Fixing device and image-forming device

Abstract

To aim at gaining both of a high speed of fixing processing and a long life of a heating unit.SOLUTION: In a fixing device having a heating unit for heating a sheet and an opposing roller 61 that opposes the heating unit and forms a fixing nip with the heating unit, one end in a width direction W crossing a sheet conveyance direction of a sheet conveyed to the fixing device passes a predetermined position in a width direction W of a fixing nip regardless of the size of the sheet, and the opposing roller 61 has a roller section 26 including a base section 261, and an elastic layer 262 having elasticity provided around the base section 261. The roller section 26 has a first end 26a that is the end in a first side W1 and a second end 26b that is the end in a second side W2 in the width direction W, and the thickness d2 of the elastic layer 262 in the second end 26b is smaller than the thickness d1 of the elastic layer 262 in the first end 26a.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a fixing device used in an image forming apparatus using an electrophotographic method or an electrostatic recording method, and an image forming apparatus including the same.

Background Art

[0002] Conventionally, for example, in an electrophotographic image forming apparatus, a fixing device that fixes an unfixed toner image formed on a sheet to the sheet has been used. As the fixing device, for example, a film heating type is widespread (see Patent Document 1). The fixing device of the film heating type has a heating unit that heats a sheet, and a counter roller that faces the heating unit and forms a fixing nip together with the heating unit. The heating unit is provided with a cylindrical film having high heat resistance and flexibility (hereinafter referred to as a fixing film), and a ceramic heater (hereinafter referred to as a heater) provided in the internal space of the fixing film.

[0003] In addition, as an image forming apparatus, there is known one that adopts a conveyance method with a one-side reference in which the position reference in the width direction of the sheet is provided at one-side end instead of the center in the width direction (see Patent Document 2). Such an image forming apparatus with a one-side reference has, for example, a configuration of a conveyance unit that abuts against the wall surface on the reference side and conveys the recording material.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when the one-sided reference conveyance method described in Patent Document 2 is applied to the fixing device described in Patent Document 1, since the non-paper-passing portion heats up more than the paper-passing portion, a force (hereinafter referred to as the pulling force) that pulls the fixing film in the sheet width direction may be generated. When the fixing film receives the pulling force, it may rotate while the end face in the pressing direction of the pulling force is pressed against the regulating member, resulting in wear, damage, etc., which may prevent the heating unit from having a long service life. On the other hand, if the thickness of the fixing film is increased to achieve a long service life, the thermal conductivity of the fixing film may decrease, leading to a risk of slowing down the fixing process.

[0006] An object of the present invention is to provide a fixing device and an image forming apparatus that achieve both high-speed fixing processing and a long service life of the heating unit.

Means for Solving the Problems

[0007] A first aspect of the present invention includes a heating unit that heats a sheet, and an opposing roller that faces the heating unit and forms a fixing nip together with the heating unit, and in the fixing device that fixes the toner image carried on the sheet by applying heat and pressure in the fixing nip, one end portion in the width direction intersecting the sheet conveyance direction of the sheet conveyed to the fixing device passes through a predetermined position in the width direction of the fixing nip regardless of the size of the sheet, and the opposing roller has a roller portion including a base portion and an elastic layer provided around the base portion, and when the side where the predetermined position is located with respect to the central portion of the roller portion in the width direction is the first side and the side opposite to the first side is the second side, the roller portion has a first end portion that is an end portion on the first side and a second end portion that is an end portion on the second side in the width direction, and the thickness of the elastic layer at the second end portion is thinner than the thickness of the elastic layer at the first end portion.

[0008] A second aspect of the present invention is a fixing device that includes a heating unit for heating a sheet, a counter roller that faces the heating unit and forms a fixing nip together with the heating unit, and a biasing unit that biases either one of the heating unit and the counter roller toward the other one of the heating unit and the counter roller, and fixes a toner image carried on the sheet to the sheet by applying heat and pressure in the fixing nip. One end portion in the width direction intersecting the sheet conveyance direction of the sheet conveyed to the fixing device passes through a predetermined position in the width direction of the fixing nip regardless of the size of the sheet. The counter roller has a roller portion including a base portion and an elastic layer provided around the base portion. When a side where the predetermined position is located with respect to the central portion of the roller portion in the width direction is defined as a first side and a side opposite to the first side is defined as a second side, the roller portion has a first end portion that is an end portion on the first side and a second end portion that is an end portion on the second side in the width direction. The biasing unit is configured such that a biasing force at the first end portion is greater than a biasing force at the second end portion. The elastic layer is provided on the first side and has a high hardness region having a higher hardness than the elastic layer at the central portion.

[0009] A third aspect of the present invention includes a heating unit that heats a sheet, and a counter roller that faces the heating unit and forms a fixing nip together with the heating unit, and in a fixing device that fixes a toner image carried on the sheet by applying heat and pressure in the fixing nip, one end portion in the width direction intersecting the sheet conveyance direction of the sheet conveyed to the fixing device passes through a predetermined position in the width direction of the fixing nip regardless of the size of the sheet, the heating unit includes an endless rotatable flexible rotating body, a heater disposed in an internal space of the rotating body that heats the rotating body, and a regulating member, the counter roller has a roller portion including a base portion and an elastic elastic layer provided around the base portion, when the side where the predetermined position is located with respect to the central portion of the roller portion in the width direction is the first side and the side opposite to the first side is the second side, the regulating member has a regulating surface that contacts an end surface on the second side in the width direction of the rotating body to regulate movement of the rotating body to the second side, the rotating body has a base layer and an elastic layer provided around the base layer and containing a filler, and the base layer protrudes to the second side more than the elastic layer and has a protruding portion that can contact the regulating surface in the width direction. The fixing device is characterized by this.

[0010] A fourth aspect of the present invention is a fixing device that includes a heating unit for heating a sheet, and a counter roller that faces the heating unit and forms a fixing nip together with the heating unit, and fixes a toner image carried on the sheet to the sheet by applying heat and pressure in the fixing nip. One end portion in the width direction intersecting the sheet conveyance direction of the sheet conveyed to the fixing device passes through a predetermined position in the width direction of the fixing nip regardless of the size of the sheet. The heating unit includes an endless rotatable flexible rotating body, a heater disposed in an internal space of the rotating body for heating the rotating body, a first support member disposed in the internal space for supporting the heater, and a second support member disposed in the internal space for supporting the first support member. The counter roller has a roller portion including a base portion and an elastic layer provided around the base portion. When a side where the predetermined position is located with respect to the central portion of the roller portion in the width direction is defined as a first side and the side opposite to the first side is defined as a second side, the first support member is provided on the first side in the width direction, and has a first guide portion capable of guiding the rotating body upstream in the sheet conveyance direction from the fixing nip, and a second guide portion provided on the second side in the width direction and capable of guiding the rotating body upstream in the sheet conveyance direction from the fixing nip. The second support member is disposed at a position spaced apart from the fixing nip more than the first guide portion and the second guide portion in a direction orthogonal to the sheet conveyance direction and the width direction, and has a facing portion facing an inner peripheral surface on the upstream side of the rotating body in the sheet conveyance direction. In the sheet conveyance direction, a distance from the facing portion to an upstream end of the second guide portion is longer than a distance from the facing portion to an upstream end of the first guide portion.

[0011] A fifth aspect of the present invention includes a heating unit that heats a sheet, and a counter roller that faces the heating unit and forms a fixing nip together with the heating unit, and fixes a toner image carried on the sheet to the sheet by applying heat and pressure in the fixing nip. In the fixing device, one end portion in the width direction intersecting the sheet conveyance direction of the sheet conveyed to the fixing device passes through a predetermined position in the width direction of the fixing nip regardless of the size of the sheet. The heating unit includes an endless rotatable flexible rotating body, a heater disposed in an internal space of the rotating body for heating the rotating body, a first support member disposed in the internal space for supporting the heater, and a second support member disposed in the internal space for supporting the first support member. The counter roller has a roller portion including a base portion and an elastic layer provided around the base portion. The second support member has an opposing portion that opposes an inner peripheral surface on the upstream side in the sheet conveyance direction of the rotating body at an end portion on the opposite side of the roller portion with respect to the fixing nip in a direction orthogonal to the sheet conveyance direction and the width direction. The heating unit is a cover disposed on the opposite side of the predetermined position from the central portion of the roller portion in the width direction, and has a cover provided between the opposing portion of the second support member and the inner peripheral surface on the upstream side in the sheet conveyance direction of the rotating body.

[0012] A sixth aspect of the present invention includes a heating unit that heats a sheet, and an opposing roller that faces the heating unit and forms a fixing nip together with the heating unit, and in a fixing device that fixes a toner image carried on the sheet by applying heat and pressure at the fixing nip, one end portion in the width direction intersecting the sheet conveyance direction of the sheet conveyed to the fixing device passes through a predetermined position in the width direction of the fixing nip regardless of the size of the sheet, the heating unit includes an endless rotatable flexible rotating body, a heater disposed in an internal space of the rotating body for heating the rotating body, and a regulating member, the opposing roller has a roller portion including a base portion and an elastic elastic layer provided around the base portion, when the side where the predetermined position is located with respect to the central portion of the roller portion in the width direction is the first side and the side opposite to the first side is the second side, the regulating member has a regulating surface that contacts an end surface on the second side in the width direction of the rotating body to regulate movement of the rotating body to the second side, and a guide portion that protrudes in the width direction from the regulating surface toward the rotating body and contacts an inner peripheral surface of the rotating body to guide the rotating body, the regulating member is movable between a first position and a second position where the guide portion is located upstream in the sheet conveyance direction from the first position, and when located at the first position, the regulating surface is pressed by the rotating body to the second side, and the fixing device is characterized in that it moves from the first position to the second position.

Advantages of the Invention

[0013] According to the present invention, it is possible to achieve both high-speed fixing processing and extended service life of the heating unit.

Brief Description of the Drawings

[0014]

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Embodiments for Carrying Out the Invention

[0015] <First Embodiment> First, the first embodiment of the present invention will be described. The image forming apparatus 100 is an electrophotographic laser beam printer that forms a monochrome toner image. FIG. 1(a) is an overall schematic cross-sectional view showing the image forming apparatus 100 according to the first embodiment.

[0016] In the following, each direction is defined as indicated by each arrow showing the direction in FIGS. 1(a) and 1(b). That is, the upward direction on the paper surface of FIG. 1(a) is referred to as the upward direction U, the downward direction on the paper surface is referred to as the downward direction D, the rightward direction on the paper surface is referred to as the forward direction F (front direction), the leftward direction on the paper surface is referred to as the backward direction B (rear direction), the front direction of the paper surface is referred to as the leftward direction L, and the back direction of the paper surface is referred to as the rightward direction R (see FIG. 1(b)). Further, as shown in FIG. 1(b), the left-right direction is referred to as the width direction W that intersects (orthogonal in this embodiment) the sheet conveyance direction DF.

[0017] [Schematic Configuration of Image Forming Apparatus] The image forming apparatus 100 includes an image forming unit 140 that forms a toner image on a sheet as a recording material, a feeding unit 150 that feeds the sheet to the image forming unit 140, a skew correction device 19, and a fixing device 6 that heat-fixes the toner image on the sheet to the sheet. The image forming unit 140 has a photosensitive drum 1 that is a drum-type electrophotographic photoreceptor as an image carrier. The photosensitive drum 1 is rotatably supported by a device main body 100a that constitutes the housing of the image forming apparatus 100. The image forming unit 140 includes a charging roller 2, a laser scanner 3, a developing device 4, a transfer roller 5, and a cleaning device 8 that are sequentially arranged along the rotation direction around the outer peripheral surface of the photosensitive drum 1.

[0018] The image forming apparatus 100 of the first embodiment has a control unit 31. The control unit 31 controls the image forming unit 140, the feeding unit 150, the fixing device 6, and the like. The control unit 31 includes a CPU and a memory such as a ROM and a RAM, and various programs necessary for image formation are stored in the memory. This control unit 31 captures a print signal from an external device such as a host computer and executes a predetermined image formation control sequence based on the print signal.

[0019] When the control unit 31 executes the control sequence, a drum motor (not shown) is rotationally driven, and the photosensitive drum 1 rotates in the direction of the arrow at a predetermined peripheral speed (process speed). The surface of the rotated photosensitive drum 1 is uniformly charged to a predetermined potential of the same polarity as the toner (negative polarity in this embodiment) by the charging roller 2. With respect to the charged surface of the photosensitive drum 1, the laser scanner 3 scans the laser beam LB based on the image information to expose the surface of the photosensitive drum 1. By this exposure, the charges in the exposed portion are removed, and an electrostatic latent image is formed on the surface of the photosensitive drum 1.

