Heating device, fixing device and image forming apparatus

Abstract

To prevent a variation in temperature in a heating device.SOLUTION: The length La between an end 55a on one side in the longitudinal direction X of a base material 55 of a heater 23 and an end 60a on one side of a heating area 60 is longer than the length Lb between an end 55b on the other side in the longitudinal direction X of the base material 55 and an end 60b on the other side of the heating area 60. The length Ga between the end 60a on one side of the heating area 60 and an end 22a on one side of a pressure roller 22 is smaller than the length Gb between the end 60b on the other side of the heating area 60 and an end 22b on the other side of the pressure roller 22.SELECTED DRAWING: Figure 7

Description

[Technical Field]

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

[0002] 2. Description of the Related Art As an example of a heating device mounted in an image forming apparatus such as a copier or a printer, a fixing device is known that heats a sheet carrying an unfixed image to fix the unfixed image on the sheet.

[0003] In a fixing device, a heating source such as a heater is arranged symmetrically with respect to the center of the sheet passage area through which the sheet passes so that the sheet can be heated uniformly. However, for various reasons, other components constituting the fixing device may not necessarily be arranged symmetrically with respect to the center of the sheet passage area. In such cases, the amount of heat transferred from the heating element of the heating source to the surrounding components is not the same on one end and the other end of the heating source with respect to the center of the sheet passage area. This results in a problem of insufficient heat to heat the sheet, particularly on the side with a large amount of heat transfer, and conversely, a significant temperature rise on the side with a small amount of heat transfer.

[0004] To address this issue, Patent Document 1 (JP 2008-76857 A) proposes a configuration in which the amount of heat generated per unit area of ​​the heat generating element is made different between one end and the other end of the heat source. In this case, the amount of heat generated on the higher temperature side is made lower than the amount of heat generated on the lower temperature side, thereby suppressing temperature variations in the fixing device. Summary of the Invention [Problem to be solved by the invention]

[0005] However, as described above, if the heat generation amount per unit area of ​​the heat generating element is made different between one end and the other end of the heat source, temperature variations in the fixing device will be significant when the heat generating element is operated at maximum heat generation. In particular, in areas where the heat generation amount is large, thermal expansion of the heat source and heated components will be localized and significant, which may result in damage to the components. Therefore, as a measure to suppress temperature variations in a heating device such as a fixing device, the method of making the heat generation amount different is not desirable, and another measure is required. [Means for solving the problem]

[0006] In order to solve the above problems, there is provided a heating device including a rotatable first rotor, a rotatable second rotor that contacts an outer peripheral surface of the first rotor to form a nip portion, and a heat source that heats the first rotor, wherein the heat source has a base and a heating element provided on the base, the base has a heating region in which the heating element is arranged, the length between one end of the base in a longitudinal direction and the one end of the heating region is longer than the length between the other end of the base in the longitudinal direction and the other end of the heating region, and the length between the one end of the heating region and the one end of the second rotor is shorter than the length between the other end of the heating region and the other end of the second rotor. and the frictional force between the first rotating body and the second rotating body on the other side of the center of the first rotating body in the longitudinal direction is greater than the frictional force between the first rotating body and the second rotating body on the one side of the center. It is characterized by: [Effects of the Invention]

[0007] According to the present invention, it is possible to suppress temperature variations in the heating device. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram illustrating the configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram illustrating the configuration of a fixing device according to the present embodiment. [Figure 3] FIG. 2 is a cross-sectional view of the fixing belt according to the embodiment. [Figure 4] FIG. 2 is a plan view of the heater according to the embodiment. [Figure 5]1 is a perspective view showing a state in which a connector as a power supply member is connected to the heater according to the embodiment. FIG. [Figure 6] FIG. 2 is a plan view of the heater according to the embodiment. [Figure 7] 1 is a diagram showing a configuration according to a first embodiment of the present invention. [Figure 8] FIG. 10 is a diagram showing a configuration according to a second embodiment of the present invention. [Figure 9] FIG. 10 is a diagram showing a configuration according to a third embodiment of the present invention. [Figure 10] FIG. 10 is a diagram showing a configuration according to a fourth embodiment of the present invention. [Figure 11] 10A and 10B are diagrams showing an example in which the central heating element is composed of a plurality of resistance heating elements; [Figure 12] FIG. 10 is a diagram showing an example in which electrode portions are provided on both ends of a substrate. [Figure 13] FIG. 10 is a diagram showing a configuration of a fixing device different from that of the above embodiment. [Figure 14] FIG. 10 is a diagram showing a configuration of a fixing device different from that of the above embodiment. [Figure 15] FIG. 10 is a diagram showing a configuration of a fixing device different from that of the above embodiment. [Figure 16] FIG. 10 is a diagram showing a configuration of a fixing device different from that of the above embodiment. [Figure 17] FIG. 10 is a diagram showing a configuration of an image forming apparatus different from that of the above embodiment. [Figure 18] 18 is a diagram showing the configuration of the fixing device shown in FIG. 17. FIG. [Figure 19] FIG. 19 is a plan view of the heater shown in FIG. 18. [Figure 20] FIG. 19 is a perspective view of the heater and heater holder shown in FIG. 18. [Figure 21] 19 is a diagram showing a method of attaching a connector to the heater shown in FIG. 18. [Figure 22] 18 is a diagram showing the arrangement of temperature sensors and thermostats included in the fixing device shown in FIG. 17. FIG. [Figure 23] 22 is a view showing a groove portion of the flange shown in FIG. 21. FIG. [Figure 24]FIG. 10 is a diagram showing a configuration of a fixing device different from that of the above embodiment. [Figure 25] 25 is a perspective view of the heater, the first high thermal conductive member, and the heater holder shown in FIG. 24. FIG. [Figure 26] FIG. 2 is a plan view of the heater showing the arrangement of the first high thermal conductivity members. [Figure 27] 10 is a plan view of a heater showing another example of the arrangement of the first high thermal conductivity members. FIG. [Figure 28] FIG. 10 is a plan view of a heater showing yet another example of the arrangement of the first high thermal conductivity members. [Figure 29] FIG. 2 is a plan view of the heater showing enlarged divided regions. [Figure 30] FIG. 10 is a diagram showing a configuration of a fixing device different from that of the above embodiment. [Figure 31] 31 is a perspective view of the heater, the first highly thermally conductive member, the second highly thermally conductive member, and the heater holder shown in FIG. 30. FIG. [Figure 32] FIG. 3 is a plan view of the heater showing the arrangement of the first and second high thermal conductive members. [Figure 33] 10 is a plan view of a heater showing another example of the arrangement of the first and second high thermal conductive members. FIG. [Figure 34] FIG. 10 is a plan view of a heater showing yet another example of the arrangement of second high-thermal-conductivity members. [Figure 35] FIG. 10 is a diagram showing a configuration of a fixing device different from that of the above embodiment. [Figure 36] FIG. 1 illustrates the atomic crystal structure of graphene. [Figure 37] FIG. 1 illustrates the atomic crystal structure of graphite. 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 the description thereof will be omitted once it has been explained once.

[0010] FIG. 1 is a schematic diagram of an image forming apparatus according to one embodiment of the present invention. In this specification, the term "image forming apparatus" includes a printer, a copier, a facsimile, a printing machine, or a multifunction machine that combines two or more of these. Furthermore, the term "image formation" used in the following description refers not only to the formation of meaningful images such as characters and figures, but also to the formation of meaningless images such as patterns. First, the overall configuration and operation of the image forming apparatus according to this embodiment will be described with reference to FIG. 1.

[0011] As shown in FIG. 1, the image forming apparatus 100 according to this embodiment includes an image forming unit 200 that forms an image on a sheet-like recording medium such as paper, a fixing unit 300 that fixes the image on the recording medium, a recording medium supply unit 400 that supplies the recording medium to the image forming unit 200, and a recording medium discharge unit 500 that discharges the recording medium outside the apparatus.

[0012] The image forming section 200 is provided with four process units 1Y, 1M, 1C, and 1Bk as image-forming units, an exposure device 6 that forms an electrostatic latent image on the photosensitive member 2 provided in each of the process units 1Y, 1M, 1C, and 1Bk, and a transfer device 8 that transfers the image onto a recording medium.

[0013] Each of the process units 1Y, 1M, 1C, and 1Bk has basically the same configuration, except that it contains toner (developer) of a different color: yellow, magenta, cyan, or black, which corresponds to the color separation components of a color image. Specifically, each of the process units 1Y, 1M, 1C, and 1Bk includes a photoconductor 2 as an image carrier that carries an image on its surface, a charging member 3 that charges the surface of the photoconductor 2, a developing device 4 that supplies toner as developer to the surface of the photoconductor 2 to form a toner image, and a cleaning member 5 that cleans the surface of the photoconductor 2.

