Fixing apparatus and image forming apparatus

Abstract

To achieve stable fixation performance over a long period of time. [Solution] The fixing device holds the recording material between a first rotating body and a second rotating body in the nip section and transports it, while heating and fixing the image on the recording material with the first rotating body heated by a heater. The holder member that holds the heater is provided on the side of the second rotating body in the thickness direction perpendicular to both the longitudinal and transverse directions of the heater in the nip section and has a first surface that supports the heater, a second surface provided on the opposite side of the first surface in the thickness direction and supported by a support member on the upstream and downstream sides of the first surface in the transverse direction, and a rib portion that protrudes from the second surface and extends in the transverse direction over at least the area where the first surface is provided in the transverse direction.

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 method 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 orbit 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 reduction 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 is a fixing apparatus comprising: 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 holding the heater; and a pressure roller that forms a nip portion together with the heater via the fixing film, wherein the fixing apparatus heats and fixes an image on a recording material by the heater while the recording material is held and transported by the nip portion, wherein the heater holder has a first surface facing the pressure roller in a vertical direction perpendicular to both the longitudinal direction of the heater and the transport direction of the recording material in the nip portion, and the first surface supporting the heater; a second surface provided on the opposite side of the first surface in the vertical direction; and an upstream projection provided at the upstream end of the heater holder in the transport direction, projecting away from the first surface in a direction perpendicular to the second surface, and having an upstream outer wall surface facing the inner surface of the fixing film, and the transport The fixing device is characterized by having an upstream projection having an upstream inner wall surface provided on the opposite side of the upstream outer wall surface in the direction of transport, a downstream projection provided at the downstream end of the heater holder in the transport direction and projecting away from the first surface in the direction perpendicular to the second surface, 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 of the downstream outer wall surface in the transport direction, and a rib portion projecting from the second surface and provided between the upstream inner wall surface and the downstream inner wall surface in the transport direction, a rib portion connected to the upstream inner wall surface and the downstream inner wall surface, wherein in a cross section including the rib portion and perpendicular to the longitudinal direction, the top surface of the rib portion is located further from the first surface than the second surface in the vertical direction over the entire area from the upstream inner wall surface to the downstream inner wall surface in the transport direction. [Effects of the Invention]

[0007] According to this disclosure, stable fixing performance can be obtained over a long period of time. [Brief explanation of the drawing]

[0008] [Figure 1] A schematic diagram of the image forming apparatus according to Example 1. [Figure 2] Schematic diagrams (a, b) of the fixing device according to Example 1. [Figure 3] A diagram illustrating the crown shape of the heater holder according to Example 1. [Figure 4] Figures (a, b) illustrating the shape of the opening of the heater holder according to Example 1. [Figure 5] Cross-sectional view of the heater holder according to Example 1. [Figure 6] A diagram showing the rib portion of the heater holder according to Example 1. [Figure 7] A cross-sectional view of the portion of the heater holder having ribs according to Example 1. [Figure 8] A diagram illustrating the stress acting on the heater holder. [Figure 9] Cross-sectional view of the heater holder in the example. [Figure 10] A perspective view showing a part of the heater holder according to Example 2. [Figure 11] Cross-sectional views (a-c) of the fixing device according to a modified example. [Modes for carrying out the invention]

[0009] The embodiments relating to this disclosure will be described below with reference to the drawings. [Examples]

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

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

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

[0013] A feeding tray for loading recording material P is provided at the bottom of the image forming apparatus 50. A variety of sheet materials of different sizes and materials can be used as recording material P, including paper such as plain paper and cardboard, plastic film, cloth, sheet materials with surface treatments such as coated paper, and sheet materials of special shapes such as 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 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 a 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 adhered matter such as residual transferred toner or paper dust adhering to the surface of the photosensitive drum 1 that has passed through the transfer nip Ntr is 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 a fixing device 100 of a heat fixing method described below and undergoes a 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 this embodiment, an image forming apparatus of the direct transfer method is exemplified, but any other type of image forming apparatus may be used as long as it includes 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 of an intermediate transfer method in which the toner image formed on the image carrier is first transferred to an intermediate transfer body such as an intermediate transfer belt and then the toner image is transferred from the intermediate transfer body to the recording material. Also, the fixing device described below may be applied to an image forming apparatus that forms a color image on a 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 using FIGS. 2(a, 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 relationships of the components in the fixing device 100 will be explained using the recording material transport direction A, the longitudinal direction B, and the vertical direction C. The recording material transport direction A is the transport direction of the recording material P in the fixing nip Nf, which is the nip section of the fixing device 100. The longitudinal direction B is the width direction of the recording material P in the fixing nip Nf (the direction perpendicular to the recording material transport 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 transport direction A and the longitudinal direction B.

[0019] As shown in Figure 2(a, b), the fixing device 100 includes a film unit 101 (film assembly) which includes a fixing film 112, a heater 113, a heater holder 130, and a pressure stay 119, and a pressure roller 110 which faces the film unit 101. The fixing film 112, heater 113, heater holder 130, pressure stay 119, and pressure roller 110 are all elongated members that extend in the longitudinal direction B. In other words, the longitudinal direction B of the fixing device 100 is also the longitudinal direction of the fixing film 112, heater 113, heater holder 130, pressure stay 119, and pressure roller 110. Furthermore, the recording material transport direction A is also the short 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 a holder member or holding member in this embodiment. The pressure stay 119 is a support member or reinforcing member in this embodiment. The pressure roller 110 is a second rotating body in the fixing device 100 in this embodiment. The pressure roller 110 is also a pressure member in this embodiment.

