JP6012462B2 - Fixing device - Google Patents

Description

  The present invention relates to a fixing device used in an electrophotographic image forming apparatus such as a copying machine or an LBP.

  In recent years, a film fixing method has been used as a fixing device provided in an electrophotographic image forming apparatus. The fixing device of the film fixing system includes a cylindrical film, a heater that contacts the inner surface of the film, a support member that supports a surface opposite to the surface that contacts the inner surface of the film of the heater, and the heater through the film. A configuration having a pressure member that forms a nip portion is common. The recording material carrying the toner image is heated while being conveyed at the nip portion to fix the toner image on the recording material.

  A heater in which a heating resistor is formed on a substrate made of a ceramic such as alumina or aluminum nitride is generally used. One surface of the heater is in contact with the inner surface of the film, and the surface opposite to the surface in contact with the film is in contact with and supported by the support member, and a temperature sensitive element such as a thermistor or a fuse is in contact therewith. In the heater, the amount of power supplied to the heater is controlled using wave number control or phase control so that the temperature detected by the thermistor becomes the target temperature. When the heater temperature rises abnormally, the power supply to the heater is cut off by a fuse or a thermostat.

  Here, one of the problems in the fixing device described above is heater cracking due to runaway. The heater cracking due to the runaway means that the triac used for heater control breaks down, the heater control becomes impossible, power is continuously supplied to the heater, and the heater cracks. As a cause of the cracking of the heater, there are a heat difference caused by a temperature difference in the heater and a mechanical stress generated in the heater due to partial melting of the support member.

  In particular, when a heater cracks due to thermal stress, when the heater overheats, the temperature difference between the part where the thermistor etc. is in contact and the part where it is not in contact increases, resulting in large thermal stress, and the thermistor etc. comes into contact. The heater may break at the starting point.

  As countermeasures against this cracking of the heater, the safety element such as a fuse described above is used to cut off the energization of the heater before the heater is overheated and the substrate is cracked by thermal stress.

  However, in recent years, there has been an increasing demand for shortening FPOT (First Page Out Time) and improving productivity, and in the future, it will be necessary to supply a large amount of electric power to the heater, and heater cracking will occur at an early stage. Possible.

  Therefore, Patent Document 1 discloses a heating apparatus in which a metal plate 14a is provided between a heater 12 and a heat insulating support member 11 as shown in FIG. By interposing the metal plate 14a, which is a high heat conductive member, between the heat insulating support part 11 and the heater 12, the uneven temperature rise can be eliminated.

  Therefore, if the safety element is provided on the surface of the metal plate 14a opposite to the surface in contact with the heater 12, the temperature difference between the contacted portion of the safety element and the non-contacting portion is reduced. It is considered that the stress is also reduced and heater cracking is less likely to occur.

JP 11-84919 A

  However, in the configuration disclosed in Patent Document 1, although the metal plate 14a is fixed to the heat insulating support member 11 with an adhesive, the heater 12 and the metal plate 14a are brought into contact with each other by the pressure contact force of the nip portion of the heating device. I'm just doing it.

  Therefore, in a heating apparatus having a pressure release mechanism that releases the pressure contact state of the nip portion or relaxes the pressure contact force when the device is stopped, the heater 12 and the metal plate 14a are released when the pressure contact state of the nip portion is released or the pressure contact force is relaxed. There may be situations where there is not enough contact. That is, when the pressure contact force at the nip portion is sufficient, the metal plate 14a and the heater are sufficiently in contact with each other due to the pressure contact force at the nip portion. However, when the press-contact state of the nip portion is released or the press-contact force is relaxed, there may be a situation where the heater 12 and the metal plate 14a are not sufficiently in contact with each other due to the influence of thickness tolerance or warpage of the metal plate 14a.

  If a runaway occurs in which the heater cannot be controlled in a situation where the heater 12 and the metal plate 14a are not sufficiently in contact with each other, the effect of leveling the heater temperature distribution by the metal plate 14a is not sufficiently exhibited and the heater cracks. May occur.

  Accordingly, an object of the present invention is to provide a fixing device capable of stably contacting a heater and a metal plate even when the pressure contact state of the nip portion of the fixing device is released or the pressure contact force is reduced. .

