Fixing device and image forming apparatus

Abstract

To improve an increase in the temperature of a non-paper feed part with a simple configuration.SOLUTION: A fixing device fixes a toner image on a recording material to the recording material, and includes: a heating member; an endless rotatable belt member that is heated by the heating member; a nip forming member that is provided on an inner peripheral surface side of the belt member and is in contact with an inner peripheral surface of the belt member to support the belt member from the inner peripheral surface side; and a pressure member that is in pressure contact with the nip forming member with the belt member therebetween and forms a nip part between the belt member and the pressure member. The nip forming member includes a heat conduction member having anisotropic thermal conductivity.SELECTED DRAWING: Figure 4

Description

[Technical field]

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

[0002] 2. Description of the Related Art In image forming apparatuses such as electrophotographic apparatuses and electrostatic recording apparatuses, an unfixed toner image is formed on a sheet-like recording material, and the toner image is then fixed to the recording material by applying heat and pressure using a fixing device.

[0003] As one of the conventional fixing devices, Patent Document 1 discloses a fixing device of a so-called belt heating type that uses a fixing belt and a pressure roller. In this fixing device, a pressure roller is rotated, and the outer peripheral surface of the belt is placed in contact with the pressure roller, and the belt is rotated by the pressure roller. A heating roller is placed in contact with the inner peripheral surface of the belt, and the heating roller heated by a heat source supplies heat to the belt. While a recording material carrying an unfixed toner image is nipped and conveyed in the fixing nip portion, which is the contact portion between the belt and the pressure roller, the toner image is fixed to the recording material by heat and pressure. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2003-195671 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the conventional fixing device, in order to widen the fixing nip, the roller that presses the belt is made larger in diameter and the rubber layer on the surface of the roller is made thicker, so that the outer diameter of the roller is easily thermally expanded, and when recording materials are continuously passed through the roller, the non-paper passing portion of the roller is heated, causing wrinkles on the recording materials and image defects.

[0006] Conventionally, this problem has been addressed by blowing air (cooling air) generated by a fan onto the non-paper passing parts of the roller, but this causes the device to become larger due to the effect of the fan, and the air that passes through the fixing device and contains water vapor due to its high temperature flows out of the fixing device, raising the temperature of other devices within the image forming apparatus, and the water vapor adheres to the other devices, causing condensation to form on them.

[0007] SUMMARY OF THE PRESENTLY PREFERRED EMBODIMENTS An object of the present invention is to improve the temperature rise in non-sheet passing areas with a simple configuration without using a fan. [Means for solving the problem]

[0008] A typical configuration of the present invention is a fixing device that fixes a toner image on a recording material to the recording material, and is characterized in that it has a heating member, an endless rotatable belt member that is heated by the heating member, a nip forming member that is provided on the inner surface of the belt member and contacts the inner surface of the belt member to support the belt member from the inner surface side, and a pressure member that is pressed against the nip forming member via the belt member and forms a nip portion between the nip forming member and the belt member, and includes a heat conductive member having anisotropic thermal conductivity. Effect of the Invention

[0009] According to the present invention, it is possible to reduce the temperature rise in the non-sheet passing portion with a simple configuration. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a schematic configuration of an image forming apparatus. [Diagram 2] 1 is a cross-sectional view of a fixing device according to a first embodiment of the present invention; [Diagram 3] Cross-sectional view of a pad in Example 1 [Figure 4] Cross-sectional view of the vicinity of the pad in Example 1 [Diagram 5] (a) and (b) are cross-sectional views of a pad in Example 2. [Figure 6] (a) and (b) are cross-sectional views of a pad in Example 3. [Figure 7] 11 is a cross-sectional view of a fixing device according to a fourth embodiment of the present invention; [Figure 8] Cross-sectional view of a pad in Example 4 [Figure 9] Cross-sectional view of the vicinity of the pad in Example 4 [Figure 10] (a)(b) Cross-sectional view of the pad in Example 5 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Preferred embodiments of the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the following examples may be changed as appropriate depending on the configuration of the device to which the present invention is applied and various conditions, and are not intended to limit the scope of the present invention to these alone.

[0012] <Example 1> (Schematic configuration of image forming apparatus) The schematic configuration of an image forming apparatus according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic cross-sectional view showing the schematic configuration of a full-color image forming apparatus according to this embodiment.

