Fixing device and image forming apparatus

Abstract

To obtain stable fixing performance over a long period.SOLUTION: A fixing device heats and fixes an image on a recording material with a first rotating body heated by a heater, while sandwiching and conveying the recording material between the first rotating body and a second rotating body at a nip part. A holder member holding the heater is provided on the side of the second rotating body in a thickness direction perpendicular to both a longitudinal direction and a short direction of the heater at the nip part, and has a first surface that supports the heater, a second surface that is provided on the opposite side of the first surface in the thickness direction and supported by a support member on the upstream side and the downstream side of the first surface in the short direction, and rib parts that are provided projected on the second surface and extend in the short direction over a range in which at least the first surface is provided with respect to the short direction.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a fixing device for fixing an image on a recording material and an image forming device for forming an image on a recording material.

Background Art

[0002] An image forming device such as an electrophotographic system includes a heat fixing type fixing device that heats and fixes a toner image transferred onto a recording material. Patent Document 1 describes a fixing device of a film heating type having a heater in which a resistance heating element is formed on a ceramic substrate, a holder member that holds the heater, a cylindrical film externally fitted to the heater, and a pressure roller that is pressed against the heater with the film interposed therebetween. Further, the above document describes that the film is efficiently heated by dispersing particles having a low thermal conductivity in the holder member.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when the fixing device is used over a long period of time, the holder member may creep and deform due to continuously receiving heat and load. For example, if the holder member creeps and deforms in the configuration of the above document, the rotation trajectory of the film that rotates around the holder member changes, and there is a possibility that effects such as a decrease in fixing performance due to a decrease in the contact area between the film and the heater may appear.

[0005] Therefore, an object of the present invention is to provide a fixing device capable of obtaining stable fixing performance over a long period of time and an image forming device including the same.

Means for Solving the Problems

[0006] One aspect of the present disclosure includes a first rotating body, an elongated heater, and a holder member that holds the heater. A nip forming unit is disposed in the internal space of the first rotating body, and a second rotating body that is pressed against the nip forming unit with the first rotating body interposed therebetween and forms a nip portion between the nip forming unit. A support member is disposed in the internal space of the first rotating body and supports the nip forming unit. The fixing device heats and fixes an image on the recording material by the first rotating body heated by the heater while sandwiching and conveying the recording material by the first rotating body and the second rotating body at the nip portion. The holder member is provided on the side of the second rotating body in the thickness direction orthogonal to both the longitudinal direction and the short-side direction of the heater at the nip portion, and has a first surface that supports the heater, a second surface that is provided on the opposite side of the first surface in the thickness direction and is supported by the support member on the upstream side and the downstream side of the first surface in the short-side direction, and a rib portion that protrudes from the second surface and extends in the short-side direction over at least the range where the first surface is provided.

Effects of the Invention

[0007] According to the present disclosure, stable fixing performance can be obtained over a long period.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Mode for Carrying Out the Invention

[0009] Hereinafter, embodiments according to the present disclosure will be described with reference to the drawings.

Example

[0010] (Image forming apparatus) An image forming apparatus according to the first embodiment (Example 1) will be described using the schematic diagram shown in FIG. 1. The image forming apparatus 50 in this example is an electrophotographic apparatus of a direct transfer type that directly transfers a toner image formed on the photosensitive drum 1 onto a recording material P (that is, without passing through an intermediate transfer member).

[0011] The image forming apparatus 50 includes, as an image forming means, an electrophotographic unit including a photosensitive drum 1, a charger 2, an exposure device 3, a developing device 5, a transfer roller 10, and a drum cleaner 16. The photosensitive drum 1, which is an image carrier, is an electrophotographic photoreceptor formed in a drum shape (cylindrical shape). The charger 2, the exposure device 3, the developing device 5, the transfer roller 10, and the drum cleaner 16 are arranged in this order along the rotation direction (arrow R1 direction) of the photosensitive drum 1 around the photosensitive drum 1.

[0012] When an image formation request is input from an external computer to the image forming apparatus 50, the photosensitive drum 1 is rotationally driven in the direction of arrow R1, and the surface of the photosensitive drum 1 is charged to a predetermined polarity (here, negative polarity) by the charger 2. Next, the laser beam L is irradiated from the exposure device 3 onto the surface of the charged photosensitive drum 1, and an electrostatic latent image is formed on the surface of the photosensitive drum 1. The developing device 5 accommodates the black toner which is the developer of this embodiment, and supplies the negatively charged black toner to the photosensitive drum 1 by the developing roller. As a result, toner adheres to the electrostatic latent image area on the photosensitive drum 1, and a toner image is formed on the surface of the photosensitive drum 1.

[0013] A feed tray on which the recording material P is loaded is provided at the lower part of the image forming apparatus 50. As the recording material P, various sheet materials with different sizes and materials can be used, such as paper like plain paper and cardboard, plastic film, cloth, sheet materials with surface treatment like coated paper, and special-shaped sheet materials like envelopes and index paper.

[0014] The recording material P loaded on the feed tray is fed one by one by the feed roller 4, and is conveyed via the conveying roller 6 to the transfer nip Ntr as a transfer unit where the toner image is transferred onto the recording material P. The transfer nip Ntr is the nip portion between the photosensitive drum 1 and the transfer roller 10. Then, a positive voltage which is the opposite polarity to the normal charging polarity of the toner is applied to the transfer roller 10 from a power source (not shown), so that the toner image on the photosensitive drum 1 is transferred onto the recording material P at the transfer nip Ntr. The transfer residual toner or deposits such as paper powder adhering to the surface of the photosensitive drum 1 that has passed through the transfer nip Ntr are removed by the drum cleaner 16 having an elastic blade.

[0015] The recording material P onto which the toner image has been transferred is conveyed to the fixing device 100 of the heat fixing method described below and undergoes the fixing process of the toner image. The recording material P that has passed through the fixing device 100 is discharged to the outside of the image forming apparatus 50 as a finished product by the discharge roller pair.

[0016] In addition, although an image forming apparatus using a direct transfer method has been exemplified in this embodiment, any other type of image forming apparatus may be used as long as it is equipped with a fixing device that heats and fixes the toner image formed on the recording material P. For example, the fixing device described below may be applied to an image forming apparatus using an intermediate transfer method in which the toner image formed on the image carrier is first transferred to an intermediate transfer member such as an intermediate transfer belt and then transferred from the intermediate transfer member to the recording material. Further, the fixing device described below may be applied to an image forming apparatus that forms a color image on the recording material using a plurality of colors of toner.

