Fixing device, image forming apparatus

Abstract

To ensure certain insulating properties between a separation member and a housing or between an urging member and the housing.SOLUTION: A fixing device 9 comprises: a fixing belt 20; a pressure roller 21 that faces the fixing belt 20; a heater 22 that has a resistance heating element 31, and is in contact with an inner face of the fixing belt 20 directly or with a conductive member therebetween to apply heat to the fixing belt 20; a conductive separation plate 41 that is in contact with the fixing belt 20; a conductive fixing frame 40 that is grounded; a collar 42 that is provided on the fixing frame 40; and a torsion spring 44 that urges the separation plate 41 toward the fixing belt 20. The separation plate 41 and the torsion spring 44 are attached to the fixing frame 40 with the collar 42.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a fixing device and an image forming apparatus. [Background technology]

[0002] The fixing device is provided with a heater as a heating element that heats the fixing belt as a rotating member. Some types of heater generate heat by applying an AC voltage to a resistance heating element formed on a base material, and heat the inner surface of the fixing belt through an insulating layer or the like.

[0003] Such a fixing device is provided with a separating member for separating paper as a recording medium that has passed through the fixing nip from the fixing belt. For example, in Patent Document 1 (Japanese Patent No. 6422563), a metallic separating member is provided.

[0004] However, if the insulating layer on the heater is damaged and current flows from the heater to the fixing belt, the current will flow to the housing of the fixing device via the conductive separating member or the biasing member that biases the separating member, which can affect the amount of heat generated by the heater or have adverse electrical effects on surrounding components. Summary of the Invention [Problem to be solved by the invention]

[0005] In view of the above circumstances, an object of the present invention is to ensure a certain level of insulation between the separating member and the housing, or between the biasing member and the housing. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the present invention provides a fixing device including a rotating member, an opposing rotating member that faces the rotating member, a heating element that has a resistance heating element and that heats the rotating member by contacting the inner surface of the rotating member directly or via a conductive element, a conductive separating member that contacts the rotating member, a grounded conductive housing, a resistor provided in the housing, and a biasing member that biases the separating member toward the rotating member, wherein the separating member and the biasing member are attached to the housing via the resistor. The separating member has a separating portion and a contact portion that branches off from the separating portion and contacts the rotating member, and the contact portion contacts the rotating member, thereby providing a gap between the separating portion and the rotating member. It is characterized by: [Effects of the Invention]

[0007] According to the present invention, a certain level of insulation can be ensured between the separating member and the housing, and between the biasing member and the housing. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram illustrating the configuration of an image forming apparatus. [Figure 2] 1 is a side cross-sectional view showing a schematic configuration of a fixing device according to an embodiment of the present invention. [Figure 3] FIG. [Figure 4] 3 is a cross-sectional view taken along the line B2-B2 in FIG. 2. [Figure 5] FIG. 1A is a cross-sectional view showing a fixing device different from that of the present embodiment, and FIG. 1B is a cross-sectional view showing a state in which the fixing belt of FIG. 1A has become kinked. [Figure 6] 10 is a cross-sectional view of the fixing device according to the present embodiment, showing a state in which a fixing belt is curled. FIG. [Figure 7] FIG. 4 is a diagram showing a conductive path of a fixing device different from that of the present embodiment. [Figure 8] FIG. 3 is a diagram illustrating a conductive path of the fixing device according to the present embodiment. [Figure 9] FIG. 2 is a side cross-sectional view of a fixing device having a heat equalizing plate. [Figure 10] FIG. [Figure 11] FIG. 10 is a diagram illustrating power supply to a heater. [Figure 12] FIG. 11 is a plan view of a heater having a different shape of the resistance heating element from that in FIG. [Figure 13] FIG. 13 is a plan view of a heater having a resistance heating element with a different shape from those in FIGS. 10 and 12. [Figure 14] 1A and 1B are diagrams showing the temperature distribution in the arrangement direction of the fixing belt, in which FIG. 1A is a plan view of the heater, and FIG. 1B is a diagram showing the temperature distribution of the fixing belt. [Figure 15] FIG. 13 is a diagram showing divided regions of the heater in FIG. 12. [Figure 16] FIG. 16 is a diagram showing divided regions having a different shape from that shown in FIG. 15. [Figure 17] FIG. 14 is a diagram showing divided regions of the heater in FIG. 13. [Figure 18] FIG. 2 is a perspective view of a heater, a first high thermal conductive member, and a heater holder. [Figure 19] FIG. 2 is a plan view of the heater showing the arrangement of the first high thermal conductivity members. [Figure 20] 10A and 10B are plan views of a heater showing different examples of the arrangement of first high thermal conductivity members. [Figure 21] FIG. 10 is a plan view of a heater showing yet another example of the arrangement of first high thermal conductivity members. [Figure 22] 3 is a side cross-sectional view showing a schematic configuration of a fixing device according to an embodiment different from that shown in FIG. 2. [Figure 23] FIG. 2 is a perspective view of a heater, a first highly thermally conductive member, a second highly thermally conductive member, and a heater holder. [Figure 24] FIG. 3 is a plan view of the heater showing the arrangement of the first and second high thermal conductive members. [Figure 25] 3A to 3C are plan views of a heater showing examples of different arrangements of the first and second high thermal conductive members. [Figure 26] FIG. 1 illustrates the atomic crystal structure of graphene. [Figure 27] FIG. 1 illustrates the atomic crystal structure of graphite. [Figure 28] 25 is a plan view showing a heater in which the arrangement of the second high thermal conductive members is different from that in FIG. 24. FIG. [Figure 29] 2. FIG. 23 is a side cross-sectional view showing a schematic configuration of a fixing device according to an embodiment different from that shown in FIGS. [Figure 30] FIG. 2 is a side cross-sectional view showing a schematic configuration of a fixing device different from the above. [Figure 31] FIG. 2 is a side cross-sectional view showing a schematic configuration of a fixing device different from the above. [Figure 32] FIG. 2 is a side cross-sectional view showing a schematic configuration of a fixing device different from the above. [Figure 33] FIG. 2 is a schematic diagram illustrating the configuration of an image forming apparatus different from that in FIG. [Figure 34] 1 is a side cross-sectional view showing a schematic configuration of a fixing device according to an embodiment of the present invention. [Figure 35] FIG. 35 is a plan view of a heater in the fixing device of FIG. 34. [Figure 36] FIG. 2 is a perspective view of a heater and a heater holder. [Figure 37] FIG. 4 is a perspective view showing a state in which a connector is attached to a heater. [Figure 38] FIG. 2 is a diagram showing the arrangement of a thermistor and a thermostat. [Figure 39] FIG. 10 is a view showing a groove portion of a flange. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention will be described below with reference to the accompanying drawings. In each drawing for explaining the present invention, components such as members and components having the same function or shape are designated by the same reference numerals as far as they can be distinguished, and descriptions thereof will be omitted once they have been described.

[0010] 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention, which includes a fixing device that fixes a toner image on a sheet of paper to the sheet of paper, as an aspect of the heating device of the present invention.

[0011] The image forming apparatus 100 shown in FIG. 1 includes four imaging units 1Y, 1M, 1C, and 1Bk that are detachable from the image forming apparatus main body. Each imaging unit 1Y, 1M, 1C, and 1Bk has the same configuration except that it contains a different color developer: yellow, magenta, cyan, or black. These color developers correspond to the color separation components of a color image. Each imaging unit 1Y, 1M, 1C, and 1Bk includes a drum-shaped photoconductor 2 as an image carrier, a charging device 3, a developing device 4, and a cleaning device 5. The charging device 3 charges the surface of the photoconductor 2. The developing device 4 supplies toner as a developer to the surface of the photoconductor 2 to form a toner image. The cleaning device 5 cleans the surface of the photoconductor 2.

[0012] The image forming apparatus 100 also includes an exposure device 6, a paper feed device 7, a transfer device 8, a fixing device 9 as a heating device, and a paper discharge device 10. The exposure device 6 exposes the surface of each photoconductor 2 to light and forms an electrostatic latent image on that surface. The paper feed device 7 supplies paper P as a recording medium to a paper transport path 14. The transfer device 8 transfers the toner image formed on each photoconductor 2 to the paper P. The fixing device 9 fixes the toner image transferred to the paper P to the surface of the paper P. The paper discharge device 10 discharges the paper P outside the apparatus. The imaging units 1, photoconductors 2, charging devices 3, exposure device 6, transfer device 8, etc. constitute image forming means for forming an image on paper.

