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 rotatable fixing belt; a heater 23 that has a belt contact surface 23a in contact with an inner peripheral surface of the fixing belt; a soaking member 25 that has a front-side contact surface 25a that is in contact with a surface 23b 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 with the fixing belt 21. The back-side contact surface 25b of the soaking member 25 and a bottom face 41a of the accommodation recess 41 of the holding member 27 are in contact with each other with a smaller area than the contact area when the back-side contact surface 25b and the bottom face 41a are in surface contact with each other.SELECTED DRAWING: Figure 4A

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, the fixing device of the present invention comprises a rotatable endless fixing belt, a heater having a belt contact surface in contact with the inner surface of the fixing belt, a heat-equalizing member having a front contact surface in contact with the surface of the heater opposite the belt contact surface and a back contact surface opposite the front 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 by the heater across the fixing belt to form a pressure region between the fixing belt and the pressure member for heating and pressurizing paper onto which a toner image has been transferred, wherein the back contact surface of the heat-equalizing member and a bottom surface of the accommodation recess of the holding member are in contact over an area smaller than the contact area when the back contact surface and the bottom surface are in surface contact.

[0008] In the present invention, the rear contact surface may be processed to have a predetermined surface roughness.

[0009] In the present invention, a recess may be formed in the rear contact surface.

[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, the contact area between the rear contact surface of the heat spreader and the bottom surface of the recessed accommodation portion can be reduced, thereby suppressing heat transfer from the heat spreader 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] 4 is a cross-sectional view showing a temperature equalizing member held by a holding member in a fixing device according to one embodiment of the present invention. FIG. [Figure 4B] 10 is a plan view showing a modified example of a heat equalizing member of a fixing device according to an embodiment of the present invention. FIG. 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 the 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 heat equalizing member 25 will be described with reference to FIG. 4A. FIG. 4A is a cross-sectional view showing the heater 23 and heat equalizing member 25 held by a holding member 27. The heat equalizing member 25 is a plate-like member having the same width and length as the heater 23 and a predetermined thickness. The heat equalizing member 25 is made of a material with high thermal conductivity, such as a metal such as aluminum or a graphite sheet. The heat equalizing member 25 has a front contact surface 25a that contacts the surface 23b 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 is formed flat. The back contact surface 25b is processed to have a predetermined surface roughness. A temperature sensor 37 is attached to the back contact surface 25b.

[0024] Next, the holding member 27 will be described with reference to Figures 2 and 4A. The holding member 27 is a substantially semi-cylindrical member having a width equal to that of the fixing belt 21 and a predetermined length along the circumferential direction X. The holding member 27 is made of a heat-resistant resin such as a liquid crystal polymer.

[0025] The outer peripheral surface 27a of the holding member 27 is curved to fit the inner peripheral surface 21a of the fixing belt 21. The outer peripheral surface of the top portion 27b of the holding member 27 is formed flat. A rectangular parallelepiped accommodating recess 41 for accommodating the heater 23 and the heat equalizing member 25 is formed in this top portion 27b. The accommodating recess 41 has the same width and length as the heater 23 and the heat equalizing member 25, and a depth equal to the combined thickness of the heater 23 and the heat equalizing member 25.

[0026] 4A, the heat equalizing member 25 is housed at the back (inside) of the housing recess 41, and the heater 23 is housed at the front (outside) of the heat equalizing member 25. The back contact surface 25b of the heat equalizing member 25 contacts the bottom surface 41a of the housing recess 41, and the front contact surface 25a contacts the surface 23b of the heater 23 opposite the belt contact surface 23a. The belt contact surface 23a of the heater 23 is flush with the outer peripheral surface of the top part 27b of the holding member 27.

[0027] As shown in FIG. 2, the holding member 27 is supported by a stay 35 in the hollow portion of the fixing belt 21.

[0028] 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.

[0029] 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 area N between the fixing belt 21 and the pressure roller 29. 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 driven to rotate clockwise in FIG. 2, which is opposite to the rotation of the pressure roller 29. This allows the paper S to pass through the pressure area N.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] Furthermore, because the backside contact surface 25b of the temperature equalizing member 25 is processed to have a predetermined surface roughness, the contact area between the backside contact surface 25b of the temperature equalizing member 25 and the bottom surface 41a of the accommodation recess 41 is relatively small. For example, compared to when the backside contact surface 25b and the bottom surface 41a are in surface contact, the backside contact surface 25b contacts the bottom surface 41a at multiple points, resulting in a smaller contact area. 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 the present invention, the small contact area between the temperature equalizing member 25 and the holding member 27 suppresses heat transfer from the temperature equalizing member 25 to the holding member 27, reducing heat loss from the heater 23.

[0034] Next, a modified example of the temperature equalizing member 25 will be described with reference to Fig. 4B. Fig. 4B is a plan view showing the temperature equalizing member 25.

[0035] In this modification, a large number of hemispherical recesses 51 are formed on the rear contact surface 25b of the heat equalizing member 25. Even with this configuration, the contact area can be narrowed by the amount of the recesses 51 compared to when the rear contact surface 25b and the bottom surface 41a are in surface contact. The shape of the recesses 51 is not limited to a hemispherical shape. Also, a large number of grooves may be formed on the rear contact surface 25b instead of the recesses 51.

[0036] In the above embodiment, the contact area between the temperature equalizing member 25 and the holding member 27 is reduced by roughening the back contact surface 25b of the temperature equalizing member 25 or by forming recesses 51 on the back contact surface 25b. However, the bottom surface 41a of the accommodation recess 41 of the holding member 27 may also be processed to have a predetermined surface roughness or by forming recesses on the bottom surface 41a. In this case, the contact area between the temperature equalizing member 25 and the holding member 27 can also be reduced. Alternatively, both the back contact surface 25b and the bottom surface 41a may be roughened.

[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 25a Back contact surface 27 Retaining member 29 Pressure roller (pressure member) 41 Recessed storage area 51 Recess

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, a fixing device characterized in that the rear contact surface of the heat equalizing member and the bottom surface of the accommodating recess of the holding member are in contact with each other over an area smaller than the contact area when the rear contact surface and the bottom surface are in surface contact.

2. 2. The fixing device according to claim 1, wherein the rear contact surface is processed to have a predetermined surface roughness.

3. The fixing device according to claim 1 , wherein a recess is formed in the rear contact surface.

4. 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