Heating unit

Abstract

To prevent an excessive increase in temperature at the ends of a heater through which a sheet does not pass.SOLUTION: A heating unit 1 comprises: a substrate 11; a heater 10 that has a resistance heating element 12 supported by the substrate 11; an endless belt 3 that has an inner peripheral surface in contact with a nip surface of the heater 10 and rotates around the heater 10; a pressure member (pressure roller 40) that sandwiches the belt 3 with the heater 10 to form a nip part NP; a holder 20 that supports the heater 10; and a heat conduction member 30 that is located between the holder 20 and a rear side surface on the opposite side of the nip surface of the heater 10 and has a larger thermal conductivity than that of the substrate 11. The ends 38A, 38B of the heat conduction member 30 in a longitudinal direction of the substrate 11 are located, in the longitudinal direction, on the outside of the ends NP1, NP2 in the longitudinal direction of the nip part NP.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] A conventional heating unit includes an endless belt, a plate-shaped heater in contact with the inner circumferential surface of the belt, a heat-conducting member that makes the temperature distribution of the heater in the longitudinal direction more uniform, and a pressure roller that forms a nip portion by sandwiching the belt between the heater and the heat-conducting member (see Patent Document 1). In this technology, the longitudinal end of the heat-conducting member is located inside the longitudinal end of the nip portion. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-43075 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the conventional technology, the longitudinal end of the heat conduction member is located inside the longitudinal end of the nip portion, and therefore the heat flow differs between the inside and outside of the longitudinal end of the heat conduction member within the nip portion, resulting in overheating at the longitudinal end of the nip portion and the risk of not being able to mitigate the overheating at the end of the heater where the sheet does not pass.

[0005] Therefore, an object of the present invention is to prevent the end of the heater through which the sheet does not pass from becoming overheated. [Means for solving the problem]

[0006] In order to solve the above problem, the heating unit of the present invention comprises a heater having a substrate and a resistive heating element supported on the substrate, an endless belt having an inner surface in contact with a nip surface of the heater and rotating around the heater, a pressure member that forms a nip portion by clamping the belt between the heater and a holder that supports the heater, and a heat conductive member that is located between the holder and a back side of the heater opposite the nip surface and has a thermal conductivity greater than that of the substrate. An end of the heat conductive member in a longitudinal direction of the substrate is located outboard of an end of the nip portion in the longitudinal direction.

[0007] According to this configuration, the heat conductive member can prevent the end of the nip portion in the longitudinal direction from becoming too hot, so that the end of the heater through which the sheet does not pass can be prevented from becoming too hot.

[0008] Further, the end portion in the longitudinal direction of the nip portion may be located outboard of the end portion in the longitudinal direction of the resistive heating element.

[0009] With this configuration, compared to, for example, a configuration in which the longitudinal end of the resistive heating element is positioned outside the longitudinal end of the nip portion, it is possible to prevent the end of the heater through which the sheet does not pass from overheating.

[0010] In addition, the heating unit may further include a guide member having a guide surface that guides the longitudinal end portion of the inner surface of the belt, and a portion of the heat conduction member may be located at the same position in the longitudinal direction as at least a portion of the guide surface.

[0011] According to this configuration, at least a portion of the guide surface that guides the end of the inner surface of the belt and a portion of the heat conductive member are positioned in the same position, so that the heat conductive member can prevent the end of the belt from overheating.

[0012] The thermal conduction member may also have a first portion located at a position corresponding to the resistive heating element in the longitudinal direction and in contact with the back side of the heater, a second portion located outside the first portion in the longitudinal direction and not in contact with the back side of the heater, and a third portion located outside the second portion in the longitudinal direction and in contact with the back side of the heater.

[0013] According to this configuration, the thermal conduction from the first portion to the third portion can be slowed down, so that the end portion of the heater can be prevented from becoming excessively hot.

