JP2019040015A - Fixing device and image forming apparatus - Google Patents

Abstract

To provide a fixing device that improves fixing performance and sheet separation performance.SOLUTION: A fixing device comprises: a rotatable endless fixing belt 21; a pressure roller 23 that forms a pressurization area N with the fixing belt 21; and a pressing pad 27 that is in contact with an inner peripheral surface of the fixing belt 21 in the pressurization area N and has a slide surface 41 sliding with respect to the rotating fixing belt 21. The slide surface 41 has a plurality of circular surfaces 43, 45, 47 that are provided continuously along a sheet conveyance direction and concave on the opposite side of the pressure roller 23. The plurality of circular surfaces 43, 45, 47 have their radii of curvature gradually reduced toward downstream from the circular surface 43 on the uppermost stream that has a radius of curvature larger than the radius of curvature of the pressure roller 34. The boundary B between the circular surface 43 on the uppermost stream and the circular surface 45 downstream of the circular surface 43 corresponds to the downstream of the center Nc in the conveyance direction of the pressurization area N.SELECTED DRAWING: Figure 4

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.

  In the fixing device, a pressure region is formed between a fixing member such as a fixing belt or a fixing roller and a pressure member such as a pressure roller, and the paper on which the toner image is transferred passes through the pressure region. The toner image is melted and fixed on the paper. In order to reliably fix the toner image on the paper, it is preferable that the length of the pressure region along the paper transport direction is long. To increase the length of the pressure area, use a large-diameter pressure roller, increase the thickness of the elastic layer on the surface of the pressure roller, or rubber hardness of the elastic layer on the surface of the pressure roller. There are known a method for reducing the pressure, a method for increasing the pressing force of the pressure member to the fixing member, and the like.

  However, when a large-diameter pressure roller is used, there is a problem that the fixing device is enlarged. Further, when the thickness of the elastic layer of the pressure roller is increased, there is a problem that the warm-up time of the fixing device becomes longer. Furthermore, when the rubber hardness of the elastic layer of the pressure roller is lowered, the outer diameter is likely to change depending on the temperature, and the transportability and durability are lowered. When the pressing force of the pressure member is increased, there is a problem that the amount of deflection of the surface of the pressure roller increases, and the transportability is deteriorated or the fixing frame needs to be reinforced.

  In order to solve such a problem, a sliding belt fixing system using an endless fixing belt having flexibility has been devised. In this sliding belt fixing system, the fixing belt is supported from the inside by a belt support member, brought into pressure contact with the pressure roller, and rotated by frictional force with the pressure roller. By adjusting the shape of the belt support member, it is possible to increase the length of the pressurizing region with a low pressing force.

  The sheet on which the toner image is fixed in the pressure area is separated from the fixing member by the separation member. In the case of the above sliding belt fixing method, there is a problem that it is difficult to separate the paper from the surface of the fixing belt. This problem becomes prominent when, for example, a color image having a large amount of toner adhesion is formed on a paper having weak stiffness.

  Therefore, the shape and material of the pressing pad that contacts the inner peripheral surface of the fixing belt in the pressurizing region are being studied. For example, in Patent Document 1, the radius of curvature of the heating body in the region where the heating body (fixing belt) and the recording material (paper) contact each other is larger on the upstream side in the recording material conveyance direction than on the downstream side. A fixing device set to be described is described. Patent Document 2 describes a fixing device using a pressing member (pressing pad) having elasticity. Further, in Patent Document 3, the sliding surface of the pressing pad that contacts the inner peripheral surface of the fixing belt has a flat portion, and a fixing portion having a flat portion and an arc-shaped portion on the downstream side in the paper transport direction from the flat portion. An apparatus is described.

JP-A-4-309984 JP 2002-148932 A JP 2013-156399 A

  However, in the fixing device described in Patent Document 1, since the radius of curvature changes in the pressure region, the pressure in the pressure region may be non-uniform. In addition, the fixing device described in Patent Document 2 has a problem that the pressure pad bites into the surface of the pressure roller easily fluctuates, the pressure region easily fluctuates, and the paper separation property is unstable. . Further, in the fixing device described in Patent Document 3, paper separation is obtained, but as in Patent Document 1, since the radius of curvature changes in the pressure region, the pressure in the pressure region is not uniform. There is a risk of becoming.

