JP2007240623A - Image heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image heating device capable of appropriately controlling pressure distribution in an image heating nip even when the image heating nip is made long in length, and to provide a fixing device. <P>SOLUTION: The image heating device is constituted so that a roller nip surface which a fixing roller 23 and a pressurization roller 26 form via a fixing belt 20 and a pressurization belt 21 and a pad nip surface which the fixing pad and the pressurization pad form the fixing belt and the pressurization belt are approximately in parallel and not on the same plane. As a result, the pressure distribution in the nip is rationalized, a poor image and poor separation are prevented. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image heating apparatus that heats an image formed on a recording material.

  In an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, a toner image is formed on a sheet, and the image is formed by fixing the image by heating and pressing it. As such a fixing device, a roller fixing method in which a fixing nip is formed by pressing a pressure roller against a fixing roller having a heater therein to perform fixing has been conventionally employed.

  By the way, in order to increase the glossiness of the image and increase the speed of image formation, it is preferable to lengthen the sheet nip passage time and sufficiently melt the toner. In the case of the roller fixing method, in order to achieve this, the roller diameter must be increased, and the fixing device is increased in size.

  Therefore, a belt fixing method has been proposed that can obtain a sufficient nip width (length in the sheet conveying direction) while achieving a reduction in size and speed of the apparatus as compared with the roller fixing method (patent). Reference 1). In this proposal, a fixing belt and a pressure belt that are opposed to each other are provided, and fixing is performed while a sheet is sandwiched and conveyed between these belts. Therefore, a sufficient nip width is obtained as compared with the prior art.

  However, the configuration of Patent Document 1 has the following problems. That is, in the fixing nip formed between both belts, a high pressure portion pressed by the suspension rollers of both belts, a low pressure portion pressed only by the fixing member, There is a pressure-relieved part where nothing is supported from both sides of the belt.

  For this reason, when an unfixed toner image is to be fixed, a difference occurs in the sheet conveyance speed between the high-pressure portion and the portion where the pressure is lost. Since the belt has a certain degree of flexibility, there arises a problem that the belt expands and contracts due to a difference in conveyance speed, and an image on the sheet shifts.

  In addition, the water pressure generated at the time of fixing cannot be suppressed at the pressure relief portion. Therefore, uneven gloss due to the contact state between the toner surface and the belt surface in the portion where the air or water vapor is accumulated and the portion where it is not in the width direction (direction perpendicular to the sheet conveying direction) of the pressure relief portion is different. appear. In particular, it tends to occur in a sheet having low air permeability such as coated paper.

  In order to solve such problems, the pressure roll side of the pressure applying member is made into a triangular shape and brought close to the vicinity of the nip area of the pressure roll, thereby preventing the pressure drop portion and causing image defects such as gloss unevenness. It has been proposed to prevent (Patent Document 2).

However, the configuration of Patent Document 2 has the following problems. That is, the pressure roll side tip of the pressure applying member requires a certain thickness from the viewpoint of processing and strength, and therefore the pressure release portion between the pressure roll and the nip region cannot be made sufficiently small. In addition, the pressure applying member is caught in the nip region of the pressure roll, and the pressure in the pressure roll nip region cannot be sufficiently ensured, resulting in separation failure.
JP 2004-341346 A JP-A-11-45025

  Therefore, an object of the present invention is to provide an image heating apparatus and a fixing apparatus that can optimize the pressure distribution in the image heating nip even when the image heating nip is configured to be long. Another object of the present invention is to provide an image heating apparatus that can prevent image defects and separation defects by optimizing the pressure distribution in the nip.

  Further objects of the present invention will become apparent upon reading the following detailed description with reference to the accompanying drawings.

  According to the present invention, the above object can be achieved.

  The present invention includes a first belt and a second belt for nipping and conveying a recording material carrying an image, and a nip forming unit for forming an image heating nip between the first belt and the second belt, In the image heating apparatus, the nip forming means includes a high friction roller that drives the first belt, a low friction roller that faces the high friction roller and presses the second belt, and is not in contact with the high friction roller. An image having a first fixing member that is arranged and pressurizes the first belt, and a second fixing member that opposes the first fixing member and is placed in contact with the low friction roller and pressurizes the second belt. A heating device, a roller nip surface formed via a first belt and a second belt formed by a high friction roller and a low friction roller, a first fixing member, and a second fixing member are the first belt and the first belt. Formed through 2 belts That it pad nip plane is not on the same plane substantially parallel to, and having a.