  To achieve the above object, a cylindrical film, a plate-like heater that contacts the inner surface of the film, and a support member that supports a surface of the heater opposite to the surface that contacts the inner surface of the film, A high thermal conductivity member provided between the heater and the support member and in contact with the heater; and both end portions of the heater in the generatrix direction do not move in the thickness direction of the heater with respect to the support member. And a pressure member that forms a nip portion together with the heater via the film, and heated while conveying a recording material carrying a toner image at the nip portion. In the fixing device for fixing an image to a recording material, the first state in which the pressure contact force of the nip portion is set to a pressure contact force capable of fixing processing, and the pressure contact state of the nip portion is released or It is possible to switch to a second state in which the pressure contact force of the top portion is set to a pressure contact force smaller than the first state, and the heat of the heater is sensed through the high heat conductive member. As described above, the surface of the support member facing the high heat conductive member has a temperature sensing element provided on the high heat conductive member. It has the shape which protruded in the direction approaching.

  According to the present invention, it is possible to provide a fixing device capable of stably contacting the heater and the metal plate even when the pressure contact state of the nip portion of the fixing device is released or the pressure contact force is reduced.

Sectional schematic diagram for explaining the configuration of the fixing device according to the first embodiment. (A) Front schematic diagram for explaining the configuration of the fixing device according to the first embodiment (when pressure is applied), (b) Front schematic diagram for explaining the configuration of the fixing device according to the first embodiment (when pressure is released) ) Illustration of ceramic heater Illustration of thermistor and thermal fuse (A) The figure for demonstrating the holding method and the metal plate holding method which concern on Example 1, (b) The figure for demonstrating the holding method of the metal plate in Example 1, (c) The heater in Example 1, The figure explaining the relationship between a support member and a metal plate (A) Explanatory drawing of power supply connector, (b) Explanatory drawing of clip The figure for demonstrating the holding method of the heater and metal plate in Example 1 when the bending rigidity of a heater is large. Diagram for explaining the heat flow of the heater and metal plate The figure which shows the shape and structure of a metal plate in Example 2. The figure for demonstrating the control part of the heater which concerns on Example 1. FIG. (A) The supporting member of the modification of Example 1, (b) The figure explaining the holding method of the heater and metal plate of the modification of Example 1. The figure for demonstrating the structure of the heater and metal plate which concern on a prior art example

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, the outline of the fixing device in the present embodiment will be described, and then the features of the present embodiment will be described.

  In the following description of the apparatus configuration, the longitudinal direction is a direction orthogonal to the recording material conveyance direction on the recording material conveyance path surface. The width direction is the same direction as the recording material conveyance direction.

  FIG. 1 is a schematic cross-sectional view of the fixing device 18 according to the present embodiment as viewed from the longitudinal direction, and FIG. 2 is a schematic view of the end portion of the fixing device 18 as viewed from the width direction.

  31 is a film unit including a flexible cylindrical film 36, and 32 is a pressure roller as a pressure member. The film unit 31 and the pressure roller 32 are disposed substantially in parallel between the left and right side plates 34 of the apparatus frame 33.

  The pressure roller 32 includes a cored bar 32a, an elastic layer 32b formed outside the cored bar 32a, and a releasable layer 32c formed outside the elastic layer 32b. As the material of the elastic layer 32b, silicone rubber, fluorine rubber, or the like is used. As the material of the release layer 32c, PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), FEP (tetrafluoroethylene / hexafluoropropylene copolymer), or the like is used. .

  In this embodiment, a silicone rubber layer 32b having a thickness of about 3.5 mm is formed by injection molding on a core metal 32a made of stainless steel and having an outer diameter of 11 mm, and a PFA resin tube 32c having a thickness of about 40 μm is coated on the outside thereof. A pressure roller 32 was used. The outer diameter of the pressure roller 32 is 18 mm. The hardness of the pressure roller 32 is desirably in the range of 40 ° to 70 ° from the viewpoint of securing the nip N and durability, etc. at a load of 9.8 N with an ASKER-C hardness meter. In this embodiment, the angle is set to 54 °. The length of the elastic layer in the longitudinal direction of the pressure roller 32 is 226 mm. As shown in FIG. 2, the pressure roller 32 is rotatably supported between the apparatus frame side plates 34 via bearing members 35 at both ends in the longitudinal direction of the cored bar 32a. G is a drive gear fixed to one end of the pressure roller core 32a. A rotational force is transmitted to the drive gear G from a drive source (not shown), and the pressure roller 32 is rotationally driven.