[0021] The fixing film 112 is the first rotating body in the fixing device 100 of this embodiment. The fixing film 112 is a flexible cylindrical (endless) film member (belt member). In this embodiment, the fixing film 112 has an outer diameter of 18 mm in its undeformed 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 to maintain the strength of the film and a release layer to reduce the adhesion of dirt to the surface.

[0022] The base layer material is preferably one that has heat resistance to withstand the heat of the heater 113 and sufficient strength to slide against the heater 113. Suitable base layer materials include metals such as stainless steel and nickel, and heat-resistant resins such as polyimide. In this example, a polyimide resin with a carbon-based filler added to improve thermal conductivity and strength was used as the base layer material for the fixing film 112. A thinner base layer makes it easier to transfer heat from the heater 113 to the recording material P surface, but reduces its strength, so a thickness of about 15 μm to 100 μm is preferred, and in this example, it was set to 60 μm.

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

[0024] A heater holder 130 is provided on the inner circumference side of the fixing film 112. The heater holder 130 has a roughly semi-circular trough shape in its cross-section (cross-section in a plane perpendicular to the longitudinal direction B). In other words, the surface of the heater holder 130 facing the fixing nip Nf is 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 approximately in the center of the curved surface in the recording material transport direction A. The heater holding portion opens toward 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 made of a highly heat-resistant liquid crystal polymer resin to satisfy the requirements for 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 seat surface S1 that supports the heater 113, an upstream projection 131 and a downstream projection 132 adjacent to the heater seat surface S1, and a stay contact surface S3 provided on the side opposite to the heater seat surface S1 in the vertical direction C1. The heater seat 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, which is perpendicular to both the recording material transport direction A and the longitudinal direction B. The heater seat surface S1 supports the side of the heater 113 opposite to the pressure roller 110 in the vertical direction C (i.e., the side opposite to the sliding surface S2).

[0026] The upstream projection 131 is provided on the upstream side of the heater seat surface S1 in the recording material transport direction A, and protrudes toward the pressure roller 110 in the vertical direction C compared to the heater seat surface S1. The downstream projection 132 is provided on the downstream side of the heater seat surface S1 in the recording material transport direction A, and protrudes toward the pressure roller 110 in the vertical direction C compared to the heater seat surface S1. The heater seat surface S1 is the bottom of the groove shape (heater holding part) formed between the upstream projection 131 and the downstream projection 132. Furthermore, the upstream projection 131 and the downstream projection 132 have sliding surfaces that slide against the inner surface of the fixing film 112 upstream and downstream of the sliding surface S2 of the heater 113 in the recording material transport direction A, respectively.

[0027] Furthermore, the heater holder 130 has an upstream guide 126 that guides the fixing film 112 upstream of the fixing nip Nf in the recording material transport direction A, and a downstream guide 127 that guides the fixing film 112 downstream of the fixing nip Nf. In other words, the heater holder 130 holds the heater 113 and also plays a role in guiding the rotation of the fixing film 112.

[0028] Both the upstream guide 126 and the downstream guide 127 extend perpendicularly to the stay contact surface S3 of the heater holder 130 in direction C, away from the pressure roller 110. More specifically, as shown in Figure 6, the upstream guide 126 and the downstream guide 127 include a wall portion 124 rising perpendicularly to the end of the stay contact surface S3 in the recording material transport direction A, and guide ribs 129 provided at multiple positions on the wall portion 124 in the longitudinal direction B. The end faces of the guide ribs 129 are curved along the natural shape (Figure 2(a)) formed when the fixing film 112 is pressed by the fixing nip Nf, as described above. The upstream guide 126 and the downstream guide 127 guide the rotational trajectory of the fixing film 112 by the end faces of the guide ribs 129. The upstream guide 126 is the first guide portion of this embodiment, guiding 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, which guides the inner surface of the fixing film 112 after it has passed through the fixing nip Nf.

[0029] Alternatively, instead of using guide ribs 129 protruding from the wall portion 124 to guide the fixing film 112, the wall portion 124 itself may have the same cross-sectional shape as the guide ribs 129 in this embodiment, and the fixing film 112 may be guided by the outer surface of the wall portion 124. In this case, the guide ribs 129 may be continuous with the outer surface of the wall portion 124 and guide the fixing film 112 upstream or downstream of the outer surface of the wall portion 124 in the rotational direction of the fixing film 112, or the guide ribs 129 may be omitted.

[0030] The heater 113 and heater holder 130 are positioned in the internal space of the fixing film 112 and function as a nip forming unit that forms a fixing nip Nf by being pressed against the pressure roller 110 with the fixing film 112 in between. In this embodiment, a configuration is described in which the heater 113 directly slides against the inner surface of the fixing film 112, but a configuration in which a sliding member is interposed between the heater 113 and the fixing film 112 is also possible. As the sliding member, a material with high thermal conductivity and high sliding properties against the inner surface of the fixing film 112 can be used, for example, a sheet-like member of ferroalloy or aluminum can be used. In other words, the nip forming unit may be configured in which the heater 113 indirectly heats the fixing film 112 via a sliding member.

