiment of the present invention. It is sectional drawing of the boundary periphery of the press pad which concerns on one Embodiment of this invention. It is a bottom view of the press pad concerning one embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating a pressure region of a fixing device according to an embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating a pressing pad of a fixing device according to an embodiment of the present invention. It is sectional drawing of the boundary periphery of the press pad which concerns on one Embodiment of this invention. FIG. 3 is a cross-sectional view illustrating a pressure region of a fixing device according to an embodiment of the present invention.

  Hereinafter, an image forming apparatus and a fixing device of the present invention will be described with reference to the drawings.

  First, the overall configuration of a printer as an image forming apparatus will be described with reference to FIG. FIG. 1 is a front view schematically showing the internal configuration of the printer 1. In the following, the front side of the paper in FIG. 1 is the front side (front side) of the printer 1, and the left and right directions will be described with reference to the direction when the printer 1 is viewed from the front. In each figure, U, Lo, L, R, Fr, and Rr indicate up, down, left, right, front, and back, respectively.

  The apparatus main body 2 of the printer 1 includes a paper feed cassette 3 that accommodates the paper S, a paper feed device 5 that feeds the paper S from the paper feed cassette 3, an image forming unit 7 that forms a toner image on the paper S, A fixing device 9 that fixes the toner image onto the paper S, a paper discharge device 11 that discharges the paper S, and a paper discharge tray 13 that receives the discharged paper S are provided. Further, a conveyance path 15 for the sheet S from the sheet feeding device 5 to the sheet discharge device 11 through the image forming unit 7 and the fixing device 9 is formed in the apparatus main body 2.

  The paper S fed from the paper feed cassette 3 by the paper feeding device 5 is transported to the image forming unit 7 along the transport path 15, and a toner image is formed on the paper S. The sheet S is sent to the fixing device 9 along the conveyance path 15 and the toner image is fixed on the sheet S. The paper S on which the toner image is fixed is discharged from the paper discharge device 11 to the paper discharge tray 13.

  Next, the fixing device 9 will be described with reference to FIG. FIG. 2 is a cross-sectional view of the fixing device 9.

  As shown in FIG. 2, the fixing device 9 includes a fixing belt 21, a pressure roller 23, an IH heater 25, and a pressing pad 27. Further, the fixing device 9 includes a fixing housing (not shown) in which these are supported. The pressure pad 27 is disposed at a position facing the pressure roller 23 in the hollow portion of the fixing belt 21, and sandwiches the fixing belt 21 between the pressure roller 23. By the pressing pad 27 and the pressure roller 23 being pressed against each other. A pressure region N is formed between the pressure roller 23 and the fixing belt 21.

  The fixing belt 21 is an endless belt having a predetermined inner diameter and a width longer than the width of the paper S. The fixing belt 21 is formed of a flexible material, and includes a base material layer, an elastic layer provided on the outer peripheral surface of the base material layer, and a release layer provided on the outer peripheral surface of the elastic layer. Yes. The base material layer is formed of a polyimide resin provided with a magnetic metal such as Ni or a metal such as Cu, Ag, or Al. The elastic layer is made of silicon rubber or the like. The release layer is formed of a PFA tube or the like. Moreover, a sliding layer may be formed on the inner peripheral surface of the base material layer. The sliding layer is made of polyimide amide or PTFE.

  The fixing belt 21 is rotatably supported by a fixing housing by a belt guide 31. The belt guide 31 is supported by a support member 33 provided in the hollow portion of the fixing belt 21. The support member 33 is a square cylindrical member, and penetrates the hollow portion of the fixing belt 21 and is fixed to the fixing housing at both ends.

  The belt guide 31 has an arcuate cross-sectional shape along the inner peripheral surface of the fixing belt 21 and is formed of a material having a spring property. The belt guide 31 is fixed to the upper portion of the support member 33, applies tension to the fixing belt 21, and opposes the IH heater 25 with a predetermined interval. Instead of the belt guide 31, an arcuate flange portion provided at both ends of the fixing belt 21 may be provided in the fixing housing.

