Heating unit

Abstract

To detect an accurate temperature with a temperature detection member.SOLUTION: A heating unit 1 comprises: a heater 10; a temperature detection member (thermistor 50) that detects the temperature of the heater 10; a belt 3; a holder 20 that supports the heater 10; a sheet-like first heat conduction member 30 that is located between the heater 10 and the holder 20, the first heat conduction member 30 having a first heater side surface 31 directed toward the heater 10, a first opposite surface 32 on the opposite side of the first heater side surface 31, and openings (first openings 35A, 35B); and a sheet-like second heat conduction member 45 that is arranged at a position corresponding to at least the openings when seen from an orthogonal direction orthogonal to the first opposite surface 32, the second heat conduction member 45 having a second heater side surface 45F directed toward the heater 10 and a second opposite surface 45R on the opposite side of the second heater side surface 45F. The temperature detection member is in contact with the second opposite surface 45R of the second heat conduction member 45.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a heating unit used in a fixing device of an electrophotographic image forming apparatus. [Background technology]

[0002] Conventionally, a fixing device in which a rotating belt is sandwiched between a ceramic heater and a pressure roller is known (Patent Document 1). In this fixing device, the ceramic heater has a substrate and a resistance heating element, and a sheet-like heat conductive member is arranged in contact with the back surface opposite to the nip surface that contacts the belt. A through hole is formed in the heat conductive member, and a temperature detection member contacts the back surface of the ceramic heater through this through hole. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-194719 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when a heater has a resistance heating element provided on a substrate, there is a difference in temperature between the area close to the resistance heating element and the area far from the resistance heating element. Therefore, if a temperature detection member is placed in direct contact with the rear surface of the heater as in the conventional technology, there is a possibility that the temperature cannot be detected accurately due to the influence of temperature unevenness caused by the arrangement of the resistance heating element.

[0005] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to detect temperature accurately using a temperature detection member. [Means for solving the problem]

[0006] The heating unit for solving the above-mentioned problems includes a substrate, a resistive heating element supported on the substrate, a heater having a nip surface and a back surface opposite the nip surface, a temperature detection member for detecting the temperature of the heater, an endless belt having an inner surface in contact with the nip surface and rotating around the heater, a holder for supporting the heater, a sheet-like first heat conduction member located between the heater and the holder and having a thermal conductivity higher than that of the substrate, the first heat conduction member having a first heater side surface facing the heater side, a first opposite surface opposite the first heater side surface, and an opening, and a sheet-like second heat conduction member arranged at a position corresponding to at least the opening when viewed from an orthogonal direction perpendicular to the first opposite surface, the second heat conduction member having a second heater side surface facing the heater side and a second opposite surface opposite the second heater side surface. The temperature detection member is in contact with the second opposite surface of the second thermally conductive member.

[0007] With this configuration, the temperature detection member does not directly contact the rear side of the heater, but contacts the second opposite side of a second thermal conduction member that is separate from the first thermal conduction member. This allows temperature unevenness caused by the arrangement of the resistive heating element to be averaged out, allowing the temperature detection member to detect an accurate temperature.

[0008] It is desirable for the thermal conductivity from the heater to the second opposing surface to be better than the thermal conductivity from the heater to the first opposing surface.

[0009] According to this configuration, the responsiveness of the temperature detection member to the temperature of the heater can be ensured, and the temperature can be accurately detected by the temperature detection member.

[0010] The second thermally conductive member may have a thermal conductivity greater than that of the first thermally conductive member, and the second thermally conductive member may have a thickness smaller than that of the first thermally conductive member.

[0011] According to such a configuration, the responsiveness of the temperature detection member to the temperature of the heater can be ensured, and the temperature can be detected accurately by the temperature detection member.

[0012] When viewed from the orthogonal direction, the second thermal conductive member may be smaller in size than the first thermal conductive member.

[0013] The second thermally conductive member may also be located within the opening.

[0014] In the longitudinal direction of the heater, the length of the first thermally conductive member may be longer than the length of the resistive heating element.

[0015] With this configuration, the temperature of the heater can be made uniform over the entire area in the longitudinal direction of the heater where the resistance heating element is disposed.

[0016] The temperature detection member may be positioned in the longitudinal direction of the heater so as to detect the temperature at a position within a range through which a recording material of a maximum width that can be used with the heating unit can pass, and outside a range through which a recording material of a minimum width that can be used with the heating unit can pass.

[0017] According to this configuration, the temperature rise in the portion where the minimum-width sheet does not pass can be detected by the temperature detection member.

[0018] The first thermally conductive member may be made of aluminum or an aluminum alloy.

