Heating device, fixing device, and image forming apparatus

Abstract

To ensure good responsiveness of a thermostat.SOLUTION: A heating device comprises: a heater 23 that is in contact with an inner peripheral surface of a rotating body and heats the rotating body; a heat transfer assisting member 24 that is in contact with a surface 23b of the heater 23 that is on the opposite side of a rotating body contact surface 23a in contact with the inner peripheral surface of the rotating body; a thermostat 28 that is in contact with the surface 23b of the heater 23 that is on the opposite side of the rotating body contact surface 23a, and detects the temperature of the heater 23; and a contact prevention member 40 that is in contact with at least one of the thermostat 28 and the heat transfer assisting member 24, and prevents the thermostat 28 and the heat transfer assisting member 24 from directly contacting each other.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 copying machine or a printer, a fixing device that heats a sheet to fix an image onto the sheet is known.

[0003] Generally, a fixing device includes a pair of rotating bodies that come into contact with each other to form a nip portion, and a heater that heats at least one of the pair of rotating bodies. When a sheet enters between the rotating bodies (the nip portion) in a state in which one or both of the rotating bodies are heated to a predetermined temperature by the heater, an unfixed image on the sheet is heated and pressurized, and the unfixed image is fixed to the sheet. In addition, the fixing device is provided with a temperature sensor such as a thermistor or thermostat that detects the temperature of the heater in order to maintain the temperature of the heater at an appropriate level and prevent excessive temperature rise.

[0004] For example, Patent Document 1 (JP 2019-90938 A) discloses a configuration in which a thermostat that penetrates a highly thermally conductive portion and contacts a heat source is sandwiched between a protrusion that rises from the periphery of the through hole in the highly thermally conductive portion.

[0005] It is preferable for the thermostat to detect the temperature of the heat source with good responsiveness. However, in the case of the configuration described in Patent Document 1, the thermostat is sandwiched between the protruding parts of the highly thermally conductive part, and so heat from the thermostat transfers to the highly thermally conductive part through the contact part between the thermostat and the protruding parts, which may result in a failure to detect the temperature of the heat source with good responsiveness.

[0006] In this manner, in a configuration in which a mating member such as a highly thermally conductive portion is disposed around the thermostat, the thermostat comes into contact with the mating member, which can cause a problem of reduced responsiveness of the thermostat. Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, an object of the present invention is to ensure good responsiveness of a thermostat. [Means for solving the problem]

[0008] In order to solve the above problems, the heating device of the present invention is characterized in that it comprises a rotating body, a heater in contact with the inner surface of the rotating body and heating the rotating body, a heat transfer auxiliary member in contact with the surface of the heater opposite to the rotating body contact surface that contacts the inner surface of the rotating body, a thermostat in contact with the surface of the heater opposite to the rotating body contact surface and detecting the temperature of the heater, and a contact prevention member in contact with at least one of the thermostat and the heat transfer auxiliary member to prevent direct contact between the thermostat and the heat transfer auxiliary member. Effect of the Invention

[0009] According to the present invention, good responsiveness of the thermostat can be ensured. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention. [Diagram 2] 1 is a schematic configuration diagram of a fixing device according to a first embodiment of the present invention. [Diagram 3] FIG. 2 is a plan view of the heater according to the first embodiment of the present invention. [Figure 4] FIG. 2 is a block diagram of a temperature control mechanism for a heater according to the first embodiment of the present invention. [Diagram 5] 1 is a conceptual diagram showing how the temperature of a thermostat rises when the thermostat is in direct contact with a heater and when the thermostat is in indirect contact with a heater via a heat transfer assistance member. FIG. [Figure 6] FIG. 4 is a diagram showing a temperature distribution in the short side direction of the heater. [Figure 7]1 is a cross-sectional view of a heater, a heat transfer assistance member, and a heater holder according to a first embodiment of the present invention, taken along the short side direction of the heater at the position of a thermostat. [Figure 8] 1 is a rear view of a heater, a heat transfer assistant member, and a thermostat according to a first embodiment of the present invention, viewed from the side opposite to the heater contact surface of the heat transfer assistant member. FIG. [Figure 9] 13A and 13B are diagrams illustrating other examples of arrangement of the contact-preventing member. [Figure 10] FIG. 11 is a cross-sectional view of a heater, a heat transfer assistance member, and a heater holder according to a second embodiment of the present invention, taken along the short side direction of the heater at the position of the thermostat. [Figure 11] FIG. 11 is a cross-sectional view of a heater, a heat transfer assistance member, and a heater holder according to a third embodiment of the present invention, taken along the short side direction of the heater at the position of the thermostat. [Figure 12] 13A and 13B are diagrams showing other examples of arrangement of the engagement portion of the heat transfer assistance member. [Figure 13] FIG. 13 is a plan view of a heat transfer assistant member and a heater holder according to a fourth embodiment of the present invention, as viewed from the heat transfer assistant member side. [Figure 14] FIG. 11 is a cross-sectional view of a heater, a heat transfer assistance member, and a heater holder according to a fourth embodiment of the present invention, taken along the short side direction of the heater at the position of the thermostat. [Figure 15] FIG. 13 is a cross-sectional view of a heater, a heat transfer assistance member, and a heater holder according to a fifth embodiment of the present invention, taken along the short side direction of the heater at the position of the thermostat. [Figure 16] FIG. 13 is a rear view of a heater, a heat transfer assistant member, and a thermostat according to a fifth embodiment of the present invention, as viewed from the opposite side to the heater contact surface of the heat transfer assistant member. [Figure 17] FIG. 13 is a diagram showing a modified example of the resistive heating element. [Figure 18] FIG. 13 is a diagram showing another modified example of the resistive heating element. [Figure 19] FIG. 4 is a cross-sectional view of a fixing belt that does not have an elastic layer. [Figure 20] 11 is a diagram showing the configuration of another fixing device to which the present invention can be applied. [Figure 21] 11 is a diagram showing the configuration of another fixing device to which the present invention can be applied. [Figure 22] FIG. 13 is a diagram showing the configuration of still another fixing device to which the present invention can be applied. [Figure 23] FIG. 13 is a diagram showing the configuration of still another fixing device to which the present invention can be applied. [Figure 24] FIG. 13 is a diagram showing the configuration of still another fixing device to which the present invention can be applied. [Diagram 25] FIG. 13 is a diagram showing a configuration of another image forming apparatus to which the present invention can be applied. [Figure 26] 26 is a diagram showing a configuration of the fixing device shown in FIG. 25. [Figure 27] FIG. 27 is a plan view of the heater shown in FIG. 26. [Figure 28] FIG. 27 is a perspective view of the heater, heat transfer assistance member, and heater holder shown in FIG. 26. [Figure 29] 27A to 27C are diagrams showing a method of attaching a connector to the heater holder shown in FIG. 26. [Diagram 30] FIG. 27 is a diagram showing the arrangement of the temperature sensors shown in FIG. 26. [Diagram 31] FIG. 30 is a diagram showing a groove portion of the flange shown in FIG. 29. [Diagram 32] 13A and 13B are diagrams showing other examples of the arrangement of the heat transfer assistance members. [Diagram 33] FIG. 13 is a diagram showing yet another example of the arrangement of the heat transfer assistance members. [Diagram 34] FIG. 4 is a diagram showing an enlarged divided region of a heater. [Diagram 35] FIG. 13 is a diagram showing the configuration of still another fixing device to which the present invention can be applied. [Diagram 36] 36 is a perspective view of the heater, the first heat transfer assistant member, the second heat transfer assistant member, and the heater holder shown in FIG. 35. FIG. [Figure 37] FIG. 2 is a diagram showing the arrangement of a first heat transfer assistance member and a second heat transfer assistance member. [Figure 38] 13A and 13B are diagrams showing other examples of the arrangement of the first heat transfer assistant members and the second heat transfer assistant members. [Figure 39]FIG. 13 is a diagram showing yet another example of the arrangement of the second heat transfer assistance member. [Diagram 40] 13 is a diagram showing an example in which a gap is provided between the first heat transfer assistant member and the heater holder. FIG. [Diagram 41] FIG. 1 illustrates the atomic crystal structure of graphene. [Diagram 42] FIG. 1 illustrates the atomic crystal structure of graphite. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] 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 given the same reference numerals as far as they can be distinguished, and the description thereof will be omitted after it has been described once.

[0012] <Overall configuration of image forming apparatus> FIG. 1 is a schematic diagram of an image forming apparatus 1000 according to a first 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. In addition, "image formation" used in the following description means not only forming an image having meaning such as characters and figures, but also forming an image having no meaning such as a pattern. First, the overall configuration and operation of the image forming apparatus according to the first embodiment of the present invention will be described with reference to FIG. 1.

[0013] As shown in FIG. 1, an image forming apparatus 1000 according to the first embodiment of the present invention includes an image forming section 100, a fixing section 200, a sheet supply section 300, and a sheet discharge section 400.

[0014] (Image forming section) The image forming section 100 is a section that forms an image on a sheet as a recording medium. The image forming section 100 includes four imaging units 1Y, 1M, 1C, and 1Bk, an exposure device 6, and a transfer device 8.

[0015] Each of the four imaging units 1Y, 1M, 1C, and 1Bk includes an electrostatic latent image carrier 2, a charging member 3, a developing device 4, and a cleaning member 5.

[0016] The electrostatic latent image carrier 2 is a rotating body that carries an electrostatic latent image on its surface. As the electrostatic latent image carrier 2, for example, a photosensitive drum or an endless photosensitive belt may be used.

[0017] The charging member 3 is a member that charges the surface of the electrostatic latent image carrier 2. There are no particular limitations on the charging member 3 as long as it can apply a voltage to the surface of the electrostatic latent image carrier 2 to uniformly charge it, and it can be appropriately selected depending on the purpose. Specific examples of the charging member 3 include contact-type charging members such as conductive or semiconductive charging rollers, magnetic brushes, fur brushes, films, and rubber blades, as well as non-contact-type charging members that utilize corona discharge.

[0018] The developing device 4 is a device that forms a toner image by supplying toner as a developer to the electrostatic latent image on the electrostatic latent image carrier 2. The developing device 4 contains toner (developer) of different colors such as yellow, magenta, cyan, and black, which correspond to the color separation components of the color image, for each of the imaging units 1Y, 1M, 1C, and 1Bk.

[0019] The cleaning member 5 is a member that removes toner and other foreign matter remaining on the electrostatic latent image carrier 2. As the cleaning member 5, a cleaning blade that is arranged so as to come into contact with the surface of the electrostatic latent image carrier 2, or the like, is used.

[0020] The exposure device 6 is a device that forms an electrostatic latent image by exposing the charged surface of the electrostatic latent image carrier 2. The exposure device 6 is not particularly limited as long as it can expose the charged surface of the electrostatic latent image carrier 2, and can be appropriately selected depending on the purpose. Specific examples of the exposure device include various exposure devices such as a copying optical system, a rod lens array system, a laser optical system, a liquid crystal shutter optical system, and an LED optical system.