[0017] (Fixing Device) The outline of the fixing device 100 of this embodiment will be described with reference to FIGS. 2(a) and 2(b). The fixing device 100 of this embodiment is a film heating type fixing device that is excellent in shortening the startup time and reducing power consumption. FIG. 2(a) is a cross-sectional view of the central portion in the longitudinal direction of the fixing device 100. FIG. 2(b) is a cross-sectional view along the longitudinal direction of the fixing device 100, showing only both end portions in the longitudinal direction of the fixing device 100.

[0018] In the following description, the shape and positional relationship of the members in the fixing device 100 will be described using the recording material conveyance direction A, the longitudinal direction B, and the vertical direction C. The recording material conveyance direction A is the conveyance direction of the recording material P at the fixing nip Nf, which is the nip portion of the fixing device 100. The longitudinal direction B is the width direction of the recording material P at the fixing nip Nf (the direction perpendicular to the recording material conveyance direction A). The longitudinal direction B is also the main scanning direction during image formation. The vertical direction C is the direction perpendicular to both the recording material conveyance direction A and the longitudinal direction B.

[0019] As shown in FIGS. 2(a) and 2(b), the fixing device 100 includes a film unit 101 (film assembly) including a fixing film 112, a heater 113, a heater holder 130, and a pressing stay 119, and a pressing roller 110 facing the film unit 101. The fixing film 112, the heater 113, the heater holder 130, the pressing stay 119, and the pressing roller 110 are all members elongated in the longitudinal direction B. That is, the longitudinal direction B of the fixing device 100 is also the longitudinal direction of the fixing film 112, the heater 113, the heater holder 130, the pressing stay 119, and the pressing roller 110. Further, the recording medium conveyance direction A is also the short-side direction of the heater 113, and the vertical direction C is also the thickness direction of the heater 113.

[0020] The heater holder 130 is the holder member or holding member of the present embodiment. The pressing stay 119 is the support member or reinforcing member of the present embodiment. The pressing roller 110 is the second rotating body in the fixing device 100 of the present embodiment. Further, the pressing roller 110 is the pressing member of the present embodiment.

[0021] The fixing film 112 is the first rotating body in the fixing device 100 of the present embodiment. The fixing film 112 is a flexible cylindrical (endless) film member (belt member). The fixing film 112 of the present embodiment has an outer diameter of 18 mm in a non-deformed cylindrical state and has a multilayer structure in the thickness direction. The layer structure of the fixing film 112 includes at least a base layer for maintaining the strength of the film and a release layer for reducing the adhesion of dirt to the surface.

[0022] The material of the base layer preferably has heat resistance to withstand the heat of the heater 113 and sufficient strength for sliding against the heater 113. As the material of the base layer, metals such as stainless steel and nickel, and heat-resistant resins such as polyimide can be preferably used. In this embodiment, as the material of the base layer of the fixing film 112, a material in which a carbon-based filler is added to a polyimide resin to improve the thermal conductivity and strength is used. The thinner the base layer, the easier it is to transfer the heat of the heater 113 to the surface of the recording material P, but the strength decreases. Therefore, about 15 μm to 100 μm is preferable, and it is set to 60 μm in this embodiment.

[0023] As the material of the release layer of the fixing film 112, fluororesins such as perfluoroalkoxy resin (PFA), polytetrafluoroethylene resin (PTFE), and tetrafluoroethylene-hexafluoropropylene resin (FEP) can be preferably used. In this embodiment, PFA, which is excellent in releasability and heat resistance among fluororesins, is used. The release layer may be formed by coating a tube on the base layer, or may be formed by coating the surface of the base layer with a paint. In this embodiment, the release layer is formed by a coating method excellent in thin-wall molding. The thinner the release layer, the easier it is to transfer the heat of the heater 113 to the surface of the fixing film 112, but if it is too thin, it becomes difficult to ensure durability. Therefore, about 5 μm to 30 μm is preferable, and it is set to 10 μm in this embodiment. Also, although not used in this embodiment, an elastic layer may be provided between the base layer and the release layer. In that case, as the material of the elastic layer, silicone rubber, fluororubber, or the like is used.

[0024] On the inner circumferential side of the fixing film 112, a heater holder 130 is provided. The heater holder 130 has a substantially semi-circular arc-shaped trough in cross-section (the cross-section in a plane perpendicular to the longitudinal direction B). That is, the heater holder 130 has a surface facing the fixing nip Nf curved convexly toward the pressure roller 110 side in the vertical direction C, and a heater holding portion (fitting portion) for holding the heater 113 is provided at substantially the center of the curved surface in the recording material conveyance direction A. The heater holding portion opens to the pressure roller 110 side in the vertical direction C and has an elongated groove shape in the longitudinal direction B. The heater holder 130 is formed of a liquid crystal polymer resin with high heat resistance in order to satisfy heat resistance and rigidity. In this embodiment, Sumika Super E5204L (registered trademark) manufactured by Sumitomo Chemical Co., Ltd. is used as the liquid crystal polymer resin.

[0025] The heater holder 130 has a heater seating surface S1 that supports the heater 113, an upstream protruding portion 131 and a downstream protruding portion 132 adjacent to the heater seating surface S1, and a stay contact surface S3 provided on the side opposite to the heater seating surface S1 in the vertical direction C1. The heater seating surface S1 is the first surface of the heater holder 130 provided on the side of the pressure roller 110 in the vertical direction C perpendicular to both the recording material conveyance direction A and the longitudinal direction B. The heater seating surface S1 supports the surface of the heater 113 on the side opposite to the pressure roller 110 in the vertical direction C (that is, the surface opposite to the sliding surface S2).

[0026] The upstream protruding portion 131 is provided on the upstream side of the heater seating surface S1 in the recording material conveyance direction A and protrudes toward the pressure roller 110 side in the vertical direction C compared to the heater seating surface S1. The downstream protruding portion 132 is provided on the downstream side of the heater seating surface S1 in the recording material conveyance direction A and protrudes toward the pressure roller 110 side in the vertical direction C compared to the heater seating surface S1. The heater seating surface S1 is the bottom of the groove shape (heater holding portion) formed between the upstream protruding portion 131 and the downstream protruding portion 132. Also, the upstream protruding portion 131 and the downstream protruding portion 132 each have a sliding surface that slides on the inner surface of the fixing film 112 upstream and downstream of the sliding surface S2 of the heater 113 in the recording material conveyance direction A.

[0027] Furthermore, the heater holder 130 has an upstream guide 126 that guides the fixing film 112 on the upstream side of the fixing nip Nf in the recording material conveyance direction A, and a downstream guide 127 that guides the fixing film 112 on the downstream side of the fixing nip Nf. That is, the heater holder 130 holds the heater 113 and also has a role of guiding the rotation of the fixing film 112.