[0014] The transfer device 8 includes an intermediate transfer belt 11, a primary transfer roller 12, and a secondary transfer roller 13. The intermediate transfer belt 11 is an endless belt member that is stretched by a plurality of support rollers. Four primary transfer rollers 12 are provided inside the intermediate transfer belt 11. Each primary transfer roller 12 contacts each photoconductor 2 via the intermediate transfer belt 11, thereby forming a primary transfer nip between the intermediate transfer belt 11 and each photoconductor 2. The secondary transfer roller 13 contacts the outer peripheral surface of the intermediate transfer belt 11, thereby forming a secondary transfer nip.

[0015] The fixing section 300 is provided with a fixing device 20. The fixing device 20 includes a fixing belt 21 made of an endless belt, and a pressure roller 22 as an opposing member facing the fixing belt 21. The fixing belt 21 and the pressure roller 22 come into contact with each other on their outer circumferential surfaces to form a nip portion (fixing nip).

[0016] The recording medium supply unit 400 is provided with a paper feed cassette 14 that stores paper P as a recording medium, and a paper feed roller 15 that feeds paper P from the paper feed cassette 14. Hereinafter, the "recording medium" will be described as "paper," but the "recording medium" is not limited to paper (paper). The "recording medium" includes not only paper (paper), but also transparencies, fabrics, metal sheets, plastic films, and prepreg sheets made of carbon fiber pre-impregnated with resin. Furthermore, "paper" includes not only plain paper, but also cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, and the like.

[0017] The recording medium ejection section 500 is provided with a pair of ejection rollers 17 for ejecting the paper P outside the image forming apparatus, and an ejection tray 18 on which the paper P ejected by the ejection rollers 17 is placed.

[0018] Next, the printing operation of the image forming apparatus 100 according to this embodiment will be described with reference to FIG.

[0019] When a printing operation is started in the image forming apparatus 100, the photosensitive elements 2 of the process units 1Y, 1M, 1C, and 1Bk and the intermediate transfer belt 11 of the transfer device 8 start to rotate. Also, the paper feed roller 15 starts to rotate, and a sheet of paper P is fed out of the paper feed cassette 14. The fed sheet of paper P comes into contact with a pair of timing rollers 16 and stops, and the transport of the sheet of paper P is temporarily stopped until an image to be transferred onto the sheet of paper P is formed.

[0020] In each process unit 1Y, 1M, 1C, and 1Bk, the surface of the photoconductor 2 is first charged to a uniform high potential by the charging member 3. Next, the exposure device 6 exposes the surface (charged surface) of each photoconductor 2 based on the image information of the original document read by the document reader or the print image information instructed to be printed from a terminal. This reduces the potential of the exposed area, forming an electrostatic latent image on the surface of each photoconductor 2. The developing device 4 then supplies toner to this electrostatic latent image, forming a toner image on each photoconductor 2. As each photoconductor 2 rotates, the toner image formed on each photoconductor 2 reaches the primary transfer nip (the position of the primary transfer roller 12), where it is transferred sequentially onto the rotating intermediate transfer belt 11 so as to overlap one another. In this way, a full-color toner image is formed on the intermediate transfer belt 11. In the image forming apparatus 100, it is possible to form a monochrome image using any one of the process units 1Y, 1M, 1C, and 1Bk, or to form a two-color or three-color image using any two or three of the process units. After the toner image is transferred from the photoreceptor 2 to the intermediate transfer belt 11, the cleaning member 5 removes residual toner and the like from each photoreceptor 2.

[0021] The toner image transferred onto intermediate transfer belt 11 is transported to the secondary transfer nip (position of secondary transfer roller 13) as intermediate transfer belt 11 rotates, and is transferred onto the transported paper P by timing roller 16. Thereafter, paper P is transported to fixing device 20, where the toner image on paper P is heated and pressed by fixing belt 21 and pressure roller 22, thereby fixing the toner image to paper P. Paper P is then transported to recording medium discharge section 500, and is discharged onto paper discharge tray 18 by paper discharge roller 17. This completes the series of printing operations.

[0022] Next, the configuration of the fixing device according to this embodiment will be described in detail with reference to FIG.

[0023] As shown in FIG. 2, the fixing device 20 according to this embodiment includes a fixing belt 21, a pressure roller 22, a heater 23, a heater holder 24, a stay 25, a guide member 26, a temperature sensor 27, and the like.

[0024] The fixing belt 21 is a rotating body (first rotating body or fixing member) that comes into contact with the unfixed toner carrying surface of the paper P to fix the unfixed toner (unfixed image) to the paper P, and is made of a flexible endless belt. The diameter of the fixing belt 21 is set to be, for example, 15 to 120 mm. In this embodiment, the inner diameter of the fixing belt 21 is set to be 25 mm.

[0025] As shown in FIG. 3, the fixing belt 21 is, for example, formed by laminating a substrate 210, an elastic layer 211, and a release layer 212 in this order from the inner circumferential surface to the outer circumferential surface, with the total thickness set to 1 mm or less. The substrate 210 has a thickness of 30 to 50 μm and is made of a metal material such as nickel or stainless steel, or a resin material such as polyimide. The elastic layer 211 has a thickness of 100 to 300 μm and is made of a rubber material such as silicone rubber, foamed silicone rubber, or fluororubber. The fixing belt 21 includes the elastic layer 211, which prevents minute irregularities from forming on the surface of the fixing belt 21 at the nip portion, thereby facilitating uniform heat transfer to the toner image on the paper P. The release layer 212 has a thickness of 10 to 50 μm and is made of a material such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), polyimide, polyetherimide, or PES (polyether sulfide). The fixing belt 21 has the release layer 212, so that the release properties (peelability) of the toner (toner image) are ensured.

[0026] 2, pressure roller 22 is a rotating body (second rotating body or opposing member) disposed opposite the outer circumferential surface of fixing belt 21. Pressure roller 22 contacts heater 23 via fixing belt 21, forming a nip N between pressure roller 22 and fixing belt 21.

[0027] Pressure roller 22 is a roller with an outer diameter set to, for example, 25 mm, and has a hollow iron core material 220, an elastic layer 221 provided on the outer peripheral surface of this core material 220, and a release layer 222 provided on the outer peripheral surface of elastic layer 221. Elastic layer 221 has a thickness of, for example, 3.5 mm and is made of silicone rubber or the like. Release layer 222 has a thickness of, for example, about 40 μm and is made of fluororesin or the like.

[0028] The heater 23 is a heat source that heats the inside of the fixing belt 21. The heater 23 is a planar or plate-shaped heater that extends longitudinally across the length of the fixing belt 21 (the paper width direction that intersects with the paper transport direction), and is disposed so as to contact the inner circumferential surface of the fixing belt 21. The heater 23 according to this embodiment includes a base material 55, a resistance heating element 56 provided on the base material 55, an insulating layer 57 that covers the resistance heating element 56, and the like.

[0029] 2, in this embodiment, the resistance heating elements 56 are provided on the surface of the base material 55 facing the pressure roller 22 (the nip portion N side), but they may also be provided on the opposite surface. In this case, since the heat from each resistance heating element 56 is transferred to the fixing belt 21 via the base material 55, it is preferable that the base material 55 be made of a material with high thermal conductivity, such as aluminum nitride.

[0030] The heater holder 24 is disposed inside the fixing belt 21 and is a heat source holding member that holds the heater 23. The heater holder 24 is preferably made of a heat-resistant material because it is prone to becoming hot due to the heat from the heater 23. For example, if the heater holder 24 is made of a heat-resistant resin with low thermal conductivity, such as LCP or PEEK, the heat resistance of the heater holder 24 is ensured while heat transfer from the heater 23 to the heater holder 24 is suppressed, allowing the fixing belt 21 to be heated efficiently.

[0031] The stay 25 is a support member that supports the heater holder 24. The stay 25 supports the surface of the heater holder 24 opposite to the surface on the pressure roller 22 side across the longitudinal direction of the fixing belt 21, thereby preventing the heater holder 24 from being deflected by the pressure force of the pressure roller 22 and forming a nip portion N of uniform width between the fixing belt 21 and the pressure roller 22. The stay 25 is preferably made of an iron-based metal material such as SUS or SECC to ensure its rigidity.

[0032] The guide members 26 are members that guide the fixing belt 21 from the inside. The guide members 26 have an arc-shaped cross section that follows the inner circumferential surface of the fixing belt 21, and are respectively disposed on the upstream side and downstream side of the heater 23 in the rotation direction (the direction of the arrow in FIG. 2) of the fixing belt 21. In this embodiment, each guide member 26 is configured integrally with the heater holder 24, but may be configured separately.

[0033] The temperature sensor 27 is a temperature detection member that detects the temperature of the heater 23. Known temperature sensors such as a thermopile, a thermostat, a thermistor, or an NC sensor can be used as the temperature sensor 27. In this embodiment, a contact-type temperature sensor is used that detects the temperature by contacting the surface of the heater 23 opposite to the pressure roller 22 side. The temperature sensor 27 is not limited to a contact-type temperature sensor, and may be a non-contact-type temperature sensor that is disposed in a non-contact state with the heater 23 and detects the ambient temperature near the heater 23.