[0020] The developing device 4 includes a developing roller 41 and a toner container 42 that stores toner. The toner is frictionally charged to a predetermined polarity (negative polarity in this embodiment) by a member such as a urethane blade (not shown). The developing device 4 applies a negative potential to the developing roller 41 by a developing voltage power source (not shown), and uses the potential difference to attach the toner to the electrostatic latent image on the surface of the photosensitive drum 1, and develops the electrostatic latent image into a toner image T. The toner image T formed on the surface of the photosensitive drum 1 is transferred to the sheet S by using the potential difference due to the transfer voltage by applying a positive potential, which is the opposite polarity to the toner, to the transfer roller 5.

[0021] On the other hand, the feeding unit 150 includes a feeding roller 11 and a conveyance drive motor (not shown) that drives the feeding roller 11. The control unit 31 rotationally drives the conveyance drive motor, and the feeding roller 11 rotates to send out the sheet S loaded and stored in the cassette 7 to the conveyance path. The sheet S is conveyed to the skew correction device 19.

[0022] As shown in FIG. 1(b), the skew correction device 19 includes a plurality of conveying roller pairs 14, 15, skew rollers pairs 17a, 17b, 17c, and side abutting plates 18. When the sheet S is conveyed in the sheet conveying direction DF by the plurality of conveying roller pairs 14, 15 in a state where the sheet S is skewed, for example, the skew correction device 19 operates as follows. First, when the sheet S reaches the skew roller pairs 17a, 17b, 17c, a conveying force is applied to the sheet S not only in the sheet conveying direction DF but also in the width direction W, and the sheet S is conveyed while moving toward the side abutting plate 18. When the side end of the sheet S abuts against the side abutting plate 301, the skew roller pairs 17a, 17b, 17c slip, so that the sheet S is rotated and the skew is corrected by following the side abutting plate 18. Also, for example, even when the sheet S is conveyed in the sheet conveying direction DF by the plurality of conveying roller pairs 14, 15 in a state where the sheet S is not skewed, the sheet S is conveyed by the skew roller pairs 17a, 17b, 17c so as to follow the side abutting plate 18. In the present embodiment, the abutting surface of the side abutting plate 18 is defined as the paper passing reference position P0. As a result, the sheet S is conveyed by one-side reference in which one end portion in the width direction W of the sheet S passes through the paper passing reference position P0 (predetermined position) with respect to the transfer nip N1 of the image forming unit 140 and the fixing nip N2 of the fixing device 6 regardless of the size of the sheet. That is, the skew correction device 19 is an example of the conveying unit, is disposed upstream of the image forming unit 140 in the sheet conveying direction DF, and conveys the sheet in the sheet conveying direction DF while moving the sheet in the width direction W so that one end portion of the sheet passes through the paper passing reference position P0 of the fixing nip N2.

[0023] Downstream of the skew correction device 19 and upstream of the transfer nip N1 between the surface of the photosensitive drum 1 and the outer peripheral surface of the transfer roller 5, a registration roller pair 16 is provided. The control unit 31 adjusts the conveyance timing of the sheet S by the registration roller pair 16 and starts the conveyance of the sheet S so that the toner image is transferred from the photosensitive drum 1 to the sheet S at the transfer nip N1. In the present embodiment, in order to realize the one-sided reference, the case where the skew correction device 19 that conveys following the side abutting plate 18 by the skew roller pairs 17a, 17b, and 17c is applied has been described, but the present invention is not limited to this. For example, without providing such a skew correction device 19, the one-sided reference may be realized by positioning the position in the width direction of the sheet by moving the registration roller pair in the width direction while sandwiching the sheet with the registration roller pair or the like.

[0024] The sheet S onto which the toner image formed on the surface of the photosensitive drum 1 has been transferred is conveyed to the fixing device 6 along the conveyance guide 10, and the toner image on the sheet S is heated and pressed by the fixing device 6 and heat-fixed onto the sheet S. The sheet S on which the toner image T has been fixed is conveyed in the order of the conveyance roller pair 12 and the discharge roller pair 13 and discharged to the discharge tray 100b provided on the upper surface of the apparatus main body 100a. The transfer residual toner remaining on the surface of the photosensitive drum 1 after transferring the toner image to the sheet S is removed by the cleaning blade 81 of the cleaning device 8 and accumulated in the cleaning device 8. By repeating the above operations, image formation is sequentially performed. The image forming apparatus 100 of the first embodiment is assumed to be capable of performing image formation at a printing speed of 70 sheets per minute, for example, in the case of A4 size.

[0025] [Fixing device] Next, the fixing device 6 will be described with reference to FIGS. 2 and 3. FIG. 2 is a cross-sectional side view of the fixing device 6, and FIG. 3 is a schematic view of the fixing nip N2 as seen from the upstream side (front side) in the sheet conveyance direction DF. The fixing device 6 fixes the toner image formed by the image forming unit 140 onto the sheet. The fixing device 6 includes a heating unit 60 that heats the sheet S, a counter roller 61 that faces the heating unit 60 and forms the fixing nip N2 together with the heating unit 60, and a biasing unit 48 (see FIG. 3). The counter roller 61 is rotationally driven in the R1 direction by receiving rotational drive from the drive gear 47. The fixing film 25 is rotationally driven in the R2 direction opposite to the R1 direction by receiving rotational drive from the counter roller 61 that abuts at the fixing nip N2. The fixing device 6 sandwiches the sheet S at the fixing nip N2 and applies heat and pressure to fix the toner image T carried on the sheet S onto the sheet S.

[0026] [Counter Roller] The counter roller 61 includes a roller portion 26 that forms the fixing nip N2 together with the heating unit 60, and shaft portions 264a and 264b that are continuously provided on both sides in the width direction W from the roller portion 26. The shaft portions 264a and 264b are rotatably supported by a frame (not shown) of the fixing device 6. The roller portion 26 includes a base portion 261 that is the axis, an elastic layer 262 that is an example of a second elastic layer provided around the base portion 261, and a release layer 263 provided around the elastic layer 262.

[0027] Here, in the present embodiment, with respect to the width direction W, the side where the paper passage reference position P0 is located with respect to the central portion PC of the roller unit 26 is defined as the first side W1, and the side opposite to the first side W1 is defined as the second side W2. That is, the first side W1 is the left direction L side in the width direction W, and the second side W2 is the right direction R side in the width direction W. The roller unit 26 has a first end portion 26a that is an end portion on the first side W1 and a second end portion 26b that is an end portion on the second side W2 in the width direction W. Note that in this specification, the first side W1 not only indicates the side where the paper passage reference position P0 is located with respect to the central portion PC of the roller unit 26 in the width direction W, but may also mean the direction (left direction L in this embodiment) from the side without the paper passage reference position P0 toward the side with the paper passage reference position P0. Similarly, in this specification, the second side W2 not only indicates the side opposite to the first side W1 in the width direction W, but may also mean the direction (right direction R in this embodiment) from the side with the paper passage reference position P0 toward the side without the paper passage reference position P0.

[0028] In the present embodiment, the outer diameter of the central portion PC of the roller unit 26 in the width direction W is approximately 25 mm. The base portion 261 is made of a metal material such as aluminum or iron and has a solid or hollow shape. In the present embodiment, the base portion 261 is made of aluminum and has a solid shape. The elastic layer 262 is made of heat-resistant silicone rubber and is made conductive by adding an electric conductive material such as carbon.

[0029] The release layer 263 that contacts the outer surface of the fixing film 25 is a release tube made of a fluororesin such as PFA, PTFE, or FEP and having a thickness of 10 to 80 μm. Here, PFA is an abbreviation for tetrafluoroethylene·perfluoroalkyl vinyl ether copolymer, PTFE is an abbreviation for polytetrafluoroethylene (tetrafluoride), and FEP is an abbreviation for tetrafluoroethylene·hexafluoropropylene copolymer (tetra- and hexafluoride).

[0030] From the perspective of preventing charge-up during paper feeding, it is desirable to impart conductivity to the release layer 263. However, on the other hand, if a conductive material is added to impart conductivity, the releasability may decrease, and there is a risk of a problem (hereinafter referred to as roller contamination) in which a mixture of toner and paper dust adheres to the roller portion 26. In order to suppress charge-up and roller contamination, it is known that a means of applying a potential to the base portion 261 while using a high-resistance fluororesin material for the release layer 263 is effective. Therefore, in the present embodiment, the release layer 263 of the roller portion 26 is configured as a PFA tube with a thickness of 30 μm, and a potential of +300 V is applied to the base portion 261.

[0031] [Heating unit] As shown in FIGS. 2 and 3, the heating unit 60 includes a heater 20, a heater holder 29, a metal stay 22, a cylindrical fixing film 25, and flanges 40a and 40b. The energization control unit 272 connected to the commercial AC power supply 27 supplies power to the base portion 261 based on a signal from the control circuit 271.

[0032] [Heater] The heater 20 is disposed in the internal space of the fixing film 25 and heats the fixing film 25. The heater 20 has a heat-resistant heater substrate 201 made of aluminum nitride, alumina, or the like. On the surface of the heater substrate 201, a resistor pattern 202 as a conductive heating resistance layer that generates heat by energization is formed, for example, by screen printing. The resistor pattern 202 is covered with a heat-resistant coating material 203, and a thermistor 204 as a temperature detection member for detecting the temperature of the heater 20 is provided on the coating material 203. In the present embodiment, the case where the heater substrate 201 is made of a ceramic such as aluminum nitride or alumina has been described, but it is not limited thereto, and the heater substrate 201 may be made of metal. In this case, an insulating layer such as glass may be provided on the surface of the heater substrate 201, and the resistor pattern 202 may be provided thereon.

[0033] [Heater holder] The heater holder 29 is a holding member that holds the heater 20 as a heating element. That is, the heater holder 29 is an example of a first support member, which is disposed in the internal space of the fixing film 25 and supports the heater 20. As the material of the heater holder 29, heat-resistant resins such as liquid crystal polymer, phenolic resin, PPS, and PEEK are used. The heater holder 29 functions as a support member for supporting the heater 20 and also functions as a guide member for guiding the rotation of the fixing film 25.

[0034] [Stay] The stay 22 is an example of a second support member, which is disposed in the internal space of the fixing film 25 and supports the heater holder 29. The stay 22 is fixedly supported by a frame (not shown) of the fixing device 6.

[0035] [Fixing Film] The fixing film 25 is an example of an endless rotatable flexible rotating body, and is in a cylindrical shape with a diameter of 24 mm in the present embodiment. The fixing film 25 is loosely externally fitted to the heater holder 29 with a gap. The fixing film 25 is composed of a base layer 251, an elastic layer 252 which is an example of a first elastic layer provided around the base layer 251, and a surface layer 253 provided around the elastic layer 252, which are laminated. As the material of the base layer 251, heat-resistant resin materials with low heat capacity such as general materials like polyimide, polyamideimide, PEEK, and PES are used. Since the base layer 251 needs to reduce the heat capacity to satisfy the quick start property and at the same time satisfy the mechanical strength, it is desirable that the thickness is not less than 18 μm and not more than 150 μm. The base layer 251 of the first embodiment is a cylindrical polyimide base layer with a thickness of 70 μm.

[0036] The elastic layer 252 is made of a material having elasticity typified by silicone rubber. By providing the elastic layer 252, the toner image T can be wrapped and heat can be uniformly applied, so that a high-quality image without unevenness can be obtained. Since the silicone rubber alone has low thermal conductivity, a thermally conductive filler made of an inorganic material is added to the elastic layer 252. As the filler, those containing ceramic powder, metal oxide powder, or metal powder can be applied. In the present embodiment, thermally conductive fillers such as alumina, metal silicon, silicon carbide, and zinc oxide are added as the filler to impart high thermal conductivity to the elastic layer 252. In a high-speed machine such as the image forming apparatus 100 of the first embodiment, it is preferable to appropriately adjust the addition amount (content) of the filler to ensure 0.9 W / m·K or more. In the present embodiment, alumina and metal silicon are added as thermally conductive fillers to the rubber material of the elastic layer 252, and the thermal conductivity is 1.5 W / m·K. The thickness of the elastic layer 252 is 270 μm.