[0028] Both the upstream guide 126 and the downstream guide 127 extend in the direction C perpendicular to the stay contact surface S3 of the heater holder 130 on the side opposite to the pressure roller 110. Specifically, as shown in FIG. 6, the upstream guide 126 and the downstream guide 127 include a wall portion 124 that rises in the direction C from the end of the stay contact surface S3 in the recording material conveyance direction A, and guide ribs 129 provided at a plurality of positions of the wall portion 124 in the longitudinal direction B. The end face of the guide rib 129 is curved along the natural shape (FIG. 2(a)) formed when the fixing film 112 is pressed at the fixing nip Nf as described above. The upstream guide 126 and the downstream guide 127 guide the rotation locus of the fixing film 112 by the end face of the guide rib 129. The upstream guide 126 is the first guide portion of this embodiment that guides the inner surface of the fixing film 112 toward the fixing nip Nf. The downstream guide 127 is the second guide portion of this embodiment that guides the inner surface of the fixing film 112 that has passed through the fixing nip Nf.

[0029] Instead of the configuration in which the guide rib 129 protruding from the wall portion 124 guides the fixing film 112, the wall portion 124 itself may have the same cross-sectional shape as the guide rib 129 of this embodiment, and the outer surface of the wall portion 124 may guide the fixing film 112. In this case, the guide rib 129 may be continuous with the outer surface of the wall portion 124 and guide the fixing film 112 upstream or downstream in the rotation direction of the fixing film 112 from the outer surface of the wall portion 124, or the guide rib 129 may be omitted.

[0030] The heater 113 and the heater holder 130 are arranged in the internal space of the fixing film 112, and function as a nip forming unit that forms a fixing nip Nf by being brought into pressure contact with the pressure roller 110 with the fixing film 112 interposed therebetween. In this embodiment, a configuration in which the heater 113 directly slides on the inner surface of the fixing film 112 will be described, but a configuration in which a sliding member is interposed between the heater 113 and the fixing film 112 may also be used. As the sliding member, one having high thermal conductivity and high slidability with respect to the inner surface of the fixing film 112 is used, and for example, a sheet-like member of alloy iron or aluminum can be used. That is, the nip forming unit may be configured such that the heater 113 indirectly heats the fixing film 112 via the sliding member.

[0031] The pressure stay 119 is disposed along the longitudinal direction B of the heater holder 130. The pressure stay 119 is formed by bending a highly rigid sheet metal such as stainless steel in order to uniformly pressurize the heater holder 130 in the longitudinal direction. The pressure stay 119 is formed in a U-shape (a square C-shape) that is open on the side of the pressure roller 110 in the vertical direction C when viewed in the longitudinal direction B. That is, the pressure stay 119 has a first portion 91 extending in the recording material conveyance direction A, and a second portion 92 and a third portion 93 respectively extending from the upstream end and the downstream end of the first portion 91 in the recording material conveyance direction A toward the heater holder 130 in the vertical direction C.

[0032] One end 119a of the pressure stay 119 is in contact with the stay contact surface S3 of the heater holder 130 upstream of the heater seat surface S1 in the recording material conveyance direction A. The other end 119b of the pressure stay 119 is in contact with the stay contact surface S3 of the heater holder 130 downstream of the heater seat surface S1 in the recording material conveyance direction A. That is, the pressure stay 119 is in contact with the stay contact surface S3 (the second surface) of the heater holder 130 at the ends 119a and 119b which are the tips of the second portion 92 and the third portion 93.

[0033] The pressing stay 119 supports the heater holder 130 against the nip pressure in the fixing nip Nf by pressing the stay contact surface S3 at the end portion 119a toward the pressing roller 110 in the vertical direction C. That is, the pressing stay 119 functions as a support member that supports the nip forming unit including the heater 113 and the heater holder 130.

[0034] The pressing roller 110 of this embodiment has an outer diameter of 20 mm, and an elastic layer 116 with a thickness of 3.0 mm is formed on the outer periphery of an iron core metal 117 with a diameter of 14 mm. As the material of the elastic layer 116, solid rubber or foamed rubber is used. Foamed rubber has a low heat capacity and a low thermal conductivity, and it is difficult for the heat on the surface of the pressing roller 110 to be absorbed internally. Therefore, the surface temperature is likely to rise, and there is an advantage that the startup time of the fixing device 100 can be shortened. In this embodiment, foamed rubber obtained by foaming silicone rubber is used as the elastic layer 116. On the elastic layer 116, a release layer 118 made of perfluoroalkoxy resin (PFA) is formed as a release layer. The release layer 118 may be a coated tube or a surface coated with paint like the release layer of the fixing film 112. In this embodiment, the release layer 118 is formed by coating the outer peripheral surface of the elastic layer 116 with a tube having excellent durability. As the material of the release layer 118, in addition to PFA, fluororesins such as PTFE and FEP, fluororubbers and silicone rubbers with good releasability may be used. The lower the surface hardness of the pressing roller 110, the wider the width of the fixing nip Nf can be obtained with a light pressure, but it is determined in consideration of durability at the same time. In this embodiment, a pressing roller 110 with an Asker-C hardness (4.9 N load) of 50° is used. Instead of the pressing roller 110, a belt unit including a belt member stretched over a plurality of rollers may be used as the pressing member.

[0035] The heater 113 of this embodiment uses a structure in which a resistive heating element is provided on a ceramic substrate. Specifically, as the substrate of the heater 113, alumina with a width of 6 mm in the recording material conveyance direction A and a thickness of 1 mm in the vertical direction C is used. On the surface of this substrate, a resistive heating element of Ag / Pd (silver palladium) is coated by screen printing to a thickness of several micrometers, and a glass layer is formed thereon with a thickness of 60 μm to protect the heating element and improve slidability, thereby creating the heater 113.

[0036] The fixing device 100 is configured to be able to adjust the temperature of the heater 113 by appropriately controlling the current flowing through the resistive heating element according to the signal of a temperature detection element (heat-sensitive element), which will be described later, that detects the temperature of the substrate of the heater 113 or the fixing film 112. The heater 113 is fitted and fixedly supported in a groove portion provided in the heater holder 130. In this embodiment, the center of the heater 113 in the recording material conveyance direction A is located 0.4 mm upstream of the center (rotation axis) of the pressure roller 110.

[0037] As shown in FIG. 2(b), the pressure stay 119 has extension portions 119e that penetrate through side plates 134 on both sides in the longitudinal direction B of the frame 133 of the fixing device 100 and extend to the outside of the side plates 134. Fixing flanges 120 are respectively fitted onto the extension portions 119e on both sides of the pressure stay 119. The film unit 101 is mounted between the side plates 134 on both sides in a posture in which the heater 113 is pressed toward the pressure roller 110 in the vertical direction C because the fixing flanges 120 are supported by the side plates 134. Each fixing flange 120 is provided with a longitudinal groove portion extending in the vertical direction C, and the longitudinal groove portion is engaged with the edge of a longitudinal guide slit provided in the side plate 134. Thereby, each fixing flange 120 is supported by the side plate 134 so as to be movable in the vertical direction C. In this embodiment, a liquid crystal polymer resin is used as the material of the fixing flange 120.