[0013] The transfer device 8 has an endless intermediate transfer belt 11 as an intermediate transfer body, four primary transfer rollers 12 as primary transfer members, and a secondary transfer roller 13 as a secondary transfer member. The intermediate transfer belt 11 is stretched by multiple rollers. The primary transfer rollers 12 transfer the toner images on the photoconductors 2 to the intermediate transfer belt 11. The secondary transfer rollers 13 transfer the toner images transferred onto the intermediate transfer belt 11 to paper P. Each of the multiple primary transfer rollers 12 contacts the photoconductors 2 via the intermediate transfer belt 11. This brings the intermediate transfer belt 11 and each photoconductor 2 into contact with each other, forming a primary transfer nip between them. Meanwhile, the secondary transfer roller 13 contacts one of the rollers stretching the intermediate transfer belt 11 via the intermediate transfer belt 11. This forms a secondary transfer nip between the secondary transfer roller 13 and the intermediate transfer belt 11.

[0014] Further, a pair of timing rollers 15 is provided in the paper transport path 14 between the paper feeder 7 and the secondary transfer nip (secondary transfer roller 13).

[0015] Next, the printing operation of the image forming apparatus will be described with reference to FIG.

[0016] When a command to start a printing operation is issued, in each of the imaging units 1Y, 1M, 1C, and 1Bk, the photoconductor 2 is rotated clockwise in FIG. 1, and the charging device 3 charges the surface of the photoconductor 2 to a uniform high potential. Next, the exposure device 6 exposes the surface of each photoconductor 2 based on the image information of the original document read by the document reading device or the print information instructed to be printed from the terminal. This reduces the potential of the exposed area, forming an electrostatic latent image. Toner is then supplied from the developing device 4 to this electrostatic latent image, and a toner image is formed on each photoconductor 2.

[0017] The toner images formed on each photoconductor 2 rotate with the rotation of the photoconductor 2 and reach the primary transfer nip (the position of the primary transfer roller 12). The toner images are then transferred to the intermediate transfer belt 11, which rotates counterclockwise in FIG. 1, so that they overlap one another. The toner images transferred onto the intermediate transfer belt 11 are then transported to the secondary transfer nip (the position of the secondary transfer roller 13) with the rotation of the intermediate transfer belt 11. The toner images are then transferred to the paper P transported at the secondary transfer nip. This paper P is supplied from the paper feeder 7. The paper P supplied from the paper feeder 7 is temporarily stopped by timing roller 15 and then transported to the secondary transfer nip in time with the toner image on the intermediate transfer belt 11 reaching the secondary transfer nip. In this way, a full-color toner image is carried on the paper P. After the toner image is transferred, any toner remaining on each photoconductor 2 is removed by the cleaning devices 5.

[0018] The paper P onto which the toner image has been transferred is transported to a fixing device 9, which fixes the toner image onto the paper P. The paper P is then discharged outside the apparatus by a paper discharge device 10, completing the series of printing operations.

[0019] Next, the configuration of the fixing device will be described.

[0020] As shown in FIG. 2, the fixing device 9 according to this embodiment includes a fixing frame 40 as a housing, a fixing belt 20, a pressure roller 21, a heater 22 as a heating element, a heater holder 23 as a holding member, a stay 24 as a support member, a thermistor 25 as a temperature detection member, a first high thermal conductivity member 28, and a separation plate 41 as a separation member. The fixing belt 20 is an endless belt. The pressure roller 21 contacts the outer surface of the fixing belt 20 and forms a fixing nip N between the fixing belt 20 and the pressure roller 21. The heater 22 heats the fixing belt 20. The heater holder 23 holds the heater 22. The stay 24 supports the heater holder 23. The thermistor 25 detects the temperature of the first high thermal conductivity member 28. The separation plate 41 separates the paper P from the fixing belt 20 after it has passed through the fixing nip N. The fixing frame 40 holds these components within itself. The fixing frame 40 is made of metal and is grounded.

[0021] The direction perpendicular to the plane of the paper in FIG. 2 is the longitudinal direction of the fixing belt 20, pressure roller 21, heater 22, heater holder 23, stay 24, first high thermal conductivity member 28, separation plate 41, etc., and hereinafter, this direction will be simply referred to as the longitudinal direction. This longitudinal direction also corresponds to the width direction of the paper being conveyed, the belt width direction of the fixing belt 20, and the axial direction of the pressure roller 21. The fixing member provided in the fixing device is one aspect of the rotating member provided in the heating device of the present invention. The fixing device 9 of this embodiment is provided with the fixing belt 20 as a specific example of this fixing member. The pressure member provided in the fixing device is one aspect of the opposing rotating member provided in the heating device of the present invention. The fixing device 9 of this embodiment is provided with the pressure roller 21 as a specific example of this pressure member.

[0022] The fixing belt 20 has a cylindrical substrate made of polyimide (PI) with an outer diameter of 25 mm and a thickness of 40 to 120 μm. A release layer made of a fluorine-based resin such as PFA or PTFE and having a thickness of 5 to 50 μm is formed on the outermost surface of the fixing belt 20 to enhance durability and ensure releasability. A 50 to 500 μm elastic layer made of rubber or the like may be provided between the substrate and the release layer. The substrate of the fixing belt 20 is not limited to polyimide, and may be a heat-resistant resin such as PEEK or a metal substrate such as nickel (Ni) or SUS. The inner peripheral surface of the fixing belt 20 may be coated with a sliding layer made of polyimide, PTFE, or the like.

[0023] The pressure roller 21 has an outer diameter of, for example, 25 mm. From the inside, the pressure roller 21 has a core 21a as a first layer, an elastic layer 21b as a second layer, and a surface layer 21c as a third layer. The solid core 21a is made of a conductive material, which is made of iron in this embodiment. The elastic layer 21b is made of a non-conductive material, which is made of silicone rubber with a thickness of 3.5 mm in this embodiment. By making the elastic layer 21b a non-conductive layer, there is no need to add a material such as a filler to impart conductivity to the elastic layer 21b, and its elasticity and stretchability can be ensured.

[0024] The pressure roller 21 is urged toward the fixing belt 20 by the urging means, so that the pressure roller 21 is pressed against the heater 22 via the fixing belt 20. This forms a fixing nip N between the fixing belt 20 and the pressure roller 21. The pressure roller 21 is also configured to be rotationally driven by a driving means, and when the pressure roller 21 rotates in the direction of the arrow in FIG. 2, the fixing belt 20 is rotated accordingly.

[0025] The heater 22 is a planar heating element provided longitudinally across the width direction of the fixing belt 20. The heater 22 is composed of a plate-shaped base material 30, a resistance heating element 31 provided on the base material 30, an insulating layer 32 covering the resistance heating element 31, and the like. The insulating layer 32 side of the heater 22 is in contact with the inner circumferential surface of the fixing belt 20, and heat generated from the resistance heating element 31 is transferred to the fixing belt 20 via the insulating layer 32. However, the heater 22 may be in contact with the inner circumferential surface of the fixing belt 20 via another conductive member such as a heat equalizer plate. When an AC voltage is applied to the heater 22 from a power source 200 (see FIG. 11 ), the resistance heating element 31 mainly generates heat. In this embodiment, the resistance heating element 31 and the insulating layer 32 are provided on the fixing belt 20 side (fixing nip N side) of the substrate 30, but conversely, the resistance heating element 31 and the insulating layer 32 may be provided on the heater holder 23 side of the substrate 30. In that case, since the heat of the resistance heating element 31 is transferred to the fixing belt 20 via the substrate 30, it is desirable that the substrate 30 be made of a material with high thermal conductivity such as aluminum nitride. Furthermore, by making the substrate 30 of a material with high thermal conductivity, it is possible to sufficiently heat the fixing belt 20 even if the resistance heating element 31 is arranged on the opposite side of the substrate 30 from the fixing belt 20 side.

[0026] The heater holder 23 and the stay 24 are disposed on the inner circumferential side of the fixing belt 20. The stay 24 is made of a metal channel material, and both ends thereof are supported by both side plates of the fixing device 9. By supporting the heater holder 23 and the heater 22 by the stay 24, the heater 22 can reliably receive the pressing force of the pressure roller 21 while the pressure roller 21 is pressed against the fixing belt 20. This ensures that the fixing nip N is stably formed between the fixing belt 20 and the pressure roller 21. In this embodiment, the thermal conductivity of the heater holder 23 is set to be smaller than that of the base material 30.