  A film unit 31 shown in FIG. 1 includes a film 36, a plate-like heater 37 that contacts the inner surface of the film 36, a support member 38 that supports the heater 37, and a metal plate 39 as a high heat conduction member. The film unit 31 further includes a pressure stay 40 that reinforces the support member, a flange 41 that restricts movement of the film 36 in the longitudinal direction, and the like.

  The film 36 has a base layer, an elastic layer formed outside the base layer, and a release layer formed outside the elastic layer, and is a cylindrical flexible member. The film 36 of this example has an inner diameter of 18 mm, a polyimide base material having a thickness of 60 μm as a base layer, a silicone rubber layer having a thickness of about 150 μm as an elastic layer, and a PFA resin tube having a thickness of 15 μm as a release layer. ing. As shown in FIG. 1, the support member 38 has a substantially semicircular saddle shape in cross section, is a member having rigidity, heat resistance, and heat insulation, and is formed of a liquid crystal polymer (Liquid Crystal Polymer) or the like. ing. The support member 38 has a role of supporting the inner surface of the film 36 fitted on the support member 38 and a role of supporting the heater 37 on one surface.

  As shown in FIG. 3, the heater 37 has a heating resistor 37b made of a silver / palladium alloy or the like formed on a substrate 37a made of ceramic such as alumina or aluminum nitride by screen printing or the like. The electrical contact portion 37c is connected. In the present embodiment, two heating resistors 37b are connected in series, and the resistance value is 18Ω. By forming a glass coat 37d as a protective layer on the heating resistor, the heating resistor is protected and the slidability with the film 36 is improved. The heater 37 is disposed along the generatrix direction of the film 36 while facing the support surface of the support member 38.

  FIG. 4 is a view showing the support member 38, the thermistor 42 and the thermal fuse 43, which are temperature sensitive elements. A through hole is provided in the support member 38, and a thermistor 42 as a temperature detection element and a thermal fuse 43 as a safety element are arranged to contact the metal plate 39 from the through hole. That is, the temperature sensitive element is provided on the high heat conductive member so as to sense the heat of the heater 37 through the high heat conductive member.

  In the thermistor 42, a thermistor element is disposed on a casing via ceramic paper or the like for stabilizing the contact state with the heater 37, and an insulator such as polyimide tape is further covered. The thermal fuse 43 is a component that senses abnormal heat generation of the heater when the heater 37 abnormally heats up and cuts off the power supply to the heater 37. The thermal fuse 43 is mounted with a fuse element that melts at a predetermined temperature in a cylindrical metal casing, and shuts off a circuit for energizing the heater 37 when the fuse element is blown by an abnormal temperature rise of the heater 37. . The size of the thermal fuse 43 in this embodiment is such that the length of the portion of the metal casing that contacts the heater 37 is about 10 mm, and the width of the metal casing is about 4 mm. The thermal fuse 43 is installed on the metal plate 39 via thermal conductive grease, and the thermal fuse 43 floats with respect to the heater 37 to prevent malfunction.

  The control unit that controls the amount of power supplied to the heater 37 will be described with reference to FIG. The CPU 82 turns on the triac 81 and energizes the heating resistor 37 b from the commercial power supply 80 through the electrical contact portion 37 c of the heater 37 to raise the temperature of the heater 37. Then, the temperature of the heater 37 is detected by the thermistor 42, and the output of the thermistor 42 is A / D converted and taken into the CPU 82. The CPU 82 controls the power supplied to the heating resistor 37b by the triac 81 based on the captured temperature information by phase control or wave number control. That is, the CPU 82 controls the triac 81 so that the heater 37 is heated when the temperature detected by the thermistor 42 is higher than the target temperature. Further, the CPU 82 controls the triac 81 so that the heater 37 falls when the temperature detected by the thermistor 42 is lower than the target temperature. By such control, the heater 37 can be maintained at the target temperature. Further, as shown in FIG. 10, the thermal fuse 43 is arranged so that the current flowing from the commercial power source 80 to the heater 37 can be cut off regardless of the CPU 82 when the heater 37 is abnormally heated.