[0021] The transfer device 8 is a device that transfers an image onto a sheet. 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, and 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 electrostatic latent image carrier 2 via the intermediate transfer belt 11, thereby forming a primary transfer nip between the intermediate transfer belt 11 and each electrostatic latent image carrier 2. Meanwhile, the secondary transfer roller 13 contacts the outer peripheral surface of the intermediate transfer belt 11. As a result, a secondary transfer nip is formed between the secondary transfer roller 13 and the intermediate transfer belt 11.

[0022] (Fixing part) The fixing section 200 has a fixing device 20 that heats the sheet to fix an image onto the sheet. The fixing device 20 includes a pair of rotating bodies 19A and 19B that contact each other, and a heater that heats at least one of the pair of rotating bodies 19A and 19B.

[0023] (Sheet supply section) The sheet supply unit 300 is a part that supplies sheets to the image forming unit 100. The sheet supply unit 300 has a paper feed cassette 14 that stores paper P as a sheet, and a paper feed roller 15 that feeds paper P from the paper feed cassette 14. In addition to paper, the term "sheet" also includes overhead projector sheets or fabrics, metal sheets, plastic films, and prepreg sheets in which carbon fibers have been impregnated with resin in advance. In addition to plain paper, the term "paper" also includes cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, etc.

[0024] (Sheet ejection section) The sheet discharge section 400 is a section that discharges the paper P to the outside of the apparatus. The sheet discharge section 400 has a pair of paper discharge rollers 17 that discharge the paper P, and a paper discharge tray 18 on which the paper P discharged by the paper discharge rollers 17 is placed.

[0025] <Image formation operation> Next, the operation of the image forming apparatus 1000 according to the first embodiment of the present invention will be described with reference to FIG.

[0026] When an image forming operation is started by an instruction from the operation panel or an external terminal, the electrostatic latent image carrier 2 starts to rotate in each of the imaging units 1Y, 1M, 1C, and 1Bk. Next, each charging member 3 charges the surface of each electrostatic latent image carrier 2 to a uniform high potential. Next, the exposure device 6 exposes the surface (charged surface) of each electrostatic latent image carrier 2 based on the image information of the document read by the document reading device or the print image information instructed from the external terminal. This reduces the potential of the exposed portion, and an electrostatic latent image is formed on the surface of each electrostatic latent image carrier 2. Thereafter, toner is supplied from each developing device 4 to each electrostatic latent image carrier 2, and a toner image of a different color is formed on each electrostatic latent image carrier 2.

[0027] The toner images on the electrostatic latent image carriers 2 reach the primary transfer nip (the position of the primary transfer roller 12) as the electrostatic latent image carriers 2 rotate. Then, at the primary transfer nip, the toner images are transferred from the electrostatic latent image carriers 2 to the intermediate transfer belt 11, which is rotating, so as to be superimposed one on the other. Thus, a full-color toner image is formed on the intermediate transfer belt 11. Note that the image formation is not limited to the case where a full-color image is formed using all four imaging units 1Y, 1M, 1C, and 1Bk, but it is also possible to form a monochromatic image using any one of the imaging units 1Y, 1M, 1C, and 1Bk, or to form a two-color or three-color image using any two or three imaging units. After the toner images are transferred to the intermediate transfer belt 11, the electrostatic latent image carriers 2 are cleaned by the cleaning member 5. As a result, foreign matter such as residual toner is removed from the surface of each electrostatic latent image carrier 2.

[0028] The toner image transferred onto the intermediate transfer belt 11 is transported to the secondary transfer nip (the position of the secondary transfer roller 13) as the intermediate transfer belt 11 rotates. Then, the toner image is transferred from the intermediate transfer belt 11 onto a sheet of paper P at the secondary transfer nip. This sheet of paper P is supplied from the sheet supply unit 300. After the image forming operation starts, the sheet of paper P is sent out from the sheet feed cassette 14 by the rotation of the sheet feed roller 15. The sent sheet of paper P comes into contact with the timing roller pair 16 on the way to the secondary transfer nip, and the transport is temporarily stopped. Thereafter, the timing roller pair 16 rotates at a predetermined timing, and the sheet of paper P is transported to the secondary transfer nip in synchronization with the toner image on the intermediate transfer belt 11, and the toner image is transferred onto the sheet of paper P.

[0029] The paper P onto which the toner image has been transferred is transported to the fixing section 200. In the fixing section 200, the paper P passes between a pair of rotating rotors 19A, 19B, whereby the toner image on the paper P is heated and pressurized, and the toner image is fixed to the paper P. The paper P is then transported to the sheet discharge section 400, and discharged to the paper discharge tray 18 by the paper discharge rollers 17. This completes a series of image forming operations.

[0030] <Configuration of the fixing device> FIG. 2 is a schematic diagram of a fixing device 20 according to the first embodiment of the present invention.

[0031] As shown in FIG. 2, the fixing device 20 includes a pair of rotating bodies 19A and 19B, as well as a heater 23, a heat transfer auxiliary member 24, a heater holder 25, a stay 26, and the like.

[0032] Of the pair of rotors 19A, 19B, the first rotor 19A is a fixing belt 21 that is disposed on the unfixed image bearing surface side of the paper P. The other, second rotor 19B, is a pressure roller 22 that is disposed to face the fixing belt 21. The fixing belt 21 and the pressure roller 22 are pressurized by a pressure member such as a spring so as to come into contact with each other. As a result, a nip portion N is formed between the fixing belt 21 and the pressure roller 22.

[0033] The fixing belt 21 is composed of a cylindrical substrate and an endless belt member having a release layer provided on the outer peripheral surface of the substrate. The substrate is formed of, for example, a metal material such as nickel or stainless steel, or a resin material such as polyimide. The release layer is formed of, for example, a material such as PFA (tetrafluoroethylene-perfluoroalkylvinylether copolymer), PTFE (polytetrafluoroethylene), polyimide, polyetherimide, or PES (polyether sulfide). The fixing belt 21 has a release layer, which improves the separation of the toner image from the fixing belt 21 and suppresses the wrapping of the paper P around the fixing belt 21. The fixing belt 21 may also have an elastic layer between the substrate and the release layer. For example, a rubber material such as silicone rubber, foamed silicone rubber, or fluororubber is used as the material for the elastic layer. When the fixing belt 21 has an elastic layer, minute irregularities are less likely to be formed on the surface of the fixing belt 21, so that heat is more easily transferred uniformly to the toner image on the paper P, improving the fixing quality.

[0034] The pressure roller 22 is composed of a roller having a hollow or solid core material, an elastic layer provided on the outer peripheral surface of the core material, and a release layer provided on the outer peripheral surface of the elastic layer. The core material is made of a metal material such as iron. The elastic layer is made of silicone rubber, foamed silicone rubber, fluororubber, etc. The release layer is made of a fluororesin such as PFA or PTFE.

[0035] The heater 23 is disposed so as to contact the inner circumferential surface of the fixing belt 21 at the nip portion N. The heater 23 sandwiches the fixing belt 21 between itself and the pressure roller 22, whereby the fixing belt 21 is pressurized and the nip portion N is formed between the fixing belt 21 and the pressure roller 22. The heater 23 may directly contact the inner circumferential surface of the fixing belt 21, or may contact the fixing belt 21 via a low-friction sliding sheet. In this specification, "contact" includes not only direct contact without any other member, but also indirect contact via other member, unless otherwise specified.

[0036] The heater 23 includes a base material 50, a resistance heating element 51, an insulating layer 52, and the like. The resistance heating element 51 is provided on the base material 50 and is covered with the insulating layer 52. When the resistance heating element 51 generates heat by energization, the heat is transferred to the inner circumferential surface of the fixing belt 21 via the insulating layer 52, and the fixing belt 21 is heated. The heater 23 may be arranged so that the base material 50 contacts the inner circumferential surface of the fixing belt 21 by changing the direction of the heater 23. In that case, since the heat of the resistance heating element 51 is transferred to the fixing belt 21 via the base material 50, it is preferable that the base material 50 is made of a material having high thermal conductivity.

[0037] The substrate 50 is formed of a non-metallic material such as ceramics, glass, or mica, such as alumina or aluminum nitride, which have excellent heat resistance and insulation. In addition, the substrate 50 can be formed of a conductive material such as metal by interposing a separate insulating layer between the substrate 50 and the resistance heating element 51. As the metal material, aluminum or stainless steel is preferable in terms of low cost. In addition, in order to suppress temperature unevenness of the heater 23 and improve image quality, the substrate 50 may be formed of a material with high thermal conductivity, such as copper, graphite, or graphene. Graphene is a sheet-like substance formed by bonding carbon atoms.

[0038] The resistance heating element 51 is formed by a method such as screen printing. For example, a paste made of silver palladium (AgPd) and glass powder is applied to the base material 50 by screen printing, and then the base material 50 is fired to form the resistance heating element 51. In addition to silver palladium, other resistive materials such as silver alloy (AgPt) or ruthenium oxide (RuO2) may be used as the material for the resistance heating element 51. The insulating layer 52 is formed of, for example, heat-resistant glass.

[0039] The heat transfer assistant member 24 is a member that assists the transfer of heat generated from the heater 23. The heat transfer assistant member 24 is formed of a material having a higher thermal conductivity than the heater holder 25 and the like. The material of the heat transfer assistant member 24 is copper, aluminum, graphene, or the like, and an example thereof is an aluminum plate having a thickness of 0.3 mm. The heat transfer assistant member 24 is disposed so as to contact a surface 23b of the heater 23 opposite to a rotor contact surface 23a that contacts the inner circumferential surface of the fixing belt 21. The heat transfer assistant member 24 is not limited to being a single-layer member, and may be composed of a multi-layer member.

[0040] In particular, in the first embodiment of the present invention, the heat transfer assistant member 24 is disposed so as to be in direct contact with the heater 23, so that the heat of the heater 23 can be effectively dispersed by the heat transfer assistant member 24. Generally, in the non-passing area where the paper P does not pass, the heat of the nip portion N is not easily consumed, so that when paper P having a width smaller than the heat generating area of ​​the heater 23 is continuously passed, there is a risk that the temperature of the fixing belt 21 and the heater 23 in the non-passing area will rise excessively. However, in the first embodiment of the present invention, since the heat transfer assistant member 24 is provided, the heat of the nip portion N in the non-passing area can be dispersed to the surroundings via the heat transfer assistant member 24. This makes it possible to suppress a local temperature rise of the fixing belt 21 and the heater 23. In addition, since the heat of the nip portion N in the non-passing area can be transferred to the passing area where the paper P passes, it can be effectively utilized as heat for the fixing process, and improvement in energy saving can be expected.

