Heating member, fixing device, and image forming apparatus

Abstract

A heating member includes two electrode portions; and a planar heating element electrically connected to the electrode portions. The heating element extends in a first direction or a plurality of the heating elements are arranged side by side and extend in the first direction to constitute the longitudinal heating portion. The heating portion has a center portion in the first direction and an end portion on at least one end side in the first direction. A width of the end portion in a second direction is larger than a width of the center portion in the second direction when a direction orthogonal to the first direction along a surface of the heating element is the second direction. There is no portion having a width smaller than the width of the center portion in the second direction between the center portion and the end portion.

Description

HEATING MEMBER, FIXING DEVICE, AND IMAGE FORMING APPARATUS

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

[0002] An electrophotographic image forming apparatus for transferring a toner image formed on the surface of a photoconductor to a recording medium such as a paper sheet is known as an image forming apparatus such as a copying machine or a printer.

[0003] Generally, an electrophotographic image forming apparatus is equipped with a fixing device for fixing, to a recording medium, a toner image that has been transferred to the recording medium.

[0004] The fixing device includes, for example, a pair of rotating bodies such as a roller or a belt, and a heating member for heating at least one of the two rotating bodies. When the rotating bodies are heated by the heating member and a recording medium carrying an unfixed image (toner image) enters a space (nip portion) between the rotating bodies in a state where the temperature of the rotating bodies rises to a predetermined temperature, the unfixed image is heated and pressurized together with the recording medium to be fixed to the recording medium.

[0005] Further, the heating member provided in such a fixing device includes a “single-type” heating member in which the heat generation portions are integrally controlled, and a “dual type” heating member in which a plurality of heat generation portions are independently controlled.

[0006] The single-type heating member has an advantage that the temperature control can be implemented with a simple configuration as compared with the dual type heating member. However, in the single-type heating member, because the heat generation amount cannot be partially adjusted, there is a problem that the temperature of a part of the heating member becomes relatively high or low. For example, in a region outside the region through which the recording medium passes, the temperature tends to rise because heat is not easily consumed by the recording medium, and on the other hand, in the end side of the image passing region through which the image on the recording medium passes, the temperature tends to drop more than in the center side.

[0007] In response to this problem, Patent Literature 1 (Japanese Unexamined Patent Application Publication No. 2021-89330) proposes an invention in which the electric resistance value of the heating portion is changed for each portion by varying the width of the heating portion to adjust the amount of heat generated. For example, in a portion where the temperature tends to drop, that is, in the end side portion of the image passing region, by making the width of the heating portion narrower than that in the center side portion, the amount of heat generated in the end side portion of the image passing region can be increased and the temperature drop can be suppressed.

[0008] However, if the amount of heat generated in the end side portion of the heating portion is made larger than that in the center side portion, when a recording medium having a size that makes the end side portion become a recording medium sheet non-passing region is allowed to pass, the heat generated in the end side portion is not consumed and the temperature may rise excessively.

[0009] Japanese Unexamined Patent Application Publication No. 2021-89330

[0010] It is therefore an object of the present invention to propose a configuration of a single-type heating member capable of suppressing both local temperature rise and temperature drop.

[0011] According to an aspect of the present invention, there is provided a heating member including two electrode portions; and a planar heating element electrically connected to the two electrode portions, wherein the heating element extends in a first direction or a plurality of the heating elements are arranged side by side and extend in the first direction to constitute the longitudinal heating portion, the heating portion has a center portion including a center in the first direction and an end portion positioned on at least one end side in the first direction with respect to the center portion, a width of the end portion in a second direction is larger than a width of the center portion in the second direction when a direction orthogonal to the first direction along a surface of the heating element is the second direction, and there is no portion having a width smaller than the width of the center portion in the second direction between the center portion and the end portion.

[0012] According to an embodiment of the present invention, both local temperature rise and temperature drop can be suppressed in a single-type heating device.

[0013] FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention.FIG. 2 is a schematic configuration diagram of a fixing device according to a first embodiment of the present invention.FIG. 3 is a plan view of a heating member according to a first embodiment of the present invention.FIG. 4 is an exploded perspective view of a heating member according to a first embodiment of the present invention.FIG. 5 is a perspective view illustrating a state in which a connector is connected to a heating member according to a first embodiment of the present invention.FIG. 6 is a diagram illustrating a configuration of a control system for controlling the temperature of a heating member according to a first embodiment of the present invention.FIG. 7 is a plan view illustrating, in a heating member according to a first embodiment of the present invention, a direction in which the two heating portions extend as a first direction, and a direction perpendicular to the first direction X along the surface of the heating element as a second direction.FIG. 8 is a plan view illustrating a positional relationship of the heating portions with respect to a sheet-passing region and an image-passing region when a heating member according to a first embodiment of the present invention is mounted in a fixing device and a sheet of a specific width size is passed through the fixing device.FIG. 9 is a diagram comparing a temperature distribution in a sheet width direction of a fixing belt according to a first embodiment of the present invention and a conventional example.FIG. 10 is a diagram comparing a temperature distribution in a sheet passing direction of a fixing belt according to a first embodiment of the present invention and a conventional example.FIG. 11A is a plan view illustrating a relationship between the heating portion and an inner nip when the width of the end portion is as illustrated in FIG. 11A.FIG. 11B is a plan view illustrating a relationship between the heating portion and an inner nip when the width of the end portion is as illustrated in FIG. 11B.FIG. 12 is a plan view of a heating member according to the second embodiment of the present invention.FIG. 13 is a plan view of a heating member according to the third embodiment of the present invention.FIG. 14 is a plan view of a heating member according to the fourth embodiment of the present invention.FIG. 15 is a plan view of a heating member according to the fifth embodiment of the present invention.FIG. 16 is a plan view illustrating an example of a heating portion constituted by a plurality of heating elements arranged in a longitudinal direction.FIG. 17 is a diagram illustrating the configuration of another fixing device to which the present invention is applicable.FIG. 18 is a diagram illustrating the configuration of another fixing device to which the present invention is applicable.FIG. 19 is a diagram illustrating the configuration of yet another fixing device to which the present invention is applicable.FIG. 20 is a plan view of a conventional heating member.FIG. 21 is a plan view of the heating member described in Patent Literature 1.FIG. 22 is a plan view for explaining problems in the heating member described in Patent Literature 1.

[0014] Hereinafter, the present invention will be described with reference to the accompanying drawings. In each of the drawings for explaining the present invention, elements such as members and components having the same function or shape are denoted by the same reference numerals as far as possible to distinguish them, and the description thereof will be omitted after the description has been made. <First embodiment of the Present Invention> <Configuration of Image Forming Apparatus>

[0015] FIG. 1 is a schematic configuration diagram of an image forming apparatus 1000 according to a first embodiment of the present invention.

[0016] First, the configuration of an image forming apparatus 1000 according to a first embodiment of the present invention will be described with reference to FIG. 1. Incidentally, “image forming apparatus” in the present specification includes a printer, a copying machine, a facsimile machine, a printing machine, or a multifunction peripheral in which two or more of these are combined. Further, “image forming” as used in the following description means not only forming images having meanings such as characters and graphics, but also forming images having no meanings such as patterns.

[0017] As illustrated in FIG. 1, the image forming apparatus 1000 according to a first embodiment of the present invention includes an image forming unit 100, a fixing unit 200, a sheet supplying unit 300, and a sheet discharging unit 400. (Image Forming Unit)

[0018] The image forming unit 100 is provided with four image forming units 1Y, 1M, 1C, and 1Bk detachable from the main body of the image forming apparatus, an exposure device 6, and a transfer device 8.

[0019] The four image forming units 1Y, 1M, 1C, and 1Bk have basically the same configuration except that developers (toners) of different colors such as yellow, magenta, cyan, and black are contained therein. Specifically, each of the image forming units 1Y, 1M, 1C, and 1Bk includes a photoconductor 2, a charging member 3, a developing device 4, a cleaning member 5, and the like.

[0020] The photoconductor 2 is an example of a latent image carrier or an image carrier that carries a latent image or a toner image on its surface (outer peripheral surface). The photoconductor 2 may be an endless belt member other than a drum-shaped member as illustrated in FIG. 1.

[0021] The charging member 3 is a conductive or semiconductive member that uniformly charges the surface of the photoconductor 2 by applying a voltage thereto. The charging member 3 may be a charging roller as illustrated in FIG. 1, another contact type charging member such as a magnetic brush, a fur brush, a film, a rubber blade, or a non-contact type charging member using corona discharge.

