JP7639515B2 - Heating unit - Google Patents

Description

The present invention relates to a heating unit used in a fixing device of an image forming apparatus.

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, a pressure roller that forms a nip portion by sandwiching the belt between the pressure roller and the heater, and a guide member having a guide surface that guides the longitudinal end of the inner circumferential surface of the belt (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.

JP 2015-43075 A

In the prior art, the positional relationship between the end of the heat transfer member and the guide surface cannot be clearly recognized, but it is expected that the end of the heat transfer member is far away from the outer end of the guide surface in the longitudinal direction. In such a case, since the end of the heat transfer member is far away from the longitudinal end of the belt, there is a risk that the end of the belt will overheat. If the end of the belt overheats, problems will arise, such as the end of the belt coming into contact with the guide member and buckling.

Therefore, the present invention aims to prevent the ends of the belt from overheating.

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 holder supporting the heater, a heat conductive member having a higher thermal conductivity than the substrate and located between the holder and a back side of the heater opposite the nip surface, and a guide member having a guide surface that guides the longitudinal end of the substrate on the inner surface of the belt.
The ends of the heat conducting member in the longitudinal direction are located outboard in the longitudinal direction relative to a center of the guide surface in the longitudinal direction.

With this configuration, a portion of the heat-conducting member is located near the end of the belt in the longitudinal direction, so the heat-conducting member can prevent the end of the belt from overheating.

The guide member may have a restricting surface that restricts movement of the belt in the longitudinal direction, and the longitudinal end of the heat transfer member may be located outside the restricting surface in the longitudinal direction.

With this configuration, the ends of the belt are located within the range of the heat-conducting member in the longitudinal direction, so that the ends of the belt can be more reliably prevented from overheating.

The heat conducting member may 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, and a portion of the third portion may be located in the same position as at least a portion of the guide surface in the longitudinal direction.

This configuration slows down the heat conduction from the first part to the third part, preventing the end of the belt from overheating.

The second portion may also face the rear surface of the heater with a gap therebetween.

This configuration prevents the second part from coming into contact with the rear side of the heater.

The heat conducting member may have a first portion located at a position corresponding to the resistive heating element in the longitudinal direction and in contact with the rear side of the heater, a second portion located outside the first portion in the longitudinal direction and in contact with the rear side of the heater, the second portion having a smaller cross-sectional area in a cross section perpendicular to the longitudinal direction than the first portion, and a third portion located outside the second portion in the longitudinal direction and in contact with the rear side of the heater, the third portion having a cross-sectional area in a cross section perpendicular to the longitudinal direction that is the same as the first portion, and a portion of the third portion may be located at the same position as at least a portion of the guide surface in the longitudinal direction.

This configuration slows down the heat conduction from the first part to the third part, preventing the end of the belt from overheating.

The second portion may also have a hole.

This configuration makes it easy to form a second portion with a small cross-sectional area in the heat conduction member.

Furthermore, the longitudinal end of the resistive heating element may be located within the range of the second portion in the longitudinal direction.

This configuration prevents the heat from the resistive heating element from being transferred outside the end of the resistive heating element, and prevents the temperature from dropping near the end of the resistive heating element.

The present invention makes it possible to prevent the ends of the belt from overheating.

FIG. 2 is a cross-sectional view showing the configuration of the heating unit. FIG. 2A is a vertical cross-sectional view showing the configuration of a heating unit according to the first embodiment, and FIG. 2B is a view showing the configuration of a surface on which a resistive heating element of a heater is arranged. 4 is an enlarged view showing both longitudinal end portions of the heating unit. FIG. FIG. 11 is a vertical cross-sectional view showing the configuration of a heating unit according to a second embodiment. FIG. 11 is a perspective view showing a configuration of a heat conduction member according to a second embodiment. 13A and 13B are enlarged views showing both longitudinal end portions of a heating unit according to a third embodiment.

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.

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.

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.

The substrate 11 is a long, rectangular ceramic plate. The heater 10 is a so-called ceramic heater.

The resistive heating elements 12 are formed by printing on one surface of the substrate 11. As shown in FIG. 2B, in this embodiment, two resistive heating elements 12 are provided. The two resistive 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 in the lateral direction perpendicular to the longitudinal direction. A conductor 19A is connected to one end 12A of each resistive heating element 12 in the longitudinal direction, and a terminal 18 for supplying power to the resistive heating element 12 is provided at each end of the conductor 19A. The other end 12B of each resistive heating element 12 in the longitudinal direction is connected to each other by the conductor 19B.