[0034] The fixing device 20 according to this embodiment operates as follows.

[0035] 2, when pressure roller 22 is driven to rotate, the driving force is transmitted to fixing belt 21, causing fixing belt 21 to rotate. Then, fixing belt 21 is heated by heater 23, and fixing belt 21 is heated. The temperature of heater 23 at this time is detected by temperature sensor 27, and the amount of heat generated by heater 23 is controlled based on the detected temperature. This maintains the temperature of fixing belt 21 at a temperature at which an image can be fixed (fixing temperature). Then, when paper P carrying an unfixed image is transported between fixing belt 21 and pressure roller 22 (nip portion N), the toner image on paper P is heated and pressurized by fixing belt 21 and pressure roller 22, and the image is fixed to paper P.

[0036] FIG. 4 is a plan view of the heater according to this embodiment.

[0037] 4, the heater 23 according to this embodiment has a plate-shaped substrate 55 extending in one direction (the direction of the arrow X in FIG. 4). The substrate 55 is disposed so that its longitudinal direction X is oriented along the longitudinal direction of the fixing belt 21 or the axial direction of the pressure roller 22. Two resistance heating elements 56 extend in the longitudinal direction X of the substrate 55 on the surface thereof and are disposed side by side in the lateral direction Y of the substrate 55. Note that the "lateral direction" here refers to a direction perpendicular to the longitudinal direction X along the surface of the substrate 55 on which the resistance heating elements 56 are provided.

[0038] As shown in Fig. 4, a pair of electrode portions 58 are provided on one side of the base material 55 in the longitudinal direction X. Each electrode portion 58 is connected to a corresponding resistance heating element 56 via a power supply line 59. Furthermore, the ends of each resistance heating element 56 opposite to the end connected to the electrode portion 58 are connected to each other via another power supply line 59. Each resistance heating element 56 and each power supply line 59 are covered with an insulating layer 57 to ensure insulation. In contrast, each electrode portion 58 is not covered by the insulating layer 57 and is exposed so that a connector serving as a power supply terminal, which will be described later, can be connected thereto.

[0039] The substrate 55 is made of a material with excellent heat resistance and insulation, such as ceramics such as alumina or aluminum nitride, glass, mica, or polyimide. Alternatively, the substrate 55 may be made of a metal (conductive material) such as stainless steel (SUS), iron, or aluminum, on which an insulating layer is formed. In particular, when the substrate 55 is made of a highly thermally conductive material such as aluminum, copper, silver, graphite, or graphene, the uniform heating of the heater 23 is improved, resulting in enhanced image quality. The insulating layer 57 is made of a material with excellent heat resistance and insulation, such as ceramics such as alumina or aluminum nitride, glass, mica, or polyimide. The resistance heating element 56 is formed, for example, by applying a paste containing silver palladium (AgPd) and glass powder to the surface of the substrate 55 by screen printing or the like, and then firing the substrate 55. Alternatively, a resistive material such as silver alloy (AgPt) or ruthenium oxide (RuO) can be used as the material for the resistance heating element 56. The electrode portion 58 and the power supply line 59 are formed by screen printing silver (Ag) or silver palladium (AgPd).

[0040] FIG. 5 is a perspective view showing a state in which a connector 40 serving as a power supply member is connected to the heater 23. As shown in FIG.

[0041] 5, connector 40 has a resin housing 41, a plurality of contact terminals 42 provided in housing 41, and a power supply harness 43 connected to each of contact terminals 42. Each contact terminal 42 is made of an elastically deformable member such as a leaf spring.

[0042] 5, the connector 40 is attached so as to sandwich the heater 23 and the heater holder 24 together. As a result, the heater 23 and the heater holder 24 are held together by the connector 40. In this state, the tips (contact portions 42a) of the contact terminals 42 of the connector 40 elastically contact (pressure-contact) with the corresponding electrode portions 58, thereby electrically connecting the contact terminals 42 and the electrode portions 58. As a result, power can be supplied to the heater 23 (each resistance heating element 56) from a power source provided in the image forming apparatus via the connector 40.

[0043] In the heater according to this embodiment, as shown in FIG. 6 , the electrode portion 58 is provided only on one side of the substrate 55 in the longitudinal direction X, and no electrode portion 58 is provided on the other side. Therefore, it is necessary to secure a space for arranging the electrode portion 58 on one side of the substrate 55. If the space for arranging the electrode portion 58 is secured, the substrate 55 becomes longer on one side. That is, in this embodiment, the electrode portion 58 is provided only on one side of the substrate 55. Therefore, the length La between the electrode portion-side end 60 a of the heat-generating region 60 where each resistance heating element 56 is disposed and the electrode portion-side end 55 a of the substrate 55 is longer than the length Lb between the end 60 b of the heat-generating region 60 on the side opposite to the electrode portion side (hereinafter referred to as the “anti-electrode portion side”) and the anti-electrode portion-side end 55 b of the substrate 55. Note that the “heat-generating region” here does not refer to the region where one resistance heating element 56 is disposed, but rather refers to the region from one end to the other of all the resistance heating elements 56 on the substrate 55. The same applies to the “heat-generating region” in the following description.

[0044] In this configuration in which the substrate 55 of the heater 23 is elongated on one side of the longitudinal direction X, when the heater 23 is activated, the amount of heat transferred to the substrate 55 is greater at the longer end of the substrate 55 than at the shorter end. In other words, more heat transfers to the end where the electrode portion 58 is provided. Therefore, the heater temperature tends to be relatively lower on the electrode portion side than on the opposite electrode portion side. In particular, when the fixing device is first started up after the image forming apparatus is powered on, the temperature of the fixing device is low, so the heater temperature on the electrode portion side is less likely to rise. This can lead to temperature variations in the fixing belt, which can result in inconsistent heating of paper passing through the nip. Therefore, in this embodiment, the following measures are taken to suppress such temperature variations in the fixing device.

[0045] The configuration of the fixing device according to this embodiment is shown in Fig. 7. Fig. 7 shows the heater 23 and pressure roller 22 provided in the fixing device, as well as the maximum paper passage area (maximum sheet passage area) W through which the widest paper P passes, but does not include the fixing belt or the like.

[0046] As shown in FIG. 7 , the heating region 60 of the heater 23 is arranged symmetrically with respect to the width center m of the maximum paper-passing region W, within a range equal to or larger than the maximum paper-passing region W, so that paper of any size can be uniformly heated across its width (the direction perpendicular to the paper-passing direction along the paper surface). That is, the length Ea from the width center m of the maximum paper-passing region W to the electrode-side edge 60a of the heating region 60 is the same as the length Eb from the width center m of the maximum paper-passing region W to the non-electrode-side edge 60b of the heating region 60 (Ea = Eb). Note that this embodiment employs a so-called center-based transport method, in which paper of various width sizes is transported based on the width center of each paper. Therefore, the width center m of the maximum paper-passing region W is also the width center of the paper-passing region for paper other than the widest paper.

[0047] On the other hand, since the base material 55 of the heater 23 is formed long on the electrode portion side, it is arranged asymmetrically with respect to the center m in the width direction of the maximum paper passage area W. That is, the length Da from the center m in the width direction of the maximum paper passage area W to the end 55a on the electrode portion side of the base material 55 is set to be longer than the length Db from the center m in the width direction of the maximum paper passage area W to the end 55b on the counter electrode portion side of the base material 55 (Da > Db). Therefore, as described above, the amount of heat transferred from the heat generation region 60 to the electrode portion side of the base material 55 is larger than the amount of heat transferred to the counter electrode portion side.

[0048] Here, a part of the heat generated in the heat generation region 60 moves not only to the base material 55 but also to the pressure roller 22 via the fixing belt 21. Therefore, the amount of heat transferred to the pressure roller 22 affects the temperature distributions of the heater 23 and the fixing belt 21. Thus, if the amount of heat transferred to the pressure roller 22 can be adjusted on the electrode portion side and the counter electrode portion side, it is possible to adjust the temperature distributions of the heater 23 and the fixing belt 21. Focusing on this point, in the present embodiment, the pressure roller 22 is made shorter on the electrode portion side than on the counter electrode portion side.

[0049] That is, as shown in FIG. 7, the length Fa from the center m in the width direction of the maximum paper passage area W to the end 22a on the electrode portion side of the pressure roller 22 is made shorter than the length Fb from the center m in the width direction of the maximum paper passage area W to the end 22b on the counter electrode portion side of the pressure roller 22 (Fa < Fb). Note that this "end of the pressure roller" means the end of the roller portion 62 made of an elastic layer or the like, not the end of the shaft portion 61 (core material 220) of the pressure roller 22 supported by a bearing or the like.