  According to the present invention, even when the image heating nip is lengthened, the pressure distribution in the image heating nip can be optimized. Furthermore, the pressure distribution in the nip can be optimized, and image defects such as image misalignment and separation defects can be prevented.

  Hereinafter, the present invention will be described more specifically with reference to examples. Although these examples are examples of embodiments to which the present invention can be applied, the present invention is not limited to these examples, and various modifications are possible within the scope of the idea of the present invention.

(First embodiment)
First, the overall configuration of the image forming apparatus will be described with reference to FIG.

  The image forming apparatus shown in FIG. 6 is an image forming apparatus (so-called printer) that employs an electrophotographic system.

  The image forming apparatus 1 is roughly divided into an image forming unit for forming a toner image on a sheet as a recording material, and a fixing device as an image heating apparatus for fixing the toner image formed on the sheet by heating and pressing. It has been.

  First, the image forming means is provided with a device described below. A charger 3 as a charging unit is provided around the photosensitive drum 2 as an image carrier, and the surface of the photosensitive drum 2 is uniformly charged by the charger 3. Then, an electrostatic latent image is formed on the photosensitive drum 2 by irradiating light 5 corresponding to the image from an exposure device 4 as an exposure unit. This electrostatic latent image is developed by a developing device 6 as developing means to form a toner image. On the other hand, the sheet S is stored in a feeding cassette 9 at the lower part of the apparatus and fed by a feeding roller 10. The sheet is conveyed in synchronism with the toner image on the photosensitive drum 2 by a pair of registration rollers 11 as conveying means. The toner image on the photosensitive drum is electrostatically transferred onto a sheet by a transfer roller 7 as a transfer unit, and is conveyed to the fixing device A. Thereafter, the toner remaining on the photosensitive drum 2 is removed by a cleaning device 8 as a cleaning unit.

  Then, the toner image formed on the sheet S by the image forming means is fixed on the sheet by being heated and pressed in the fixing device A as an image heating device. Thereafter, the sheet S on which the toner image is fixed is conveyed and discharged by the discharge roller pair 12 to the discharge tray 13 at the upper part of the apparatus.

  FIG. 1 is a cross-sectional view of a fixing device A according to this embodiment, and FIG. 2 is a cross-sectional view illustrating a comparative example. As shown in the figure, the fixing device A includes a fixing belt (fixing means) 20 as an example of a first belt and a pressure belt (pressure means) 21 as an example of a second belt. .

  The fixing belt 20 has an inner diameter of 40 mm and a thickness of 50 μm as a base layer, and an elastic layer is provided on the outer periphery of the base layer with a thickness of 300 μm. As a material for the base layer, a resin such as SUS or polyimide can be used instead of Ni. Moreover, as a material of an elastic layer, a well-known elastic material can be used, for example, silicone rubber, fluororubber, etc. can be used. In this embodiment, silicone rubber is used, the hardness is JIS-A 20 degrees, and the thermal conductivity is 0.8 W / mK. Due to the deformation of the elastic layer, it is possible to prevent the sheet from being wound around the fixing belt 20 and to obtain good separation performance from the belt. Further, on the outer periphery of the elastic layer, a fluororesin layer (for example, PFA or PTFE) is provided with a thickness of 30 μm as a surface release layer.

  The pressure belt 21 has an inner diameter of 40 mm and a thickness of 50 μm Ni as a base layer, and the surface is provided with a PFA tube made of fluororesin as a release layer with a thickness of 30 μm. As a material for the base layer, a resin such as SUS or polyimide can be used instead of Ni.

  The fixing belt 20 is stretched by a heating roller 22 as a suspension roller and a fixing roller 23. The heating roller 22 is a 1 mm-thick iron hollow roller having an outer diameter of 20 mm and an inner diameter of 18 mm, and a halogen heater 22a as a heating means is disposed inside. The heating roller also has a function as a tension roller.

  The fixing roller 23 is a high friction elastic roller in which a silicone rubber layer as an elastic layer is provided on a cored bar made of an iron alloy having an outer diameter of 20 mm and a diameter of 18 mm. By providing the elastic layer in this way, it is possible to satisfactorily transmit the driving force input from the driving source (motor) via the driving gear train to the fixing belt and to ensure separation of the sheet from the fixing belt. A fixing nip can be formed. As will be described later, the pressure of the fixing nip is set to a maximum value in the region suspended by the fixing roller 23.

