Fixing device and image forming apparatus

Abstract

To provide a fixing device that easily uniforms the temperature distribution in a width direction of a fixing belt without reducing the thermal efficiency of a heater.SOLUTION: A fixing device comprises: a fixing belt 21; a heater 23 that has a belt contact surface 23a in contact with an inner peripheral surface of the fixing belt 21; a soaking member that has a front-side contact surface 25a that is in contact with a surface of the heater 23 on the opposite side of the belt contact surface 23a, and a back-side contact surface 25b that is opposite to the front-side contact surface 25a; a holding member 27 that has an accommodation recess 41 accommodating the heater 23 and the soaking member 25; and a pressure member 29 that forms a pressure area N. The accommodation recess 41 has, in order in a depth direction, a soaking member accommodation part 53 in which the soaking member 25 is accommodated, a gap part 55 that has a smaller cross-sectional area than the soaking member accommodation part 53, and a step surface 59 that is formed between the soaking member accommodation part 53 and the gap part 55. The back-side contact surface 25b of the soaking member 25 is in contact with the step surface 59.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a fixing device that fixes a toner image on a sheet of paper and an image forming apparatus equipped with the fixing device. [Background technology]

[0002] A sliding-type fixing device includes an endless fixing belt heated by a heater and a pressure roller that contacts the fixing belt to form a pressure area, and fixes a toner image onto a sheet of paper transported to the pressure area as the fixing belt and pressure roller rotate. In such a fixing device, it is necessary to make the temperature distribution of the fixing belt uniform across the width of the paper, for example, to eliminate uneven fixing between non-paper-passing areas and paper-passing areas.

[0003] The fixing device described in Patent Document 1 includes a heat-conducting member that contacts the heater's surface opposite to the surface that contacts the film (corresponding to the fixing belt). The heat-conducting member is sandwiched between the heater and the heater holder so that it contacts the heater's heat-generating area. The provision of such a heat-conducting member promotes the transfer of heat from the non-paper-passing area to the paper-passing area, making it possible to uniform the temperature distribution of the film. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-95433 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the fixing device described in Patent Document 1, the heat conducting member is also in contact with the heater holder, so heat also transfers from the heat conducting member to the heater holder, which may reduce the thermal efficiency of the heater.

[0006] In consideration of the above circumstances, the present invention aims to provide a fixing device that can easily achieve a uniform temperature distribution in the width direction of a fixing belt without reducing the thermal efficiency of the heater, and an image forming apparatus equipped with this fixing device. [Means for solving the problem]

[0007] In order to solve the above problem, a fixing device of the present invention includes a rotatable endless fixing belt, a heater having a belt contact surface in contact with the inner peripheral surface of the fixing belt, a heat-equalizing member having a front-side contact surface in contact with the heater's surface opposite the belt contact surface and a back-side contact surface opposite the front-side contact surface, a holding member having an accommodation recess to accommodate the heater and the heat-equalizing member, and a pressure member that is pressed against the heater across the fixing belt to form a pressure region between the fixing belt and the holding member to heat and pressurize paper onto which a toner image has been transferred, wherein the accommodation recess includes, in order in a depth direction, a heat-equalizing member accommodation section to accommodate the heat-equalizing member, a gap section having a cross-sectional area smaller than that of the heat-equalizing member accommodation section, and a stepped surface formed between the heat-equalizing member accommodation section and the gap section, and the back-side contact surface of the heat-equalizing member is in contact with the stepped surface.

[0008] In the present invention, the step surface may be in the shape of a rectangular frame.

[0009] The image forming apparatus of the present invention is characterized by comprising an image forming section that forms a toner image on a sheet of paper, and the fixing device that fixes the toner image on the sheet of paper.

[0010] The image forming apparatus of the present invention is characterized by comprising an image forming section that forms a toner image on a sheet of paper, and the fixing device that fixes the toner image on the sheet of paper. [Effects of the Invention]

[0011] According to the present invention, since a gap is provided between the rear contact surface of the temperature equalizing member and the bottom surface of the gap, the contact area between the temperature equalizing member and the holding member can be made as small as possible, thereby suppressing heat transfer from the temperature equalizing member to the holding member and reducing heat loss from the heater. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a side view schematically illustrating an internal configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] 1 is a cross-sectional view schematically illustrating an internal configuration of a fixing device according to an embodiment of the present invention. [Figure 3] FIG. 2 is a plan view showing a heater of a fixing device according to an embodiment of the present invention. [Figure 4A] FIG. 2 is a cross-sectional view showing a holding member of a fixing device according to an embodiment of the present invention. [Figure 4B] FIG. 2 is a plan view showing a holding member of a fixing device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an image forming apparatus and a fixing device according to the present invention will be described with reference to the drawings.

