JP2016090960A - Image heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image heating device that can deal with an increase in temperature at the ends of sheets with various sizes.SOLUTION: There is provided an image heating device 40 including conveying, while holding, a sheet P carrying a toner image T at a nip part N to heat the toner image, and including: a cylindrical first rotor 41; a slide-contact member 46 that is fixedly provided to be in slide-contact with an inner face of the first rotor; a heating element 43 that is fixedly provided on the inside of the first rotor; a reflecting member 42 that is fixedly provided on the inside of the first rotor 41 and reflects radiation heat from the heating element to the inner face of the first rotor; and a second rotor 44 that is in contact with the slide-contact member with the first rotor 41 therebetween to form a nip part with the first rotor, where the shape of both end areas 42B of the reflecting member are deformed, with respect to a center part area 42A in the longitudinal direction, to reflect the radiation heat from the heating element arranged opposite to both end areas to the inner face of the center part in the longitudinal direction of the first rotor, according to an increase in temperature at the ends of sheets caused by continuous insertion of sheets having a width smaller than the width of sheets having the maximum width usable in the device.SELECTED DRAWING: Figure 8

Description

  The present invention relates to an image heating apparatus suitable for use as a fixing device mounted on an image forming apparatus such as an electrophotographic copying machine, a printer, a fax machine, or a multifunction machine thereof.

  Various types of fixing devices that heat and fix an unfixed toner image carried on a sheet (hereinafter referred to as paper) as a recording medium as a fixed image are known.

  Patent Document 1 discloses a fixing device that uses a fixing belt (endless belt) in which a heating unit (halogen lamp) is provided and uses a pressure roller as an on-demand fixing device having a short warm-up time. Yes. Specifically, a pressure member (pressure pad) as a fixing member is fixed so as to be in sliding contact with the inner peripheral surface of the fixing belt while being urged toward the nip portion by a spring. As a result, the pressure member is pressed against the pressure roller via the fixing belt to form a nip portion. The toner image on the paper conveyed toward the nip portion is fixed by receiving heat and pressure at the nip portion.

  The fixing device has a non-sheet-passing temperature rise that occurs when a sheet of paper with a smaller sheet width (small size) than the maximum sheet width that can be introduced and used in the apparatus is continuously fed and heat-fixed. There is a problem of (end temperature rise). That is, when small-size paper is continuously fed, heat consumed for heating the paper is compensated by the temperature control system at the fixing belt and the pressure roller, and maintained at a predetermined temperature. On the other hand, in the non-sheet passing portion, heat is not consumed due to heating of the sheet but is stored, and the temperature of the non-sheet passing portion is higher than that of the sheet passing portion maintained at a predetermined temperature. .

  Patent Document 1 shows a configuration in which the end portion of the reflector is raised so that the radiant heat from the heat source is concentrated from the longitudinal center in order to prevent overheating of the non-sheet passing portion of the fixing belt and improve fixing efficiency. Has been. In addition, a technique is shown in which a shielding plate is provided in a non-sheet passing portion so that radiant heat is concentrated in the center in the longitudinal direction.

JP 2013-178511 A

  However, in Patent Document 1, there is a problem that the sheet size (paper size) cannot be dealt with, that is, the edge temperature rise of sheets having different width sizes cannot be dealt with.

  Therefore, an object of the present invention is to provide an image heating apparatus that solves the sheet size correspondence of edge temperature rise.

  In order to achieve the above object, a typical configuration of an image heating apparatus according to the present invention is an image heating apparatus that heats a toner image by sandwiching and conveying a sheet carrying a toner image at a nip portion. A first rotating body, a sliding contact member fixed so as to be in sliding contact with the inner surface of the first rotating body, a heating element fixed inside the first rotating body, and the first A reflecting member that is fixed inside the rotating body and reflects radiant heat from the heating element toward the inner surface of the first rotating body, and abuts against the sliding contact member via the first rotating body. A second rotating body that forms the nip portion with the first rotating body, and the reflecting member is a continuous sheet having a smaller width than the maximum width sheet that can be used in the apparatus. The shape of both end regions with respect to the longitudinal central region according to the end temperature rise caused by the introduction Characterized by deforming the radiant heat from the heating element facing the the both end regions in the direction of reflection toward the inner surface of the longitudinal central region of the first rotating body.

  ADVANTAGE OF THE INVENTION According to this invention, the image heating apparatus which solves sheet size correspondence of edge part temperature rising can be provided.

FIG. 3 is an enlarged cross-sectional model view of a main part of the fixing device in Embodiment 1. 1 is a schematic diagram of an image forming apparatus in Embodiment 1. FIG. FIG. 3 is a longitudinal front view of a main part of the fixing device with a part omitted. It is a disassembled perspective view of a heating unit. FIG. 3 is a schematic diagram of a layer configuration of a fixing belt. FIG. 2 is a configuration explanatory diagram (No. 1) of a reflecting plate. FIG. 2 is a configuration explanatory diagram (No. 1) of a reflecting plate. It is a structure explanatory view (the 3) of a reflecting plate. It is a figure explaining the shape which the bimetal plate bent by temperature rise. It is a figure explaining the temperature dependence of a thermal expansion coefficient. It is a figure which shows the film thickness ratio (n) dependence of the proportionality constant (a) which determines a curvature coefficient (K). It is a figure explaining plate | board thickness when the non-sheet passing area | region of the baseplate part of a reflecting plate is bent to angle (theta). FIG. 6 is a diagram illustrating a fixing belt longitudinal temperature distribution. It is a figure explaining that non-sheet-passing part temperature rising can be suppressed by giving angle (theta). It is a figure explaining the temperature of the non-paper passing area | region with respect to angle (theta). FIG. 6 is a configuration explanatory diagram of a reflector in Example 2.