[0027] Note that the stay 24 supporting the heater holder 23 means that the stay 24, which has a portion extending in the pressure direction of the pressure roller 21 (the left-right direction in the figure) or a portion with a thickness, abuts against the heater holder 23 from the side opposite the pressure roller 21 (the left side in the figure). This makes it possible to suppress deflection of the heater holder 23 due to the pressure from the pressure roller 21 (particularly deflection in the longitudinal direction in this embodiment). However, the above-mentioned abutment does not necessarily mean that the stay 24 abuts against the heater holder 23 directly, but also includes a case where the stay 24 abuts against the heater holder 23 via another member. "Abutment via another member" refers to a state where another member is sandwiched between the stay 24 and the heater holder 23 in the left-right direction in the figure, and the stay 24 abuts against the other member at a position where at least a portion of the other member corresponds to the other member, and the other member abuts against the heater holder 23. Furthermore, the term "extending in the pressure direction" mentioned above does not necessarily mean the same direction as the pressure direction of the pressure roller 21, but also includes the case of extending in a direction at a certain angle from the pressure direction of the pressure roller 21. Even in these cases, it goes without saying that the stay 24 can suppress the deflection of the heater holder 23 against the pressure force from the pressure roller 21.

[0028] The heater holder 23 is desirably made of a heat-resistant material because it is prone to becoming hot due to the heat from the heater 22. For example, if the heater holder 23 is made of a heat-resistant resin with low thermal conductivity such as LCP, heat transfer from the heater 22 to the heater holder 23 is suppressed. This allows the heater 22 to heat the fixing belt 20 efficiently.

[0029] The heater holder 23 is also provided with guide portions 26 that guide the fixing belt 20. The guide portions 26 are provided on the upstream side (below the heater 22 in FIG. 2) and downstream side (above the heater 22 in FIG. 2) of the heater 22 in the belt rotation direction. The upstream and downstream guide portions 26 are arranged at intervals along the longitudinal direction of the heater 22. Each guide portion 26 is formed in a roughly fan shape and has a belt-facing surface 260 that is arc-shaped or convexly curved and extends in the belt circumferential direction so as to face the inner circumferential surface of the fixing belt 20.

[0030] Heater holder 23 has a plurality of openings 23a in the longitudinal direction. Openings 23a are openings that penetrate heater holder 23 in the thickness direction. Thermistor 25 and a thermostat, which will be described later, are provided in these openings 23a. These thermistors 25 and thermostats are pressed against the back surface of first high thermal conductivity member 28 by spring 29. However, openings may also be similarly provided in first high thermal conductivity member 28 (and second high thermal conductivity member, which will be described later), so that thermistor 25 and thermostat are pressed against the back surface of base material 30.

[0031] Separator plate 41 is made of a metal material, and is obtained by processing a metal plate such as rust-proofed iron, stainless steel, aluminum, etc. The width of separator plate 41 in the longitudinal direction is set to be larger than the maximum width of paper that fixing device 9 can accommodate.

[0032] The first high thermal conductivity member 28 is made of a material having a higher thermal conductivity than the base material. In this embodiment, the first high thermal conductivity member 28 is made of plate-shaped aluminum. Alternatively, the first high thermal conductivity member 28 may be made of, for example, copper, silver, graphene, or graphite. By making the first high thermal conductivity member 28 plate-shaped, the positional accuracy of the heater 22 with respect to the heater holder 23 and the first high thermal conductivity member 28 can be improved.

[0033] Next, a method for calculating the thermal conductivity will be described. When calculating the thermal conductivity, first, the thermal diffusivity of the object is measured, and then the thermal conductivity is calculated using the measured thermal diffusivity.

[0034] The thermal diffusivity was measured using a thermal diffusivity / thermal conductivity measuring device (trade name: ai-Phase Mobile 1u, ai-Phase Corporation).

[0035] To convert the thermal diffusivity to thermal conductivity, the density and specific heat capacity values ​​are required. A dry-type automatic densitometer (product name: Accupyc 1330, manufactured by Shimadzu Corporation) was used to measure the density. A differential scanning calorimeter (product name: DSC-60, manufactured by Shimadzu Corporation) was used to measure the specific heat capacity, using sapphire as a reference material with a known specific heat capacity. In this example, the specific heat capacity was measured five times, and the average value at 50°C was used. When the density and specific heat capacity are ρ and C, respectively, the thermal conductivity λ can be calculated from the thermal diffusivity α obtained from the thermal diffusivity measurement using the following equation (1):

[0036]

number

[0037] In the fixing device 9 according to this embodiment, when a printing operation is started, the pressure roller 21 is driven to rotate, and the fixing belt 20 begins to rotate. At this time, the inner circumferential surface of the fixing belt 20 contacts and is guided by the belt-facing surface 260 of the guide portion 26, thereby allowing the fixing belt 20 to rotate stably and smoothly. Furthermore, power is supplied to the resistance heating element 31 of the heater 22, thereby heating the fixing belt 20. Then, when the temperature of the fixing belt 20 reaches a predetermined target temperature (fixing temperature), as shown in FIG. 2, a sheet of paper P carrying an unfixed toner image is transported between the fixing belt 20 and the pressure roller 21 (fixing nip N), whereby the unfixed toner image is heated and pressurized to be fixed to the sheet of paper P. The fixing belt 20 is a heated member that is heated by the heater 22.

[0038] Next, separation plate 41 and its surrounding structure provided in the fixing device of this embodiment will be described in more detail with reference to Figures 2, 3, and 4. Figure 3 is a plan view of the fixing device. Figures 2 and 4 are side cross-sectional views of the fixing device, Figure 2 is a cross-sectional view taken along line B1-B1 in Figure 3, and Figure 4 is a cross-sectional view taken along line B2-B2 in Figure 3.

[0039] 2, separation plate 41 of this embodiment has a separation portion 411, an abutment portion 412, and an attachment portion 413. The abutment portion 412 is a portion that branches off from the main body of separation plate 41 including separation portion 411, and is a portion that abuts against fixing belt 20 at a position downstream of fixing nip N of fixing belt 20 in the rotation direction of fixing belt 20 and farther from fixing nip N. The attachment portion 413 is provided at the end of separation plate 41 opposite separation portion 411.

[0040] 3, the attachment portions 413 are provided on both longitudinal sides of the separation plate 41. The fixing frame 40 also has a pair of holding pins 401 for holding the attachment portions 413 of the separation plate 41. A collar 42 serving as a resistor is provided on one of the holding pins 401. The collar 42 is attached so as to cover the end of the holding pin 401. A second collar 43 serving as an insulating member is provided on the other holding pin 401. The second collar 43 is made of an insulating material.

[0041] 2, the attachment portion 413 is fitted into the collar 42 so as to cover the outer peripheral surface of the collar 42. In other words, the separation plate 41 is attached to the holding pin 401 of the fixing frame 40 via the collar 42. The separation plate 41 is provided rotatably with respect to the collar 42 and the holding pin 401.

[0042] Collar 42 is made of a conductive resin material and has a volume resistance set to 100 kΩ or more. This allows the current flowing through collar 42 to be 1.0 mA or less, as stipulated in Article 7, Paragraph 2 of Appendix 12 of the Electrical Appliance and Material Safety Act, when the power supply voltage of the image forming apparatus is 100 V. The volume resistance of collar 42 can be calculated by applying a voltage of 100 V to the surface of collar 42 and the exposed portion of retaining pin 401, and measuring the current flowing through collar 42 after 10 seconds have elapsed.

[0043] 4, one end of a torsion spring 44 serving as a biasing member is attached to a collar 42. That is, the torsion spring 44 is attached to a holding pin 401 of the fixation frame 40 via the collar 42. The end of the torsion spring 44 opposite to the portion attached to the collar 42 is fixed to the separation plate 41. The torsion spring 44 biases the separation plate 41 in the direction of the arrow in Figure 4, which is toward the fixing belt 20. As a result, the abutment portion 412 of the separation plate 41 shown in Figure 2 comes into contact with the outer peripheral surface of the fixing belt 20.

[0044] In order to ensure the separation performance of the separation plate 41 for the paper P, it is necessary to locate the leading edge of the separation plate 41 closer to the downstream edge in the paper transport direction of the fixing nip N. In contrast, by forming the separation plate 41 from a metal material as in this embodiment, the dimensional accuracy of the separation plate 41 can be improved, and the leading edge of the separation plate 41 can be positioned closer to the downstream edge in the paper transport direction of the fixing nip N.

[0045] However, by bringing the leading edge of the separator plate 41 closer to the fixing nip N, there is a risk that the leading edge of the separator plate 41 may come into contact with the fixing belt 20. For example, in a fixing device 9′ shown in FIG. 5A, which differs from the present embodiment, the separator plate 41′ is provided close to the downstream end of the fixing nip N in the paper conveyance direction. Then, after the fixing belt 20 is heated and a sheet passes through the fixing nip N, if the heating by the heater 22 is stopped and the fixing belt 20 is left standing, the fixing belt 20 becomes warped at the fixing nip N portion, resulting in deformation as shown in FIG. 5B. This warping occurs due to the difference in cooling rate between the fixing nip N portion and other portions of the fixing belt 20, and is particularly exacerbated by the pressure applied to the fixing belt 20 by the pressure roller 21. This deformation of the fixing belt 20 causes the leading edge of the separator plate 41′ to come into contact with the fixing belt 20, which can cause wear or scratches on the surface of the fixing belt 20 and adhesion of toner and paper dust to the leading edge of the separator plate 41′.