[0022] The developing device 4 supplies a developer to the photoconductor 2. In this case, the developing device 4 accommodates a developer (toner) of a different color for each of the plurality of image forming units 1Y, 1M, 1C, and 1Bk, and supplies a developer of a different color for each of the photoconductors 2.

[0023] The cleaning member 5 comes into contact with the surface of the photoconductor 2 and removes toner and other foreign matter remaining on the photoconductor 2. The cleaning member 5 may be, other than a cleaning blade as illustrated in FIG. 1, a brush roller rotating while coming into contact with the surface of the photoconductor 2.

[0024] The exposure device 6 is an example of a latent image forming apparatus for forming a latent image on the surface of the photoconductor 2. The exposure device 6 includes an optical system 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.

[0025] The transfer device 8 is a device for transferring an image from the photoconductor 2 to a sheet serving as a recording medium. Here, “sheet” is described as “paper”, but the “sheet” may be, in addition to paper, an OHP sheet, a cloth, a metal sheet, a plastic film, or a prepreg sheet in which a carbon fiber is impregnated with a resin in advance. The “paper” includes, in addition to plain paper, thick paper, postcards, envelopes, thin paper, coated paper (art paper, etc.), tracing paper, and the like.

[0026] The transfer device 8 includes an intermediate transfer belt 11, a primary transfer roller 12, a secondary transfer roller 13, and the like. The intermediate transfer belt 11 is an endless belt member which is wound around and supported by a plurality of rollers including the primary transfer roller 12. At least one roller among the plurality of rollers supporting the intermediate transfer belt 11 functions as a driving roller, whereby the intermediate transfer belt 11 is rotated and driven in the direction of the arrow in FIG. 1. The belt member constituting the intermediate transfer belt 11 may be a single-layer structure or a multilayer structure. In the case of the multilayer structure, it is preferable that a base layer made of a fluororesin having little elongation, PVDF (polyvinylidene fluoride), or a polyimide resin is coated with a coat layer made of a material having good smoothness such as a fluororesin. In the case of the single-layer structure, it is preferable that a belt member made of PVDF (polyvinylidene fluoride), PC (polycarbonate), or polyimide is used.

[0027] Four primary transfer rollers 12 are provided inside the intermediate transfer belt 11 and are arranged to face the respective photoconductors 2 through the intermediate transfer belt 11. Each primary transfer roller 12 contacts the inner peripheral surface of the intermediate transfer belt 11 at a position facing the photoconductors 2, and forms a primary transfer nip between the intermediate transfer belt 11 and each photoconductor 2. Each of the primary transfer rollers 12 is not limited to a position facing a corresponding photoconductor 2 via the intermediate transfer belt 11, but may be arranged at a position offset by a predetermined distance from a contact position (primary transfer nip) between each of the photoconductors 2 and the intermediate transfer belt 11 toward the downstream side in the surface moving direction (rotational direction) of the intermediate transfer belt 11.

[0028] The secondary transfer roller 13 is arranged so as to face one of a plurality of rollers for supporting the intermediate transfer belt 11. When the secondary transfer roller 13 contacts the opposing roller via the intermediate transfer belt 11, a secondary transfer nip is formed between the secondary transfer roller 13 and the intermediate transfer belt 11. (Fixing Unit)

[0029] A fixing device 20 for fixing an image to a sheet is arranged in the fixing unit 200. The fixing device 20 includes a fixing belt 21 as a first rotating body, a pressure roller 22 as a second rotating body for forming a nip by contacting the outer peripheral surface of the fixing belt 21, and the like. (Sheet supplying unit)

[0030] The sheet supplying unit 300 is provided with a sheet feed cassette 14 for storing the sheet P, a sheet feed roller 15 for feeding the sheet P from the sheet feed cassette 14, and the like. (Sheet discharging unit)

[0031] On the other hand, the sheet discharging unit 400 is provided with a pair of sheet discharge rollers 17 for discharging the sheet, a sheet discharge tray 18 for placing the discharged sheet, and the like. <Image forming operation>

[0032] Next, an image forming operation of the image forming apparatus 1000 according to the first embodiment of the present invention will be described with reference to FIG. 1.

[0033] When the image forming operation is started, first, the photoconductors 2 in each of the image forming units 1Y, 1M, 1C, and 1Bk rotate in the direction of an arrow in FIG. 1, and the surfaces of the photoconductors 2 are charged to a uniform high potential by the charging member 3. Then, the exposure device 6 irradiates the surfaces (charging surfaces) of the photoconductors 2 with a laser beam and exposes them based on the image information of the original document read by the original document reading apparatus or image information instructing to print from an external terminal. Accordingly, the potential of the exposed portion is lowered, and a latent image (electrostatic latent image) is formed on the surface of each photoconductor 2. Thereafter, toner is supplied from each developing device 4 to each photoconductor 2, whereby a toner image of each color is formed on each photoconductor 2.

[0034] The toner image formed on each photoconductor 2 reaches the primary transfer nip (position of the primary transfer roller 12) as the photoconductor 2 rotates, and is transferred to the intermediate transfer belt 11 in the primary transfer nip. At this time, the toner image on each photoconductor 2 is sequentially transferred to the intermediate transfer belt 11 which rotates synchronously with each photoconductor 2, thereby forming a full-color image in which the toner images of each color are overlapped. Note that image formation is not limited to the case of forming a full-color image, and a monochromatic image may be formed by using any one of the four image forming units 1Y, 1M, 1C, and 1Bk, or a two-color image or a three-color image may be formed by using any two or three image forming units. After the toner image is transferred to the intermediate transfer belt 11, the surface of the photoconductor 2 is cleaned by the cleaning member 5, and foreign matter such as residual toner is removed from the surface of each photoconductor 2.

[0035] The toner image transferred to the intermediate transfer belt 11 reaches the secondary transfer nip (the position of the secondary transfer roller 13) as the intermediate transfer belt 11 rotates, and is transferred to a sheet in the secondary transfer nip. The sheet P is supplied from the sheet supplying unit 300. More specifically, when the sheet P is passed from the sheet feed cassette 14 by the rotation of the sheet feed roller 15, the sheet P abuts against the pair of timing rollers 16 on the way to the secondary transfer nip, and the feeding is temporarily stopped. Thereafter, the pair of timing rollers 16 rotates at a predetermined timing, and the sheet P is passed to the secondary transfer nip in synchronization with the timing of the toner image on the intermediate transfer belt 11.

[0036] The sheet on which the toner image is transferred is passed to the fixing unit 200, and passes through the nip between the fixing belt 21 and the pressure roller 22. At this time, the toner image is heated and pressed together with the sheet, and is fixed to the sheet. Then, the sheet is passed to the sheet discharging unit 400, and discharged out of the apparatus by the discharge roller 17, and placed on the discharge tray 18. As described above, a series of image forming operations is completed. <Configuration of the Fixing Device>

[0037] Next, a configuration of the fixing device 20 according to a first embodiment of the present invention will be described.

[0038] FIG. 2 is a schematic diagram of the fixing device 20 according to a first embodiment of the present invention.

[0039] As illustrated in FIG. 2, a fixing device 20 according to a first embodiment of the present invention includes a fixing belt 21, a pressure roller 22, a heating member 23, a high heat conduction member 24, a holding member 25, a support member 26, a separation member 27, a thermistor 28, and a thermostat 29.

[0040] The fixing belt 21 and the pressure roller 22 are mutually pressurized by a pressurizing means such as a spring. Accordingly, a nip portion N for passing the sheet P is formed between the fixing belt 21 and the pressure roller 22. The pressure roller 22 is rotationally driven by a driving means such as an electric motor. Therefore, when the pressure roller 22 is rotationally driven, the fixing belt 21 is driven to rotate. When the sheet P passes between the rotating pressure roller 22 and the fixing belt 21 (nip portion N), the sheet P is heated and pressurized, and an unfixed image (unfixed toner 10) is fixed to the sheet P.

[0041] The fixing belt 21 is composed of a cylindrical base material and an endless belt member having a release layer provided on the outer peripheral surface of the base material. The base material of the fixing belt 21 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-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), polyimide, polyetherimide, or PES (polyether sulfide). The fixing belt 21 having the release layer improves the separability of the toner image with respect to the fixing belt 21 and suppresses the winding of the sheet P with respect to the fixing belt 21. The fixing belt 21 may have an elastic layer between the base material and the release layer. As the material of the elastic layer, a rubber material such as silicone rubber, expandable silicone rubber or fluororubber is used. When the fixing belt 21 has an elastic layer, minute irregularities are not appreciably formed on the surface of the fixing belt 21, so that heat is easily transmitted uniformly to the toner image on the sheet P and the fixing quality is improved.