[0019] The first thermally conductive member may be an anisotropic thermally conductive member having a higher thermal conductivity in a direction parallel to the first heater side surface than in a direction perpendicular to the first heater side surface.

[0020] The heating unit may further include a sheet-like third thermally conductive member having a third heater side surface in contact with the back side surface of the heater and a third opposite surface opposite the third heater side surface. In this case, the first thermally conductive member may have the first heater side surface in contact with the third opposite surface, and the second thermally conductive member may have the second heater side surface in contact with the third opposite surface.

[0021] The third heat conducting member may be an anisotropic heat conducting member having a higher thermal conductivity in a direction parallel to the third heater side surface than in a direction perpendicular to the third heater side surface.

[0022] The anisotropic heat conductive member is, for example, a graphite sheet.

[0023] The second thermally conductive member may be made of aluminum or an aluminum alloy.

[0024] The temperature sensing member may have a protrusion, and the second thermally conductive member may be positioned relative to the temperature sensing member by engaging the protrusion.

[0025] With this configuration, the second thermal conductive member can be appropriately positioned with respect to the temperature detection member.

[0026] The second thermally conductive member may have a protrusion, and the protrusion may be engaged with the temperature detection member, thereby positioning the second thermally conductive member with respect to the temperature detection member.

[0027] With this configuration, the second thermal conductive member can be appropriately positioned with respect to the temperature detection member.

[0028] The temperature detection member may be a thermistor or a current interrupting member that cuts off the current to the resistance heating element when the heater becomes abnormally hot. Effect of the Invention

[0029] According to the present invention, the temperature can be accurately detected by the temperature detection member. [Brief description of the drawings]

[0030] [Figure 1] FIG. 2 is a cross-sectional view of the heating unit at the location of the thermistor. [Diagram 2]FIG. 3A shows the surface on which the resistive heating element of the heater is arranged, FIG. 3B shows the heater, the first thermal conductive member and the second thermal conductive member as viewed from the rear surface side of the heater, and FIG. 3C shows the holder as viewed from the opposite side to the heater. [Diagram 3] 1A is a perspective view of a thermistor, and FIG. 1B is a perspective view of a current interrupting member. [Figure 4] 4 is a cross-sectional view of the heating unit at the position of the current interrupting member. FIG. [Diagram 5] FIG. 1A is a cross-sectional view along the longitudinal direction of the heating unit, explaining the positioning of the second heat conductive member and thermistor, and FIG. 1B is a cross-sectional view along the longitudinal direction of the heating unit, explaining the positioning of the second heat conductive member and the current interruption member. [Figure 6] 11 is a cross-sectional view of the heating unit when the second heat conducting member is larger than the opening. FIG. [Figure 7] 13 is a cross-sectional view of a heating unit including a third heat conductive member. FIG. [Figure 8] 13 is a cross-sectional view of a heating unit according to a modified example in which the second heat conducting member is thinner than the first heat conducting member. FIG. [Figure 9] FIG. 1A is a cross-sectional view along the longitudinal direction of the heating unit illustrating another embodiment of the positioning of the second heat conductive member and thermistor; FIG. 1B is a cross-sectional view along the longitudinal direction of the heating unit illustrating another embodiment of the positioning of the second heat conductive member and the current-blocking member; and FIG. 1C is an enlarged cross-sectional view along the longitudinal direction of the heating unit illustrating yet another embodiment of the positioning of the second heat conductive member and thermistor. [Figure 10] FIG. 1(a) shows the surface on which the resistive heating element of a modified heater is arranged, FIG. 1(b) shows the heater, the first thermal conductive member and the second thermal conductive member as viewed from the back side of the heater, and FIG. 1(c) shows the holder as viewed from the opposite side to the heater. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] The heating unit 1 according to the embodiment is used in a fixing device of an image forming apparatus, a device for transferring foil by heat, etc. As shown in Fig. 1, the heating unit 1 includes a belt 3, a heater 10, a holder 20, a first heat conductive member 30, second heat conductive members 45, 46 (see Fig. 4), a thermistor 50 as an example of a temperature detection member, and a current interrupting member 60 as another example of a temperature detection member (see Fig. 4).

[0032] The belt 3 is endless and made of metal or resin. The belt 3 rotates around the heater 10 while being guided by the holder 20. The belt 3 has an outer circumferential surface and an inner circumferential surface. The outer circumferential surface comes into contact with the sheet to be heated. The inner circumferential surface comes into contact with the heater 10.