[0014] The second portion may face the back surface of the heater with a gap therebetween.

[0015] With this configuration, the second portion can be prevented from coming into contact with the rear side surface of the heater.

[0016] The thermal conduction member may also have a first portion located at a position corresponding to the resistive heating element in the longitudinal direction and in contact with the back side of the heater, a second portion located outside the first portion in the longitudinal direction and in contact with the back side of the heater, the second portion having a cross-sectional area perpendicular to the longitudinal direction smaller than that of the first portion, and a third portion located outside the second portion in the longitudinal direction and in contact with the back side of the heater.

[0017] According to this configuration, the thermal conduction from the first portion to the third portion can be slowed down, so that the end portion of the heater can be prevented from becoming excessively hot.

[0018] The second portion may also have a hole.

[0019] With this configuration, the second portion having a small cross-sectional area can be easily formed in the heat conducting member.

[0020] Moreover, the end portion in the longitudinal direction of the resistive heating element may be located within a range of the second portion in the longitudinal direction.

[0021] According to this configuration, the heat of the resistive heating element can be prevented from being transferred outside the end of the resistive heating element, and a decrease in temperature can be suppressed near the end of the resistive heating element. Effect of the Invention

[0022] According to the present invention, it is possible to prevent the end portion of the heater through which the sheet does not pass from being excessively heated. [Brief description of the drawings]

[0023] [Figure 1] FIG. 2 is a cross-sectional view showing the configuration of a heating unit. [Diagram 2] FIG. 1A is a vertical cross-sectional view showing the configuration of a heating unit according to a first embodiment, and FIG. 1B is a view showing the configuration of a surface on which a resistive heating element of a heater is arranged. [Diagram 3] 4 is an enlarged view showing both longitudinal end portions of the heating unit. FIG. [Figure 4] FIG. 11 is a vertical cross-sectional view showing the configuration of a heating unit according to a second embodiment. [Diagram 5] FIG. 11 is a perspective view showing a configuration of a heat conduction member according to a second embodiment. [Figure 6] 13A and 13B are enlarged views showing both longitudinal end portions of a heating unit according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Next, the first embodiment will be described in detail with reference to the drawings as appropriate. 1, the heating unit 1 is used in a fixing device of an electrophotographic image forming apparatus, a foil transfer device that transfers foil by heat, etc. The heating unit 1 includes a belt 3, a heater 10, a holder 20, a stay 25, a heat conductive member 30, a pressure roller 40 as an example of a pressure member, and a guide member 50.

[0025] The belt 3 is an endless belt made of metal, resin, or the like. The belt 3 rotates around the heater 10. The belt 3 has an outer peripheral surface 3A and an inner peripheral surface 3B. The outer peripheral surface 3A contacts the sheet to be heated or the pressure roller 40. The inner peripheral surface 3B contacts the nip surface 15 of the heater 10.

[0026] The heater 10 has a substrate 11, a resistance heating element 12 supported by the substrate 11, and a cover 13. The heater 10 also has a nip surface 15 that contacts the inner circumferential surface 3B of the belt 3, and a back surface 16 opposite the nip surface 15.

[0027] The substrate 11 is made of a long and narrow rectangular ceramic plate. The heater 10 is a so-called ceramic heater.

[0028] The resistance heating element 12 is formed by printing on one surface of the substrate 11. As shown in FIG. 2(b), 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 parallel to each other and spaced apart from each other in the lateral direction perpendicular to the longitudinal direction. A conductor 19A is connected to one end 12A of each resistance heating element 12 in the longitudinal direction, and a terminal 18 for supplying power to the resistance heating element 12 is provided at each end of the conductor 19A. The other end 12B of each resistance heating element 12 in the longitudinal direction is connected to each other by the conductor 19B.