[0013] The image forming apparatus 1 comprises an image reading section 2 and an image forming apparatus main body 3. The image reading section 2 reads an original placed on an original platen glass 21, and light emitted from a light source 22 is reflected by the original and an image is formed on a CCD sensor 24 via an optical system member 23 such as a lens. Such an optical system unit converts the original into an electric signal data string for each line by scanning in the direction of the arrow. The image signal obtained by the CCD sensor 24 is sent to the image forming apparatus main body 3, and image processing is performed in a control section 30 according to each image forming section described later. The control section 30 also receives external inputs as image signals from an external host device such as a print server and an operation section 4.

[0014] The image forming apparatus main body 3 includes a plurality of image forming units Ua, Ub, Uc, and Ud, and each image forming unit forms an image based on the image signal. That is, the image signal is converted into a laser beam that is PWM (pulse width modulation) controlled by a control unit 30. In Fig. 1, a polygon scanner 31 as an exposure device scans with a laser beam according to the image signal. Then, the laser beam is irradiated onto photosensitive drums 200a to 200d as image carriers of the image forming units Ua to Ud.

[0015] The yellow (Y) image forming unit Ua, magenta (M) image forming unit Ub, cyan (C) image forming unit Uc, and black (Bk) image forming unit Ud each form an image of a corresponding color. Since the image forming units Ua to Ud are substantially the same, the image forming unit Ua will be described in detail below, and the other image forming units Ub, Uc, and Ud will not be described. In the image forming unit Ua, a toner image is formed on the surface of the photosensitive drum 200a based on an image signal, as described below.

[0016] The primary charger 201a charges the surface of the photosensitive drum 200a to a predetermined potential to prepare for the formation of an electrostatic latent image. An electrostatic latent image is formed on the surface of the photosensitive drum 200a, which has been charged to a predetermined potential, by a laser beam from the polygon scanner 31. The developer 202a develops the electrostatic latent image on the photosensitive drum 200a to form a toner image. The transfer roller 203a discharges from the rear side of the intermediate transfer belt 204 and applies a primary transfer bias of opposite polarity to the toner, transferring the toner image on the photosensitive drum 200a onto the intermediate transfer belt 204. After transfer, the surface of the photosensitive drum 200a is cleaned by a cleaner 207a.

[0017] The toner image on the intermediate transfer belt 204 is conveyed to the next image forming section, where the toner images of each color formed in each image forming section are transferred in the order of Y, M, C, and Bk, forming a four-color image on the surface. The toner image that has passed through the Bk image forming section Ud is secondarily transferred to the recording material P in a secondary transfer section formed of a pair of secondary transfer rollers 205 and 206 by applying a secondary transfer electric field of the opposite polarity to the toner image on the intermediate transfer belt 204. The recording material P fed from the paper feed cassette 8 or the paper feed cassette 9 waits in a registration section 208, and then the timing is controlled to align the position of the toner image on the intermediate transfer belt 204 with the recording material P, and the recording material P is conveyed from the registration section 208. The toner image on the recording material P is then fixed to the recording material P by a fixing device F as an image heating device. In the case of a one-sided job, the recording material P is discharged outside the machine after passing through the fixing device F. In the case of a double-sided JOB, when the transfer and fixing of the toner on the first side (first surface) of the image formation is completed, the recording material P passes through a reversing section 209 provided inside the image forming apparatus after fixing, and the front and back of the recording material are reversed. Then, the recording material P has the toner on the second side (second surface) of the image formation transferred and fixed, and is discharged outside the apparatus and stacked on the paper discharge tray 7.

[0018] (Configuration of Fixing Device) Next, the configuration of the fixing device F in this embodiment will be described with reference to FIG.

[0019] A schematic diagram of the overall configuration of a belt heating type fixing device F according to this embodiment is shown in Fig. 2. In the figure, the X direction indicates the transport direction of the recording material P. The Y direction indicates the width direction of the recording material P (hereinafter referred to as the paper width direction) which is perpendicular to the transport direction of the recording material P. The Z direction indicates the pressure direction of the pressure roller 305 against the pressure pad 303 which is perpendicular to the transport direction and the width direction.

[0020] The image forming apparatus 1 has a fixing device F that fixes the toner image on the recording material P to the recording material P, as an image heating device that heats the toner image on the recording material.

[0021] The fixing device F includes a fixing belt 301 , a pressure pad 303 , a stay 302 for supporting the pad 303 , a heating roller 307 , a steering roller 308 , and a pressure roller 305 .