The number of resistive heating elements 12 is not particularly limited. In addition, a resistive heating element having a larger heat generation amount at the longitudinal center than at the longitudinal ends, and a resistive heating element having a larger heat generation amount at the longitudinal ends than at the longitudinal center may be provided, and each resistive heating element may be individually controlled to adjust the heat generation distribution in the longitudinal direction.

Returning to FIG. 1, the cover 13 covers the resistive heating element 12. The cover 13 is made of, for example, glass.

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.

The guide parts 22 are provided at both ends of the support part 21 in the short direction. Each guide part 22 has a guide surface 22G that runs along the inner peripheral surface 3B of the belt 3.

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 with greater rigidity than the holder 20, such as a steel plate, into an approximately U-shape when viewed in the longitudinal direction.

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.

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 not shown in FIG. 2(a) etc.

The guide member 50 has a guide surface 51 and a regulating surface 52. The guide surface 51 is a surface that guides the longitudinal end of 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 regulating 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.

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 the 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.

As shown in FIG. 1, the heat conducting member 30 is a member that conducts 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 that is located between the back side 16 of 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 the pressure roller 40, 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 30A that contacts the back side 16 of the heater 10, and an opposite side 30B opposite the heater side 30A. The opposite side 30B contacts the support surface 21A of the support part 21.

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 the thermal conductivity in the planar direction of the substrate 11. The material of the heat conducting member 30 is not particularly limited, but metals with high thermal conductivity such as aluminum, aluminum alloys, and copper can be used. In addition, it is desirable that the heat conducting member 30 is an anisotropic heat conducting member whose thermal conductivity in the planar direction is greater than the thermal conductivity 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 it may be, for example, a film-like member thinner than 0.1 mm, or a plate-like member thicker than 1 mm.

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

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

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 back surface 16 of the heater 10. In detail, the second portion 32 is formed by bending a part of the sheet-like material constituting the thermal conductive member 30 into a substantially U-shape so as to be convex in a direction away from the back surface 16 of the heater 10. The second portion 32 faces the back surface 16 of the heater 10 with a gap therebetween.

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

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 width W1 of a sheet that can be used in heating unit 1

One end 12A and the other end 12B of the resistive 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 resistive 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.

The resistive 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 resistive 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 resistive heating element 12 in the longitudinal direction.

One end 38A of the heat conduction member 30 in the longitudinal direction 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 one end side. More specifically, one end 38A of the heat conduction member 30 is located outside the restriction surface 52 on one end side in the longitudinal direction.

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 in the longitudinal direction. 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 regulating surface 52 on the other end side in the longitudinal direction.

A portion of the heat conducting member 30 is located at the same position as the entire 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. In more detail, 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.

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.

By positioning the ends NP1 and NP2 of the nip portion NP longitudinally outboard of the ends 12A and 12B of the resistive 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 resistive heating element is longitudinally outboard of the end of the nip portion.

By positioning a portion of the heat conducting member 30 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 conducting member 30 in the longitudinal direction, so that the heat of the end of the belt 3 can be diffused by the heat conducting member 30 via the heater 10. Therefore, the heat conducting member 30 can prevent the end of the belt 3 from overheating.

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, and the end of the heater 10 can be prevented from overheating.

The second portion 32 faces the rear surface 16 of the heater 10 with a gap therebetween, so that the second portion 32 does not come into contact with the rear surface 16 of the heater 10.

The ends 12A, 12B of the resistive heating element 12 are located within the range of the second portion 32 in the longitudinal direction, so that the heat of the resistive heating element 12 is prevented from being transmitted outside the ends 12A, 12B of the resistive heating element 12, and a decrease in temperature near the ends 12A, 12B of the resistive heating element 12 can be suppressed.

By positioning the ends 38A, 38B of the heat conducting member 30 on the longitudinal outside of the centers C1, C2 of the guide surface 51, a portion of the heat conducting member 30 is positioned longitudinally near the end of the belt 3, so that the heat of the end of the belt 3 can be diffused by the heat conducting member 30 via the heater 10. Therefore, the heat conducting member 30 can prevent the end of the belt 3 from overheating.

By positioning the ends 38A and 38B of the heat conductive member 30 outside the regulating surface 52 in the longitudinal direction, the end of the belt 3 is positioned 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, it is possible to more reliably prevent the end of the belt 3 from overheating.

Next, a second embodiment will be described. Note that, below, 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.

As shown in Figs. 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 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 along 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 resistive heating element 12 in the longitudinal direction.