[0029] The number of the resistance heating elements 12 is not particularly limited. Alternatively, a resistance heating element having a larger heat generation amount at the longitudinal center than at the longitudinal end portions and a resistance heating element having a larger heat generation amount at the longitudinal end portions than at the longitudinal center portion may be provided, and the heat generation distribution in the longitudinal direction may be adjusted by individually controlling each resistance heating element.

[0030] Returning to Fig. 1, the cover 13 covers the resistance heating element 12. The cover 13 is made of, for example, glass.

[0031] 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 which faces the side where the heater 10 is arranged, and an inner surface 21B opposite to the support surface 21A.

[0032] 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 circumferential surface 3B of the belt 3.

[0033] The stay 25 is provided on the inner surface 21B side of the support portion 21 of the holder 20, and is a member that supports the holder 20. The stay 25 extends in the longitudinal direction and is formed by bending a plate material having greater rigidity than the holder 20, such as a steel plate, into a substantially U-shape when viewed in the longitudinal direction.

[0034] The pressure roller 40 forms a nip portion NP by sandwiching the belt 3 between itself and the heater 10. The pressure roller 40 has a cylindrical shaft 41 and a cylindrical roller portion 42. The shaft 41 is made of, for example, metal. The roller portion 42 is made of, for example, rubber. The roller portion 42 covers a portion of the shaft 41. The roller portion 42 contacts the belt 3. One of the holder 20 and the pressure roller 40 is biased toward the other.

[0035] The guide member 50 is a member that guides the longitudinal end of the belt 3. The guide member 50 is provided at both longitudinal ends of the stay 25. As shown in FIG. 2(a), the guide member 50 is disposed at one end and the other end of the belt 3 in the longitudinal direction. Note that, for convenience, the stay 25 is omitted from illustration in FIG. 2(a) etc.

[0036] The guide member 50 has a guide surface 51 and a restricting surface 52. The guide surface 51 is a surface that guides an end portion in the longitudinal direction on the inner circumferential surface of the belt 3. The guide surface 51 is an arc-shaped surface that follows the inner circumferential surface 3B of the belt 3 (see FIG. 1). The guide surface 51 extends inward in the longitudinal direction from the restricting surface 52. The belt 3 is guided by the guide surface 51 and the guide surface 22G of the guide portion 22, and rotates around the heater 10, the holder 20, and the stay 25.

[0037] The regulating surface 52 is a surface that regulates the movement of the belt 3 in the longitudinal direction. The regulating surface 52 is a surface that extends in a direction perpendicular to the longitudinal direction. The regulating surface 52 faces an end of the belt 3 in the longitudinal direction. The regulating surface 52 protrudes outward from the belt 3 further than the guide surface 51.

[0038] As shown in FIG. 1, 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 rear side surface 16 of the heater 10 and the support portion 21 of the holder 20. When the heating unit 1 sandwiches a sheet, which is an object to be heated, between the pressure roller 40 and the heat conducting member 30, the heat conducting member 30 is sandwiched between the heater 10 and the support portion 21. The heat conducting member 30 has a heater side surface 30A that contacts the rear side surface 16 of the heater 10 and an opposite surface 30B opposite to the heater side surface 30A. The opposite surface 30B is in contact with the support surface 21A of the support portion 21.

[0039] The heat conducting member 30 is a member whose thermal conductivity in a direction parallel to the heater side surface 30A (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, metals with high thermal conductivity such as aluminum, aluminum alloys, and 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 30A. 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.

[0040] As shown in FIG. 2( a ), the heat conducting member 30 has a first portion 31 , two second portions 32 , and two third portions 33 .

[0041] The first portion 31 is located at a position corresponding to the resistance heating element 12 in the longitudinal direction. The first portion 31 is located inside one end 12A and the other end 12B of the resistance heating element 12 in the longitudinal direction. The first portion 31 is in contact with the back side surface 16 of the heater 10.