[0031] The pressure stay 119 is arranged along the longitudinal direction B of the heater holder 130. The pressure stay 119 is made of a highly rigid sheet metal such as stainless steel that has been bent in order to apply uniform pressure to the heater holder 130 in the longitudinal direction. The pressure stay 119 is formed in a U-shape (angular C-shape) that opens to the side of the pressure roller 110 in the vertical direction C when viewed in the longitudinal direction B. In other words, the pressure stay 119 has a first portion 91 that extends in the recording material transport direction A, and a second portion 92 and a third portion 93 that extend from the upstream and downstream ends of the first portion 91 in the recording material transport direction A toward the heater holder 130 in the vertical direction C, respectively.

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

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

[0034] The pressure roller 110 in this embodiment has an outer diameter of 20 mm, and a 3.0 mm thick elastic layer 116 is formed on the outer circumference of a 14 mm diameter iron core 117. The elastic layer 116 can be made of solid rubber or foamed rubber. Foamed rubber has a low heat capacity and low thermal conductivity, and because heat from the surface of the pressure roller 110 is not easily absorbed into the interior, the surface temperature rises easily, which has the advantage of shortening the start-up time of the fixing device 100. In this embodiment, foamed rubber, obtained by foaming silicone rubber, was used as the elastic layer 116. On top of the elastic layer 116, a release layer 118 made of perfluoroalkoxy resin (PFA) is formed as a release layer. The release layer 118, like the release layer of the fixing film 112, may be a tube covering the elastic layer 116, or the surface of the elastic layer 116 may be coated with paint. In this embodiment, the release layer 118 was formed by covering the outer circumference of the elastic layer 116 with a durable tube. In addition to PFA, the release layer 118 may be made of fluororesins such as PTFE or FEP, or fluororubber or silicone rubber with good release properties. The surface hardness of the pressure roller 110 should be determined considering durability, as a lower hardness allows for a wider fixing nip Nf with lighter pressure. In this embodiment, an Asker-C hardness (4.9N load) roller with a hardness of 50° was used. Alternatively, a belt unit including a belt member stretched across multiple rollers may be used as the pressure member instead of the pressure roller 110.

[0035] The heater 113 in this embodiment uses a ceramic substrate on which a resistive heating element is provided. Specifically, the substrate for the heater 113 is alumina with a width of 6 mm in the recording material transport direction A and a thickness of 1 mm in the vertical direction C. An Ag / Pd (silver-palladium) resistive heating element is coated onto the surface of this substrate to a thickness of several μm by screen printing, and a glass layer with a thickness of 60 μm is formed on top of it to protect the heating element and improve sliding properties, thereby creating the heater 113.

[0036] The fixing device 100 is configured to adjust the temperature of the heater 113 by appropriately controlling the current flowing through the resistive heating element in response to a signal from a temperature sensing element (thermosensitive element), described later, which detects the temperature of the substrate or fixing film 112 of the heater 113. The heater 113 is fixedly supported by being fitted into a groove provided in the heater holder 130. In this embodiment, the center of the heater 113 in the recording material transport direction A is located 0.4 mm upstream of the center (rotation axis) of the pressure roller 110.

[0037] As shown in Figure 2(b), the pressure stay 119 has extensions 119e that extend outwards from the side plates 134, which are located on both sides of the frame 133 in the longitudinal direction B of the fixing device 100. Fixing flanges 120 are fitted to the extensions 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 position where the heater 113 is oriented towards the pressure roller 110 in the vertical direction C, with the fixing flanges 120 supported by the side plates 134. Each fixing flange 120 is provided with a vertical groove extending in the vertical direction C, and the vertical groove is engaged with the edge of a vertical guide slit provided in the side plate 134. As a result, each fixing flange 120 is supported by the side plate 134 so as to be movable in the vertical direction C. In this embodiment, liquid crystal polymer resin is used as the material for the fixing flange 120.

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

[0039] Then, a pressure spring 122 is compressed between the pressure 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 pressure spring 122 is transmitted to the heater 113 via the fixing flanges 120 on both sides, the pressure stay 119, and the heater holder 130, and the heater 113 pressurizes the fixing film 112 against the pressure roller 110 with a predetermined pressing force.

[0040] In this embodiment, the spring constant and compression amount of the pressure spring 122 are set so that the pressing force between the fixing film 112 and the pressure roller 110 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 to conform to the sliding surface S2, which is the flattened surface on the front side of the heater 113, so that the inner surface of the fixing film 112 is in close contact (surface contact) with the sliding surface S2. The film restricting portion 120a of the fixing flange 120 is shaped to conform to the natural shape (see Figure 2(a)) formed when the fixing film 112 is pressed at the fixing nip Nf.

[0041] When a driving force transmitted from a drive source (not shown) is input to the drive gear 117g (Figure 2(b)) provided on the shaft portion 117a of the pressure roller 110, the pressure roller 110 is rotated at a predetermined speed in the direction of arrow R2 in Figure 2(a). As the pressure roller 110 rotates, 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 slides its inner surface against the sliding surface S2 of the heater 113 and rotates around the heater 113 and heater holder 130 in the direction of arrow R3 in the figure, following the rotation of the pressure roller 110. The rotational speed of the pressure roller 110 is set so that the surface movement speed of the pressure roller 110 and the fixing film 112 at the fixing nip Nf is 200 mm / sec.