[0041] The heater holder 25 is a member that holds the heater 23 and the heat transfer assistant member 24. The heater holder 25 has a recess 25a that accommodates the heater 23 and the heat transfer assistant member 24. The heater 23 and the heat transfer assistant member 24 are accommodated in the recess 25a of the heater holder 25, thereby restricting the movement of the heater 23 and the heat transfer assistant member 24 in the vertical direction and the direction perpendicular to the paper surface in FIG. 2. The heater holder 25 is preferably made of a heat-resistant material because it is likely to become hot due to the heat of the heater 23. In particular, when the heater holder 25 is made of a heat-resistant resin with low thermal conductivity such as LCP, unnecessary heat transfer from the heater 23 to the heater holder 25 is suppressed, thereby improving the heating efficiency of the heater 23.

[0042] The stay 26 is a support member that supports the heater holder 25. The stay 26 supports the heater holder 25 from the side opposite to the pressure roller 22, thereby suppressing deflection of the heater 23 due to the pressure force of the pressure roller 22, and obtaining a uniform width of the nip portion N. The material of the stay 26 is preferably an iron-based metal material such as SUS or SECC in order to ensure rigidity.

[0043] <Operation of the fixing device> The fixing device 20 according to the first embodiment of the present invention operates as follows.

[0044] When the image forming operation is started, the pressure roller 22 starts to rotate in the direction of the arrow in Fig. 2, and the fixing belt 21 is rotated accordingly. Furthermore, the heater 23 is energized, so that the fixing belt 21 is heated. Then, when the temperature of the fixing belt 21 reaches a predetermined target temperature, the paper P carrying the unfixed image is transported to the nip portion N between the fixing belt 21 and the pressure roller 22. As a result, the toner image on the paper P is heated and pressurized, and fixed to the paper P. The paper P is then discharged from the nip portion N and transported to the sheet discharge portion 400.

[0045] <Heater configuration> FIG. 3 is a plan view of the heater 23 according to the first embodiment of the present invention.

[0046] 3, the heater 23 according to the first embodiment of the present invention is a planar or plate-shaped heater extending long in the X direction in the figure. The heater 23 is disposed in the fixing belt 21 such that the longitudinal direction X of the heater 23 is aligned with the longitudinal direction of the fixing belt 21. Note that the "longitudinal direction of the fixing belt 21" here means a direction along the outer circumferential surface of the fixing belt 21 that is perpendicular to the rotation direction of the fixing belt 21. The heater 23 has an elongated base material 50, a resistance heating element 51, an insulating layer 52, an electrode portion 53, and a power supply line 54.

[0047] The resistance heating elements 51 are arranged at intervals along the longitudinal direction of the base material 50. The gap between adjacent resistance heating elements 51 is preferably 0.2 mm or more, more preferably 0.4 mm or more, from the viewpoint of ensuring insulation between the resistance heating elements 51. However, if the gap between the resistance heating elements 51 is too large, the temperature is likely to decrease in the gap, so the gap is preferably 5 mm or less, more preferably 1 mm or less, from the viewpoint of suppressing temperature unevenness along the longitudinal direction. Each resistance heating element 51 is connected to a pair of electrode parts 53 via a power supply line 54. In the example shown in FIG. 3, a pair of electrode parts 53 is provided at both ends of the base material 50 in the longitudinal direction, and each resistance heating element 51 is electrically connected in parallel to each electrode part 53. The arrangement, number, shape, etc. of the resistance heating elements 51, the electrode parts 53, and the power supply line 54 are not limited to the example shown in FIG. 3, and can be changed as appropriate.

[0048] The electrode portions 53 and the power supply lines 54 are provided on the same surface of the substrate 50 as the resistance heating elements 51. The power supply lines 54 are covered with an insulating layer 52, like the resistance heating elements 51, to ensure insulation and durability. On the other hand, the electrode portions 53 are exposed and not covered with the insulating layer 52, because a connector serving as a power supply member is connected to the electrode portions 53. When the connector is connected to each electrode portion 53, each resistance heating element 51 and a power source are electrically connected, so that each resistance heating element 51 can be supplied with power from the power source.

[0049] <Temperature control mechanism> FIG. 4 is a block diagram of a temperature control mechanism for the heater 23 according to the first embodiment of the present invention.

[0050] As shown in FIG. 4, the fixing device 20 according to the first embodiment of the present invention includes a thermistor 27, a thermostat 28, a triac 10, and a control unit 7 as a temperature control mechanism for controlling the temperature of the heater 23.

[0051] The thermistor 27 is a temperature sensor for temperature control provided to maintain the temperature of the heater 23 at a predetermined temperature. Meanwhile, unlike the thermistor 27, the thermostat 28 is a temperature sensor for preventing excessive temperature rise provided to prevent an abnormal temperature rise of the heater 23. In the first embodiment of the present invention, the thermistor 27 is disposed at the longitudinal center and one longitudinal end of the heat generation region H of the heater 23, and the thermostat 28 is disposed at the other longitudinal end opposite to the one longitudinal end of the heat generation region H. The arrangement and number of the thermistor 27 and the thermostat 28 are not limited to the example in FIG. 4 and can be changed as appropriate.

[0052] Each thermistor 27 is disposed so as to be in indirect contact with surface 23b of heater 23 opposite rotor contact surface 23a via heat transfer assisting member 24. This prevents temperature unevenness in heater 23 caused by direct contact of the thermistor 27 with heater 23.

[0053] On the other hand, the thermostat 28 is disposed so as to be in direct contact with the surface 23b of the heater 23 opposite to the rotor contact surface 23a. The thermostat 28 is a temperature sensor provided to prevent an abnormal temperature rise in the heater 23, and therefore it is preferable that the thermostat 28 be able to detect an abnormal temperature rise in the heater 23 with good responsiveness. For this reason, the thermostat 28 is disposed so as to be in direct contact with the heater 23 without the heat transfer assistance member 24 being interposed therebetween. When the thermostat 28 detects an abnormal temperature rise in the heater 23, the thermostat 28 operates and the power supply to the heater 23 is cut off.

[0054] The triac 10 is a current control means that controls the current duty from the AC power supply 30 to the heater 23 under instructions from the control unit 7. The "current duty" refers to the ratio of time that current is applied to the heater 23 per control cycle. The control unit 7 is composed of a microcomputer including a CPU, ROM, RAM, an I / O interface, etc. The control unit 7 outputs a control signal that controls the triac 10 based on the temperature detected by each thermistor 27, and the triac 10 controls the current duty based on the control signal, so that the temperature of the heater 23 is maintained at a predetermined target temperature.

[0055] <Thermostat responsiveness issue> Here, the problem regarding the responsiveness of the thermostat will be described using the configuration according to the first embodiment of the present invention as an example.

[0056] In a configuration using a planar or plate-shaped heater 23 with a small heat capacity as a heating source as in the first embodiment of the present invention, the heater 23 quickly rises in temperature, which has the advantage of shortening the first print time and saving energy. On the other hand, if the temperature difference between the heat generating portion and the non-heat generating portion increases due to a sudden temperature rise in the heater 23, there is a risk that the base material 50 of the heater 23 will be damaged due to the stress difference caused by thermal expansion.

[0057] For this reason, in the first embodiment of the present invention, a thermostat 28 is provided that detects the temperature of the heater 23, and in the event of an abnormal temperature rise in the heater 23, power to the heater 23 is cut off to stop heat generation. Also, since it is preferable for the thermostat 28 to detect the temperature of the heater 23 with good responsiveness, in the first embodiment of the present invention, as shown in Fig. 4, a hole 24a is provided in the heat transfer assistance member 24, and the thermostat 28 is in direct contact with the heater 23 through the hole 24a.

[0058] Fig. 5 is a conceptual diagram showing the state of temperature rise of thermostat 28 when thermostat 28 is in direct contact with heater 23 and when thermostat 28 is in indirect contact with heater 23 via heat transfer assistance member 24. In Fig. 5, the solid line shows the temperature rise when thermostat 28 is in direct contact with heater 23, and the dotted line shows the temperature rise when thermostat 28 is in indirect contact with heater 23.

[0059] 5, when the thermostat 28 is indirectly contacted, there is a delay in the temperature rise of the thermostat 28 compared to when the thermostat 28 is in direct contact. This causes a delay in the operation of the thermostat 28, which may result in a failure to quickly cut off the power to the heater 23. In contrast, when the thermostat 28 is in direct contact, the temperature of the thermostat 28 rises in responsiveness to the temperature rise of the heater 23, so that if an abnormality occurs in the heater 23, the power can be quickly cut off, and problems such as damage to the heater 23 due to the temperature rise can be effectively prevented.

[0060] However, if holes 24a are provided in the heat transfer assistant member 24 to bring the thermostat 28 into direct contact with the heater 23, the contact area between the heat transfer assistant member 24 and the heater 23 will be reduced by the area of ​​the holes 24a. This raises the concern that it will be difficult to obtain the heat dispersion effect of the heat transfer assistant member 24. Therefore, it is preferable that the holes 24a are as small as possible.

[0061] On the other hand, when hole 24a is made smaller, the inner circumferential surface of hole 24a approaches thermostat 28, increasing the possibility of direct contact between thermostat 28 and the inner circumferential surface of hole 24a. If thermostat 28 were to directly contact the inner circumferential surface of hole 24a, heat from thermostat 28 would transfer to heat transfer assistance member 24, making it impossible for thermostat 28 to keep up with the temperature rise of heater 23, and the responsiveness of thermostat 28 would decrease.

[0062] For example, as shown in Fig. 6, in a configuration in which the thermostat 28 and the resistance heating element 51 are disposed at the center of the heater 23 in the short-side direction Y, the temperature at the center of the heater 23 in the short-side direction Y is the highest, and a temperature gradient corresponding to the temperature distribution of the heater 23 is generated between the thermostat 28 and the heat transfer assistant member 24. Therefore, in this case, if the thermostat 28 comes into direct contact with the inner circumferential surface of the hole 24a of the heat transfer assistant member 24, heat will transfer from the thermostat 28, which has a higher temperature, to the heat transfer assistant member 24, which has a lower temperature, and the thermostat 28 may not be able to quickly and accurately detect the temperature rise of the heater 23. In addition, not limited to the example of Fig. 6, if there is a temperature gradient between the thermostat 28 and the heat transfer assistant member 24, if the thermostat 28 comes into direct contact with the inner circumferential surface of the hole 24a, the heat of the thermostat 28 will similarly transfer to the heat transfer assistant member 24, and the responsiveness of the thermostat 28 may be reduced. If the responsiveness of the thermostat 28 decreases, it becomes impossible to effectively prevent malfunctions such as damage to the heater 23 caused by a rise in temperature. Therefore, in the first embodiment of the present invention, the following measures are taken to ensure good responsiveness of the thermostat 28.