  Next, specific examples (examples) of the embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following examples.

[Example 1]
(1) Image Forming Unit FIG. 2 is a schematic configuration diagram of an example of the image forming apparatus 1 in which the image heating apparatus according to the present invention is mounted as the fixing device 40. This image forming apparatus 1 is an intermediate transfer type, tandem four-color full-color electrophotographic laser printer, which can form a full-color toner image on a sheet P and print it out. The sheet P is a recording material (recording medium) on which a toner image can be formed, and examples thereof include plain paper, glossy paper, resin sheet, cardboard, postcard, envelope, and OHP sheet. Hereinafter referred to as paper. Since the printer configuration other than the fixing device 40 is known, only the following printer configuration will be briefly described.

  An image forming unit 2 includes four image forming units 3 (3Y, 3M, 3C, 3K) and an intermediate transfer belt unit 10. Each image forming unit 3 includes a rotating drum type photosensitive member 4, a charging member 5, a laser scanner 6, a developing device 7, a primary transfer member 8, a photosensitive member cleaner 9, and the like, and includes yellow (Y) color, magenta (M), cyan (C), and black (K) toner images are formed. Then, the four color toner images are sequentially superposed on the intermediate transfer belt 11 from the photoreceptor 4 of each image forming unit 3 in a predetermined manner and primarily transferred to form a full color toner image on the intermediate transfer belt 11. .

  The full-color toner image is secondarily transferred onto the paper P at a secondary transfer nip portion that is a pressure contact portion between the intermediate transfer belt 11 and the secondary transfer roller 12. The sheet P is separated and fed from the sheet cassette 19 or 20 or the multi-feed tray 21 and is introduced into the secondary transfer nip portion from the transport mechanism 22 including the registration roller pair 22a at a predetermined control timing. Then, the paper P that has undergone the secondary transfer of the toner image is introduced into the fixing device 40 and undergoes heat-pressure fixing of the toner image.

  The paper P exiting the fixing device 40 is routed to the first path 14 side or the second path 15 side by the flapper 13 according to the mode selection in advance. The paper P introduced into the first path 14 is discharged to the face down tray 16 on the upper surface side of the apparatus. The paper P introduced into the second path 15 is discharged to the face-up tray 17 on the side surface side of the apparatus.

  In the double-sided image forming mode, the first-side image-formed paper P that has exited the fixing device 40 is once introduced into the first path 14 and then switched back and introduced into the third path (recirculation path) 18. Is done. Then, it is conveyed again through the conveying mechanism 22 in a state where the front and back are reversed with respect to the secondary transfer nip portion of the image forming unit 2. As a result, the paper on which the double-sided image is formed is discharged to the face-down tray 16 or the face-up tray 17.

  In the image forming apparatus 1 of the present example, the conveyance of the paper P in the apparatus is performed by so-called central reference conveyance. This paper transport is a form in which the center line in the width direction of the paper is aligned with the center in the width direction of the paper transport path regardless of the width of the paper that can be used (passable) in the apparatus. That is.

(2) Fixing Device (2-1) Overall Schematic Configuration The fixing device 40 of this embodiment is an image heating device of a belt heating method and a pressure roller driving method (tensionless type). FIG. 1 is an enlarged schematic cross-sectional view of the main part of the fixing device 40, and FIG.

  Here, in this embodiment, regarding the fixing device 40 or its constituent members, the front side is a surface viewed from the paper inlet side, the back surface is the opposite surface (paper outlet side), and the left and right sides are the front of the device. Left (one end side) or right (the other end side) when viewed from the side. Up and down are up or down in the direction of gravity. The upstream side and the downstream side are the upstream side and the downstream side in the paper transport direction a. The longitudinal direction (or the width direction) and the paper width direction are directions substantially parallel to the direction orthogonal to the paper transport direction a on the paper transport path surface. The short direction is a direction substantially parallel to the paper transport direction a on the paper transport path.

  The fixing device 40 includes a heating unit (belt unit) 4A including a fixing belt (fixing member: endless belt) 41 as a cylindrical (endless) first rotating body. Further, a pressure roller 44 is provided as a second rotating body that forms a nip portion N between the fixing belt 41 and sandwiches and conveys the paper P carrying the toner image T. Moreover, it has the housing | casing 60 which accommodated them.

  FIG. 4 is an exploded perspective view of the heating unit 4A. The heating unit 4A has a cylindrical flexible fixing belt 41 and a nip forming member (pressure pad, backup member) 46 as a sliding contact member. Further, it has a reinforcing stay 47, a heater 43 as a heating element (heating source, heating element, heating means), a reflection plate (reflection member) 42, left and right flange members 49L and 49R, and the like. The nip forming member 46, the reinforcing stay 47, the heater 43, and the reflection plate 42 are disposed inside the fixing belt 41. In the above, members other than the left and right flange members 49L and 49R are members that are long in the left-right direction.

  The fixing belt 41 is a cylindrical heat-resistant member as a heating member that transmits heat. In the present embodiment, as shown in the schematic diagram of the layer structure of FIG. 5, the fixing belt 41 is arranged in order from the inner peripheral surface side to the outer peripheral surface side, an inner surface coat layer 41d, a base material layer 41a, an elastic layer 41b, and a surface layer ( This is a four-layer composite structure in which release layers 41c are sequentially stacked. It is a thin and flexible member in which the thickness of the entire four layers is set to 1 mm or less. The fixing belt 41 has a substantially cylindrical shape due to its elasticity in a free state.