[0042] When fixing the image, the pressure roller 110 is driven while power is supplied to the heater 113, so that the recording material is sandwiched between the pressure roller 110 and the fixing film 112 at the fixing nip Nf and transported. 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] Furthermore, a heat-resistant lubricant is applied to the inner surface of the fixing film 112, thereby ensuring smooth sliding between the heater 113 and heater holder 130 and the inner surface of the fixing film 112. In this embodiment, a fluorine-based grease was used as the lubricant. Specifically, a grease was used which consisted of perfluoropolyether (PFPE) oil as the base oil and polytetrafluoroethylene (PTFE) powder as a thickening agent.

[0044] (Heater holder) Figure 3 is a schematic diagram illustrating the crown shape of the heater holder 130 in the longitudinal direction B. As shown in Figure 3, the heater holder 130 has a gently curved shape (i.e., a crown shape) such that the central part of the heater seat surface S1 that supports the heater 113 in the longitudinal direction B protrudes toward the pressure roller 110 in the vertical direction C compared to both ends. The heater 113 is fixed to the heater holder 130 at both ends in the longitudinal direction B by the heater power supply section 136 and the heater clip 137. Therefore, the heater 113 is mounted in a curved state that follows 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 the region CR with a longitudinal width of 225 mm corresponding to the longitudinal direction B where the heater 113 faces the pressure roller 110, the crown shape is a gentle quadratic curve when viewed in the recording material transport direction A. The amount of protrusion of the central part of the heater seat surface S1 in the perpendicular direction C relative to both ends 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 almost the entire length B. In other words, when the film unit 101 is pressed against the pressure roller 110 by the biasing force of the pressure spring 122, a slight deflection occurs in the pressure stay 119 and the core metal 117 of the pressure roller 110. If the heater seat surface S1 is not provided with a crown shape, the heater 113 will be strongly pressed against the pressure roller 110 at both ends of the length B, causing the nip width of the fixing nip Nf to widen, while the nip width of the fixing nip Nf will narrow in the center of the length B. In contrast, by providing a crown shape as in this embodiment, the difference in the nip width of the fixing nip Nf between the center and both ends of the length B can be reduced. In this embodiment, the width of the fixing nip Nf in the recording material transport direction A is approximately 6.2 mm over the entire region CR in the length B.

[0047] Next, the opening O of the heater holder 130 will be described. Figure 4(a) is a perspective view of the heater holder 130 as seen from the heater seating surface S1 side. Figure 4(b) is a cross-sectional view (cross-section in a plane perpendicular to the longitudinal direction B) of the fixing device 100 in the portion where the temperature sensing element T is located (dashed line 4B-4B in Figure 4(a)).

[0048] As shown in Figure 4(a), the heater seat surface S1 of the heater holder 130 is provided with an opening O for fitting a temperature sensing element T such as a thermal fuse, thermoswitch, or thermistor. As shown in Figure 4(b), the opening O is a hole that penetrates the heater holder 130 vertically 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 makes it possible to position the temperature sensing element T in contact with the heater 113. The temperature sensing element T emits a signal corresponding to the temperature of the heater 113. Alternatively, the temperature sensing element T may be positioned close to the heater 113 with a predetermined gap between them, rather than in contact with the heater 113.

[0049] By using a thermal fuse or thermoswitch as the temperature sensing 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 from the temperature sensing 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 power supply to 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 a cutoff means (safety device) that senses an abnormal rise in the temperature of the heater 113 and cuts off the power supply to the heater 113. Alternatively, by using a thermistor as the temperature sensing element T, the control unit 51 can control the amount of power supplied from the power supply circuit 52 to the heater 113 based on the signal from the temperature sensing element T. In this case, the control unit 51 functions as a temperature control means (temperature control device) that controls the temperature of the heater 113 to match a predetermined target temperature.

[0050] Here, the area around the opening O of the heater holder 130 has lower rigidity compared to other parts of the heater holder 130. Therefore, as will be described later, in this embodiment, a reinforcing rib 123 is provided near the opening O on the stay contact surface S3 on the back side of the heater seat surface S1.

[0051] Next, we will describe the rotational trajectory of the fixing film 112, which is restricted by the heater holder 130. Figure 5 is a cross-sectional view near the fixing nip Nf in the central part of the longitudinal direction B.

[0052] As described above, the heater holder 130 has an upstream projection 131 that protrudes upstream of the heater 113 in the recording material transport direction A, and toward the pressure roller 110 side of the heater seat surface S1. The projection height H of the upstream projection 131 relative to the sliding surface S2 of the heater 113 should be of a certain height in order to restrict the trajectory of the fixing film 112 so that it does not come into contact with the edge of the heater 113 (the upstream edge in the recording material transport direction A). However, if the projection height H is made too high, the fixing film 112 will be pressed by the upstream projection 131, reducing the contact width (inner surface nip width Nn) between the inner surface of the fixing film 112 and the heater 113. In this case, heat transfer from the heater 113 to the fixing film 112 will be impaired, which will be a cause of fixing failure.