  Next, the pressure stay 40 of FIG. 1 has a U-shaped cross section and is a member that is long in the generatrix direction of the film 36. The role of the pressure stay 40 is to increase the bending rigidity of the film unit 31. The pressure stay 40 of this embodiment is formed by bending stainless steel having a plate thickness of 1.6 mm.

  Next, the assembly of the film unit 31 will be described. As shown in FIG. 2A, the pressure stay 40 is formed by inserting a support member 38 holding the heater 37 and attaching the pressure stay 40 into the inside of the film 36, and The flanges 41 are attached to both ends of the film 36 in the generatrix direction.

  As shown in FIG. 1, the film unit 31 is disposed between the left and right side plates 34 of the apparatus frame 33 so that the heater 37 of the film unit 31 faces the pressure roller 32 through the film 36. In the left and right flanges 41, the vertical groove portions 41 a included therein are engaged with the vertical groove portions 34 a included in the left and right side plates 34 of the apparatus frame 33. In this embodiment, a liquid crystal polymer resin is used as the material of the flange 41.

  Then, as shown in FIG. 2A, a pressure spring 45 is provided between the pressure portions 41 b and the pressure arms 44 of the left and right flanges 41. Accordingly, the heater 37 is pressed against the pressure roller 32 with the film 36 interposed therebetween via the left and right flanges 41, the pressure stay 40, and the support member 38. As a result, the heater 37 resists the elasticity of the pressure roller 32 through the film 36, and a nip portion N of about 6 mm is formed together with the pressure roller 32.

  In this embodiment, the pressure of the pressure spring 45 is set so that the pressure contact force between the film 36 and the pressure roller 32 is 160 N in total pressure.

  Then, a rotational force is transmitted from a drive source (not shown) to the drive gear G of the pressure roller 32, and the pressure roller 32 is rotated at a predetermined speed in the clockwise direction in FIG. As the pressure roller 32 is driven to rotate, a rotational force acts on the film 36 by a frictional force acting between the pressure roller 32 and the film 36 in the nip portion N. As a result, as shown in FIG. 2, the film 36 slides while contacting one surface of the heater 37, and rotates around the support member 38 in the counterclockwise direction following the rotation of the pressure roller 32. The inner surface of the film 36 is coated with heat-resistant grease, so that the slidability between the heater 37 and the support member 38 and the inner surface of the film 36 is improved.

  The film 36 is rotated to energize the heater 37, and the recording material P is introduced with the temperature detected by the thermistor 42 of the heater 37 reaching the target temperature. The entrance guide 30 plays a role of guiding the recording material P on which the toner image t in an unfixed state is directed toward the nip portion N.

  The recording material P carrying the unfixed toner image t is introduced into the nip portion N, and the surface of the recording material P carrying the toner image in the nip portion N is in close contact with the film 36 and is conveyed along with the film 36 through the nip portion N. . In this conveyance process, the unfixed toner image t on the recording material P is heated and pressed on the recording material P and fixed by the heat of the film 36 heated by the heater 37. The recording material P that has passed through the nip portion N is discharged after being separated from the surface of the film 36 by a curvature, and is discharged outside the apparatus by a pair of discharge rollers (not shown).

  Further, by rotating a pressure release cam (not shown), the flange 40 is moved away from the pressure roller 32, and the film unit 31 is moved to the pressure roller as shown in FIGS. 2 (a) to 2 (b). A pressure release mechanism is provided that is spaced from 32. One purpose of performing this operation is to facilitate the jam processing of the recording material P when the recording device is jammed in the fixing device 18. The second purpose is to prevent the film 36 from being plastically deformed due to the press-contact force of the nip portion in a situation where the rotation of the film 36 is stopped such as during sleep, resulting in an image defect.

  That is, the fixing device 18 of the present embodiment has a first state where the pressure contact force of the nip portion is set to a pressure contact force capable of fixing processing, and a state where the pressure contact state of the nip portion is released or the pressure contact force of the nip portion is changed to the first state. It is possible to switch to the second state in which the pressure contact force is set to be smaller than that in the state.