[0038] The core metal 117 of the pressure roller 110 has shaft portions 117a that penetrate through the side plates 134 on both sides, and each shaft portion 117a is held by a bearing member 135 engaged with the side plate 134. Thereby, the pressure roller 110 is rotatably supported by the frame 133.

[0039] Then, a compression spring 122 is provided between the pressing portion 120b of the fixing flange 120 and the spring support portion 121 fixed to the frame 133. As a result, the biasing force of the compression spring 122 is transmitted to the heater 113 through the fixing flanges 120, the pressing stays 119, and the heater holders 130 on both sides, and the heater 113 is pressed against the pressure roller 110 with a predetermined pressing force while sandwiching the fixing film 112.

[0040] In this embodiment, the spring constant and the compression amount of the compression spring 122 are set so that the pressing force at which the fixing film 112 and the pressure roller 110 press against each other in the vertical direction C at the fixing nip Nf is 15 kgf. At the fixing nip Nf, the fixing film 112 is sandwiched between the heater 113 and the pressure roller 110 and bends following the sliding surface S2 which is the flat surface on the front side of the heater 113, and the inner surface of the fixing film 112 is in close contact (surface contact) with the sliding surface S2. Note that the film regulating portion 120a of the fixing flange 120 has a shape along the natural shape (see Fig. 2(a)) formed when the fixing film 112 is pressed at the fixing nip Nf.

[0041] When a driving force transmitted from a driving source (not shown) is input to the driving gear 117g (Fig. 2(b)) provided on the shaft portion 117a of the pressure roller 110, the pressure roller 110 is rotationally driven at a predetermined speed in the direction of arrow R2 in Fig. 2(a). Along with the rotational driving of the pressure roller 110, a rotational force acts on the fixing film 112 due to the frictional force between the pressure roller 110 and the fixing film 112 at the fixing nip Nf. As a result, the fixing film 112 rotates in the direction of arrow R3 in the figure around the heater 113 and the heater holder 130 following the rotation of the pressure roller 110 while sliding the inner surface against the sliding surface S2 of the heater 113. The rotational speed of the pressure roller 110 is set so that the surface moving speeds of the pressure roller 110 and the fixing film 112 at the fixing nip Nf are 200 mm / sec.

[0042] When performing image fixing, while energizing the heater 113, the pressure roller 110 is driven, so that the recording material is sandwiched and conveyed between the pressure roller 110 and the fixing film 112 at the fixing nip Nf. At the same time, the image on the recording material is heated by the fixing film 112 heated by the heater 113, thereby performing thermal fixing of the image.

[0043] Note that a heat-resistant lubricant is applied to the inner surface of the fixing film 112, thereby ensuring the slidability between the heater 113 and the heater holder 130 and the inner surface of the fixing film 112. In this embodiment, a fluorine-based grease is used as the lubricant. Specifically, a grease mixed with perfluoropolyether (PFPE) oil as the base oil and polytetrafluoroethylene (PTFE) powder as the thickener is used.

[0044] (Heater Holder) FIG. 3 is a schematic diagram for explaining the crown shape in the longitudinal direction B of the heater holder 130. As shown in FIG. 3, the heater holder 130 has a shape (i.e., a crown shape) that is gently curved such that the central portion of the heater seat surface S1 that supports the heater 113 protrudes toward the pressure roller 110 in the vertical direction C compared to both end portions in the longitudinal direction B. The heater 113 is fixed to the heater holder 130 by the heater power supply portion 136 and the heater clip 137 at both end portions in the longitudinal direction B. Therefore, the heater 113 is attached in a curved state following the crown shape of the heater seat surface S1.

[0045] As a specific example of the crown shape of the heater seat surface S1, in a region CR having a longitudinal width of 225 mm corresponding to the range in the longitudinal direction B where the heater 113 faces the pressure roller 110, it has a gently curved quadratic curve shape when viewed in the recording material conveyance direction A. The amount by which the central portion of the heater seat surface S1 protrudes in the vertical direction C with respect to both end portions is, for example, 0.4 mm.

[0046] By providing such a crown shape, a fixing nip Nf with a uniform width can be formed over substantially the entire length in the longitudinal direction B. That is, when the film unit 101 is pressed against the pressure roller 110 by the biasing force of the pressure spring 122, slight deflection occurs in the pressure stay 119 and the shaft core 117 of the pressure roller 110. If the crown shape is not provided on the heater seat surface S1, at both ends in the longitudinal direction B, the heater 113 is strongly pressed against the pressure roller 110 and the nip width of the fixing nip Nf becomes wider, while at the central portion in the longitudinal direction B, the nip width of the fixing nip Nf becomes narrower. On the contrary, by providing a crown shape as in this embodiment, the difference in the nip width of the fixing nip Nf between the central portion and both ends in the longitudinal direction B can be reduced. The width of the fixing nip Nf in the recording material conveyance direction A in this embodiment is approximately 6.2 mm over the entire region CR in the longitudinal direction B.

[0047] Next, the opening O of the heater holder 130 will be described. FIG. 4(a) is a perspective view of the heater holder 130 as viewed from the heater seat surface S1 side. FIG. 4(b) is a cross-sectional view of the fixing device 100 (a cross-section in a plane perpendicular to the longitudinal direction B) at the portion where the temperature detection element T is disposed (broken line 4B-4B in FIG. 4(a)).

[0048] As shown in FIG. 4(a), an opening O for fitting a temperature detection element T such as a temperature fuse, a thermoswitch, or a thermistor is provided in the heater seat surface S1 of the heater holder 130. As shown in FIG. 4(b), the opening O is a hole that penetrates the heater holder 130 in the vertical direction C from the heater seat surface S1 to the stay contact surface S3 on the opposite side. The opening O of the heater holder 130 enables the temperature detection element T to be arranged in contact with the heater 113. The temperature detection element T emits a signal according to the temperature of the heater 113. Note that the temperature detection element T may be arranged in proximity with a predetermined gap without being in contact with the heater 113.