[0037] The surface layer 253, as a release layer, is required to have high releasability from toner and high wear resistance. As the material, fluororesins such as PFA, PTFE, and FEP are used. The surface layer 253 is formed of a coating layer or a tube layer obtained by baking a resin dispersion. Further, additives such as carbon and ion conductive materials may be added to the fluororesin to impart conductivity. The surface layer 253 of the first embodiment uses a fluororesin (PFA) as the material, does not add a conductive material, and is a tube layer with a thickness of 25 μm.

[0038] [Flange] Next, the flanges 40a and 40b of the present embodiment will be described with reference to FIG. 3. In FIG. 3, the fixing film 25 is shown by a dashed line, and its interior is shown as being visible through. The fixing film 25 may have a tendency to shift to either the left or right in the width direction W. The flanges 40a and 40b are provided so as to abut against both ends of the fixing film 25 from the width direction W in order to regulate such a shift. The first flange 40a is provided facing the end face 25a on the first side W1 in the width direction W of the fixing film 25, and the second flange 40b is provided facing the end face 25b on the second side W2 in the width direction W of the fixing film 25.

[0039] The first flange 40a has a regulating surface 41a and a guide portion 42a. The second flange 40b is an example of a regulating member and has a regulating surface 41b and a guide portion 42b. Since the first flange 40a and the second flange 40b are symmetric in shape, hereinafter, mainly the second flange 40b will be described. The regulating surface 41b regulates the movement of the fixing film 25 to the second side W2 (right direction R) by contacting the end face 25b on the second side W2 in the width direction W of the fixing film 25. The guide portion 42b is provided to protrude leftward L from the regulating surface 41b toward the fixing film 25 and contacts the inner peripheral surface of the fixing film 25 to guide the fixing film 25.

[0040] For example, when a shift to the right direction R occurs in the fixing film 25, the end face 25b of the fixing film 25 abuts against the regulating surface 41b of the second flange 40b, and the shift is regulated. The guide portion 42b contacts the inner peripheral surface of the fixing film 25 and guides the inner peripheral surface of the fixing film 25 in the end region on the end face 25b side of the fixing film 25. In FIG. 3, it is shown that the guide portion 42a of the first flange 40a contacts the inner peripheral surface of the fixing film 25 in the contact region SL, and the guide portion 42b of the second flange 40b contacts the inner peripheral surface of the fixing film 25 in the contact region SR.

[0041] For example, when the inner peripheral surface of the fixing film 25 and the guide portion 42b of the second flange 40b come into contact and slide in the contact region SR, there is a risk that the heat required for toner fixing escapes from the fixing film 25 to the second flange 40b. Therefore, the guide portion 42b of the second flange 40b is provided outside the width direction W (right direction R) of the maximum conveyance region Ar0, which is the conveyance region of the sheet with the maximum width. Similarly, the guide portion 42a of the first flange 40a is provided outside the width direction W (left direction L) of the maximum conveyance region Ar0.

[0042] The material of the flanges 40a and 40b is preferably the same hardness as the base layer 251 of the fixing film 25, which is the sliding mating member. The reason is that if the hardness of the flanges 40a and 40b is harder than the base layer 251 of the fixing film 25, wear will occur on the inner peripheral surface of the base layer 251 of the fixing film 25, and conversely, if it is softer than the base layer 251, wear will occur on the outer peripheral surface of the guide portions 42a and 42b. Therefore, in this embodiment, liquid crystal polymer (LCP) is used as the material of the flanges 40a and 40b.

[0043] [Biasing Unit] In this embodiment, as shown in FIG. 3, the biasing unit 48 biases the heating unit 60 toward the counter roller 61. The biasing unit 48 includes a first biasing spring 48a, which is an example of a first biasing portion that biases the first flange 40a toward the counter roller 61, and a second biasing spring 48b, which is an example of a second biasing portion that biases the second flange 40b toward the counter roller 61. Each of the biasing springs 48a and 48b is composed of, for example, a compression coil spring, but the type of spring is not limited to this, and for example, a tension coil spring or other springs may be applied.

[0044] The first biasing spring 48a biases the first flange 40a, and the second biasing spring 48b biases the second flange 40b, thereby applying a biasing force to the heater holder 29 via the stay 22 and pressing the fixing film 25 against the counter roller 61. Thereby, a fixing nip N is formed between the fixing film 25 and the counter roller 61.

[0045] In this embodiment, the first biasing spring 48a is provided to bias the first flange 40a toward the opposing roller 61, and the second biasing spring 48b is provided to bias the second flange 40b toward the opposing roller 61. However, the present invention is not limited to this. For example, at least one of the first biasing spring 48a and the second biasing spring 48b may be provided to bias the opposing roller 61 toward the flanges 40a and 40b. That is, the first biasing spring 48a biases either one of the heating unit 60 and the opposing roller 61 at the first end portion 26a of the roller portion 26 toward the other of the heating unit 60 and the opposing roller 61. Further, the second biasing spring 48b biases either one of the heating unit 60 and the opposing roller 61 at the second end portion 26b of the roller portion 26 toward the other of the heating unit 60 and the opposing roller 61.

[0046] Similarly, in this embodiment, the biasing unit 48 has been described for the case of biasing the heating unit 60 toward the opposing roller 61. However, the present invention is not limited to this. For example, the opposing roller 61 may be biased toward the heating unit 60. That is, the biasing unit 48 biases either one of the heating unit 60 and the opposing roller 61 toward the other of the heating unit 60 and the opposing roller 61.

[0047] [Toward the fixing film] Here, the vicinity of the fixing film 25 will be described with reference to FIGS. 5(a) and 5(b). FIG. 5(a) is a schematic view of the fixing nip N2 when the sheet is passed through on one side standard, as viewed from the upstream (front side) in the sheet conveyance direction DF. The sheet S is sandwiched and conveyed at the fixing nip N2 formed by the fixing film 25 and the roller portion 26. In this embodiment, the maximum width of the sheet S that can be passed through the fixing device 6 is the width of the letter size, and the maximum conveyance area Ar0 is set to the letter size. The sheet S shown in FIG. 5(a) is an A6 size sheet S having a dimension in the width direction W smaller than the maximum width of the letter size.

[0048] Fig. 5(b) shows the distribution in the width direction W of the surface temperature of the opposing roller 61 when the A6-size sheet S is continuously fed. As shown in Fig. 5(b), the surface temperature of the opposing roller 61 is relatively higher in the non-paper-passing portion Ar2 than in the paper-passing portion Ar1. In the paper-passing portion Ar1, heat transfer occurs from the surface of the opposing roller 61 to the sheet S, causing the temperature of the opposing roller 61 to decrease. On the other hand, in the non-paper-passing portion Ar2, since the sheet S does not exist, heat is constantly supplied from the fixing film 24 to the opposing roller 61, so the temperature of the opposing roller 61 becomes higher.

[0049] Here, the opposing roller 61 has an elastic layer 262 made of heat-resistant silicone rubber on the outer periphery of the base 261, and silicone rubber has the property of being prone to thermal expansion when the temperature becomes high. Therefore, due to the thermal expansion of the silicone rubber, the outer diameter of the non-paper-passing portion Ar2 of the opposing roller 61 becomes larger than that of the paper-passing portion Ar1. Thus, a speed difference occurs in the circumferential speed of the opposing roller 61 in the width direction W, with the paper-passing portion Ar1 being relatively slower and the non-paper-passing portion Ar2 being relatively faster.

[0050] The opposing roller 61 is rotationally driven from the drive gear 47 and rotates in the R1 direction in Fig. 5(a). The fixing film 25 is rotationally driven by the opposing roller 61 at the fixing nip N2 and rotates passively in the R2 direction in Fig. 5(a). At this time, when there is a speed difference in the circumferential speed of the opposing roller 61, a biasing force is generated on the passively rotating fixing film 25 in the direction of rotation at a higher speed, that is, in the right direction R in Fig. 5(a). Due to this biasing force, the fixing film 25 moves in the right direction R along the width direction W and abuts against the second flange 40b. If the temperature of the non-paper-passing portion Ar2 of the opposing roller 61 becomes even higher and the biasing force becomes even greater, there is a risk that the fixing film 25 may deform (lateral buckling) if the biasing force exceeds the rigidity of the fixing film 25.

[0051] Here, the mechanism for generating the pulling force will be described. Due to the temperature rise of the non-paper-passing portion Ar2, the roller portion 26 of the non-paper-passing portion Ar2 thermally expands, and the outer diameter of the roller portion 26 increases, resulting in an increase in the peripheral speed. In the fixing device 6 with one-side reference, the temperature rise of the non-paper-passing portion Ar2 occurs only on the side opposite to the reference surface in the width direction W. Therefore, in the fixing device 6 with one-side reference, an outer diameter difference occurs in the width direction W of the roller portion 26, and a left-right difference occurs in the feeding speed of the fixing film 25 in the fixing nip N2 in the width direction W. As a result, a pulling force is generated on the side where the rotational speed of the fixing film 25 is faster. The magnitude of the pulling force increases as the left-right difference in the width direction W of the outer diameter of the roller portion 26, that is, as the temperature rise of the non-paper-passing portion Ar2 increases.

[0052] Therefore, in the present embodiment, by making the thickness of the elastic layer 262 that thermally expands in the opposing roller 61 different in the width direction W, the change in the outer diameter after expansion is suppressed. Hereinafter, the opposing roller 61 of the present embodiment will be described with reference to FIGS. 4(a) and (b).

[0053] FIG. 4(a) is a schematic diagram showing a cross-section in the width direction W of the opposing roller 61, which has an elastic layer 262 on the outer periphery of the base portion 261. In the present embodiment, in the roller portion 26, the elastic layer 262 is provided on the base portion 261, and the maximum outer diameter D1 of the base portion 261 at the first end portion 26a of the roller portion 26 is made smaller than the maximum outer diameter D2 of the base portion 261 at the second end portion 26b. In the present embodiment, D1 is 20 mm and D2 is 22 mm. The shape between D1 and D2 may be a tapered shape connecting D1 and D2, or there may be a straight portion where the outer diameter does not change in part, and the portion other than the straight portion is connected in a tapered shape.

[0054] And since the outer diameter of the roller portion 26 does not change significantly in the width direction W, the thickness d2 of the elastic layer 262 at the second end portion 26b is made thinner than the thickness d1 of the elastic layer 262 at the first end portion 26a. As a result, as shown in FIG. 5(a), even when the non-paper-passing portion Ar2 becomes relatively hotter than the paper-passing portion Ar1, the amount of expansion of the elastic layer 262 in the non-paper-passing portion Ar2 can be made smaller than the amount of expansion of the elastic layer 262 in the paper-passing portion Ar1. For this reason, it is possible to suppress a significant increase in the outer diameter of the non-paper-passing portion Ar2 compared to the paper-passing portion Ar1 at the outer diameter of the roller portion 26, and to reduce the generation of the pulling force.

[0055] The thickness d2 of the elastic layer 262 at the second end portion 26b is preferably 65% or more and 75% or less of the thickness d1 of the elastic layer 262 at the first end portion 26a. In the present embodiment, it is set to about 69%. In view of the fixing temperature and the coefficient of thermal expansion of the elastic layer, if the thickness d2 of the elastic layer 262 is 65% or more and 75% or less of the thickness d1 of the elastic layer 262, the generation of the pulling force can be suppressed more effectively than when it is less than 65% or exceeds 75%.

[0056] FIG. 4(b) is a profile when measuring the outer diameter shape of the counter roller 61, which has an inverse crown shape in which the central portion PC is the smallest and increases quadratically from the central portion PC toward the end surface PL on the first side W1 and the end surface PR on the second side W2. Since the outer diameter shape is an inverse crown shape, when the sheet S is conveyed, the outer diameter of the end portion of the roller portion 26 becomes larger and the conveyance speed becomes faster, and a force for pulling both ends of the sheet S in the width direction W is generated, so that the occurrence of paper wrinkles and the like can be suppressed.

[0057] Further, in the present embodiment, the maximum outer diameter of the second end portion 26b of the roller portion 26 is made larger than the maximum outer diameter of the first end portion 26a. The maximum outer diameter of the first end portion 26a of the roller portion 26 is the outer diameter of the end face PL on the first side W1 of the roller portion 26, and the maximum outer diameter of the second end portion 26b of the roller portion 26 is the outer diameter of the end face PR on the second side W2 of the roller portion 26. Thus, for example, when the entire roller portion 26 serves as a paper passage portion and is heated substantially uniformly, as in the case of a letter-sized sheet S, even if the first side W1 in the width direction W expands more than the second side W2, the outer diameter difference in the width direction W of the roller portion 26 can be reduced.