[0053] The protrusion height H of the upstream projection 131 relative to the sliding surface S2 of the heater 113 is preferably about 0.1 to 0.7 mm, and in this embodiment it is set to 0.2 mm. Furthermore, the inner surface nip width Nn is preferably 4 mm or more, and in this embodiment it is set to 4.2 mm.

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

[0055] Figure 6 is a perspective view of the heater holder 130 from the opposite side of the heater seat surface S1, and is a magnified view of the area around the opening O where the temperature sensing element T is located. As shown in Figure 6, two reinforcing ribs 123 are formed in the recording material transport direction A, sandwiching the opening O of the heater holder 130 from both sides in the longitudinal direction B. The reinforcing ribs 123 are rib portions (protruding parts) that protrude vertically C from the stay contact surface S3 (second surface) of the heater holder 130 and extend in the recording material transport direction A (short direction of the heater 113).

[0056] Figure 7 is a cross-sectional view of the fixing device 100 in the longitudinal direction B where the reinforcing rib 123 is located. As shown in Figures 6 and 7, in this embodiment, the reinforcing rib 123 extends in the recording material transport direction A to connect the upstream guide 126 and the downstream guide 127 of the heater holder 130. The connection of the upstream guide 126 and the downstream guide 127 by the reinforcing rib 123 improves the bending rigidity of the heater holder 130 against forces received from the pressure stay 119 and the pressure roller 110. Note that the reinforcing rib 123 only needs to be connected to either the wall portion 124 or the guide rib 129 of the upstream guide 126 and the downstream guide 127.

[0057] Incidentally, the reinforcing rib 123 has a shape that protrudes in the vertical direction C from the stay contact surface S3 of the heater holder 130 on the opposite side from the pressure roller 110. For this reason, the ends 119a and 119b of the pressure stay 119 facing the heater holder 130 are provided with notches 119c to avoid the reinforcing rib 123 (Figure 7). When viewed in the recording material transport direction A, the notches 119c are concave shapes in which a part of the ends 119a and 119b of the heater holder 130 extending in the longitudinal direction B is recessed in the vertical direction C toward the opposite side from the pressure roller 110. In other words, the second part 92 and the third part 93 of the support member pressure stay 119 are provided with notches 119c as concave shapes that are recessed in the vertical direction C away from the stay contact surface S3 (second surface) of the heater holder 130 and extend in the recording material transport direction A. The reinforcing rib 123, which serves as a rib section, extends in the recording material transport direction A, passing through the inside of the notch 119c.

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

[0059] (Effects of this embodiment) The suppression of creep deformation of the heater holder 130 by the configuration of this embodiment will be explained with reference to Figures 7 to 9.

[0060] Figure 8 is a schematic diagram illustrating the stress acting on the heater holder 130 under the pressurized state of the fixing nip Nf. As shown in Figure 8, the heater holder 130 receives a force F1 from the ends 119a and 119b of the pressure stay 119 in the vertical direction C toward the pressure roller 110 at the stay contact surface S3. In addition, the heater holder 130 receives a force F2 in the vertical direction C toward the opposite side of the pressure roller 110 as a reaction force received from the pressure roller 110, which is supported by the bearing member 135, via the fixing film 112 and 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 opposite side from the pressure roller 110 between the contact points with the pressure stay 119 (first position P1, second position P2). In other words, a bending moment is generated that attempts to flex the heater holder 130 so that the upstream projection 131 and the downstream projection 132 are displaced in the vertical direction C toward the pressure roller 110 relative to the heater 113.

[0062] Such bending moments can cause deformation of the heater holder 130, potentially reducing the fixing performance of the fixing device 100.

[0063] Next, using a reference example, we will explain the case where deformation of the heater holder 130 occurs due to a bending moment. Figure 9 is a cross-sectional view of the anchoring device 100 near the opening of the heater holder 130 in the reference example, and the heater holder 130 does not have the reinforcing ribs 123 as in this embodiment.

[0064] When a paper feed test was conducted using the image forming apparatus 50 equipped with the fixing device 100 of this reference example to form an image on LTR-sized paper, no damage to the heater holder 130 or wrinkling of the recording material occurred. If the mechanical strength or dimensional accuracy of the heater holder 130 were insufficient, damage to the heater holder 130 or unstable movement of the fixing film 112, leading to shifting of the fixing film 112 or wrinkling of the recording material, could occur. In contrast, it is considered that the mechanical strength and dimensional accuracy of the heater holder 130 in the fixing device 100 of this reference example were sufficiently ensured.

[0065] On the other hand, in this reference example, when durability tests were conducted by repeatedly forming images on a large number of sheets of paper, fixing failures occurred as the cumulative number of sheets passed through increased, and the results gradually worsened. This is thought to be because the creep deformation of the heater holder 130 caused by the bending moment mentioned above reduced the inner surface nip width Nn, which is the contact width between the inner surface of the fixing film 112 and the heater 113. In other words, it is thought that the upstream protrusion 131 and the downstream protrusion 132 were displaced in the vertical direction C toward the pressure roller 110 relative to the heater 113, causing the fixing film 112 to separate from a part of the heater 113. When the inner surface nip width Nn decreases, the surface temperature of the fixing film 112 decreases, and when it falls below the lower limit of the temperature range suitable for image fixing, it manifests as fixing failure.