  In this embodiment, the pressure contact state of the nip portion is automatically released by a pressure release motor (not shown), but the pressure release cam may be manually rotated to release the pressure contact state of the nip portion.

(Features of this embodiment)
The configuration of the fixing device 18 having the metal plate 39 as a high heat conductive member, which is a feature of this embodiment, will be described with reference to FIG. FIG. 5A is a cross-sectional view around the heater 37 viewed from the recording material conveyance direction, and FIG. 5B is a view of the state in which the metal plate 39 is provided on the support member 38 with the heater 37 removed. In FIG. 5, the thermistor 42 and the thermal fuse 43 are not shown. FIG. 5C will be described later.

  In this embodiment, an aluminum plate having a constant thickness of 0.3 mm in the direction of the generatrix of the film 36 is used as the metal plate 39. The abutting portion that abuts on the heater has a straight shape in which the length in the generatrix direction of the film 36 is 226 mm and the width in the direction orthogonal to the generatrix direction of the film 36 is 5 mm. The metal plate 39 has a bent portion 39 a of 1.5 mm at both ends in the generatrix direction of the film 36 and is inserted into the hole 38 a of the support member 38. This hole is provided slightly larger than the metal plate in order to absorb the difference in linear expansion coefficient between the metal plate 39 and the support member 38, so that the metal plate 39 is completely fixed to the support member 38. It ’s difficult. In this embodiment, aluminum is used as the material of the high thermal conductivity member, but other members having higher thermal conductivity than the substrate of the heater 37 such as a metal plate such as copper or a graphite sheet can be used.

  The substrate of the heater 37 of this embodiment has a rectangular parallelepiped shape in which the length of the film 36 in the generatrix direction is 260 mm, the length of the film 36 in the generatrix direction is 5.8 mm, and the thickness is 1.0 mm. Further, the material of the substrate of this embodiment is alumina.

In the present embodiment, the metal plate 39 is more easily bent than the support member 38 and the heater 37 with respect to a load perpendicular to the recording material conveyance path surface. That is, when the Young's modulus is E (GPa) and the secondary moment of inertia is I (m ⁴ ), the bending rigidity EI (N · m ² ) of the metal plate is larger than the bending rigidity of the heater 37 and the support member 38. small. Further, the bending rigidity of the heater 37 is smaller than that of the support member 38.

The metal plate 39 of the present embodiment is made of aluminum, has a Young's modulus of about 70 (GPa), and a secondary moment of about 0.011 (mm ⁴ ), so that the bending rigidity EI is about 7.9. × 10 ² (N · mm ² ) On the other hand, since the Young's modulus of the substrate of the heater 37 is about 350 (GPa) and the second moment of section is about 0.483 (mm ⁴ ), the bending rigidity EI is 1.7 × 10 ⁵ (N · mm ² ). It becomes. Since the Young's modulus of the liquid crystal polymer used for the support member 38 is approximately 13 (GPa) and the second moment of section is approximately 29.4 (mm ⁴ ), the bending rigidity EI is 3.8 × 10 ⁵ (N · mm ² ). Note that the cross-sectional shape of the support member 38 is shown as an average value because ribs or the like actually stand partially and are not the same in the generatrix direction of the film 36.

  Here, the role of the metal plate 39 will be described. The role of the metal plate 39 is to suppress heater cracking by equalizing the heater 37 when the heater 37 runs away. If the thermistor 42, fuse 43, or the like is in direct contact with the substrate of the heater 37, the heater cracks due to thermal stress due to a temperature difference between the portion that is in contact and the portion that is not in contact when the heater 37 runs away. May end up. Therefore, by providing the thermistor 42 and the fuse 43 on the metal plate 39 in contact with the heater 37 as in this embodiment, the substrate of the heater 37 is soaked during the runaway of the heater 37 and the heater cracks due to thermal stress. It becomes difficult to occur.