[0058] In the present embodiment, in a room temperature environment, the maximum outer diameter at the first end portion 26a is 24.8 mm, the maximum outer diameter at the second end portion 26b is 25.3 mm, and the outer diameter at the central portion PC is 24.7 mm. Further, the maximum outer diameter of the second end portion 26b is preferably 101% or more and 103% or less of the maximum outer diameter of the first end portion 26a, and in the present embodiment, it is 102%. In view of the fixing temperature and the thermal expansion coefficient of the elastic layer, if the maximum outer diameter of the second end portion 26b is 101% or more and 103% or less, the generation of the biasing force can be suppressed more effectively than when it is less than 101% or exceeds 103%.

[0059] [Examples and Comparative Examples] A comparative experiment was conducted using Example 1 to which the opposing roller 61 of the present embodiment was applied and Comparative Example 1 to which the opposing roller 161 shown in FIG. 6(a) was applied.

[0060] Comparative Example 1 will be described. As shown in FIG. 6(a), the roller portion 76 of the opposing roller 161 in Comparative Example 1 has a base portion 761, an elastic layer 762 provided around the base portion 761, and a release layer 763 provided around the elastic layer 762. The maximum outer diameter D1 of the base portion 761 is 20 mm and is uniform in the width direction W. As shown in FIG. 6(b), the outer diameter profile has a bilaterally symmetric inverse crown shape that increases toward both ends in the width direction W with the central portion PC as a reference. The outer diameters at the end face PL on the first side W1 and the end face PR on the second side W2 are 24.8 mm, and the outer diameter at the central portion PC is 24.7 mm.

[0061] As a comparative experiment, 40 sheets of letter-sized paper were continuously fed through at a speed of 40 sheets per minute, and the temperature and outer diameter of the roller part were measured when the trailing edge of the last 20th sheet passed through the fixing nip N2. Also, 20 sheets of A6-sized paper were continuously fed through at a speed of 75 sheets per minute, and the temperature and outer diameter of the roller part were measured when the trailing edge of the last 20th sheet passed through the fixing nip N2. The results are shown in Table 1.

Table 1

[0062] In Table 1, PL of the outer diameter refers to the maximum outer diameter of the first end part of the roller part, that is, the outer diameter at the end face PL of the first side W1. PR of the outer diameter refers to the maximum outer diameter of the second end part of the roller part, that is, the outer diameter at the end face PR of the second side W2. In the state before paper feeding, the outer diameter of PL is 24.8 mm, and the outer diameter of PR is 25.3 mm. Also, in Table 1, PL of the temperature refers to the average value of the temperature in the region from the central part PC in the width direction W of the roller part to half of the first side W1, and PR of the temperature refers to the average value of the temperature in the region from the central part PC in the width direction W of the roller part to half of the second side W2.

[0063] When feeding a letter-sized sheet which is the maximum width through which paper can be fed, in Example 1, since the heated region of the roller part 26 and the region through which the sheet passes generally coincide, both PL and PR reached 90°C. At this time, the outer diameter of PL changed from 24.8 mm before paper feeding to 25.5 mm due to the expansion of the elastic layer 262, an increase of 0.7 mm. On the other hand, the outer diameter of PR changed from 25.3 mm before paper feeding to 25.4 mm due to the expansion of the elastic layer 262, an increase of 0.1 mm. This difference is because even though the temperature of the elastic layer 262 of the roller part 26 is the same, the thickness of the elastic layer 262 is different, so the expansion amount of PL with a thicker elastic layer 262 is larger.

[0064] In Comparative Example 1, the temperature became 90°C for both PL and PR, similar to Example 1. Also, in Comparative Example 1, since the thickness of the elastic layer 762 of the roller part 26 is uniform in the width direction W, the expansion amount of the elastic layer 762 is the same for both PL and PR, so the outer diameters of both PL and PR became 25.5 mm.

[0065] Next, when passing a sheet of A6 size, in Example 1, the temperature at PL was 90°C because the sheet passed through. On the other hand, in PR, a non-paper-passing part Ar2 where the sheet did not pass occurred, so the temperature increased due to the temperature rise of the non-paper-passing part Ar2, and the average value of the temperature of PR became 180°C. The outer diameter of the roller part 26 was 25.5 mm for PL, the same as when using a letter-sized sheet. On the other hand, for PR, since the temperature was high and the expansion amount of the elastic layer 262 became large, the outer diameter became 25.6 mm.

[0066] In Comparative Example 1, PL was 90°C and PR was 180°C, similar to Example 1. The outer diameter of PL was 25.5 mm, the same as in Example 1, but for PR, since the temperature was as high as 180°C and the thickness of the elastic layer 762 was also thick, the outer diameter became 25.9 mm.

[0067] As can be seen from the results shown in Table 1, when passing a sheet of A6 size, in Example 1, the difference between the outer diameters of PL and PR could be made smaller compared to Comparative Example 1.

[0068] Next, Table 2 shows the ratio of the outer diameter of PR to the outer diameter of PL of the opposing roller when the outer diameter of PL was set to 100% during this comparative experiment.

Table 2

[0069] In Example 1, when passing a letter-sized sheet, the outer diameter of the PR was 99.6%, and when passing an A6-sized sheet, it was 100.4%. In Comparative Example 1, when passing a letter-sized sheet, the outer diameter of the PR was 100%, but when passing an A6-sized sheet, it was 101.6%. It is considered that the larger the size exceeding 100% of the outer diameter of the PR, the greater the difference in the peripheral speed between the PL and the PR, and the greater the lateral force generated on the fixing film 25. As can be seen from the results shown in Table 2, when passing an A6-sized sheet, in Example 1, the lateral force generated on the fixing film 25 could be suppressed to be smaller than that in Comparative Example 1.

[0070] Next, Table 3 shows the results of whether or not deformation (buckling) of the fixing film 25 due to the lateral force occurred during this comparative experiment.

Table 3

[0071] In Example 1, no deformation of the fixing film 25 was observed for both the letter-sized sheet and the A6-sized sheet. In Comparative Example 1, no deformation of the fixing film 25 was observed when passing a letter-sized sheet, but deformation of the fixing film 25 was observed when passing an A6-sized sheet. This is because as the left-right difference in the outer diameter of the roller part increases, the difference in the peripheral speed between the PL and the PR of the roller part also increases, and a lateral force is generated on the fixing film 25 that is rotating passively toward the direction of faster rotation. Therefore, in Example 1, no deformation of the fixing film 25 due to the lateral force occurs for both the letter-sized sheet and the A6-sized sheet, but in the case of Comparative Example 1, it was confirmed that there is a possibility that deformation of the fixing film 25 due to the lateral force may occur when passing an A6-sized sheet.

[0072] As described above, according to the fixing device 6 of the present embodiment, the thickness d2 of the elastic layer 262 at the second end portion 26b of the roller portion 26 is thinner than the thickness d1 of the elastic layer 262 at the first end portion 26a. Therefore, even when the non-paper-passing portion Ar2 becomes relatively hotter than the paper-passing portion Ar1, the amount of expansion of the elastic layer 262 in the non-paper-passing portion Ar2 can be made smaller than the amount of expansion of the elastic layer 262 in the paper-passing portion Ar1. Thus, it is possible to suppress the non-paper-passing portion Ar2 from becoming significantly larger than the paper-passing portion Ar1 in the outer diameter of the roller portion 26, and to reduce the generation of the biasing force in the fixing film 25. Thereby, when the conveyance method is based on one side, it is possible to speed up the fixing process without increasing the thickness of the fixing film 25, reduce the biasing force, extend the service life of the heating unit 60, and achieve both the speeding up of the fixing process and the extension of the service life of the heating unit 60.

[0073] Further, according to the fixing device 6 of the present embodiment, at the base portion 261 of the roller portion 26, the maximum outer diameter D2 on the second end portion 26b side is made thinner than the maximum outer diameter D1 on the first end portion 26a side. Thereby, the thickness of the elastic layer 262 at the second end portion 26b can be made thinner without significantly changing the outer diameter of the roller portion 26 in the width direction W.

[0074] <Second Embodiment> Next, a second embodiment of the present invention will be described. The second embodiment is configured by changing the opposing roller 61 of the first embodiment. Therefore, for the same configurations as those in the first embodiment, illustration will be omitted or the same reference numerals will be given in the drawings for explanation.

[0075] For example, as shown in FIG. 5(a), when there is a paper-passing reference position P0 on one side and a sheet having a width narrower than the maximum width through which paper can be passed is passed, a biasing force may be generated in the right direction R in FIG. 5(a) with respect to the fixing film 25. One of the reasons will be explained.

[0076] When the sheet is paper, the paper has the property of absorbing (hygroscopic) moisture in the atmosphere into the paper fibers. When the paper containing this moisture is rapidly heated at the fixing nip N2, the contained moisture is released into the fixing device 6A as water vapor. When the sheet is continuously passed through the fixing device 6A, the amount of generated water vapor also increases, so it becomes easier for water droplets to adhere to the opposing roller 61A. When water droplets adhere to the surface of the opposing roller 61A, the friction coefficient between the surface of the opposing roller 61A and the sheet decreases, so a slip phenomenon occurs where the conveyance speed of the sheet decreases relative to the peripheral speed of the opposing roller 61A. When the conveyance speed of the sheet decreases, the rotation speed of the fixing film 25 that is in contact with the sheet and rotates passively also decreases.

[0077] On the other hand, since no water vapor is generated in the non-paper-passing portion Ar2 where the sheet does not pass, it is difficult for water droplets to adhere to the surface of the opposing roller 61A. Therefore, no slip phenomenon occurs in the non-paper-passing portion Ar2, and the rotation speed of the fixing film 25 does not decrease. Due to the above phenomenon, the rotation speed of the paper-passing portion Ar1 of the fixing film 25 becomes slow, and the rotation speed of the non-paper-passing portion Ar2 becomes fast, and a biasing force is generated in the direction of increasing rotation speed. When this biasing force becomes large, there is a risk that the fixing film 25 may be deformed because the biasing force exceeds the rigidity of the fixing film 25.

[0078] [Opposing roller] Therefore, in the present embodiment, by making the biasing force of the biasing unit 48 on the first end 26aA of the first side W1 of the roller portion 26A larger than the biasing force on the second end 26bA of the second side W2, the occurrence of the above slip phenomenon is reduced. Hereinafter, the opposing roller 61A of the present embodiment will be described with reference to FIGS. 7(a) and (b). FIG. 7(a) shows a cross-sectional side view of the roller portion 26A of the opposing roller 61A of the second embodiment. The roller portion 26A has an elastic layer 262A on the outer periphery of a base portion 261A, and a release layer 263A on the outer periphery of the elastic layer 262A.

[0079] FIG. 7(b) is a cross-sectional view along the width direction W of the fixing device 6A of the present embodiment. The hardness of the elastic layer of the roller unit 26A is different between the region ArL provided on the first end portion 26aA side and the region ArR provided on the second end portion 26bA side, and the hardness of the region ArL is higher than the hardness of the region ArR. The region ArL is an example of a high-hardness region provided in the elastic layer 262A, is provided on the first side W1 in the width direction W, and has a higher hardness than the elastic layer 262A at the central portion PC. The region ArR is an example of a low-hardness region provided in the elastic layer 262A, is provided on the second side W2 in the width direction W, and has a lower hardness than the elastic layer 262A at the central portion PC. The hardness adjustment of the elastic layer 262A is performed by changing the blending ratio of materials such as silicone rubber. In the present embodiment, the hardness of the region ArL is 60° in terms of the hardness by AskerC, and the hardness of the region ArR is 54°. The configurations such as other dimensions are the same as those in Comparative Example 1.

[0080] Further, at least a part of the region ArL is arranged so as to overlap the conveyance region of the smallest-size sheet to be conveyed when viewed from the crossing direction (for example, the vertical direction) crossing the sheet conveyance direction DF and the width direction W. Further, the region ArL is arranged between the central portion PC and the paper passage reference position P0 in the width direction W. Thereby, even for the smallest-size sheet to be conveyed, the urging force by the urging unit 48 can be increased to reduce slip.

[0081] [Biasing Unit] The biasing forces of the first biasing spring 48a and the second biasing spring 48b of the biasing unit 48 shown in FIG. 7(b) on the flanges 40a and 40b are set such that the first biasing spring 48a is greater. Specifically, the biasing force by the first biasing spring 48a is 147 N, and the biasing force by the second biasing spring 48b is 98 N. That is, the biasing unit 48 is configured such that the biasing force at the first end portion 26aA is greater than the biasing force at the second end portion 26bA. Thereby, by increasing the biasing force on the first side W1 where slipping easily occurs due to moisture, the occurrence of the slip phenomenon can be reduced.