  The hardness of the silicone rubber is JIS-A 15 degrees, and the thermal conductivity is 0.8 W / mK. The silicone rubber layer is also effective in shortening the warm-up time because heat conduction to the inside is reduced.

  The fixing belt 20 is rotated by driving the fixing roller 23 by a motor, and the fixing belt 20 is rotated by friction between the silicone rubber surface of the fixing roller 23 and the inner surface Ni layer of the fixing belt 20.

  A fixing pad 24 as a first fixing member that presses the fixing belt 20 toward the pressure belt 21 is disposed in close contact with the fixing roller 23 in a non-contact manner. In this example, the separation distance (gap) at the closest portion between the fixing roller 23 and the fixing pad 24 is set to 5 mm. In this manner, the fixing roller 23 is an elastic roller having a large coefficient of friction in order to satisfy the function as a driving roller, and the fixing pad 24 is arranged in a non-contact proximity to the fixing roller 23 to drive the fixing roller 23. It is possible to prevent the conveyance torque required for the toner from becoming excessively large, and to stabilize the conveyance performance of the fixing belt 20.

  Further, the fixing roller 23 and the fixing pad 24 are positioned by a side plate (not shown), and the fixing roller 23 and the fixing pad 24 are fixed in a direction connecting the axis center of the pressure roller 26 and the axis center of the fixing roller 23 as will be described in detail later. The lower surface of the fixing pad 24 (including the above-described cover) with respect to the lower surface of the roller 23 is configured to be 0.2 mm higher.

  The fixing pad 24 is made of a glass fiber cloth as a low friction sheet in order to reduce the frictional resistance between the SUS fixing stay having a width of about 12 mm and the inner surface of the fixing belt 20 that slides on the surface of the fixing stay. A cover coated with fluororesin is provided. Since the pad cover suppresses the driving torque of the fixing roller 23, the belt can be stably rotated without increasing the size of the motor.

  The pressure belt 21 is stretched between a tension roller 25 and a pressure roller 26. The tension roller 25 has an iron alloy cored bar having an outer diameter of 20 mm and a diameter of 16 mm, and a silicone sponge layer is provided to reduce the thermal conductivity and reduce the thermal conduction from the pressure belt 21. is there. The pressure roller 26 is a low-friction rigid roller made of an iron alloy having an outer diameter of 23.5 mm and an inner diameter of 19.5 mm and a thickness of 2 mm.

  A pressure pad 27 as a second fixing member for pressing the pressure belt 21 toward the fixing belt 20 (fixing pad 24) is disposed in contact with the pressure roller 26 which is a rigid roller.

  Here, in order to form a fixing nip as an image heating nip, the pressure roller 26 is directed toward the fixing roller 23 with a predetermined pressing force by a pressure mechanism with both ends of the rotating shaft directed in the direction of the arrow in FIG. Is pressurized. Thus, the fixing roller 23 and the pressure roller 26 form a roller nip surface RN via the fixing belt 20 and the pressure belt 21.

  A wedge-shaped space Z (FIG. 1) between the inner surface of the pressure belt 21 and the pressure roller 26 is used in order to obtain a continuous pressure distribution with no pressure relief at one fixing nip along the sheet conveyance direction. In order to fill as much as possible, the shape of the pressure pad 27 on the pressure roller 26 side is a shape along the pressure roller 26, that is, the pressure pad 27 (cover described later) is in contact with the pressure roller 26. Has been placed.

  The pressure pad 27 is made of heat-resistant silicone rubber as an elastic body having a thickness of about 3 mm and a width of about 15 mm.

  Further, a wire having a radius of 0.3 mm as a rod-shaped member is formed on the inner surface of the pressure belt 21 and the pressure pad portion located in the wedge-shaped space of the pressure roller 26 in the longitudinal direction of the pressure pad (perpendicular to the sheet conveying direction). (In the width direction of the sheet) is provided in substantially the entire region. Specifically, the wire is fixed to the heat resistant silicone rubber. As a result, the drop of the nip pressure in this space can be further suppressed. In this case, the wire is configured to be covered with the above-described silicone rubber with a low-friction cover described later.

  The pressure pad 27 may be made of a resin material such as PPS or a metal such as SUS.