[0042] The second portion 32 is a portion located outside the first portion 31 in the longitudinal direction. The second portion 32 does not contact the rear side surface 16 of the heater 10. More specifically, the second portion 32 is formed by bending a part of the sheet-like member constituting the thermally conductive member 30 into a substantially U-shape so as to be convex in a direction away from the rear side surface 16 of the heater 10. The second portion 32 faces the rear side surface 16 of the heater 10 with a gap therebetween.

[0043] The third portion 33 is a portion located outside the second portion 32 in the longitudinal direction. The third portion 33 is in contact with the rear side surface 16 of the heater 10.

[0044] The relationship between the lengths of the respective members in the longitudinal direction is as follows. Holder 20 > substrate 11 > heat conductive member 30 > longitudinal distance between two regulating surfaces 52 > belt 3 > roller portion 42 (nip portion NP) of pressure roller 40 > resistance heating element 12 > maximum sheet width W1 that can be used in heating unit 1

[0045] One end 12A and the other end 12B of the resistance heating element 12 are located outside the range through which a sheet of maximum width W1 can pass in the longitudinal direction. One end 12A and the other end 12B of the resistance heating element 12 are each located within the range of the second portion 32 in the longitudinal direction. The first portion 31 and the second portion 32 are located within the range of the nip portion NP in the longitudinal direction.

[0046] The resistance heating element 12 is located within the range of the nip portion NP in the longitudinal direction. In other words, as shown in Fig. 3, one end NP1 of the nip portion NP in the longitudinal direction is located outside one end 12A of the resistance heating element 12 in the longitudinal direction. The other end NP2 of the nip portion NP in the longitudinal direction is located outside the other end 12B of the resistance heating element 12 in the longitudinal direction.

[0047] One end 38A in the longitudinal direction of the heat conduction member 30 is located outside one end NP1 of the nip portion NP in the longitudinal direction. More specifically, one end 38A of the heat conduction member 30 is located outside the longitudinal center C1 of the guide surface 51 on the one end side. More specifically, one end 38A of the heat conduction member 30 is located outside the restriction surface 52 on the one end side in the longitudinal direction.

[0048] The other end 38B of the heat conduction member 30 in the longitudinal direction is located outside the other end NP2 of the nip portion NP. More specifically, the other end 38B of the heat conduction member 30 is located outside the longitudinal center C2 of the guide surface 51 on the other end side. More specifically, the other end 38B of the heat conduction member 30 is located outside the restriction surface 52 on the other end side in the longitudinal direction.

[0049] A portion of the heat conducting member 30 is located at the same position as the entirety of the guide surface 51 in the longitudinal direction. In other words, the guide surface 51 is located within the range of the heat conducting member 30 in the longitudinal direction. Specifically, a portion of the third portion 33 is located at the same position as a portion of the guide surface 51 in the longitudinal direction, and a portion of the second portion 32 is located at the same position as the other portion of the guide surface 51 in the longitudinal direction.

[0050] As described above, the following effects can be obtained in this embodiment. Since the ends 38A, 38B of the heat conduction member 30 are positioned outside the ends NP1, NP2 of the nip portion NP in the longitudinal direction, the heat conduction member 30 can suppress excessive heating of the ends NP1, NP2 of the nip portion NP, thereby suppressing excessive heating of the ends of the heater 10 through which the sheet does not pass.

[0051] By positioning the ends NP1 and NP2 of the nip portion NP longitudinally outboard of the ends 12A and 12B of the resistance heating element 12, it is possible to prevent the end of the heater 10 through which the sheet does not pass from overheating, compared to a configuration in which, for example, the end of the resistance heating element is longitudinally outboard of the ends of the nip portion.

[0052] Since a part of the heat conductive member 30 is located at the same position as the entire guide surface 51 in the longitudinal direction, the end of the belt 3 is located within the range of the heat conductive member 30 in the longitudinal direction, so that the heat of the end of the belt 3 can be diffused by the heat conductive member 30 via the heater 10. Therefore, the heat conductive member 30 can prevent the end of the belt 3 from becoming overheated.

