Heating unit

Abstract

To prevent heat radiation from a heater to an energization cut-off member to prevent faulty fixing in an initial stage of fixing.SOLUTION: A heating unit 1 comprises: a heater 10 that has a substrate 11 and a resistance heating element 12 supported on the substrate 11; an endless belt 3 that has an inner peripheral surface in contact with a nip surface 15 of the heater 10 and rotates around the heater 10; an energization cut-off member 60 that cuts off energization to the resistance heating element 12 when an abnormal increase in temperature of the heater 10 occurs, the energization cut-off member 60 having a thermo-sensitive surface 62A; and a heat insulating member (film 63) that is arranged between the energization cut-off member 60 and a rear side surface 16 of the heater 10 on the opposite side of the nip surface 15, the heat insulating member having a smaller thermal conductivity than that of material forming the thermo-sensitive surface 62A. The thermo-sensitive surface 62A of the energization cut-off member 60 is in contact with the heat insulating member.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 heater and a pressure roller is known (Patent Document 1). In this fixing device, a safety element is arranged in contact with the rear side of the heater. In the event that a malfunction of the control unit or the like causes continuous uncontrolled current to flow to the heater, the safety element detects an overheating of the heater and functions as a current interrupting member that cuts off current to the heater. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-212589 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the conventional technology, since the current cutoff member is in contact with the back side of the heater, when the fixing operation is started while the heating unit is still cold, the heat of the heater is easily taken by the current cutoff member in the early stage of the fixing operation (hereinafter referred to as "initial fixing stage"). Therefore, the temperature of the heater and the belt is easily insufficient in the area where the current cutoff member is located, which may cause fixing failure.

[0005] Therefore, an object of the present invention is to suppress the radiation of heat from the heater to the current-cutting member and to suppress poor fixing during the initial fixing stage. [Means for solving the problem]

[0006] The heating unit for solving the above-mentioned problems includes a heater having a substrate and a resistance heating element supported by the substrate, an endless belt having an inner circumferential surface in contact with the nip surface of the heater and rotating around the heater, a current interrupting member that interrupts current to the resistance heating element when the heater becomes abnormally hot, the current interrupting member having a heat-sensitive surface, and a heat insulating member that is disposed between the current interrupting member and the back surface of the heater opposite to the nip surface, the heat insulating member having a lower thermal conductivity than the material that constitutes the heat-sensitive surface. The heat-sensitive surface of the current interrupting member is in contact with the heat insulating member.

[0007] According to this configuration, since the heat insulating member is interposed between the heat sensitive surface of the current interrupting member and the rear surface of the heater, when the temperature of the current interrupting member is not high enough at the beginning of the fixing process, it is possible to suppress the heat radiation from the heater to the current interrupting member, thereby suppressing the fixing failure at the beginning of the fixing process.

[0008] The heating unit may further include a sheet-like heat-conducting member that is in contact with the rear side of the heater, has a thermal conductivity greater than that of the substrate, and is positioned between the heat insulating member and the heater.

[0009] With this configuration, the temperature of the heater can be made uniform in the longitudinal direction of the heater.

[0010] In the longitudinal direction of the heater, the length of the heat conducting member is desirably longer than the length of the resistive heating element.

[0011] 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.

[0012] The heat insulating member may include polyimide.

[0013] The heat insulating member may be in a sheet form.

[0014] It is preferable that the heat insulating member cover the entire heat sensitive surface.

[0015] According to this configuration, it is possible to more effectively suppress the radiation of heat from the heater to the current interrupting member in the initial stage of fixing.

[0016] The current interrupting member may be positioned in the longitudinal direction of the heater within a range through which a sheet of the maximum width usable with the heating unit can pass, and outside a range through which a sheet of the minimum width usable with the heating unit can pass.

[0017] According to this configuration, the current interrupting member can detect a rise in temperature in a range where a minimum-width sheet does not pass.

[0018] The current interrupting member may be disposed in a range in the longitudinal direction of the heater that allows a sheet of the smallest width that can be used in the heating unit to pass through.

[0019] According to this configuration, the current interrupting member can detect an abnormal temperature rise of the heater regardless of the size of the sheet in the width direction.

[0020] The insulating member may be located between the back surface of the heater and the thermally conductive member.