[0033] The heater 10 includes a substrate 11, a resistance heating element 12 supported by the substrate 11, and a cover 13. The substrate 11 is made of a long and narrow rectangular ceramic plate. The heater 10 is a so-called ceramic heater. The resistance heating element 12 is formed on one surface of the substrate 11 by printing. As shown in FIG. 2(a), in this embodiment, two resistance heating elements 12 are provided. The two resistance heating elements 12 are each long in the longitudinal direction of the heater 10 (hereinafter, the longitudinal direction of the heater 10 is simply referred to as the "longitudinal direction") and are arranged in parallel and spaced apart from each other in a lateral direction perpendicular to the longitudinal direction. A conductor 19A is connected to one end 12A of each resistance heating element 12, and a terminal 18 for supplying power is provided at each end of the conductor 19A. The other ends 12B of each resistance heating element 12 are connected to each other by the conductor 19B. The number of resistance heating elements 12 is not particularly limited. In addition, a resistive heating element having a greater heat generation amount at the longitudinal center than at the longitudinal ends, and a resistive heating element having a greater heat generation amount at the longitudinal ends than at the longitudinal center may be provided, and by controlling each resistive heating element individually, the heat generation distribution in the longitudinal direction can be adjusted.

[0034] The cover 13 covers the resistance heating element 12. The cover 13 is made of, for example, glass. The heater 10 has a nip surface 15 that contacts the inner circumferential surface of the belt 3 and a back surface 16 opposite to the nip surface 15.

[0035] The holder 20 is a member that supports the heater 10. The holder 20 has a support portion 21 and a guide portion 22. The support portion 21 has a plate shape corresponding to the shape of the heater 10. The support portion 21 has a support surface 21A that faces the side where the heater 10 is arranged, and an inner surface 21B opposite to the support surface 21A. As shown in FIG. 2(c), the support portion 21 has holder openings 25A, 25B, and 26 that penetrate the support portion 21. The holder opening 25A is disposed in the center of the support portion 21 in the longitudinal direction, and is a rectangle that is long in the longitudinal direction. The holder opening 26 is disposed at one end of the support portion 21 in the longitudinal direction, and is a rectangle that is long in the longitudinal direction. The holder opening 25B is disposed at the other end of the support portion 21 in the longitudinal direction, and is a rectangle that is long in the longitudinal direction.

[0036] The thermistor 50 includes two thermistors, a first thermistor 50A and a second thermistor 50B. The first thermistor 50A and the second thermistor 50B are the same component. The first thermistor 50A detects the temperature of the center of the heater 10 in the longitudinal direction. The first thermistor 50A is used to control the temperature of the heater 10 to a target temperature based on the temperature detected by the first thermistor 50A. The second thermistor 50B detects the temperature of the heater 10 at a position closer to the end of the heater 10 than the position detected by the first thermistor 50A in the longitudinal direction of the heater 10. The second thermistor 50B is used to detect an increase in temperature at a position closer to the end of the heater 10. The holder opening 25A is disposed at a position corresponding to the first thermistor 50A. The first thermistor 50A and the second thermistor 50B do not have to be the same component. In this case, it is desirable that the first thermistor 50A is a member that has higher temperature detection accuracy than the second thermistor 50B within the temperature range during the printing operation.

[0037] The current interrupting member 60 is a member that interrupts the flow of electricity to the resistance heating element 12 when the temperature of the heater 10 increases abnormally. The holder opening 26 is disposed at a position corresponding to the current interrupting member 60.

[0038] Returning to Fig. 1, the guide portions 22 are provided on both ends in the short direction of the support portion 21. Each guide portion 22 has a guide surface 22G along the inner peripheral surface of the belt 3. As shown in Fig. 1 and Fig. 2(c), the guide portion 22 has a plurality of guide ribs 22A aligned in the longitudinal direction.

[0039] The first heat conducting member 30 is a member for conducting heat in the longitudinal direction of the heater 10 to make the temperature of the heater 10 uniform in the longitudinal direction. The first heat conducting member 30 is a sheet-like member and is located between the heater 10 and the support part 21 of the holder 20. When the heating unit 1 sandwiches a sheet, which is an object to be heated, between itself and another pressing member, the first heat conducting member 30 is sandwiched between the heater 10 and the support part 21. The first heat conducting member 30 has a first heater side surface 31 that contacts the back side surface 16 of the heater 10 and a first opposite surface 32 that is opposite to the first heater side surface 31. The first opposite surface 32 is in contact with the support surface 21A of the support part 21.