  In view of the above circumstances, an object of the present invention is to provide a fixing device that improves fixing performance and sheet separation performance, and an image forming apparatus including the fixing device.

  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, And a pressing pad having a sliding surface that contacts the inner peripheral surface of the fixing belt in the pressurizing region and slides relative to the rotating fixing belt, and the sliding surface is along a sheet conveyance direction. A plurality of arcuate surfaces recessed in the opposite side to the pressure roller, the plurality of arcuate surfaces having a radius of curvature larger than the radius of curvature of the pressure roller. It is formed so that the radius of curvature gradually decreases from the arcuate surface on the most upstream side in the conveying direction toward the downstream side in the conveying direction, and the arcuate surface on the most upstream side and the arcuate shape on the most upstream side The boundary with the arcuate surface on the downstream side in the transport direction of the surface is the front Characterized in that it is formed so as to correspond to the downstream side than the center in the transport direction of the pressure area.

  In the present invention, the two arcuate surfaces that are continuous in the transport direction may be connected by a relaxed curved surface.

  In the present invention, the most downstream end of the sliding surface in the transport direction is located closer to the pressure roller than an extended surface obtained by extending the arcuate surface on the most upstream side to the downstream side in the transport direction. It is good also as a feature.

  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, the sliding surface of the pressing pad is formed of a plurality of arcuate surfaces whose curvature radii gradually decrease in order from the upstream side in the transport direction, and a sudden curvature change in the pressurizing region occurs. Since it does not occur, stable fixing performance can be obtained. Furthermore, since the radius of curvature is smaller toward the downstream side of the sliding surface, it is easy to separate the curvature of the sheet from the fixing belt.

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. 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. Hereinafter, 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. L and R of each figure show the left direction and the right direction, 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.

  As shown in FIG. 2, the fixing device 9 includes a fixing belt 21, a pressure roller 23 that forms a pressure region N between the fixing belt 21, an IH heater 25 that heats the fixing belt 21, and fixing. And a pressing pad 27 provided in the hollow portion of the belt 21. Further, the fixing device 9 includes a fixing housing (not shown) in which these are supported.

  The fixing belt 21 is an endless belt having a predetermined inner diameter and a width longer than the width of the paper. 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 come into contact with the fixing belt 21 from below 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 upper half of 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 that is long in 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 fixed to the lower surface of the support member 33. A surface 41 of the pressing pad 27 facing the pressure region N is in contact with the inner peripheral surface of the fixing belt 21 via the sliding sheet 35. When the fixing belt 21 rotates as described above, the surface 41 facing the pressure region N slides with respect to the fixing belt 21. A surface 41 that slides against the fixing belt so as to face the pressure region N 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 paper conveyance direction from the pressure area N, and a separation member 39 provided on the downstream side in the paper conveyance direction from the pressure area N. ing. The paper entry guide 37 is disposed along the conveyance path so as to incline upward toward the pressure region N. The separation member 39 is supported from the counter direction toward the surface of the fixing belt 21 with respect to the rotation direction of the fixing belt 21.

  Next, the pressing pad 27 will be described in detail with reference to FIGS. 3 and 4. FIG. 3 is a cross-sectional view of the pressing pad, and FIG. 4 is a cross-sectional view of the pressure region.

  As shown in FIG. 3, the sliding surface 41 of the pressing pad 27 includes a first arcuate surface 43 and a second arcuate surface that are continuously provided from the upstream side along the sheet conveyance direction Y. A surface 45 and a third arcuate surface 47 are provided. These arc-shaped surfaces 43, 45, 47 are concavely curved on the side opposite to the pressure roller 23. Further, the radius of curvature of each arcuate surface decreases in order from the upstream side. That is, the radius of curvature of the first arcuate surface 43 is larger than the radius of curvature of the pressure roller 23. The radius of curvature of the second arcuate surface 45 is smaller than the radius of curvature of the first arcuate surface 43, and the radius of curvature of the third arcuate surface 47 is greater than the radius of curvature of the second arcuate surface 45. small. As an example, the radius of curvature of the first arcuate surface 43 is preferably at least twice the radius of curvature of the pressure roller 23, and particularly preferably at least four times. However, when the radius of curvature of the first arcuate surface 43 is increased, the length of the pressurizing region N along the transport direction Y is shortened, and therefore, the length is set according to the length of the pressurizing region N. The radius of curvature of the second arcuate surface 45 is preferably within about 1.1 times the radius of curvature of the first arcuate surface 43, and the radius of curvature of the third arcuate surface 47 is the second circle. About 1.1 times or more of the radius of curvature of the arcuate surface 45 is preferable. In addition, the center of curvature of each arcuate surface may be different. Two arcuate surfaces adjacent along the transport direction Y are smoothly connected by a relaxed curved surface. The downstream end of the sliding surface 41 (third arcuate surface 47) is closer to the pressure roller 23 than the extended surface 43a that extends the first arcuate surface 43 downstream in the transport direction. Inclined.