[0042] 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 formed of a metal material such as iron. As the material of the elastic layer, silicone rubber, foamable silicone rubber, fluororubber or the like is used. The material of the release layer is a fluororesin such as PFA or PTFE.

[0043] In addition to the heating member 23, a high heat conduction member 24, a holding member 25, a support member 26, a thermistor 28, and a thermostat 29 are arranged inside the fixing belt 21.

[0044] The heating member 23 is arranged at a position facing the pressure roller 22 inside the fixing belt 21. The heating member 23 is arranged so as to contact the inner peripheral surface of the fixing belt 21. Thus, the fixing belt 21 is sandwiched between the heating member 23 and the pressure roller 22, and a nip portion N is formed between the heating member 23 and the pressure roller 22. In the first embodiment of the present invention, the heating member 23 includes a plate-like base material 50, a planar heating element 51 provided on the base material 50, an insulating layer 52 covering the heating element 51, and the like. As illustrated in FIG. 2, when the heating element 51 comes into contact with the inner peripheral surface of the fixing belt 21 via the insulating layer 52, the heating element 51 generates heat, which is transmitted to the inner peripheral surface of the fixing belt 21 via the insulating layer 52. Thus, the fixing belt 21 is heated from the inner peripheral surface side. Further, when the fixing belt 21 is heated to a predetermined temperature by the heating member 23, the sheet P carrying the unfixed image (unfixed toner 10) enters the nip portion N, whereby the sheet P is heated and pressurized, and the unfixed image is fixed to the sheet P. In contrast to the first embodiment of the present invention, the heating member 23 may be inverted so that the base material 50 comes into contact with the inner peripheral surface of the fixing belt 21. In this case, because the heat of the heating element 51 is transferred to the fixing belt 21 through the base material 50, the base material 50 is preferably formed of a material having a high heat conduction.

[0045] The high heat conduction member 24 comes into contact with the surface of the heating member 23 on the side opposite to the surface coming into contact with the fixing belt 21, and moves the heat of the heating member 23 to a portion of the heating member 23 having a relatively low temperature. Therefore, the high heat conduction member 24 is formed of a material having a higher heat conduction than the holding member 25 or the like. As the material of the high heat conduction member 24, for example, copper, aluminum, or graphene is used. The high heat conduction member 24 is not limited to a single layer member, and may be formed of a plurality of layers.

[0046] The holding member 25 is a member for holding the heating member 23 and the high heat conduction member 24. In the first embodiment of the present invention, the holding member 25 has a recess 25a for accommodating the heating member 23 and the high heat conduction member 24. The holding member 25 is preferably made of a heat-resistant material because the holding member tends to become high in temperature due to heat from the heating member 23. When the holding member 25 is made of a heat-resistant resin having low heat conduction, such as LCP, unnecessary heat transfer from the heating member 23 to the holding member 25 is suppressed, so that the heating efficiency by the heating member 23 is enhanced.

[0047] The support member 26 supports the holding member 25. As illustrated in FIG. 2, the support member 26 supports the surface of the holding member 25 opposite to the side of the pressure roller 22, so that the bending of the holding member 25 due to the pressure applied by the pressure roller 22 is suppressed, and a nip portion N having a uniform width is obtained. The support member 26 is preferably made of an iron-based metal material such as SUS or SECC to ensure rigidity.

[0048] The separation member 27 is arranged downstream of the nip portion N in the sheet passing direction and separates the sheet P from the surface of the fixing belt 21. As illustrated in FIG. 2, when the leading edge of the sheet P passes through the nip portion N, the separation member 27 enters between the leading edge of the sheet P and the fixing belt 21, whereby the sheet P is separated from the surface (outer peripheral surface) of the fixing belt 21. In order to enhance the separability of the sheet P, it is preferable that the leading edge of the separation member 27 be arranged close to the outer peripheral surface of the fixing belt 21 so as not to contact with the fixing belt 21. The separation member 27 may be fixed to the frame member of the fixing device 20 or may be provided so as to be able to approach and separate from the fixing belt 21. In the first embodiment of the present invention, in order to enhance the separability of the sheet P, the edge of the recess 25a of the holding member 25 projects toward the pressure roller 22 side more than the heating member 23. Accordingly, the fixing belt 21 largely bends in accordance with the edge of the holding member 25 on the downstream side of the nip portion N in the sheet passing direction, so that the sheet P is easily separated by the bending. Further, because the edge of the recess 25a of the holding member 25 projects toward the pressure roller 22 side more than the heating member 23, the fixing belt 21 can be prevented from coming into contact with the edge of the heating member 23, so that the fixing belt 21 can be prevented from being damaged by the contact with the edge. If there is no fear of the fixing belt 21 being damaged by the contact with the edge of the heating member 23 or if the separability of the sheet P can be sufficiently secured, the heating member 23 may project toward the pressure roller 22 side more than the edge of the recess 25a of the holding member 25.

[0049] The thermistor 28 is a temperature sensor for temperature control for maintaining the heating member 23 at a predetermined temperature. On the other hand, the thermostat 29 is a temperature sensor used for preventing excessive temperature rise of the heating member 23. The thermistor 28 indirectly detects the temperature of the heating member 23 by contacting the heating member 23 through the high heat conduction member 24. On the other hand, the thermostat 29 is arranged so as to penetrate the high heat conduction member 24 and directly contact the heating member 23 in order to speed up the response. Depending on the conditions, the thermostat 29 may be arranged so as to indirectly contact the heating member 23 through the high heat conduction member 24 in the same manner as the thermistor 28. The temperature detected by the thermistor 28 is sent to a control unit described below as temperature information, and the control unit controls the heat generation of the heating member 23 based on the temperature information, thereby maintaining the temperature of the heating member 23 at a predetermined target temperature. Further, when an abnormal temperature rise of the heating member 23 is detected by the thermostat 29, the power distribution to the heating member 23 is cut off, and the heat generation of the heating member 23 is forcibly stopped. <Configuration of the Heating Member>

[0050] Next, a configuration of the heating member 23 according to a first embodiment of the present invention will be described with reference to FIGS. 3 and 4.

[0051] FIG. 3 is a plan view of the heating member 23 according to the first embodiment of the present invention, and FIG. 4 is an exploded perspective view of the heating member 23 according to the first embodiment of the present invention.

[0052] As illustrated in FIGS. 3 and 4, the heating member 23 includes a plate-like base material 50, a heating element 51, an insulating layer 52, an electrode portion 53, and a power supply line 54. The heating element 51, the electrode portion 53, and the power supply line 54 are provided on the same surface of the base material 50. In order to ensure insulation between the heating member 23 and the fixing belt 21, the entire heating element 51 and a portion of the power supply line 54 are covered with the insulating layer 52. On the other hand, the electrode portion 53 is not covered with the insulating layer 52 in order to ensure connection with a connector described below, and at least a portion thereof is exposed.

[0053] The base material 50 is formed of, for example, a nonmetallic material such as alumina or aluminum nitride having excellent heat resistance and insulation, such as ceramics, glass, mica, or the like. It is also possible to form the base material 50 of a conductive material such as a metal by interposing a separate insulating layer between the base material 50 and the heating element 51. The metal material is preferably aluminum or stainless steel because of its low cost. Further, in order to suppress temperature unevenness of the heating member 23 and improve image quality, the base material 50 may be formed of a material having high heat conduction such as copper, graphite, or graphene. Graphene is a sheet-like material formed by bonding carbon atoms.

[0054] The heating element 51 may be formed by a method such as screen printing. For example, the heating element 51 may be formed by coating the base material 50 with a paste prepared by mixing silver palladium (AgPd) and glass powder by screen printing, and then baking the base material 50. Further, as the material of the heating element 51, other than silver palladium, a resistive material such as silver alloy (AgPt) or ruthenium oxide (RuO2) may be used. The electrode portion 53 and the power supply line 54 are formed of a conductor having a resistance value lower than that of the heating element 51. For example, the electrode portion 53 and the power supply line 54 are formed by screen printing silver (Ag) or silver palladium (AgPd). As the material of the insulating layer 52, for example, heat-resistant glass is used.