[0040] 2(b), first thermal conductive member 30 has first openings 35A and 35B as an example of an opening penetrating first thermal conductive member 30, and second opening 36 as another example of an opening. First opening 35A is disposed in the center of first thermal conductive member 30 in the longitudinal direction, and has a rectangular shape that is long in the longitudinal direction. First opening 35A is disposed at a position corresponding to holder opening 25A, that is, at a position corresponding to first thermistor 50A. The second opening 36 is disposed at one end of the first heat conductive member 30 in the longitudinal direction, and has a rectangular shape that is long in the longitudinal direction. The second opening 36 is disposed at a position corresponding to the holder opening 26, that is, a position corresponding to the current interruption member 60. First opening 35B is disposed at the other end of first thermal conductive member 30 in the longitudinal direction, and has a rectangular shape that is long in the longitudinal direction. First opening 35B is disposed at a position corresponding to holder opening 25B, that is, at a position corresponding to second thermistor 50B.

[0041] As shown in FIG. 1, the first heat conducting member 30 is a member whose thermal conductivity in a direction parallel to the first heater side surface 31 (hereinafter simply referred to as the "planar direction") is greater than that in the planar direction of the substrate 11. The material of the first heat conducting member 30 is not particularly limited, and for example, metals with high thermal conductivity such as aluminum, aluminum alloys, and copper can be used. The first heat conducting member 30 may be an anisotropic heat conducting member whose thermal conductivity in the planar direction is greater than that in the thickness direction perpendicular to the first heater side surface 31. For example, a graphite sheet can be used as the anisotropic heat conducting member. The thickness of the first heat conducting member 30 is not particularly limited, and for example, it may be a film-like member thinner than 0.1 mm, or a plate-like member thicker than 1 mm.

[0042] The second thermal conductive members 45, 46 are intended to conduct heat in a planar direction to uniformly distribute the temperature at the portions where the second thermal conductive members 45, 46 are in contact with the heater 10, and to quickly transfer heat from the heater 10 to the temperature detection member (thermistor 50 or current interruption member 60). The second thermally conductive member 45 is a sheet-like member, and has a second heater side surface 45F facing the heater 10 side, and a second opposite surface 45R opposite to the second heater side surface 45F. As shown in FIG. 4, second thermally conductive member 46 similarly has second heater side surface 46F facing the heater 10, and second opposite surface 46R opposite to second heater side surface 46F.

[0043] 1 and 4, second heat conduction members 45, 46 are disposed at positions corresponding to first openings 35A, 35B and second opening 36 when viewed from a direction perpendicular to first opposite surface 32 of first heat conduction member 30. Second heat conduction member 45 includes second heat conduction member 45A and second heat conduction member 45B. In this embodiment, second heat conduction member 45A and second heat conduction member 45B are the same component, except that they are disposed at different positions. In this embodiment, the size of the second heat conductive members 45A, 45B, 46 is smaller than the first heat conductive member 30. The second heat conductive member 45A is located in the first opening 35A. The second heat conductive member 45B is located in the first opening 35B. The second heat conductive member 46 is located in the second opening 36.

[0044] The second heat conductive members 45, 46 are members whose thermal conductivity in a planar direction is greater than that of the substrate 11 in the planar direction. The material of the second heat conductive members 45, 46 is not particularly limited, but may be, for example, a metal with a high thermal conductivity, such as aluminum, an aluminum alloy, or copper. The thickness of the second heat conductive members 45, 46 is not particularly limited, and may be, for example, a film-like member thinner than 0.1 mm, or a plate-like member thicker than 1 mm.

[0045] The size of the second thermal conductive members 45, 46 in a short side direction perpendicular to the longitudinal direction is larger than the size of the short side direction of the resistance heating body 12. In this embodiment, the second thermal conductive members 45, 46 are located between the two resistance heating bodies 12 in the short side direction.

[0046] The second heat conducting members 45, 46 have better thermal conductivity at least in the thickness direction than the first heat conducting member 30. Therefore, the thermal conductivity from the heater 10 to the second opposite surface 45R, 46R is better than the thermal conductivity from the heater 10 to the first opposite surface 32. Here, good thermal conductivity does not only mean that the thermal conductivity of the material of the second heat conducting members 45, 46 is high, but also means that heat is transferred quickly including the thickness of the second heat conducting members 45, 56. For example, as shown in Figs. 1 and 4, when the first heat conducting member 30 and the second heat conducting members 45, 46 have the same thickness, if the thermal conductivity of the second heat conducting members 45, 46 in the thickness direction is higher than the thermal conductivity of the first heat conducting member 30 in the thickness direction, heat is transferred faster from the heater 10 to the second opposite surface 45R, 46R than from the heater 10 to the first opposite surface 32. Furthermore, when the first heat conduction member 30 and the second heat conduction member 45 are made of the same material and have the same thermal conductivity, if the thickness of the second heat conduction member 45 is smaller than the thickness of the first heat conduction member 30, as in the modified example shown in Figure 8, heat is conducted faster from the heater 10 to the second opposite surfaces 45R, 46R than from the heater 10 to the first opposite surface 32.