[0021] According to this configuration, it is possible to more effectively suppress the radiation of heat from the heater to the current interrupting member in the initial stage of fixing. Effect of the Invention

[0022] According to the present invention, in the initial stage of fixing, heat dissipation from the heater to the current interrupting member can be suppressed, and fixing failures in the initial stage of fixing can be suppressed. [Brief description of the drawings]

[0023] [Figure 1] 4 is a cross-sectional view of the heating unit at the position of the current interrupting member. FIG. [Diagram 2]FIG. 3A shows the surface on which the resistive heating element of the heater is arranged, FIG. 3B shows the heater and heat conductive member as viewed from the back 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 temperature detection member, and FIG. 1B is a perspective view of a current interruption member. [Figure 4] FIG. 4 is a cross-sectional view of the heating unit at the position of the temperature detection member. [Diagram 5] FIG. 1(a) shows the surface on which the resistive heating element of a modified heater is arranged, FIG. 1(b) shows the heater and heat 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. [Figure 6] 13 is a cross-sectional view of a heating unit according to a modified example, taken at the position of a current interrupting member. FIG. [Figure 7] 13 is a cross-sectional view of a heating unit according to a modified example in which a second heat conductive member is provided. FIG. [Figure 8] 13 is a cross-sectional view of a heating unit according to another modified example in which a second heat conductive member is provided. FIG. [Figure 9] 1 is an exploded perspective view of a heater, a heat conductive member, a heat insulating member, and a current interrupting member when the heat insulating member is attached to the heat conductive member. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] 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 heat conductive member 30, a temperature detection member 50 (see Fig. 4), and a current interruption member 60.

[0025] 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.

[0026] 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.

[0027] 1, 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.

[0028] 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 approximately a square. 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.

[0029] The temperature detection member 50 includes two members, a first temperature detection member 50A and a second temperature detection member 50B. The temperature detection member 50 is, for example, a thermistor. The first temperature detection member 50A and the second temperature detection member 50B are the same part. The first temperature detection member 50A detects the temperature of the central portion of the heater 10 in the longitudinal direction. The first temperature detection member 50A is used to control the temperature of the heater 10 to a target temperature based on the temperature detected by the first temperature detection member 50A. The second temperature detection member 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 temperature detection member 50A in the longitudinal direction of the heater 10. The second temperature detection member 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 temperature detection member 50A. The first temperature detection member 50A and the second temperature detection member 50B do not have to be the same part. In this case, it is preferable that the first temperature detection member 50A is a member that has higher temperature detection accuracy than the second temperature detection member 50B within the temperature range during the printing operation.

[0030] 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.

[0031] 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.

[0032] The 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 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 heat conducting member 30 is sandwiched between the heater 10 and the support part 21. The heat conducting member 30 has a heater side surface 31 that contacts the back side surface 16 of the heater 10, and an opposite surface 32 opposite to the heater side surface 31. The opposite surface 32 is in contact with the support surface 21A of the support part 21.

[0033] The heat conducting member 30 is a member whose thermal conductivity in a direction parallel to the 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 heat conducting member 30 is not particularly limited, but for example, a metal with a high thermal conductivity such as aluminum, an aluminum alloy, or copper can be used. In addition, the heat conducting member 30 is preferably an anisotropic heat conducting member whose thermal conductivity in the planar direction is greater than that in the thickness direction perpendicular to the heater side surface 31. For example, a graphite sheet can be used as the anisotropic heat conducting member. In addition, the thickness of the 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.

[0034] As shown in FIG. 3(a), the temperature detection member 50 (50A, 50B) has a support plate 51, a biasing member 52, 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). A film 53 is attached to the temperature detection member 50 as a heat insulating member. The film 53 is attached to the support plate 51 so as to be wrapped around the biasing member 52 and the support plate 51. The film 53 is in a sheet shape, and is, for example, a sheet of a resin having high heat resistance. The film 53 contains, for example, polyimide.

[0035] As shown in FIG. 3(b), the current interrupting member 60 is a thermostat having a bimetallic interrupting mechanism therein, and has a case 61 in which the interrupting mechanism is housed, and a detection section 62 having a heat-sensitive surface 62A for detecting temperature, protruding from the case 61. A film 63 is attached to the current interrupting member 60 as a heat insulating member. The film 63 is attached to the current interrupting member 60 so as to be wrapped around the detection section 62 and the case 61. The heat-sensitive surface 62A is in contact with the film 63. The film 63 covers the entire heat-sensitive surface 62A. The film 63 is in a sheet shape, and is, for example, a sheet of resin having high heat resistance. The film 63 includes, for example, polyimide. The film 63 has a lower thermal conductivity than the material constituting the heat-sensitive surface 62A. The material constituting the heat-sensitive surface 62A is, for example, aluminum.