  The diameter of the fixing belt 41 is set to be 15 to 120 mm. In this embodiment, the inner diameter is set to 30 mm. The length (width) W41) of the fixing belt 41 is 340 mm.

  In order to improve the quick start property, the base material layer 41a can use a heat-resistant material having a thickness of 100 μm or less, preferably 50 μm or less and 20 μm or more. For example, a cylindrical metal film such as SUS or nickel can be used. In this example, a cylindrical nickel metal film having a thickness of 30 μm and a diameter of 30 mm was used.

  The elastic layer 41b can use a rubber material having a thickness of 1000 μm or less, preferably 500 μm or less in order to reduce the heat capacity and improve the quick start. For example, silicone rubber, fluorine rubber and the like can be mentioned. In this embodiment, silicone rubber having a rubber hardness of 10 degrees (JIS-A), a thermal conductivity of 1.3 W / m · K, and a thickness of 300 μm is used.

  As the surface layer 41c, a fluororesin material having a thickness of 100 μm or less, preferably 20 to 70 μm can be used. For example, examples of the fluororesin layer include PTFE, FEP, PFA, and the like. In this example, a PFA tube having a thickness of 30 μm was used.

  Since the inner surface coating layer 41d is in sliding contact with the nip forming member 46, a heat-resistant resin layer, ceramics, metal, or the like can be used. Examples include engineering plastics and diamond-like carbon (DLC). For example, polyimide, polyimide amide, PEEK, polytetrafluoroethylene resin (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer resin (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin ( PFA).

  The nip forming member 46 is a member that is in sliding contact with the inner surface of the fixing belt 41, and the nip forming member 46 is in pressure contact with the pressure roller 44 through the fixing belt 41, so that the gap between the fixing belt 41 and the pressure roller 44 is reached. A nip portion N where the paper P is nipped and conveyed is formed. The nip forming member 46 is formed of a material that is synthesized to some extent so that it does not bend greatly even if it receives pressure applied by the pressure roller 44. The length is 340 mm which is the same as that of the fixing belt 41.

  The reinforcing stay 47 is longer than the fixing belt 41, and both left and right ends protrude outward from the left and right ends of the fixing belt 41. The nip forming member 46 is disposed and supported on the lower surface side of the reinforcing stay 47. That is, in this embodiment, the reinforcing stay 47 functions as a support member for the nip forming member 46. The reinforcing stay 47 is preferably formed of a metal material having high mechanical strength such as stainless steel (SUS) or iron in order to satisfy the deflection prevention mechanism of the nip forming member.

  The reflecting plate 42 is disposed and supported on the upper surface side of the reinforcing stay 47. The length (width W42) of the reflecting plate 42 is slightly shorter than the fixing belt 41, and is 330 mm in this embodiment. A halogen heater (rod-shaped halogen lamp) 43 is disposed inside the reflector 42. The effective heat generation length of the heater 43 is 330 mm, which is the same as the length of the reflection plate 42. The heater 43 may be another heating element such as a carbon heater. The reflection plate 42 reflects the radiant heat from the heater 43 toward the inner surface of the fixing belt 41.

  That is, inside the fixing belt 41, there is a heater 43 that directly heats the fixing belt 41 at a place other than the nip portion, and a reflecting plate that reflects radiant heat to the nip portion side of the heater 43 on the inner surface of the fixing belt opposite to the nip portion. 42 is arranged.

  In this embodiment, it is preferable that the temperature of the fixing belt 41 is transmitted to the reflecting plate 42 earlier, and therefore, the nip forming member 46 and the reinforcing stay 47 are preferably made of a metal having high thermal conductivity. In this embodiment, an aluminum material having a thickness of about 1.5 mm is used as the nip forming member 46. The nip forming member 46 and the reinforcing stay 47 may be a one-piece member that serves both. That is, the entire nip forming member 46 and the reinforcing stay 47 may be defined as the nip forming member.

  The left and right flange members 49L and 49R are fitted to both ends of the reinforcing stay protruding outward from the left and right ends of the fixing belt 41, respectively. That is, the left and right end portions of the reinforcing stay 47 are fitted into the hole portions 49b formed in the left and right flange members 49L and 49R, respectively.

  Each of the left and right flange members 49L and 49R includes a flange portion 49a that regulates the end portion of the fixing belt 41 and an arcuate guide portion 49c that guides the inner peripheral surface of the end portion of the fixing belt 41. In a state where the left and right flange members 49L and 49R are respectively attached to both ends of the reinforcing stay, the guide portion 49c is fitted inside the left and right end portions of the fixing belt 41. Further, the metal ports 43a at the left and right end portions of the heater 43 are fitted into the sockets (connectors) 62 disposed on the left and right flange members 49L and 49R, respectively, and are electrically connected to the sockets 62. .

  The fixing belt 41 is loosely fitted outside the nip forming member 46, the reinforcing stay 47, the reflector 42, the heater 43, and the left and right guide portions 49c between the flange portions 49a of the left and right flange members 49L and 49R. .

  The assembly (assembly) of the fixing belt 41, the nip forming member 46, the reinforcing stay 47, the reflecting plate 42, the heater 43, and the left and right flange members 49L and 49R is the heating unit 4A.