[0022] The fixing belt (hereinafter, belt) 301 is an endless rotatable belt member (heating rotor) and is heated by a heating roller 307. The belt 301 has thermal conductivity, heat resistance, and the like, and is a thin-walled cylindrical shape. In this embodiment, the belt 301 has a three-layer structure including a base layer (not shown), an elastic layer on the outer periphery of the base layer, and a release layer on the outer periphery of the elastic layer. The base layer is 80 μm thick and made of polyimide resin (PI), the elastic layer is 300 μm thick and made of silicone rubber, and the release layer is 30 μm thick and made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin. The belt 301 is stretched by a pressure pad 303, a heating roller 307, and a steering roller 308. Note that the structure, thickness, material, and the like of the belt are merely examples and are not limited thereto.

[0023] Pressure pad (hereinafter, pad) 303 is provided on the inner peripheral surface side of belt 301 and is a nip forming member for contacting the inner peripheral surface of belt 301 to support belt 301 from the inner peripheral surface side. Pad 303 is pressed against pressure roller 305 with belt 301 sandwiched therebetween. Pad 303 is supported by stay 302.

[0024] Silicone oil S is interposed between pad 303 and belt 301 as a lubricant. This allows belt 301 to slide smoothly against pad 303. Note that although silicone oil is exemplified as a lubricant, the lubricant is not limited to this, and other oils or other lubricants other than oils may also be used.

[0025] Heating roller 307 is a stainless steel pipe having a thickness of 1 mm, and has halogen heater 306 disposed therein as a heat source, capable of generating heat up to a predetermined temperature. Belt 301 is heated by heating roller 307 as a heating member.

[0026] The pressure roller 305 is pressed against the pad 303 via the belt 301, forming a nip N between the pressure roller 305 and the belt 301. The pressure roller 305 is a pressure member having a core metal layer, an elastic layer on the outer periphery of the shaft, and a release layer on the outer periphery of the elastic layer. The shaft is made of a SUS member with a diameter of 72 mm, the elastic layer is made of conductive silicone rubber with a thickness of 8 mm, and the release layer is made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin with a thickness of 100 μm. The pressure roller 305 is axially supported by the fixing frame (not shown) of the fixing device F, and a gear is fixed to one end of the pressure roller 305, which is connected to a driving source M1 via the gear and is driven to rotate.

[0027] In the nip portion N formed between the belt 301 and the pressure roller 305, the recording material P carrying the toner image is sandwiched and the toner image is heated while being transported. In this way, the fixing device F fixes the toner image to the recording material P while sandwiching and transporting the recording material P. Therefore, the fixing device F needs to have both a function of applying heat and pressure and a function of transporting the recording material P. The pressure roller 305 is pressed against the pad 303 via the belt 301. The pressure force (NF) in the nip portion N during printing is set to 1600 [N], and the width of the nip portion N in the X direction (transport direction) is set to 24.5 [mm], and the width in the Y direction (paper width direction) is set to 326 [mm].

[0028] A steering roller 308 is disposed inside the belt 301. The steering roller 308 has a rotation center at one end or near the center in the Y direction (paper width direction) and rotates relative to the belt 301 to generate a tension difference between the front and rear, thereby controlling the position of the belt 301 in the Y direction (paper width direction). The steering roller is formed of a hollow SUS shaft with a diameter of 20 mm. The steering roller may be provided with a rubber material or the like on its surface to increase its grip on the belt 301.

[0029] (Pad configuration) Next, the pad 303 in this embodiment will be described with reference to Fig. 3. Fig. 3 is a cross-sectional view of the pad 303 portion of the fixing device F in this embodiment.

[0030] Pad 303 is composed of base material 303a and coating layer 303b formed on at least the contact surface (sliding surface) with belt 301. Base material 303a (pad 303) uses a heat conductive member having anisotropic thermal conductivity, and is formed in a flat plate shape with pressure direction Z as the thickness direction. That is, pad 303 as a nip forming member includes a heat conductive member having anisotropic thermal conductivity.

[0031] The base material 303a (pad 303) which is a thermally conductive member is made of an anisotropic material having a thermal conductivity in the X and Y directions greater than that in the Z direction. Specifically, the base material 303a is made of a graphite material. The thermal conductivity of the base material 303a in the Z direction is 1 [W / m·K] or more and 20 [W / m·K] or less. The thermal conductivity of the base material 303a in the X and Y directions is 300 [W / m·K] or more and 2000 [W / m·K] or less. In other words, the pad 303 (base material 303a) is a thermally conductive member having an anisotropic thermal conductivity that easily transmits heat in the horizontal directions (X and Y directions) and easily uniforms the heat.