  The pressure roller 23 includes a metal core, an elastic layer provided on the outer peripheral surface of the metal core, and a release layer provided on the outer peripheral surface of the elastic layer. The elastic layer is made of silicon rubber or the like. The release layer is formed of a PFA tube or the like.

  The pressure roller 23 is disposed so as to contact the fixing belt 21 and is rotatably supported by the fixing housing. As a result, a pressure region N is formed between the pressure roller 23 and the fixing belt 21. The pressure roller 23 is connected to a drive source (not shown) and is driven to rotate. When the pressure roller 23 is rotated in the counterclockwise direction of FIG. 2 by the driving source, the fixing belt 21 is driven by the pressure roller 23 to rotate in the clockwise direction opposite to the rotation direction of the pressure roller 23. . As a result, the conveyed paper S passes through the pressure area N.

  The IH heater 25 includes a coil portion 25a, a coil bobbin 25b that holds the coil portion 25a in a winding shape, and an arch core 25c. The IH heater 25 is disposed so as to cover the outer peripheral surface of the fixing belt 21 and is supported by the fixing housing. A magnetic field is generated by applying a high-frequency AC voltage to the coil portion 25a. Due to the action of this magnetic field, an eddy current is generated in the base material layer of the fixing belt 21, the base material layer generates heat, and the fixing belt 21 is heated. The

  The pressing pad 27 is a flat, substantially rectangular parallelepiped member whose longitudinal direction is the width direction of the fixing belt 21, and is formed of a resin such as a liquid crystal polymer. The pressing pad 27 is disposed at a position facing the pressure roller 23 of the support member 33. A sliding sheet 35 that covers the surface of the pressing pad 27 that faces the pressure roller 23 is disposed, and the pressing pad 27 contacts the inner peripheral surface of the fixing belt 21 via the sliding sheet 35. When the fixing belt 21 rotates as described above, the fixing belt 21 slides with respect to the surface of the pressing pad 27 facing the pressure roller 23. Hereinafter, the surface of the pressing pad 27 that faces the pressure roller 23 is referred to as a sliding surface 41.

  Further, the fixing device 9 includes a paper entry guide 37 provided on the upstream side in the transport direction Y of the paper S with respect to the pressure region N, and a separation provided on the downstream side in the transport direction Y of the paper S with respect to the pressure region N. And a member 39. The sheet entry guide 37 is a member arranged to extend along the conveyance path 15 and guides the leading end of the sheet S conveyed from the image forming unit 7 to the pressure region N. The separating member 39 is arranged so that the tip thereof is positioned in the vicinity of the fixing belt, and separates the paper S from the fixing belt.

  Next, the pressing pad 27 will be described with reference to FIGS. 3, 4, 5, and 6. 3 is a sectional view of the pressing pad 27, FIG. 4 is a sectional view around the boundary B1 of the pressing pad 27, FIG. 5 is a bottom view of the pressing pad 27, and FIG.

  As shown in FIG. 3, the sliding surface 41 of the pressing pad 27 includes an arcuate surface 43 on the downstream side in the transport direction Y of the paper S and a first flat surface provided continuously from the arcuate surface 43 to the upstream side. And a surface 45. The arcuate surface 43 and the first flat surface 45 are smoothly continuous. The arc-shaped surface 43 is concavely curved on the side opposite to the pressure roller 23. The radius of curvature of the arcuate surface 43 is larger than the radius of curvature of the pressure roller 23. As an example, the radius of curvature of the arcuate surface 43 is preferably at least twice that of the pressure roller 23, and more preferably at least four times. However, when the radius of curvature of the arcuate surface 43 is increased, the length of the pressurizing region N along the transport direction Y is shortened. Therefore, the radius of curvature of the arcuate surface 43 is set according to the length of the pressurizing region N. Is done. The first flat surface 45 is inclined more toward the pressure roller 23 than a virtual extension surface 43a obtained by extending the arcuate surface 43 to the upstream side in the transport direction Y. Further, the upstream end 53c of the first flat surface 45 in the transport direction Y is located closer to the pressure roller 23 than the extended surface 43a.