[0049] By using a temperature fuse or a thermoswitch as the temperature detection element T, the control unit 51 of the image forming apparatus 50 can control the power supply circuit 52 of the heater 113 based on the signal of the temperature detection element T to cut off the power supply to the heater 113. The power supply circuit 52 has a cutoff circuit such as a relay that can cut off the energization of the heater 113 based on a command from the control unit 51. In this case, the control unit 51 and the cutoff circuit function as cutoff means (safety device) that senses abnormal temperature rise of the heater 113 and cuts off the power supply to the heater 113. Also, by using a thermistor as the temperature detection element T, the control unit 51 can control the amount of electric power supplied from the power supply circuit 52 to the heater 113 based on the signal of the temperature detection element T. In this case, the control unit 51 functions as temperature control means (temperature adjustment device) that controls the temperature of the heater 113 to match a predetermined target temperature.

[0050] Here, the peripheral portion of the opening O of the heater holder 130 has a lower rigidity than other portions of the heater holder 130. Therefore, as will be described later, in this embodiment, a reinforcing rib 123 is provided in the vicinity of the opening O on the stay contact surface S3 on the back side of the heater seat surface S1.

[0051] Next, the rotation orbit of the fixing film 112 regulated by the heater holder 130 will be described. FIG. 5 is a cross-sectional view near the fixing nip Nf at the central portion in the longitudinal direction B.

[0052] As described above, the heater holder 130 has an upstream protruding portion 131 that protrudes toward the pressure roller 110 side from the heater seating surface S1 on the upstream side in the recording material conveyance direction A from the heater 113. The protruding height H of the upstream protruding portion 131 with respect to the sliding surface S2 of the heater 113 should desirably be a certain height to regulate the trajectory of the fixing film 112 so that the fixing film 112 does not contact the edge portion of the heater 113 (the edge portion on the upstream side in the recording material conveyance direction A). However, if the protruding height H is made too high, the fixing film 112 is pressed by the upstream protruding portion 131, and the contact width (inner surface nip width Nn) between the inner surface of the fixing film 112 and the heater 113 decreases. In this case, heat transfer from the heater 113 to the fixing film 112 is impaired, which becomes a factor causing poor fixing.

[0053] The protruding height H of the upstream protruding portion 131 with respect to the sliding surface S2 of the heater 113 is desirably about 0.1 to 0.7 mm, and is 0.2 mm in this embodiment. Also, it is desirable that the inner surface nip width Nn is ensured to be 4 mm or more, and it is 4.2 mm in this embodiment.

[0054] (Reinforcing rib of heater holder) Next, regarding the reinforcing rib 123 provided on the heater holder 130 according to this embodiment, its shape and positional relationship with the pressure stay 119 will be described.

[0055] FIG. 6 is a perspective view of the heater holder 130 as viewed from the side opposite to the heater seating surface S1, and particularly shows an enlarged view of the vicinity of the opening O where the temperature detection element T is disposed. As shown in FIG. 6, two reinforcing ribs 123 extending in the recording material conveyance direction A are formed so as to sandwich the opening O of the heater holder 130 from both sides in the longitudinal direction B. The reinforcing rib 123 is a rib portion (ridge portion) that protrudes in the vertical direction C from the stay contact surface S3 (second surface) of the heater holder 130 and extends in the recording material conveyance direction A (the short side direction of the heater 113).

[0056] FIG. 7 is a cross-sectional view of the fixing device 100 in a portion where the reinforcing rib 123 is disposed in the longitudinal direction B. As shown in FIGS. 6 and 7, the reinforcing rib 123 in the present embodiment extends in the recording material conveyance direction A so as to connect the upstream guide 126 and the downstream guide 127 of the heater holder 130. By connecting the upstream guide 126 and the downstream guide 127 with the reinforcing rib 123, the bending rigidity of the heater holder 130 against the force received from the pressure stay 119 and the pressure roller 110 is improved. Note that the reinforcing rib 123 may be connected to either the wall portion 124 of the upstream guide 126 and the downstream guide 127 or the guide rib 129.

[0057] Incidentally, the reinforcing rib 123 has a shape protruding in the vertical direction C from the stay contact surface S3 of the heater holder 130 to the side opposite to the pressure roller 110. Therefore, notch portions 119c for avoiding the reinforcing rib 123 are provided at the end portions 119a and 119b of the pressure stay 119 facing the heater holder 130 (FIG. 7). The notch portion 119c has a concave shape in which a part of the end portions 119a and 119b of the heater holder 130 extending in the longitudinal direction B is recessed in the vertical direction C toward the side opposite to the pressure roller 110 when viewed in the recording material conveyance direction A. That is, the second portion 91 and the third portion 93 of the pressure stay 119, which are support members, are provided with notch portions 119c formed in a concave shape recessed in the direction away from the stay contact surface S3 (second surface) of the heater holder 130 in the vertical direction C and extending in the recording material conveyance direction A. The reinforcing rib 123 as a rib portion extends in the recording material conveyance direction A through the inside of the notch portion 119c.

[0058] In the present embodiment, the height Hr of the reinforcing rib 123 in the vertical direction C is 1.5 mm, and the width Wr of the reinforcing rib 123 in the longitudinal direction B is 2.0 mm. Further, the height of the notch portion 119c of the pressure stay 119 in the recording material conveyance direction A is 2.0 mm, and the width of the notch portion 119c in the longitudinal direction B is 2.5 mm. Thereby, contact between the reinforcing rib 123 and the pressure stay 119 is avoided, and even when the reinforcing rib 123 is provided, the pressure stay 119 can press the heater holder 130 with a substantially uniform force in the longitudinal direction B.

[0059] (Operation and Effect of this Embodiment) Regarding that the creep deformation of the heater holder 130 is suppressed by the configuration of this embodiment, it will be described with reference to FIGS. 7 to 9.

[0060] FIG. 8 is a schematic diagram for explaining the stress acting on the heater holder 130 in the pressurized state of the fixing nip Nf. As shown in FIG. 8, the heater holder 130 receives a force F1 from the end portions 119a and 119b of the pressure stay 119 toward the pressure roller 110 in the vertical direction C at the stay contact surface S3. Further, the heater holder 130 receives a force F2 on the opposite side of the pressure roller 110 in the vertical direction C as a reaction force received from the pressure roller 110 supported by the bearing member 135 via the fixing film 112 and the heater 113.

[0061] As a result, a bending moment acts on the heater holder 130 such that the heater seat surface S1 is displaced in the vertical direction C toward the side opposite to the pressure roller 110 between the contact portions (the first position P1 and the second position P2) with the pressure stay 119. In other words, a bending moment is generated to bend the heater holder 130 so that the upstream protruding portion 131 and the downstream protruding portion 132 are displaced toward the side of the pressure roller 110 in the vertical direction C with respect to the heater 113.

[0062] If the deformation of the heater holder 130 occurs due to such a bending moment, the fixing performance of the fixing device 100 may deteriorate.