  In the pressure roller 44, an elastic layer 44b made of foamable silicone rubber, silicone rubber, fluorine rubber, or the like is formed on the outer peripheral surface of a hollow cored bar 44a. Further, a release layer 44c such as PFA or PTFE may be provided on the outer peripheral surface of the elastic layer 44b. A shaft portion 44d is mounted substantially concentrically and integrally on both left and right ends of the core metal 44a. The pressure roller 44 of this embodiment has an outer diameter of 30 mm, a thickness of the elastic layer 44b of 300 μm, and a length (width W44) of the roller portion of 330 mm.

  The pressure roller 44 is disposed such that left and right shaft portions 44d are rotatably held (both supported) via bearing members 61 between the left and right side plates 60L and 60R of the housing 60, respectively. ing. A drive gear G is disposed substantially concentrically and integrally at the end of the right shaft 44d.

  The heating unit 4A is arranged between the left and right side plates 60L and 60R of the housing 60 so that the nip forming member 46 side faces downward and is arranged substantially parallel to the pressure roller 44 above the pressure roller 44. . That is, the vertical groove portions 49d (FIG. 4) respectively provided in the left and right flange members 49L and 49R of the heating unit 4A are vertically connected to the vertical guide slits 60L-a and 60R-a provided in the left and right side plates 60L and 60R, respectively. Engage with the edge. Accordingly, the left and right flange members 49L and 49R are held so as to be slidable in the vertical direction with respect to the left and right side plates 60L and 60R, respectively.

  A predetermined pressing force F is applied to the pressure receiving portions 49e of the left and right flange members 49L and 49R by the pressure springs 63, respectively. In the present embodiment, a pressing biasing force F of 150 N (total pressure of 300 N) is applied to the pressure receiving portions 49e of the flange members 49L and 49R. Accordingly, a pressing force acts on the nip forming member 46, and the fixing belt 41 is pressed against the upper surface of the pressure roller 44 by the nip forming member 46 with a predetermined pressing force. By this pressure contact, a nip portion N having a predetermined width is formed between the fixing belt 41 and the pressure roller 44 in the short direction.

  A driving force of a motor (drive source) M controlled by the control unit 100 is transmitted to the drive gear G through a drive transmission mechanism (not shown). As a result, the pressure roller 44 is driven to rotate at a predetermined peripheral speed in the counterclockwise direction of the arrow R44 in FIG.

  A rotational force (rotational torque) acts on the fixing belt 41 by a frictional force at the nip portion N between the pressure roller 44 and the outer surface of the fixing belt 41 due to the rotational driving of the pressure roller 44. As a result, the fixing belt 41 slides with its inner surface in close contact with the surface (downward surface) of the nip forming member 46 in the nip portion N, while the rotational peripheral speed of the pressure roller 44 in the clockwise direction of the arrow R41 in FIG. It is driven to rotate at a peripheral speed almost corresponding to. The nip forming member 46 also functions as a rotation guide member for the fixing belt 41.

  In order to make the driven rotation of the fixing belt 41 smooth, a lubricant (not shown) may be interposed (applied) in the sliding contact portion between the fixing belt 41 and the nip forming member 46. The seat portions 49a of the left and right flange members 49L and 49R receive and move toward the end of the belt on the near side when the rotating fixing belt 31 moves left or right along the length of the nip forming member 46. To regulate. Further, the guide portions 49c of the flange members 49L and 49R are arranged on both ends of the fixing belt 41 so that the circumferential shape of both ends of the fixing belt 41 is regulated when the fixing belt is driven by the pressure roller 44. Guide the inner surface.

  The heater 43 receives heat from the power supply unit 101 controlled by the control unit 100 through the sockets 62 and 62 and generates heat. The radiant heat of the heater 43 reaches the inner surface of the fixing belt 41 directly and by being reflected by the reflecting plate 42, and the fixing belt 41 is heated from the inside.

  Reference numeral 45a denotes a first temperature sensor disposed at the longitudinal center of the fixing belt 41, which detects (measures) the surface temperature of the sheet passing area of the fixing belt 41 through which the paper of any size is passed. Reference numeral 45b denotes a second temperature sensor disposed at the end of the fixing belt 41, and fixing when a sheet (small size sheet) having a width smaller than the maximum sheet passing width usable in the apparatus is passed (introduced). The surface temperature of the non-sheet passing region of the belt 41 is detected. In this example, the first and second temperature sensors 45a and 45b are both contact thermistors. The temperature detection information of the first and second temperature sensors 45 a and 45 b is input to the control unit 100.

  The configuration of the fixing device 40 is summarized as follows. In this device, the paper P carrying the toner image T is nipped and conveyed by the nip portion N to heat the toner image. It has a fixing belt 41 as a cylindrical first rotating body. A nip forming member 46 is provided as a sliding contact member fixed so as to be in sliding contact with the inner surface of the fixing belt 41. A heater 43 is provided as a heating element fixed inside the fixing belt 41. A reflecting plate 42 is provided as a reflecting member that is fixed inside the fixing belt 41 and reflects radiant heat from the heater 43 toward the inner surface of the fixing belt 41.

  A pressure roller 44 is provided as a second rotating body that contacts the nip forming member 46 via the fixing belt 41 and forms a nip portion N between the fixing belt 41.

(2-2) Fixing Operation The control unit 100 starts the motor M based on the image formation start signal and starts to rotate the pressure roller 44. In addition, power supply from the power supply unit 101 to the heater 43 is started. As a result, the fixing belt 41 is driven and rotated from the inside by the radiant heat of the heater 43. The control unit 100 raises the surface temperature of the fixing belt 41 to a predetermined fixing temperature (about 200 ° C. in the present embodiment) based on temperature information detected by the first temperature sensor 45a. Then, the surface temperature of the fixing belt 41 is controlled by controlling the power supplied to the heater 43 so that the fixing temperature is maintained.