[0063] <Configuration according to the first embodiment of the present invention> The configuration according to the first embodiment of the present invention will be described below with reference to Fig. 7 and Fig. 8. Fig. 7 is a cross-sectional view of the heater 23, the heat transfer assistant member 24, and the heater holder 25 according to the first embodiment of the present invention, cut in the short-side direction Y of the heater 23 at the position of the thermostat 28. In this specification, the "short-side direction Y of the heater 23" means a direction perpendicular to the longitudinal direction X of the heater 23 along the rotor contact surface 23a of the heater 23. Fig. 8 is a rear view of the heater 23, the heat transfer assistant member 24, and the thermostat 28 according to the first embodiment of the present invention, seen from the opposite side to the heater contact surface side of the heat transfer assistant member 24.

[0064] As shown in FIG. 7, the thermostat 28 has a heat-sensing part 31 and a holding part 32. The heat-sensing part 31 is a part that directly contacts the heater 23 and detects the temperature of the heater 23. Specifically, the heat-sensing part 31 is composed of a bimetal that deforms when a certain temperature threshold is exceeded, and a metal cap 33 that covers the bimetal. When the temperature of the heater 23 increases abnormally, the bimetal is deformed by heat, and the deformation cuts off the flow of electricity to the heater 23. The holding part 32 is a part that holds the heat-sensing part 31. The holding part 32 is provided with an urging member 34 such as a spring. The urging member 34 urges the thermostat 28 toward the heater 23, so that the heat-sensing part 31 of the thermostat 28 is held in direct contact with the heater 23.

[0065] The heat-sensing part 31 is disposed so as to directly contact the surface 23b of the heater 23 opposite the rotor contact surface 23a through a hole 25b provided in the heater holder 25 and a hole 24a provided in the heat transfer assistant member 24. In this state, a contact prevention member 40 is provided between the heat-sensing part 31 and the heat transfer assistant member 24 to prevent direct contact between the heat-sensing part 31 and the heat transfer assistant member 24.

[0066] 8, the contact prevention member 40 is provided around the entire circumference of the heat-sensing part 31 in the hole 24a of the heat transfer assistant member 24. Therefore, even if at least one of the thermostat 28 and the heat transfer assistant member 24 is misaligned in the longitudinal direction X or the lateral direction Y of the heater 23, the heat-sensing part 31 and the heat transfer assistant member 24 are held so as not to come into direct contact with each other. In other words, because the contact prevention member 40 is interposed over the entire area between the outer circumferential surface of the heat-sensing part 31 and the inner circumferential surface of the hole 24a, the heat-sensing part 31 and the heat transfer assistant member 24 are held so as not to come into direct contact with each other even if at least one of the thermostat 28 and the heat transfer assistant member 24 is misaligned.

[0067] In this way, in the first embodiment of the present invention, the heat-sensing part 31 of the thermostat 28 is configured not to come into direct contact with the heat transfer assistant member 24, thereby avoiding a decrease in the responsiveness of the thermostat 28 caused by direct contact between the heat-sensing part 31 and the heat transfer assistant member 24. This ensures good responsiveness of the thermostat 28, effectively preventing problems such as damage to the heater 23 due to a rise in temperature, improving reliability.

[0068] Furthermore, according to the configuration of the first embodiment of the present invention, it is not necessary to make the hole 24a of the heat transfer assistant member 24 larger than necessary in order to avoid direct contact between the thermostat 28 and the heat transfer assistant member 24, so the function of the heat transfer assistant member 24 can be ensured well. That is, the size of the hole 24a can be made the minimum size sufficient to accommodate the heat-sensing part 31 and the contact prevention member 40, so that a decrease in the heat dispersion effect caused by making the hole 24a larger can be suppressed. Therefore, according to the configuration of the first embodiment of the present invention, it is possible to ensure good responsiveness of the thermostat 28 while maintaining good function of the heat transfer assistant member 24.

[0069] The contact-preventing member 40 is preferably a low-thermal-conductive member having a lower thermal conductivity than the heat transfer assistant member 24 and the heat-sensing portion 31 (cap 33) of the thermostat 28. By using the contact-preventing member 40 as a low-thermal-conductive member, the transfer of heat from the thermostat 28 to the heat transfer assistant member 24 can be effectively suppressed, so that a decrease in the responsiveness of the thermostat 28 can be more reliably avoided. Furthermore, the material for the contact-preventing member 40 is preferably a heat-resistant resin such as polyimide. Furthermore, the contact-preventing member 40 may be a sheet made of a heat-resistant resin or a heat-resistant nonwoven fabric.

[0070] The contact prevention member 40 may be attached to the heat-sensing portion 31 of the thermostat 28, or may be attached to the inner circumferential surface of the hole 24a of the heat transfer assistance member 24. Methods for attaching the contact prevention member 40 include attachment using double-sided adhesive tape, as well as adhesion using an adhesive.

[0071] Furthermore, the contact prevention member 40 may be provided around the entire circumference of the heat sensing unit 31, or may be provided around a portion of the circumference of the heat sensing unit 31. In particular, when there is a risk of heat transfer from the thermostat 28 to the heat transfer assistant member 24 in the short-side direction Y of the heater 23, it is preferable to dispose the contact prevention member 40 at least between the thermostat 28 and the heat transfer assistant member 24 in the short-side direction Y of the heater 23, as in the example shown in Fig. 9. This makes it possible to suppress the transfer of heat from the thermostat 28 to the heat transfer assistant member 24 in the short-side direction Y of the heater 23, and effectively avoid a decrease in the responsiveness of the thermostat 28.

[0072] <Configuration of other embodiments> Next, another embodiment of the present invention will be described. Below, differences from the first embodiment of the present invention will be mainly described, and descriptions of the same parts will be omitted as appropriate.

[0073] Second embodiment of the present invention FIG. 10 is a cross-sectional view of a heater 23, a heat transfer assistance member 24, and a heater holder 25 according to a second embodiment of the present invention, taken at the position of a thermostat 28 in the short-side direction Y of the heater 23. As shown in FIG.

[0074] In the second embodiment of the present invention, the configuration of the heat transfer assistant member 24 is different from that of the first embodiment of the present invention. Specifically, the heat transfer assistant member 24 according to the second embodiment of the present invention is different in that it has a protrusion 24b that is inserted into the hole 25b of the heater holder 25. The protrusion 24b contacts the inner circumferential surface of the hole 25b when inserted into the hole 25b of the heater holder 25. This positions the heat transfer assistant member 24 relative to the heater holder 25 in the longitudinal direction X (the direction perpendicular to the paper surface of FIG. 10) and the lateral direction Y of the heater 23. The protrusion 24b may be a cylinder arranged over the entire circumference of the hole 25b, or may be composed of a plurality of protruding pieces that are arranged intermittently over the circumference of the hole 25b.

[0075] Moreover, the protrusion 24b has a hole 24a inside which the thermostat 28 and the contact prevention member 40 are disposed. By disposing the contact prevention member 40 between the protrusion 24b and the thermostat 28, direct contact between the thermostat 28 and the heat transfer assistance member 24 is prevented also in the second embodiment of the present invention.

[0076] Furthermore, in the second embodiment of the present invention, since the heat transfer assistant member 24 has the protrusions 24b, the heat capacity of the heat transfer assistant member 24 is increased, and therefore the heat dispersion effect of the heat transfer assistant member 24 is improved at the center side in the short-side direction Y of the heater 23 where the protrusions 24b are arranged. In particular, since the heat dispersion effect is improved at a position close to the resistance heating element 51, it is possible to suppress thermal stress accompanying a temperature rise of the heater 23, and it is possible to effectively suppress damage to the heater 23.

[0077] Third embodiment of the present invention FIG. 11 is a cross-sectional view of a heater 23, a heat transfer assistance member 24, and a heater holder 25 according to a third embodiment of the present invention, taken at the position of a thermostat 28 in the short-side direction Y of the heater 23. As shown in FIG.

[0078] The third embodiment of the present invention differs from the first embodiment of the present invention in that it does not have a separate contact prevention member 40. In this case, in the third embodiment of the present invention, the heater holder 25 functions as the contact prevention member 40 that prevents direct contact between the thermostat 28 and the heat transfer assistant member 24.

[0079] Specifically, the heater holder 25 has a hole 25b with an opening width W2 smaller than the opening width W1 of the hole 24a of the heat transfer assistant member 24. Therefore, the inner circumferential surface of the hole 24a of the heat transfer assistant member 24 is disposed at a position farther away from the thermostat 28 than the inner circumferential surface of the hole 25b of the heater holder 25. Also, the heat transfer assistant member 24 is positioned with respect to the heater holder 25 at a position farther away from the thermostat 28. In this case, the heat transfer assistant member 24 is positioned with respect to the heater holder 25 in the longitudinal direction X and the lateral direction Y of the heater 23 by engaging the convex engaging portion 24c with the groove-like or hole-like engaging portion 25c of the heater holder 25.

[0080] In this way, in the third embodiment of the present invention, the inner circumferential surface of the hole 24a of the heat transfer assistant member 24 is positioned at a position farther away from the thermostat 28 than the inner circumferential surface of the hole 25b of the heater holder 25, so that even if the thermostat 28 is misaligned, the thermostat 28 is prevented from coming into direct contact with the heat transfer assistant member 24. That is, if the thermostat 28 is misaligned, the thermostat 28 comes into contact with the inner circumferential surface of the hole 25b of the heater holder 25 before the inner circumferential surface of the hole 24a of the heat transfer assistant member 24, so that the thermostat 28 is prevented from approaching and coming into contact with the heat transfer assistant member 24. As a result, in the third embodiment of the present invention, direct contact between the thermostat 28 and the heat transfer assistant member 24 is prevented, so that good responsiveness of the thermostat 28 can be ensured. Moreover, in the third embodiment of the present invention, it is not necessary to provide a separate contact prevention member 40, so that the number of parts can be reduced.

[0081] The opening width W2 of the hole 25b of the heater holder 25 may be equal to or greater than the width of the cap 33 (heat-sensing part 31) of the thermostat 28. In particular, when the opening width W2 of the hole 25b is set to be the same as the width of the cap 33 (heat-sensing part 31), the cap 33 (heat-sensing part 31) fits into the inner circumferential surface of the hole 25b of the heater holder 25, so that the thermostat 28 is positioned so as not to come close to the heat transfer assistant member 24. In this case, direct contact between the thermostat 28 and the heat transfer assistant member 24 can be more reliably prevented.