  The soaking of the heater 37 will be described with reference to FIG. In this embodiment, the thermal conductivity of alumina used as the substrate 37a of the heater 37 is approximately 26 W / mK. On the other hand, the thermal conductivity of aluminum used as the metal plate 39 is about 230 W / mK, which is larger than the base 37a. Here, as shown in FIG. 8, a case is considered where a portion H in the direction of the generatrix of the film 36 of the substrate 37a is hotter than other portions. In addition to the heat flow A in the generatrix direction of the film 36 inside the substrate 37a, a heat flow from the substrate 37a to the metal plate 39 occurs in the portion of the substrate 37a that is in contact with the metal plate 39. Furthermore, a heat flow B that returns to the substrate 37 a again in the direction of the bus line of the film 36 is generated in the metal plate 39. By this action, the heater 37 is soaked.

  Next, the shape of the support surface that supports the heater 37 via the metal plate 39 of the support member 38 will be described. As shown in FIG. 5A, the central portion of the support surface of the film 36 in the generatrix direction has a region C protruding in a direction closer to the pressure roller 32 than the end portion. The region C of the present embodiment has a gentle curved surface shape (hereinafter referred to as a crown shape) that gradually approaches the pressure roller 32 from the end in the generatrix direction to the center of the film 36. The length in the generatrix direction of the film 36 in the region C is 226 mm, which is the same as the length of the pressure roller 32.

  Next, the configuration of the power supply connector 46 and the clip 47 as the regulating members will be described with reference to FIG. In the first embodiment, the power supply connector 46 or the clip 47 is used to maintain the state where both ends of the film 36 of the heater 37 are in contact with the support member 38.

  The power supply connector 46 includes a housing portion 46a and a contact terminal 46b formed of a U-shaped resin (FIG. 6A). The housing part 46a sandwiches the heater 37 and the support member 38 from the outside, thereby restricting the end part of the film 36 of the heater 37 from moving in the thickness direction of the heater 37 with respect to the support member 38. Further, the contact terminal 46b is elastically contacted with the electrical contact portion 37c of the heater 37 at a predetermined contact pressure to maintain an electrical connection. Further, the contact terminal 46b is connected to a bundle 48, and the bundle 48 is connected to the commercial power supply 80 and the triac 81 shown in FIG. The housing portion and the contact terminal may be configured separately.

  The clip 47 is a U-shaped metal plate and elastically sandwiches the heater 37 and the support member 38 from the outside, and both ends of the film 36 of the heater 37 in the generatrix direction with respect to the support member 38. To prevent movement in the thickness direction (FIG. 6B).

  In addition, the power supply connector 46 and the clip 47 restrict the both end portions of the heater 36 in the bus line direction of the film 36 from moving in the film thickness direction with respect to the support member 38, and are not changed to the surface of the heater 37. It is configured to be movable in the direction. Therefore, it is possible to prevent unnecessary stress from being applied to the heater 37 when the heater 37 is thermally expanded or bent during pressurization and separation.

(Operation of this embodiment)
The effect of this embodiment is that the heater 37 and the metal plate 39 are stably in contact even when the pressure contact state of the nip portion is released or the pressure contact force of the nip portion is reduced. .

  The mechanism of this action will be described with reference to FIG. For ease of viewing, FIG. 5C shows only the support member 38, the metal plate 39, and the heater 37. In the present embodiment, a portion corresponding to the region C of the heater 37 is supported by a support surface having a crown shape of the support member 38 through the metal plate 39, and both ends of the film 36 of the heater 37 in the bus bar direction are end support. It is supported in contact with the surface 90.

  The movement in the thickness direction of the heater 37 with respect to the support member 38 is regulated at both ends in the bus bar direction of the film 36 of the heater 37 of this embodiment with respect to the support member 38 and the like. Accordingly, the positions in the thickness direction of the heater 37 with respect to the support members 38 at both ends of the heater 37 are in a state where the pressure contact state of the nip portion N is set to a pressure contact force capable of fixing processing. Even if it is released or the pressure contact force of the nip portion is reduced, it does not change.