  In this fixing device state, the paper P carrying the unfixed toner image T is introduced into the fixing device 40 from the image forming unit 2 side. Then, the toner image carrying side surface of the paper P is in close contact with the outer surface of the fixing belt 41 at the nip portion N, and the nip portion N is nipped and conveyed together with the fixing belt 41. As a result, the toner image T and the paper P are heated and pressed by the heat of the fixing belt 41 and the nip pressure, whereby the toner image T is fixed to the paper P as a fixed image. The sheet P sandwiched and conveyed by the nip N is separated from the surface of the fixing belt 41 at the sheet exit of the nip N and is discharged and conveyed from the fixing device 40.

  The pressing member 46 slidably contacting the inner peripheral surface of the fixing belt 41 has a concave shape so that the surface facing the pressure roller 44 (fixing belt slidable contact surface) follows the curvature of the pressure roller 44 as shown in FIG. Is formed. Accordingly, since the paper P is sent from the nip portion N so as to follow the curvature of the pressure roller 44, the occurrence of a situation in which the paper P after the fixing process is not attracted to and separated from the fixing belt 41 is suppressed. can do.

(2-3) Reflector In order to cope with the paper size of the edge temperature rise caused by continuously introducing paper having a width smaller than the maximum width of paper that can be used in the fixing device 40 in this embodiment. The reflector 42 is configured as follows. That is, the reflecting plate 42 radiates the radiant heat from the heater 43 with the shape of both end regions opposed to the both end regions in the longitudinal center region of the fixing belt 41 according to the temperature rise at the end. It is comprised so that it may deform | transform in the direction reflected toward an inner surface.

  6A is an external perspective view of the reflecting plate 42 in this embodiment, and FIG. 6B is a plan view. The reflecting plate 42 has an elongated bottom plate portion 42a having a short width of 10 mm, and an elongated side plate portion 42b provided symmetrically so as to be opposed to the long sides on one side and the other side of the bottom plate portion 42a. This is a horizontally long material having a substantially U-shaped cross section. The inner surface is made a high light reflecting surface (mirror surface) by vapor deposition of Al or the like.

  The side plates 42b on the one side and the other side have a predetermined opening with respect to the bottom plate 42a so that a predetermined irradiation angle of radiant heat to the inner surface of the fixing belt 41 can be obtained in a positional relationship with the heater 43 in the cross section of the reflecting plate 42. They are arranged at an angle.

  The reflection plate 42 is composed of three parts in the longitudinal direction, that is, a longitudinal central region 42A and both end regions 42B. The length of the longitudinal central region 42A is set to the sheet passing width of the minimum width size (assumed minimum size width) that can be used in the fixing device 40. In this embodiment, the width of B5R is set to 182 mm. The length of the longitudinal central region 42A may be a sheet passing width of a sheet having a smaller width.

  Both end regions 42B are portions corresponding to the non-sheet passing region when the paper P of the minimum width size is passed. In this embodiment, the maximum width size paper that can be used for the fixing device 40 is A3R (A4 landscape orientation: 297 mm), and the length of the reflector 42 and the heater 43 is 330 mm, which is more than the paper width. . Accordingly, the lengths of the both end region 42B are 74 mm, corresponding to the length of the non-sheet passing portion region when the paper P having the minimum width size is passed.

  Further, in both end regions 42B, a slit portion (elongated gap) 42c is inserted at the meeting portion between the bottom plate portion 42a and the side plate portion 42b, and the bottom plate portion 42a and the side plate portion 42b are separated at the slit portion 42c. Yes. The bottom plate portion 42a in the both end regions 42B has a bimetal plate structure in which a plurality of metal plates having different thermal expansion coefficients are bonded together.

  As shown in FIG. 7A, the reflecting plate 42 is disposed by fixing the bottom plate portion 42a in the central region 42A to the upper surface side of the reinforcing stay 47 that supports the nip forming member 46 on the lower surface side. It is. The bottom plate portion 42 a in the both end region 42 </ b> B is not fixed to the upper surface side of the reinforcing stay 47. That is, a part of the reflecting plate 42 (a central region 42A) is fixed to a reinforcing stay 47 that is a support member of the nip forming member 46.

  The bimetal plate structure of the bottom plate portion 42a in both end region 42B of the reflecting plate 42 is configured as follows. The shape of the bottom plate part 42a in the both end regions 42B of the reflector 42 is such that the radiant heat from the heater 43 facing the both end regions 42B is converted into the longitudinal central region of the fixing belt 41 in accordance with the temperature rise at the end of the fixing device 40. It is comprised so that it may deform | transform in the direction reflected toward the inner surface.

  This will be described more specifically with reference to FIG. FIG. 7A shows a standby state in which the sheet is not introduced into the fixing device 40, and the entire length of the fixing belt 41 is raised to a predetermined fixing temperature and adjusted in temperature. In this standby state, the fixing device 40 does not raise the temperature at the end. Therefore, the bottom plate portion 42a in the both end region 42B of the reflecting plate 42 is not subjected to bimetal deformation (curvature deformation), and the flat plate state that is flush with the bottom plate portion 42a in the longitudinal central region 42A is maintained.

  That is, both end regions 42B of the reflecting plate 42 are held in the same shape as the longitudinal central region 42A, and the radiant heat from the heater 43 facing the both end regions 42B is transferred to the inner surface of the fixing belt 41 corresponding to the both end regions 42B. It reflects toward the part ((a) of FIG. 8).