  As shown in FIG. 4, the inclination angle θ1 of the first flat surface 45 with respect to the tangential plane 431 of the arc-shaped surface 43 at the boundary B1 between the arc-shaped surface 43 and the first flat surface 45 is 5 ° or more. 10 ° or less is desirable.

  As shown in FIG. 5, the upstream end 53 of the first flat surface 45 in the transport direction Y of the paper S has a central portion 53c in the width direction of the paper S (a direction perpendicular to the transport direction Y) in the width direction. It is formed so that it may be located in the upstream of the conveyance direction Y rather than both the edge parts 53e.

  As shown in FIG. 6, the fixing belt 21 is pressed against the pressure roller 23 by the sliding surface 41 of the pressing pad 27 to form a pressure region N between the fixing belt 21 and the pressure roller 23. ing. The pressure region N is not formed in a portion corresponding to the entire surface of the sliding surface 41, and the fixing belt 21 and the pressure roller 23 are in contact with each other at the upstream and downstream ends in the transport direction Y. Not. A boundary B1 between the arcuate surface 43 and the first flat surface 45 is provided so as to correspond to the upstream end Nx of the pressurizing region N. That is, the pressure region N is formed between the portion pressed by the arcuate surface 43 of the fixing belt 21 and the pressure roller 23. The portion pressed by the first flat surface 45 of the fixing belt 21 does not contact the pressure roller 23 and does not contribute to the pressure region N. Note that the boundary B1 is in the vicinity of the upstream end Nx of the pressurizing region N, a position that is about 0.5 to 1 mm away from the upstream end Nx, and a position that is about 0.5 to 1 mm away from the downstream side. Between.

  The fixing operation of the fixing device 9 having the above configuration will be described. First, the pressure roller 23 is driven to rotate, and the fixing belt 21 is driven to rotate in a direction opposite to the rotation direction of the pressure roller 23. At the same time, the IH heater 25 is driven to heat the fixing belt 21. The fixing belt 21 is heated to a predetermined control temperature (for example, 160 ° C.). After the fixing belt 21 is heated in this way, the sheet S on which the toner image is transferred is guided by the sheet entry guide 37 and conveyed to the space between the first flat surface 45 and the pressure roller 23, and the first 1 is conveyed in a direction along the flat surface 45 (indicated by an arrow A in FIG. 6). In the pressure region N, the paper S is nipped between the fixing belt 21 and the pressure roller 23 and conveyed. At this time, the sheet S is heated by the fixing belt 21 and is pressed by the pressure roller 23 and the fixing belt 21 to fix the toner image on the sheet S. The sheet S on which the toner image is fixed is separated from the fixing belt 21 by the separating member 39 and conveyed along the conveying path 15.

  As described above, the pressure region N is formed between the fixing belt 21 and the pressure roller 23 pressed by the arcuate surface 43 having a radius of curvature larger than the radius of curvature of the pressure roller 23. Compared with the case where the pressure area N is flat, the length of the pressure area N along the transport direction Y can be increased, and the fixing performance can be stabilized. However, since the conveyance state when the sheet S enters is determined by the upstream end Nx of the pressure region N and the sheet entry guide 37, the upstream end Nx is not necessarily in a stable conveyance state when the sheet S enters. Is not limited. Further, by tilting the sliding surface 41 of the pressing pad 27 toward the pressure roller 23 side or the paper entry guide 37 side, it is possible to improve the conveyance state when the paper S enters, but within the pressure region N If the curvature is changed, the influence on the pressurizing region N is increased. In particular, since the toner is in an unstable molten state upstream of the pressure region N, the change in the curvature affects the fixing property and the image.

  Therefore, in the present embodiment, as described above, the sliding surface 41 of the pressing pad 27 includes the arcuate surface 43 on the downstream side in the transport direction Y and the first flat surface 45 on the upstream side, A boundary B1 between the surface 43 and the first flat surface 45 corresponds to the upstream end Nx in the conveyance direction Y of the pressurizing region N. According to this configuration, since it is not necessary to change the curvature in the pressurizing area N, it is possible to stabilize the conveyance state when the sheet S enters the pressurizing area N and to affect the fixability and the image. Can be suppressed.