[0055] As illustrated in FIGS. 3 and 4, the heating element 51 extends in the longitudinal direction (lateral direction in FIG. 3) of the base material 50 and constitutes two longitudinal heating portions 60A and 60B arranged in the lateral direction (longitudinal direction in FIG. 3) of the base material 50. The two heating portions 60A and 60B are connected to each other at one end (right end in FIG. 3) in the longitudinal direction of the base material 50 via the power supply line 54, and are connected to the two electrode portions 53 at the other end (left end in FIG. 3) in the longitudinal direction of the base material 50. That is, the respective heating portions 60A and 60B are electrically connected in series to the two electrode portions 53 via the power supply line 54. Therefore, when a voltage is applied to the respective electrode portions 53, the respective heating portions 60A and 60B constitute what is referred to as a single-type heating portion in which heat generation is controlled integrally.

[0056] FIG. 5 is a perspective view illustrating a state in which the connector 70 is connected to the heating member 23 according to the first embodiment of the present invention.

[0057] As illustrated in FIG. 5, the connector 70 has a housing 71, a contact terminal 72, and a harness 73. The harness 73 is connected to the contact terminal 72. The contact terminal 72 is made of a conductive elastic member such as a leaf spring, and has a pair of contact portions 72a which contact the two electrode portions 53.

[0058] As illustrated in FIG. 5, the connector 70 is attached so as to sandwich the heating member 23 together with the holding member 25. Accordingly, the contact portions 72a of the contact terminals 72 are brought into contact with the electrode portions 53, and the connector 70 and the heating member 23 are electrically connected. In this state, power can be supplied to the heating member 23 from a power supply or the like provided in the main body of the image forming apparatus.

[0059] FIG. 6 is a diagram illustrating the configuration of a control system for controlling the temperature of the heating member 23 according to the first embodiment of the present invention.

[0060] As illustrated in FIG. 6, the fixing device 20 according to the first embodiment of the present invention includes a control unit 7 and a TRIAC 9 (Triode for Alternating Current) as a control system for controlling the temperature of the heating member 23.

[0061] The TRIAC 9 is an energization control means for controlling the energization duty from the AC power supply 30 to the heating member 23 in accordance with an instruction from the control unit 7. The “energization duty” is a ratio of energization time to the heating member 23 per control cycle. The control unit 7 is composed of a microcomputer including a CPU, a ROM, a RAM, an I / O interface, and the like. The control unit 7 outputs a control signal for controlling the TRIAC 9 based on the temperature detected by the thermistor 28, and the TRIAC 9 controls the energization duty based on the control signal. Thus, the temperature of the heating member 23 is controlled to be a predetermined target temperature. Further, when the thermostat 29 detects an abnormal temperature rise of the heating member 23, the thermostat 29 operates to cut off the energization of the heating member 23.

[0062] In the example of FIG. 6, the thermistor 28 is arranged at the center and one end side of the heating member 23 in the longitudinal direction, and the thermostat 29 is arranged at the other end side of the heating member 23 from the center in the longitudinal direction, but the arrangement and the number of the thermistors 28 and the thermostat 29 are not limited to the example of FIG. 6. <Problems in the Heating Member>

[0063] Problems in the conventional heating member 23A will now be described with reference to FIG. 20.

[0064] As illustrated in FIG. 20, the conventional heating member 23A has 2 heating portions 60A and 60B electrically connected in series to the 2 electrode portions 53, in the same manner as the heating member 23 according to the first embodiment of the present invention. That is, the heating member 23A is what is referred to as a single-type heating member. Although the heating portions 60A and 60B are covered with an insulating layer also in the conventional example, the insulating layer is omitted here.

[0065] In FIG. 20, reference numeral W1 denotes a sheet passing region (recording medium passing region) of a sheet P1 when the sheet (recording medium) P1 having a specific width is passed in the direction of arrow Y1, and reference numeral W2 denotes an image passing region W2 through which an image region Q carried on the sheet P1 passes. Here, “image region Q” means the largest region in the width direction in which an image can be formed on the sheet P1 having a specific width. In FIG. 20, regions A, B, and C denote widthwise regions determined based on the sheet passing region W1 and the image passing region W2. Specifically, region C is a region at the center of the image including the widthwise centers of the sheet passing region W1 and the image passing region W2, and region B is a region at the edge of the image indicating a region closer to the edge of the image passing region W2 in the width direction than region C at the center of the image. Region A is a region outside the image including a sheet non-passing region (recording medium sheet non-passing region) through which the sheet P1 outside the image passing region W1 does not pass.

[0066] The graph in FIG. 20 illustrates the temperature distribution of the fixing belt in the paper width direction when the fixing device is cold started-up after the power of the image forming apparatus is turned on, and when the fixing process is performed by continuously passing a plurality of sheets P1 of a specific width size. In FIG. 20, α’ represents the temperature distribution at the time of cold start-up, and β’ represents the temperature distribution at the time of continuous sheet passing.

[0067] As illustrated in the temperature distribution α’, at the time of cold start-up, the temperature of the fixing belt tends not to rise particularly at the end portions in the longitudinal direction of the heating portions 60A and 60B. Therefore, when the image is formed immediately after the fixing device is started up, the temperature of the fixing belt is low in the region B on the side of the image end, and therefore a good fixing property may not be obtained. Therefore, in a conventional fixing device, as illustrated in FIG. 20, a measure is generally taken to improve the insufficient temperature rise in the region B on the side of the image end by arranging the heating portions 60A and 60B that are longer than the sheet passing region W1. Further, because the heating portions 60A and 60B are longer than the sheet passing region W1, the sheet P1 can be included within the heating range even when the sheet P1 is conveyed while slightly shifted in the width direction.

[0068] However, if the heating range is widened by lengthening the heating portions 60A and 60B, when the sheet P1 is continuously passed, the temperature rise of the fixing belt may be excessive in the region A on the outside of the image including the sheet non-passing region through which the sheet P1 does not pass, as illustrated in the temperature distribution β’. That is, in the sheet non-passing region, because heat is not easily consumed by sheet-passing, if the heating range is widened by lengthening the heating portions 60A and 60B, the amount of heat stored in the region A outside the image including the sheet non-passing region increases, and the temperature rise becomes remarkable. In this case, the temperature of the peripheral members in addition to the heating member 23 increases excessively, and there is a risk of deformation or damage.

[0069] As one method for improving such problems, there is a method using a “dual-type” heating member having a plurality of heating portions for which heat generation can be independently controlled. However, the “dual-type” heating member has a disadvantage of complicating the structure of temperature control and increasing the cost compared with the “single-type” heating member.

[0070] Further, the above-mentioned Patent Literature 1 (Japanese Unexamined Patent Application Publication No. 2021-89330) proposes a method for improving both problems of the “single-type” heating member, such as insufficient temperature rise on the edge side (edge temperature dropping) and temperature rise in the sheet non-passing region.

[0071] Specifically, in the heating member 23B described in Patent Literature 1, as illustrated in FIG. 21, widths H11, H12, and H13 of the heating portions 60A and 60B are varied for each of the regions A, B, and C so that H11>H13>H12 is satisfied. The regions A, B, and C illustrated in FIG. 21 are the same as the regions A, B, and C illustrated in FIG. 20.

[0072] Because the widths H11, H12, and H13 of the heating portions 60A and 60B satisfy H11>H13>H12 for each of the regions A, B, and C, the amount of heat generated for each of the regions A, B, and C can be made different. That is, as the width of the heating portion increases, the electric resistance value of the heating portion decreases and the amount of heat generated tends to decrease in accordance with the electric resistance value. Therefore, as described above, by making the widths H11, H12, and H13 of the heating portions 60A and 60B different for each of the regions A, B, and C, the amount of heat generated for each of the regions A, B, and C can be made different. Specifically, in this case, because the width H12 of the region B on the image edge side is the smallest among the regions A, B, and C, the amount of heat generated in the region B on the image edge side is the largest, and on the contrary, because the width H11 of the region A on the outer side of the image is the largest, the amount of heat generated in the region A on the outer side of the image is the smallest.

[0073] As described above, in the configuration described in Patent Literature 1, by making the widths H11, H12, and H13 of the heating portions 60A and 60B different for each of the regions A, B, and C to make the amount of heat generated different, the unfixed image on the sheet can be sufficiently heated in the region B on the image edge side, where the amount of heat generated is the largest, so that the problem of poor fixing due to insufficient temperature rise during cold start-up or the like can be improved. On the other hand, because the amount of heat generated in the region A on the outer side of the image is the smallest, it is possible to suppress excessive temperature rise in the sheet non-passing region when the sheet P1 of a specific width size is continuously passed through the region A.