  In this device state, when the A3R paper of the maximum width size is passed through the fixing device 40, the device 40 also raises the end portion temperature, so that the bottom plate portion 42a in the both end region 42B of the reflecting plate 42 does not undergo bimetal deformation. Therefore, both end regions 42B of the reflector 42 are held in the same shape as the longitudinal central region 42A, and the radiant heat from the heater 43 facing the both end regions 42B is directed toward the inner surfaces of both end regions of the fixing belt 41. Reflected ((a) of FIG. 8).

  FIG. 7B shows a case where B5R paper of the minimum width size that can be used in the fixing device 40 is continuously passed. In this case, the entire end area 42B of the reflecting plate 42 becomes a non-sheet passing area, and the temperature of the end increases. When the end portion temperature rises to a predetermined temperature or more, the entire bottom plate portion 42a of both end region 42B, which is a non-sheet passing region, is bent by a bimetal from the boundary with the sheet passing region. The curved shape is bent and deformed in a direction in which the radiant heat from the heater 43 facing the bottom plate portion 42a of the both end regions 42B is reflected toward the inner surface of the longitudinal central region of the fixing belt 41 ((b) of FIG. 8). .

  Thereby, the amount of radiant heat reflected from the reflecting plate 42 with respect to the inner surface corresponding to the non-sheet passing region of the fixing belt 41 is reduced, so that the temperature rise at the end of the fixing device 40 is alleviated. At the same time, the radiant heat from the heater 43 facing the both end regions 42B of the reflecting plate 42 is reflected (condensed and distributed) to the longitudinal central region, which is the paper passing region of the fixing belt 41, so that the paper passing region. The thermal efficiency of can be increased.

  FIG. 7C shows a medium-size sheet, which is larger than a minimum width B5R sheet usable for the fixing device 40 but smaller than a maximum width sheet, here an A4R (210 mm) sheet. This is the case where the paper is continuously passed.

  In this case, of the both end regions 42B of the reflecting plate 42, the region outside the A4R paper width becomes a non-sheet passing region, and the temperature of the end of the non-sheet passing region increases. When the end portion temperature rises to a predetermined temperature or more, the bottom plate portion 42a having the bimetal plate structure of the reflection plate 42 is bent and deformed from the boundary with the sheet passing region. That is, the direction in which the portion corresponding to the non-sheet passing region in the bottom plate portion 42a of the both end regions 42B of the reflecting plate 42 reflects the radiant heat from the heater 43 opposite to the inner surface of the longitudinal central region of the fixing belt 41. It is deformed by bimetal movement.

  In this case as well, as in the case of FIGS. 7B and 8B, the amount of radiant heat reflected from the reflecting plate 42 on the inner surface corresponding to the non-sheet passing region of the fixing belt 41 is reduced. The temperature rise at the end of the fixing device 40 is alleviated. At the same time, the radiant heat from the heater 43 facing the both end regions 42B of the reflecting plate 42 is reflected by the longitudinal central region, which is the paper passing region of the fixing belt 41, thereby increasing the thermal efficiency of the paper passing region. Can do.

  Then, as shown in FIGS. 7A, 7B, and 7C described above, it is possible to sufficiently cope with the temperature rise at the edge of various types of sheets having different width sizes of large, medium, and small.

FIG. 9 is a diagram for explaining a shape in which a bimetal plate is bent due to a temperature rise. FIG. 9 shows a case in which a bimetallic metal plate Q having a length l is bent. The relationship between the length l and the curve D is referred to as “a flat one-form formula” and is expressed as D = K (T ₂ −T ₁ ) 1 ² / t. The curvature coefficient K is K = 3 (α2−α1) / {3+ (1 + mn) (1 + n ³ m) / mn2 (1 + n) ² }.

Each parameter of the “flat plate one song formula” will be described. α1 is a thermal expansion coefficient with a low expansion coefficient, and α2 is a thermal expansion coefficient with a high expansion coefficient. m is the longitudinal elastic modulus ratio m = E ₁ / E ₂ . E ₁ is a longitudinal elastic modulus with a low expansion coefficient, and E ₂ is a longitudinal elastic modulus ratio with a high expansion coefficient. n is the thickness ratio n = h ₁ / h ₂ . h ₁ is a plate thickness with a low expansion coefficient, and h ₂ is a plate thickness with a high expansion coefficient.

  In this embodiment, tungsten (W) is used as the low expansion material, and Invar (36% Ni—Fe) is used as the high expansion material. Invar with a high expansion coefficient has a low reflectance, it is preferable to deposit Al on the surface. The point of this embodiment is that the metal with a high expansion coefficient has a higher coefficient of thermal expansion than the metal with a low expansion coefficient above the temperature at which it is desired to start distorting the bimetal. Therefore, the metal with a low expansion coefficient and the metal with a high expansion coefficient are not limited to the metal of this embodiment.

  FIG. 10 is a diagram for explaining the temperature dependence of the thermal expansion coefficients of Invar and Tungsten. The thermal expansion coefficient of Invar is larger than that of tungsten at around 200 ° C. The thermal expansion coefficient of tungsten is constant from room temperature to 1000 ° C.

  As described above, the bottom plate portion 42a (at least a part of the reflection plate 42) in the both end regions 42B of the reflection plate 42 has a bimetal plate structure in which a plurality of metal plates having different thermal expansion coefficients are bonded together. The thermal expansion coefficient of at least one of the plurality of metal plates varies with temperature.