  When this embodiment is compared with the case where the first flat surface 45 is not provided and the extended surface 43a is provided, when the paper is conveyed along the extended surface 43a, the conveyance path is curved. On the other hand, in the present embodiment, since the paper is transported along the first flat surface 45, the transport path is linear. Therefore, in the present embodiment, the transport distance of the paper until entering the pressurizing region N is shorter, and the change in the posture of the paper being transported is less. Therefore, according to the present embodiment, paper wrinkles and transport disturbance on the upstream side in the transport direction Y from the pressurization region N are suppressed as compared with the case where the extended surface 43a is provided without the first flat surface 45. .

  In addition, since the boundary B1 between the arcuate surface 43 and the first flat surface 45 corresponds to the upstream end Nx of the pressurizing region N, a sudden curvature change does not occur in the pressurizing region N. Yes. Therefore, it is difficult for pressure loss or fluctuation of the length of the pressure region N to occur in the pressure region N, and stable fixing performance can be obtained.

  Further, the first flat surface 45 is inclined toward the pressure roller 23 with respect to a virtual extension surface 43 a obtained by extending the arcuate surface 43 to the upstream side in the transport direction Y. According to this configuration, since the space between the first flat surface 45 and the pressure roller 23 is narrower than the space between the extended surface 43a and the pressure roller 23, the conveyance direction Y is more than the pressure region N. Variations in the posture of the sheet S on the upstream side are suppressed.

  Further, the upstream end 53 in the transport direction Y of the first flat surface 45 of the pressing pad 27 is positioned such that the central portion 53c in the width direction of the sheet S is upstream in the transport direction Y from both end portions 53e in the width direction. It is formed to do. According to this configuration, the sheet S comes into contact with the portion corresponding to the central portion 53 c of the fixing belt 21 at a timing earlier than the portion corresponding to the both end portions 53 e of the fixing belt 21. Further, since the moving path of the part corresponding to the central part 53c of the fixing belt 21 is longer than the moving path of the part corresponding to the both end parts 53e, the moving speed of the part corresponding to the central part 53c of the fixing belt 21 is It becomes faster than the moving speed of the part corresponding to both ends 53e. As a result, the straightness of conveyance of the paper S is improved.

  In addition to the above configuration, the sliding surface 41 may have a flat surface on the downstream side of the pressure region N. Hereinafter, the pressing pad 27 in which the sliding surface 41 has the second flat surface 47 on the downstream side of the pressurizing region N will be described with reference to FIGS. 7, 8, and 9. FIG. 7 is a sectional view of the pressing pad 27B, FIG. 8 is a sectional view around the boundary B2 of the pressing pad 27B, and FIG. 9 is a sectional view of the pressing region.

  As shown in FIG. 7, the sliding surface 41 of the pressing pad 27 </ b> B has a second flat surface 47 provided continuously from the arcuate surface 43 to the downstream side in the transport direction Y of the paper S. The arcuate surface 43 and the second flat surface 47 are smoothly continuous. The second flat surface 47 is inclined more toward the pressure roller 23 than a virtual extension surface 43b obtained by extending the arcuate surface 43 to the downstream side in the transport direction Y.

  As shown in FIG. 8, the inclination angle θ2 of the second flat surface 47 with respect to the tangent plane 432 of the arc-shaped surface 43 at the boundary B2 between the arc-shaped surface 43 and the second flat surface 47 is 5 ° or more. 10 ° or less is desirable.

  As shown in FIG. 9, the boundary B <b> 2 between the arcuate surface 43 and the second flat surface 47 is provided so as to correspond to the downstream end Ny of the pressurizing region N. The portion pressed by the second flat surface 47 of the fixing belt 21 does not contact the pressure roller 23 and does not contribute to the pressure region N. Note that the boundary B2 is in the vicinity of the downstream end Ny of the pressurizing region N, a position that is about 0.5 to 1 mm away from the downstream end Ny, and a position that is about 0.5 to 1 mm away from the downstream side. Between.