[0074] Incidentally, in a fixing device mounted on an image forming apparatus such as a copying machine or a printer, sheets of various width sizes are often configured to pass through the region A. Therefore, in the fixing device provided with the heating member 23B as in Patent Literature 1 (FIG. 21), for example, when the sheet P2 of a width size as illustrated in FIG. 22 is passed through, the region B on the image edge side, where the amount of heat generated is large, will include the sheet non-passing region, and, therefore, the temperature rise in the sheet non-passing region may become significant. Therefore, there is room for improvement in a configuration in which the width H12 of each of the heating portions 60A and 60B in the region B on the image end side is made small as in Patent Literature 1.

[0075] Therefore, the present invention proposes a configuration of a single-type heating member that can effectively suppress both temperature rise and temperature drop. Hereinafter, a configuration of a characteristic portion of a heating member according to an embodiment of the present invention will be described with reference to a first embodiment of the present invention. <Configuration of a Characteristic Portion of a Heating Member>

[0076] FIG. 7 is a plan view illustrating a heating member 23 according to a first embodiment of the present invention in which a direction (longitudinal direction) in which the two heating portions 60 and 60B extend is a first direction X, and a direction perpendicular to the first direction X along the surface of the heating element 51 (the heating portions 60A, 60B) is a second direction Y.

[0077] As illustrated in FIG. 7, the two heating portions 60A and 60B extend in the first direction X and are arranged side by side parallel to each other in the second direction Y. Here, in FIG. 7, if the lower heating portion 60A is referred to as a “first heating portion” and the upper heating portion 60B is referred to as a “second heating portion”, the width H3 of the first heating portion 60A in the second direction Y is formed to have the same width over the first direction X. On the other hand, in the second heating portion 60B, the width H2 of the pair of end portions 62 positioned on either end of the first direction X is formed larger than the width H1 of the center portion 61 including the center of the first direction X (H2>H1). That is, the second heating portion 60B has a center portion 61 having a smaller width H1 and a pair of end portions 62 having a larger width H2 than the center portion 61 and positioned continuously at either end of the center portion 61 in the first direction X. The end portions 62 are arbitrarily set in relation to the width size of the sheet and the image area on the sheet, which will be described below, and are generally set in a shorter range in the longitudinal direction X than the center portion 61, but the size of the end portions 62 (the size in the first direction X) can be appropriately changed in accordance with the specifications of the heating member 23, the amount of heat generated, and the like.

[0078] Hereinafter, the first direction X will be referred to as the “longitudinal direction ” for convenience, and the widths H1, H2, and H3 in the second direction Y will be referred to simply as the “widths”, and the relationship between the widths H1, H2, and H3 and the amount of heat generated in the longitudinal direction of the heating portions 60A and 60B will be described in detail.

[0079] Because the width H3 of the first heating portion 60A is the same in the longitudinal direction X, the amount of heat generated in the first heating portion 60A is basically the same in the longitudinal direction X. On the other hand, in the second heating portion 60B, because the width H2 of the end portions 62 is larger than the width H1 of the center portion 61, the amount of heat generated in the end portions 62 is smaller than the amount of heat generated in the center portion 61. That is, in this case, because the heating portions 60A and 60B are formed of the same material and have the same thickness, especially in the end portions 62 of the second heating portion 60B having a larger width H2, the electric resistance value is smaller than that of the center portion 61, and the amount of heat generated is also smaller. Thus, in the heating member 23 according to the first embodiment of the present invention, the amount of heat generated is reduced by increasing the width H2 of the end portions 62 of the second heating portion 60B. The “heat generation amount” mentioned here and the “heat generation amount” in the following description mean the heat generation amount per unit length in the sheet width direction of the heating portion (the width direction of the recording medium or the first direction X).

[0080] FIG. 8 is a plan view illustrating the positional relationship of the heating portions 60A and 60B with respect to the sheet passing region W1 and the image passing region W2 when the heating member 23 according to the first embodiment of the present invention is mounted on the fixing device and the sheet P1 of a specific width size is passed through the fixing device. The sheet P1 of a specific width size is, for example, a sheet of a size most frequently used in the image forming apparatus. In FIG. 8, only the positional relationship at one end side in the longitudinal direction X is illustrated, but because the opposite positional relationship is also the same (symmetrical), only the positional relationship at one end side will be described.

[0081] As illustrated in FIG. 8, when the heating member 23 is mounted on the fixing device, the heating portions 60A and 60B are arranged over a wider range than the sheet passing region W1 through which the sheet P passes. Because the heating portions 60A and 60B are arranged over a wider range than the sheet passing region W1, it is possible to increase the amount of heat generated at the image end side as in the conventional example. Further, when the heating member 23 is mounted on the fixing device, the first heating portion 60A is arranged upstream of the second heating portion 60B in the sheet passing direction Y1 (recording medium passing direction) through which the sheet P1 passes through the nip portion. That is, the second heating portion 60B is arranged downstream of the first heating portion 60A in the sheet passing direction Y1.

[0082] As illustrated in FIG. 8, in the second heating portion 60B arranged on the downstream side, the width H2 of the end portion 62 is formed larger than the width H1 of the center portion 61. Further, the end portion 62 of the second heating portion 60B having a large width H2 is arranged so as to correspond to the region B on the widthwise end side of the image passing region W2 through which the image region Q on the sheet P1 passes, and the region A on the outside of the image passing region W2 including the sheet non-passing region (recording medium sheet non-passing region) through which the sheet P1 does not pass. Therefore, the end portion 62 of the second heating portion 60B has an image end portion 62a arranged in the region B on the widthwise end side of the image passing region W2, and a portion 62b on the outside of the image region arranged in the region A on the outside of the image including the sheet non-passing region. On the other hand, the center portion 61 is arranged in the region C on the center side of the image including the widthwise centers of the sheet passing region W1 and the image passing region W2.

[0083] As described above, in the first embodiment of the present invention, because the end portion 62 having a large width H2 (the image end portion 62a and the image outside portion 62b) is arranged so as to correspond to both the image end portion region B and the image outside region A, the amount of heat generated in the image end portion region B and the image outside region A can be reduced. That is, because the amount of heat generated in the end portion 62 having a large width H2 decreases as the electric resistance value decreases, the amount of heat generated in the image end portion region B and the image outside region A can be reduced. Accordingly, it is possible to suppress an excessive temperature rise in the sheet non-passing region during continuous notification or the like. Further, in the first embodiment of the present invention, unlike the configuration described in Patent Literature 1 of FIG. 21, there is no portion having a width smaller than that of the center portion 61 (a portion corresponding to the width 12 in FIG. 21) between the center portion 61 having a small width H1 and the end portion 62 having a large width H2, and, therefore, it is possible to suppress an excessive temperature rise in the end portion 62 when a sheet for which the end portion 62 becomes the sheet non-passing region is passed. Therefore, according to the first embodiment of the present invention, even when sheets of different width sizes are passed, an excessive temperature rise in the sheet non-passing region in each case can be suppressed, and deformation or damage of the heating member 23 and peripheral members can be avoided.

[0084] FIG. 9 is a diagram comparing the temperature distribution in the sheet width direction of the fixing belt in the first embodiment of the present invention and the conventional example.

[0085] In FIG. 9, α represents a temperature distribution at the time of cold start-up in which the fixing device is started up after the power supply of the image forming apparatus is turned on in the first embodiment of the present invention, and β represents a temperature distribution at the time of continuous sheet passing in which a plurality of sheets P1 of a specific width size are continuously passed and fixed in the first embodiment of the present invention. Further, α′ and β′ in FIG. 9 represent a temperature distribution at the time of cold start-up and a temperature component at the time of continuous sheet passing in the conventional configuration (FIG. 20).

[0086] As illustrated in FIG. 9, in the first embodiment of the present invention, because the width H2 of the end portion 62 is increased to reduce the amount of heat generated, it is possible to suppress the temperature rise in the sheet non-passing region at the time of continuous sheet passing as compared with the conventional case (temperature distribution β′) as illustrated in the temperature distribution β. On the other hand, in the first embodiment of the present invention, because the temperature at the end portion side (regions A, B) of the fixing belt decreases as compared with the conventional case (temperature distribution α′) at the time of cold start-up as illustrated in the temperature distribution α, there is a concern that the fixing property at the end portion side of the image may be impaired if the image is formed immediately after start-up.