[0082] Here, by increasing the biasing force in the high-hardness region (region ArL) where the hardness of the roller portion 26A is high and decreasing the biasing force in the low-hardness region (region ArR) where the hardness of the roller portion 26A is low, the amount of deformation of the elastic layer 262A due to biasing can be made equal on the left and right. Therefore, even if the biasing forces on the fixing film 25 are different between the first side W1 and the second side W2 of the roller portion 26A, the width in the longitudinal direction of the fixing nip N2 formed by the fixing film 25 and the counter roller 70 can be made substantially constant with respect to the width direction W.

[0083] The hardness of the elastic layer 262A in the region ArL is preferably 110% or more and 120% or less of the hardness of the elastic layer 262A in the region ArR. In this embodiment, it is 111%. In view of the fixing temperature and the thermal expansion coefficient of the elastic layer, if the hardness of the elastic layer 262A in the region ArL is 110% or more and 120% or less of the hardness in the region ArR, the generation of the biasing force can be suppressed more effectively than when it is less than 110% or more than 120%.

[0084] The biasing force of the first biasing spring 48a is preferably 130% or more and 170% or less of the biasing force of the second biasing spring 48b. In this embodiment, it is 150%. In view of the fixing temperature and the thermal expansion coefficient of the elastic layer, if the biasing force of the first biasing spring 48a is 130% or more and 170% or less of the biasing force of the second biasing spring 48b, slippage can be reduced more effectively than when it is less than 130% or more than 170%.

[0085] [Examples and Comparative Examples] A comparative experiment was conducted using Example 2 to which the counter roller 61A of this embodiment was applied and Comparative Example 2 to which the counter roller 161 shown in FIG. 6(a) was applied. First, the hardness of the elastic layer of the roller portion and the biasing force by the biasing unit 48 were measured in Example 2 and Comparative Example 2. The results are shown in Table 4. The region corresponding to ArL in terms of hardness in Comparative Example 2 is the region at the same position as the region ArL in Example 2, and the region corresponding to ArR in terms of hardness is the region at the same position as the region ArR in Example 2.

Table 4

[0086] As shown in Table 4, the hardness of the elastic layer of the opposing roller 161 in Comparative Example 2 is generally uniform in the width direction W, and the hardness is 57° according to Asker C. The pressing forces by the biasing unit 48 in Comparative Example 2 are equal on the left and right, each being 122.5 N.

[0087] As a comparative experiment, passing 20 consecutive letter-sized sheets at a speed of 40 sheets per minute and passing 20 consecutive A6-sized sheets at a speed of 75 sheets per minute were carried out. Table 5 shows the results of whether or not deformation (buckling) of the fixing film 25 due to the approaching force occurred during the implementation of this comparative experiment.

Table 5

[0088] In Example 2, since the width of the fixing nip N2 in the front-rear direction is constant with respect to the width direction W, when passing a letter-sized sheet, there is no left-right difference in the sheet conveyance speed, so deformation of the fixing film 25 was not observed either. When passing an A6-sized sheet, in the area where the sheet passed, steam may be generated due to the sheet being heated at the fixing nip N2, which may cause a decrease in the sheet conveyance speed. However, in Example 2, by increasing the pressing force on the first side W1, the slip phenomenon caused by water droplets adhering to the surface of the roller portion 26A can be minimized. Therefore, when passing an A6-sized sheet, the left-right difference in the speed of the fixing film 25 can be minimized, so deformation of the fixing film 25 was not observed.

[0089] In Comparative Example 2, when a letter-sized sheet was passed through, there was no left-right difference in the pressing force, and the width of the fixing nip N2 in the front-rear direction was constant with respect to the width direction W. Therefore, no left-right difference in the sheet conveyance speed occurred, and no deformation of the fixing film 25 was observed. On the other hand, when an A6-sized sheet was passed through, in the area where the sheet passed, steam was generated when the sheet was heated by the fixing nip N2, resulting in a significant decrease in the sheet conveyance speed. Therefore, in the paper passage portion Ar1, the rotation speed of the fixing film 25 decreased due to the influence of the slip phenomenon caused by steam, and the biasing force generated by the difference from the rotation speed of the fixing film 25 in the non-paper passage portion Ar2 increased, causing deformation (buckling) of the fixing film 25.

[0090] As described above, according to the fixing device 6A of the present embodiment, since the biasing force of the biasing unit 48 on the first end portion 26aA of the roller unit 26A is made larger than the biasing force on the second end portion 26bA, the occurrence of the slip phenomenon of the fixing film 25 due to moisture can be reduced. For this reason, it is possible to suppress an increase in the biasing force of the fixing film 25 and prevent deformation. As a result, the generation of the biasing force of the fixing film 25 can be reduced, and a fixing device 6A capable of coping with high speed and long life can be realized.

[0091] In the present embodiment, the case where the biasing unit 48 has the first biasing spring 48a and the second biasing spring 48b has been described, but it is not limited thereto. For example, only the first biasing spring 48a may be provided, and the second biasing spring 48b may not be provided and the biasing may be performed by its own weight. Alternatively, the first biasing spring 48a may not be provided on the first side W1, and for example, even if it is provided on the second side W2, a biasing force may be applied to the first end portion 26aA while interposing an appropriate transmission member.

[0092] In addition, in this embodiment, the case where a hardness difference and a biasing force difference of the elastic layer 262A in the width direction W of the roller portion 26A are provided has been described, but the present invention is not limited to this. For example, similar effects can be obtained by providing only a left - right difference in the hardness of the elastic layer 262A of the roller portion 26A, or similar effects can be obtained by providing only a left - right difference in the pressing force of the biasing springs 48a and 48b.

[0093] <Third Embodiment> Next, a third embodiment of the present invention will be described. The third embodiment is configured by modifying the fixing film 25 of the first embodiment. Therefore, for the same configurations as those in the first embodiment, illustration will be omitted or the same reference numerals will be used in the drawings for explanation.

[0094] Here, the problem of the fixing film 25 being prone to buckling, which is a conventional problem, will be described in detail. When the amount of the heat - conductive filler contained in the elastic layer 252 is increased to achieve high - thermal - conductivity of the fixing film 25, wear of the base layer 251 of the fixing film 25 may easily occur. In particular, in the case of a configuration in which the flanges 40a and 40b have the restricting surfaces 41a and 41b and the guide portions 42a and 42b, inner - surface wear (hereinafter referred to as inner - surface wear) of the end portions in the width direction W of the fixing film 25 may easily occur. Due to the inner - surface wear, the end portions in the width direction W of the base layer 251 of the fixing film 25 become thin, making buckling likely to occur, which may prevent the extension of the service life.

[0095] The mechanism of inner surface wear of the fixing film 25 having the elastic layer 252 containing the heat conduction filler will be described with reference to FIG. 8. FIG. 8 is a cross-sectional configuration view of the vicinity of the second flange 40b in a fixing device of a comparative example in which the fixing film 25 is not configured according to the present embodiment, as viewed from the upstream (front side) in the sheet conveyance direction DF. In the figure, a cross-section along the width direction W of the fixing film 25 and the side surface of the second flange 40b are shown. Note that FIG. 8 shows a state in which the fixing film 25 is biased toward the right direction R due to the influence of the temperature rise of the non-paper passing portion Ar2 described in the first embodiment, and the fixing film 25 is in contact with the regulating surface 41b of the second flange 40b in FIG. 5(a). Also, for the comparative example, elements corresponding to those of the present embodiment are denoted by the same reference numerals and will be described.

[0096] Due to the influence of the temperature rise of the non-paper passing portion Ar2 described in the first embodiment, the fixing film 25 may receive a force toward the right direction R and slide and rotate while being pressed against the regulating surface 41b of the second flange 40b. The fixing film 25 and the regulating surface 41b of the second flange 40b slide in the sliding region ArB. The fixing film 25 is composed of a base layer 251, an elastic layer 252, and a surface layer 253, and the base layer 251 and the elastic layer 252 are worn by sliding friction with the regulating surface 41b.

[0097] The elastic layer 252 contains a heat conduction filler. Therefore, as the elastic layer 252 is worn by the regulating surface 41b of the second flange 40b, the heat conduction filler contained in the elastic layer 252 is scraped out from the end face of the elastic layer 252. A part of the scraped-out heat conduction filler passes through the sliding region ArB between the end portion in the width direction W of the fixing film 25 and the regulating surface 41b of the second flange 40b. Then, the heat conduction filler gets into the contact region SR between the inner peripheral surface of the base layer 251 of the fixing film 25 and the guide portion 42b of the second flange 40b. As a result, the heat conduction filler intervenes in this contact region Sr.

[0098] The heat conduction filler is made of a material harder than the polyimide which is the material of the base layer 251 of the fixing film 25 in the present embodiment. Therefore, when the fixing film 25 slides and rotates with respect to the guide portion 42b of the second flange 40b, in the contact region SR, the heat conduction filler interposed between the inner peripheral surface of the base layer 251 and the guide portion 42b promotes the inner surface wear of the end portion in the width direction W of the base layer 251.

[0099] When inner surface wear of the base layer 251 of the fixing film 25 occurs, as the thickness of the base layer 251 decreases with an increase in the usage amount of the fixing film 25, the strength decreases, and buckling may occur with a lower approaching force. Therefore, it may prevent the extension of the service life. On the other hand, in order to suppress this buckling and satisfy the extension of the service life, it may be considered to increase the thickness of the base layer 251 of the fixing film 25. However, if the base layer 251 is made too thick, the thermal conductivity may decrease, the fixing performance may deteriorate, and the cost may also increase. Thus, in the conventional configuration, it may be difficult to achieve both high speed and long life.

[0100] Therefore, in the present embodiment, the base layer 251B of the fixing film 25B is projected toward the second side W2 in the width direction W to avoid wear of the elastic layer 252B. Hereinafter, the fixing film 25B of the present embodiment will be described with reference to FIGS. 9(a) to 10(b).

[0101] FIG. 9(a) is a cross-sectional view taken along the width direction W of the fixing film 25B in the present embodiment. In the present embodiment, the fixing film 25B is configured such that when the base layer 251B contacts the regulating surface 41b of the second flange 40b at the end portion 25bB on the second side W2 in the width direction W, the elastic layer 252B does not contact the regulating surface 41b. As shown in FIG. 9(a), the fixing film 25B has a protruding portion 254 at the end portion 25bB on the second side W2 in the width direction W, which is a portion composed only of the base layer 251B without having the elastic layer 252B and the surface layer 253B. In other words, in the present embodiment, at the end portion 25bB on the second side W2 of the fixing film 25B, there is a protruding portion 254 which is a portion where the base layer 251B is located more outward than the elastic layer 252B. That is, the protruding portion 254 protrudes in the right direction R on the second side W2 from the elastic layer 252 and can contact the regulating surface 41b of the second flange 40b in the width direction W.

[0102] Note that it is desirable that in any phase in the circumferential direction of the fixing film 25B, when the base layer 251B contacts the regulating surface 41b of the second flange 40b, the elastic layer 252B is configured not to contact the regulating surface 41b. Therefore, in the present embodiment, the protruding portion 254 is continuously provided over the entire circumferential direction of the fixing film 25B, and the end face 254a of the end portion 25bB in the width direction W of the fixing film 25B is composed of the end face of the protruding portion 254.

[0103] However, as long as the effects of the present embodiment can be fully exhibited, there may be a portion in the circumferential direction of the fixing film 25B where the protruding portion 254 is not provided. In the portion where the protruding portion 254 is not provided, the end faces of the ends in the width direction W of the fixing film 25B are constituted by the base layer 251 and the elastic layer 252 (and further the surface layer 253 in the present embodiment). The protruding portion 254 is preferably provided over 70% or more of the circumferential length of the fixing film 25B, more preferably 80% or more, still more preferably 90% or more, and most preferably over the entire area. If the protruding portion 254 is 70% or more of the circumferential length of the fixing film 25B, the elastic layer 252B can be more effectively prevented from contacting the regulating surface 41b than when it is less than 70%. In the present embodiment, since the protruding portion 254 is continuously provided over the entire circumferential direction of the fixing film 25B, it is provided in an area of 70% or more of the end face of the second side W2 of the fixing film 25B.