[0014] First, the overall configuration of the image forming apparatus 1 will be described with reference to Fig. 1. Fig. 1 is a front view that schematically shows the internal configuration of the image forming apparatus 1. Hereinafter, the right side of the paper in Fig. 1 will be referred to as the front side (front side) of the image forming apparatus 1.

[0015] The device body 3 of the image forming device 1 is provided with a paper feed cassette 5 that stores paper sheets S, a paper feed device 7 that feeds paper sheets S from the paper feed cassette 5, an image forming section 9 that forms a toner image on paper sheets S by electrophotography, a fixing device 11 that fixes the toner image on paper sheets S, a paper discharge device 13 that discharges paper sheets S, and a paper discharge tray 15 on which the discharged paper sheets S are stacked. Furthermore, the device body 3 is formed with a transport path 17 for paper sheets S that runs from the paper feed device 7, through the image forming section 9 and the fixing device 11, and toward the paper discharge device 13.

[0016] The image forming operation will be briefly explained. First, paper S is sent out from paper feed cassette 5 to transport path 17 by paper feed device 7. The sent paper S is transported along transport path 17 to image forming unit 9, where a toner image is formed on the paper S by electrophotography. The paper S with the toner image formed is transported along transport path 17 to fixing device 11. Fixing device 11 fixes the toner image on the paper S. The paper S with the fixed toner image is transported along transport path 17 to paper discharge device 13. Paper discharge device 13 discharges the paper S onto paper output tray 15.

[0017] Next, the fixing device 11 will be described with reference to Fig. 2. Fig. 2 is a cross-sectional view that schematically shows the internal configuration of the fixing device 11.

[0018] The fixing device 11 includes a fixing belt 21, a heater 23 for heating the fixing belt 21, a heat equalizing member 25 in contact with the heater 23, a holding member 27 for holding the heater 23 and the heat equalizing member 25, a pressure roller 29 as a pressure member for forming a pressure area N between the fixing belt 21 and the holding member 27, and a conveying guide 31.

[0019] First, the fixing belt 21 will be described. The fixing belt 21 is an endless belt having a predetermined inner diameter and a width greater than the width of a paper-passing area (for example, A4 landscape size). The fixing belt 21 is made of a flexible material and has a base layer, an elastic layer provided on the outer surface of the base layer, and a release layer provided on the outer surface of the elastic layer. The base layer is made of a metal such as SUS or Ni. The elastic layer is made of silicone rubber or the like. The release layer is made of a PFA tube or the like. A sliding layer may be formed on the inner surface of the base layer. The sliding layer is made of polyimide amide, PTFE or the like.

[0020] Both ends of the fixing belt 21 are rotatably supported by end holders (not shown). The end holders are supported by a fixing housing (not shown). A stay 35 penetrates the hollow portion of the fixing belt 21. Both ends of the stay 35 are supported by the end holders.

[0021] Next, the heater 23 will be described with reference to Fig. 3. Fig. 3 is a plan view showing the heater 23.

[0022] The heater 23 is a flat plate-shaped member having a width equal to that of the fixing belt 21, a predetermined length along the circumferential direction X of the fixing belt 21, and a predetermined thickness. The heater 23 is composed of a stainless steel or ceramic substrate, an electrical insulating layer made of glass or the like, a resistance heating layer, and a protective layer, laminated in this order from the back side to the front side. The resistance heating layer includes a plurality of resistance heating elements 23x and an electrode 23y. The plurality of resistance heating elements 23x are arranged side by side in the width direction Y of the fixing belt 21 in an area corresponding to the paper-passable area of the fixing belt 21. The electrode 23y is arranged outside the plurality of resistance heating elements 23x in the width direction Y. The resistance heating layer generates heat when current is applied to the resistance heating elements 23x through the electrode 23y. The surface of the protective layer is formed flat and forms the belt contact surface 23a that contacts the inner circumferential surface 21a of the fixing belt 21.

[0023] Next, the temperature equalizing member 25 will be described with reference to FIG. 2. The temperature equalizing member 25 is a plate-shaped member having a width narrower than that of the heater 23, a length shorter than that of the heater 23, and a predetermined thickness. The temperature equalizing member 25 is made of a material with high thermal conductivity, such as a metal such as aluminum or a graphite sheet. The temperature equalizing member 25 has a front contact surface 25a that contacts the surface of the heater 23 opposite the belt contact surface 23a, and a back contact surface 25b opposite the front contact surface 25a. The front contact surface 25a and the back contact surface 25b are formed flat. In addition, a temperature sensor 37 is attached to the back contact surface 25b.