[0082] In addition, the engagement structure between the heater holder 25 and the heat transfer assistant member 24 can be changed as appropriate. In FIG. 11, the convex engagement parts 24c of the heat transfer assistant member 24 are provided at both ends of the heat transfer assistant member 24 in the short-side direction Y of the heater 23, but as in the example shown in FIG. 12, the convex engagement parts 24c may be provided at the center of the short-side direction Y of the heater 23. In this case, the heat capacity of the heat transfer assistant member 24 is large at a position close to the resistance heating element 51, so that the heat dispersion effect is improved and it is possible to suppress the thermal stress caused by the temperature rise of the heater 23. In addition, the engagement structure between the heater holder 25 and the heat transfer assistant member 24 may be reversed in the concave-convex relationship. That is, the heat transfer assistant member 24 may be provided with a groove-shaped or hole-shaped engagement part, and the heater holder 25 may be provided with a convex engagement part.

[0083] <Fourth embodiment of the present invention> Fig. 13 is a plan view of a heat transfer assistant member 24 and a heater holder 25 according to a fourth embodiment of the present invention, as viewed from the heat transfer assistant member 24 side. Also, Fig. 14 is a cross-sectional view of a heater 23, a heat transfer assistant member 24, and a heater holder 25 according to the fourth embodiment of the present invention, cut at the position of a thermostat 28 in the short-side direction Y of the heater 23.

[0084] 13, in the fourth embodiment of the present invention, a plurality of restricting portions 25d for restricting movement of the heat transfer assisting member 24 in the short-side direction Y of the heater 23 are provided in a recess 25a of a heater holder 25 in which the heat transfer assisting member 24 is housed. In this case, a total of four restricting portions 25d are provided at different positions in the longitudinal direction X of the heater 23 so as to face the short-side direction Y of the heater 23. Note that the number and arrangement of the restricting portions 25d are not limited to the example shown in FIG. 13 and can be changed as appropriate.

[0085] 14, when the heat transfer assistant member 24 is accommodated in the recess 25a of the heater holder 25, the restricting portions 25d come into contact with both ends of the heat transfer assistant member 24 in the short-side direction Y of the heater 23. This restricts the movement of the heat transfer assistant member 24 in the short-side direction Y of the heater 23, so that the heat transfer assistant member 24 is positioned in the heater holder 25. Also in the fourth embodiment of the present invention, the opening width W2 of the hole 25b of the heater holder 25 is smaller than the opening width W1 of the hole 24a of the heat transfer assistant member 24. Therefore, when the heat transfer assistant member 24 is positioned in the heater holder 25, the inner circumferential surface of the hole 24a of the heat transfer assistant member 24 is located farther away from the thermostat 28 than the inner circumferential surface of the hole 25b of the heater holder 25.

[0086] In this manner, also in the fourth embodiment of the present invention, the inner circumferential surface of the hole 24a of the heat transfer assistant member 24 is positioned farther from the thermostat 28 than the inner circumferential surface of the hole 25b of the heater holder 25, so that even if the thermostat 28 is misaligned, the thermostat 28 is prevented from coming into direct contact with the heat transfer assistant member 24. Therefore, also in the fourth embodiment of the present invention, good responsiveness of the thermostat 28 can be ensured. Note that in the fourth embodiment of the present invention, the length L from the tip to the base end of the heat sensing part 31 is set to be greater than the thickness T of the heat transfer assistant member 24 so that the heat sensing part 31 of the thermostat 28 comes into contact with the inner circumferential surface of the hole 25b of the heater holder 25 before the inner circumferential surface of the hole 24a of the heat transfer assistant member 24 comes into contact with the inner circumferential surface of the hole 25b of the heater holder 25 when the thermostat 28 is misaligned.

[0087] In the fourth embodiment of the present invention, the movement of the heat transfer assistant member 24 in the short-side direction Y of the heater 23 is restricted by the restricting portion 25d of the heater holder 25, so that direct contact between the thermostat 28 and the heat transfer assistant member 24 in the short-side direction Y can be particularly prevented. The restricting portion 25d is not limited to being disposed so as to sandwich the heat transfer assistant member 24 in the short-side direction Y of the heater 23, but may be disposed so as to sandwich the heat transfer assistant member 24 in the longitudinal direction X of the heater 23. In that case, it is preferable to provide a gap between the heat transfer assistant member 24 and the restricting portion 25d in consideration of the amount of thermal expansion so that the heat transfer assistant member 24 does not interfere with the restricting portion 25d and become deformed or damaged when the heat transfer assistant member 24 thermally expands in the longitudinal direction X of the heater 23.

[0088] Also in the fourth embodiment of the present invention, since the heater holder 25 functions as the contact prevention member 40, it is not necessary to provide a separate contact prevention member 40, and the number of parts can be reduced.

[0089] Furthermore, in the fourth embodiment of the present invention, the opening width W2 of the hole 25b of the heater holder 25 may also be made the same as the width of the cap 33 (heat sensing part 31), so that the cap 33 (heat sensing part 31) fits onto the inner circumferential surface of the hole 25b of the heater holder 25. In this case, the thermostat 28 is positioned relative to the heater holder 25, so that direct contact between the thermostat 28 and the heat transfer assistance member 24 can be more reliably prevented.

[0090] Fifth embodiment of the present invention Fig. 15 is a cross-sectional view of the heater 23, the heat transfer assistant member 24, and the heater holder 25 according to the fifth embodiment of the present invention, cut at the position of the thermostat 28 in the short direction Y of the heater 23. Also, Fig. 16 is a rear view of the heater 23, the heat transfer assistant member 24, and the thermostat 28 according to the fifth embodiment of the present invention, seen from the side opposite to the heater contact surface side of the heat transfer assistant member 24.

[0091] 15, in the fifth embodiment of the present invention, a sensor holder 35 for holding a thermostat 28 is provided in addition to a heater holder 25 for holding a heater 23 and a heat transfer assistant member 24. The sensor holder 35 is positioned in the longitudinal direction X and lateral direction Y of the heater 23 by fitting into the inner circumferential surface of a hole 25b of the heater holder 25. The heat transfer assistant member 24 is also positioned in the heater holder 25 in addition to the sensor holder 35. In this case, the heat transfer assistant member 24 is positioned in the longitudinal direction X and lateral direction Y of the heater 23 by engaging with the heater holder 25 via a convex engaging portion 24c.

[0092] 15, when the heat transfer assistant member 24 and the sensor holder 35 are positioned relative to the heater holder 25, the tip 35a of the sensor holder 35 arranged on the heater 23 side is arranged to enter between the outer circumferential surface of the heat sensing part 31 of the thermostat 28 and the inner circumferential surface of the hole 24a of the heat transfer assistant member 24. Also, as shown by the hatched portion in FIG. 16, the tip 35a of the sensor holder 35 is interposed between the heat sensing part 31 and the heat transfer assistant member 24 over the entire circumference of the heat sensing part 31.

[0093] Therefore, even if at least one of the thermostat 28 and the heat transfer assistant member 24 is misaligned in the longitudinal direction X or the lateral direction Y of the heater 23, the outer circumferential surface of the heat sensing part 31 and the inner circumferential surface of the hole 24a are held so as not to come into direct contact with each other by the tip 35a of the sensor holder 35 interposed between the outer circumferential surface of the heat sensing part 31 and the inner circumferential surface of the hole 24a. Therefore, in the fifth embodiment of the present invention, the sensor holder 35 functions as a contact prevention member 40 that prevents direct contact between the thermostat 28 and the heat transfer assistant member 24. This makes it possible to ensure good responsiveness of the thermostat 28.

[0094] In addition, the tip 35a of the sensor holder 35 is not limited to being interposed between the outer surface of the heat sensing part 31 and the inner surface of the hole portion 24a around the entire circumference of the heat sensing part 31, but may be provided around a portion of the circumference of the heat sensing part 31.

[0095] Furthermore, at least the tip 35a of the sensor holder 35 may be made of a low thermal conductive material having a lower thermal conductivity than the heat transfer assistance member 24 and the heat sensing part 31 (cap 33) of the thermostat 28. In this case, the transfer of heat from the thermostat 28 to the heat transfer assistance member 24 is effectively suppressed, making it possible to more reliably avoid a decrease in the responsiveness of the thermostat 28.

[0096] As described above, according to the configurations of the embodiments of the present invention, direct contact between the thermostat 28 and the heat transfer auxiliary member 24 can be prevented, so that good responsiveness of the thermostat 28 can be ensured and reliability can be improved. In addition, the present invention is preferably applied to a configuration in which a plurality of resistance heating elements 51 are arranged in the longitudinal direction X of the heater 23 as shown in FIG. 3. In a configuration in which a plurality of resistance heating elements 51 are arranged in the longitudinal direction X of the heater 23, the heater 23 becomes long, so that the heat transfer auxiliary member 24 needs to be formed long accordingly. However, if the heat transfer auxiliary member 24 becomes long, it becomes difficult to ensure the positional accuracy of the hole portion 24a in which the thermostat 28 is arranged, so that the risk of direct contact between the thermostat 28 and the heat transfer auxiliary member 24 increases. Therefore, by applying the present invention to such a configuration, the risk of direct contact between the thermostat 28 and the heat transfer auxiliary member 24 is eliminated, so that a great effect can be expected.

[0097] The resistance heating element 51 is not limited to a rectangular shape as shown in Fig. 3, but may be a parallelogram as shown in Fig. 17, or a folded shape as shown in Fig. 18. As shown in Fig. 17 or 18, the pair of electrode parts 53 may be provided at either end of the base material 50 in the longitudinal direction X of the heater 23.

[0098] The present invention is also suitable for a configuration including a fixing belt 21 that does not have an elastic layer as shown in FIG. 19. The fixing belt 21 shown in FIG. 19 does not have an elastic layer such as a rubber layer between the surface layer (release layer) 212 and the base material 210, and therefore has lower insulation and better thermal conductivity from the heater to the fixing belt surface (outer circumferential surface) than a fixing belt having an elastic layer. However, on the other hand, since the temperature rise of the fixing belt 21 in the non-paper passing area tends to be significant, it is preferable to apply the present invention so that the function of the heat transfer assistant member 24 can be obtained well while ensuring good responsiveness of the thermostat 28. That is, according to the present invention, the size of the hole 24a of the heat transfer assistant member 24 can be minimized, so that the function of the heat transfer assistant member 24 can be ensured well and local temperature rise of the fixing belt 21 can be effectively suppressed.

[0099] The present invention is also applicable to fixing devices having the configurations shown in Figures 20 to 24, in addition to the fixing device 20 shown in Figure 2. The fixing devices having the configurations shown in Figures 20 to 24 will be described below. Note that in Figures 20 to 24, the same components as those in the fixing device 20 shown in Figure 2 are denoted by the same reference numerals as in Figure 2, and description thereof will be omitted.