[0053] By interposing the second part 32, which does not contact the heater 10, between the first part 31 and the third part 33, which are in contact with the heater 10, the thermal conduction from the first part 31 to the third part 33 can be slowed down, thereby preventing the end part of the heater 10 from overheating.

[0054] Since the second portion 32 faces the rear side surface 16 of the heater 10 with a gap therebetween, the second portion 32 can be prevented from contacting the rear side surface 16 of the heater 10.

[0055] Since the ends 12A, 12B of the resistive heating element 12 are located within the range of the second portion 32 in the longitudinal direction, the heat of the resistive heating element 12 can be prevented from being transmitted outside the ends 12A, 12B of the resistive heating element 12, and a drop in temperature near the ends 12A, 12B of the resistive heating element 12 can be suppressed.

[0056] By positioning ends 38A, 38B of heat conduction member 30 on the outer side of centers C1, C2 of guide surface 51 in the longitudinal direction, a part of heat conduction member 30 is positioned near the end of belt 3 in the longitudinal direction, so that heat from the end of belt 3 can be diffused by heat conduction member 30 via heater 10. Therefore, heat conduction member 30 can prevent the end of belt 3 from becoming overheated.

[0057] As the ends 38A, 38B of the heat conductive member 30 are located outside the restricting surface 52 in the longitudinal direction, the end of the belt 3 is located within the range of the heat conductive member 30 in the longitudinal direction, so that the heat of the end of the belt 3 can be diffused by the heat conductive member 30 via the heater 10. Therefore, the end of the belt 3 can be more reliably prevented from overheating.

[0058] Next, a second embodiment will be described. In the following, differences from the previously described embodiment will be described in detail, and explanations of similarities to the previously described embodiment will be omitted as appropriate, for example, by assigning the same reference numerals to similar components.

[0059] 4 and 5, the heat conduction member 30 has a first portion 31, two second portions 34, and two third portions 33. As shown in FIG. 5, the heat conduction member 30 is in the form of a flat sheet without bending, and the length of the short side perpendicular to the longitudinal direction of the heat conduction member 30 is approximately constant throughout the longitudinal direction. The longitudinal length of the first portion 31 is longer than the longitudinal length of the second portion 34. The first portion 31 is a portion located at a position corresponding to the resistance heating element 12 in the longitudinal direction.

[0060] The second portion 34 is a portion located outside the first portion 31 in the longitudinal direction. The second portion 34 has a rectangular hole 34H that penetrates through it. The hole 34H is adjacent to the outer end of the first portion 31 and the inner end of the third portion 33 in the longitudinal direction. The second portion 34 has portions on both sides of the hole 34H in the short direction of the heat conduction member 30 in contact with the back side surface 16 of the heater 10. One end 12A and the other end 12B of the resistance heating element 12 are each located within the range of the hole 34H in the longitudinal direction.

[0061] A cross-sectional area S34 of the second portion 34 in a cross section perpendicular to the longitudinal direction is smaller than a cross-sectional area S31 of the first portion 31 in a cross section perpendicular to the longitudinal direction. That is, the contact area between the second portion 34 and the rear side surface 16 of the heater 10 per unit length in the longitudinal direction is smaller than the contact area between the first portion 31 and the rear side surface 16 of the heater 10 per unit length in the longitudinal direction.

[0062] In addition, when the first part 31 has a through hole or notch (not shown) for arranging a temperature detection member such as a thermistor or thermostat, the cross section of the first part 31 perpendicular to the longitudinal direction is taken as a cross section perpendicular to the longitudinal direction at a position in the longitudinal direction where no such through hole or notch is provided.