[0024] Next, holding member 27 will be described with reference to Figures 4A and 4B. Figure 4A is a cross-sectional view showing holding member 27, and Figure 4B is a plan view showing holding member 27 as viewed from below. Holding member 27 is a substantially semi-cylindrical member that has a width equal to that of fixing belt 21 and a predetermined length along the circumferential direction X. Holding member 27 is made of heat-resistant resin such as liquid crystal polymer.

[0025] 4A, the outer peripheral surface 27a of the holding member 27 is curved to fit the inner peripheral surface 21a of the fixing belt 21 (see FIG. 2). The outer peripheral surface of the top portion 27b of the holding member 27 is formed flat. A storage recess 41 for storing the heater 23 and the heat equalizing member 25 is formed in this top portion 27b. As shown in FIG. 2, the heat equalizing member 25 and the heater 23 are located at the same center in the width direction Y and the circumferential direction X, with the heat equalizing member 25 stored on the far side (inside) of the storage recess 41 and the heater 23 stored on the near side (outside) of the heat equalizing member 25.

[0026] The accommodating recess 41 is formed in a three-stepped shape with a cross-sectional area that gradually narrows in the depth direction. The accommodating recess 41 includes a heater accommodating section 51 at the front (outside), a temperature equalizing member accommodating section 53 at the rear (inside) of the heater accommodating section 51, and a gap 55 at the rear of the temperature equalizing member accommodating section 53. As described above, the width and length of the heater 23 are greater than those of the temperature equalizing member 25, and the temperature equalizing member 25 and the heater 23 are arranged with their centers at the same position in the width direction Y and the circumferential direction X. Therefore, as shown in FIG. 4B , a rectangular frame-shaped outer stepped surface 57 is formed between the heater accommodating section 51 and the temperature equalizing member accommodating section 53. The width and length of the gap 55 are smaller than those of the temperature equalizing member 25. Therefore, a rectangular frame-shaped inner stepped surface 59 is formed between the temperature equalizing member accommodating section 53 and the gap 55.

[0027] The temperature equalizing member 25 is accommodated in the temperature equalizing member accommodation section 53. The outer periphery of the back contact surface 25b of the temperature equalizing member 25 contacts the inner stepped surface 59. As shown in FIG. 2 , a gap is provided between the center of the back contact surface 25b and the bottom surface of the gap section 55. The heater 23 is accommodated in the heater accommodation section 51. The belt contact surface 23a of the heater 23 is flush with the outer periphery of the top portion 27b of the holding member 27. The outer periphery of the surface of the heater 23 opposite to the belt contact surface 23a contacts the outer stepped surface 57. The center of the opposite surface contacts the front contact surface 25a of the temperature equalizing member 25.

[0028] As shown in FIG. 2, the holding member 27 is supported by a stay 35 in the hollow portion of the fixing belt 21.

[0029] Next, the pressure roller 29 will be described with reference to Fig. 2. The pressure roller 29 has a core, an elastic layer provided on the outer peripheral surface of the core, and a release layer provided on the outer peripheral surface of the elastic layer. The elastic layer is made of silicone rubber or the like. The release layer is made of a PFA tube or the like.

[0030] The pressure roller 29 is supported so as to be pressed against the heater 23 from below the fixing belt 21. This forms a pressure region N between the fixing belt 21 and the pressure roller 29. The width of the pressure region N is narrower than the width of the heat equalizing member 25, and the length of the pressure region N is shorter than the length of the heat equalizing member 25. The pressure roller 29 is driven by a motor (not shown) to rotate counterclockwise in FIG. 2. When the pressure roller 29 is driven to rotate by the motor, the fixing belt 21 is rotated clockwise in FIG. 2, opposite to the pressure roller 29. This allows the paper S to pass through the pressure region N.

[0031] Next, the conveying guide 31 will be described with reference to Fig. 2. The conveying guide 31 is disposed upstream of the pressure region N in the conveying direction of the paper S, and guides the paper S conveyed along the conveying path 17 to the pressure region N.