[0063] Next, a case where the heater holder 130 is deformed by a bending moment will be described using a reference example. FIG. 9 is a cross-sectional view of the fixing device 100 in the vicinity of the opening of the heater holder 130 in the reference example, and the reinforcing rib 123 as in this embodiment is not arranged on the heater holder 130.

[0064] When a paper passage test was conducted to form an image on LTR-sized paper using the image forming apparatus 50 equipped with the fixing device 100 of this reference example, no damage to the heater holder 130 or wrinkles in the recording material occurred. If the mechanical strength and dimensional accuracy of the heater holder 130 were not sufficient, there might be a possibility of damage to the heater holder 130, or the fixing film 112 might shift or the recording material might wrinkle due to unstable running of the fixing film 112. On the other hand, in the fixing device 100 of the reference example, it is considered that the mechanical strength and dimensional accuracy of the heater holder 130 were sufficiently ensured.

[0065] On the other hand, in this reference example, when a durability test was conducted to repeatedly form images on a large number of sheets of paper, fixing failures occurred as the cumulative number of sheets passed increased, and the result was a gradual deterioration. This is presumably because creep deformation of the heater holder 130 occurred due to the bending moment described above, resulting in a decrease in the inner surface nip width Nn, which is the contact width between the inner surface of the fixing film 112 and the heater 113. That is, it is considered that the upstream protrusion 131 and the downstream protrusion 132 were displaced toward the pressure roller 110 side in the vertical direction C with respect to the heater 113, causing the fixing film 112 to be separated from a part of the heater 113. When the inner surface nip width Nn decreases, the surface temperature of the fixing film 112 drops, and when it falls below the lower limit of the temperature range suitable for image fixing, it becomes apparent as a fixing failure.

[0066] Also, in the durability test, the fixing failures occurred at positions on the sheet corresponding to the vicinity of the opening O of the heater holder 130 in the longitudinal direction B. This is presumably because creep deformation of the heater holder 130 mainly occurred in the vicinity of the opening O, which has relatively low rigidity, due to the bending moment described above.

[0067] Next, the case of this embodiment will be described with reference to FIG. 7. As described above, in the heater holder 130 of this embodiment, a reinforcing rib 123 is formed so as to protrude from the stay contact surface S3 and extend in the recording material conveyance direction A. Due to this reinforcing rib 123, the bending rigidity of the heater holder 130 with respect to the bending moment (FIG. 8) received by the heater holder 130 in the pressurized state of the fixing nip Nf is improved, and creep deformation of the heater holder 130 is less likely to occur.

[0068] In particular, in this embodiment, the reinforcing rib 123 is disposed in the vicinity of the opening O of the heater holder 130 in the longitudinal direction B. Thereby, it is possible to improve the bending rigidity in the vicinity of the opening O, which has lower rigidity than the portion without the opening O, and effectively suppress the creep deformation of the heater holder 130.

[0069] The reinforcing rib 123 is preferably disposed over at least the range where the heater seating surface S1 (first surface) is provided with respect to the recording material conveyance direction A. Thereby, the bending rigidity of the portion where the thickness of the heater holder 130 in the vertical direction C is reduced by the space for receiving the heater 113 is improved by the reinforcing rib 123, and creep deformation can be suppressed.

[0070] More preferably, the reinforcing rib 123 is disposed over at least the range from the first position P1 to the second position P2 in FIG. 8 with respect to the recording material conveyance direction A. The first position P1 is the position where the pressurizing stay 119 abuts on the stay contact surface S3 of the heater holder 130 on the upstream side of the heater 113, and the second position P2 is the position where the pressurizing stay 119 abuts on the stay contact surface S3 of the heater holder 130 on the downstream side of the heater 113. Thereby, the bending rigidity of the range where the bending moment acts on the heater holder 130 due to the forces F1 and F2 received by the heater holder 130 from the pressurizing stay 119 and the pressurizing roller 110 is improved by the reinforcing rib 123, and creep deformation can be more effectively suppressed.

[0071] More preferably, as in this embodiment, the reinforcing rib 123 is configured to be continuous in the recording material conveyance direction A from the upstream guide 126 (first guide portion) to the downstream guide 127 (second guide portion) of the heater holder 130. Thereby, the bending rigidity of the heater holder 130 can be further improved, and creep deformation can be further suppressed.

[0072] When a paper passing test was performed using the image forming apparatus 50 equipped with the fixing device 100 of this embodiment on LTR size paper, no breakage occurred in the heater holder 130, nor were there any wrinkles in the recording material. Further, even when a durability test was conducted, a state in which a uniform fixing image was obtained over the entire longitudinal direction B without the occurrence of abnormal images such as poor fixing was maintained over a long period. This is presumably because the creep deformation of the heater holder 130 was suppressed by the reinforcing rib 123 disposed near the opening O of the heater holder 130.

[0073] As an alternative means for improving the bending rigidity of the heater holder 130 and preventing creep deformation, it is also conceivable to increase the thickness of the heater holder 130 at the portions where the heater seat surface S1 and the stay contact surface S3 are provided. However, in this configuration, the heat capacity of the heater holder 130 increases, and the warm-up time of the fixing device 100 becomes longer. On the other hand, by using the reinforcing rib 123 as in this embodiment, it is possible to improve the bending rigidity of the heater holder 130 while suppressing an increase in the heat capacity of the heater holder 130. That is, with the configuration of this embodiment, it is possible to suppress creep deformation of the heater holder 130 while suppressing the influence on the warm-up time of the fixing device 100.

Embodiment

[0074] Example 2 in the present disclosure will be described below. After performing a paper passing evaluation using the image forming apparatus 50 equipped with the fixing device 100 of Example 1 on A4 size paper and then checking the image of the LTR size paper, slight fixing defects were sometimes observed at both the left and right ends of the image. This embodiment makes it possible to further suppress the occurrence of such fixing defects.

[0075] In this embodiment, a reinforcing rib 123 is further added to the heater holder 130 used in the first embodiment. The other configurations are substantially the same as those in the first embodiment. Hereinafter, elements denoted by the same reference numerals as those in the first embodiment are assumed to have substantially the same configurations and operations as those described in the first embodiment, and the differences from the first embodiment will be mainly described.

[0076] (Reinforcing Rib of Heater Holder) The reinforcing rib 123 of the heater holder 130 according to this embodiment will be described with reference to FIG. 10. As shown in FIG. 10, the reinforcing rib 123 added in this embodiment is disposed between the end position of an A4-sized paper and the end position of the resistive heating element on the heater 113 in the longitudinal direction B. That is, the rib portion of this embodiment is disposed inside the region where the heater 113 generates heat in the longitudinal direction B and outside the region through which a recording material having a smaller width in the longitudinal direction B than the recording material having the largest width in the longitudinal direction B among the recording materials on which the fixing device 100 can fix an image passes in the longitudinal direction B.