[0036] 4, the portion of the first temperature detection member 50A protruding from the support plate 51 enters the holder opening 25A and contacts the opposite surface 32 of the heat conduction member 30 through the holder opening 25A. The portion of the second temperature detection member 50B protruding from the support plate 51 enters the holder opening 25B and contacts the opposite surface 32 of the heat conduction member 30 through the holder opening 25B. The biasing members 52 of the first temperature detection member 50A and the second temperature detection member 50B are crushed, and the temperature detection elements 55 are pressed against the rear side surface 16.

[0037] As shown in FIG. 1, the current interrupting member 60 has a detection part 62 protruding from a case 61 that fits into the holder opening 26, and a heat-sensitive surface 62A of the detection part 62 contacts the opposite surface 32 of the heat conducting member 30 through the holder opening 26.

[0038] As shown in Fig. 2, the first temperature detection member 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 temperature detection member 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 (in Fig. 2, the range on the other end side where the second temperature detection member 50B can be disposed is shown as an end range AE1). In addition, 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 (in Fig. 2, the range on one end side where the current interrupting member 60 can be disposed is shown as an end range AE2).

[0039] One end 12A and the other end 12B of the resistance heating element 12 are located outside the maximum width W1 in the longitudinal direction and inside one end 38A and the other end 38B of the heat conducting member 30. In other words, the length of the heat conducting member 30 is longer than the length of the resistance heating element 12 in the longitudinal direction. Moreover, one end 38A and the other end 38B of heat conduction 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. In other words, the length of substrate 11 is longer than the length of heat conduction member 30 in the longitudinal direction.

[0040] The effects of the heating unit 1 described above will now be described. When the fixing operation is started when the heating unit 1 is in a cold state, electricity is applied to the resistance heating element 12 while rotating the belt 3, and the heater 10 is heated to a target temperature at which fixing becomes possible. Then, after the temperature detected by the first temperature detection member 50A reaches the target temperature, fixing of the toner or foil is started. At this time, when the heat capacity of the detection section 62 of the current interrupting member 60 is larger than that of the temperature detection element 55 of the first temperature detection member 50A, the temperature of the detection section 62 may be lower than the target temperature. In the heating unit 1 of this embodiment, the film 63 as a heat insulating member is interposed between the heat sensitive surface 62A of the current interrupting member 60 and the rear surface 16 of the heater 10, so that when the temperature of the current interrupting member 60 is not sufficiently high in the early stage of fixing, it is possible to suppress heat dissipation from the heater 10 to the current interrupting member 60. Therefore, fixing failure in the early stage of fixing can be suppressed.

[0041] Furthermore, in the heating unit 1, since the thermally conductive member 30 is disposed between the film 63 and the heater 10, the temperature of the heater 10 can be made uniform in the longitudinal direction of the heater 10.

[0042] Furthermore, since the length of the heat conducting member 30 in the longitudinal direction is longer than the length of the resistance heating element 12, the temperature of the heater 10 can be made uniform over the entire range in which the resistance heating element 12 is arranged in the longitudinal direction.

[0043] Furthermore, since the film 63 covers the entire heat-sensitive surface 62A, the radiation of heat from the heater 10 to the current-cutting member 60 in the early stage of fixing can be more effectively suppressed.

[0044] 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.

[0045] For example, in the above embodiment, the film 63, which is a resin sheet, is shown as the heat insulating member, but the heat insulating member may be any member having a lower thermal conductivity than the material constituting the heat-sensitive surface 62A, and may be, for example, an amorphous member such as grease. The heat insulating member may be in a block shape. The heat insulating member may be disposed so as to cover a part of the heat-sensitive surface 62A rather than covering the entire surface.

[0046] The number of temperature detection members and current interruption members is not limited, and the number of temperature detection members may be one or three or more, and the number of current interruption members may be two or more.

[0047] 5, 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, a film 63 as a heat insulating member is interposed between the heat-sensitive surface 62A of the current interrupting member 60 and the rear surface 16 of the heater 10, so that when the temperature of the current interrupting member 60 is not sufficiently high at the beginning of fixing, it is possible to suppress heat dissipation from the heater 10 to the current interrupting member 60. Furthermore, 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, it is possible to detect an abnormal temperature rise of the heater 10 regardless of the size of the sheet in the width direction.