  Further, on the surface of the pressure pad 27, as with the fixing pad 24, a glass fiber cloth as a low friction sheet is used to reduce the frictional resistance between the inner surface of the sliding pressure belt 21 and the pressure roller 26. A cover having a thickness of 0.1 mm coated with a fluororesin is wound.

  In this embodiment, the tip of the pressure pad 27 on the wedge-shaped space Z side has a 0.1 mm thick cover wrapped around a 0.3 mm wire as described above, and has an R shape with r = 0.4 mm. ing.

  Further, as will be described in detail later, the portion of the pressure pad 27 that is closest to the roller nip surface RN from the center position of the roller nip surface RN and that contacts the pressure belt 21, that is, the pressure pad 27 on the wedge-shaped space Z side. The position in the conveyance direction of the pressure pad 27 is configured so that the distance to the tip portion is g = 4.5 mm.

  At this time, the friction coefficient of the pressure roller 26 against the pressure pad 27 (with the cover described above) is 200 ° C. and the load is 50 N in a thrust type frictional wear test using a test piece of a predetermined shape. When the speed was measured under the condition of 30 mm / s, it was 0.15.

  By reducing the friction coefficient of the pressure roller 26 in this way, it contributes to the formation of a fixing nip without a large pressure missing part while preventing the conveyance load of the pressure belt from becoming too large.

  Here, in order to form a fixing nip also between the fixing pad 24 and the pressure pad 27, the pressure pad 27 has a predetermined structure by a pressure mechanism in which the support plate holding the silicone rubber is directed in the direction of the arrow in FIG. Pressurized with pressure.

  In this example, the width of the fixing nip between the fixing belt 20 and the pressure belt 21 in the sheet conveyance direction is about 18 mm. Since the nip width is wide as described above, it is possible to sufficiently fix the image forming speed. In addition, the use of endless belts on the fixing side and the pressure side as members related to fixing makes it possible to achieve a lower heat capacity than before. As a result, it contributes to shortening the warm-up time (the time required from when the image forming apparatus is turned on until it can be fixed).

  The fixing belt 20 is rotationally driven in the direction of arrow X in FIG. 1 by rotating the fixing roller 23 by a motor at least during execution of image formation. The peripheral speed of the fixing belt 20 is slightly lower than the transport speed of the sheet S transported from the image forming unit side to form a loop on the sheet.

  The pressure belt 21 rotates in the arrow Y direction following the fixing belt 20. Here, the configuration is such that the most downstream part of the fixing nip (the part where the pressure distribution (sheet conveying direction) in the fixing nip is maximum) is conveyed with the fixing belt 20 and the pressure belt 21 sandwiched by a pair of rollers. Belt slip can be prevented. In this embodiment, the peripheral speed of the fixing belt 20 is 300 mm / sec, and it is possible to fix 70 A4 size full color images per minute.

  In a state where the fixing belt 20 rises to a predetermined fixing temperature and is temperature-controlled, the sheet S having the unfixed toner image T is conveyed to the fixing nip between the fixing belt 20 and the pressure belt 21. The sheet S is introduced with the surface carrying the unfixed toner image facing the fixing belt 20 side. The unfixed toner image T on the sheet S is nipped and conveyed while being in close contact with the outer peripheral surface of the fixing belt 20, so that heat is mainly applied from the fixing belt 20 and the surface of the sheet S is subjected to pressure. To be established.

  Further, since the fixing roller 23 in the fixing belt 20 is an elastic roller having a rubber layer, and the pressure roller 26 in the pressure belt 21 is a rigid roller made of iron alloy, the fixing belt 20, the pressure belt 21, The deformation of the fixing roller 23 is large at the fixing nip exit. As a result, the fixing belt is also greatly deformed, and the sheet S carrying the toner image is separated from the fixing belt 20 by the curvature thereof by its own strain.

  By adopting such a configuration, a pressure relief portion does not occur in the fixing nip while stably securing the driving of the fixing belt and the separation of the sheet.

  Next, the nip configuration which is a feature of the present invention will be described in detail with reference to FIG. As shown in FIG. 7, the fixing roller 23 and the pressure roller 26 are pressed through the fixing belt 20 and the pressure belt 21 to form a roller nip surface RN, and the fixing pad 24 and the pressure pad 27 are connected to the fixing belt 20 and the pressurizing belt 20. Pressure is applied via the pressure belt 21 to form a pad nip surface PN.