[0032] The base material 303a is provided with a coating layer 303b on all of its outer surfaces, including the surface that comes into contact with the belt 301. Here, a configuration in which the coating layer 303b is provided on all of the outer surfaces of the base material 303a is illustrated as an example, but the present invention is not limited to this. The base material 303a may be configured to have a coating layer 303b provided at least on the surface that comes into contact with the belt 301. The coating layer 303b may be a PTFE coating that has both sliding properties and heat resistance, but nickel is used in this embodiment. By providing the coating layer (nickel layer) 303b using nickel, the mechanical strength of the pad 303 is increased, heat transfer is improved, and heat uniformity can be achieved.

[0033] In this example, a nickel layer using nickel is used as the coating layer 303b, but the present invention is not limited to this. A coating layer using other materials may be provided as long as the material can increase the mechanical strength of the pad 303, improve heat transfer, and provide uniform heating.

[0034] Furthermore, pad 303 is formed so that the length in the Y direction, which is the paper width direction, is longer than the length in the Y direction of pressure roller 305 (see FIG. 4). Furthermore, pad 303 is formed so that the length in the Y direction, which is the paper width direction, is longer than the length in the Y direction of belt 301. Pad 303 (base material 303a) has the property of easily transmitting heat in the horizontal directions (X direction and Y direction) and easily equalizing the heat, so that it is possible to improve the temperature rise in non-paper passing portions in nip portion N.

[0035] Heat transfer during continuous feeding of small size paper in this embodiment will be described with reference to Fig. 4. Fig. 4 is a cross-sectional view of the nip portion and its surroundings of the fixing device F in this embodiment.

[0036] According to this embodiment, graphite having high thermal conductivity in the Y direction, which is the paper width direction, is used as the material of the pad 303 (base material 303a). That is, the pad 303 (base material 303a) is a heat-conducting member having anisotropic thermal conductivity that easily transmits heat in the horizontal direction (X direction and Y direction) and easily uniforms the heat. Therefore, as shown in FIG. 4, when small-sized paper is continuously passed through, the heat of the non-paper passing area in the nip portion N of the pressure roller 305 and the belt 301 can be transferred more in the paper width direction (Y direction). That is, as shown by the arrow direction W in FIG. 4, the heat of the non-paper passing area can be transferred more to the paper passing area via the pad 303. As a result, the temperature distribution of the nip portion N of the pressure roller 305 and the belt 301 can be uniformized, and the temperature rise of the non-paper passing area can be improved.

[0037] As described above, according to this embodiment, in order to suppress the temperature rise of the non-paper passing area of ​​the pressure roller when small size paper is continuously passed through, the temperature of the non-paper passing area of ​​the pressure roller can be suppressed to a desired temperature or lower without blowing cooling air from a fan to the non-paper passing area of ​​the pressure roller. This makes it possible to prevent the non-paper passing area of ​​the pressure roller from heating up, causing wrinkles in the paper, and image defects. It is also possible to prevent the device from becoming larger due to the influence of the fan, the air containing water vapor due to high heat that has passed through the fixing device flowing out of the fixing device, raising the temperature of other devices in the image forming device, and the water vapor adhering to the other devices causing condensation.

[0038] <Example 2> A description will be given of a fixing device and an image forming apparatus according to Example 2. The schematic configurations of the image forming apparatus 1 and the fixing device F are similar to those of Example 1 described above, so members having equivalent functions are given the same reference numerals and descriptions thereof will be omitted.

[0039] The configuration of the pad 303 of the fixing device F in this embodiment will be described below with reference to Figures 5(a) and 5(b). Figures 5(a) and 5(b) are cross-sectional views of the pad 303 in the second embodiment.

[0040] As shown in FIG. 5(a), the pad 303 of this embodiment has a coating layer 303b on a base material 303a made of graphite. The coating layer 303b is formed on the contact surface of the base material 303a with the belt 301. Furthermore, in this embodiment, the coating layer 303b is etched on the contact surface with the belt 301 to form an embossed shape, which is mainly a round, triangular, or hemispherical shape. This improves the lubricity between the belt 301 and the pad 303, further improving the sliding properties. The coating layer 303b of this embodiment may be a PTFE coating that has both sliding properties and heat resistance, but the use of nickel increases the mechanical strength of the pad 303 and improves heat transfer, allowing for uniform heating.

[0041] Also, as shown in Fig. 5(b), the coating layer 303b may be applied to the entire circumference of the base material 303a in the conveying direction. In other words, the base material 303a may have the coating layer 303b formed on all outer surfaces including the contact surface with the belt 301. This further improves the mechanical strength of the pad 303. Also in this case, the coating layer 303b forms an embossed shape on the contact surface with the belt 301. This improves the lubricity between the belt 301 and the pad 303, further improving the sliding properties.