[0087] However, in the first embodiment of the present invention, the fixing property on the edge side of the image can be secured by lengthening the heating time of the fixing belt on the edge side of the image in order to address the problem of a temperature drop during cold start-up or the like. This point will be described in detail below.

[0088] FIG. 10 is a diagram comparing the temperature distribution of the fixing belt in the sheet passing direction Y1 (second direction Y) in the first embodiment of the present invention and the conventional example.

[0089] In FIG. 10, γ represents the temperature distribution of the fixing belt in the sheet passing direction Y1 corresponding to the end portion 62 (regions A, B) in the first embodiment of the present invention, and γ′ represents the temperature distribution of the fixing belt in the sheet passing direction Y1 corresponding to the edge side region (regions A, B) in the conventional example (FIG. 20).

[0090] As illustrated in FIG. 10, in the first embodiment of the present invention, because the upstream heating portion 60A is formed with the same width as the heating portion 60A of the conventional example (see FIG. 20), the amount of heat generated in the upstream side of the sheet passing direction Y1 is similar to that in the conventional example. On the other hand, because the width H2 of the downstream second heating portion 60B in the first embodiment of the present invention is formed larger in the end portion 62, the amount of heat generated in the downstream side of the sheet passing direction Y1 is smaller than that in the conventional example. Therefore, in the first embodiment of the present invention, as seen in the temperature distribution γ illustrated by the solid line in FIG. 10, the temperature of the fixing belt is lower in the downstream side of the sheet passing direction Y1 than that in the conventional example (temperature distribution γ′). However, in the first embodiment of the present invention, because the width H2 of the end portion 62 is increased in the sheet passing direction Y1, the heating range in which the fixing belt can be heated can be increased by the increase in the width H2. Therefore, in the first embodiment of the present invention, the heating time in which the fixing belt can be heated can be secured longer than in the conventional example.

[0091] As described above, in the first embodiment of the present invention, because the heating time of the fixing belt can be secured longer by increasing the width H2 of the end portion 62 in the sheet passing direction Y1, the time in which the temperature of the fixing belt can be maintained in a high state can be secured longer. Accordingly, because the time in which heat can be transmitted from the fixing belt to the sheet at the nip portion becomes longer, the sheet can be heated sufficiently and fixability can be secured. Although the width H3 of the first heating portion 60A and the width H1 of the center portion 61 of the second heating portion 60B in the first embodiment of the present invention are described as the same width as the widths of the respective heating portions 60A and 60B in the conventional example, the width H3 of the first heating portion 60A and the width H1 of the center portion 61 of the second heating portion 60B may be different from the widths in the conventional example.

[0092] As described above, according to the configuration of the first embodiment of the present invention, because no portion having a width smaller than the center portion 61 is provided between the end portion 62 having a large width H2 and the center portion 61 having a small width H1, it is possible to suppress an excessive temperature rise in the sheet non-passing region, and at the time of cold start-up or the like, because the heating time can be secured longer by the end portion 62 having a large width H2, it is possible to suppress a temperature drop. Therefore, according to the configuration of the first embodiment of the present invention, it is possible to effectively suppress both an excessive temperature rise in the sheet non-passing region at the time of continuous sheet passing or the like and insufficient temperature rise (edge temperature dropping) at the time of cold start-up or the like. Further, according to the configuration of the first embodiment of the present invention, it is possible to suppress a local temperature rise and temperature drop in a single-type heating member, and therefore, it is possible to provide a heating member excellent in safety and fixability at a low cost.

[0093] The heating portion whose width H2 (width H2 of the end portion 62) is increased is not limited to the second heating portion 60B on the downstream side, but may be the first heating portion 60A on the upstream side. However, in order to ensure good fixability, as in the first embodiment of the present invention, it is preferable to increase the width H2 of the second heating portion 60B, and to make the first heating portion 60A a heating portion having a uniform width H as in the conventional example. By making the width H3 of the first heating portion 60A a uniform width and increasing the amount of heat generated on the upstream side of the nip portion, it is possible to ensure good fixability.

[0094] Further, in the second heating portion 60B on the downstream side, it is preferable that the direction in which the width H2 of the end portion 62 is increased is the downstream side of the sheet passing direction Y1. For example, as in the example of FIG. 11B, it is also possible to increase the width H2 of the end portion 62 toward the upstream side of the sheet passing direction Y1, but in this case, because the space J2 between the heating portions 60A and 60B increases, there is a possibility that the portions of the heating portions 60A and 60B, especially on the center side in the longitudinal direction, may protrude from the inner nip portion N1 where the fixing belt 21 and the heating member 23 come into contact. Normally, the width of the inner nip portion N1 tends to be smaller on the center side than on both the end sides in the longitudinal direction (first direction X) due to the deflection of the pressure roller 22 when the fixing belt 21 and the pressure roller 22 are pressurized or the deflection of the heating member 23 and the holding member 25. Therefore, if the width H2 of the end portion 62 on the downstream side is increased toward the upstream side of the sheet passing direction Y1, there is a possibility that the portions of the heating portions 60A and 60B, especially on the center side in the longitudinal direction, may protrude from the inner nip portion N1. In this case, heat transfer to the fixing belt 21 cannot be performed satisfactorily at the portions where the heating portions 60A and 60B protrude from the inner nip portion N1, and, therefore, the heating member 23 becomes hot, which may cause volatilization of the lubricant applied to the inner circumferential surface of the fixing belt 21 and increase frictional resistance between the fixing belt 21 and the heating member 23.

[0095] On the other hand, as in the first embodiment of the present invention, when the width H2 of the downstream end portion 62 is increased toward the downstream side in the sheet passing direction Y1, the space J1 between the heating portions 60A and 60B can be reduced as illustrated in FIG. 11A, so that the heating portions 60A and 60B can be arranged close to each other, and the heating portions 60A and 60B can be arranged so as not to protrude from the inner nip portion N1. Therefore, although the direction in which the width H2 of the downstream end portion 62 is increased may be the upstream side in the sheet passing direction Y1, it is preferable to be the downstream side in the sheet passing direction Y1 in consideration of the relationship with the inner nip portion N1.

[0096] Next, another embodiment of the present invention will be described. In the following description, parts different from those in the first embodiment of the present invention will be mainly described, and descriptions of the same parts will be omitted as appropriate. <Second embodiment of the present invention>

[0097] FIG. 12 is a plan view of a heating member 23 according to the second embodiment of the present invention.

[0098] In the second embodiment of the present invention illustrated in FIG. 12, unlike the first embodiment of the present invention, the width H21 of the image end portion 62a of the second heating portion 60B is not increased, but is made equal to the width H1 of the center portion 61. That is, in the second embodiment of the present invention, only the portion 62b outside the image region of the end portion 62 of the second heating portion 60B has a width H22 larger than that of the center portion 61 and the image end portion 62a (H22>H21=H1). Other than that, the configuration is the same as that of the first embodiment of the present invention.

[0099] As described above, only the portion 62b outside the image region may have a larger width H22. In this case as well, because the amount of heat generated in the portion 62b outside the image region arranged in the region A outside the image region can be reduced, it is possible to suppress an excessive temperature rise in the sheet non-passing region during continuous sheet passing or the like. On the other hand, because the amount of heat generated in the image end portion 62a arranged in the region B on the image end side is larger than that in the first embodiment of the present invention, it is possible to more effectively suppress insufficient temperature rise (edge temperature dropping) during cold start-up or the like. That is, the second embodiment of the present invention is an embodiment in which the amount of heat generated in the image end portion 62a is larger than that in the first embodiment of the present invention, and the speed rise of the region B on the image end side is improved. Therefore, if it is desired to give priority to shortening the start-up time, it is preferable to adopt the configuration of the second embodiment of the present invention. <Third embodiment of the Present Invention>

[0100] FIG. 13 is a plan view of a heating member 23 according to a third embodiment of the present invention.

[0101] In the third embodiment of the present invention illustrated in FIG. 13, the width H21 of the image end portion 62a and the width H22 of the portion 62b outside the image region of the end portion 62 of the second heating portion 60B are different. In this case, the width H21 of the image end portion 62a and the width H22 the portion 62b outside the image region are both larger than the width H1 of the center portion 61, but in particular, the width H22 of the portion 62b outside the image region is formed to be even larger than the width H21 of the image end portion 62a (H22>H21>H1).