[0048] 6, the heat-sensitive surface 62A of the detection unit 62 of the current interrupting member 60 may be in contact with the back surface 16 of the heater 10 through the holder opening 26. In this case, the heat conductive member 30 has an opening 36 penetrating the heat conductive member 30. The opening 36 is disposed at a position corresponding to the holder opening 26, that is, at a position corresponding to the current interrupting member 60. The detection unit 62 of the current interrupting member 60 protruding from the case 61 enters the holder opening 26 and the opening 36 and contacts the back surface 16 of the heater 10 through the holder opening 26 and the opening 36. Even in such a case, the film 63 as a heat insulating member is interposed between the heat-sensitive surface 62A of the current interrupting member 60 and the back surface 16 of the heater 10, so that when the temperature of the current interrupting member 60 is not sufficiently high at the beginning of fixing, it is possible to suppress heat radiation from the heater 10 to the current interrupting member 60. In addition, since the current interrupting member 60 contacts the back surface 16 of the heater 10 through the opening 36, the current interrupting member 60 can responsively detect an abnormal rise in temperature of the heater 10 and quickly cut off the flow of electricity to the heater 10 when an abnormal rise in temperature occurs.

[0049] Furthermore, when the current interrupting member 60 contacts the rear side surface 16 of the heater 10, the heat conducting member 30 does not need to be provided.

[0050] 7, the heat-sensitive surface 62A of the detector 62 of the current-carrying cutoff member 60 may be in contact with the second heat-conducting member 46 through the holder opening 26. In this case, the heat-conducting member 30 has an opening 36 penetrating the heat-conducting member 30, similar to the embodiment shown in FIG. 6. The second heat-conducting member 46 is located within the opening 36. The size of the second heat-conducting member 46 is smaller than that of the heat-conducting member 30. The second heat-conducting member 46 is a member having a thermal conductivity in a planar direction greater than that of the substrate 11 in the planar direction. The material of the second heat-conducting member 46 is not particularly limited, but may be a metal having a high thermal conductivity, such as aluminum, an aluminum alloy, or copper. The second heat-conducting member 46 is located between the two resistance heating elements 12. It is desirable that the second heat-conducting member 46 has a better thermal conductivity than the heat-conducting member 30 at least in the thickness direction. The current interrupting member 60 has a detection portion 62 protruding from the case 61 that enters the holder opening 26 and contacts the surface of the second heat conducting member 46 opposite to the heater 10 side through the holder opening 26. Even in such a case, the film 63 as a heat insulating member is interposed between the heat sensitive surface 62A of the current interrupting member 60 and the second heat conducting member 46, so that when the temperature of the current interrupting member 60 is not sufficiently high at the initial stage of fixing, it is possible to suppress heat dissipation from the heater 10 to the current interrupting member 60. In addition, since the current interrupting member 60 contacts the second heat conducting member 46 that is separate from the heat conducting member 30, the second heat conducting member 46 can average out temperature unevenness due to the arrangement of the resistance heating element 12. This allows the current interrupting member 60 to detect an accurate temperature.

[0051] 8, the second heat conducting member 46 may be disposed at a position corresponding to the holder opening 26 and in contact with the heat conducting member 30. In this case, unlike the embodiment shown in FIG. 7, the heat conducting member 30 does not have an opening penetrating the heat conducting member 30. The current interrupting member 60 has a detection section 62 protruding from a case 61 that enters the holder opening 26 and contacts the surface of the second heat conducting member 46 opposite to the heater 10 side through the holder opening 26. Even in this case, since the film 63 as a heat insulating member is interposed between the heat sensitive surface 62A of the current interrupting member 60 and the second heat conducting member 46, it is possible to suppress the heat dissipation from the heater 10 to the current interrupting member 60 when the temperature of the current interrupting member 60 is not sufficiently high in the initial fixing stage. Furthermore, since the current interrupting member 60 contacts the second heat conducting member 46 that is separate from the heat conducting member 30, the temperature unevenness due to the arrangement of the resistance heating element 12 can be averaged by the second heat conducting member 46. This allows the current interruption member 60 to detect the temperature accurately.