[0046] In contrast, in the fixing device 9 of this embodiment, when the fixing belt 20 becomes warped as shown in FIG. 6 , the abutting portion 412 follows the deformation of the fixing belt 20, changing the position of the separation plate 41. In other words, the abutting portion 412 is maintained in contact with a predetermined position on the fixing belt 20. As a result, a certain gap A is formed between the tip of the separation portion 411 and the outer circumferential surface of the fixing belt 20, and the tip of the separation portion 411 does not come into contact with the fixing belt 20. This prevents wear and scratches on the surface of the fixing belt 20 and the adhesion of toner and paper dust to the tip of the separation plate 41. Note that the torsion spring 44 biases the separation plate 41 toward the fixing belt 20, ensuring stable contact of the abutting portion 412 with the outer circumferential surface of the fixing belt 20.

[0047] However, in such a configuration in which the conductive separation plate 41 contacts the fixing belt 20, current flows from the heater 22 side to the separation plate 41 and then to the fixing frame 40, causing problems such as fluctuations in the heat generation amount of the heater 22, adverse effects on electronic components within the image forming device, and certain components within the image forming device becoming charged and toner adhering thereto, which can cause contamination of the components and contamination of workers when clearing jams.

[0048] The conductive path from the heater 22 to the fixing frame 40 will be described below with reference to Fig. 7. Fig. 7 shows the conductive path when the collar 42 described above is not provided between the fixing frame 40 and the separation plate 41.

[0049] As shown in FIG. 7, the conductor layer of the heater 22, to which an AC voltage is applied, and the fixing belt 20 are basically insulated by an insulating layer 32 having a thickness of less than 0.1 mm. However, if the insulating layer 32 is damaged, the heater 22 and the fixing belt 20 become electrically connected, and current flows to the fixing frame 40 via the fixing belt 20 and the separator plate 41. This causes the above-mentioned problems. Meanwhile, in a fixing device using a halogen heater as a heating element, the energized filament is covered by a glass tube, which serves as an insulating layer. This glass tube is 0.4 mm or thick, providing reinforced insulation between the halogen heater and the fixing belt 20. Furthermore, the halogen heater and the fixing belt 20 are not in contact with each other. Therefore, the above-mentioned problems are less likely to occur.

[0050] In contrast, in this embodiment, as shown in FIG. 8 , a collar 42 is provided between the separator plate 41 and the fuser frame 40, thereby ensuring a certain level of insulation between the separator plate 41 and the fuser frame 40. Furthermore, a collar 42 is provided between the torsion spring 44 and the fuser frame 40, thereby ensuring a certain level of insulation between the torsion spring 44 and the fuser frame 40. This reduces the current flow from the heater 22 to the fuser frame 40 via the fuser belt 20 and the separator plate 41, or via the separator plate 41 and the torsion spring 44. This reduces fluctuations in the amount of heat generated by the heater 22, adverse effects on electronic components within the image forming apparatus, and contamination of components within the image forming apparatus. Furthermore, compared to when the collar 42 is made of an insulating material, this also reduces the accumulation of electric charge on the separator plate 41. In particular, by setting the volume resistance value of the collar 42 to 100 kΩ or more, the current flowing from the separation plate 41 or the torsion spring 44 to the fixing frame 40 side is limited, which effectively prevents the above-mentioned problems and also prevents electric charges from accumulating on the separation plate 41.

[0051] Furthermore, it is preferable to provide a creepage distance and a clearance distance equivalent to basic insulation between the separator plate 41 and the fixation frame 40 and between the torsion spring 44 and the fixation frame 40. Specifically, it is preferable to provide a creepage distance of 2.5 mm or a clearance distance of 2.2 mm or more. In this embodiment, the creepage distance or clearance distance between the separator plate 41 and the fixation frame 40 is the distance from the attachment portion 413 of the separator plate 41 to the exposed portion of the retaining pin 401 of the fixation frame 40, that is, distance L1 in FIG. 3 , plus the thickness of the collar 42. The creepage distance or clearance distance between the torsion spring 44 and the fixation frame 40 is the distance from the attachment portion of the torsion spring 44 to the collar 42 to the exposed portion of the retaining pin 401, that is, distance L2 in FIG. 3 , plus the thickness of the collar 42. By providing these distances of 2.5 mm or more, insulation equivalent to basic insulation can be ensured between the separator plate 41 and the fixation frame 40 or between the torsion spring 44 and the fixation frame 40. The "thickness of collar 42" mentioned above is a distance equivalent to the radial distance L3 between the inner peripheral surface and the outer peripheral surface of collar 42 shown in Fig. 2. However, strictly speaking, this "thickness of collar 42" is not the distance at the cross-sectional position in Fig. 2, but rather the distance equivalent to the distance L3 at the left end of collar 42 in Fig. 3 (the leftmost end of distance L1 or distance L2).

[0052] In this embodiment, the position where the abutting portion 412 of the separation plate 41 comes into contact with the fixing belt 20 is located outside the paper passing area in the paper width direction. Specifically, the abutting portion 412 comes into contact with the fixing belt 20 at the position of the cross-sectional line B1-B1 in FIG. 3 (see FIG. 2), which is outside the paper passing area C in the longitudinal direction shown in FIG. 3. This prevents wear of the fixing belt 20 within the paper passing area and prevents toner and paper dust from adhering to the abutting portion 412. The paper passing area C is the area through which the recording medium passes, and in this embodiment, it is the area through which the fixing device 9 can accommodate the widest paper. The paper width direction is the left-right direction in FIG. 3, the direction perpendicular to the paper transport direction and along the surface of the paper.

[0053] 9, the above-described configuration of the fixing frame 40, separation plate 41, collar 42, torsion spring 44, etc. can also be applied to a configuration having a heat equalizing plate 45 between the heater 22 and the inner surface of the fixing belt 20. The heat equalizing plate 45 is made of a conductive material such as aluminum or copper. In this embodiment, a certain level of insulation can be ensured between the separation plate 41 and the fixing frame 40, and between the torsion spring 44 and the fixing frame 40.

[0054] FIG. 10 is a plan view of the heater according to this embodiment.

[0055] 10, a plurality of (four) resistance heating elements 31, power supply lines 33A and 33B as conductors, a first electrode portion 34A, and a second electrode portion 34B are provided on the surface of a plate-shaped substrate 30. However, the number of resistance heating elements 31 is not limited to that in this embodiment.

[0056] In this embodiment, the longitudinal direction of the heater 22, etc. (the direction perpendicular to the plane of the paper in FIG. 2) is also the arrangement direction X of the multiple resistance heating elements 31, as shown in FIG. 10. Hereinafter, this direction will also be simply referred to as the arrangement direction. Furthermore, the up-down direction Y in FIG. 10, which is a direction intersecting the arrangement direction (a direction perpendicular to the plane of the paper in this embodiment) and different from the thickness direction of the base material 30, will also be referred to as the direction intersecting the arrangement direction of the multiple resistance heating elements 31, or simply as the intersecting arrangement direction. The intersecting arrangement direction Y is the direction along the surface of the base material 30 on which the resistance heating elements 31 are provided, and is also the widthwise direction of the heater 22 or the transport direction of paper passed through the fixing device 9.

[0057] The plurality of resistance heating elements 31 constitute a heating section 35 divided into a plurality of sections in the arrangement direction. Each resistance heating element 31 is electrically connected in parallel to a pair of electrodes 34A, 34B provided at one end of the substrate 30 in the arrangement direction (the left end in FIG. 10 ) via power supply lines 33A, 33B. The power supply lines 33A, 33B are made of a conductor having a lower resistance value than the resistance heating elements 31. To ensure insulation between the resistance heating elements 31, the gap between adjacent resistance heating elements 31 is preferably 0.2 mm or more, more preferably 0.4 mm or more. Furthermore, if the gap between adjacent resistance heating elements 31 is too large, a temperature drop is likely to occur in the gap. Therefore, to suppress temperature unevenness across the arrangement direction, the gap is preferably 5 mm or less, more preferably 1 mm or less.