[0042] <Example 3> A description will be given of a fixing device and an image forming apparatus according to Example 3. The schematic configurations of the image forming apparatus 1 and the fixing device F are similar to those of Example 1 described above, so members having equivalent functions are given the same reference numerals and descriptions thereof will be omitted.

[0043] The configuration of the pad 303 of the fixing device F in this embodiment will be described below with reference to Figures 6(a) and 6(b). Figures 6(a) and 6(b) are cross-sectional views of the pad 303 in the third embodiment.

[0044] As shown in FIG. 6(a), the pad 303 of this embodiment has an embossed shape formed by subjecting the contact surface side of the base material 303a made of graphite, which contacts the belt 301, to etching or cutting.

[0045] Furthermore, the base material 303a has a coating layer 303b formed of nickel on the contact surface with the belt 301, which is formed in an embossed shape. Furthermore, the coating layer 303b has an embossed shape on the contact surface with the belt 301. This improves the lubricity between the belt 301 and the pad 303, further improving the sliding properties. The coating layer 303b in this embodiment may be a PTFE coating that has both sliding properties and heat resistance, but by using nickel, the mechanical strength of the pad 303 is increased and the heat transfer is improved, allowing for uniform heating.

[0046] 6(b), the coating layer 303b may be applied to the entire circumference of the base material 303a in the conveying direction. In other words, the base material 303a may have the coating layer 303b formed on all outer surfaces including the contact surface with the belt 301. This further improves the mechanical strength of the pad 303. Also in this case, the coating layer 303b forms an embossed shape on the contact surface with the belt 301. This improves the lubricity between the belt 301 and the pad 303, further improving the sliding properties.

[0047] <Example 4> A description will be given of a fixing device and an image forming apparatus according to Example 4. The schematic configuration of the image forming apparatus 1 is similar to that of Example 1 described above, so members having equivalent functions are given the same reference numerals and descriptions thereof will be omitted.

[0048] Hereinafter, the configuration of the fixing device F in this embodiment will be described with reference to Fig. 7, and the configuration of the pad 303 of the fixing device F in this embodiment will be described with reference to Fig. 8. In the following description, members having the same functions as those in the above-mentioned embodiment will be denoted by the same reference numerals.

[0049] (Configuration of Fixing Device) First, the configuration of the fixing device F in this embodiment will be described with reference to Fig. 7. Fig. 7 is a cross-sectional view of the fixing device F in this embodiment.

[0050] A schematic diagram of the overall configuration of a belt heating type fixing device F according to this embodiment is shown in Fig. 8. In the figure, the X direction indicates the transport direction of the recording material P. The Y direction indicates the width direction of the recording material P (hereinafter referred to as the paper width direction) which is perpendicular to the transport direction of the recording material P. The Z direction indicates the pressure direction of the pressure roller 305 against the pressure pad 303 which is perpendicular to the transport direction and the width direction.

[0051] The fixing device F includes a fixing belt 301 , a pressure pad 303 , a stay 302 for supporting the pad 303 , a heating roller 307 , a steering roller 308 , a pressure roller 305 , and a sliding member 311 .

[0052] In the fixing device F of this embodiment, except for the pressure pad 303 and the sliding member 311, the configurations of the fixing belt 301, the heating roller 307, the steering roller 308, and the pressure roller 305 are the same as those of the above-described first embodiment, so a description thereof will be omitted here.

[0053] Pressure pad (hereinafter, pad) 303 is provided on the inner peripheral surface side of belt 301 and is a nip forming member for contacting the inner peripheral surface of belt 301 to support belt 301 from the inner peripheral surface side. Pad 303 is pressed against pressure roller 305 with belt 301 sandwiched therebetween. Pad 303 is supported by stay 302.

[0054] Furthermore, between the pad 303 and the belt 301, a sliding member 311 having a surface coated with polytetrafluoroethylene resin (PTFE) is provided. The sliding member 311 contacts the inner peripheral surface of the belt 301. Silicone oil S is interposed between the sliding member 311 and the belt 301 as a lubricant. This allows the belt 301 to slide smoothly against the sliding member 311.

[0055] The sliding member 311 is made of a polyimide base material having a thickness of 70 μm, and is formed by coating the surface of the contact surface with the belt 301 with PTFE. Note that, although a polyimide base material is used as the material of the sliding member 311 in this embodiment, other materials such as a stainless steel or aluminum plate having a thickness of 1 mm may be used.

[0056] (Pad configuration) Next, the pad 303 of this embodiment will be described with reference to Fig. 8. Fig. 8 is a cross-sectional view of the pad 303 portion of the fixing device F of this embodiment.