[0104] By using the fixing film 25B of the present embodiment, the inner surface wear of the fixing film 25 described above can be suppressed. Referring to FIG. 9(b), the reason will be described. FIG. 9(b) is a schematic cross-sectional side view of the vicinity of the second flange 40b in the fixing device 6B of the present embodiment as viewed from the upstream side in the conveying direction of the sheet S. In the figure, a cross-section along the width direction W of the fixing film 25B and the side surface of the second flange 40b are shown. Note that FIG. 9(b) shows a state where the fixing film 25B is shifted toward the right direction R in FIG. 5(a) and the fixing film 25B is in contact with the regulating surface 41b of the second flange 40b.

[0105] As shown in Fig. 9(b), in the sliding region ArB between the end of the fixing film 25B in the width direction W and the regulating surface 41b of the flange 40, the regulating surface 41b of the second flange 40b contacts only the base layer 251B of the fixing film 25B and does not contact the elastic layer 252B. That is, the protruding portion 254, by contacting the regulating surface 41b, regulates the elastic layer 252B from contacting the regulating surface 41b. As a result, the heat conduction filler contained in the elastic layer 252B is not shaved off or is sufficiently suppressed. As a result, in the contact region SR between the inner peripheral surface of the base layer 251B of the fixing film 25B and the guide portion 42b of the second flange 40b, the inner peripheral surface of the base layer 251B of the fixing film 25B and the guide portion 42b of the second flange 40b slide without the heat conduction filler intervening. Therefore, wear of the inner peripheral surface of the end portion 25bB in the width direction W of the fixing film 25B can be suppressed.

[0106] Thus, according to the present embodiment, wear of the inner surface of the fixing film 25B can be suppressed, and even when a pulling force due to temperature rise in the non-paper-passing portion Ar2 is generated, buckling of the fixing film 25B can be prevented. As a result, a long life of the fixing film 25B can be realized.

[0107] [Length of the protruding portion] Next, the setting of the protruding length of the protruding portion 254 will be described. Fig. 10(a) is a cross-sectional side view of the vicinity of the second flange 40b in the fixing device 6B of the present embodiment as viewed from the upstream (front side) in the sheet S conveyance direction. The figure shows a cross-section along the width direction W of the fixing film 25B and the side surfaces of the second flange 40b and the opposing roller 61. Note that Fig. 10(a) shows a state in which the fixing film 25B is pulled to the right direction R and the fixing film 25B is in contact with the regulating surface 41b of the second flange 40b on the right side.

[0108] The length of the protruding portion 254 in the width direction W of the fixing film 25B (hereinafter referred to as the protruding length) is indicated by the protruding length L1 in Fig. 10(a). Note that the protruding length L1 is represented by the value (initial value) at the initial stage of use (when new) of the fixing film 25B. The protruding length L1 is set so that, for example, even considering the expansion of the elastic layer 252B due to heating or the wear from the end face of the base layer 251B accompanying the increase in the usage amount, the elastic layer 252B does not protrude outside the base layer 251B with respect to the width direction W of the fixing film 25B.

[0109] From such a viewpoint, it is preferable to set the protruding length L1 to 0.1 mm or more. If it is 0.1 mm or more, the elastic layer 252B can be made to contact the regulating surface 41b less effectively than in the case of less than 0.1 mm. Also, from the above viewpoint, it is more preferable to set the protruding width to 0.5 mm or more. The protruding length L1 can be arbitrarily set in consideration of the life of the fixing film 25B and the like. For example, the longer the life of the fixing film 25B used in the fixing device 6B, the larger the protruding length L1 may be set. However, from the viewpoints of the mechanical strength and running stability of the fixing film 25B, etc., the protruding length L1 is preferably 10 mm or less. Therefore, in the present embodiment, the protruding amount of the protruding portion 254 on the second side W2 with respect to the elastic layer 252B is set to be 0.1 mm or more and 10 mm or less.

[0110] Also, regarding the width direction W of the fixing film 25B, the width of the portion having the elastic layer 252B of the fixing film 25B is larger than the maximum conveyance area Ar0 (see Fig. 3), and the maximum conveyance area Ar0 is accommodated inside the portion. In the present embodiment, at one end in the width direction W of the fixing film 25B, the protruding length L1 of the protruding portion 254 is set to 2 mm over the entire circumferential direction of the fixing film 25B.

[0111] In this embodiment, the protruding length L1 is 2 mm, and the length L2 of the guide portion 42b of the second flange 40b in the width direction W of the fixing film 25B is 4 mm. In this embodiment, even when at least the fixing film 25B is in contact with the first flange 40a, the guide portion 42b of the second flange 40b and the region where the elastic layer 252B of the fixing film 25B is located overlap in the width direction W of the fixing film 25B. That is, the protruding length L1, which is the protruding amount of the second side W2 with respect to the elastic layer 252B of the protruding portion 254, is shorter than the length L2 in the width direction W of the guide portion 42b. In this way, by overlapping the region where the elastic layer 252B of the fixing film 25B is located and the guide portion 42b of the second flange 40b, the running stability of the fixing film 25B can be kept high. That is, it is preferable to set the protruding length L1 to be smaller than the length L2 of the guide portion 42b of the second flange 40b in the width direction W of the fixing film 25B.

[0112] [Position of the end of the opposing roller] In this embodiment, on the second side W2 in the width direction W, the positional relationship between the end of the fixing film 25B and the end of the roller portion 26 of the opposing roller 61 is set as follows. As described above, in this embodiment, the roller portion 26 is composed of a conductive base portion 261, an elastic layer 262, and an electrically insulating release layer 263. Further, a potential of +300 V is applied to the base portion 261 using an AC power supply 27. On the other hand, the fixing film 25B is composed of a conductive base layer 251B, an electrically insulating elastic layer 252B, and a surface layer 253B. In this embodiment, the base layer 251B of the fixing film 25B is electrically grounded from the inner peripheral surface (see FIG. 2).

[0113] Thus, in order to obtain a good image, it is desirable to provide a predetermined potential difference between the base layer 251B of the fixing film 25B and the roller unit 26. That is, due to the electric field formed by this potential difference, the toner with negatively charged particles receives a force that presses it against the sheet S, so that scattering and offset of the toner can be suppressed. If discharge occurs between the base layer 251B of the fixing film 25B and the elastic layer 262 of the roller unit 26, the above potential difference cannot be properly maintained, and image defects may occur. In order to properly maintain the above potential difference, it is desirable to ensure a sufficient creepage distance between the elastic layer 262 of the opposing roller 61 and the base layer 251 of the protruding portion 254 of the fixing film 25B at the end portion in the width direction W of the fixing film 25B to suppress discharge.

[0114] Therefore, in the present embodiment, at the end portion of the second side W2 of the fixing film 25B, the positional relationship between the end portion of the fixing film 25B and the end portion of the roller unit 26 is set as follows. Here, as shown in FIG. 10(a), the region where the elastic layer 262 of the roller unit 26 and the base layer 251 of the protruding portion 254 of the fixing film 25B are adjacent is defined as the adjacent region ArC. At this time, in the adjacent region ArC, the end faces 255 of the elastic layer 252B and the surface layer 253 of the fixing film 25B are positioned outside (on the right direction R side) of the end face of the second end portion 26b of the elastic layer 262 of the roller unit 26. That is, the elastic layer 252B and the surface layer 253B of the fixing film 25B are configured to have an extension portion 256 that extends outside the end face of the second end portion 26b of the elastic layer 262 of the roller unit 26 by a length L3 in the width direction W of the fixing film 25B. That is, the end face 254a (see FIG. 9(a)) of the second side W2 of the protruding portion 254 is provided on the second side W2 rather than the end face of the second side W2 of the elastic layer 262 of the roller unit 26.

[0115] As a result, a sufficient creepage distance can be ensured between the elastic layer 262 of the roller portion 26 and the base layer 251B of the protruding portion 254 of the fixing film 25B, and the above potential difference can be appropriately maintained. The length L3 of the extension portion 256 can be appropriately set according to the potential applied to the base portion 261 of the roller portion 26, the potential difference between the base layer 251B of the fixing film 25B, etc., so as to sufficiently suppress the above-described discharge. In the present embodiment, the length L3 of the extension portion 256 is set to 2 mm over the entire circumferential direction of each of the fixing film 25B and the roller portion 26.

[0116] Considering the protruding length L1 of the protruding portion 254 and the length L3 of the extension portion 256 for ensuring the creepage distance, the end face 254a of the protruding portion 254 of the fixing film 25B is set to the right direction R by (L1 + L3) more than the end face of the second end portion 26b of the roller portion 26. In the present embodiment, it is set 4 mm to the right direction R.

[0117] [Protruding portion] The configuration of the fixing film 25B of the present embodiment is shown in FIG. 9(a). In the present embodiment, the protruding portion 254 of the fixing film 25B is configured to be provided only at one end portion on the second side W2 opposite to the paper passing reference position P0. FIG. 10(b) is a cross-sectional side view of the vicinity of the first flange 40a on the first side W1 in the fixing device 6B of the present embodiment as viewed from the upstream (front side) in the sheet S conveyance direction. Note that FIG. 10(b) shows a state where the fixing film 25B is in contact with the regulating surface 41a of the first flange 40a on the first side W1.

[0118] In the present embodiment, on the first side W1, in the sliding region ArB in FIG. 10(b), the regulating surface 41a of the first flange 40a and the elastic layer 252B of the fixing film 25B are in contact with each other. However, on the first side W1, even with this configuration, almost no inner surface wear of the base layer 251 of the fixing film 25B occurs. The reason therefor will be described below.

[0119] On the first side W1, since the attracting force due to the temperature rise of the non-paper-passing portion Ar2 does not occur, even when the elastic layer 252B and the regulating surface 41a of the first flange 40a slide, the heat conduction filler contained in the elastic layer 252B is not scraped off or is sufficiently suppressed. As a result, in the contact region SL between the inner peripheral surface of the base layer 251B of the fixing film 25B and the guide portion 42a (see FIG. 3) of the first flange 40a, the inner peripheral surface of the base layer 251B of the fixing film 25B and the guide portion 42a of the first flange 40a slide without the heat conduction filler intervening therebetween. Therefore, on the first side W1, wear does not occur on the inner peripheral surface of the end portion of the fixing film 25B.

[0120] Further, the fixing film 25B of the present embodiment also has an extension portion 256 extending outward (leftward L side) in the width direction W by a length L3 from the end surface of the end portion 26a of the elastic layer 262 of the opposing roller 61 on the first side W1 with respect to the width direction W. Here, the length L3 should be set to ensure the creeping distance between the elastic layer 262 of the opposing roller 61 and the base layer 251B of the fixing film 25B, similar to the second side W2. Therefore, it can be appropriately set according to the potential difference between the potential applied to the base 261 of the roller portion 26 and the base layer 251B of the fixing film 25B so as to sufficiently suppress discharge. In the present embodiment, on the first side W1, the length L3 of the extension portion 256 is set to 2 mm over the entire circumferential direction of each of the fixing film 25B and the roller portion 26.

[0121] [Examples and Comparative Examples] A comparison was made using Example 3 to which the fixing film 25B of the present embodiment was applied, Comparative Example 3 to which the fixing film 125 shown in FIG. 11(a) was applied, and Comparative Example 4 to which the fixing film 225 shown in FIG. 11(b) was applied.

[0122] Comparative Examples 3 and 4 will be described. FIGS. 11(a) and (b) are cross-sectional views along the width direction W of the fixing films 125 and 225 used in the configurations of Comparative Examples 3 and 4. FIG. 11(a) shows the configuration of the fixing film 125 of Comparative Example 3, which has protrusions 1254 at both ends 125a and 125b of the fixing film 125. FIG. 11(b) shows the configuration of the fixing film 225 of Comparative Example 4, which is configured without providing protrusions at both ends 225a and 225b of the fixing film 225.

[0123] In the fixing film 125 of Comparative Example 3, it is configured to have protrusions 1254 at both ends in the width direction W. For this reason, heat shaving of the heat conductive filler due to sliding between the elastic layer 252 of the fixing film 125 and the regulating surfaces 41a and 41b of the flanges 40a and 40b at both ends is eliminated or sufficiently suppressed, so that internal surface wear of the fixing film 125 is suppressed. However, on the other hand, the fixing film 125 of Comparative Example 3 has demerits in terms of the manufacturing procedure and the size of the fixing device compared to the fixing film 25B of Example 3. Regarding the manufacturing procedure, in the fixing film 125 of Comparative Example 3 compared to the fixing film 25B of Example 3, there is a demerit that the procedure for forming the protrusion 1254 on the first side W1 increases, resulting in a cost increase.