[0066] Furthermore, in the durability test, the fixing failure occurred at a location on the sheet corresponding to the vicinity of the opening O of the heater holder 130 in the longitudinal direction B. This is thought to be because, due to the bending moment described above, creep deformation of the heater holder 130 mainly occurred near the opening O, where the rigidity is relatively low.

[0067] Next, this embodiment will be explained using Figure 7. As mentioned above, the heater holder 130 of this embodiment has a reinforcing rib 123 that protrudes from the stay contact surface S3 and extends in the recording material transport direction A. This reinforcing rib 123 improves the bending rigidity of the heater holder 130 against the bending moment (Figure 8) that the heater holder 130 receives when the fixing nip Nf is pressurized, and makes creep deformation of the heater holder 130 less likely to occur.

[0068] In particular, in this embodiment, reinforcing ribs 123 are placed near the opening O of the heater holder 130 in the longitudinal direction B. This improves the bending rigidity near the opening O, which is lower than the portion without the opening O, and effectively suppresses creep deformation of the heater holder 130.

[0069] The reinforcing ribs 123 are preferably arranged over an area where the heater seat surface S1 (first surface) is provided, with respect to the recording material transport direction A. This improves the bending rigidity of the portion of the heater holder 130 where the thickness in the vertical direction C is reduced due to the space for receiving the heater 113, thereby suppressing creep deformation.

[0070] More preferably, the reinforcing rib 123 is arranged over a range from the first position P1 to the second position P2 in Figure 8 with respect to the recording material transport direction A. The first position P1 is the position upstream of the heater 113 where the pressure stay 119 abuts against the stay contact surface S3 of the heater holder 130, and the second position P2 is the position downstream of the heater 113 where the pressure stay 119 abuts against the stay contact surface S3 of the heater holder 130. As a result, the bending stiffness of the heater holder 130 in the range where a bending moment acts on the heater holder 130 due to the forces F1 and F2 received by the heater holder 130 from the pressure stay 119 and the pressure roller 110 is improved by the reinforcing rib 123, and creep deformation can be suppressed more effectively.

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

[0072] When a paper feeding test was conducted using an image forming apparatus 50 equipped with the fixing device 100 of this embodiment with LTR-sized paper, no damage to the heater holder 130 or wrinkles in the recording material occurred. Furthermore, even when durability tests were conducted, a uniform fixed image was obtained over the entire length B without the occurrence of abnormal images such as fixing failures, and this condition was maintained for a long period of time. This is thought to be because the creep deformation of the heater holder 130 was suppressed by the reinforcing ribs 123 arranged near the opening O of the heater holder 130.

[0073] As an alternative to 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 in the portion where the heater seat surface S1 and stay contact surface S3 are provided. However, in this configuration, the heat capacity of the heater holder 130 increases, and the start-up time of the fixing device 100 becomes longer. In contrast, by using reinforcing ribs 123 as in this embodiment, it is possible to improve the bending rigidity of the heater holder 130 while suppressing the increase in the heat capacity of the heater holder 130. In other words, with the configuration of this embodiment, it is possible to suppress creep deformation of the heater holder 130 while suppressing the impact on the start-up time of the fixing device 100. [Examples]

[0074] Example 2 of this disclosure is described below. When an image forming apparatus 50 equipped with the fixing device 100 of Example 1 was used to perform a paper feeding evaluation with A4 size paper, and then the image on LTR size paper was checked, very slight fixing defects were sometimes observed at both the left and right edges of the image. This example makes it possible to further suppress the occurrence of such fixing defects.

[0075] In this embodiment, reinforcing ribs 123 are added to the heater holder 130 used in Embodiment 1. The other configurations are substantially the same as those in Embodiment 1. Hereinafter, elements denoted by the same reference numerals as in Embodiment 1 have substantially the same configuration and function as those described in Embodiment 1, and the differences from Embodiment 1 will be mainly described.

[0076] (Reinforcement ribs for the heater holder) The reinforcing rib 123 of the heater holder 130 according to this embodiment will be explained with reference to Figure 10. As shown in Figure 10, the reinforcing rib 123 added in this embodiment is positioned between the edge of the A4 size paper and the edge of the resistance heating element on the heater 113, with respect to the longitudinal direction B. In other words, the rib portion of this embodiment is positioned inside the area where the heater 113 generates heat, with respect to the longitudinal direction B, and outside the area through which recording materials with a width in the longitudinal direction B smaller than the recording material with the largest width in the longitudinal direction B among the recording materials on which the fixing device 100 can fix images pass.

[0077] In this embodiment, reinforcing ribs 123 are added to both sides of the longitudinal direction B at a distance of 107.5 mm from the reference position of the center of the recording material passing through the fixing nip Nf in the longitudinal direction B (hereinafter referred to as the center of the recording material transport). This is based on the fact that the distance to the edge of an A4 size sheet of paper is 105 mm and the distance to the edge of the resistance heating element on the heater 113 is 110 mm, with the center of the recording material transport in the longitudinal direction B as the reference point.