[0058] The resistance heating element 31 is made of a material with a PTC (positive temperature coefficient of resistance) characteristic, and is characterized in that the resistance value increases (heater output decreases) as the temperature increases. In this embodiment, the temperature coefficient of resistance of the resistance heating element 31 is set to 500 ppm.

[0059] The PTC characteristics of the resistance heating element 31 and the divided heating section 35 configuration in the arrangement direction prevent excessive temperature rise of the fixing belt 20 when small-size paper is passed through. In other words, when paper narrower than the overall width of the heating section 35 is passed through, the paper does not absorb heat from the fixing belt 20 in the area outside the paper width, so the temperature of the resistance heating element 31 corresponding to that area rises. Because the voltage applied to the resistance heating element 31 is constant, the temperature of the resistance heating element 31 outside the paper width rises, and when its resistance value increases, the output (heat generation amount) decreases relatively, suppressing the temperature rise at the edge. Furthermore, by electrically connecting multiple resistance heating elements 31 in parallel, it is possible to suppress the temperature rise in non-paper passing areas while maintaining printing speed. The heating elements constituting the heating section 35 may be other than resistance heating elements having PTC characteristics. Furthermore, the resistance heating elements may be arranged in multiple rows in the direction crossing the arrangement of the heaters 22.

[0060] The resistance heating element 31 can be formed, for example, by applying a paste made of silver palladium (AgPd) and glass powder to the substrate 30 by screen printing or the like, and then firing the substrate 30. In this embodiment, the resistance value of the resistance heating element 31 is set to 80 Ω at room temperature. In addition to the materials mentioned above, the resistance heating element 31 may also be made of resistance materials such as silver alloy (AgPt) or ruthenium oxide (RuO2). The power supply line 33 and the electrode portion 34 can be made of silver (Ag) or silver palladium (AgPd) by screen printing or the like. The power supply line 33 is made of a conductor with a lower resistance value than the resistance heating element 31.

[0061] The substrate 30 is preferably made of ceramics such as alumina or aluminum nitride, which have excellent heat resistance and insulation properties, or non-metallic materials such as glass or mica. In this embodiment, an alumina substrate is used, which is 8 mm wide in the cross-array direction, 270 mm wide in the array direction, and 1.0 mm thick. Alternatively, the substrate 30 may be made of a conductive material such as a metal laminated with an insulating material. Aluminum and stainless steel are preferred metal materials for the substrate 30, as they are low-cost. By constructing the substrate 30 from a stainless steel plate, cracks due to thermal stress can be suppressed. Furthermore, to improve the thermal uniformity of the heater 22 and enhance image quality, the substrate 30 may be made of a highly thermally conductive material such as copper, graphite, or graphene.

[0062] The insulating layer 32 is made of heat-resistant glass having a thickness of, for example, 75 μm. The insulating layer 32 covers the resistance heating element 31 and the power supply line 33, insulating and protecting them and maintaining sliding properties with the fixing belt 20.

[0063] FIG. 11 is a diagram showing a power supply circuit to the heater according to this embodiment.

[0064] 11, in this embodiment, a power supply circuit for supplying power to each resistance heating element 31 is configured by electrically connecting an AC power source 200 and the electrodes 34A, 34B of the heater 22. The power supply circuit is also provided with a triac 210 that controls the amount of power supplied. The amount of power supplied to each resistance heating element 31 is controlled by a control unit 220 via the triac 210 based on the temperature detected by the thermistor 25. The control unit 220 is configured by a microcomputer including a CPU, ROM, RAM, I / O interface, etc.

[0065] In this embodiment, thermistors 25 are disposed in a central region in the arrangement direction of heaters 22, which is within the minimum paper passing width, and at one end side in the arrangement direction of heaters 22. Furthermore, at one end side in the arrangement direction of heaters 22, a thermostat 27 is disposed as a power cut-off device that cuts off the supply of power to resistance heating elements 31 when the temperature of resistance heating elements 31 reaches or exceeds a predetermined temperature. Thermistors 25 and thermostat 27 contact first high thermal conductivity member 28 to detect its temperature.

[0066] In this embodiment, the first electrode portion 34A and the second electrode portion 34B are provided on the same side in the arrangement direction, but they may be provided on different sides. The shape of the resistance heating element 31 is not limited to that of this embodiment. For example, as shown in FIG. 12, the resistance heating element 31 may be rectangular. Alternatively, as shown in FIG. 13, the resistance heating element 31 may be formed of a linear portion that is folded back to form a substantially parallelogram shape. As shown in FIG. 12, the portion extending from the block-shaped portion of the resistance heating element 31 toward the power supply line 33 (the portion extending in the intersecting direction) may be part of the resistance heating element 31, or may be made of the same material as the power supply line 33.

[0067] 14A and 14B are diagrams showing the temperature distribution in the arrangement direction of the fixing belt 20. (a) shows the arrangement of the heaters 22. (b) shows the vertical axis representing the temperature T of the fixing belt 20, and the horizontal axis representing each position in the arrangement direction of the fixing belt 20.

[0068] As shown in FIGS. 14(a) and 14(b), the heater 22 has a plurality of resistance heating elements 31 divided in the arrangement direction, forming divided regions B between the resistance heating elements 31. In other words, the heater 22 has a plurality of resistance heating elements 31 arranged at intervals B. Hereinafter, the range B of the divided region will be referred to as interval B. In interval B, the area occupied by the resistance heating elements 31 is smaller than in other regions, resulting in a smaller amount of heat generation. As a result, the temperature of the fixing belt 20 in interval B is lower than in other regions, causing temperature unevenness in the arrangement direction of the fixing belt 20. Furthermore, in an expanded divided region C (hereinafter simply referred to as region C) including the region surrounding interval B, which is a divided region, the temperatures of the heater 22 and the fixing belt 20 are also lower. Note that the temperature of the heater 22 is also lower in interval B. Here, as shown in the enlarged view of FIG. 14(a), interval B refers to the arrangement direction region including all of the regions into which the resistance heating elements 31, which are the main heat-generating portions of the heater 22, are divided in the arrangement direction. Furthermore, an area including the interval B and a range corresponding to the connection portion 311 of the resistance heating element 31 is defined as an area C. The connection portion 311 refers to the portion of the resistance heating element 31 that extends in the cross-arrangement direction and is connected to each of the power supply lines 33A and 33B.

[0069] As shown in Fig. 15, in heater 22 having rectangular resistance heating element 31 as shown in Fig. 12, the temperature in interval B is also lower than in other parts. Also in heater 22 having resistance heating element 31 shaped as shown in Fig. 16, the temperature in interval B is also lower than in other parts. Furthermore, as shown in Fig. 17, in heater 22 having resistance heating element 31 shaped as shown in Fig. 13, the temperature in interval B is also lower than in other parts. However, by overlapping adjacent resistance heating elements 31 in the arrangement direction as in Figs. 14, 16 and 17, the temperature drop in interval B relative to other parts can be suppressed.

[0070] In this embodiment, the above-described first high thermal conductivity member 28 is provided to suppress the temperature drop in the above-mentioned interval and to suppress temperature unevenness in the arrangement direction of the fixing belt 20. The first high thermal conductivity member 28 will be described in more detail below.

[0071] 2, first high thermal conductivity member 28 is disposed between heater 22 and stay 24 in the left-right direction of FIG. 2, and is particularly sandwiched between heater 22 and heater holder 23. That is, first high thermal conductivity member 28 has one surface abutting against the back surface of base material 30 and the other surface abutting against heater holder 23.

[0072] The stay 24 supports the heater holder 23, the first high thermal conductive member 28, and the heater 22 by bringing contact surfaces 24a1 of two vertical portions 24a, which extend in the thickness direction of the heater 22 and other components, into contact with the heater holder 23. In the cross-array direction (the vertical direction in FIG. 2), the contact surfaces 24a1 are provided outside the range in which the resistance heating elements 31 are provided. This makes it possible to suppress heat transfer from the heater 22 to the stay 24, and allows the heater 22 to heat the fixing belt 20 efficiently.

[0073] As shown in Fig. 18, first high thermal conductivity member 28 is made of a plate material having a thickness of 0.3 mm, a length in the arrangement direction of 222 mm, and a width in the direction crossing the arrangement of 10 mm. In this embodiment, first high thermal conductivity member 28 is made of a single plate material, but it may be made of multiple members. Note that illustration of guide portion 26 of Fig. 2 is omitted in Fig. 18.