The second portion 34 is 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. In the second portion 34, both sides of the hole 34H are in contact with the rear side surface 16 of the heater 10 in the short direction of the heat conduction member 30. 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.

The cross-sectional area S34 of the second portion 34 perpendicular to the longitudinal direction is smaller than the cross-sectional area S31 of the first portion 31 perpendicular to the longitudinal direction. In other words, the contact area between the second portion 34 and the rear 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 surface 16 of the heater 10 per unit length in the longitudinal direction.

When the first part 31 is provided with 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 the cross section perpendicular to the longitudinal direction at a position in the longitudinal direction where no such through hole or notch is provided.

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

In the second embodiment, a part of the third portion 33 is located at the same position as the entire guide surface 51 in the longitudinal direction. 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 inside the guide surface 51 in the longitudinal direction.

The second embodiment described above can achieve the same effects as the first embodiment.

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

In addition, by configuring the second portion 34 to have a hole 34H, it is possible to easily form the second portion 34 with a small cross-sectional area in the heat conduction member 30.

In the second embodiment, one hole 34H is formed in each second portion 34, but this is not limited to this and multiple holes 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) cut out at one end in the short direction, instead of a hole 34H.

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, thereby preventing the end portion of the belt 3 from overheating.

Next, a third embodiment will be described. Note that, below, 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.

As shown in FIG. 6, the heat conduction member 30 according to the third embodiment is a flat sheet shape 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 regulating 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 regulating 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 conduction member 30 is located outside the other end NP2 of the nip portion NP in the longitudinal direction.

In the third embodiment, the relationship between the lengths of the respective members in the longitudinal direction is 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 width W1 of a sheet that can be used in heating unit 1

Even in the third embodiment described above, 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, so that the heat conduction member 30 can prevent the ends NP1, NP2 of the nip portion NP from overheating, thereby preventing the ends of the heater 10 through which the sheet does not pass from overheating.

Although the embodiment has been described above, the present invention is not limited to the above embodiment, and can be modified as appropriate as shown in the following examples.

In addition, in the above embodiment, the heat conducting member 30 is made of one sheet-like member, but this is not limited to this. 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 be different from each other in terms of material, thermal conductivity, shape, etc., or may be the same as each other.

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

In addition, 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 this is not limited to this. 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.

In the above embodiment, the substrate 11 of the heater 10 is made of a long and narrow rectangular ceramic plate, but this is not limited as long as it has a lower thermal conductivity than the heat-conducting member. For example, the heater substrate may be made of a long and narrow rectangular metal plate such as stainless steel.

Furthermore, the elements described in the above embodiments and variations may be implemented in any combination.

REFERENCE SIGNS LIST 1 heating unit 3 belt 3B inner peripheral surface 10 heater 11 substrate 12 resistance heating element 15 nip surface 16 back surface 20 holder 30 heat conductive member 38A one end 38B other end 50 guide member 51 guide surface C1 center C2 center

Claims (6)

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 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;
a guide member having a guide surface that guides an end portion of the inner circumferential surface of the belt in the longitudinal direction of the substrate ,
an end portion of the heat conducting member in the longitudinal direction is located outside of a center of the guide surface in the longitudinal direction ;
The thermal conductive member is
a first portion located at a position corresponding to the resistance heating element in the longitudinal direction and in contact with the back side surface of the heater;
a second portion located outside the first portion in the longitudinal direction and not in contact with the back surface of the heater;
a third portion located outside the second portion in the longitudinal direction and in contact with the back side surface of the heater,
A heating unit, characterized in that a part of the third portion is located at the same position in the longitudinal direction as at least a part of the guide surface . the guide member has a restricting surface that restricts movement of the belt in the longitudinal direction,
The heating unit according to claim 1 , wherein the end portion in the longitudinal direction of the heat conducting member is located outside the restricting surface in the longitudinal direction. 3. The heating unit according to claim 1 , wherein the second portion faces the rear surface of the heater with a gap therebetween. 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 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;
a guide member having a guide surface that guides an end portion of the inner circumferential surface of the belt in the longitudinal direction of the substrate,
an end portion of the heat conducting member in the longitudinal direction is located outside of a center of the guide surface in the longitudinal direction;
The thermal conductive member is
a first portion located at a position corresponding to the resistance heating element in the longitudinal direction and in contact with the back side 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 surface of the heater, the third portion having a cross-sectional area perpendicular to the longitudinal direction that is the same as that of the first portion;
A heating unit, characterized in that a part of the third portion is located at the same position in the longitudinal direction as at least a part of the guide surface. The heating unit of claim 4 , wherein the second portion has a hole. 6. 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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