[0057] The pad 303 is made of a heat conductive material having anisotropic thermal conductivity, and is formed in a flat plate shape with the pressure direction Z being the thickness direction.

[0058] Pad 303, which is a thermally conductive member, is made of an anisotropic material whose thermal conductivity in the X and Y directions is greater than that in the Z direction. Specifically, pad 303 is made of a graphite material. Pad 303 has a thermal conductivity in the Z direction of 1 [W / m·K] or more and 20 [W / m·K] or less. Furthermore, base material 303a has a thermal conductivity in the X and Y directions of 300 [W / m·K] or more and 2000 [W / m·K] or less.

[0059] The thickness of the pad 303 is not less than 100 [μm] and not more than 5000 [μm]. The thickness of the pad 303 is the length in the Z direction, which is the pressure direction.

[0060] Furthermore, pad 303 is formed so that its length in the Y direction, which is the paper width direction, is longer than the length in the Y direction of pressure roller 305 (see FIG. 9). Furthermore, pad 303 is formed so that its length in the Y direction, which is the paper width direction, is longer than the length in the Y direction of belt 301. Pad 303 has the property of easily transmitting heat in the horizontal direction (X direction and Y direction) and easily equalizing the heat, so that it is possible to improve the temperature rise in non-paper passing portions in nip portion N.

[0061] Heat transfer during continuous feeding of small size paper in this embodiment will be described with reference to Fig. 9. Fig. 9 is a cross-sectional view of the nip portion and its surroundings of the fixing device F in this embodiment.

[0062] According to this embodiment, the material of the pad 303 is graphite, which has a high thermal conductivity in the Y direction, which is the paper width direction. That is, the pad 303 (base material 303a) is a heat-conducting member with anisotropic thermal conductivity that easily transmits heat in the horizontal direction (X direction and Y direction) and easily uniforms the heat. Therefore, as shown in FIG. 9, when small-sized paper is continuously passed through, the heat of the non-paper passing area in the nip portion N of the pressure roller 305 and the belt 301 can be transferred more in the paper width direction (Y direction). That is, as shown by the arrow direction W in FIG. 9, the heat of the non-paper passing area can be transferred more to the paper passing area via the pad 303. As a result, the temperature distribution of the nip portion N of the pressure roller 305 and the belt 301 can be uniformized, and the temperature rise of the non-paper passing area can be improved.

[0063] As described above, according to this embodiment, in order to suppress the temperature rise of the non-paper passing area of ​​the pressure roller when small size paper is continuously passed through, the temperature of the non-paper passing area of ​​the pressure roller can be suppressed to a desired temperature or lower without blowing cooling air from a fan to the non-paper passing area of ​​the pressure roller. This makes it possible to prevent the non-paper passing area of ​​the pressure roller from heating up, causing wrinkles in the paper, and image defects. It is also possible to prevent the device from becoming larger due to the influence of the fan, the air containing water vapor due to high heat that has passed through the fixing device flowing out of the fixing device, raising the temperature of other devices in the image forming device, and the water vapor adhering to the other devices causing condensation.

[0064] <Example 5> A description will be given of a fixing device and an image forming apparatus according to Example 5. The schematic configurations of the image forming apparatus 1 and the fixing device F are the same as those in Example 4 described above, so members having equivalent functions are given the same reference numerals and descriptions thereof will be omitted.

[0065] 10(a) and 10(b), the configuration of the pad 303 of the fixing device F in this embodiment will be described. Figures 10(a) and 10(b) are cross-sectional views of the pad 303 in the fifth embodiment.

[0066] As shown in FIG. 10(a), the pad 303 of this embodiment has a coating layer 303b between the lower surface of the pad 303 and the upper surface of the sliding member 311. In other words, the pad 303 has a coating layer 303b on the contact surface with the sliding member 311. This fills in the fine unevenness of the surface of the pad 303, improves adhesion with the sliding member 311, and reduces thermal resistance during contact. In this embodiment, a coating layer (nickel layer) 303b with a thickness of 10 μm is provided by welding nickel. The above configuration improves the contact rate between the pad 303 and the sliding member 311, and further improves thermal conductivity compared to the above-mentioned embodiment 4. As a result, the temperature distribution of the pressure roller 305 and the belt 301 can be made uniform, and the temperature rise of the non-paper passing portion can be improved more than before.

[0067] In the above configuration, in order to improve the adhesion between the pad 303 and the sliding member 311, the coating layer 303b using nickel is provided between the pad 303 and the sliding member 311, but it is not limited to a metal layer. In order to improve the adhesion between the pad 303 and the sliding member 311, for example, a thermally conductive sheet material may be sandwiched between them, or a grease layer with good thermal conductivity may be interposed.