[0074] The first high thermal conductive member 28 is fitted into the recess 23b of the heater holder 23, and the heater 22 is attached thereto, thereby sandwiching and holding the first high thermal conductive member 28 between the heater holder 23 and the heater 22. In this embodiment, the width of the first high thermal conductive member 28 in the arrangement direction is set to be substantially the same as the width of the heater 22 in the arrangement direction. Movement of the first high thermal conductive member 28 and the heater 22 in the arrangement direction is restricted by both side walls (arrangement direction restricting portions) 23b1 in the arrangement direction that form the recess 23b. In this manner, restricting misalignment of the first high thermal conductive member 28 in the arrangement direction within the fixing device 9 improves heat conduction efficiency within a target range in the arrangement direction. Movement of the first high thermal conductive member 28 and the heater 22 in the arrangement direction is restricted by both side walls (arrangement cross direction restricting portions) 23b2 in the arrangement cross direction that form the recess 23b.

[0075] The range in the arrangement direction in which the first high thermal conductivity members 28 are provided is not limited to the above. For example, as shown in FIG. 19, the first high thermal conductivity members 28 may be provided only in the range corresponding to the heat generating portions 35 in the arrangement direction (see the hatched area in FIG. 19). Alternatively, as shown in FIG. 20, the first high thermal conductivity members 28 may be provided only in the entire area at a position corresponding to the interval B in the arrangement direction. Note that in FIG. 20, for convenience, the resistance heating elements 31 and the first high thermal conductivity members 28 are shown shifted in the vertical direction in FIG. 20, but they are actually disposed at approximately the same position in the cross-array direction. However, this is not a limitation, and the first high thermal conductivity members 28 may be provided only in part of the resistance heating elements 31 in the cross-array direction, or may be provided so as to cover the entire cross-array direction as shown in FIG. 21 described later. Furthermore, as shown in FIG. 21, the first high thermal conductivity members 28 may be provided in addition to the position corresponding to the interval B in the arrangement direction, straddling the resistance heating elements 31 on both sides of the interval B. "Provided across the resistance heating elements 31 on both sides" here means that the first high thermal conductivity members 28 at least partially overlap with the resistance heating elements 31 on both sides in the arrangement direction. Note that the first high thermal conductivity members 28 may be provided to correspond to all of the intervals B of the heaters 22, or may be provided only at positions corresponding to some of the intervals B, such as by providing the first high thermal conductivity members 28 only at positions corresponding to one of the intervals B as shown in Figure 21. Here, "provided at a position corresponding to the interval B in the arrangement direction" means that the first high thermal conductivity members 28 at least partially overlap with the interval B in the arrangement direction.

[0076] Due to the pressure of the pressure roller 21, the first highly thermally conductive member 28 is sandwiched between the heaters 22 and the heater holder 23 and is in close contact with these members. The contact of the first highly thermally conductive member 28 with the heaters 22 improves the thermal conduction efficiency in the arrangement direction of the heaters 22. Furthermore, by providing the first highly thermally conductive member 28 at a position corresponding to the spacing B between the heaters 22 in the arrangement direction, the thermal conduction efficiency at the spacing B can be improved, increasing the amount of heat transferred to the position at the spacing B in the arrangement direction and raising the temperature at the spacing B in the arrangement direction. This reduces temperature unevenness in the arrangement direction of the heaters 22. This reduces temperature unevenness in the arrangement direction of the fixing belt 20. This reduces uneven fixing and glossiness of the image fixed to the paper. Alternatively, there is no need for extra heating by the heaters 22 to ensure sufficient fixing performance at the spacing B, thereby achieving energy savings in the fixing device 9. Furthermore, by providing the first high thermal conductivity member 28 over the entire heat generating section 35 in the arrangement direction, the heat transfer efficiency of the heater 22 can be improved over the entire main heating area (i.e., the image forming area of ​​the paper being passed through), thereby suppressing temperature unevenness in the arrangement direction of the heater 22 and, ultimately, the fixing belt 20.

[0077] In particular, in this embodiment, the combination of the configuration of the first high thermal conductivity member 28 and the resistance heating element 31 having the PTC characteristic described above can effectively suppress excessive temperature rise in the non-paper passing area when small size paper is passed. In other words, the PTC characteristic suppresses the amount of heat generated by the resistance heating element 31 in the non-paper passing area, and the heat of the non-paper passing area with an increased temperature can be efficiently transferred to the paper passing area, effectively suppressing excessive temperature rise in the non-paper passing area.

[0078] Furthermore, it is preferable to arrange first high thermal conductivity members 28 around gap B, since the temperature there is also low due to the small amount of heat generated in gap B. For example, in this embodiment, by providing first high thermal conductivity members 28 at positions corresponding to region C (see FIG. 15), the heat transfer efficiency in the arrangement direction in gap B and its periphery is particularly improved, and temperature unevenness in the arrangement direction of heaters 22 can be further suppressed. Particularly in this embodiment, first high thermal conductivity members 28 are provided over the entire area of ​​heat-generating section 35 in the arrangement direction. This makes it possible to further suppress temperature unevenness in the arrangement direction of heaters 22 (fixing belt 20).

[0079] Next, a different embodiment of the fixing device will be described.

[0080] 22, fixing device 9 of the present embodiment has second high thermal conductivity member 36 between heater holder 23 and first high thermal conductivity member 28. Second high thermal conductivity member 36 is provided at a different position from first high thermal conductivity member 28 in the stacking direction (left-right direction in FIG. 22) of members such as heater holder 23, stay 24, and first high thermal conductivity member 28. More specifically, second high thermal conductivity member 36 is provided overlapping first high thermal conductivity member 28. Note that, unlike FIG. 2, FIG. 22 shows a cross section in which second high thermal conductivity member 36 is arranged in the arrangement direction and thermistor 25 is not arranged.

[0081] The second high thermal conductivity member 36 is made of a material having a higher thermal conductivity than the base material 30, such as graphene or graphite. In this embodiment, the second high thermal conductivity member 36 is formed of a graphite sheet having a thickness of 1 mm. However, the second high thermal conductivity member 36 may also be formed of a plate material such as aluminum, copper, or silver.

[0082] As shown in Figure 23, a plurality of second high thermal conductive members 36 are arranged in the arrangement direction, each of which is partially provided in the arrangement direction. The portion of recess 23b of heater holder 23 where second high thermal conductive members 36 are provided is one level deeper than the remaining portion. A gap is provided between second high thermal conductive members 36 and heater holder 23 on both sides in the arrangement direction. This suppresses heat transfer from second high thermal conductive members 36 to heater holder 23, allowing heater 22 to efficiently heat fixing belt 20. Note that illustration of guide portion 26 from Figure 2 is omitted in Figure 23.

[0083] 24, second high thermal conductivity members 36 (see hatched areas) are provided in positions corresponding to interval B in the arrangement direction so as to overlap at least a portion of adjacent resistance heating elements 31, and in this embodiment in particular, are provided over the entire area of ​​interval B. However, although FIG. 24 (and FIG. 28 described later) shows a case where first high thermal conductivity members 28 are provided only in areas corresponding to heat generating portions 35 in the arrangement direction, as mentioned above, this is not limited to this.

[0084] In this embodiment, in addition to the first high thermal conductivity members 28, second high thermal conductivity members 36 are provided at positions corresponding to the interval B in the arrangement direction, overlapping at least a portion of adjacent resistance heating elements 31. This particularly improves the heat transfer efficiency in the arrangement direction at the interval B, thereby further suppressing temperature unevenness in the arrangement direction of the heaters 22. Most preferably, as shown in FIG. 25 , the first high thermal conductivity members 28 and the second high thermal conductivity members 36 are provided only over the entire area of ​​the position corresponding to the interval B. This particularly improves the heat transfer efficiency in the position corresponding to the interval B compared to other areas. For convenience, FIG. 25 illustrates the resistance heating elements 31, the first high thermal conductivity members 28, and the second high thermal conductivity members 36 offset from one another in the vertical direction, but they are actually positioned at approximately the same position in the cross-array direction. However, this is not a limitation, and the first high thermal conductivity members 28 and the second high thermal conductivity members 36 may be provided only over a portion of the resistance heating elements 31 in the cross-array direction, or may be provided so as to cover the entire resistance heating elements 31 in the cross-array direction.

[0085] In one embodiment of the present invention different from the above, first high thermal conductivity member 28 and second high thermal conductivity member 36 are formed from the graphene sheet. This allows first high thermal conductivity member 28 and second high thermal conductivity member 36 to be formed with high thermal conductivity in a predetermined direction along the graphene surface, that is, in the arrangement direction rather than the thickness direction. This makes it possible to effectively suppress temperature unevenness in the arrangement direction of heater 22 and fixing belt 20.