[0063] The third portion 33 is a portion located outside the second portion 34 in the longitudinal direction. A cross-sectional area S33 of the third portion 33 perpendicular to the longitudinal direction is the same as a cross-sectional area S31 of the first portion 31 perpendicular to the longitudinal direction. That is, the contact area between the third portion 33 and the rear side surface 16 of the heater 10 per unit length in the longitudinal direction is the same as the contact area between the first portion 31 and the rear side surface 16 of the heater 10 per unit length in the longitudinal direction.

[0064] In the second embodiment, a part of the third portion 33 is located at the same position in the longitudinal direction as the entire guide surface 51. In other words, the guide surface 51 is located within the range of the third portion 33 in the longitudinal direction. The second portion 34 is located more inward than the guide surface 51 in the longitudinal direction.

[0065] According to the second embodiment described above, it is possible to obtain the same effects as those of the first embodiment.

[0066] In the second embodiment, unlike the first embodiment, the second portion 34 is in contact with the heater 10, but since the contact area is small, it is possible to suppress the transfer of heat in the heater 10 from the second portion 34 to the heat conductive member 30. This makes it possible to promote the transfer of heat between the heater 10 and the heat conductive member 30 in the region where the first portion 31, which has a large contact area, is located.

[0067] Moreover, by configuring second portion 34 to have hole 34H, second portion 34 having a small cross-sectional area can be easily formed in heat conduction member 30.

[0068] In the second embodiment, one hole 34H is formed in each second portion 34, but the present invention is not limited to this and multiple holes 34H may be formed. The shape of the hole 34H is arbitrary and is not limited to a rectangle, and may be, for example, a circle. The hole 34H may not be a through hole, but may be a non-through hole (recess) that opens toward the heater 10. The second portion 34 may have a notch (recess) formed by cutting out one end in the short direction, instead of the hole 34H.

[0069] By making the cross-sectional area S34 of the second portion 34 smaller than the cross-sectional areas S31, S33 of the first portion 31 and the third portion 33, the heat conduction from the first portion 31 to the third portion 33 can be slowed down, and therefore, excessive heating of the end portion of the belt 3 can be suppressed.

[0070] Next, a third embodiment will be described. In the following, differences from the previously described embodiment will be described in detail, and explanations of similarities to the previously described embodiment will be omitted as appropriate, for example, by assigning the same reference numerals to similar components.

[0071] As shown in FIG. 6, the heat conduction member 30 according to the third embodiment is in the form of a flat sheet without bending. That is, the heat conduction member 30 according to the third embodiment has a structure in which the hole 34H is removed from the heat conduction member 30 according to the second embodiment. In the third embodiment, one end 38A of the heat conduction member 30 is located outside the center C1 of the guide surface 51 on the one end side in the longitudinal direction and inside the restriction surface 52 on the one end side. In addition, the other end 38B of the heat conduction member 30 is located outside the center C2 of the guide surface 51 on the other end side in the longitudinal direction and inside the restriction surface 52 on the other end side. In other words, in the third embodiment, a part of the heat conduction member 30 is located at the same position as a part of the guide surface 51 in the longitudinal direction. In addition, one end 38A of the heat conduction member 30 is located outside one end NP1 of the nip portion NP in the longitudinal direction. The other end 38B of the heat conducting member 30 is located outside the other end NP2 of the nip portion NP in the longitudinal direction.

[0072] In the third embodiment, the relationships between the lengths of the respective members in the longitudinal direction are as follows. Holder 20 > substrate 11 > longitudinal distance between two regulating surfaces 52 > belt 3 > heat conductive member 30 > roller portion 42 (nip portion NP) of pressure roller 40 > resistance heating element 12 > maximum sheet width W1 that can be used in heating unit 1

[0073] Even in the third embodiment described above, since the ends 38A, 38B of the heat conduction member 30 are positioned outside the ends NP1, NP2 of the nip portion NP in the longitudinal direction, the heat conduction member 30 can suppress excessive heating of the ends NP1, NP2 of the nip portion NP, thereby suppressing excessive heating of the ends of the heater 10 through which the sheet does not pass.