[0032] The fixing operation of the fixing device 11 having the above configuration will be described. First, the pressure roller 29 is driven to rotate by a motor, and the fixing belt 21 is driven by the pressure roller 29 to rotate in the direction opposite to the rotation direction of the pressure roller 29 (clockwise in FIG. 2 ). At the same time, the heater 23 is driven to heat the fixing belt 21. The fixing belt 21 is heated to a predetermined control temperature (e.g., 160°C) based on the temperature detected by the temperature sensor 37 attached to the heat equalizing member 25. After the fixing belt 21 is heated in this manner, the paper S onto which the toner image has been transferred is guided by the transport guide 31 and transported to the pressure zone N. As the paper S passes through the pressure zone N, it is heated by the fixing belt 21 and pressed by the pressure roller 29 and the fixing belt 21, so that the toner image is fixed to the paper S. The paper S onto which the toner image has been fixed is transported from the pressure zone N along the transport path 17.

[0033] As described above, according to the fixing device 11 of the present invention, the heat generated by the resistance heating element layer of the heater 23 is transferred in the width direction Y via the heat equalizing member 25. Therefore, even when a sheet S having a width narrower than the width of the maximum sheet passing area is conveyed, the heat is transferred from the non-sheet passing portion to the sheet passing portion via the heat equalizing member 25. Therefore, the temperature of the heater 23 in the width direction Y can be made uniform, and the temperature of the fixing belt 21 in the width direction Y can be made uniform.

[0034] Furthermore, the back contact surface 25b of the temperature equalizing member 25 is in contact with the rectangular frame-shaped inner stepped surface 59 of the holding member 27, leaving a gap between the back contact surface 25b and the bottom surface of the gap 55. This makes it possible to make the contact area between the temperature equalizing member 25 and the holding member 27 as small as possible. Because the temperature equalizing member 25 is in contact with the holding member 27, heat transferred from the heater 23 to the temperature equalizing member 25 also transfers to the holding member 27. In this case, by making the contact area between the temperature equalizing member 25 and the holding member 27 as small as possible, it is possible to suppress the transfer of heat from the temperature equalizing member 25 to the holding member 27 and reduce heat loss from the heater 23.

[0035] Furthermore, since the outer stepped surface 57 and the inner stepped surface 59 are formed in a rectangular frame shape, the heater 23 and the temperature equalizing member 25 can be stably supported in the accommodation recess 41 .

[0036] In the above embodiment, an example has been described in which the width and length of the temperature equalizing member 25 are shorter than those of the heater 23. However, the width and length of the temperature equalizing member 25 may be equal to those of the heater 23. In this case, the heater accommodating section 51 and the temperature equalizing member accommodating section 53 of the accommodating recess 41 of the holding member 27 are formed to have the same dimensions, and the gap 55 is formed to have a cross-sectional area narrower than those of the heater accommodating section 51 and the temperature equalizing member accommodating section 53.

[0037] Furthermore, the above-mentioned description of the embodiments of the present invention describes preferred embodiments of the present invention, and therefore may include various technically preferable limitations, but the technical scope of the present invention is not limited to these aspects unless there is a description that specifically limits the present invention. [Explanation of symbols]

[0038] 1. Image forming device 9 Image forming unit 11 Fixing device 21 Fixing belt 23 Heater 25 Heat-equalizing element 25b Back side contact surface 27 Retaining member 29 Pressure roller (pressure member) 41 Recessed storage area 53 Heat equalizing member housing 55 Cavity 59 Step surface

Claims

1. a rotatable endless fixing belt; a heater having a belt contact surface that contacts the inner circumferential surface of the fixing belt; a heat equalizing member having a front contact surface that contacts the heater on the side opposite to the belt contact surface, and a back contact surface opposite to the front contact surface; a holding member having an accommodation recess for accommodating the heater and the temperature equalizing member; a pressure member that is pressed by the heater across the fixing belt and forms a pressure region between the fixing belt and the sheet of paper onto which the toner image has been transferred, and that heats and presses the sheet of paper, the accommodating recess includes, in order in a depth direction, a heat-equalizing member accommodating portion in which the heat-equalizing member is accommodated, a gap portion having a cross-sectional area smaller than that of the heat-equalizing member accommodating portion, and a stepped surface formed between the heat-equalizing member accommodating portion and the gap portion, and the back contact surface of the heat-equalizing member is in contact with the stepped surface.

2. 2. The fixing device according to claim 1, wherein the step surface is in the shape of a rectangular frame.

3. an image forming unit that forms a toner image on a sheet; 2. An image forming apparatus comprising: a fixing device according to claim 1, which fixes the toner image onto the paper.

Images