[0047] 5(b), second heat conductive member 46 has protrusions 46B that protrude in the thickness direction toward current interruption member 60. Protrusions 46B protrude from ends of second heat conductive member 46 in the longitudinal direction.

[0048] As shown in FIG. 3(b), thermistor 50 (50A, 50B) has a support plate 51, a biasing member 52, a film 53, and a temperature detection element 55. The biasing member 52 is a member having sponge-like elasticity, and is supported by the support plate 51. The biasing member 52 has a D-shaped cross section. The temperature detection element 55 is disposed so as to be located at the most protruding portion of the biasing member 52, and is connected to wiring (not shown). The film 53 is disposed so that the temperature detection element 55 is located at the most protruding portion of the biasing member 52, and is attached to the support plate 51 by being wrapped around the biasing member 52 and the support plate 51.

[0049] As shown in Fig. 3(a), film 53 has slits 53X at both ends in the longitudinal direction, extending in a direction perpendicular to the longitudinal direction. Thus, film 53 has central portion 53A located at the longitudinal center and in contact with biasing member 52, and protruding portions 53B located at both ends in the longitudinal direction. As shown in Fig. 5(a), when the thermistor 50 is attached to holder 20 and pressed against second heat conductive members 45A and 45B, biasing member 52 is crushed, and protruding portions 53B are portions that protrude relative to central portion 53A. Both ends in the longitudinal direction of second heat conductive members 45A and 45B engage with protruding portions 53B, and the second heat conductive members 45A and 45B are positioned relative to thermistor 50.

[0050] 3(b), current interrupting member 60 is a thermostat having an internal bimetallic interrupting mechanism, and has a case 61 that houses the interrupting mechanism, and a detection portion 62 that detects temperature and protrudes from case 61. As shown in FIG. 5(b), second heat conducting member 46 is positioned with respect to current interrupting member 60 by convex portions 46B engaging with both longitudinal ends of detection portion 62.

[0051] 1, the portion of first thermistor 50A protruding from support plate 51 enters holder opening 25A and contacts second opposite surface 45R of second heat conductive member 45A through holder opening 25A. Biasing member 52 of first thermistor 50A is crushed and temperature detection element 55 is pressed toward second opposite surface 45R of second heat conductive member 45A. The configuration in which second thermistor 50B contacts second opposite surface 45R is the same as the configuration in which first thermistor 50A contacts second opposite surface 45R, so a description thereof will be omitted.

[0052] The first openings 35A, 35B are preferably as small as possible so that the second heat conductive members 45A, 45B can be disposed therein. For example, the longitudinal size of the first openings 35A, 35B is preferably 1.5 times or less the longitudinal size of the second heat conductive members 45A, 45B. The lateral size of the first openings 35A, 35B is preferably 1.5 times or less the lateral size of the second heat conductive members 45A, 45B. The planar size of the second heat conductive members 45A, 45B is, for example, equal to that of the biasing member 52. It is preferable that the second heat conductive members 45A, 45B are larger than the width of one resistance heating element 12 and larger than the interval between adjacent resistance heating elements 12 in the lateral direction.

[0053] As shown in FIG. 4, in the current interrupting member 60, the detection portion 62 protruding from the case 61 fits into the holder opening 26 and contacts the second opposite surface 46R of the second heat conducting member 46 through the holder opening 26. It is desirable that the second opening 36 is as small as possible so that the second thermal conductive member 46 can be disposed therein. For example, it is desirable that the size of the second opening 36 in the longitudinal direction is 1.5 times or less the size of the second thermal conductive member 46 in the longitudinal direction. It is also desirable that the size of the second opening 36 in the lateral direction is 1.5 times or less the size of the second thermal conductive member 46 in the lateral direction. As an example, the size of the second thermal conductive member 46 in the planar direction is equal to the size of the detection unit 62. It is desirable that the second thermal conductive member 46 is larger than the width of one resistive heating element 12 and larger than the interval between adjacent resistive heating elements 12 in the lateral direction.

[0054] As shown in Fig. 2, the first thermistor 50A is disposed so as to detect the temperature at a position within a range through which a sheet of the minimum width W2 usable in the heating unit 1 can pass. The second thermistor 50B is disposed so as to detect the temperature at a position within a range through which a sheet of the maximum width W1 usable in the heating unit 1 can pass, and outside the range through which a sheet of the minimum width W2 usable in the heating unit 1 can pass (the range on the other end side where the second thermistor 50B can be disposed is shown as an end range AE1 in Fig. 2). The current interrupting member 60 is disposed so as to detect the temperature at a position within a range through which a sheet of the maximum width W1 usable in the heating unit 1 can pass, and outside the range through which a sheet of the minimum width W2 usable in the heating unit 1 can pass (the range on one end side where the current interrupting member 60 can be disposed is shown as an end range AE2 in Fig. 2).