[0078] The reinforcing rib 123 added in this embodiment is formed to connect the upstream guide 126 and the downstream guide 127 of the heater holder 130, just like the reinforcing rib 123 described in Embodiment 1. 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, to accommodate the reinforcing ribs 123, a notch is added to the pressure stay 119 to receive the reinforcing ribs 123. The height of the notch formed in the pressure stay 119 in the recording material transport direction A is set to 2.0 mm, and the width in the longitudinal direction B is set to 2.5 mm, so that the reinforcing ribs 123 do not come into contact with the pressure stay 119.

[0080] (Regarding the temperature rise of non-transmitted paper) The fixing device 100 and image forming apparatus 50 of this embodiment can form images on LTR size paper (width of the longitudinal direction B of 216 mm), similar to Embodiment 1. In other words, LTR size paper is the maximum paper size that can be fed in this embodiment. Accordingly, the width of the resistance heating element on the heater 113 in the longitudinal direction B is set to encompass an effective image area on the maximum paper size that can be fed in.

[0081] Here, when image formation is performed on recording material (small-sized paper) whose longitudinal width B is smaller than the maximum paper size that can be fed, there will be a region in the fixing nip Nf that the recording material does not pass through and is heated by the resistance heating element (hereinafter referred to as the non-feeding region). Therefore, when image formation is performed continuously on small-sized paper (for example, A4 size paper), the surface temperature of the fixing film 112 and pressure roller 110 in the non-feeding region may be higher than in the feeding region through which the small-sized paper passes. This is because, in the non-feeding region, heat is not absorbed by the recording material in the fixing nip Nf, and the heat generated by the resistance heating element gradually accumulates. This phenomenon is called "heat rise in the non-feeding region".

[0082] When image formation is performed continuously on small-sized paper by raising the temperature of the non-paper-feeding area, the heater holder 130 will have a thermal peak within the non-paper-feeding area (outside the paper-feeding area and within the heat-generating area of ​​the heater 113). In other words, if the temperature of the non-paper-feeding area of ​​the heater holder 130 remains higher than that of the paper-feeding area due to the temperature rise of the non-paper-feeding area, creep deformation of the heater holder 130 may occur in the non-paper-feeding area.

[0083] (Effects of this embodiment) This embodiment will explain how creep deformation in the non-paper-feeding region of the heater holder 130 is suppressed. In this embodiment, reinforcing ribs 123 are placed in the non-paper-feeding region of the heater holder 130, thereby improving the bending rigidity of the heater holder 130 in the non-paper-feeding region. Therefore, even if forces F1 and F2 and heat due to the heating of the non-paper-feeding region act simultaneously on the heater holder 130 in the non-paper-feeding region, as shown in Figure 8, creep deformation of the heater holder 130 is less likely to occur.

[0084] When a paper feeding test was conducted using the image forming apparatus 50 equipped with the fixing device 100 of this embodiment to form an image on A4 size paper, no damage to the heater holder 130 or wrinkles in the recording material occurred. Furthermore, even when durability tests were conducted, a uniform fixed image was obtained over the entire length B without the occurrence of abnormal images such as fixing failures, and this condition was maintained for a long period of time.

[0085] Furthermore, even when a paper feeding test with LTR-sized paper was performed after a durability test using A4-sized paper, no fixing failures occurred. This is thought to be because the reinforcing ribs 123 added in this embodiment were able to suppress creep deformation of the heater holder 130 in the non-paper feeding area.

[0086] In this embodiment, we have illustrated a configuration in which reinforcing ribs 123 are placed in the non-paper-feeding area in addition to the reinforcing ribs 123 described in Embodiment 1. However, it is also possible to place only the reinforcing ribs 123 in the non-paper-feeding area as described in this embodiment.

[0087] (modified version) In Examples 1 and 2, a reinforcing rib 123 was provided protruding from a flat stay contact surface S3 between the upstream guide 126 and the downstream guide 127 in the recording material transport direction A. However, the reinforcing rib 123 can also be provided even if there are irregularities on the surface of the heater holder 130 opposite to the heater seat surface S1 (first surface) when viewed in the longitudinal direction B. For example, as shown in Figure 11(a), if the heater holder 130 has two ribs 128 extending in the longitudinal direction B between the upstream guide 126 or the downstream guide 127, 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 recesses that receive the ends 119a and 119b of the pressure stay 119. As a further variation of Figure 11(a), the reinforcing rib 123 may be configured to intersect with the rib 128 and extend to the outside of the rib 128, connecting to the upstream guide 126 and the downstream guide 127.

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

[0089] As another variation, as shown in Figure 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 ribs 123 shown in Figure 11(a-c) are examples of rib sections that are not arranged to be continuous from the upstream guide 126 (first guide section) to the downstream guide 127 (second guide section) of the heater holder 130. Even with these modified examples, the reinforcing ribs 123 improve the bending rigidity of the heater holder 130 and suppress creep deformation, thereby enabling stable anchoring performance over a long period of time.

[0091] Furthermore, in Examples 1 and 2, reinforcing ribs 123 were provided as examples of reinforcing ribs 123 placed in the vicinity of the opening O or in the non-paper-passing area at the end of the longitudinal direction B of the heater holder 130. The arrangement of the reinforcing ribs 123 is not limited to this. For example, multiple reinforcing ribs 123 may be arranged at predetermined intervals in the longitudinal direction B. Alternatively, at least one reinforcing rib 123 may be provided. In any of these modifications, the bending rigidity of the heater holder 130 is improved by the reinforcing ribs 123, thereby suppressing creep deformation of the heater holder 130.