  In the above configuration in which the sliding surface 41 has the second flat surface 47, the paper S that has passed through the pressurizing region N is conveyed in a direction along the second flat surface 47. That is, the sheet S is transported in a direction away from the fixing belt 21 and approaching the pressure roller 23. Accordingly, the sheet S can be easily separated from the fixing belt 21. Further, since the curvature of the fixing belt 21 also changes at the downstream end in the conveyance direction Y of the pressure area N (exit of the pressure area N), the sheet S can be easily separated from the fixing belt 21 due to the curvature separation. Become.

  In addition, since the boundary B2 between the arcuate surface 43 and the second flat surface 47 corresponds to the downstream end Ny of the pressurization region N, a sudden curvature change does not occur in the pressurization region N. Yes. Therefore, it is difficult for pressure loss or fluctuation of the length of the pressure region N to occur in the pressure region N, and stable fixing performance can be obtained.

  Note that the boundary B2 between the arcuate surface 43 and the second flat surface 47 may not strictly correspond to the downstream end Ny of the pressurization region N. It may be shifted to the side. As an example, it may be shifted to the upstream side and the downstream side by about 1 mm from the downstream end Ny. Even in the pressurization area N, if it is in the vicinity of the downstream end Ny, the toner is melted in the pressurization area N and fixed on the paper S. Therefore, even if the pressure fluctuates, the toner image is not easily displaced.

  The above description of the embodiments of the present invention describes preferred embodiments of the fixing device and the image forming apparatus according to the present invention, and thus may have various technically preferable limitations. The technical scope of the present invention is not limited to these embodiments unless specifically described to limit the present invention. That is, the above-described components in the embodiment of the present invention can be appropriately replaced with existing components and the like, and various variations including combinations with other existing components are possible. The description of the embodiment of the present invention described above does not limit the contents of the invention described in the claims.

1 Printer (image forming device)
7 Image forming unit 9 Fixing device 21 Fixing belt 23 Pressure roller 27 Press pad 41 Sliding surface 43 Arc-shaped surface 45 First flat surface

Claims (8)

A rotatable endless fixing belt;
A pressure roller that forms a pressure region where the paper is nipped and conveyed between the fixing belt and the fixing belt;
A pressure pad that has a sliding surface that contacts the inner peripheral surface of the fixing belt in the pressure region and slides relative to the rotating fixing belt;
The sliding surface is
An arcuate surface having a radius of curvature greater than the radius of curvature of the pressure roller and recessed to the opposite side of the pressure roller;
A first flat surface formed continuously from the arcuate surface to the upstream side in the paper conveyance direction;
The fixing device according to claim 1, wherein a boundary between the arcuate surface and the first flat surface corresponds to an upstream end of the pressure region in the transport direction.   The upstream end portion of the first flat surface in the transport direction is formed such that the central portion in the width direction of the sheet is located upstream of the both end portions in the width direction in the transport direction. The fixing device according to claim 1.   3. The fixing device according to claim 1, wherein the first flat surface is inclined to the pressure roller side with respect to an extended surface obtained by extending the arc-shaped surface to the upstream side in the transport direction. .   The fixing device according to claim 3, wherein an end portion of the first flat surface on the upstream side in the transport direction is located on the pressure roller side with respect to the extended surface. The sliding surface is
Having a second flat surface formed continuously from the arcuate surface to the downstream side in the paper transport direction;
5. The fixing according to claim 1, wherein a boundary between the arcuate surface and the second flat surface corresponds to a downstream end of the pressure region in the transport direction. apparatus.   The fixing device according to claim 5, wherein the second flat surface is inclined toward the pressure roller side with respect to an extended surface obtained by extending the arc-shaped surface toward the downstream side in the transport direction. A sliding sheet covering the sliding surface;
The fixing device according to claim 1, wherein the pressing pad contacts an inner peripheral surface of the fixing belt via the sliding sheet. An image forming unit that forms a toner image on paper;
An image forming apparatus comprising: the fixing device according to claim 1 that fixes the toner image onto the sheet.

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