  Further, when the metal plate 39 is assembled on the support surface having the crown shape of the support member 38, the surfaces of the metal plate 39 that are in contact with the central portion of the film 36 of the heater 37 are at both ends in the bus direction of the film 36 of the heater 37. It protrudes from the end support surface 90 with which the part comes into contact. That is, the heater 37 is deformed by being pushed in a direction in which the central portion of the film 36 in the busbar direction approaches the pressure roller 32 in a state where movement in the thickness direction of the heater 37 at both ends in the busbar direction of the film 36 is restricted. It is in a state. Accordingly, a restoring force F is generated in the heater 37 itself to return to the original straight shape. The bending rigidity in the present embodiment is that the metal plate 39 <the heater 37 <the support member 38, so that the metal plate 39 contacts with the heater 37 along the crown shape of the support member 38 stably by the restoring force F of the heater 37. Will do. The stable contact state between the metal plate and the heater 37 is caused by the restoring force F of the heater 37 itself, and therefore changes even when the pressure contact state of the nip portion is released or the pressure contact force of the nip portion is reduced. Absent.

  Here, the magnitude of the restoring force in this example was measured. When the load required for the heater 37 to be bent 0.6 mm from the straight shape to the center portion of the film 36 of the support member 38 in the generatrix direction was measured, the simple center load was 0.42N. In the present embodiment, since the crown shape of the support member 38 is a gently curved shape, it is actually close to a uniform load, and a restoring force of 0.42 N or more over the generatrix direction of the film 36 of the heater 37. F is generated. Therefore, even when the pressure contact force at the nip portion of the fixing device 18 is released or the pressure release state is eased, the metal plate 39 is stably contacted by the restoring force F of the heater 37 itself.

  In addition, since the support member 38 of this embodiment is backed up by the pressure stay 40 having high bending rigidity, the support member does not bend due to the restoring force F of the heater. Even if the support member 38 is not backed up by the pressure stay 40, if the bending rigidity of the support member 38 is sufficiently large with respect to the heater 37, the heater 37 bends and a restoring force F is generated. . When the bending rigidity of the support member 38 is smaller than that of the heater 37, the support member 38 is deformed upward in the figure due to its crown shape as shown in FIG. In this case, the metal plate 39 is pressed against the heater 37 side by the restoring force F ′ of the support member 38, but the bending rigidity of the metal plate 39 is small, so that it does not resist the restoring force F ′ by the support member 38, The contact between the metal plate 39 and the heater 37 can be ensured. When both of the bending stiffnesses are approximately the same, both the heater 37 and the support member 38 bend, and the restoring force F of the heater and the restoring force F ′ of the support member 38 are balanced, so that the metal plate 39 and the heater The contact with 37 is ensured.

  As described above, according to the present embodiment, the heater 37 and the metal plate 39 are stably in contact with each other even when the pressure contact state of the nip portion is released or the pressure contact force of the nip portion is reduced. To do.

  Therefore, the effect of making the temperature distribution of the heater 37 of the metal plate 39 uniform can be sufficiently exerted, and heater cracking can be suppressed.

  In the present embodiment, the support surface has a crown shape in the region C of the support member 38. However, if there is a convex shape in which the central portion protrudes from the end in the generatrix direction of the film 36 in the region C. good. A modification of the first embodiment is shown in FIG. FIG. 11A shows a support member 95 of this modification. FIG. 11B is a diagram in which the support member 38 of the first embodiment is replaced with the support member 95 of FIG. Also in this modified example, the heater 37 is pushed in a direction in which the central portion of the film 36 in the busbar direction approaches the pressure roller 32 in a state where movement in the thickness direction of the heater 37 at both ends of the film 36 in the busbar direction is restricted. Is in a deformed state. Accordingly, as in the first embodiment, a restoring force acts on the heater 37 and the heater 37 and the metal plate 39 are in stable contact.

  However, in the configuration of the first embodiment, the heater 37 that receives the pressure contact force in the state where the pressure contact force of the nip portion N is set to a pressure contact force capable of fixing processing supports the support member via the metal plate 39 in the longitudinal direction. Therefore, there is an advantage that the pressure in the nip portion is stabilized.

  In the present embodiment, the crown shape is not provided on the support surface of the support member 38 as in the first embodiment, but is provided on the surface of the metal plate 39 facing the heater 37. The metal plate 39 is made of aluminum as in the first embodiment. The only difference between the present embodiment and the first embodiment is the support member 38 and the metal plate 39, and the other fixing device configurations are substantially the same as those of the first embodiment, and are therefore omitted.