[0052] 9, the film 63 as a heat insulating member may be attached to the heat conducting member 30 and may be in contact with the heat sensitive surface 62A of the current interrupting member 60. In this case, the film 63 is wrapped around the heat conducting member 30 in the short direction at a position corresponding to the heat sensitive surface 62A in the longitudinal direction, for example. The film 63 is located between the opposite surface 32 of the heat conducting member 30 and the heat sensitive surface 62A, and is in contact with the opposite surface 32 and the heat sensitive surface 62A. The film 63 is also located between the rear surface 16 of the heater 10 and the heater side surface 31 of the heat conducting member 30, and is in contact with the heater side surface 31 and the rear surface 16. As in the above embodiment, the film 63 is in a sheet shape, and is, for example, a sheet of a resin having high heat resistance, and is made of polyimide. The film 63 has a smaller thermal conductivity than the material constituting the heat sensitive surface 62A. Even in such a case, since the film 63 as a heat insulating member is interposed between the heat sensitive surface 62A of the current interrupting member 60 and the rear side surface 16 of the heater 10, when the temperature of the current interrupting member 60 is not sufficiently high in the initial stage of fixing, it is possible to suppress heat dissipation from the heater 10 to the current interrupting member 60. In addition, since the film 63 as a heat insulating member is also interposed between the heat conducting member 30 and the rear side surface 16 of the heater 10, it is possible to further suppress heat dissipation from the heater 10 to the current interrupting member 60.

[0053] In the above embodiment, the heat conducting member 30 is made of one sheet-like member, but it may be made of a combination of multiple sheet-like members. In this case, the multiple sheet-like members may be different from each other in terms of material, thermal conductivity, shape, etc., or may be the same as each other.

[0054] In the above embodiment, the substrate 11 of the heater 10 is made of a long and narrow rectangular ceramic plate, but it may be made of a long and narrow rectangular metal plate such as stainless steel.

[0055] Furthermore, the elements described in the above embodiment and modified examples can be implemented in appropriate combinations. [Explanation of symbols]

[0056] 1 Heating unit 3 Belt 10 Heater 11 Substrate 12 Resistance heating element 15 Nip surface 16 Back side 20 Holder 30 Thermal Conductive Materials 60 Current interrupting member 63 Film

Claims

1. a heater having a substrate and a resistive heating element supported by the substrate; an endless belt having an inner circumferential surface in contact with the nip surface of the heater and rotating around the heater; a current interruption member that interrupts current to the resistance heating element when the heater abnormally rises in temperature, the current interruption member having a heat-sensitive surface; a heat insulating member disposed between the current interrupting member and a back surface of the heater opposite to the nip surface, the heat insulating member having a thermal conductivity lower than that of a material constituting the heat sensitive surface; The heat-sensitive surface of the current-cutting member is in contact with the heat-insulating member, The heating unit according to claim 1, wherein the heat insulating member is wrapped around the current interrupting member to cover the current interrupting member.

2. The heating unit according to claim 1, further comprising a sheet-shaped thermally conductive member in contact with the back surface of the heater, the thermally conductive member having a higher thermal conductivity than the substrate, and positioned between the insulating member and the heater.

3. 3. The heating unit according to claim 2, wherein the length of the heat conducting member in the longitudinal direction of the heater is longer than the length of the resistive heating element.

4. The heating unit according to claim 1 , wherein the heat insulating member contains polyimide.

5. The heating unit according to any one of claims 1 to 4, wherein the heat insulating member is in a sheet shape.

6. The heating unit according to claim 1 , wherein the heat insulating member covers the entire heat sensitive surface.

7. A heating unit as described in any one of claims 1 to 6, characterized in that the current interrupting member is arranged in a position in the longitudinal direction of the heater within a range through which a sheet of a maximum width that can be used with the heating unit can pass, and outside a range through which a sheet of a minimum width that can be used with the heating unit can pass.

8. 7. The heating unit according to claim 1, wherein the current interrupting member is disposed within a range in the longitudinal direction of the heater that allows a sheet having a minimum width usable in the heating unit to pass therethrough.

9. A heater having a substrate and a resistive heating element supported on the substrate; an endless belt having an inner circumferential surface in contact with the nip surface of the heater and rotating around the heater; a current interruption member that interrupts current to the resistance heating element when the heater abnormally rises in temperature, the current interruption member having a heat-sensitive surface; a heat insulating member disposed between the current interrupting member and a back surface of the heater opposite to the nip surface, the heat insulating member having a thermal conductivity lower than that of a material constituting the heat sensitive surface; a sheet-like heat conductive member having a thermal conductivity greater than that of the substrate and positioned between the heat insulating member and the heater; The heat-sensitive surface of the current-cutting member is in contact with the heat-insulating member, The heating unit according to claim 1, wherein the heat insulating member is also located between the rear side surface of the heater and the heat conductive member.

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