[0068] In addition, in FIG. 10(a), the pad 303 is illustrated as having a coating layer 303b on the contact surface with the sliding member 311, but the present invention is not limited thereto. As shown in FIG. 10(b), the entire surface of the pad 303 may be covered with the coating layer 303b. That is, the pad 303 may be configured to have the coating layer 303b on all outer surfaces including the contact surface. In FIG. 10(b), the entire surface of the pad 303 is covered with a nickel coating layer 303b having a thickness of 10 μm. With the configuration shown in FIG. 10(b), the surface properties of the pad 303 are improved, the contact rate with the sliding member 311 is improved, and the thermal resistance during contact can be reduced. As a result, the temperature distribution of the pressure roller 305 and the belt 301 can be made uniform, and the temperature rise of the non-paper passing portion can be improved compared to the conventional case. In addition, by covering the entire surface of the pad 303 with the coating layer 303b, the mechanical strength of the pad 303 can be increased. Therefore, deformation of the pad 303 when pressed by the pressure roller 305 can be more reliably prevented.

[0069] In the fixing device F of the fourth embodiment and the present embodiment described above, the surface layer of the sliding member 311 on the side of contact with the belt 301 may be embossed with uneven shapes, mainly round, triangular, hemispherical, etc. This makes it easier for the silicone oil S to lubricate between the belt 301 and the sliding member 311, further improving the slidability.

[0070] According to this embodiment, by using a heat conductive material (graphite) having anisotropic thermal conductivity for pad 303, which is a nip forming member of fixing device F, it is possible to improve the temperature rise in the non-paper passing portion of nip portion N with a simple configuration.

[0071] Other Examples In the above-described embodiment, graphite is exemplified as the heat conductive member having anisotropic thermal conductivity that constitutes the pressure pad 303, but the present invention is not limited to this. The heat conductive member having anisotropic thermal conductivity that constitutes the pressure pad 303 may be a material other than graphite as long as it is made of an anisotropic material whose thermal conductivity in the X direction and Y direction is greater than that in the Z direction.

[0072] In the above-described embodiment, the fixing device F uses the heating roller 307 as a heating member for heating the belt 301, but the present invention is not limited to this. For example, the fixing device F may be a fixing device in which a halogen heater is disposed inside the belt 301 to heat the belt 301. Alternatively, the fixing device F may be a fixing device in which an electromagnetic induction (IH) heating member is disposed outside the belt 301 to heat the belt 301. Alternatively, the fixing device may use other heating members as a heating member for heating the belt. In any of the fixing device configurations, a similar effect can be obtained by using a heat transfer member (e.g., graphite) having high thermal conductivity in the Y direction, which is the paper width direction, for the pad (nip forming member) that forms the nip.

[0073] The present invention is also effective in a fixing device that uses a pressure belt that presses against a fixing member and forms a nip with a pad member provided in the pressure belt, as described in JP 2007-79036 A. In other words, the same effect can be obtained by using a heat transfer member (e.g., graphite) having high thermal conductivity in the Y direction, which is the paper width direction, for the pad member.

[0074] The present invention is also effective in a fixing device using a fixing belt and a pressure belt, in which a nip is formed by a pad member provided in the fixing belt and a pad member provided in the pressure belt, as described in JP 2009-3088 A. In other words, the same effect can be obtained by using a heat transfer material (e.g., graphite) having high thermal conductivity in the Y direction, which is the paper width direction, for each pad member.

[0075] In the above-described embodiment, an example was described in which the present invention is applied to an electrophotographic full-color image forming apparatus having multiple photosensitive drums, but the present invention is not limited to this and can also be applied to various types of image forming apparatuses, monochrome image forming apparatuses, etc.

[0076] In the above-mentioned embodiment, a copying machine is exemplified as an image forming apparatus, but the present invention is not limited thereto. For example, other image forming apparatuses such as a printer, a facsimile machine, or other image forming apparatuses such as a multifunction machine combining the functions of these may be used. In addition, an image forming apparatus that uses an intermediate transfer body, transfers toner images of each color to the intermediate transfer body in a sequentially overlapping manner, and transfers the toner images carried on the intermediate transfer body to a recording material all at once is exemplified, but the present invention is not limited thereto. An image forming apparatus that uses a recording material carrier, transfers toner images of each color to the recording material carried on the recording material carrier in a sequentially overlapping manner. The same effect can be obtained by applying the present invention to a fixing device (image heating device) used in these image forming apparatuses.