[0077] In this embodiment, the reinforcing rib 123 is added at positions 107.5 mm away from both sides in the longitudinal direction B from the position serving as a reference for the center position of the recording material passing through the fixing nip Nf in the longitudinal direction B (hereinafter, the conveyance center of the recording material). This is considered in view of the fact that the distance from the conveyance center of the recording material in the longitudinal direction B to the end position of the A4-sized paper is 105 mm and the distance from the conveyance center of the recording material in the longitudinal direction B to the end position of the resistive heating element on the heater 113 is 110 mm.

[0078] The reinforcing rib 123 added in this embodiment is formed so as to connect the upstream guide 126 and the downstream guide 127 of the heater holder 130, similar to the reinforcing rib 123 described in the first embodiment. In this embodiment, the height Hr in the vertical direction C of the reinforcing rib 123 is 1.5 mm and the width Wr is 2.0 mm.

[0079] In addition, in accordance with the addition of the reinforcing rib 123, a notch for receiving the reinforcing rib 123 is added to the pressing stay 119. The height of the notch formed in the pressing stay 119 in the recording material conveyance direction A is 2.0 mm, and the width in the longitudinal direction B is 2.5 mm, so that the reinforcing rib 123 does not contact the pressing stay 119.

[0080] (Regarding non-paper-passing temperature rise) Similar to Example 1, the fixing device 100 and the image forming apparatus 50 of this embodiment can perform image formation on LTR size paper (width in the longitudinal direction B: 216 mm) at the maximum. That is, the LTR size paper is the maximum paper that can pass through in this embodiment. Accordingly, the width of the resistive heating element on the heater 113 in the longitudinal direction B is set to include an effective image area where an image can be formed on the maximum paper that can pass through.

[0081] Here, when performing image formation on a recording material (small size paper) having a width in the longitudinal direction B smaller than the maximum paper that can pass through, the recording material does not pass through the fixing nip Nf, and there is a region (hereinafter referred to as a non-paper-passing region) that is heated by the resistive heating element. Therefore, when continuously performing image formation on small size paper (for example, A4 size paper), the surface temperatures of the fixing film 112 and the pressure roller 110 in the non-paper-passing region may be higher than those in the paper-passing region through which the small size paper passes. This is because in the non-paper-passing region, heat is not taken away from the recording material at the fixing nip Nf, so the heat generated by the resistive heating element gradually accumulates. This phenomenon is referred to as "non-paper-passing part temperature rise".

[0082] Due to the non-paper-passing part temperature rise, when continuously performing image formation on small size paper, the heater holder 130 will have a thermal peak in the non-paper-passing region (outside the paper-passing region and within the heating region of the heater 113). That is, if the temperature of the non-paper-passing region of the heater holder 130 remains higher than that of the paper-passing region due to the non-paper-passing part temperature rise, creep deformation of the heater holder 130 may occur in the non-paper-passing region.

[0083] (Operation and effect of this embodiment) The suppression of creep deformation in the non-sheet-passing area of the heater holder 130 will be described according to this embodiment. In this embodiment, since the reinforcing rib 123 is arranged within the non-sheet-passing area of the heater holder 130, the bending rigidity of the heater holder 130 in the non-sheet-passing area is improved. Therefore, even if forces F1 and F2 and heat due to the temperature rise in the non-sheet-passing area act on the heater holder 130 simultaneously as shown in FIG. 8 in the non-sheet-passing area, creep deformation of the heater holder 130 is less likely to occur.

[0084] When a sheet-passing test for forming an image on A4-size paper was carried out using the image forming apparatus 50 equipped with the fixing device 100 of this embodiment, neither damage to the heater holder 130 nor wrinkles in the recording material occurred. Also, even when a durability test was conducted, a state where a uniform fixed image was obtained over the entire longitudinal direction B without the occurrence of abnormal images such as poor fixing was maintained over a long period.

[0085] Furthermore, even when a sheet-passing test for LTR-size paper was carried out after the durability test using A4-size paper, no fixing failure occurred. This is presumably because the creep deformation of the heater holder 130 in the non-sheet-passing area could be suppressed by the reinforcing rib 123 added in this embodiment.

[0086] Note that in this embodiment, a configuration in which the reinforcing rib 123 is arranged in the non-sheet-passing area in addition to the reinforcing rib 123 described in Embodiment 1 is illustrated, but only the reinforcing rib 123 in the non-sheet-passing area described in this embodiment may be arranged.

[0087] (Modification example) In Examples 1 and 2, the reinforcing rib 123 was protruding on the flat stay contact surface S3 between the upstream guide 126 and the downstream guide 127 in the recording material conveyance direction A. Not limited to this, even when there are irregularities on the surface opposite to the heater seat surface S1 (the first surface) of the heater holder 130 when viewed in the longitudinal direction B, the reinforcing rib 123 can be provided. For example, as shown in Fig. 11(a), when having two ribs 128 extending in the longitudinal direction B between the upstream guide 126 or the downstream guide 127 of the heater holder 130, a reinforcing rib 123 connecting the ribs 128 may be provided. The ribs 128, together with the upstream guide 126 or the downstream guide 127, form a recess for receiving the end portions 119a, 119b of the pressure stay 119. In addition, as a further modification of Fig. 11(a), the reinforcing rib 123 may be configured to intersect the rib 128 and extend to the outside of the rib 128 and be connected to the upstream guide 126 and the downstream guide 127.

[0088] Also, as shown in Fig. 11(b), in a configuration having a step portion 138 inside the upstream guide 126 and the downstream guide 127 in the recording material conveyance direction A, the reinforcing rib 123 may be formed so as to connect the step portions 138. In this case, since the pressure stay 119 is in contact with the heater holder 130 at the step portion 138, the reinforcing rib 123 is located inside the contact position of the pressure stay 119 and the heater holder 130, and a notch portion is not required for the pressure stay 119.

[0089] As another modification example, as shown in Fig. 11(c), a film guide 139 for guiding the rotation of the fixing film 112 may be provided separately from the heater holder 130.

[0090] The reinforcing rib 123 shown in Figs. 11(a) to 11(c) is an example of a rib portion that is not arranged to be continuous from the upstream guide 126 (the first guide portion) to the downstream guide 127 (the second guide portion) of the heater holder 130. Even in these modification examples, since the reinforcing rib 123 is provided, the bending rigidity of the heater holder 130 is improved and creep deformation is suppressed, so that stable fixing performance can be obtained over a long period of time.