[0124] Also, in the fixing film 125 of Comparative Example 3, there is a demerit that the size of the fixing device increases. The reason will be explained below. In the fixing film 125 of Comparative Example 3, it is necessary to appropriately set the protrusion length L1 of the protrusion 1254 and the length L3 of the extension part 256 (see FIGS. 10(a) and (b)) at both ends 125a and 125b. In Comparative Example 3, at both ends 125a and 125b of the fixing film 125, the end face of the fixing film 125 needs to be set (L1 + L3) outside in the width direction W with respect to the end face of the roller part 26. That is, in the fixing film 125 of Comparative Example 3, it is necessary to make it about 2×(L1 + L3) larger in the width direction W with respect to the roller part 26. For example, when L1 = L3 = 2 mm is set, it is necessary to increase the width of the fixing film 125 by 8 mm.

[0125] On the other hand, in the fixing film 25B of Example 3, at the end 25bB of the second side W2, the protruding portion 254 is provided, but at the end 25aB of the first side W1, the protruding portion 254 is not provided (see Fig. 9(a)). As a result, the end face 25a of the second side W2 of the fixing film 25B of Example 3 needs to be set (L1 + L3) outward in the width direction W, and on the first side W1, it needs to be set L3 outward. That is, the fixing film 25B of Example 3 needs to be made about (L1 + 2×L3) larger than the roller portion 26 in the width direction W. Therefore, the fixing film 25B of Example 3 can be set smaller by about L1 than the fixing film 125 of Comparative Example 3 in the width direction W. In Example 3, L1 = L3 = 2 mm, and it is configured to be 6 mm larger than the roller portion 26 in the width direction W.

[0126] That is, the fixing film 25B of Example 3 can be made 2 mm smaller than the fixing film 125 of Comparative Example 3 in the width direction W. The regulating surfaces 41a and 41b of the flanges 40a and 40b are set to regulate the movement of the fixing film in the width direction W. For this reason, the interval with respect to the fixing film is set with a predetermined clearance with respect to the length of the fixing film in the width direction W so that the fixing film does not stretch when thermally expanded. Therefore, the interval between the flanges 40a and 40b is set according to the length of the fixing film, and the interval between the flanges 40a and 40b of Example 3 can be set 2 mm smaller than that of Comparative Example 3. As a result, the fixing device 6B of Example 3, and thus the image forming apparatus 100, can be made smaller than Comparative Example 3.

[0127] Next, in the fixing film 225 of Comparative Example 4, no protrusion is formed in the width direction W of the base layer 251. As a result, at the end 225b of the second side W2, while receiving the pulling force due to the temperature rise of the non-printing portion Ar2, the elastic layer 252 of the fixing film 225 and the regulating surface 41b of the second flange 40b slide. Thereby, the heat conduction filler contained in the elastic layer 252 is scraped off, and inner surface wear of the base layer 251 of the fixing film 225 occurs. For this reason, it hinders the extension of the service life of the fixing film 225. Below, the results of the durability test comparing the durability performances of Example 3 and Comparative Example 4 are shown.

[0128] [Print Durability Test] To compare the durability performances of Example 3 and Comparative Example 4, a comparative test between Example 3 and Comparative Example 4 was conducted. In the configuration of Example 3, the fixing film 25B shown in FIG. 9(a) was used. In the configuration of Comparative Example 4, the fixing film 225 shown in FIG. 11(b) was used. The configuration of the image forming apparatus of Comparative Example 4 is substantially the same as the configuration of the image forming apparatus 100 of the present embodiment except for the above points. Regarding Comparative Example 4 as well, the same reference numerals are given to the corresponding components in the present embodiment for explanation.

[0129] In Example 3 and Comparative Example 4, the test was conducted under the following conditions. The pressing force between each fixing film and the roller unit 26 was 186.2 N (19 kgf). The width (nip width) of the fixing nip N2 in the sheet conveyance direction DF was 9 mm. The test environment was a temperature of 23 degrees and a relative humidity of 50%. As the evaluation sheet, CS068 (A4 size 68 g / cm 2 ) and PB PAPER (A5 size 68 g / cm 2 ) were appropriately mixed and used. Under the above conditions, in Example 3 and Comparative Example 4, a paper passing durability test of printing 200,000 sheets with a low print rate character image was conducted to evaluate the durability.

[0130] Table 6 shows the evaluation results of the durability test. The evaluation criteria for durability are as follows. When there is no problem with the durability of the fixing film and it is good, it is marked as "○ (good)". When there are problems related to the durability of the fixing film that may cause practical problems, it is marked as "× (bad)". The evaluation criteria for fixability are marked as "○ (good)" when there is no problem and it is good, and "× (bad)" when the fixability is insufficient.

Table 6

[0131] As shown in Table 6, in Comparative Example 4, when 100,000 prints were made, buckling occurred at the second-side end 225b in the width direction W of the fixing film 225. As a result, the running of the fixing film 225 became unstable and image defects occurred, so the paper-passing durability test was aborted. It was found that the reason for the buckling at the second-side end 225b in the width direction W2 of the fixing film 225 was the inner surface wear of the fixing film 225. That is, in Comparative Example 4, the thickness of the base layer 251 at the second-side end 225b of the fixing film 225 when 100,000 prints were made had become thinner from the initial 70 μm to about 40 μm. Therefore, when the fixing film 225 abutted against the regulating surface 41b of the second flange 40b, the fixing film 225 could not withstand the lateral force in the width direction W (right direction R) it received, and it is considered that buckling occurred at the end 225b in the width direction W of the fixing film 225. Thus, it was difficult to satisfy the durability in Comparative Example 4.

[0132] In Example 3, no problems related to durability and fixability occurred through 200,000 prints. Therefore, according to the configuration of Example 3, it was confirmed that in the image forming apparatus 100 having a conveyance configuration with a single-side reference, it is possible to achieve both a long service life, high speed, and miniaturization.

[0133] As described above, according to the fixing device 6B of the present embodiment, since the protruding portion 254 is provided at the end of the second side W2 of the fixing film 25B, even if a pulling force of the fixing film 25B occurs, the inner surface wear of the fixing film 25B can be reduced and its long life can be achieved. As a result, the inner surface wear due to the pulling force in the fixing film 25B can be reduced, and a fixing device 6B capable of coping with high speed and long life can be realized. Further, according to the present embodiment, by using the fixing device 6B shown in the present embodiment, the inner surface wear of the fixing film 25B can be suppressed to achieve long life, and miniaturization and cost reduction can be achieved. It can be said that the configuration of the present embodiment is suitable for a high-speed machine or a long-life machine that requires high durability for the fixing film 25B.

[0134] In the present embodiment, the case where the protruding portion 254 is provided at the end 25bB of the second side W2 of the fixing film 25B and not provided at the end 25aB of the first side W1 has been described, but the present invention is not limited to this. For example, the protruding portion may be provided at the end 25aB of the first side W1. In this case, the protruding amount of the protruding portion at the end 25aB of the first side W1 may be larger than, the same as, or smaller than the protruding amount of the protruding portion 254 at the end 25bB of the second side W2. However, from the viewpoint of miniaturization, it is preferable that the protruding amount of the protruding portion at the end 25aB of the first side W1 is smaller than the protruding amount of the protruding portion 254 at the end 25bB of the second side W2.

[0135] <The Fourth Embodiment> Next, a fourth embodiment of the present invention will be described. The fourth embodiment is configured by modifying the heater holder 29 of the first embodiment. Therefore, the same configurations as those in the first embodiment will be omitted from the drawings or described with the same reference numerals in the drawings.

[0136] When feeding a small-sized sheet with a fixing device based on one-side reference, the fixing film 25 may be shifted in the width direction W due to the temperature rise in the non-paper-feeding part Ar2. In addition to the shift of the fixing film 25, the longitudinal shape of the fixing film 25 may change due to the influence of the temperature rise in the non-paper-feeding part Ar2. There is a risk that the shifting force may deteriorate due to this shape change, and there is also a risk that the fixing film 25 may come into contact with the members in the internal space, resulting in heat being taken away and fixing failure. The mechanism of occurrence of problems due to the change in the longitudinal shape of the fixing film 25 will be described below using a comparison between the case of feeding a letter-sized sheet, which is the maximum width that can be fed, and an A6-sized sheet with a narrow width.

[0137] Fig. 12(a) shows a schematic diagram of the paper-feeding areas of a letter-sized sheet and an A6-sized sheet S. Fig. 12(b) shows the surface temperature distribution in the width direction W of the opposing roller 61 when the letter size and the A6 size are continuously fed. In the letter size, the surface temperature of the roller part 26 is substantially uniform within the maximum conveyance area Ar0 (the paper-feeding part of the letter-sized sheet). In the A6 size, due to the temperature rise in the non-paper-feeding part Ar2, the temperature in the non-paper-feeding part Ar2 is higher than that in the paper-feeding part Ar1. At this time, when the configuration of the roller part 26 is such that the outer diameter in the width direction W of the base part 261 shown in Fig. 6(a) is uniform and the outer diameter shape is a left-right symmetric inverse crown shape shown in Fig. 6(b), the conveyance speed in the width direction W of the roller part 26 has a distribution as shown in Fig. 12(c) for each size.

[0138] As shown in Fig. 12(c), in the letter size, since the temperature of the roller part 26 is substantially uniform in the width direction W, the conveyance speed is also substantially uniform in the width direction W. In the A6 size, due to the temperature rise in the non-paper-feeding part Ar2, the conveyance speed in the width direction W also has a distribution due to the temperature distribution in the width direction W of the roller part 26. This is because the elastic layer 262 of the roller part 26 thermally expands according to the temperature, so the outer diameter in the non-paper-feeding part Ar2 becomes larger than that in the paper-feeding part Ar1, resulting in an outer diameter difference and a peripheral speed difference, which leads to a conveyance speed difference. The conveyance speed difference in the width direction W may affect the shape of the fixing film 25 in the width direction W.

[0139] Fig. 13(a) shows a cross-sectional view taken from above of the state of being cut along line I-I in Fig. 12(a) when the letter-sized paper in Comparative Example 5 is continuously fed. The heater holder 29 in Comparative Example 5 is provided with an upstream guide portion 291 provided on the upstream side in the sheet conveyance direction DF and a downstream guide portion 292 provided on the downstream side, and guides the rotation of the fixing film 25 from the inside. As shown in Fig. 12(c), since the conveyance speed distribution in the width direction W of the roller portion 26 is substantially uniform, the shape of the fixing film 25 in the width direction W is also substantially straight as shown in Fig. 13(a).

[0140] Fig. 14(a) shows a cross-sectional view taken along line II-II in Fig. 12(a) when the letter-sized sheet in Comparative Example 5 is continuously fed. The fixing film 25 is not in contact with the stay 22, the upstream guide portion 291 of the heater holder 29, or the downstream guide portion 292, which are the built-in components thereof.

[0141] Next, Fig. 13(b) shows a cross-sectional view taken from above of the cross-section cut along line I-I in Fig. 12(a) when the A4-sized sheet in Comparative Example 5 is continuously fed. As shown in Fig. 12(c), since the conveyance speed of the roller portion 26 is faster in the non-paper-feed portion Ar2 than in the paper-feed portion Ar1, the fixing film 25 bulges downstream in the non-paper-feed portion Ar2. The posture of the fixing film 25 is the same as the state with a tolerance angle with respect to the roller portion 26.

[0142] Here, the force acting on the fixing film 25 when a tolerance angle is provided between the fixing film 25 and the roller portion 26 will be described with reference to Fig. 15. The fixing film 25 receives a force F0 from the roller portion 26 due to frictional resistance. Since this force F0 can be decomposed into a component force F1 in the short-side direction (radial direction) of the fixing film 25 and a component force F2 in the width direction W, in the width direction W, it receives a force toward the second side W2, that is, the second flange 40b side. Therefore, in the fixing film 25 shown in Fig. 13(b), the biasing force toward the side with a faster conveyance speed due to the temperature rise in the non-paper-feed portion Ar2 and the biasing force generated by the tolerance angle act together, making it easier for lateral buckling to occur.

[0143] Next, a cross-sectional view taken along line II-II when the A6-size sheet in Comparative Example 5 is continuously fed is shown in FIG. 14(b). Since the fixing film 25 bulges on the downstream side in the sheet conveyance direction DF, the inner peripheral surface of the fixing film 25 contacts the stay 22 on the upstream side. When contacting the stay 22 having a large heat capacity, the temperature of the fixing film 25 may significantly decrease, leading to poor fixing.