[0050] Thus, in this embodiment, since the pressure roller 22 is formed short on the electrode part side, as shown in FIG. 7, the length Ga between the end 60a on the electrode part side of the heat generation region 60 and the end 22a on the electrode part side of the pressure roller 22 is shorter than the length Gb between the end 60b on the counter electrode part side of the heat generation region 60 and the end 22b on the counter electrode part side of the pressure roller 22. For this reason, the amount of heat transferred from the heater 23 to the pressure roller 22 on the electrode side is less than that on the counter electrode part side, and a temperature drop on the electrode part side can be suppressed. That is, in this embodiment, as the base material 55 is formed long on the electrode part side (La > Lb), the amount of heat transferred to the electrode part side of the base material 55 increases. On the other hand, by reducing the protrusion amount of the pressure roller 22 toward the electrode part side with respect to the heat generation region 60 (Ga < Gb), the amount of heat transferred to the electrode part side of the pressure roller 22 is reduced, and heat balance between the electrode part side and the counter electrode part side is achieved. As a result, in this embodiment, variations in temperature in the fixing device can be suppressed, and a temperature drop on the electrode part side and an excessive temperature rise on the counter electrode part side can be suppressed, so that the fixing quality can be improved.

[0051] Further, according to this embodiment, as in Patent Document 1, variations in temperature in the fixing device can be suppressed without making the calorific value different between one end side and the other end side in the longitudinal direction of the heater. For this reason, adverse effects (temperature variations when the heating element generates heat maximally, and breakage of components due to local thermal expansion) caused by making the calorific value different can also be avoided. Therefore, according to this embodiment, the reliability of the device is also improved.

[0052] Next, an embodiment of the present invention different from the above-described embodiment (the first embodiment) will be described. In the following description, mainly the parts different from the above embodiment will be described, and for the other parts, since the basic configuration is the same, the description will be omitted as appropriate.

[0053] FIG. 8 is a diagram showing a configuration according to the second embodiment of the present invention.

[0054] In the second embodiment shown in FIG. 8, a high friction portion 63 is provided on the counter electrode portion side of the pressure roller 22. Thus, in this embodiment, since the high friction portion 63 is provided on the counter electrode portion side of the pressure roller 22, the frictional force between the fixing belt 21 and the pressure roller 22 on the counter electrode portion side (high friction portion 63 side) with respect to the center m in the width direction of the maximum paper passage area W is larger than the frictional force between the fixing belt 21 and the pressure roller 22 on the electrode portion side with respect to the center m in the width direction of the maximum paper passage area W. In other words, the frictional force between the fixing belt 21 and the pressure roller 22 on the counter electrode portion side (high friction portion 63 side) with respect to the center of the fixing belt 21 in the longitudinal direction X of the base material 55 (the position of m in FIG. 8) is larger than the frictional force between the fixing belt 21 and the pressure roller 22 on the electrode portion side with respect to the center of the fixing belt 21 in the longitudinal direction X of the base material 55. Otherwise, it has the same configuration as the first embodiment described above. The frictional force (F) between the fixing belt and the pressure roller is obtained by the following formula (1) using the coefficient of friction (μ) between the fixing belt and the pressure roller and the contact pressure (N) of the pressure roller against the fixing belt.

[0055] (Equation 1) F = μ × N ····· (1)

[0056] Also in this embodiment, similar to the first embodiment described above, by forming the base material 55 longer on the electrode portion side (La > Lb) and forming the pressure roller 22 shorter on the electrode portion side (Ga < Gb), the heat balance between the electrode portion side and the counter electrode portion side is achieved. However, when the pressure roller 22 is made shorter on the electrode portion side, the contact area (contact range in the longitudinal direction) between the pressure roller 22 and the fixing belt 21 on the electrode portion side decreases, so the rotational transmission force between the pressure roller 22 and the fixing belt 21 decreases. As a result, the fixing belt 2 cannot rotate smoothly following the pressure roller 22, and there is a risk that the fixing belt 21 slips when the paper passes through the nip portion.

[0057] Therefore, in the second embodiment, a high-friction portion 63 that has a large friction force against the fixing belt 21 is provided on the opposite electrode portion side of the pressure roller 22, thereby improving the grip force between the fixing belt 21 and the pressure roller 22. This makes it possible to compensate for the decrease in rotation transmission force caused by shortening the pressure roller 22 on the electrode portion side, and enables the rotation to be transmitted from the pressure roller 22 to the fixing belt 21 well.

[0058] Specifically, in this embodiment, the release layer 222 (see FIG. 2) serving as a surface layer is not provided on a portion of the outer peripheral surface of the elastic layer 221 of the pressure roller 22, and a portion of the elastic layer 221 is exposed to form the high-friction portion 63. The high-friction portion 63 is preferably located outside the maximum paper-passing area W (on the side opposite the electrode portion) so that the high-friction portion 63 can come into contact with the fixing belt 21 regardless of the size of the paper that is passed through (see FIG. 8). The high-friction portion 63 is not limited to being provided on the surface of the pressure roller 22, and may also be provided on a portion of the surface of the fixing belt 21.

[0059] FIG. 9 is a diagram showing a configuration according to the third embodiment of the present invention.

[0060] In the third embodiment shown in FIG. 9, in the same way as in the above-described embodiments, in order to balance the heat between the electrode side and the counter-electrode side, the base material 55 is formed longer toward the electrode side (La>Lb), and the pressure roller 22 is formed shorter toward the electrode side (Ga <Gb)。

[0061] Furthermore, in the present embodiment, in order to raise the temperature of the electrode portion side where the temperature tends to decrease, the heating region 60 is extended toward the electrode portion side. Therefore, the heating region 60 is not arranged symmetrically with respect to the center m in the width direction of the maximum paper passing region W. That is, in the present embodiment, the length Ea from the center m in the width direction of the maximum paper passing region W to the end 60a on the electrode portion side of the heating region 60 is set longer than the length Eb from the center m in the width direction of the maximum paper passing region W to the end 60b on the counter electrode portion side of the heating region 60 (Ea > Eb). For this reason, the length Ha between the end Pa on the electrode portion side of the maximum paper passing region W and the end 60a on the electrode portion side of the heating region 60 is set longer than the length Hb between the end Pb on the counter electrode portion side of the maximum paper passing region W and the end 60b on the counter electrode portion side of the heating region 60 (Ha > Hb). Here, the relationship between the left and right lengths of the heating region 60 is described based on the maximum paper passing region W. However, in the present embodiment, since it is a center-reference conveyance method, the relationship between the left and right lengths of the heating region 60 when based on a paper passing region with a different width size is the same.

[0062] As described above, in the present embodiment, since the heating region 60 is formed to be long toward the electrode portion side, the temperature drop on the electrode portion side can be more effectively suppressed. Also, such a configuration is particularly suitable when, as in the above embodiments, even if the pressure roller 22 is shortened toward the electrode portion side, the temperature drop on the electrode portion side cannot be effectively suppressed. That is, according to the present embodiment, in addition to shortening the pressure roller 22 toward the electrode portion side (Ga < Gb), by making the heating region 60 long toward the electrode portion side (Ha > Hb), the temperature drop on the electrode portion side can be more effectively suppressed.

[0063] FIG. 10 is a diagram showing a configuration according to the fourth embodiment of the present invention.

[0064] The fourth embodiment shown in FIG. 10 differs from the above-described embodiments in the configuration and arrangement of the resistance heating elements. Specifically, the heater 23 according to the fourth embodiment includes a central heating element 65 disposed at the center in the longitudinal direction X, a first heating element 66 disposed on one side of the central heating element 65 in the longitudinal direction X (the right side in FIG. 10 ), and a second heating element 67 disposed on the other side of the central heating element 65 in the longitudinal direction X (the left side in FIG. 10 ). Here, the first heating element 66 is disposed on the side where the electrode portion 58 is provided, and therefore will be referred to as the "electrode portion-side heating element" below. The second heating element 67 is disposed on the opposite side from the electrode portion side, and therefore will be referred to as the "anti-electrode side heating element" below. Note that the heating elements 65, 66, and 67 are electrically connected to the respective electrodes 58, but power supply lines connecting the heating elements 65, 66, and 67 to the respective electrodes 58 are omitted from FIG. 10 .

[0065] In this embodiment, of the three heating elements 65, 66, and 67 aligned in the longitudinal direction X of the base material 55, the central heating element 65 and the two side heating elements 66 and 67 are configured to generate heat independently of each other. This makes it possible to change the heating range depending on the width of the paper. For example, when paper of the same width as or narrower than the central heating element 65 is passed through, only the central heating element 65 is made to generate heat. When paper of a wider width than the central heating element 65 is passed through, the electrode-side heating element 66 and the non-electrode-side heating element 67 are also made to generate heat in addition to the central heating element 65. In this way, by changing the heating range depending on the width of the paper being passed through, it is possible to prevent excessive temperature rise in non-paper passing areas, especially when narrow paper is passed through.