  As described above, the lower surface of the fixing pad 24 relative to the lower surface of the fixing roller 23 (the above-described cover) with respect to the direction connecting the axial center of the pressure roller 26 and the axial center of the fixing roller 23 (that is, the normal direction of the roller nip surface RN). The position of attachment to the side plate is shifted so that the height is 0.2 mm higher. As a result, the pressure roller 26 and the pressure pad 27 are pressed against the fixing roller 23 and the fixing pad 24 positioned by the side plates, so that the roller nip surface RN and the pad nip surface PN are parallel and on the same plane. Can be configured not to be on top.

  At this time, the distance P in the normal direction between the roller nip surface RN and the pad nip surface PN is set so that the height relationship between the roller nip surface RN and the pad nip surface PN does not change due to tolerance of the fixing roller 23 or softening of the elastic layer. It is desirable that it is 0.05 mm or more. Further, when the distance P in the normal direction between the roller nip surface RN and the pad nip surface PN is 0.4 mm or more, the curvature of the fixing belt 20 decreases, and the surface release layer of the fixing belt 20 is subjected to repeated bending. Wrinkles have occurred in the PFA tube. For this reason, the distance P is preferably set to 0.4 or less.

As can be seen from FIG. 7, the configuration of the present embodiment is such that the radius of the pressure roller is R (mm), the pressure radius of the tip portion of the pressure pad 27 on the wedge-shaped space Z side is r (mm), and the roller nip surface RN is centered. If the distance from the position to the portion closest to the roller nip surface RN of the pressure pad 27, that is, the tip portion of the pressure pad 27 on the wedge-shaped space Z side, is in contact with the pressure belt 21, g (mm)
r + ((R + r) ^ 2-g ^ 2) ^ 0.5-R <P
Satisfied with the relationship.

  With such a configuration, it is possible to achieve a pressure distribution so that the maximum pressure is obtained at the sheet separation position even if the tip of the pressure pad 27 is closer to the roller nip surface RN. As a result, the area where there is no contact object on the inner surface of the belt is reduced, so that a fixing nip is continuously formed along the sheet conveying direction without causing a large pressure relief portion, and the pressure at the sheet separation position is maximized. Can be.

  FIG. 3 shows the pressure distribution in the sheet conveyance direction of the fixing nip portion in this embodiment. As can be seen from this, in this example, there is no large pressure-removal portion in the fixing nip, and the pressure gradually increases from the upstream side and reaches the maximum at the sheet separation position. Accordingly, there is no difference in the conveyance speed in spite of the wide fixing nip, and no image displacement occurs. Further, since there is no stagnation of air and water vapor in the fixing nip, uneven gloss does not occur.

  In the configuration of this embodiment, the radius R of the tip portion R of the pressure pad 27 on the wedge-shaped space Z side is r (mm), and the portion closest to the roller nip surface RN of the pressure pad 27 from the center position of the roller nip surface RN, that is, the wedge-shaped space. Table 1 shows the results of evaluating the relationship between the occurrence of image defects and separation defects when the distance from the tip of the Z-side pressure pad 27 to the portion in contact with the pressure belt 21 is g (mm). Shown in At this time, the experiment was performed by changing the tip portion R-shaped radius r by setting the wire radius of the pressure pad 27 to 0.2 to 0.5 mm.

As the recording material, a coated paper of 80 g / m 2 was used. As a result, it was confirmed that the occurrence of image displacement can be prevented by setting g to 5.0 mm or less. FIG. 4 shows the pressure distribution at the pressure contact portion when g = 5.5 mm and r = 0.5 mm, and it can be seen that there is a large pressure relief portion at the portion where the above-mentioned gap is opposed.
FIG. 5 shows the pressure distribution at the pressure contact part when g = 3.5 mm and r = 0.5 mm. It turns out that the pressure of the downstream part has become low.

  This is because r + ((R + r) ^ 2−g ^ 2) ^ 0.5−R> P, the tip shape R of the pressure pad 27 is determined by the pressure roller 26 and the pressure belt 21. This is because the downstream pressure formed by the roller nip surface RN has dropped due to being strongly sandwiched between the gaps. As a result, a sufficient pressure cannot be secured downstream of the fixing nip surface, and it can be seen that the above-described separation failure occurred.

  At this time, under the condition that the diameter r of the tip shape R of the pressure pad 27 is r = 0.3 mm, the tip portion of the pressure pad 27 is strongly engaged with the roller nip surface during the experiment, and the wire breaks from the pressure pad 27. have done. From this result, it is desirable that the diameter r of the tip shape R of the pressure pad 27 is 0.4 mm or more from the viewpoint of durability.