[0100] In the fixing device 20 shown in FIG. 20, the heating nip portion N1 and the fixing nip portion N2 are formed at different positions. Specifically, the two pressure rollers 151 and 152, large and small, contact the fixing belt 21 from opposite sides to each other, thereby forming the heating nip portion N1 and the fixing nip portion N2. That is, the pressure roller 151 on the left side of FIG. 20 contacts the heater 23 through the fixing belt 21 to form the heating nip portion N1, and the pressure roller 152 on the right side of FIG. 20 contacts the nip forming member 150 through the fixing belt 21 to form the fixing nip portion N2. In this case, when the heater 23 generates heat, the fixing belt 21 is heated in the heating nip portion N1. Also, when the paper P enters the fixing nip portion N2, the unfixed image on the paper P is heated and pressurized, and the image is fixed to the paper P.

[0101] 20, a heat transfer assistant member 24 is provided in contact with the heater 23, and a thermostat 28 is in direct contact with the heater 23 through a hole 24a in the heat transfer assistant member 24. Therefore, if the thermostat 28 were to come into direct contact with the heat transfer assistant member 24, there is a risk that the responsiveness of the thermostat 28 would decrease. Therefore, even in the fixing device 20 having such a configuration, a contact prevention member 40 is interposed between the thermostat 28 and the heat transfer assistant member 24 to prevent direct contact between the thermostat 28 and the heat transfer assistant member 24, thereby ensuring good responsiveness of the thermostat 28.

[0102] 21 is an example in which the pressure roller 151 on the left side of FIG. 20 is omitted, and the heater 23 is formed in an arc shape to match the curvature of the fixing belt 21. Other than that, the configuration is the same as that of the fixing device 20 shown in FIG. 20. In this case, since the heater 23 is formed in an arc shape, a long contact area between the fixing belt 21 and the heater 23 in the belt rotation direction is ensured, and therefore the fixing belt 21 is efficiently heated.

[0103] Next, the example shown in FIG. 22 is an example in which a pair of belts 161, 162 are arranged on both sides of a central roller 163. In this case, the belt 161 on the left side of FIG. 22 is sandwiched between the heater 23 arranged inside and the central roller 163, thereby forming a heating nip portion N1. Also, the belt 162 on the right side of FIG. 22 is sandwiched between the nip forming member 153 arranged inside and the central roller 163, thereby forming a fixing nip portion N2. In this case, when the heater 23 generates heat, the central roller 163 is heated in the heating nip portion N1. Also, when the paper P enters the fixing nip portion N2, the unfixed image on the paper P is heated and pressurized, and the image is fixed to the paper P.

[0104] 22, the thermostat 28 is in direct contact with the heater 23 through the hole 24a of the heat transfer assistant member 24, and so there is a risk that the responsiveness of the thermostat 28 will decrease if the thermostat 28 comes into direct contact with the heat transfer assistant member 24. Therefore, in this case as well, a contact prevention member 40 is interposed between the thermostat 28 and the heat transfer assistant member 24 to ensure good responsiveness of the thermostat 28.

[0105] 23 includes an IH (electromagnetic induction heating) heater 63 as a means for heating the fixing belt 21. In addition to the IH heater 63, the fixing device 20 also includes the fixing belt 21, the pressure roller 22, the stay 26, a nip forming member 62, a sliding sheet 61, the thermostat 28, and a separating member 64 including a separating plate 64A and a separating claw 64B.

[0106] The IH heater 63 is disposed outside the fixing belt 21 and fixed to the image forming apparatus body. The IH heater 63 has a coil 632, cores 633, 634, 635, and a coil holder 631. The coil holder 631 holds the coil 632. When power is supplied to the coil 632, a magnetic field is formed around the coil 632, and an eddy current is generated in the metal belt base material of the fixing belt 21. When the eddy current is generated, Joule heat is generated due to the electrical resistance of the belt base material, and the fixing belt 21 heats up. The cores 633, 634, 635 are formed of a ferromagnetic material, and form a magnetic path that allows the magnetic field (magnetic flux) generated from the coil 632 to pass through.

[0107] Thermostat 28 is in contact with the inner circumferential surface of fixing belt 21 and detects the temperature of fixing belt 21. When thermostat 28 detects an abnormal increase in temperature of fixing belt 21, power supply to IH heater 63 is cut off.

[0108] Nip forming member 62 contacts pressure roller 22 via fixing belt 21, and forms a fixing nip N between fixing belt 21 and pressure roller 22. A sliding sheet 61 containing a lubricant is provided between fixing belt 21 and nip forming member 62. By interposing sliding sheet 61 and lubricant between fixing belt 21 and nip forming member 62, the sliding resistance between fixing belt 21 and nip forming member 62 is reduced.

[0109] The stay 26 supports the thermostat 28 in addition to the nip forming member 62. The stay 26 has a convex holding portion 26a that holds the thermostat 28. Here, if the holding portion 26a of the stay 26 arranged around the thermostat 28 comes into direct contact with the thermostat 28, heat from the thermostat 28 may transfer to the stay 26, which may reduce the responsiveness of the thermostat 28. In particular, when the stay 26 is made of a material such as a metal that has a higher thermal conductivity than the resin nip forming member 62, the heat from the thermostat 28 is likely to transfer to the stay 26.

[0110] 23, it is preferable to interpose a contact prevention member 40 between the thermostat 28 and the retaining portion 26a of the stay 26 to prevent direct contact between the thermostat 28 and the retaining portion 26a. This makes it possible to prevent direct contact between the thermostat 28 and the stay 26, and ensures good responsiveness of the thermostat 28.

[0111] 24 includes a halogen heater 65 as a means for heating the fixing belt 21. In addition to the halogen heater 65, the fixing device 20 also includes the fixing belt 21, the pressure roller 22, the stay 26, a nip forming member 66, a reflecting member 67, a thermostat 28, and the like.

[0112] The nip forming member 66 contacts the pressure roller 22 via the fixing belt 21, and forms a fixing nip N between the fixing belt 21 and the pressure roller 22. In this case, since the halogen heater 65 is disposed so as to face the nip forming member 66 on the inner side of the fixing belt 21, the infrared light emitted from the halogen heater 65 is irradiated to the nip forming member 66. This heats the nip forming member 66, and the heat of the nip forming member 66 is transferred to the fixing belt 21 at the position of the nip portion N, thereby heating the fixing belt 21. The nip forming member 66 is preferably formed of a material having a higher thermal conductivity than the stay 26 so that heat can be efficiently transferred to the fixing belt 21. Examples of materials for the nip forming member 66 include copper and aluminum.

[0113] Also, a part of the infrared light emitted from the halogen heater 65 is reflected to the nip forming member 66 by a reflecting member 67 arranged inside the fixing belt 21. This effectively heats the nip forming member 66. Also, since the reflecting member 67 is interposed between the stay 26 and the halogen heater 65, the irradiation of infrared light and the transfer of heat from the halogen heater 65 to the stay 26 are suppressed, resulting in an energy saving effect.

[0114] The thermostat 28 is in contact with the inner circumferential surface of the fixing belt 21 and detects the temperature of the fixing belt 21. When the thermostat 28 detects an abnormal increase in temperature of the fixing belt 21, the power supply to the halogen heater 65 is cut off.

[0115] The stay 26 supports the thermostat 28 in addition to the nip forming member 66 and the reflecting member 67. The stay 26 has a convex holding portion 26a that holds the thermostat 28. In this case as well, if the holding portion 26a of the stay 26 arranged around the thermostat 28 comes into direct contact with the thermostat 28, heat from the thermostat 28 will be transferred to the stay 26, and the responsiveness of the thermostat 28 may decrease.

[0116] 24, it is preferable to interpose a contact prevention member 40 between the thermostat 28 and the retaining portion 26a of the stay 26 to prevent direct contact between the thermostat 28 and the retaining portion 26a. This makes it possible to prevent direct contact between the thermostat 28 and the stay 26, and ensures good responsiveness of the thermostat 28.

[0117] In this manner, the contact-preventing member 40 may be disposed between the thermostat 28 and the stay 26. In other words, the contact-preventing member 40 functions as a member that prevents direct contact between the thermostat 28 and a mating member disposed around it, and the mating member may be a heat transfer auxiliary member that diffuses heat from the heater, or a stay that supports a nip forming member or the like.

[0118] Further, the image forming apparatus according to the present invention is not limited to the image forming apparatus shown in Fig. 1, but can also be applied to an image forming apparatus 100 as shown in Fig. 25. Hereinafter, the configuration of other image forming apparatuses to which the present invention can be applied will be described.

[0119] 25 includes 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 a plurality of paper feed trays, each of which stores paper of a different size.

[0120] 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 conveying path. The timing rollers 81 convey the sheets of paper P on the conveying path to the image forming means 80.

[0121] 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 replenishing device, a transfer roller, a cleaning device, and a charge removing 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 to the outside of the image forming apparatus 100.

[0122] Next, the configuration of the fixing device 83 shown in Fig. 25 will be described with reference to Fig. 26. Note that in Fig. 26, components common to the fixing device 20 shown in Fig. 2 are denoted by the same reference numerals and description thereof will be omitted.

[0123] A fixing device 83 shown in FIG. 26 includes a fixing belt 21, a pressure roller 22, a heater 23, a heat transfer assistance member 24, a heater holder 25, a stay 26, a temperature sensor 39, and the like.

[0124] 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.

[0125] The fixing belt 21 has a polyimide base and a release layer, and does not have an elastic layer. The release layer is made of a heat-resistant film material such as fluororesin. The outer diameter of the fixing belt 21 is about 24 mm.

[0126] 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.

[0127] 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.

[0128] A heat transfer assistant member 24 made of a highly heat conductive material is disposed so as to be in contact with the surface of the heater 23 opposite to the surface that contacts the inner circumferential surface of the fixing belt 21. The heater 23 and the heat transfer assistant member 24 are held by a heater holder 25. The heater holder 25 is supported by a stay 26.

[0129] The temperature sensor 39 is a temperature detection means for detecting the temperature of the heater 23. The temperature sensor 39 is disposed so as to come into contact with the heater 23 through a hole 24a provided in the heat transfer assistance member 24.

[0130] In this way, the temperature sensor 39 is disposed so as to be in direct contact with the heater 23 through the hole 24a of the heat transfer assistant member 24, and so there is a risk that the responsiveness of the temperature sensor 39 may decrease if the temperature sensor 39 comes into direct contact with the heat transfer assistant member 24. Therefore, in this case as well, it is preferable to interpose a contact prevention member 40 between the temperature sensor 39 and the heat transfer assistant member 24 to ensure good responsiveness of the temperature sensor 39.

[0131] As shown in FIG. 27, the conductor layer of the heater 23 includes a plurality of resistance heating elements 51, a power supply line 54, and electrode portions 53A to 53C. The plurality of resistance heating elements 51 are arranged at intervals in the longitudinal direction X of the heater 23. Here, if the portions between the resistance heating elements 51 are referred to as "division regions", then, as shown in the enlarged view of FIG. 27, division regions B are formed between the resistance heating elements 51 (although the division regions B are illustrated only in the enlarged view range in FIG. 27, division regions B are actually provided between all the resistance heating elements 51). In FIG. 27, the arrow Y direction is the short-side direction of the heater 23, and is also the same as the direction intersecting the arrangement direction of the plurality of resistance heating elements 51 (arrangement intersecting direction) or the conveyance direction of the paper passed through the fixing device.