[0102] As described above, the width H21 of the image end portion 62a and the width H22 of the portion 62b outside the image region may be different. In this case, because the amount of heat generated can be separately set in the image end portion 62a and the portion 62b outside the image region, more precise temperature adjustment is possible. <Fourth embodiment of the Present Invention>

[0103] FIG. 14 is a plan view of a heating member 23 according to the fourth embodiment of the present invention.

[0104] In the fourth embodiment of the present invention illustrated in FIG. 14, in addition to the second heating portion 60B, the width H4 of the end portion 62 is made larger than the width H3 of the center portion 61 in the first heating portion 60A (H4>H3).

[0105] In this case, it is possible to reduce the amount of heat generated in the end portions 62 of both the first heating portion 60A and the second heating portion 60B, so that the temperature rise in the sheet non-passing region can be more effectively suppressed. On the other hand, although the temperature of the end portion (regions A and B) of the fixing belt becomes low at the time of cold start-up or the like, the heating time of the fixing belt can be secured to be a long time because the widths H4 and H2 of the end portions 62 of the respective heating portions 60A and 60B are large. Therefore, insufficient temperature rise (end portion temperature dropping) at the time of cold start-up or the like can be suppressed. However, from the viewpoint of securing a good fixing property, it is more preferable to increase the width H2 only in the end portion 62 of the downstream second heating portion 60B and not to increase the width H4 of the end portion 62 of the upstream first heating portion 60A as in the first embodiment (FIG. 7) of the present invention.

[0106] When increasing the widths H4 and H2 of the end portions 62 of both the first heating portion 60A and the second heating portion 60B as in the fourth embodiment of the present invention, it is preferable to increase the widths H4 and H2 toward the outside in the second direction Y as illustrated in FIG. 14. That is, in the first heating portion 60A arranged on the upstream side of the sheet passing direction Y1, it is preferable that the direction in which the width H4 increases is the upstream side of the sheet passing direction Y1, and in the second heating portion 60B arranged on the downstream side of the sheet passing direction Y1, it is preferable that the direction in which the width H2 increases is the downstream side of the sheet passing direction Y1. In this manner, protrusion of the heating portions 60A and 60B from the inner nip portion N1 can be suppressed.

[0107] Further, in the fourth embodiment of the present invention, the entire end portion 62 (the image end portion 62a and the portion 62b outside the image region) of the first heating portion 60A is formed to have the same width H4, but the width of only the portion 62b outside the image region may be increased in the same manner as the second heating portion 60B in the second embodiment of the present invention (FIG. 12), or the widths of the image end portion 62a and the portion 62b outside the image region may be made different in the same manner as the second heating portion 60B in the third embodiment of the present invention (FIG. 13). <Fifth embodiment of the Present Invention>

[0108] FIG. 15 is a plan view of the heating member 23 according to the fifth embodiment of the present invention.

[0109] In the fifth embodiment of the present invention illustrated in FIG. 15, the shapes of the one end portion 62 and the other end portion 62 of the second heating portion 60B are different, and their widths H2 are partially different. That is, the one end portion 62 and the other end portion 62 have portions whose widths H2 are different from each other.

[0110] By making the shapes (widths H2) of the end portions 62 different from each other in this way, the amount of heat generated can be adjusted in accordance with the amount of heat or the like of each end portion. For example, in a configuration in which the connector 70 is connected to only one end side in the longitudinal direction X of the heating member 23 as illustrated in FIG. 5, the amount of heat dissipation of the heating member 23 may be different between one end side to which the connector 70 is connected and the opposite other end side. In such a case, as in the fifth embodiment of the present invention, the shapes of the end portions 62 may be different between one end side and the other end side in accordance with the amount of heat dissipation, thereby making the amount of heat generation different.

[0111] Further, as in the fifth embodiment of the present invention, the shapes of the end portions 62 different from each other are not limited to the case of the second heating portion 60B, but may be the first heating portion 60A, or may be both the first heating portion 60A and the second heating portion 60B. <Other Modifications>

[0112] Although the embodiments of the present invention have been described above, the present invention is not limited to the heating member according to the embodiments described above, but is widely applicable to a single-type heating member having only two electrode portions and a heating element (heating portion) electrically connected to the two electrode portions.

[0113] For example, the heating element 51 according to an embodiment of the present invention is not limited to a heating element having two heating portions 60A and 60B extending in the longitudinal direction (first direction) X as illustrated in FIG. 7, and may have only one heating portion extending in the longitudinal direction X, or may have three or more heating portions extending in the longitudinal direction X. That is, in the present invention, the heating portion extending longitudinally in the longitudinal direction (first direction) X may be a single or a plurality of heating portions as long as they are electrically connected to the two electrode portions. Further, the heating portion is not limited to extending linearly in the longitudinal direction (first direction) X, and may be non-linear such as partially bent.

[0114] Further, when there are three or more heating portions arranged in the second direction Y (sheet passing direction Y1), when each heating portion is arranged in the inner nip portion N1, the heating portion whose width is increased is preferably one of the heating portions arranged outermost in the second direction Y (the most upstream side and the most downstream side in the sheet passing direction Y1), and the direction in which the width is increased is preferably the outside in the second direction Y. If the heating portion is arranged in the inner nip portion N1, on the contrary, the width of the heating portion may be increased inward in the second direction Y.

[0115] Further, as illustrated in the example of FIG. 16, the heating portion 60 may be a heating portion (heating element group) composed of a plurality of heating elements 51 arranged side by side in the longitudinal direction (first direction) X. In this case, by making the width H2 of each heating element 51 (end portion 62) located at both ends larger than the width H1 of the heating element 51 (center portion 61) located at the center, the same operation and effect as in the above-described embodiment can be obtained.

[0116] Further, in the above-described embodiment, the case where the width H2 of both the end portion 62 at one end side and the end portion 62 at the other end side in the longitudinal direction X are increased has been described as an example, but when the amount of heat dissipation or the like differs between one end side and the other end side of the heating member 23, the width H2 of only one end portion 62 may be increased.

[0117] The heating member according to an embodiment of the present invention is not limited to the fixing device 20 having the configuration illustrated in FIG. 2, and can also be applied to the fixing device having the following configuration, for example.

[0118] The fixing device according to an embodiment of the present invention may be, for example, a fixing device 20 having a heating nip portion N1 and a fixing nip portion N2 at separate positions as illustrated in FIG. 17. In this case, the heating nip portion N1 and the fixing nip portion N2 are formed when the two large and small pressure rollers 151,152 come into contact with the fixing belt 21 from opposite sides. That is, the heating nip portion N1 is formed when the pressure roller 151 on the left side of FIG. 17 comes into contact with the heating member 23 via the fixing belt 21, and the fixing nip portion N2 is formed when the pressure roller 152 on the right side of FIG. 17 comes into contact with the nip forming member 150 via the fixing belt 21. In the fixing device 20 in which the heating nip portion N1 and the fixing nip portion N2 are formed separately as described above, when the heating member 23 generates heat, the fixing belt 21 is heated by the heating nip portion N1, and when the sheet P enters the fixing nip portion N2, the unfixed image on the sheet P is heated and pressurized, and the image is fixed to the sheet P. Further, even in such a fixing device 20, by mounting the heating member according to an embodiment of the present invention, it is possible to effectively suppress excessive temperature rise in a sheet non-passing region during continuous sheet passing or the like and insufficient temperature rise (edge temperature dropping) during cold start-up or the like.

[0119] Further, the heating member according to an embodiment of the present invention is also applicable to the fixing device 20 illustrated in FIG. 18. The fixing device 20 illustrated in FIG. 18 is an example in which the pressure roller 151 on the left side of the fixing device 20 illustrated in FIG. 17 is omitted, and the heating member 23 is formed in an arc shape matching the curvature of the fixing belt 21. Otherwise, the fixing device 20 illustrated in FIG. 17 has the same configuration. In this case, because the heating member 23 is formed in an arc shape, a long contact region between the fixing belt 21 and the heating member 23 in the belt rotation direction is secured, and the fixing belt 21 is efficiently heated.