  As operating conditions of the fixing device 40, when the pressure condition is 30 kgf in total pressure, the rotation speed of the fixing belt 41 and the pressure roller 44 is 250 mm / s, and the input power to the heater 43 is 800 W, the sheet passing area is approximately 200 ° C. (fixing temperature). Since this temperature varies depending on the operating conditions, the temperature at which the thermal expansion coefficient of the invar rises is adjusted by changing the composition ratio of the invar. Alternatively, by using a metal having a low thermal expansion coefficient different from that of tungsten, the temperature at which the thermal expansion coefficient of Invar (36% Ni-Fe) is larger than the thermal expansion coefficient of the low expansion metal is changed. It is possible.

  During continuous passage of small-size paper, the non-passage area of the fixing device 40 is higher than 200 ° C. because of the edge temperature rise. Therefore, as described with reference to FIGS. 7 and 8, the portion corresponding to the non-sheet passing region of the bottom plate portion 42a, which is a bimetal plate, in the both end region 42B of the reflecting plate 42 is bent from the boundary with the sheet passing region.

Incidentally, since the short side direction of the bottom plate part 42a is also bimetal, it deforms. The amount of distortion is D = K (T ₂ −T ₁ ) l ² / t. When the small-size paper that is continuously passed is A4R, the long side direction curved corresponding to the non-sheet passing region corresponding portion of the bottom plate portion 42a is l = 60 mm, and the short side direction is l = 10 mm. Therefore, the amount of distortion in the long side direction and the short side direction of the non-fixed portion of the bottom plate portion 42a is about 36 times different, and the distortion in the short side direction is negligible when compared with the long side direction.

The bending amount at 250 ° C. of a bimetal composed of invar and tungsten having substantially the same thermal expansion coefficient at 200 ° C. will be described. 250 ° C. was used as an example of the temperature within a range where the fixing belt 41 is not damaged. The thermal expansion coefficient of Invar at 250 ° C. is α = 10, and the thermal expansion coefficient of tungsten is α = 4.6. The longitudinal elastic modulus of Invar is E ₂ = 140 (GPa), and the longitudinal elastic modulus of tungsten is E ₁ = 420 (GPa). m = E ₁ / E ₂ = 3.

  FIG. 11 shows the film thickness ratio (n) dependence of the proportionality constant (a) that determines the curvature coefficient (K). From FIG. 11, it is n = 0.5 that the curvature coefficient K becomes the maximum when m = 3. “A” on the vertical axis in FIG. 11 is a proportionality constant between the curvature coefficient K and the thermal expansion coefficient difference (α2−α1) (K = a (α2−α1)).

  Here, the paper passing size of the paper P will be described as A4R. The length of the non-sheet passing area in A4R is l = 60 (mm). When the above value is substituted into the “flat one-form formula”, the deflection amount D = 0.73 / t (mm). For example, in order to set θ to 10 °, since D = 1 × tan θ = 12.3 (mm), the design may be t = 0.73 / 12.3 = 0.06 (mm). FIG. 12 shows the plate thickness designed for the angle applied to each paper size. The plate thickness may be adjusted for each paper size position, but may be constant at a film thickness designed for a small size.

(3-4) Comparative Example A case where this example is not applied is referred to as a comparative example (no implementation: no implementation). In the example, the angle θ of the bending based on the temperature rise at the end of the bottom plate portion 42a formed as a bimetal plate in the both end region 42B of the reflecting plate 42 is set to two, that is, 20 °. FIG. 13 and Table 1 show “fixing belt longitudinal temperature distribution” and “temperature of the sheet passing area and the non-sheet passing area” in these three cases. FIG. 14 is a diagram for explaining that the temperature increase of the non-sheet passing portion can be suppressed by setting the angle θ. If the angle θ can be set as shown in FIG. 14A, the radiant heat to the non-sheet passing area is reflected to the sheet passing area, so that the temperature of the non-sheet passing area can be lowered.

  The operating conditions of the fixing device 40 were a pressure condition of 30 kgf in total pressure, a rotational speed of the fixing belt 41 and the pressure roller 44 of 250 mm / s, and an input power to the heater 43 of 800 W.

  First, as shown in Table 1, by applying the present embodiment (θ = 10 ° and θ = 20 °), the surface temperature of the fixing belt 41 in the non-sheet-passing region is θ = 20 as compared to the non-execution region. The result was a 26 ° C. drop at °. FIG. 15 is a diagram for explaining the temperature of the non-sheet passing region with respect to the angle θ. If it is 10 degrees or more from the result of this examination, the effect of lowering the temperature of the non-sheet passing area can be sufficiently obtained.

  However, if the angle θ is too large, it is conceivable that the bottom plate portion 42 a formed as a bimetal plate of the reflection plate 42 contacts the heater 43. When the diameter (inner diameter) of the fixing belt 41 is 30 mmφ and the diameter of the heater (halogen lamp) 43 is 5 mm, the distance between the heater 43 and the reflective electrode is smaller than 25 mm. When A5R is the smallest paper size, the boundary condition is tan θ <25 (mm) / 60 (mm) (θ <22), so θ needs to be set in a range smaller than 22 °.

  Further, by moving the radiant heat that should have been transmitted to the non-sheet passing area to the sheet passing area, the surface temperature of the fixing belt 41 in the sheet passing area is increased by 9 ° C. at the maximum. The effect of suppressing the temperature rise of the non-sheet passing portion could be shown, and at the same time, the effect of improving the heating efficiency of the sheet passing region could be shown.