[0132] In addition, the resistance heating elements 51 form a central heating section 60B and heating sections 60A and 60C at both ends that can generate heat independently of the central heating section 60B. For example, when the electrode section 53A at the left end of the three electrode sections 53A to 53C in FIG. 27 and the central electrode section 53B are energized, the heating sections 60A and 60C at both ends generate heat. When the electrode sections 53A and 53C at both ends are energized, the central heating section 60B generates heat. For example, when fixing small-sized paper, only the central heating section 60B generates heat, and when fixing large-sized paper, all of the heating sections 60A to 60C generate heat, allowing heating according to the size of the paper.

[0133] As shown in FIG. 28, the heater holder 25 has a recess 25a that accommodates and holds the heater 23 and the heat transfer auxiliary member 24. The recess 25a is formed on the heater 23 side of the heater holder 25. The recess 25a is composed of a bottom surface 25f formed in a rectangle (rectangle) of approximately the same size as the heater 23, and four side surfaces 25g, 25h, 25i, and 25j that are provided so as to intersect with the bottom surface 25f along four sides that form the outline of the bottom surface 25f. In FIG. 28, the right side surface 25j is omitted. In addition, one of the pair of (left and right) side surfaces 25g and 25j that intersect with the longitudinal direction X of the heater 23 (arrangement direction of the resistance heating element 51) may be omitted, and the recess 25a may be opened at one end side of the longitudinal direction of the heater 23.

[0134] 29, the heater holder 25 that holds the heater 23 and the heat transfer assistance member 24 is held by a connector 86. The connector 86 has a housing made of resin (for example, LCP) and a plurality of contact terminals provided in the housing.

[0135] The connector 86 is attached to the heater holder 25 in a direction intersecting the longitudinal direction X of the heater 23 (the arrangement direction of the resistance heating elements 51) (see the direction of the arrow extending from the connector 86 in FIG. 29). With the connector 86 attached, the heater 23, the heat transfer assistance member 24, and the heater holder 25 are held by being sandwiched between the front and back sides by the connector 86. In this state, each contact terminal is brought into contact (pressed) with each electrode portion of the heater 23, so that each resistance heating element 51 is electrically connected to a power source provided in the image forming apparatus via the connector 86. This makes it possible to supply power from the power source to each resistance heating element 51.

[0136] 29 are belt holding members provided at both longitudinal ends of fixing belt 21 and holding both ends of fixing belt 21 from the inside. Flanges 87 are inserted into both ends of stay 26 and fixed to a pair of side plates that are frame members of the fixing device.

[0137] FIG. 30 is a diagram showing the arrangement of the temperature sensor 39 shown in FIG.

[0138] 30, the temperature sensor 39 includes a thermistor 27 for temperature control and a thermostat 28 for preventing excessive temperature rise. Two thermistors 27 are arranged on one end side of the longitudinal center Xm of the fixing belt 21. Meanwhile, two thermostats 28 are arranged on the other end side of the longitudinal center Xm of the fixing belt 21.

[0139] 30 and 31, a flange 87 that holds both ends of the fixing belt 21 is provided with a slide groove 87a. The slide groove 87a extends in the direction in which the fixing belt 21 approaches and separates from the pressure roller 22. An engagement portion of the housing of the fixing device engages with the slide groove 87a. The engagement portion moves relatively within the slide groove 87a, so that the fixing belt 21 can move in the direction in which the fixing belt 21 approaches and separates from the pressure roller 22.

[0140] The range in which the heat transfer assistant member 24 is arranged is not limited to the entire heat generating region in the longitudinal direction X of the heater 23. For example, as shown in the example of FIG. 32, the heat transfer assistant member 24 may be arranged only in the divided region B between the resistance heating elements 51. In FIG. 32, the divided region B and the heat transfer assistant member 24 are shifted in the vertical direction of the figure for convenience, but they are arranged at approximately the same position in the short-side direction Y of the heater 23. The heat transfer assistant member 24 may be arranged over a part of the divided region B in the short-side direction Y of the heater 23, or over the entire divided region B in the short-side direction Y of the heater 23. Furthermore, as shown in FIG. 33, the heat transfer assistant member 24 may be arranged across the resistance heating elements 51 on both sides of the divided region B in addition to the divided region B between the resistance heating elements 51. That is, the heat transfer assistant member 24 may be arranged so as to overlap at least a part of the resistance heating elements 51 on both sides of the divided region B. Moreover, the heat transfer assistance members 24 may be disposed in all divided regions B of the heater 23, or may be disposed in only some of the divided regions B as in the example shown in FIG.

[0141] By disposing the heat transfer assistant member 24 in the divided region B of the heater 23, the heat transfer efficiency in the divided region B where the amount of heat generation is small can be improved, and the temperature drop in the divided region B can be suppressed. This can suppress temperature unevenness in the longitudinal direction of the heater 23, and can suppress temperature unevenness in the longitudinal direction of the fixing belt 21. As a result, it is possible to suppress uneven fixing and glossiness of the image fixed on the paper. Also, in order to ensure sufficient fixing performance in the divided region B, it is not necessary to increase the amount of heat generated by the heater 23, and energy saving of the fixing device can be realized. In particular, when the heat transfer assistant member 24 is disposed over the entire heat generation region where the resistance heating element 51 is disposed, the heat transfer efficiency of the heater 23 can be improved over the entire main heating region by the heater 23 (i.e., the image forming region of the paper to be passed) and temperature unevenness in the longitudinal direction of the heater 23 and the fixing belt 21 can be suppressed.

[0142] Furthermore, by combining the heat transfer assistant member 24 with the resistance heating element 51 having the PTC characteristic, it becomes possible to more effectively suppress excessive temperature rise in the non-passage area where paper does not pass. The PTC characteristic is a characteristic in which the resistance value increases as the temperature increases (when a constant voltage is applied, the heater output decreases). In other words, since the resistance heating element 51 has the PTC characteristic, the amount of heat generated by the resistance heating element 51 in the non-passage area can be effectively suppressed, and the heat amount in the non-passage area can be dispersed by the heat transfer assistant member 24, so that the synergistic effect of these can effectively suppress excessive temperature rise in the non-passage area.

[0143] In addition, since the temperature of the heater 23 tends to be low not only in the divided region B but also in its surroundings, the heat transfer assistance member 24 may be arranged in the enlarged divided region C including the divided region B and its surroundings shown in Fig. 34. This improves the heat transfer efficiency in the enlarged divided region C including the divided region B, and more effectively suppresses temperature unevenness in the longitudinal direction X of the heater 23.

[0144] Next, still another fixing device to which the present invention can be applied will be described.

[0145] In the fixing device 70 shown in Fig. 35, the heat transfer assistant member 24 is composed of two layers of heat transfer assistant members 48, 49. That is, a first heat transfer assistant member 48 in contact with the heater 23 and a second heat transfer assistant member 49 in contact with the first heat transfer assistant member 48 are provided. Note that, in the example shown in Fig. 35, a thermostat in contact with the heater 23 is also provided, but Fig. 35 shows a cross section in which the thermostat is not disposed.

[0146] The second heat transfer assistant member 49 is made of a material having a higher thermal conductivity than the base material 50 of the heater 23, such as graphene or graphite. One example is a graphite sheet having a thickness of 1 mm. The second heat transfer assistant member 49 may also be made of a plate material such as aluminum, copper, or silver.

[0147] 36, a plurality of second heat transfer assistant members 49 are arranged in the recess 25a of the heater holder 25. A gap is provided between each of the second heat transfer assistant members 49 in the longitudinal direction X of the heater 23. A recess that is one step deeper than other portions is formed in the portion of the heater holder 25 where the second heat transfer assistant members 49 are provided.

[0148] 37, the second heat transfer assistant member 49 (see hatched portion) is arranged so as to overlap at least a portion of each resistance heating element 51 on either side of the divided region B in the longitudinal direction X of the heater 23. Meanwhile, the first heat transfer assistant member 48 is arranged over the entire heat generating region in which all the resistance heating elements 51 are arranged. However, the arrangement range of the first heat transfer assistant member 48 and the second heat transfer assistant member 49 is not limited to this.

[0149] The second heat transfer auxiliary member 49 is arranged so as to overlap at least a part of each of the resistance heating elements 51 sandwiching the divided region B, thereby further improving the heat transfer efficiency in the divided region B and more effectively suppressing the temperature unevenness in the longitudinal direction X of the heater 23. Also, as shown in FIG. 38, the first heat transfer auxiliary member 48 and the second heat transfer auxiliary member 49 may be arranged only in a range overlapping the entire divided region B. In this case, the heat transfer efficiency in the divided region B can be improved in particular. In FIG. 38, the divided region B and the first heat transfer auxiliary member 48 and the second heat transfer auxiliary member 49 are shifted in the vertical direction of the figure for convenience, but they are arranged at approximately the same position in the short-side direction Y of the heater 23. However, this is not limited thereto, and the first heat transfer auxiliary member 48 and the second heat transfer auxiliary member 49 may be arranged over a part of the divided region B in the short-side direction Y of the heater 23, or may be arranged over the entire divided region B in the short-side direction Y of the heater 23.

[0150] In addition, both the first heat transfer assistant member 48 and the second heat transfer assistant member 49 may be made of graphene sheets. In this case, the first heat transfer assistant member 48 and the second heat transfer assistant member 49 can be formed with high thermal conductivity in a predetermined direction along the graphene surface, that is, in the longitudinal direction rather than in the thickness direction, so that temperature unevenness in the heater 23 and the fixing belt 21 in the longitudinal direction can be effectively suppressed.

[0151] Graphene is a flaky powder. Graphene consists of a planar hexagonal lattice structure of carbon atoms, as shown in FIG. 41. A graphene sheet is a sheet of graphene, usually a single layer. A graphene sheet may contain impurities in a single layer of carbon, or may have a fullerene structure. A fullerene structure is generally recognized as a compound in which the same number of carbon atoms form a polycyclic ring in which five-membered and six-membered rings are condensed into a cage shape, such as C60, C70 and C80 fullerenes or other closed cage structures with three-coordinate carbon atoms.

[0152] Graphene sheets are man-made and can be made, for example, by chemical vapor deposition (CVD) methods.

[0153] 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 below, may be measured, for example, by a transmission electron microscope (TEM).