[0066] In this embodiment, as in the above-described embodiments, in order to balance the heat between the electrode portion side and the counter-electrode portion side, the base material 55 is formed longer toward the electrode portion side (La>Lb), and the pressure roller 22 is formed shorter toward the electrode portion side (Ga <Gb)。

[0067] In this embodiment, in order to increase the temperature on the electrode side, which tends to decrease, the heat generating region 60 is lengthened toward the electrode side (Ea>Eb). Specifically, the length Ja of the electrode side heat generating element 66 in the longitudinal direction X of the base material 55 is made longer than the length Jb of the counter-electrode side heat generating element 67 (Ja>Jb), thereby lengthening the heat generating region 60 toward the electrode side (Ea>Eb).

[0068] On the other hand, the central heating element 65 has the same lengths Ka and Kb (Ka = Kb) toward the electrode portion side and the opposite electrode portion side, based on the center m of the maximum paper passing area W. That is, the central heating element 65 is disposed symmetrically toward the electrode portion side and the opposite electrode portion side, based on the center m of the maximum paper passing area W. In this manner, in this embodiment, the central heating element 65 is disposed symmetrically with respect to the center m of the maximum paper passing area W, so that when a sheet of paper narrower than the central heating element 65 is passed through, the heating widths in the left and right non-paper passing areas are the same. This prevents one non-paper passing area from excessively increasing in temperature compared to the other non-paper passing area, and prevents damage to the fixing belt due to a localized temperature rise.

[0069] 11, the central heating element 65 may be made up of multiple resistance heating elements 56. In this case as well, the resistance heating elements 56 that make up the central heating element 65 are arranged symmetrically on the electrode side and the non-electrode side with respect to the center m of the maximum paper passing area W, so that excessive temperature rise in the non-paper passing area can be suppressed when paper with a width smaller than that of the central heating element 65 is passed through.

[0070] As described above, according to the present invention, by arranging the electrode portions on only one side in the longitudinal direction of the substrate, even in a configuration in which the substrate is formed longer on one side, it is possible to achieve a balance in heat between one side and the other by adjusting the balance in the length of the pressure roller on one side and the other side, and further adjusting the balance in the length of the heat generating region. Furthermore, the present invention is not limited to a configuration in which the electrode portions are arranged on only one side of the substrate, but can also be applied to a configuration in which electrode portions 58 are arranged on both one side and the other side of substrate 55 as shown in Figure 12.

[0071] 12, electrode portions 58 are arranged on both ends of the base material 55 in the longitudinal direction X. That is, the electrode portions 58 are arranged between one end 55a of the base material 55 and one end 60a of the heat generating region 60, and between the other end 55b of the base material 55 and the other end 60b of the heat generating region 60. However, the number of electrode portions 58 arranged on one side of the base material 55 is different from the number of electrode portions 58 arranged on the other side. In this case, two electrode portions 58 are arranged between one end 55a of the base material 55 and one end 60a of the heat generating region 60, and one electrode portion 58 is arranged between the other end 55b of the base material 55 and the other end 60b of the heat generating region 60.

[0072] 12, the number of electrode portions 58 arranged on one side and the other side of the base material 55 is different, and therefore, on one side of the base material 55 where relatively more electrode portions 58 are arranged, more space must be secured for arranging the electrode portions 58 than on the other side. For this reason, in the example shown in Fig. 12, the length La between the end 55a on one side of the base material 55 and the end 60a on one side of the heat generating region 60 is set longer than the length Lb between the end 55b on the other side of the base material 55 and the end 60b on the other side of the heat generating region 60.

[0073] 12 also has the same problem as the heaters according to the above embodiments: when the heater 23 is turned on, the amount of heat transferred to the substrate 55 is greater at the longer ends of the substrate 55 than at the shorter ends. For this reason, it is preferable to apply the present invention. By applying the present invention, it is possible to achieve a heat balance between one side and the other in the longitudinal direction, thereby suppressing temperature variations in the heater and fixing belt.

[0074] The present invention is also applicable to fixing devices having the configurations shown in Figures 13 to 16. The configurations of the fixing devices shown in Figures 13 to 16 will be described below.

[0075] The fixing device 20 shown in FIG. 13 differs from the fixing device 20 shown in FIG. 2 above in the location of the temperature sensor 27 that detects the temperature of the heater 23. The rest of the configuration is the same. In the fixing device 20 shown in FIG. 13, the temperature sensor 27 is located upstream of the center M of the nip N in the paper feed direction (the nip entrance side). On the other hand, in the fixing device 20 shown in FIG. 2, the temperature sensor 27 is located at the center M of the nip N. As shown in FIG. 13, when the temperature sensor 27 is located upstream of the center M of the nip N in the paper feed direction, the temperature sensor 27 can accurately detect the temperature at the nip entrance side. The nip entrance side is an area where heat from the fixing belt 21 is particularly likely to be lost by the paper P entering the nip N. Therefore, by accurately detecting the temperature at the nip entrance side using the temperature sensor 27, image fixability can be ensured and the occurrence of fixing offset (a state in which the toner image is not sufficiently heated) can be effectively suppressed.

[0076] 14, a heating nip N1 where the heater 23 heats the fixing belt 21 and a fixing nip N2 where the paper P passes are formed at separate positions. Specifically, in this embodiment, a nip forming member 68 is disposed inside the fixing belt 21 in addition to the heater 23, and pressure rollers 69 and 70 are pressed against the heater 23 and the nip forming member 68, respectively, via the fixing belt 21, thereby forming the heating nip N1 and the fixing nip N2. In this case, the fixing belt 21 is heated at the heating nip N1, and the heat of the fixing belt 21 is applied to the paper P at the fixing nip N2, thereby fixing the unfixed image to the paper P.

[0077] 15 is an example of the fixing device 20 shown in Fig. 14, in which the pressure roller 69 on the heater 23 side is omitted and the heater 23 is formed in an arc shape to match the curvature of the fixing belt 21. Other than that, it is the same as the configuration shown in Fig. 14. In this case, since the heater 23 is formed in an arc shape, the contact length between the fixing belt 21 and the heater 23 in the belt rotation direction is ensured, and the fixing belt 21 can be heated efficiently.

[0078] 16 is an example of a fixing device 20 in which a roller 73 is disposed between a pair of belts 71 and 72. In this example, a heater 23 is disposed in the left-hand belt 71 in FIG. 16, and a nip forming member 74 is disposed in the right-hand belt 72. The heater 23 contacts the roller 73 via the left-hand belt 71, and the nip forming member 74 contacts the roller 73 via the right-hand belt 72, thereby forming a heating nip N1 and a fixing nip N2.

[0079] Furthermore, the image forming apparatus according to the present invention is not limited to the color image forming apparatus shown in Fig. 1, but can also be applied to an image forming apparatus configured as shown in Fig. 17. Below, the configuration of an image forming apparatus according to another embodiment to which the present invention can be applied will be described.

[0080] 17 includes an image forming means 80 including a photosensitive drum and the like, a paper transport section including a pair of timing rollers 81 and the like, a paper feeder 82, a fixing device 83, a paper discharge device 84, and a reading section 85. The paper feeder 82 includes multiple paper feed trays, each of which stores paper of a different size.

[0081] The reading unit 85 reads an image of the document Q. The reading unit 85 generates image data from the read image. The paper feeder 82 stores a plurality of sheets of paper P and sends the sheets of paper P to a conveyance path. The timing rollers 81 convey the sheets of paper P on the conveyance path to the image forming means 80.

[0082] The image forming means 80 forms a toner image on the paper P. Specifically, the image forming means 80 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 fixing device 83 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 84 by a transport roller or the like. The paper discharge device 84 discharges the paper P outside the image forming apparatus 100.

[0083] Next, the fixing device 83 according to this embodiment will be described with reference to Fig. 18. Note that in the configuration shown in Fig. 18, components common to the fixing device 20 of the above embodiment shown in Fig. 2 are denoted by the same reference numerals and description thereof will be omitted.

[0084] As shown in FIG. 18, the fixing device 83 includes a fixing belt 21, a pressure roller 22, a heater 23, a heater holder 24, a stay 25, a temperature sensor 27, and the like.

[0085] A nip portion N is formed between the fixing belt 21 and the pressure roller 22. The nip width of the nip portion N is 10 mm, and the linear speed of the fixing device 83 is 240 mm / s.

[0086] The fixing belt 21 has a polyimide base and a release layer, but does not have an elastic layer. The release layer is formed of a heat-resistant film material made of, for example, fluororesin. The outer diameter of the fixing belt 21 is approximately 24 mm.

[0087] The pressure roller 22 includes a core metal, an elastic layer, and a release layer. The pressure roller 22 has an outer diameter of 24 to 30 mm, and the elastic layer has a thickness of 3 to 4 mm.

[0088] The heater 23 includes a base material, a heat insulating layer, a conductive layer including a resistance heating element, and an insulating layer, and has an overall thickness of 1 mm. The width of the heater 23 in the paper transport direction is 13 mm.