  As shown in FIG. 4, 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 at the upstream and downstream ends in the transport direction Y. Not done. The boundary B between the first arcuate surface 43 and the second arcuate surface 45 is provided so as to correspond to the downstream side of the center Nc of the pressurizing region N in the transport direction.

  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 to the sheet entry guide 37 and conveyed to the pressure area N. 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 sliding surface 41 of the pressing pad 27 of the fixing device 9 according to the present invention is the three arc-shaped surfaces 43, 45, and 47 whose curvature radius gradually decreases in order from the upstream side in the transport direction Y. Is formed. As a result, the sheet S after fixing can be discharged to the pressure roller 23 side, so that the sheet S can be easily separated from the fixing belt 21. Further, since the arcuate surfaces adjacent along the transport direction Y are connected by a relaxed curved surface, the pressure in the pressurizing region N gradually increases toward the downstream side in the transport direction Y. With such a configuration, the sheet S can easily pass through the pressure region N in a curved posture along the shape of the pressure region N. That is, the sheet S is easily transported in the direction away from the fixing belt 21, so that the sheet S is 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 pressurizing area N (exit of the pressurizing area N), the paper S can be easily separated from the fixing belt 21 due to the curvature separation. Become.

  The three arcuate surfaces 43, 45, 47 are connected in the pressurizing region N, but the adjacent arcuate surfaces along the transport direction Y are connected by a relaxed curved surface. This prevents sudden changes in curvature. 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. Furthermore, the curvature change point is provided on the downstream side of the center Nc of the pressurization region N. As a result, the curvature changes after the toner is almost melted and fixed on the paper S, so that the toner image is not easily displaced even if some pressure fluctuation occurs due to the curvature change.

  Furthermore, the most downstream end of the sliding surface 41 is positioned closer to the pressure roller 23 than an extended surface 43a obtained by extending the first arcuate surface 43 to the downstream side in the transport direction. Accordingly, the sheet S that has passed through the pressurizing region N is conveyed in a direction along the third arcuate surface 47 (indicated by an arrow A in FIG. 4). That is, since the sheet S is conveyed in a direction away from the fixing belt 21, the sheet S is more easily separated from the fixing belt 21.

  In the present embodiment, the sliding surface 41 is formed by the three arcuate surfaces 43, 45, 47, but the number of arcuate surfaces is not limited to three. When the number of arcuate surfaces is large, the change in curvature can be moderated.

  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 surfaces 43, 45, 47 Arc-shaped surface

Claims (4)

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 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 is
A plurality of arcuate surfaces recessed continuously on the opposite side of the pressure roller, provided continuously along the paper conveyance direction;
The plurality of arcuate surfaces have a radius of curvature that gradually decreases from an arcuate surface on the most upstream side in the transport direction having a radius of curvature larger than the curvature radius of the pressure roller toward the downstream side in the transport direction. Formed to be
The boundary between the arcuate surface on the most upstream side and the arcuate surface on the downstream side in the transport direction of the arcuate surface on the most upstream side corresponds to the downstream side of the center in the transport direction of the pressurizing region. A fixing device characterized in that the fixing device is formed.   The fixing device according to claim 1, wherein the two arcuate surfaces that are continuous in the transport direction are connected by a relaxed curved surface.   The most downstream end of the sliding surface in the transport direction is positioned closer to the pressure roller than an extended surface obtained by extending the arcuate surface on the most upstream side to the downstream side in the transport direction. The fixing device according to claim 1, wherein the fixing device is a fixing device. An image forming unit that forms a toner image on paper;
An image forming apparatus comprising: the fixing device according to claim 1, wherein the toner image is fixed on the sheet.

Images