[0154] Moreover, graphite, which is a multi-layered graphene, has a large thermal conductivity anisotropy. As shown in FIG. 42, graphite has a layer in which the condensed six-membered ring layer plane of carbon atoms spreads in a planar shape, and has a crystal structure in which these layers are stacked on top of each other. In this crystal structure, adjacent carbon atoms in a layer form a covalent bond, and carbon atoms between layers form a van der Waals bond. The covalent bond has a larger bond strength than the van der Waals bond, and has a large anisotropy between the bond within the layer and the bond between the layers. In other words, by forming the heat transfer assistant member 24 including the first heat transfer assistant member 48 and the second heat transfer assistant member 49 from graphite, the heat transfer efficiency in the longitudinal direction of the heat transfer assistant member 24 is larger than that in the thickness direction (i.e., the stacking direction of the members), and the heat transfer to the heater holder 25 can be suppressed. Therefore, the temperature unevenness in the longitudinal direction X of the heater 23 can be efficiently suppressed, and the heat flowing out to the heater holder 25 can be minimized. Furthermore, by forming the heat transfer assistance member 24 from graphite, the heat transfer assistance member 24 can have excellent heat resistance that prevents oxidation up to approximately 700 degrees.

[0155] The physical properties and dimensions of the graphite sheet can be appropriately changed depending on the functions required of the heat transfer assistant member 24. For example, the anisotropy of the heat conduction can be increased by using high-purity graphite or single crystal graphite, or by increasing the thickness of the graphite sheet. Also, in order to increase the speed of the fixing device, a graphite sheet with a small thickness may be used to reduce the heat capacity of the fixing device. Also, when the widths of the nip portion N and the heater 23 are large, the longitudinal width of the heat transfer assistant member 24 may be increased accordingly.

[0156] From the viewpoint of increasing mechanical strength, the number of layers of the graphite sheet is preferably equal to or greater than 11. The graphite sheet may partially include a single layer portion and a multilayer portion.

[0157] Furthermore, the second heat transfer assistant member 49 may be provided at a position overlapping at least a part of the divided region B and each of the resistance heating elements 51 on both sides thereof in the longitudinal direction X of the heater 23, and is not limited to the arrangement shown in Fig. 38. For example, as in the example shown in Fig. 39, the second heat transfer assistant member 49 may be provided protruding from the base material 50 of the heater 23 to both sides in the lateral direction Y of the heater 23. The second heat transfer assistant member 49 may be provided in a range where the resistance heating elements 51 are provided in the lateral direction Y of the heater 23. The second heat transfer assistant member 49 may be provided in a part of the divided region B.

[0158] Also, as shown in the example in FIG. 40, a gap 38 may be provided between the first heat transfer auxiliary member 48 and the heater holder 25 in the thickness direction (left-right direction in FIG. 40). That is, the gap 38 is provided as a heat insulating layer in a part of the region of the recess 25a (see FIG. 36) of the heater holder 25 where the heater 23, the first heat transfer auxiliary member 48, and the second heat transfer auxiliary member 49 are arranged. The gap 38 is provided in a part of the region other than the part where the second heat transfer auxiliary member 49 (not shown in FIG. 40) is provided. Also, the gap 38 is formed by making the depth of the recess 25a of the heater holder 25 deeper than the other parts. This can reduce the contact area between the heater holder 25 and the first heat transfer auxiliary member 48, suppressing heat transfer from the first heat transfer auxiliary member 48 to the heater holder 25, and enabling efficient heating of the fixing belt 21. At the location where the second heat transfer assistant member 49 is provided, the second heat transfer assistant member 49 is held in contact with the bottom surface of the recess 25a of the heater holder 25 as shown in FIG.

[0159] Furthermore, the gap 38 is provided over the entire area in which the resistance heating element 51 is provided in the short-side direction Y of the heater 23 (the vertical direction in FIG. 40). This effectively suppresses heat transfer from the first heat transfer assistance member 48 to the heater holder 25, improving the heating efficiency of the fixing belt 21 by the heater 23. Note that a configuration in which a heat insulating member having a lower thermal conductivity than the heater holder 25 is provided in the gap 38 may also be used.

[0160] In addition, the first heat transfer assistant member 48 and the second heat transfer assistant member 49 are not limited to being formed separately from each other, and may be integrated. That is, the first heat transfer assistant member 48 may also function as the second heat transfer assistant member 49 by forming the portion corresponding to the divided region B of the first heat transfer assistant member 48 thicker than the other portions.

[0161] The configurations of the fixing device and image forming apparatus to which the present invention can be applied have been described above, but by applying the present invention to such a fixing device and image forming apparatus, the same effects as those of the above embodiment can be obtained. That is, by applying the present invention, it becomes possible to prevent direct contact between the thermostat and the mating members arranged around it, and therefore it becomes possible to ensure good responsiveness of the thermostat.

[0162] The present invention is not limited to being applied to a fixing device, which is an example of a heating device, but can also be applied to heating devices other than fixing devices. For example, the present invention 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.

[0163] To summarize the above-described aspects of the present invention, the present invention includes at least the following aspects.

[0164] [First aspect] The first aspect is a heating device comprising: a rotating body; a heater in contact with the inner surface of the rotating body and heating the rotating body; a heat transfer auxiliary member in contact with the surface of the heater opposite the rotating body contact surface that contacts the inner surface of the rotating body; a thermostat in contact with the surface of the heater opposite the rotating body contact surface and detecting the temperature of the heater; and a contact prevention member in contact with at least one of the thermostat and the heat transfer auxiliary member to prevent direct contact between the thermostat and the heat transfer auxiliary member.

[0165] [Second aspect] In a second aspect, in the first aspect, the contact prevention member is disposed between the thermostat and the heat transfer assistance member, and is a low thermal conductive member having a lower thermal conductivity than the portion of the thermostat that contacts the heater.

[0166] [Third aspect] A third aspect is the second aspect, wherein the low thermal conductive member is a heat resistant resin.

[0167] [Fourth aspect] A fourth aspect is any one of the first to third aspects, wherein the contact prevention member is attached to the thermostat.

[0168] [Fifth aspect] A fifth aspect is any one of the first to third aspects, wherein the contact prevention member is attached to the heat transfer assistance member.

[0169] [Sixth aspect] A sixth aspect is any one of the first to fifth aspects, in which, when a direction perpendicular to the longitudinal direction of the heater along the rotating body contact surface of the heater is defined as a short direction, the contact prevention member is positioned at least between the thermostat and the heat transfer auxiliary member in the short direction of the heater.

[0170] [Seventh aspect] A seventh aspect is the first aspect, wherein the contact prevention member is a heater holder that holds the heater and the heat transfer assistance member.

[0171] [Eighth aspect] In an eighth aspect, in the seventh aspect, the heat transfer assistance member is positioned on the holder so as to be located farther away from the thermostat than the heater holder.

[0172] [Ninth aspect] In a ninth aspect, in the seventh or eighth aspect, when a direction perpendicular to the longitudinal direction of the heater along the rotating body contact surface of the heater is defined as a short side direction, the heater holder has a regulating portion that at least regulates movement of the heat transfer assistance member in the short side direction of the heater.

[0173] [Tenth aspect] A tenth aspect is any one of the seventh to ninth aspects, wherein the thermostat is positioned in the heater holder so as not to be close to the heat transfer assistance member.

[0174] [Eleventh aspect] An eleventh aspect is the electronic device according to the first aspect, wherein the contact prevention member is a sensor holder that holds the thermostat.

[0175] [Twelfth aspect] A twelfth aspect is any one of the first to eleventh aspects, wherein the heater has a plurality of heating elements arranged in a longitudinal direction of the heater.

[0176] [Thirteenth aspect] A thirteenth aspect is any one of the first to twelfth aspects, in which the rotating body does not have an elastic layer.

[0177] [14th aspect] A fourteenth aspect is a fixing device that fixes an unfixed image onto a sheet using the heating device according to any one of the first to thirteenth aspects.

[0178] [Fifteenth aspect] A fifteenth aspect is an image forming apparatus including the heating device according to any one of the first to thirteenth aspects or the fixing device according to the fourteenth aspect. [Explanation of symbols]

[0179] 20 Fixing device (heating device) 21 Fixing belt (first rotating body) 22 Pressure roller (second rotating body) 23 Heater 23a Rotating body contact surface 23b Surface opposite to the surface in contact with the rotating body 24 Heat transfer auxiliary material 25 Heater holder 25d Regulatory Department 28 Thermostat (temperature sensor) 35 Sensor holder 51 Resistance heating element 1000 Image forming device P Paper (sheet) X Longitudinal direction Y Short side [Prior art documents] [Patent documents]

[0180] [Patent Document 1] JP 2019-90938 A

Claims

1. A rotating body; a heater that contacts an inner circumferential surface of the rotor and heats the rotor; a heat transfer assistance member that contacts a surface of the heater opposite to a rotor contact surface that contacts the inner circumferential surface of the rotor; a thermostat that contacts a surface of the heater opposite to the surface that contacts the rotor and detects a temperature of the heater; A heating device comprising: a contact prevention member that contacts at least one of said thermostat and said heat transfer assistance member to prevent said thermostat and said heat transfer assistance member from coming into direct contact with each other.

2. 2. The heating device according to claim 1, wherein the contact prevention member is disposed between the thermostat and the heat transfer assistance member, and is a low thermal conductive member having a thermal conductivity lower than that of a portion of the thermostat that contacts the heater.

3. 3. The heating device according to claim 2, wherein the low thermal conductive member is a heat resistant resin.

4. The heating device according to claim 1 , wherein the contact prevention member is attached to the thermostat.

5. The heating device according to claim 1 , wherein the contact prevention member is attached to the heat transfer assistance member.

6. If a direction perpendicular to the longitudinal direction of the heater along the rotor contact surface of the heater is defined as a short direction, The heating device according to claim 1 , wherein the contact prevention member is disposed at least between the thermostat and the heat transfer assistance member in the short-side direction of the heater.

7. 2. The heating device according to claim 1, wherein the contact prevention member is a heater holder that holds the heater and the heat transfer assistance member.

8. The heating device according to claim 7 , wherein the heat transfer assistance member is positioned on the holder so as to be located farther from the thermostat than the heater holder.

9. If a direction perpendicular to the longitudinal direction of the heater along the rotor contact surface of the heater is defined as a short direction, The heating device according to claim 7 , wherein the heater holder has a restricting portion that restricts at least a movement of the heat transfer assistance member in a short-side direction of the heater.

10. 8. The heating device according to claim 7, wherein the thermostat is positioned in the heater holder so as not to be in close proximity to the heat transfer auxiliary member.

11. The heating device according to claim 1 , wherein the contact prevention member is a sensor holder that holds the thermostat.

12. The heating device according to claim 1 , wherein the heater has a plurality of heating elements arranged in a longitudinal direction of the heater.

13. The heating device according to claim 1 , wherein the rotating body does not have an elastic layer.

14. A fixing device, comprising: a heating device according to claim 1, for fixing an unfixed image onto a sheet.

15. An image forming apparatus comprising the heating device according to claim 1 .

Images