  In Patent Document 1, it is possible to take measures against the temperature rise at the edge of the maximum paper size, but it has not been possible when the paper size is small. In the present embodiment, it is possible to suppress the temperature increase at the edge of a smaller size.

  Note that the second temperature sensor 45b detects a temperature rise in the non-sheet passing portion region of the fixing belt 41 during continuous passage of small size paper and feeds back temperature information to the control unit 100. When the temperature detected by the second temperature sensor 45b exceeds a predetermined temperature, the control unit 100 performs control to reduce the throughput of the image forming apparatus, for example.

[Example 2]
The bottom plate portion 42a in the both end region 42B of the reflecting plate 42 is not made bimetallic as a whole, and the portion corresponding to the width end portion of the paper of various large and small width sizes in the longitudinal direction of the bottom plate portion 42a is made bimetallic. You can also.

  An example is shown in FIG. In this example, in the reflection plate 42 according to the first embodiment, the boundary between the bottom plate portion 42a in the longitudinal central region 42A and the bottom plate portion 42a in both end regions 42B is a bimetal 42d. Further, in the longitudinal direction of the bottom plate portion 42a in the both end region 42B, a portion corresponding to the width end portion of the A4R paper which is a medium size paper is formed as a bimetal 42d.

  When the fixing device is in a standby state or when an A3R sheet having the maximum width is being passed, no temperature rise occurs at the edge, so that no bimetal 42d is deformed. Therefore, as shown in FIG. 16A, the bottom plate portion 42a of the both end regions 42B of the reflection plate 42 maintains a flat plate state that is flush with the bottom plate portion 42a in the longitudinal central region 42A.

  When B5R paper having the minimum width size is continuously fed, all the bimetals 42d are deformed by the temperature rise at the edge. Therefore, the bottom plate portion 42a of the both end regions 42B of the reflecting plate 42 has an angle θ as shown in FIG. When the A4R paper, which is a medium size paper, is continuously fed, the bimetal 42d in the portion corresponding to the width edge of the A4R paper is deformed by the temperature rise at the edge. Therefore, the bottom plate portion 42a of both end regions 42B of the reflecting plate 42 has an angle θ as shown in FIG.

  Since the bottom plate portion 42a is flat, the angle θ is appropriately set with respect to the end portion temperature rise (fixing belt temperature). The bending angle θ can be changed according to the paper width size.

[Other matters]
Here, the present invention is not limited to the embodiments described above, and within the scope of the technical idea of the present invention, the forms of the embodiments described above are not limited to those suggested in the embodiments. Obviously, it can be changed. In addition, the number, position, shape, and the like of the constituent members are not limited to the embodiments described above, and can be set to a suitable number, position, shape, and the like for carrying out the present invention.

  1) For example, in the embodiment, the first rotating body 41 has been described as an apparatus using a cylindrical belt that is driven to rotate by the rotational driving of the second rotating body 44 as a driving rotating body. However, the present invention is not limited to this, and the first rotating body 41 can be in the form of a cylindrical driving rotating body having rigidity.

  2) The 2nd rotary body 44 can also be made into the form of the endless belt body which can rotate.

  3) The image heating apparatus of the present invention is not limited to use as a fixing apparatus that heats and presses the unfixed toner image T carried on the sheet P as in the embodiment and heat-fixes it as a fixed image. It is also effective as a heat treatment apparatus that adjusts the surface properties of an image such as improving the glossiness by heating and pressing an image (fixed image or semi-fixed image) once fixed or assumed on a sheet.

  4) The image forming unit of the image forming apparatus is not limited to the electrophotographic system. The image forming unit may be an electrostatic recording system or a magnetic recording system. Further, it is not limited to the transfer method, and a configuration in which an unfixed image is formed directly on a sheet may be used.

  40..Image heating device, 41..First rotating body, 44..Second rotating body, N..Nip part, P..Sheet, T..Toner image, 46..Sliding contact member, 43. ..Heating element, 42..Reflective member, 42A..Long central region, 42B..Both ends region

Claims (6)

An image heating apparatus that heats a toner image by nipping and conveying a sheet carrying a toner image at a nip portion,
A cylindrical first rotating body;
A sliding contact member fixed to be in sliding contact with the inner surface of the first rotating body;
A heating element fixed inside the first rotating body;
A reflecting member fixed inside the first rotating body and reflecting radiant heat from the heating element toward the inner surface of the first rotating body;
A second rotating body that contacts the sliding contact member via the first rotating body and forms the nip portion between the first rotating body, and
The reflecting member has a shape of both end regions with respect to the longitudinal central region in accordance with an end temperature increase caused by continuous introduction of a sheet having a width smaller than the maximum width sheet usable in the apparatus. The image heating apparatus is characterized in that radiant heat from the heating element facing the both end regions is deformed in a direction to reflect toward the inner surface of the longitudinal central region of the first rotating body.   The image heating apparatus according to claim 1, wherein a part of the reflecting member is fixed to the sliding contact member or a support member of the sliding contact member.   3. The image heating apparatus according to claim 1, wherein at least a part of the reflection member has a bimetal plate structure in which a plurality of metal plates having different thermal expansion coefficients are bonded to each other, thereby causing the deformation.   The image heating apparatus according to claim 3, wherein at least one coefficient of thermal expansion of the plurality of metal plates varies with temperature.   The image heating apparatus according to claim 1, wherein the first rotating body is an endless belt having flexibility.   The image heating apparatus according to claim 1, wherein the second rotating body is driven.