[0055] One end 12A and the other end 12B of resistance heating element 12 are located outside maximum width W1 in the longitudinal direction and inside one end 38A and the other end 38B of first thermal conductive member 30. That is, the length of first thermal conductive member 30 is longer than the length of resistance heating element 12 in the longitudinal direction. Furthermore, one end 38A and the other end 38B of first thermal conductive member 30 are located, in the longitudinal direction, outside one end 12A and the other end 12B of resistance heating element 12 and inside one end 11A and the other end 11B of substrate 11. That is, in the longitudinal direction, the length of substrate 11 is longer than the length of first thermal conductive member 30.

[0056] The effects of the heating unit 1 described above will now be described. Thermistor 50 contacts second opposite surface 45R of second heat conductive member 45, and current interruption member 60 contacts second opposite surface 46R of second heat conductive member 46. Second heat conductive members 45, 46 have better thermal conductivity in the thickness direction than first heat conductive member 30, so that thermistor 50 and current interruption member 60 have good responsiveness to the temperature of heater 10. On the other hand, if the thermistor 50 and the current interrupting member 60 were to directly contact the rear side surface 16 of the heater 10, they may be affected by temperature unevenness due to the arrangement of the resistance heating body 12. For example, if the thermistor 50 and the current interrupting member 60 contact a portion of the rear side surface 16 that corresponds to the area between the two resistance heating bodies 12 in the short direction, there is a possibility that the temperature cannot be detected accurately. However, in this embodiment, the thermistor 50 and the current interrupting member 60 do not directly contact the rear side surface 16 of the heater 10, but contact the second opposite surfaces 45R, 46R of the second heat conducting members 45, 46 that are different from the first heat conducting member 30, so that the temperature unevenness due to the arrangement of the resistance heating body 12 can be averaged by the second heat conducting members 45, 46. As a result, the thermistor 50 and the current interrupting member 60 can detect the temperature accurately.

[0057] When a sheet with a minimum width W2 is heated, the end ranges AE1 and AE2 are portions where the temperature is likely to rise because the sheet with a minimum width W2 does not take away heat. When the temperature of the end ranges AE1 and AE2 rises, the heat of the heater 10 flows from the end ranges AE1 and AE2 toward the inner range of the minimum width W2 through the first heat conductive member 30 and the second heat conductive members 45B and 46. If the second heat conductive members 45B and 46 were not present, the heat would not be able to flow in the longitudinal direction in that portion. However, in this embodiment, since the second heat conductive members 45B and 46 are present, the thermal conductivity performance of the end ranges AE1 and AE2 is not significantly impaired. Therefore, the temperature rise at the longitudinal ends of the heater 10 can be suppressed.

[0058] Furthermore, since the thermal conductivity from the heater 10 to the second opposite surface 46R is better than the thermal conductivity from the heater 10 to the first opposite surface 32, the thermistor 50 and the current interrupting member 60 can detect the temperature accurately while ensuring the responsiveness of the thermistor 50 and the current interrupting member 60 to the temperature of the heater 10.

[0059] Furthermore, since the length of first thermally conductive member 30 is longer than the length of resistance heating element 12, the temperature of heater 10 can be made uniform over the entire area in the longitudinal direction of heater 10 where resistance heating element 12 is disposed.

[0060] The second thermistor 50B is disposed so as to detect the temperature at the position of the end area AE1, and therefore the rise in temperature in the end area AE1 can be detected by the second thermistor 50B.

[0061] Since the current interrupting member 60 is disposed so as to detect the temperature at the position of the end area AE2, the current interrupting member 60 can detect the rise in temperature of the end area AE2.

[0062] Since second thermal conductive member 45 engages with protrusion 53B of thermistor 50, second thermal conductive member 45 can be appropriately positioned with respect to thermistor 50.

[0063] Since protrusion 46B of second heat conducting member 46 engages with current interrupting member 60, second heat conducting member 46 can be appropriately positioned with respect to current interrupting member 60.

[0064] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and can be appropriately modified and carried out.