[0074] Although the embodiment has been described above, the present invention is not limited to the above embodiment, and can be modified as appropriate as exemplified below.

[0075] In the above embodiment, the heat conducting member 30 is made of one sheet-like member, but is not limited thereto. For example, the heat conducting member may be made of a combination of multiple sheet-like members. In this case, the multiple sheet-like members may have different materials, thermal conductivities, shapes, etc., or may be the same as each other.

[0076] In the above embodiment, the heat conducting member 30 is in a sheet shape (including a film shape and a plate shape), but is not limited thereto. For example, the heat conducting member may be in a shape that is thicker than a plate shape.

[0077] In the above embodiment, the ends 12A, 12B of the resistive heating element 12 are located within the range of the second portion 32 in the longitudinal direction, but are not limited thereto. For example, the ends 12A, 12B of the resistive heating element 12 may be located within the range of the first portion 31 in the longitudinal direction.

[0078] In the above embodiment, the substrate 11 of the heater 10 is a long and narrow rectangular ceramic plate, but the present invention is not limited to this as long as the thermal conductivity is smaller than that of the heat conducting member. For example, the heater substrate may be a long and narrow rectangular metal plate such as stainless steel.

[0079] Furthermore, the elements described in the above embodiment and modified examples may be implemented in any combination. [Explanation of symbols]

[0080] 1 Heating unit 3 Belt 3B Inner surface 10 Heater 11 Substrate 12 Resistance heating element 15 Nip surface 16 Back side 20 Holder 30 Thermal Conductive Materials 38A One end 38B Other end 40 Pressure roller NP Nip NP1 One end NP2 Other end

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 pressing member that sandwiches a belt between itself and the heater to form a nip portion; A holder for supporting the heater; a heat conductive member located between the holder and a rear surface of the heater opposite to the nip surface, the heat conductive member having a higher thermal conductivity than the substrate; an end portion of the heat conductive member in a longitudinal direction of the substrate is located outside an end portion of the nip portion in the longitudinal direction, The heat conductive member is a first portion located at a position corresponding to the resistive heating element in the longitudinal direction and in contact with the back surface of the heater; a second portion located outside the first portion in the longitudinal direction and not in contact with the back side surface of the heater; a third portion located outside the second portion in the longitudinal direction and in contact with the back side of the heater.

2. 2 . The heating unit according to claim 1 , wherein the end of the nip portion in the longitudinal direction is positioned outside the end of the resistance heating element in the longitudinal direction.

3. a guide member having a guide surface that guides an end portion of the inner circumferential surface of the belt in the longitudinal direction, 3. The heating unit according to claim 1, wherein a portion of the heat conducting member is located at the same position as at least a portion of the guide surface in the longitudinal direction.

4. 4. The heating unit according to claim 1, wherein the second portion faces the rear surface of the heater with a gap therebetween.

5. 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 pressing member that sandwiches a belt between itself and the heater to form a nip portion; A holder for supporting the heater; a heat conductive member located between the holder and a rear surface of the heater opposite to the nip surface, the heat conductive member having a higher thermal conductivity than the substrate; an end portion of the heat conductive member in a longitudinal direction of the substrate is located outside an end portion of the nip portion in the longitudinal direction, The heat conductive member is a first portion located at a position corresponding to the resistive heating element in the longitudinal direction and in contact with the back surface of the heater; a second portion located outside the first portion in the longitudinal direction and in contact with the back side surface of the heater, the second portion having a cross-sectional area perpendicular to the longitudinal direction smaller than that of the first portion; a third portion located outside the second portion in the longitudinal direction and in contact with the back side of the heater.

6. The heating unit of claim 5, wherein the second portion has a hole.

7. 7. The heating unit according to claim 1, wherein the end portion in the longitudinal direction of the resistance heating element is located within a range of the second portion in the longitudinal direction.

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