[0077] In the above-described embodiment, a fixing device that is mounted in an image forming apparatus such as a printer or copier and fixes a toner image on a recording material to the recording material has been exemplified as an image heating device that heats a toner image on a recording material. However, the present invention is not limited to such fixing devices, and can be applied to image heating devices such as gloss imparting devices that improve the glossiness of an image formed on a recording material. The present invention can also be applied to image heating devices that are not mounted in image forming apparatuses. [Explanation of symbols]

[0078] F... Fixing device N: Nip section P … Recording material S...Oil (lubricant) Ua,Ub,Uc,Ud...Image forming section 1. Image forming device 301 ... Fixing belt (belt member) 302 … Stay 303 ... Pressure pad (nip forming member) 303a…Base material 303b … Coating layer 305 ... Pressure roller (pressure member) 306 … Halogen heater 307 ... Heating roller (heating member) 308 ... Steering roller 311 ... Sliding members

Claims

1. A fixing device that fixes a toner image on a recording material to the recording material, A heating element; an endless, rotatable belt member that is heated by the heating member; a nip forming member provided on an inner peripheral surface side of the belt member and contacting the inner peripheral surface of the belt member to support the belt member from the inner peripheral surface side; a pressure member that is in pressure contact with the nip forming member via the belt member and forms a nip portion between the belt member and the pressure member, The fixing device according to claim 1, wherein the nip forming member includes a heat conductive member having anisotropic thermal conductivity.

2. 2. The fixing device according to claim 1, wherein the heat conducting member is made of an anisotropic material having a thermal conductivity in a width direction of the recording material perpendicular to a transport direction of the recording material, the thermal conductivity being greater than a thermal conductivity in a pressure direction of the pressure member against the nip forming member perpendicular to the transport direction and the width direction.

3. 2. The fixing device according to claim 1, wherein the heat conductive member is made of a graphite material.

4. 2. The fixing device according to claim 1, wherein the heat conductive member has a coating layer provided at least on a surface that comes into contact with the belt member.

5. 5. The fixing device according to claim 4, wherein the heat conductive member has the coating layer provided on all outer surfaces thereof including the contact surface.

6. 5. The fixing device according to claim 4, wherein the coating layer is a nickel layer made of nickel.

7. 5. The fixing device according to claim 4, wherein the coating layer has an embossed shape on a surface that comes into contact with the belt member.

8. 2. The fixing device according to claim 1, wherein the nip forming member has an embossed shape on a surface that comes into contact with the belt member.

9. 2. The fixing device according to claim 1, further comprising a lubricant interposed between the nip forming member and the belt member.

10. 2. The fixing device according to claim 1, wherein the nip forming member is formed so that a length in a width direction of the recording material perpendicular to a conveying direction of the recording material is longer than that of the pressure member.

11. A fixing device that fixes a toner image transferred onto a recording material to the recording material, A heating element; an endless, rotatable belt member that is heated by the heating member; a nip forming member provided on an inner peripheral surface side of the belt member and supporting the belt member from the inner peripheral surface side; a pressure member that is in pressure contact with the nip forming member via the belt member and forms a nip portion between the belt member and the pressure member, The fixing device according to the present invention is characterized in that the nip forming member includes a heat conductive member having anisotropic thermal conductivity, and further includes a sliding member between the nip forming member and the belt member, the sliding member being in contact with the inner peripheral surface of the belt member.

12. The fixing device according to claim 11, characterized in that the thermal conductive member is made of an anisotropic material having a thermal conductivity in a width direction of the recording material perpendicular to a transport direction of the recording material that is greater than a thermal conductivity in a pressure direction of the pressure member against the nip forming member perpendicular to the transport direction and the width direction.

13. The fixing device according to claim 11 , wherein the heat conductive member is made of a graphite material.

14. 12. The fixing device according to claim 11, wherein the heat conductive member has a coating layer provided at least on a surface that comes into contact with the sliding member.

15. 15. The fixing device according to claim 14, wherein the heat conductive member has the coating layer provided on all outer surfaces thereof including the contact surface.

16. The fixing device according to claim 14 , wherein the coating layer is a nickel layer using nickel.

17. 12. The fixing device according to claim 11, wherein the nip forming member is formed so that a length in a width direction of the recording material perpendicular to a conveying direction of the recording material is longer than that of the pressure member.

18. 18. An image forming apparatus having an image forming section that forms an image on a recording material, and a fixing section that fixes the image on the recording material, wherein the fixing section is the fixing device according to claim 1.

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