[0065] For example, as in the heating unit 1B shown in FIG. 6, the second heat conducting member 40 may be configured to be larger than the openings (first openings 35A, 35B) of the first heat conducting member 30. In this embodiment, the second heat conducting member 40 has the same size as the first heat conducting member 30 in the longitudinal direction or is larger than the first heat conducting member 30, and has a size equivalent to that of the first heat conducting member 30 in the lateral direction. The second heat conducting member 40 has a second heater side surface 40F in contact with the rear side surface 16 of the heater 10, and a second opposite surface 40R in contact with the first heater side surface 31 of the first heat conducting member 30. Even in such a case, the second heat conducting member 40 is provided at a position corresponding to the first openings 35A, 35B, and a temperature detection member (such as a thermistor 50) is in contact with the second opposite surface 40R, so that the same effect as in the above embodiment can be achieved. In this embodiment, second thermal conductive member 40 may be, for example, a graphite sheet which is an anisotropic thermal conductive member.

[0066] 7, a sheet-like third thermally conductive member 70 may be further provided between the heater 10 and the first thermally conductive member 30 and between the heater 10 and the second thermally conductive member 45. The third thermally conductive member 70 has a third heater side surface 70F in contact with the rear surface 16 of the heater 10 and a third opposite surface 70R opposite to the third heater side surface 70F. The first thermally conductive member 30 has the first heater side surface 31 in contact with the third opposite surface 70R, and the second thermally conductive member 45 has the second heater side surface 45F in contact with the third opposite surface 70R.

[0067] The third heat conducting member 70 is, for example, an anisotropic heat conducting member having a higher thermal conductivity in a direction parallel to the third heater side surface 70F than in a direction perpendicular to the third heater side surface 70F, and is, for example, a graphite sheet.

[0068] The method for positioning the second thermal conductive member may also be different from that in the above embodiment. For example, instead of thermistor 50 having a protrusion, second thermal conductive member 245 may have protrusions 245B at both ends in the longitudinal direction, and protrusions 245B may engage with both ends of film 53 of thermistor 50, as shown in FIG. 9(a). In addition, instead of the second thermal conductive member having a protrusion, as shown in Figure 9 (b), the current interruption member 60 may have a protrusion 61A at both ends in the longitudinal direction, and the protrusion 61A may engage with both ends of the second thermal conductive member 246. 9(a), second thermally conductive member 245 may not only have protrusion 245B protruding toward thermistor 50, but also may have locking portion 345C protruding inward in the longitudinal direction from protrusion 345B, as in the embodiment shown in FIG 9(c). Locking portion 345C engages with film 53, so that after film 53 and second thermally conductive member 345 are combined, the second thermally conductive member will not come off unnecessarily.

[0069] 10, the current interrupting member 60 may be arranged so as to detect the temperature at a position within a range through which a sheet of the minimum width W2 usable by the heating unit 1 can pass. Even in such a case, the temperature can be accurately detected by the thermistor 50 and the current interrupting member 60. Moreover, since the current interrupting member 60 is arranged within a range through which a sheet of the minimum width W2 usable by the heating unit 1 can pass, an abnormal temperature rise in the heater 10 can be detected regardless of the size of the sheet in the width direction.

[0070] In addition, the number of temperature detection members and current interruption members is not limited, and only one temperature detection member may be provided, or three or more may be provided. In addition, two or more current interruption members may be provided, or none may be provided. Only the first thermistor 50A may be in contact with the second opposite surface 45R of the second heat conductive member 45. For example, the second thermistor 50B and the current interruption member 60 may be in contact with the first opposite surface 32 of the first heat conductive member 30 or the back side surface 16 of the heater 10.

[0071] In the above embodiment, first thermal conductive member 30, second thermal conductive members 45, 46, and third thermal conductive member 70 are each made of a single sheet-like member, but may be made of a combination of multiple sheet-like members. In this case, the multiple sheet-like members may be different from one another in terms of material, thermal conductivity, shape, etc., or may be the same as one another.

[0072] In addition, in the above embodiment, the substrate 11 of the heater 10 is made of a long, narrow rectangular plate made of ceramic, but it may be made of a long, narrow rectangular plate made of a metal such as stainless steel as long as it has a lower thermal conductivity than the heat conduction member 30.

[0073] In the above embodiment, the opening is a through hole formed at a position away from the contour of the heat conducting member, but it may be a notch shape.