[0120] Further, the heating member according to an embodiment of the present invention may be applied to the fixing device 20 illustrated in FIG. 19. The fixing device 20 illustrated in FIG. 19 is an example in which 2 belts 161 and 162 are arranged on either side of a central roller 163. In this case, the heating nip portion N1 is formed by sandwiching the left belt 161 between the heating member 23 arranged inside and the central roller 163, and the fixing nip portion N2 is formed by sandwiching the right belt 162 between the nip forming member 153 arranged inside and the central roller 163. Even in such a fixing device 20, by mounting the heating member according to an embodiment of the present invention, it is possible to effectively suppress excessive temperature rise in a sheet non-passing region during continuous sheet-passing and insufficient temperature rise (edge temperature dropping) during cold start-up.

[0121] To summarize the aspects of the present invention, the present invention includes at least the following aspects. (First Aspect)

[0122] A first aspect is a heating member including two electrode portions; and a planar heating element electrically connected to the two electrode portions, wherein the heating element extends in a first direction or a plurality of the heating elements are arranged side by side and extend in the first direction to constitute the longitudinal heating portion, the heating portion has a center portion including a center in the first direction and an end portion positioned on at least one end side in the first direction with respect to the center portion, a width of the end portion in a second direction is larger than a width of the center portion in the second direction when a direction orthogonal to the first direction along a surface of the heating element is the second direction, and there is no portion having a width smaller than the width of the center portion in the second direction between the center portion and the end portion. (Second Aspect)

[0123] According to a second aspect, in the first aspect, a plurality of the heating portions are arranged side by side in the second direction, and among the plurality of the heating portions, a width in the second direction of the end portion of at least one of the heating portions is larger than a width in the second direction of the center portion. (Third Aspect)

[0124] According to a third aspect, in the second aspect, the heating portion having the end portion at which the width in the second direction is increased is at least one of the heating portions arranged outermost in the second direction, and a direction in which the width in the second direction is increased is toward an outside in the second direction. (Fourth Aspect)

[0125] A fourth aspect is a fixing device including a first rotating body; and a second rotating body contacting an outer peripheral surface of the first rotating body to form a nip portion; and a heating member contacting an inner peripheral surface of the first rotating body to heat the first rotating body, wherein a recording medium carrying an unfixed image is passed through the nip portion, the recording medium is heated, and the unfixed image is fixed to the recording medium, the heating member is the heating member according to any one of the first to fourth aspects, which is arranged such that the first direction is a width direction of the recording medium and the second direction is a recording medium passing direction in which the recording medium passes through the nip portion, and the width of the end portion in the recording medium passing direction is larger than the width of the center portion in the recording medium passing direction. (Fifth Aspect)

[0126] According to a fifth aspect, in the fixing device according to the fourth aspect, a plurality of the heating portions are arranged side by side in the recording medium passing direction, the heating portion having the end portion at which the width is increased in the recording medium passing direction is the heating portion arranged on a most downstream side in the recording medium passing direction, and a direction in which the width is increased in the recording medium passing direction is toward a downstream side in the recording medium passing direction. (Sixth Aspect)

[0127] According to a sixth aspect, in the fourth or fifth aspect, the heating portion includes an image center portion arranged in an image center region including a widthwise center portion of an image passing region through which the unfixed image on the recording medium passes; an image end portion arranged on a widthwise end portion of the image passing region with respect to the image center portion; and an image region outside portion that is outside the image passing region and that includes a recording medium non-passing region through which the recording medium does not pass, wherein widths of the image end portion and the image region outer portion in the recording medium passing direction are larger than a width of the image center portion in the recording medium passing direction. (Seventh Aspect)

[0128] According to a seventh aspect, in the sixth aspect, an amount of heat generated per unit length in the width direction of the recording medium is smaller in the image end portion and the image region outside portion than in the image center portion. (Eighth Aspect)

[0129] According to an eighth aspect, in the fourth or fifth aspect, the heating portion includes an image center portion arranged in an image center region including a widthwise center portion of an image passing region through which the unfixed image on the recording medium passes; an image end portion arranged on a widthwise end portion of the image passing region with respect to the image center portion; and an image region outside portion that is outside the image passing region and that includes a recording medium non-passing region through which the recording medium does not pass, wherein a width of the image region outer portion in the recording medium passing direction is larger than widths of the image center portion and the image end portion in the recording medium passing direction. (Ninth Aspect)

[0130] According to a ninth aspect, in the eighth aspect, an amount of heat generated per unit length in the width direction of the recording medium is smaller in the image region outer portion than in the image center portion and the image end portion. (Tenth Aspect)

[0131] A tenth aspect is an image forming apparatus including a fixing device according to any one of the fourth to ninth aspects.

[0132] The present application is based on and claims priority to Japanese Priority Application No. 2025-004825 filed on January 14, 2025, the entire contents of which are hereby incorporated herein by reference.

[0133] 20 Fixing device 21 Fixing belt (first rotating body) 22 Pressure roller (second rotating body) 23 Heating member 50 Base material 51 Heating element 53 Electrode portion 60A First heating portion 60B Second heating portion 61 Center portion 62 End portion 62a Image end portion 62b Portion outside the image region A Region outside the image region B Region at the end of the image C Region at the center of the image H1 Width of the center portion H2 Width of the edge portion N Nip portion P Sheet (recording medium) X First direction Y Second direction Y1 Sheet passing direction (recording medium passing direction)

Claims

1. A heating member comprising: two electrode portions; and a planar heating element electrically connected to the two electrode portions, wherein the heating element extends in a first direction or a plurality of the heating elements are arranged side by side and extend in the first direction to constitute the longitudinal heating portion, the heating portion has a center portion including a center in the first direction and an end portion positioned on at least one end side in the first direction with respect to the center portion, a width of the end portion in a second direction is larger than a width of the center portion in the second direction when a direction orthogonal to the first direction along a surface of the heating element is the second direction, and there is no portion having a width smaller than the width of the center portion in the second direction between the center portion and the end portion.

2. The heating member according to claim 1, wherein a plurality of the heating portions are arranged side by side in the second direction, and among the plurality of the heating portions, a width in the second direction of the end portion of at least one of the heating portions is larger than a width in the second direction of the center portion.

3. The heating member according to claim 2, wherein the heating portion having the end portion at which the width in the second direction is increased is at least one of the heating portions arranged outermost in the second direction, and a direction in which the width in the second direction is increased is toward an outside in the second direction.

4. A fixing device comprising: a first rotating body; and a second rotating body contacting an outer peripheral surface of the first rotating body to form a nip portion; and a heating member contacting an inner peripheral surface of the first rotating body to heat the first rotating body, wherein a recording medium carrying an unfixed image is passed through the nip portion, the recording medium is heated, and the unfixed image is fixed to the recording medium, the heating member is the heating member according to claim 1, which is arranged such that the first direction is a width direction of the recording medium and the second direction is a recording medium passing direction in which the recording medium passes through the nip portion, and the width of the end portion in the recording medium passing direction is larger than the width of the center portion in the recording medium passing direction.

5. The fixing device according to claim 4, wherein a plurality of the heating portions are arranged side by side in the recording medium passing direction, the heating portion having the end portion at which the width is increased in the recording medium passing direction is the heating portion arranged on a most downstream side in the recording medium passing direction, and a direction in which the width is increased in the recording medium passing direction is toward a downstream side in the recording medium passing direction.

6. The fixing device according to claim 4, wherein the heating portion includes an image center portion arranged in an image center region including a widthwise center portion of an image passing region through which the unfixed image on the recording medium passes; an image end portion arranged on a widthwise end portion of the image passing region with respect to the image center portion; and an image region outside portion that is outside the image passing region and that includes a recording medium non-passing region through which the recording medium does not pass, wherein widths of the image end portion and the image region outer portion in the recording medium passing direction are larger than a width of the image center portion in the recording medium passing direction.

7. The fixing device according to claim 6, wherein an amount of heat generated per unit length in the width direction of the recording medium is smaller in the image end portion and the image region outside portion than in the image center portion.

8. The fixing device according to claim 4, wherein the heating portion includes an image center portion arranged in an image center region including a widthwise center portion of an image passing region through which the unfixed image on the recording medium passes; an image end portion arranged on a widthwise end portion of the image passing region with respect to the image center portion; and an image region outside portion that is outside the image passing region and that includes a recording medium non-passing region through which the recording medium does not pass, wherein a width of the image region outer portion in the recording medium passing direction is larger than widths of the image center portion and the image end portion in the recording medium passing direction.

9. The fixing device according to claim 8, wherein an amount of heat generated per unit length in the width direction of the recording medium is smaller in the image region outer portion than in the image center portion and the image end portion.

10. An image forming apparatus comprising: the fixing device according to claim 4.

Images