[0089] As shown in FIG. 19, the conductor layer of the heater 23 includes a plurality of resistance heating elements 56, power supply lines 59, and electrode portions 58A to 58C. The plurality of resistance heating elements 56 are arranged at intervals in the longitudinal direction (arrow X direction) of the heater 23. Here, if the portions between the resistance heating elements 56 are referred to as "divided regions," then, as shown in the enlarged view of FIG. 19, divided regions B are formed between the resistance heating elements 56 (although FIG. 19 illustrates divided regions B only within the enlarged view, in reality divided regions B are provided between all of the resistance heating elements 56). In addition, in FIG. 19, the direction of arrow Y is a direction intersecting or perpendicular to the longitudinal direction X of the heater 23 (longitudinal intersecting direction) and different from the thickness direction of the substrate 55. In addition, the direction of arrow Y is a direction that intersects with the arrangement direction of the multiple resistance heating elements 56 (arrangement cross direction), or a direction along the surface of the substrate 55 on which the resistance heating elements 56 are provided, which is the same as the short side direction of the heater 23, or the transport direction of the paper passing through the fixing device.

[0090] Furthermore, the multiple resistance heating elements 56 form a central heating section 35B and heating sections 35A and 35C on both ends that can generate heat independently. For example, of the three electrode sections 58A to 58C, when electricity is applied to the leftmost electrode section 58A and the central electrode section 58B in FIG. 19, the heating sections 35A and 35C on both ends generate heat. When electricity is applied to the electrode sections 58A and 58C on both ends, the central heating section 35B generates heat. For example, when fixing small-size paper, only the central heating section 35B generates heat, and when fixing large-size paper, all of the heating sections 35A to 35C generate heat, allowing heating according to the size of the paper.

[0091] 20, the heater holder 24 according to this embodiment has a recess 24a that accommodates and holds the heater 23. The recess 24a is formed on the heater 23 side of the heater holder 24. The recess 24a is composed of a surface (bottom surface) 24f formed in a rectangular shape having approximately the same size as the heater 23, and four walls (side surfaces) 24b, 24c, 24d, and 24e that intersect with the surface 24f along the four sides that form the outline of the surface 24f. Note that the right wall 24e is not shown in FIG. 20. Alternatively, one of the pair of walls 24d and 24e (left and right) that intersect with the longitudinal direction X of the heater 23 (the direction in which the resistance heating elements 56 are arranged) may be omitted, and the recess 24a may be configured to open at one end of the heater 23 in the longitudinal direction.

[0092] 21, the heater 23 and heater holder 24 according to this embodiment are held by a connector 86. The connector 86 has a housing made of resin (for example, LCP) and a plurality of contact terminals provided inside the housing.

[0093] The connector 86 is attached to the heater 23 and the heater holder 24 in a direction intersecting the longitudinal direction X of the heater 23 (the arrangement direction of the resistance heating elements 56) (see the direction of the arrow from the connector 86 in FIG. 21). The connector 86 is attached to the heater 23 and the heater holder 24 at one end side in the longitudinal direction X of the heater 23 (the arrangement direction of the resistance heating elements 56), on the side opposite to the side on which the drive motor of the pressure roller 22 is provided. Note that when the connector 86 is attached to the heater holder 24, a convex portion provided on one of the connector 86 and the heater holder 24 may be configured to engage with a concave portion provided on the other, and the convex portion may move relatively within the concave portion.

[0094] With the connector 86 attached, the heater 23 and heater holder 24 are held by being sandwiched between them from the front and back sides by the connector 86. In this state, each contact terminal comes into contact (pressure-welded) with each electrode portion of the heater 23, electrically connecting each resistance heating element 56 to a power supply provided in the image forming apparatus via the connector 86. This enables power to be supplied from the power supply to each resistance heating element 56.

[0095] 21 are belt holding members that are provided at both longitudinal ends of the fixing belt 21 and hold both ends of the fixing belt 21 from the inside. The flanges 87 are inserted into both ends of the stay 25 and fixed to a pair of side plates that are frame members of the fixing device.

[0096] FIG. 22 is a diagram showing the arrangement of the temperature sensor 27 and the thermostat 88, which is a current interrupting member, according to this embodiment.

[0097] 22, the temperature sensors 27 according to this embodiment are disposed so as to face the inner circumferential surfaces of the fixing belt 21 on the center Xm side and the end side in the longitudinal direction X. One of these temperature sensors 27 is disposed at a position corresponding to the divided region B (see FIG. 19) between the resistance heating elements of the heater 23.

[0098] Further, on the center Xm side and end sides of the fixing belt 21, thermostats 88 as current-cutting members are arranged to face the inner circumferential surface of the fixing belt 21. Each thermostat 88 detects the temperature of the inner circumferential surface of the fixing belt 21 or the ambient temperature near the inner circumferential surface. When the temperature detected by the thermostat 88 exceeds a preset threshold value, the current to the heater 23 is cut off.

[0099] 22 and 23, flanges 87 that hold both ends of fixing belt 21 are provided with slide grooves 87a. Slide grooves 87a extend in the direction in which fixing belt 21 approaches and separates from pressure roller 22. An engagement portion of the housing of the fixing device engages with slide groove 87a. This engagement portion moves relatively within slide groove 87a, allowing fixing belt 21 to move in the direction in which fixing belt 21 approaches and separates from pressure roller 22.

[0100] The present invention is also applicable to a fixing device having the following configuration.

[0101] FIG. 24 is a schematic diagram of a fixing device according to another embodiment to which the present invention can be applied.

[0102] As shown in FIG. 24 , the fixing device 20 according to this embodiment includes a fixing belt 21 as a rotating body or fixing member, a pressure roller 22 as an opposing rotating body or pressure member, a heater 23 as a heat source, a heater holder 24 as a heat source holding member, a stay 25 as a support member, a temperature sensor (thermistor) 27 as a temperature detection member, and a first high thermal conductivity member 89. The fixing belt 21 is an endless belt. The pressure roller 22 contacts the outer surface of the fixing belt 21 and forms a nip N between the fixing belt 21 and the pressure roller 22. The heater 23 heats the fixing belt 21. The heater holder 24 holds the heater 23. The stay 25 supports the heater holder 24. The temperature sensor 27 detects the temperature of the first high thermal conductivity member 89. That is, the fixing device 20 according to this embodiment has basically the same configuration as the fixing device shown in FIG. 2 above, except for the inclusion of the first high thermal conductivity member 89. 24 is the longitudinal direction of the fixing belt 21, pressure roller 22, heater 23, heater holder 24, stay 25, and first high thermal conductivity member 89, 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 transported, the belt width direction of the fixing belt 21, and the axial direction of the pressure roller 22.

[0103] 19, the heater 23 in this embodiment has a plurality of resistance heating elements 56 arranged at intervals in the longitudinal direction of the heater 23. However, in a configuration in which a plurality of resistance heating elements 56 are arranged at intervals, the temperature of the heater 23 in divided regions B, which are the spaces between the resistance heating elements 56, tends to be lower than in the portions where the resistance heating elements 56 are arranged. Therefore, the temperature of the fixing belt 21 also becomes lower in divided regions B, and there is a risk that the temperature of the fixing belt 21 will become uneven along the longitudinal direction.

[0104] Therefore, in this embodiment, the first high thermal conductive member 89 is provided to suppress the temperature drop in the divided region B and suppress temperature unevenness in the longitudinal direction of the fixing belt 21. The first high thermal conductive member 89 will be described in more detail below.

[0105] 24, first high thermal conductivity member 89 is disposed between heater 23 and stay 25 in the left-right direction of the figure, and is particularly sandwiched between heater 23 and heater holder 24. In other words, one surface of first high thermal conductivity member 89 abuts against the back surface of base material 55 of heater 23, and the other surface of first high thermal conductivity member 89 (the surface opposite to the one surface) abuts against heater holder 24.

[0106] The stay 25 supports the heater holder 24, the first high thermal conductive member 89, and the heater 23 by bringing contact surfaces 25a1 of two vertical portions 25a extending in the thickness direction of the heater 23 and the like into contact with the heater holder 24. In the direction crossing the longitudinal axis (the up-down direction in FIG. 24), the contact surfaces 25a1 are provided outside the range in which the resistance heating element 56 is provided. This makes it possible to suppress heat transfer from the heater 23 to the stay 25, and allows the heater 23 to heat the fixing belt 21 efficiently.

[0107] As shown in Fig. 25, first high thermal conductivity member 89 is a plate-like member having a certain thickness, for example, a thickness of 0.3 mm, a length in the longitudinal direction of 222 mm, and a width in the direction transverse to the longitudinal direction of 10 mm. In this embodiment, first high thermal conductivity member 89 is formed from a single plate material, but it may also be formed from a plurality of members. Note that guide member 26 shown in Fig. 24 is omitted in Fig. 25.