[0092] (Other embodiments) In the above-described embodiments 1 and 2, a ceramic heater with a resistance heating element 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 configuration is not limited to this, and a halogen lamp may be used as the heater. That is, the nip forming unit may be configured to include a halogen lamp placed in the internal space of the first rotating body, and a sliding member (nip forming part) that contacts the inner surface of the first rotating body and heats the first rotating body by receiving radiant heat from the halogen lamp. Even in this case, creep deformation can be suppressed by providing a rib portion (reinforcement rib) on the holder member that holds the nip forming unit.

[0093] Furthermore, while the above-described examples 1 and 2 illustrate a configuration in which a film is used as the first rotating body and a roller as the second rotating body, the first and second rotating bodies are not limited to this combination. For example, a roller member may be used as the first rotating body. [Explanation of symbols]

[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 section (reinforcement rib) / 130…Holder member (heater holder) / S1…First surface (heater seating surface) / S3…Second surface (stay contact surface)

Claims

1. A cylindrical fixing film, A heater is placed in the internal space of the fixing film, A heater holder is disposed in the internal space of the fixing film and holds the heater, A pressure roller that forms a nip portion together with the heater via the fixing film, A fixing device comprising the nip portion, which holds and transports the recording material, and which heats and fixes the image on the recording material with the heater, The heater holder is, A first surface facing the pressure roller in a vertical direction perpendicular to both the longitudinal direction of the heater and the transport direction of the recording material in the nip section, the first surface supporting the heater, A second surface provided on the opposite side of the first surface in the aforementioned vertical direction, An upstream projection provided at the upstream end of the heater holder in the transport direction, projecting in a direction perpendicular to the second surface and away from the first surface, having an upstream outer wall surface facing the inner surface of the fixing film, and an upstream inner wall surface provided on the opposite side of the upstream outer wall surface in the transport direction, A downstream projection provided at the downstream end of the heater holder in the transport direction, projecting in a direction perpendicular to the second surface and away from the first surface, 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 of the downstream outer wall surface in the transport direction, A rib portion that protrudes from the second surface and is provided between the upstream inner wall surface and the downstream inner wall surface in the conveying direction, comprising a rib portion connected to the upstream inner wall surface and the downstream inner wall surface, It has, In a cross-section including the rib portion and perpendicular to the longitudinal direction, the top surface of the rib portion is located at a position further from the first surface than the second surface in the vertical direction, over the entire area from the upstream inner wall surface to the downstream inner wall surface in the conveying direction. A fixing device characterized by the following features.

2. The fixing film further comprises 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 aforementioned stay is Part 1 and, A second portion extending linearly in the vertical direction from one end to the other in the longitudinal direction, the second portion having a first contact surface at the tip of the one end in the vertical direction that contacts the heater holder, A third portion is arranged alongside the second portion in the transport direction, and extends linearly in the vertical direction from one end to the other in the longitudinal direction, the third portion having a second contact surface at the tip of one end in the vertical direction that contacts the heater holder, It has, The first portion connects the other end of the first portion in the vertical direction to the other end of the second portion in the vertical direction. The second portion has a first recess that, when viewed in the transport direction, overlaps with the rib portion in the longitudinal direction, and forms a recessed space with respect to the first contact surface, in a direction perpendicular to the second surface of the heater holder, The third portion has a second recess that, when viewed in the transport direction, overlaps with the rib portion in the longitudinal direction, and forms a space recessed with respect to the second contact surface in a direction perpendicular to the second surface of the heater holder, The rib portion is recessed into the recessed space formed by the first recess and the second recess. The fixing device according to feature 1.

3. The heater holder has a longitudinal rib portion that protrudes from the second surface and extends in the longitudinal direction, and has a longitudinal rib portion 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. The fixing device according to feature 1.

4. The rib portion includes a first rib portion and a second rib portion. The heater holder has a hole formed therein that penetrates vertically 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. The fixing device according to feature 1.

5. The system further includes a detection element positioned in the aforementioned hole, which contacts the heater and emits a signal according to the temperature of the heater. The fixing device according to feature 4.

6. The system further includes temperature control means for controlling the temperature of the heater based on the signal from the detection element. The fixing device according to feature 5.

7. The system further includes a shut-off means for shutting off the power supply to the heater based on the signal from the detection element. The fixing device according to feature 5.

8. The rib portion is positioned in the longitudinal direction, inside the region where the heater generates heat, and outside the region through which recording material with a longitudinal width smaller than the recording material with the largest longitudinal width among the recording materials on which the fixing device can fix an image passes. The fixing device according to any one of claims 1 to 7.

9. The heater comprises 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 the non-radiative heat emitted by the resistance heating element when the heater is energized. The fixing device according to any one of claims 1 to 8.

10. Image forming means for forming an image on a recording material with toner, A fixing device according to any one of claims 1 to 9, which fixes an image formed by the image forming means onto a recording material, An image forming apparatus characterized by comprising the following:

Images