[0086] Graphene is a flaky powder. As shown in Figure 26, graphene is composed of a planar hexagonal lattice structure of carbon atoms. A graphene sheet is a sheet of graphene, and is usually a single layer. The single layer of carbon may contain impurities. Graphene may also have a fullerene structure. A fullerene structure is generally recognized as a compound in which the same number of carbon atoms form a polycyclic ring in which five-membered and six-membered rings are condensed into a cage shape, and examples thereof include C 60 , C 70 and C 80 Fullerenes or other closed cage structures with three-coordinated carbon atoms.

[0087] Graphene sheets are man-made and can be produced, for example, by chemical vapor deposition (CVD).

[0088] The graphene sheet may be a commercially available product. The size and thickness of the graphene sheet, or the number of layers of the graphite sheet (described later), may be measured using, for example, a transmission electron microscope (TEM).

[0089] Furthermore, graphite, which is a multilayered graphene, has a large thermal conductivity anisotropy. As shown in FIG. 27, graphite has a crystalline structure in which layers of fused six-membered rings of carbon atoms are laid out in a planar fashion, and these layers are stacked on top of each other. In this crystalline structure, adjacent carbon atoms within a layer form covalent bonds, while carbon atoms between layers form van der Waals bonds. Covalent bonds have a stronger bonding strength than van der Waals bonds, resulting in a large anisotropy between intralayer and interlayer bonds. In other words, by constructing the first high thermal conductivity member 28 or the second high thermal conductivity member 36 from graphite, the heat transfer efficiency in the arrangement direction of the first high thermal conductivity member 28 or the second high thermal conductivity member 36 is greater than in the thickness direction (i.e., the stacking direction of the members), thereby suppressing heat transfer to the heater holder 23. This effectively suppresses temperature unevenness in the arrangement direction of the heater 22 and minimizes heat leakage toward the heater holder 23. Furthermore, by making the first high thermal conductivity member 28 or the second high thermal conductivity member 36 out of graphite, the first high thermal conductivity member 28 or the second high thermal conductivity member 36 can have excellent heat resistance, preventing oxidation up to approximately 700 degrees.

[0090] The physical properties and dimensions of the graphite sheet can be changed as appropriate depending on the functions required of first high thermal conductivity member 28 or second high thermal conductivity member 36. For example, the anisotropy of thermal conduction can be increased by using high-purity graphite or single-crystal graphite, or by increasing the thickness of the graphite sheet. Furthermore, in order to increase the speed of fixing device 9, a thin graphite sheet may be used to reduce the heat capacity of fixing device 9. Furthermore, if the width of fixing nip N or heater 22 is large, the width of first high thermal conductivity member 28 or second high thermal conductivity member 36 in the arrangement direction may be increased accordingly.

[0091] From the viewpoint of increasing the mechanical strength, the number of layers of the graphite sheet is preferably at least 11. The graphite sheet may partially include a single layer portion and a multi-layer portion.

[0092] The second high thermal conductivity members 36 may be arranged in positions corresponding to interval B (and further to region C) in the arrangement direction so as to overlap at least a portion of the adjacent resistance heating elements 31, and are not limited to the arrangement shown in FIG. 24. For example, as shown in FIG. 28, the second high thermal conductivity members 36A are arranged to protrude beyond the base material 30 on both sides in the cross-array direction. The second high thermal conductivity members 36B are arranged in the range in the cross-array direction where the resistance heating elements 31 are arranged. The second high thermal conductivity members 36C are arranged in a portion of interval B.

[0093] 29, in this embodiment, a gap is provided between the first high thermal conductivity member 28 and the heater holder 23 in the thickness direction (left-right direction in FIG. 29). That is, a recess 23c is provided as a heat insulating layer in a partial area of ​​the recess 23b (see FIG. 23) for accommodating the heater 22, the first high thermal conductivity member 28, and the second high thermal conductivity member 36 of the heater holder 23, except for the area where the second high thermal conductivity member 36 is provided in the arrangement direction. This recess 23c is located in the cross-arrangement direction and is deeper than the remaining area that accommodates the first high thermal conductivity member 28. This minimizes the contact area between the heater holder 23 and the first high thermal conductivity member 28. This suppresses heat transfer from the first high thermal conductivity member 28 to the heater holder 23, allowing the heater 22 to efficiently heat the fixing belt 20. In addition, in the cross section in the arrangement direction where second high thermal conductivity members 36 are provided, second high thermal conductivity members 36 abut against heater holder 23 as in FIG. 22 of the above-described embodiment.

[0094] Furthermore, particularly in this embodiment, relief portion 23c is provided over the entire area where resistance heating elements 31 are provided in the array cross direction (the vertical direction in FIG. 29). This particularly suppresses heat transfer from first high thermal conductivity member 28 to heater holder 23, allowing heater 22 to efficiently heat fixing belt 20. Note that, in addition to a configuration in which a space is provided like relief portion 23c as the heat insulating layer, a configuration in which a heat insulating member with lower thermal conductivity than heater holder 23 is provided may also be used.

[0095] Furthermore, in the above description, second high thermal conductivity member 36 is provided as a member different from first high thermal conductivity member 28, but this is not limiting. For example, the portion of first high thermal conductivity member 28 corresponding to interval B may be made thicker than the other portions.

[0096] 22 or 29, the same configuration as in the above-described embodiments, such as the fixing frame 40, the separation plate 41, the collar 42, and the torsion spring 44, can be applied. This ensures a certain level of insulation between the separation plate 41 and the fixing frame 40, and between the torsion spring 44 and the fixing frame 40.

[0097] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the spirit of the present invention.

[0098] Furthermore, in addition to the fixing device described above, the present invention can also be applied to fixing devices such as those shown in Figures 30 to 32. The configuration of each fixing device shown in Figures 30 to 32 will be briefly described below.

[0099] First, in the fixing device 9 shown in Figure 30, a pressure roller 64 is arranged on the opposite side of the fixing belt 20 from the pressure roller 21 side. This pressure roller 64 and heater 22 are configured to sandwich and heat the fixing belt 20. Meanwhile, on the pressure roller 21 side, a nip forming member 65 is arranged on the inner periphery of the fixing belt 20. The nip forming member 65 is supported by the stay 24. The fixing nip N is formed by the nip forming member 65 and the pressure roller 21 sandwiching the fixing belt 20.

[0100] 31, the above-mentioned pressure roller 64 is omitted, and in order to ensure the circumferential contact length between the fixing belt 20 and the heater 22, the heater 22 is formed in an arc shape to match the curvature of the fixing belt 20. The rest of the configuration is the same as that of the fixing device 9 shown in FIG.

[0101] 30 and 31, the above-described configurations of the fixing frame 40, the separation plate 41, the collar 42, the torsion spring 44, etc. can also be applied. This ensures a certain level of insulation between the separation plate 41 and the fixing frame 40, and between the torsion spring 44 and the fixing frame 40.

[0102] Finally, the fixing device 9 shown in FIG. 32 will be described. The fixing device 9 includes a heating assembly 92, a fixing roller 93 as a rotating member, and a pressure assembly 94 as an opposing member. The heating assembly 92 includes the heater 22, the first high-thermal-conductivity member 28, the heater holder 23, the stay 24, and the heating belt 120 described in the previous embodiment. The fixing roller 93 is an opposing rotating member that rotates opposite the heating belt 120 as a rotating member. The fixing roller 93 is composed of a conductive core metal 93a as a first layer, a non-conductive elastic layer 93b as a second layer, and a conductive surface layer 93c as a third layer. A pressure assembly 94 is provided on the side of the fixing roller 93 opposite the heating assembly 92. The pressure assembly 94 includes a nip forming member 95 and a stay 96, and a pressure belt 97 as an opposing rotating member that is rotatably arranged to enclose the nip forming member 95 and the stay 96. Then, the paper P is passed through the fixing nip N2 between the pressure belt 97 and the fixing roller 93, and heat and pressure are applied to fix the image.

[0103] In the embodiment of Figure 32, by applying a configuration such as a separation plate 41 that contacts the fixing roller 93, the aforementioned fixing frame 40, a collar 42, and a torsion spring 44, a certain level of insulation can be ensured between the separation plate 41 and the fixing frame 40, and between the torsion spring 44 and the fixing frame 40.

[0104] Furthermore, the image forming apparatus according to the present invention is not limited to the color image forming apparatus shown in FIG. 1, but may also be a monochrome image forming apparatus, a copying machine, a printer, a facsimile, or a combination machine of these.

[0105] Furthermore, an example of a different image forming apparatus to which the present invention is applied will be described with reference to Fig. 33. As shown in Fig. 33, image forming apparatus 100 of this embodiment includes image forming means 50 including a photosensitive drum or the like, a paper transport section including a pair of timing rollers 15 or the like, paper feeder 7, fixing device 9, paper discharge device 10, and reading section 51. Paper feeder 7 includes multiple paper feed trays, each of which stores paper of a different size.