[0074] Furthermore, the elements described in the above embodiment and modified examples can be implemented in appropriate combinations. [Explanation of symbols]

[0075] 1 Heating unit 3 Belt 10 Heater 11 Substrate 12 Resistance heating element 13 Cover 15 Nip surface 16 Back side 20 Holder 30 First heat conductive member 31 First heater side 32 1st opposite side 35A,35B 1st opening 36 Second Opening 45 (45A, 45B) Second heat conductive member 45F Second heater side 45R 2nd opposite side 46 Second heat conductive member 46F Second heater side 46R 2nd opposite side 50 Thermistor 60 Current interrupting member 70 Third heat conductive member 70F 3rd heater side 70R 3rd opposite side

Claims

1. a heater having a substrate, a resistance heating element supported by the substrate, a nip surface, and a back surface opposite the nip surface; a temperature detection member for detecting the temperature of the heater; an endless belt having an inner circumferential surface in contact with the nip surface and rotating around the heater; A holder for supporting the heater; a sheet-like first thermally conductive member located between the heater and the holder and having a thermal conductivity higher than that of the substrate, the first thermally conductive member having a first heater side surface facing the heater, a first opposite surface opposite to the first heater side surface, and an opening; a sheet-like second thermally conductive member disposed at a position corresponding to at least the opening when viewed from a direction perpendicular to the first opposite surface, the second thermally conductive member having a second heater side surface facing the heater side and a second opposite surface opposite to the second heater side surface; the temperature detection member is in contact with the second opposite surface of the second thermally conductive member; A heating unit, characterized in that, when viewed from the perpendicular direction, the second heat conducting member is smaller in size than the first heat conducting member.

2. 2. The heating unit according to claim 1, wherein the thermal conductivity from the heater to the second opposite surface is better than the thermal conductivity from the heater to the first opposite surface.

3. 3. The heating unit according to claim 1, wherein the second heat conducting member has a thermal conductivity greater than that of the first heat conducting member.

4. 4. The heating unit according to claim 1, wherein a thickness of the second heat conducting member is smaller than a thickness of the first heat conducting member.

5. The heating unit according to claim 1 , wherein the second heat conductive member is located within the opening.

6. 6. The heating unit according to claim 1, wherein a length of the first thermally conductive member in a longitudinal direction of the heater is longer than a length of the resistive heating element.

7. A heating unit as described in any one of claims 1 to 6, characterized in that the temperature detection member detects the temperature at a position in the longitudinal direction of the heater, within a range through which a recording material of a maximum width that can be used with the heating unit can pass, and outside a range through which a recording material of a minimum width that can be used with the heating unit can pass.

8. 8. The heating unit according to claim 1, wherein the first heat conducting member is made of aluminum or an aluminum alloy.

9. 8. The heating unit according to claim 1, wherein the first thermal conduction member is an anisotropic thermal conduction member having a thermal conductivity in a direction parallel to the first heater side surface greater than a thermal conductivity in a direction perpendicular to the first heater side surface.

10. a heater having a substrate, a resistance heating element supported by the substrate, a nip surface, and a back surface opposite the nip surface; a temperature detection member for detecting the temperature of the heater; an endless belt having an inner circumferential surface in contact with the nip surface and rotating around the heater; A holder for supporting the heater; a sheet-like first thermally conductive member located between the heater and the holder and having a thermal conductivity higher than that of the substrate, the first thermally conductive member having a first heater side surface facing the heater, a first opposite surface opposite to the first heater side surface, and an opening; a sheet-like second thermally conductive member disposed at a position corresponding to at least the opening when viewed from a direction perpendicular to the first opposite surface, the second thermally conductive member having a second heater side surface facing the heater side and a second opposite surface opposite to the second heater side surface; a third heat conducting member having a sheet shape, the third heat conducting member having a third heater side surface in contact with the back side surface of the heater and a third opposite surface opposite to the third heater side surface; the temperature detection member is in contact with the second opposite surface of the second thermally conductive member; the first heat conducting member has a first heater side surface in contact with the third opposite surface, The heating unit, wherein the second heat conducting member has a side surface of the second heater in contact with the third opposite surface.

11. The heating unit according to claim 10, wherein the third thermal conductive member is an anisotropic thermal conductive member having a thermal conductivity in a direction parallel to the third heater side surface greater than a thermal conductivity in a direction perpendicular to the third heater side surface.

12. The heating unit according to claim 11, wherein the anisotropic heat conductive member is a graphite sheet.

13. 13. The heating unit according to claim 1, wherein the second heat conducting member is made of aluminum or an aluminum alloy.

14. The temperature detection member has a protrusion, The heating unit according to any one of claims 1 to 13, wherein the second heat conducting member is engaged with the protrusion and positioned relative to the temperature detecting member.

15. 14. The heating unit according to claim 1, wherein the second thermally conductive member has a protrusion, and the protrusion is engaged with the temperature detection member, thereby positioning the second thermally conductive member with respect to the temperature detection member.

16. 16. The heating unit according to claim 1, wherein the temperature detection member is a thermistor or a current interrupting member that interrupts current flow to the resistance heating element when the heater becomes abnormally hot.

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