  The features of this embodiment will be described. As shown in FIG. 9, the metal plate 39 has a shape in which the central portion in the bus line direction of the film 36 protrudes in a direction closer to the heater 37 than the end portion. The metal plate 39 has a gently curved crown shape that gradually approaches the heater 37 from the end in the generatrix direction of the film 36 toward the center. The length of the metal plate 39 in the generatrix direction of the film 36 and the dimension in the direction orthogonal to the generatrix direction of the film 36 are the same as in the first embodiment. The thickness of the metal plate 39 is 0.2 mm at the end and 0.8 mm at the center in the direction of the generatrix of the film 36. In a state where the heater 37 is attached to the support member 38, there is a portion in which the surface of the metal plate 39 protrudes from the end support surface 90 of the heater 37 in the thickness direction of the heater 37. Therefore, the restoring force F generated in the heater 37 is the same as that of the first embodiment.

  As a result, also in the second embodiment, even when the pressure contact force of the nip portion N is set to a pressure contact force capable of fixing processing, the pressure contact state of the nip portion is released or the pressure contact force of the nip portion is reduced. The heater 37 and the metal plate 39 are in stable contact.

  The effects of the present embodiment that are different from the first embodiment will be described. Since both ends of the metal plate 39 in the direction of the bus of the film 36 are bent into L shapes, the heat of the heater 37 easily escapes from there during the fixing process, and the film 36 of the heater 37 in the direction of the bus An end temperature drop may occur. Therefore, in the generatrix direction of the film 36, by setting the thickness of the metal plate 39 to be thinner than the center portion, there is an effect that heat at the end portion is difficult to escape.

  In this embodiment, a crown shape is formed by changing the thickness of the metal plate 39 in the generatrix direction of the film 36, and the temperature equalizing effect of the heater 37 is suppressed while suppressing the temperature drop at the end of the heater 37 in the generatrix direction. It can be demonstrated.

  In the present embodiment, the crown shape may be formed on both the support member 38 and the metal plate 39.

18 Fixing Device 32 Pressure Roller 36 Film 37 Heater 38 Support Member 39 Metal Plate 40 Pressure Stay 42 Thermistor 43 Thermal Fuse 46 Power Supply Connector 47 Clip

Claims (6)

A cylindrical film, a plate-like heater that contacts the inner surface of the film, a support member that supports a surface of the heater opposite to the surface that contacts the inner surface of the film, and the heater and the support member A high thermal conductivity member provided between and in contact with the heater; and a regulating member for regulating the both end portions of the heater so that the both end portions of the film in the bus line direction do not move in the thickness direction of the heater with respect to the support member And a pressure member that forms a nip portion together with the heater via the film, and a fixing device that fixes the toner image on the recording material by heating the recording material carrying the toner image at the nip portion In
A first state where the pressure contact force of the nip portion is set to a pressure contact force capable of fixing processing, and a pressure contact state where the pressure contact state of the nip portion is released or the pressure contact force of the nip portion is smaller than the first state. Switch to the second state set to force,
Having a temperature sensing element provided on the high thermal conductivity member so as to sense the heat of the heater via the high thermal conductivity member;
The fixing device according to claim 1, wherein a surface of the support member that faces the high thermal conductivity member has a shape in which a central portion in a bus line direction of the film protrudes in a direction closer to the pressure member than an end portion.   2. The fixing device according to claim 1, wherein a surface of the support member that faces the high heat conductive member is a curved surface that approaches the pressure member as it goes from both ends toward the center in the generatrix direction of the film.   The fixing device according to claim 1, wherein a bending rigidity of the heater is larger than a bending rigidity of the high heat conductive member and smaller than a bending rigidity of the support member.   The fixing device according to claim 1, wherein a thermal conductivity of the high thermal conductivity member is higher than a thermal conductivity of a substrate of the heater.   The fixing device according to claim 1, wherein the high heat conductive member is a metal plate or a graphite sheet. 6. The fixing according to claim 1, wherein the temperature sensitive element is a temperature detecting element for detecting a temperature of the heater or a safety element for cutting off the energization to the heater. apparatus.

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