[0091] In addition, in Examples 1 and 2, among the heater holders 130, the reinforcing ribs 123 disposed in the vicinity of the opening O or in the non-sheet-passing region at the longitudinal end B in the longitudinal direction B were illustrated. The arrangement of the reinforcing ribs 123 is not limited to this. For example, a plurality of reinforcing ribs 123 may be arranged at predetermined intervals in the longitudinal direction B. Also, at least one reinforcing rib 123 may be arranged. In any of the modified examples, since the bending rigidity of the heater holder 130 is improved by the reinforcing ribs 123, creep deformation of the heater holder 130 can be suppressed.

[0092] (Other Embodiments) In the above-described Examples 1 and 2, a ceramic heater in which a resistive heating element is formed on a ceramic substrate was used as the heating means (heater) of the fixing device, and a configuration in which the fixing film 112 is heated by the non-radiative heat of the ceramic heater was illustrated. However, the present invention is not limited to this, and a configuration using a halogen lamp as the heater may be employed. That is, as the nip forming unit, a configuration including a halogen lamp disposed in the internal space of the first rotating body and a sliding member (nip forming portion) that contacts the inner surface of the first rotating body and receives radiant heat from the halogen lamp to heat the first rotating body may be used. Even in this case, creep deformation can be suppressed by providing a rib portion (reinforcing rib) on the holder member that holds the nip forming unit.

[0093] In addition, in the above-described Examples 1 and 2, a configuration in which a film is used as the first rotating body and a roller is used as the second rotating body was illustrated, but the first rotating body and the second rotating body are not limited to this combination. For example, a roller member may be used as the first rotating body.

Explanation of Reference Numerals

[0094] 100... Fixing device / 110... Second rotating body (pressure roller) / 112... First rotating body, film (fixing film) / 113... Heater / 119... Support member (pressure stay) / 123... Rib portion (reinforcing rib) / 130... Holder member (heater holder) / S1... First surface (heater seat surface) / S3... Second surface (stay contact surface)

Claims

1. A cylindrical fixing film; a heater disposed in the internal space of the fixing film; a heater holder disposed in the internal space of the fixing film and configured to hold the heater; a pressure roller that forms a nip portion together with the heater via the fixing film; a fixing device that heats and fixes an image on a recording material by the heater while nipping and conveying the recording material at the nip portion, The heater holder includes: a first surface that faces the pressure roller in a direction perpendicular to both the longitudinal direction of the heater and the conveying direction of the recording material in the nip portion, and that supports the heater; a second surface provided on the opposite side to the first surface in the vertical direction; an upstream protrusion provided at an upstream end of the heater holder in the transport direction and protruding in a direction away from the first surface in the direction perpendicular to the second surface, the upstream protrusion having an upstream outer wall surface facing an inner surface of the fixing film and an upstream inner wall surface provided on the opposite side to the upstream outer wall surface in the transport direction; a downstream protrusion provided at a downstream end of the heater holder in the transport direction and protruding in a direction away from the first surface in the direction perpendicular to the second surface, the downstream protrusion having a downstream outer wall surface facing the inner surface of the fixing film and a downstream inner wall surface provided on the opposite side to the downstream outer wall surface in the transport direction; a rib portion protruding from the second surface and provided between the upstream inner wall surface and the downstream inner wall surface in the conveying direction, the rib portion being connected to the upstream inner wall surface and the downstream inner wall surface; and In a cross section including the rib portion and perpendicular to the longitudinal direction, a top surface of the rib portion is located farther from the first surface than the second surface in the perpendicular direction over an entire area from the upstream inner wall surface to the downstream inner wall surface in the conveying direction. A fixing device characterized by:

2. The fixing film further includes a stay disposed in the internal space of the fixing film, extending in the longitudinal direction along the heater holder, and supporting the heater holder; The stay is A first part; and a second portion extending linearly in the vertical direction from one end to the other end in the longitudinal direction, the second portion having a first abutment surface at a tip end on the one end side in the vertical direction that abuts against the heater holder; a third portion disposed alongside the second portion in the transport direction, extending linearly in the vertical direction from one end to the other end in the longitudinal direction, the third portion having a second contact surface at a tip end on the one end side in the vertical direction that contacts the heater holder; and the first portion connects the other end side of the first portion in the vertical direction to the other end side of the second portion in the vertical direction, the second portion has a first recessed portion that forms a space recessed in a direction away from the second surface of the heater holder in the perpendicular direction relative to the first contact surface at a position that overlaps with the rib portion in the longitudinal direction when the second portion is viewed in the transport direction, the third portion has a second recessed portion that forms a space recessed in a direction away from the second surface of the heater holder in the perpendicular direction relative to the second contact surface at a position that overlaps with the rib portion in the longitudinal direction when the third portion is viewed in the transport direction, the rib portion extends into the recessed space formed by the first recess and the second recess.

2. The fixing device according to claim 1, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

3. The heater holder has a longitudinal rib portion that protrudes from the second surface and extends in the longitudinal direction, and is provided between the upstream inner wall surface and the downstream inner wall surface in the conveying direction, The rib portion intersects with the longitudinal rib portion and is connected to the upstream inner wall surface and the downstream inner wall surface.

2. The fixing device according to claim 1, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

4. The rib portion includes a first rib portion and a second rib portion, a hole is formed in the heater holder, the hole passing through the heater holder in the vertical direction from the first surface to the second surface; the first rib portion is provided on one side of the hole in the longitudinal direction, The second rib portion is provided on the other side of the hole in the longitudinal direction.

2. The fixing device according to claim 1, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

5. Further comprising a detection element disposed in the hole, contacting the heater and emitting a signal in response to the temperature of the heater.

5. The fixing device according to claim 4.

6. further comprising a temperature control means for controlling the temperature of the heater based on a signal from the detection element; 6. The fixing device according to claim 5,

7. further comprising a cutoff means for cutting off power supply to the heater based on a signal from the detection element; 6. The fixing device according to claim 5,

8. the rib portion is arranged, in relation to the longitudinal direction, inside an area where the heater generates heat and outside an area where a recording material having a width in the longitudinal direction smaller than that of a recording material having a width in the longitudinal direction that is the largest among recording materials on which the fixing device can fix an image passes.

8. The fixing device according to claim 1, wherein the fixing member is a fixing member having a fixing surface.

9. the heater includes a substrate extending in the longitudinal direction and the transport direction, and a resistance heating element formed on the substrate; the fixing film is heated by non-radiative heat generated by the resistance heating element when the heater is energized; 9. The fixing device according to claim 1, wherein the fixing member is a fixing member having a fixing surface.

10. an image forming means for forming an image on a recording material with toner; a fixing device according to claim 1 , which fixes the image formed by the image forming unit onto a recording material; An image forming apparatus comprising:

Images