[0108] The first high thermal conductivity member 89 is fitted into the recess 24a of the heater holder 24, and the heater 23 is attached thereto, thereby sandwiching and holding the first high thermal conductivity member 89 between the heater holder 24 and the heater 23. In this embodiment, the longitudinal width of the first high thermal conductivity member 89 is set to be approximately the same as the longitudinal width of the heater 23. The longitudinal movement of the first high thermal conductivity member 89 and the heater 23 is restricted by both side walls (longitudinal direction restriction portions) 24d, 24e arranged in a direction intersecting the longitudinal direction of the recess 24a. In this manner, the longitudinal positional deviation of the first high thermal conductivity member 89 within the fixing device is restricted, thereby improving the heat conduction efficiency within a target longitudinal range. Furthermore, the longitudinal movement of the first high thermal conductivity member 89 and the heater 23 is restricted by both side walls (arrangement intersecting direction restriction portions) 24b, 24c arranged in the longitudinal direction of the recess 24a.

[0109] The range in the longitudinal direction (arrow X direction) in which the first high thermal conductivity members 89 are arranged is not limited to the range shown in Fig. 25. For example, as shown in Fig. 26, the first high thermal conductivity members 89 may be arranged only in the longitudinal range in which the resistance heating elements 56 are arranged (see the hatched area in Fig. 26). Furthermore, as shown in the example in Fig. 27, the first high thermal conductivity members 89 may be arranged only in the entire area at positions corresponding to intervals (divided areas) B in the longitudinal direction (arrow X direction). Note that in Fig. 27, the resistance heating elements 56 and the first high thermal conductivity members 89 are shown shifted in the up-down direction in Fig. 27 for convenience, but they are arranged at approximately the same position in the direction intersecting the longitudinal direction (arrow Y direction). The first high thermal conductivity member 89 may be disposed across a portion of the resistance heating element 56 in the direction intersecting the longitudinal axis (direction of arrow Y), or, as in the example shown in FIG. 28, the first high thermal conductivity member 89 may be disposed across the entire resistance heating element 56 in the direction intersecting the longitudinal axis (direction of arrow Y). Furthermore, as shown in FIG. 28, the first high thermal conductivity member 89 may be disposed not only at a position corresponding to the longitudinal interval B but also across both resistance heating elements 56 on both sides of the interval B. This "disposing the first high thermal conductivity member 89 across the resistance heating elements 56 on both sides" means that the first high thermal conductivity member 89 at least partially overlaps with the resistance heating elements 56 on both sides in the longitudinal axis. The first high thermal conductivity member 89 may be disposed at a position corresponding to the entire interval B of the heater 23, or, as in the example shown in FIG. 28, it may be disposed only at a position corresponding to a portion of the interval B (in this case, one location). Here, "first high thermal conductivity member 89 is disposed at a position corresponding to interval B" means that interval B and first high thermal conductivity member 89 at least partially overlap in the longitudinal direction.

[0110] Due to the pressure of the pressure roller 22, the first highly thermally conductive member 89 is sandwiched between the heater 23 and the heater holder 24 and is in close contact with these members. The first highly thermally conductive member 89 comes into contact with the heater 23, thereby improving the thermal conductivity of the heater 23 in the longitudinal direction. Furthermore, by arranging the first highly thermally conductive member 89 at a position corresponding to the interval B between the heaters 23 in the longitudinal direction, the thermal conductivity in the interval B can be improved, increasing the amount of heat transferred to the interval B and raising the temperature in the interval B. This reduces temperature variations in the heater 23 in the longitudinal direction and in the fixing belt 21 in the longitudinal direction. As a result, uneven fixing and glossiness of the image fixed on the paper can be reduced. Furthermore, there is no need to increase the heat output of the heater 23 to ensure sufficient fixing performance in the interval B, thereby achieving energy savings in the fixing device. In particular, when the first high thermal conductivity member 89 is arranged over the entire longitudinal area where the resistance heating element 56 is arranged, the heat transfer efficiency of the heater 23 is improved over the entire area where the heater 23 is mainly heated (i.e., the image forming area of ​​the paper being passed through), and temperature unevenness in the longitudinal direction of the heater 23 and therefore the fixing belt 21 can be suppressed.

[0111] Furthermore, the combination of the first high thermal conductivity member 89 and the resistance heating element 56 having PTC characteristics can more effectively suppress excessive temperature rise in the non-paper passing area when small-size paper is passed. The PTC characteristics are such that the resistance value increases as the temperature increases (when a constant voltage is applied, the heater output decreases). In other words, the PTC characteristics of the resistance heating element 56 can effectively suppress the amount of heat generated by the resistance heating element 56 in the non-paper passing area, and the first high thermal conductivity member 89 can efficiently transfer the heat from the non-paper passing area, where the temperature has increased, to the paper passing area. Therefore, the synergistic effect of these factors can effectively suppress excessive temperature rise in the non-paper passing area.

[0112] Furthermore, since the amount of heat generated in the gap B is small, the temperature of the heater 23 is also low in the vicinity of the gap B, so it is preferable to place the first high thermal conductivity member 89. For example, by placing the first high thermal conductivity member 89 at a position corresponding to the expanded divided region C including the region around the gap B shown in Fig. 29, the heat transfer efficiency in the longitudinal direction in the gap B and its periphery can be improved, and temperature unevenness in the longitudinal direction of the heater 23 can be more effectively suppressed. Furthermore, if the first high thermal conductivity member 89 is placed over the entire longitudinal direction of the region in which all of the resistance heating elements 56 are placed, temperature unevenness in the longitudinal direction of the heater 23 (fixing belt 21) can be more reliably suppressed.

[0113] Next, still another embodiment of the fixing device will be described.

[0114] 30 has a second high thermal conductivity member 90 between heater holder 24 and first high thermal conductivity member 89. The second high thermal conductivity member 90 is provided at a different position from the first high thermal conductivity member 89 in the stacking direction (left-right direction in FIG. 30) of members such as heater holder 24, stay 25, and first high thermal conductivity member 89. More specifically, the second high thermal conductivity member 90 is provided overlapping the first high thermal conductivity member 89. In addition, in this embodiment, a temperature sensor (thermistor) 27 is provided as in the embodiment shown in FIG. 24 above, but FIG. 30 shows a cross section in which the temperature sensor 27 is not provided.

[0115] The second high thermal conductivity member 90 is made of a material having a higher thermal conductivity than the base material 55, such as graphene or graphite. In this embodiment, the second high thermal conductivity member 90 is made of a graphite sheet with a thickness of 1 mm. The second high thermal conductivity member 90 may also be made of a plate material such as aluminum, copper, or silver.

[0116] As shown in FIG. 31 , a plurality of second high thermal conductive members 90 are arranged in recess 24a of heater holder 24, with longitudinal gaps between each of the second high thermal conductive members 90. A recess that is one level deeper than the remaining portions of heater holder 24 is formed in the portion of heater holder 24 where second high thermal conductive members 90 are provided. Gaps are provided between second high thermal conductive members 90 and heater holder 24 on both longitudinal sides. This suppresses heat transfer from second high thermal conductive members 90 to heater holder 24, allowing heater 23 to efficiently heat fixing belt 21. Note that guide member 26 shown in FIG. 24 is omitted from FIG. 31 .

[0117] 32, second high thermal conductivity members 90 (see hatched areas) are arranged in positions corresponding to interval B in the longitudinal direction (direction of arrow X) so as to overlap at least a portion of adjacent resistance heating elements 56. In particular, in this embodiment, second high thermal conductivity members 90 are arranged across the entire area of ​​interval B. Note that while FIG. 32 (and FIG. 34 described below) shows a case in which first high thermal conductivity members 89 are arranged across the entire longitudinal direction of the area in which all resistance heating elements 56 are arranged, the arrangement range of first high thermal conductivity members 89 is not limited to this.

[0118] In this embodiment, in addition to the first high thermal conductivity member 89, second high thermal conductivity members 90 are disposed at positions corresponding to the longitudinal interval B so as to overlap at least a portion of adjacent resistance heating elements 56. This further improves the longitudinal heat transfer efficiency at the interval B, thereby more effectively suppressing temperature variations in the heater 23 along the longitudinal direction. Most preferably, as shown in FIG. 33 , the first high thermal conductivity member 89 and the second high thermal conductivity member 90 are disposed only over the entire area of ​​the position corresponding to the interval B. This improves the heat transfer efficiency particularly at the position corresponding to the interval B compared to other areas. For convenience, in FIG. 33 , the resistance heating elements 56, the first high thermal conductivity member 89, and the second high thermal conductivity member 90 are shown shifted from one another in the vertical direction of the figure, but they are actually disposed at approximately the same position in the direction transverse to the longitudinal direction (the direction of the arrow Y). However, this is not limited to this, and the first high thermal conductivity member 89 and the second high thermal conductivity member 90 may be arranged in a part of the longitudinal direction of the resistance heating element 56, or may be arranged so as to cover the entire longitudinal direction.

[0119] Furthermore, both the first high thermal conductivity member 89 and the second high thermal conductivity member 90 may be formed from the graphene sheet. In this case, the first high thermal conductivity member 89 and the second high thermal conductivity member 90 can be formed with high thermal conductivity in a predetermined direction along the graphene surface, that is, in the longitudinal direction rather than the thickness direction. This makes it possible to effectively suppress temperature variations in the heater 23 and the fixing belt 21 in the longitudinal direction.