[0106] The reading unit 51 reads an image of the document Q. The reading unit 51 generates image data from the read image. The paper feeder 7 stores a plurality of sheets of paper P and sends the sheets of paper P to a conveyance path. The timing rollers 15 convey the sheets of paper P on the conveyance path to the image forming means 50.

[0107] The image forming means 50 forms a toner image on the paper P. Specifically, the image forming means 50 includes a photosensitive drum, a charging roller, an exposure device, a developing device, a replenishment device, a transfer roller, a cleaning device, and a discharging device. The toner image represents, for example, an image of the original Q. The fixing device 9 applies heat and pressure to the toner image to fix the toner image to the paper P. The paper P with the fixed toner image is transported to the paper discharge device 10 by a transport roller or the like. The paper discharge device 10 discharges the paper P outside the image forming apparatus 100.

[0108] Next, the fixing device 9 of this embodiment will be described. Descriptions of the configurations common to the fixing devices of the above-described embodiments will be omitted as appropriate.

[0109] As shown in FIG. 34, the fixing device 9 includes a fixing belt 20, a pressure roller 21, a heater 22, a heater holder 23, a stay 24, a thermistor 25, a first high heat conductive member 28, a separation plate 41, and the like.

[0110] A fixing nip N is formed between the fixing belt 20 and the pressure roller 21. The nip width of the fixing nip N is 10 mm, and the linear speed of the fixing device 9 is 240 mm / s.

[0111] The fixing belt 20 has a polyimide base and a release layer, but does not have an elastic layer. The release layer is made of a heat-resistant film material such as fluororesin. The outer diameter of the fixing belt 20 is approximately 24 mm.

[0112] The pressure roller 21 includes a core metal 21a, an elastic layer 21b, and a surface layer 21c. The pressure roller 21 has an outer diameter of 24 to 30 mm, and the elastic layer 21b has a thickness of 3 to 4 mm.

[0113] The heater 22 includes a base material, a heat insulating layer, a conductor layer including a resistance heating element, and an insulating layer, and is formed to a total thickness of 1 mm. The width Y of the heater 22 in the array crossing direction is 13 mm.

[0114] As shown in FIG. 35, the conductor layer of the heater 22 includes a plurality of resistance heating elements 31, power supply lines 33, and electrode portions 34A-34C. In this embodiment, as shown in the enlarged view of FIG. 35, the plurality of resistance heating elements 31 are divided in the arrangement direction to form intervals B as divided regions (although FIG. 35 only illustrates the intervals B within the enlarged view, in reality, intervals B are provided between all of the resistance heating elements 31). The resistance heating elements 31 form three heat generating portions 35A-35C. By applying electricity to the electrode portions 34A and 34B, the heat generating portions 35A and 35C generate heat. By applying electricity to the electrode portions 34A and 34C, the heat generating portion 35B generates heat. For example, when performing a fixing operation on small-sized paper, the heat generating portion 35B is made to generate heat, and when performing a fixing operation on large-sized paper, all of the heat generating portions are made to generate heat.

[0115] As shown in Figure 36, the heater holder 23 holds the heater 22 and the first high thermal conductivity member 28 in its recess 23d. The recess 23d is provided on the heater 22 side of the heater holder 23. The recess 23d is composed of a surface 23d1 that is approximately parallel to the base material 30 and is recessed toward the stay 24 side more than the other surfaces of the heater 22, wall portions 23d2 provided on the inside of the heater holder 23 on both sides in the arrangement direction of the heater holder 23 (or on one side), and wall portions 23d3 provided on the inside of the heater holder 23 on both sides in the intersecting direction of the arrangement. The heater holder 23 has a guide portion 26. The heater holder 23 is made of LCP (liquid crystal polymer).

[0116] As shown in FIG. 37, the connector 60 includes a housing made of resin (for example, LCP), and a plurality of contact terminals provided inside the housing.

[0117] The connector 60 is attached so as to sandwich the heater 22 and heater holder 23 together from the front and back sides. In this state, each contact terminal comes into contact (pressure-welded) with each electrode portion of the heater 22, electrically connecting the heat generating portion 35 to a power supply provided in the image forming apparatus via the connector 60. This enables power to be supplied from the power supply to the heat generating portion 35. Note that, to ensure connection with the connector 60, at least a portion of each electrode portion 34 is not covered with an insulating layer and is exposed.

[0118] The flanges 53 are provided on both sides of the fixing belt 20 in the arrangement direction, and hold both ends of the fixing belt 20 from the inside of the belt. The flanges 53 are fixed to the housing of the fixing device 9. The flanges 53 are inserted into both ends of the stays 24 (see the arrow directions from the flanges 53 in Figure 37).

[0119] The direction in which the connector 60 is attached to the heater 22 and heater holder 23 is the direction that intersects the heater arrangement (see the direction of the arrow from the connector 60 in FIG. 37). When the connector 60 is attached to the heater holder 23, a convex portion on one of the connector 60 and the heater holder 23 may engage with a concave portion on the other, and the convex portion may move relatively within the concave portion. The connector 60 is attached to the heater 22 and heater holder 23 on one side in the arrangement direction, opposite the side on which the drive motor of the pressure roller 21 is provided.

[0120] 38, thermistors 25 are provided on the center side and end side of the arrangement direction of the fixing belt 20, facing the inner circumferential surface of the fixing belt 20. The heater 22 is controlled based on the temperatures detected by the thermistors 25 on the center side and end side of the arrangement direction of the fixing belt 20.

[0121] Thermostats 27 are provided facing the inner circumferential surface of the fixing belt 20, at the center and end sides in the arrangement direction of the fixing belt 20. When the temperature of the fixing belt 20 detected by the thermostat 27 exceeds a predetermined threshold, the supply of power to the heater 22 is stopped.

[0122] Flanges 53 are provided on both ends of the fixing belt 20 in the arrangement direction to hold the respective ends of the fixing belt 20. The flanges 53 are made of LCP (liquid crystal polymer).

[0123] 39, a slide groove 53a is provided in the flange 53. The slide groove 53a extends in the direction in which the fixing belt 20 approaches and separates from the pressure roller 21. An engagement portion of the housing of the fixing device 9 engages with the slide groove 53a. The engagement portion moves relatively within the slide groove 53a, allowing the fixing belt 20 to move in the direction in which the fixing belt 20 approaches and separates from the pressure roller 21.

[0124] The above-described fixing device 9 can also be configured with the fixing frame 40, the separation plate 41, the collar 42, the torsion spring 44, etc. This ensures a certain level of insulation between the separation plate 41 and the fixing frame 40, and between the torsion spring 44 and the fixing frame 40.

[0125] Recording media include paper P (plain paper), as well as cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheets, plastic film, prepreg, copper foil, etc. [Explanation of symbols]

[0126] 1. Image forming device 9 Fixing device (heating device) 20 Fixing belt (rotating member or fixing member) 21 Pressure roller (opposing rotating member or pressure member) 40 Fixing frame (housing) 41 Separation plate (separation member) 411 Separation section 412 Stop part 413 Mounting part 42 Color (resistor) 44 Torsion spring (biasing member) 45 Heat equalizer (conductive material) C. Paper passing area (area through which the widest recording medium passes) [Prior art documents] [Patent documents]

[0127] [Patent Document 1] Patent No. 6422563

Claims

1. A rotating member; an opposing rotating member opposed to the rotating member; a heating element having a resistance heating element and contacting the inner surface of the rotary member directly or via a conductive member to heat the rotary member; a conductive separating member in contact with the rotating member; a grounded conductive enclosure; a resistor provided in the housing; a biasing member that biases the separating member toward the rotating member, the separating member and the biasing member are attached to the housing via the resistor, The fixing device is characterized in that the separation member has a separation portion and a contact portion that branches off from the separation portion and contacts the rotating member, and the contact portion contacts the rotating member, thereby creating a gap between the separation portion and the rotating member.

2. 2. The fixing device according to claim 1, wherein a creepage distance of 2.5 mm or more is provided between the separating member and the housing, and a clearance distance of 2.2 mm or more is provided between the biasing member and the housing.

3. 3. The fixing device according to claim 1, wherein the heating element has an insulating layer between the rotating member and the resistance heating element.

4. 4. The fixing device according to claim 1, wherein the resistor is made of a conductive resin material.

5. 5. The fixing device according to claim 1, wherein the resistor has a volume resistance set to 100 k[Omega] or more.

6. 6. The fixing device according to claim 1, wherein the separating member contacts the rotating member at a position outside in the width direction of a region through which a recording medium of the maximum width compatible with the fixing device passes.

7. An image forming apparatus comprising the fixing device according to claim 1 .

Images