  Next, as a comparative example, Table 2 below shows the results of evaluating the relationship between the occurrence of image defects and separation defects when the distance P in the normal direction between the roller nip surface RN and the pad nip surface PN is the same.

  Also from the above conditions, in this example and the comparative example, the durability test was performed under the conditions of g = 5.0 mm and r = 0.5 mm. In this example, there was no problem in both the image shift separation property. However, in the comparative example, the fixing roller was softened and deteriorated, and image displacement occurred under the same conditions. Also from the above results, it is desirable that the fixing pad height P is 0.05 mm or more.

  As described above, in this embodiment, the roller nip surface, the fixing pad, and the pressure pad formed by the fixing roller and the pressure roller via the fixing belt and the pressure belt are formed via the fixing belt and the pressure belt. The pad nip surface to be made is configured to be substantially parallel and not on the same plane. As a result, the pressure distribution in the nip can be optimized and image defects and separation defects can be prevented.

  In the above-described embodiment, the example of the fixing device has been described as the image heating device. However, the following configuration may be used. For example, the present invention can also be applied to a gloss applying device that improves the glossiness of an image by reheating a toner image that is supposedly attached to a sheet by a fixing device.

  Further, although an example in which a halogen heater is employed as a heating source for the fixing belt has been described, a heat source (excitation coil) of an electromagnetic induction heating method with high energy efficiency may be employed. In this case, the fixing belt has a configuration including a conductive layer that generates electromagnetic induction heat by the magnetic flux generated from the exciting coil.

1 is a cross-sectional view of a fixing device according to a first embodiment. It is sectional drawing explaining the comparative example of 1st Example. 1 is a diagram illustrating a fixing device according to a first embodiment. It is a figure explaining the comparative example of 1st Example. It is a figure explaining the comparative example of 1st Example. 1 is a diagram illustrating an overall configuration of an image forming apparatus. It is sectional drawing explaining the comparative example of 1st Example in detail.

Explanation of symbols

A Fixing device S Sheet 1 Image forming device 2 Photosensitive drum 3 Charger 4 Optical device 5 Light 6 Developer 7 Transfer roller 8 Cleaning device 9 Feed cassette 10 Feed roller 11 Registration roller pair 12 Discharge roller pair 13 Discharge tray 20 Fixing belt 21 Pressure belt 22 Heating roller 22a Halogen heater 23 Fixing roller 24 Fixing pad 25 Tension roller 26 Pressure roller 27 Pressure pad

Claims (5)

Image heating having first and second belts for nipping and conveying a recording material carrying an image, and nip forming means for forming an image heating nip between the first belt and the second belt In the device
The nip forming means includes a high friction roller that drives the first belt, a low friction roller that faces the high friction roller and presses the second belt, and a non-contact arrangement with the high friction roller. A first fixing member that pressurizes, and a second fixing member that opposes the first fixing member and is disposed in contact with the low friction roller and pressurizes the second belt,
A roller nip surface formed via the first belt and the second belt formed by the high friction roller and the low friction roller, the first fixing member, and the second fixing member pass through the first belt and the second belt. An image heating apparatus characterized in that the pad nip surface formed in the step is substantially parallel and not on the same plane.   2. The image heating apparatus according to claim 1, wherein a distance P in a normal direction between the roller nip surface and the pad nip surface satisfies 0.05 mm ≦ P ≦ 0.4 mm. The radius of the low friction roller is Rmm, and the portion of the second fixing member that is in contact with the inner surface of the second belt and that is closest to the roller nip surface is an R shape having a radius of rmm. When the distance from the center position to the portion contacting the second belt at the portion closest to the roller nip surface of the second fixing member is gmm,
r + ((R + r) ^ 2-g ^ 2) ^ 0.5-R <P
The image heating apparatus according to claim 1, wherein the image heating apparatus satisfies the following relationship. The distance gmm from the center position in the conveying direction of the roller nip surface to the portion contacting the second belt at the portion closest to the roller nip surface of the second fixing member is g ≦ 5
The image heating apparatus according to any one of claims 1 to 3, wherein the relationship is satisfied. R of the R-shaped portion in the second fixing member is
r ≧ 0.4
5. The image heating apparatus according to claim 1, wherein the following relationship is satisfied.

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