[0120] Graphene is a flaky powder. Graphene consists of a planar hexagonal lattice structure of carbon atoms, as shown in Figure 36. Graphene sheets are sheet-like graphene, typically a single layer. Graphene sheets may contain impurities in the single carbon layer, or may have a fullerene structure. Fullerene structures are generally recognized as compounds consisting of polycyclic rings in which the same number of carbon atoms are fused together in a cage-like fashion with five- and six-membered rings, such as C60, C70, and C80 fullerenes, or other closed cage structures with three-coordinate carbon atoms.

[0121] Graphene sheets are man-made and can be produced, for example, by chemical vapor deposition (CVD).

[0122] 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).

[0123] Furthermore, graphite, which is a multilayered graphene, has a large thermal conductivity anisotropy. As shown in FIG. 37, graphite has layers in which the layer planes of condensed six-membered rings of carbon atoms extend in a planar fashion, forming a crystalline structure in which these layers are stacked multiple times. 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 89 or the second high thermal conductivity member 90 from graphite, the heat transfer efficiency in the longitudinal direction of the first high thermal conductivity member 89 or the second high thermal conductivity member 90 is greater than that in the thickness direction (i.e., the stacking direction of the members), thereby suppressing heat transfer to the heater holder 24. This effectively suppresses temperature unevenness in the longitudinal direction of the heater 23 and minimizes heat leakage toward the heater holder 24. Furthermore, by making the first high thermal conductivity member 89 or the second high thermal conductivity member 90 out of graphite, the first high thermal conductivity member 89 or the second high thermal conductivity member 90 can have excellent heat resistance, preventing oxidation up to approximately 700 degrees.

[0124] The physical properties and dimensions of the graphite sheet can be appropriately changed depending on the functions required of the first high thermal conductivity member 89 or the second high thermal conductivity member 90. For example, the anisotropy of the thermal conductivity 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 the fixing device, a thin graphite sheet may be used to reduce the thermal capacity of the fixing device. Furthermore, if the widths of the nip portion N and the heater 23 are large, the longitudinal width of the first high thermal conductivity member 89 or the second high thermal conductivity member 90 may be increased accordingly.

[0125] 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.

[0126] The second high thermal conductivity members 90 may be arranged in positions in the longitudinal direction corresponding to intervals B (and enlarged divided regions C) so as to overlap at least a portion of adjacent resistance heating elements 56, and are not limited to the arrangement shown in FIG. 32. For example, as shown in the example shown in FIG. 34, the second high thermal conductivity members 90A may be arranged to protrude beyond the base material 55 on both sides in the transverse direction (direction of arrow Y). Furthermore, the second high thermal conductivity members 90B may be arranged in an area in the transverse direction where the resistance heating elements 56 are arranged. Furthermore, the second high thermal conductivity members 90C may be arranged in a portion of intervals B.

[0127] In another embodiment shown in FIG. 35, a gap is provided between the first high thermal conductivity member 89 and the heater holder 24 in the thickness direction (left-right direction in FIG. 35). That is, a recess 24g serving as a heat insulating layer is provided in a portion of the recess 24a (see FIG. 31) of the heater holder 24 where the heater 23, the first high thermal conductivity member 89, and the second high thermal conductivity member 90 are disposed. The recess 24g is provided in a portion of the longitudinal direction other than the portion where the second high thermal conductivity member 90 (not shown in FIG. 35) is provided. The recess 24g is formed by making the recess 24a of the heater holder 24 deeper than the remaining portion. This minimizes the contact area between the heater holder 24 and the first high thermal conductivity member 89, thereby suppressing heat transfer from the first high thermal conductivity member 89 to the heater holder 24 and enabling the heater 23 to efficiently heat the fixing belt 21. In addition, in the cross section in the longitudinal direction where second high thermal conductivity member 90 is provided, second high thermal conductivity member 90 abuts against heater holder 24, as in the embodiment shown in FIG.

[0128] In this embodiment, the relief portion 24g is provided across the entire area where the resistance heating element 56 is provided in the transverse direction (the vertical direction in FIG. 35). This effectively suppresses heat transfer from the first high thermal conductivity member 89 to the heater holder 24, improving the heating efficiency of the heater 23 on the fixing belt 21. Note that, in addition to a configuration in which a space is provided like the relief portion 24g as the heat insulating layer, a configuration in which a heat insulating member having a lower thermal conductivity than the heater holder 24 is provided may also be used.

[0129] In addition, in the present embodiment, second high thermal conductivity member 90 is provided as a member different from first high thermal conductivity member 89, but this is not limiting. For example, first high thermal conductivity member 89 may also function as second high thermal conductivity member 90 by making the portion of first high thermal conductivity member 89 corresponding to interval B thicker than the other portions.

[0130] The above describes the configurations of other fixing devices and image forming apparatuses to which the present invention can be applied, but by applying the present invention to fixing devices and image forming apparatuses with such configurations, the same effects as those of the above-described embodiment can be obtained. That is, by applying the present invention, it is possible to suppress variations in the heater and belt temperatures and improve fixing quality.

[0131] Although the above description has been given with reference to an example where the present invention is applied to a fixing device, which is an example of a heating device, the present invention is not limited to fixing devices and can also be applied to heating devices such as a drying device that dries a liquid such as ink applied to paper, a laminator that thermocompresses a film as a covering member onto the surface of a sheet such as paper, and a heat sealer that thermocompresses a seal portion of a packaging material. [Explanation of symbols]

[0132] 20 Fixing device (heating device) 21 Fixing belt (first rotating body) 22 Pressure roller (second rotating body) 23 Heater (heat source) 55 Base material 55a One end 55b Other end 56 Resistance heating element 58 Electrode section 63 High friction area 65 Central heating element 66 Electrode side heating element (one side heating element) 67 Heating element on the opposite electrode side (other side heating element) 100 Image forming device N Nip X Longitudinal direction [Prior art documents] [Patent documents]

[0133] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-76857

Claims

1. a rotatable first rotor; a rotatable second rotor that contacts an outer peripheral surface of the first rotor to form a nip portion; A heating device including a heat source that heats the first rotating body, the heat source has a base material and a heating element provided on the base material, the substrate has a heat generating region in which the heat generating element is disposed, a length between one end of the base material in the longitudinal direction and the one end of the heat generating region is longer than a length between the other end of the base material in the longitudinal direction and the other end of the heat generating region; a length between the one end of the heat generating region and the one end of the second rotating body is shorter than a length between the other end of the heat generating region and the other end of the second rotating body, A heating device characterized in that the friction force between the first rotating body and the second rotating body on the other side of the center of the first rotating body in the longitudinal direction is greater than the friction force between the first rotating body and the second rotating body on one side of the center.

2. A rotatable first rotating body; a rotatable second rotor that contacts an outer peripheral surface of the first rotor to form a nip portion; A heating device including a heat source that heats the first rotating body, the heat source has a base material and a heating element provided on the base material, the substrate has a heat generating region in which the heat generating element is disposed, a length between one end of the base material in the longitudinal direction and the one end of the heat generating region is longer than a length between the other end of the base material in the longitudinal direction and the other end of the heat generating region; a length between the one end of the heat generating region and the one end of the second rotating body is shorter than a length between the other end of the heat generating region and the other end of the second rotating body, A heating device characterized in that the length between one end of the sheet passing area where the sheet passes through the nip portion and one end of the heat generating area is longer than the length between the other end of the sheet passing area and the other end of the heat generating area.

3. A rotatable first rotating body; a rotatable second rotor that contacts an outer peripheral surface of the first rotor to form a nip portion; A heating device including a heat source that heats the first rotating body, the heat source has a base material and a heating element provided on the base material, the substrate has a heat generating region in which the heat generating element is disposed, a length between one end of the base material in the longitudinal direction and the one end of the heat generating region is longer than a length between the other end of the base material in the longitudinal direction and the other end of the heat generating region; a length between the one end of the heat generating region and the one end of the second rotating body is shorter than a length between the other end of the heat generating region and the other end of the second rotating body, the heat source includes a central heating element, a one-side heating element disposed on the one side of the central heating element, and a other-side heating element disposed on the other side of the central heating element, A heating device, characterized in that the length of the heat generating element on one side in the longitudinal direction is longer than the length of the heat generating element on the other side in the longitudinal direction.

4. An electrode portion connected to the heating element is provided between the one end of the substrate and the one end of the heating region, The heating device according to claim 1 , wherein the electrode portion is not provided between the other end of the base material and the other end of the heat generating region.

5. The second rotating body has an elastic layer and a surface layer provided on the outer peripheral surface of the elastic layer, The heating device according to claim 1 , wherein the surface layer is not provided on at least a part of the outer circumferential surface of the elastic layer on the other side of the center, and the elastic layer is exposed.

6. A fixing device characterized by fixing an unfixed image to a sheet using a heating device described in any one of claims 1 to 5.

7. An image forming apparatus characterized by comprising a heating device described in any one of claims 1 to 5 or a fixing device described in claim 6.

Images