[0144] This phenomenon is likely to occur when the clearance between the fixing film 25 and the stay 22 becomes narrow. For example, when the outer diameter of the fixing film 25 is reduced for the purpose of reducing the size of the fixing device, or when the thickness or height of the stay 22 is increased to increase the rigidity of the stay 22. Also, when the base layer 251 or the elastic layer 252 of the fixing film 25 is thin and the strength of the fixing film 25 is low, the amount of deformation of the fixing film 25 becomes large even with the same conveyance speed difference in the width direction W of the roller unit 26, making the above phenomenon likely to occur. Further, when the temperature difference between the paper-passing portion Ar1 and the non-paper-passing portion Ar2 of the roller unit 26 becomes large, the conveyance speed difference in the width direction W of the roller unit 26 becomes large, and the amount of deformation of the fixing film 25 becomes large, making the above phenomenon likely to occur.

[0145] Therefore, in the present embodiment, a protruding guide portion 293 that protrudes upstream in the sheet conveyance direction DF from the upstream guide portion 291 is provided upstream of the heater holder 29C to suppress contact of the fixing film 25 with internal components. Hereinafter, the heater holder 29C of the present embodiment will be described with reference to FIGS. 16(a) to 17(b).

[0146] FIG. 16(a) is a cross-sectional view taken from above of the state cut along line I-I of FIG. 12(a) when a letter-size sheet in the fourth embodiment is continuously fed. The configuration of the heater holder 29C is different from that of Comparative Example 5. In the fourth embodiment, a protruding guide portion 293 for preventing film deformation is provided on the upstream side in the sheet conveyance direction DF of the heater holder 29C and on the second side W2, and the protruding amount upstream is increased compared to the upstream guide portion 291.

[0147] [Heater Holder and Stay] As shown in FIGS. 16(a) and 17(a), the heater holder 29C has a heater holding portion 290 that holds the heater 20, an upstream guide portion 291, a downstream guide portion 292, and a protruding guide portion 293 that are integrally provided on the heater holding portion 290. In the present embodiment, the heater holder 29C is integrally formed of resin. However, the present invention is not limited to this, and the heater holder 29C may be formed by integrating separate members.

[0148] The upstream guide portion 291 is an example of a first guide portion, is provided on the first side W1 in the width direction W, and can guide the fixing film 25 upstream in the sheet conveyance direction DF from the fixing nip N2. The downstream guide portion 292 is provided over the entire area of the heater holder 29C in the width direction W, and can guide the fixing film 25 downstream in the sheet conveyance direction DF from the fixing nip N2. The protruding guide portion 293 is an example of a second guide portion, is provided on the second side W2 in the width direction W, and can guide the fixing film 25 upstream in the sheet conveyance direction DF from the fixing nip N2.

[0149] The stay 22 has a facing portion 22a that faces the inner peripheral surface of the fixing film 25. Here, the orthogonal direction orthogonal to the sheet conveyance direction DF and the width direction W is defined as the vertical direction. The facing portion 22a is a part of the stay 22, is disposed at a position spaced apart from the fixing nip N2 more than the upstream guide portion 291 and the protruding guide portion 293 in the vertical direction, and is a portion that faces the upstream inner peripheral surface of the fixing film 25 in the sheet conveyance direction DF.

[0150] In the present embodiment, as shown in FIG. 17(a), in the sheet conveyance direction DF, the distance L4 from the opposing portion 22a of the stay 22 to the upstream end of the protruding guide portion 293 is longer than the distance L5 from the opposing portion 22a to the upstream end of the upstream guide portion 291. As a result, when the fixing film 25 on the second side W2 attempts to deform downstream in the sheet conveyance direction DF, the protruding guide portion 293 contacts the fixing film 25 when the amount of deformation of the fixing film 25 is smaller than when only the upstream guide portion 291 is provided on the second side W2. For this reason, the protruding guide portion 293 comes into contact before the inner peripheral surface of the fixing film 25 abuts against the opposing portion 22a, suppressing further deformation of the fixing film 25, and thus it is possible to prevent the inner peripheral surface of the fixing film 25 from contacting the opposing portion 22a.

[0151] FIG. 17(a) shows a cross-sectional view taken along line II-II of FIG. 12(a) when a letter-sized sheet is continuously fed. The protruding guide portion 293 protrudes upstream in the sheet conveyance direction DF compared to the upstream guide portion 291 of Comparative Example 5 shown in FIG. 13(a), and is approaching the fixing film 25 but is not in contact. In FIG. 17(a), the height of the protruding guide portion 293 is made higher than that of the upstream guide portion 291 of Comparative Example 5, but these heights may be the same.

[0152] FIG. 16(b) shows a cross-sectional view taken from above of the state cut along line I-I of FIG. 12(a) when an A6-sized sheet is continuously fed in the fourth embodiment. Temperature rise occurs in the non-paper-feed portion Ar2, the conveyance speed of the roller portion 26 on the non-paper-feed portion Ar2 side becomes faster, and the fixing film 25 is about to bulge downstream in the sheet conveyance direction DF, but the protruding guide portion 293 supports the fixing film 25 on the upstream side, preventing deformation. For this reason, the tolerance angle between the fixing film 25 and the roller portion 26 is not so large, preventing an increase in the pulling force due to the tolerance angle.

[0153] Figure 17(b) is a cross-sectional view taken along line II-II of Fig. 12(a) when a sheet of A6 size is continuously fed in the fourth embodiment. By supporting the fixing film 25 on the inner peripheral side by the protruding guide portion 293 on the upstream side in the sheet conveyance direction DF, it is possible to prevent the fixing film 25 from contacting the stay 22 having a large heat capacity. The protruding guide portion 293 is made of the same material as the heater holder 29C, and for example, heat-resistant resins such as liquid crystal polymer, phenolic resin, PPS, and PEEK are used. Since these resins have a lower heat capacity than the stay 22, even if they come into contact, they do not take much heat, and it is possible to suppress a significant deterioration in fixing performance.

[0154] In the present embodiment, the contact surface of the protruding guide portion 293 with the fixing film 25 is formed in a flat shape. However, it is not limited to being flat, and grooves, ribs, etc. may be provided on the surface of the protruding guide portion 293 in order to reduce the contact area with the fixing film 25. Also, in the present embodiment, five protruding guide portions 293 are arranged side by side on the tip side of the second side W2. However, it is not limited to five, and other quantities may be used. That is, the number and position are not limited to those shown in the figure, and any configuration may be used as long as it can suppress deformation of the fixing film 25.

[0155] Also, in the present embodiment, the heater holder 29C also has an upstream guide portion 291a on the second side W2 in the width direction W. This upstream guide portion 291a is an example of a third guide portion, and is provided separately from the protruding guide portion 293 in the width direction W. And in the sheet conveyance direction DF, the distance L5 from the opposing portion 22a to the upstream end of the upstream guide portion 291a is set shorter than the distance L4 from the opposing portion 22a to the upstream end of the protruding guide portion 293. That is, it is not necessary for all the guide portions provided on the second side W2 of the heater holder 29C in the width direction W to be the protruding guide portion 293, and a part of a plurality of guide portions including other upstream guide portions 291 is made to be the protruding guide portion 293. However, it is not limited to this, and all the guide portions provided on the second side W2 of the heater holder 29C in the width direction W may be made to be the protruding guide portion 293.

[0156] [Examples and Comparative Examples] A printing durability test was conducted using Example 4 to which the heater holder 29C of the present embodiment was applied and Comparative Example 5. In the printing durability test, a fixing film 25 with a varying thickness of the base layer 251 was prepared, and the fixing film 25 of each thickness was incorporated into a fixing device using Example 4 and Comparative Example 5, respectively. Then, the fixability and durability were evaluated when PB PAPER (A6 size, 68 g / cm 2 ) was passed continuously 5000 sheets at a speed of 75 sheets / min. The fixing films 25 used in the comparative test had a common thickness of 60 μm, 65 μm, and 70 μm for the base layer 251, a thickness of 250 μm for the elastic layer 252, and a thickness of 12 μm for the surface layer 253.

[0157] Table 7 shows the evaluation results of durability and fixability. The evaluation criteria for durability are as follows. When there is no problem with the durability of the fixing film 25 and it is good, it is marked as "○ (good)"; when there may be a problem related to the durability of the fixing film 25 that could cause a practical problem, it is marked as "× (bad)". Also, the evaluation criteria for fixability are marked as "○ (good)" when there is no problem and it is good, and "× (bad)" when the fixability is insufficient.

Table 7

[0158] In Comparative Example 5, for the fixing film 25 with a base layer thickness of 70 μm, there were no problems with both fixability and durability. For the fixing film 25 with a base layer thickness of 65 μm, there was no problem with durability, but the fixability deteriorated from the middle of the durability test. For the fixing film 25 with a base layer thickness of 60 μm, problems occurred with both fixability and durability.

[0159] The above results indicate that as the thickness of the base layer 251 of the fixing film 25 decreases, the strength of the fixing film 25 decreases, and as a result, the shape change in the width direction W of the fixing film 25 due to the temperature rise in the non-paper passage portion Ar2 becomes large. When the thickness of the base layer is 65 μm and 60 μm, the shape change of the fixing film 25 becomes large, and the inner peripheral surface of the fixing film 25 contacts the stay 22 by swelling on the downstream side in the sheet conveyance direction DF on the non-paper passage portion Ar2 side, resulting in fixing failure due to heat being taken away. Also, since the shape change is large and the tolerance angle with the roller portion 26 has become large, the biasing force due to the tolerance angle has also become large. When the thickness of the base layer was 65 μm, there was no problem with durability, but when the thickness of the base layer was 60 μm, the strength of the fixing film 25 decreased, resulting in biasing buckling at the end.

[0160] In Example 4, there were no problems with fixing performance and durability at all thicknesses of the base layer. This is because the shape change of the fixing film 25 due to the temperature rise in the non-paper passage portion Ar2 was supported from the inner peripheral surface side by the protruding guide portion 293, and contact of the fixing film 25 with the stay 22 was also prevented. Although the fixing film 25 is in contact with the protruding guide portion 293, since the heater holder 29C has a low heat capacity and does not take away much heat, there was no significant deterioration in fixing performance. Also, since the shape change is suppressed, it is possible to prevent the tolerance angle with the roller portion 26 from becoming large, and the biasing force can also be suppressed to some extent. As a result, it was possible to prevent the occurrence of biasing buckling due to durability even when the thickness of the base layer was 60 μm.

[0161] In this comparative experiment, the degree of shape change was changed by varying the strength by changing the thickness of the base layer of the fixing film 25. However, this method is not limited, and similar results can be obtained in configurations where the temperature difference between the paper passage portion Ar1 and the non-paper passage portion Ar2 is increased or the clearance between the fixing film 25 and the stay 22 is narrowed.

[0162] As described above, according to the heater holder 29C of the present embodiment, by providing the protruding guide portion 293, the inner peripheral surface of the fixing film 25 is supported from the inside to suppress shape changes, so that it is possible to prevent the inner peripheral surface of the fixing film 25 from contacting the opposing portion 22a. As a result, even in a configuration where the amount of deformation of the fixing film 25 tends to increase due to thinning of the fixing film 25 or the like, it is possible to suppress the occurrence of fixing defects and lateral buckling, and a fixing device capable of corresponding to high speed and long life can be realized.

[0163] <Fifth Embodiment> Next, a fifth embodiment of the present invention will be described. The fifth embodiment is configured by modifying the stay 22 of the fourth embodiment. For this reason, for the same configurations as those in the fourth embodiment, illustration is omitted or the same reference numerals are given in the drawings for explanation.

[0164] In the present embodiment, the shape change of the fixing film 25 is suppressed by a configuration different from that of the fourth embodiment, and fixing defects and lateral buckling are suppressed. The configuration of the present embodiment will be described with reference to FIGS. 18 to 19(b). FIG. 18 is a cross-sectional view taken from above of a state cut along line I-I of FIG. 12(a) when an A6-size sheet is continuously passed through in the present embodiment. In the present embodiment, with respect to the fixing device of Comparative Example 5, the heating unit 60D of the fixing device 6D has a cover 50 for preventing contact with the second side W2 of the stay 22.

[0165] FIG. 19(a) shows a cross-sectional view taken along line II-II of FIG. 12(a) when a letter-sized sheet is continuously fed. The cover 50 is not in contact with the fixing film 25 when the letter-sized sheet is fed. FIG. 19(b) shows a cross-sectional view taken along line II-II of FIG. 12(a) when an A6-sized sheet is continuously fed. By supporting the fixing film 25 from the inner peripheral surface side with the cover 50, deformation of the fixing film 25 can be suppressed. Similar to the fourth embodiment, since the fixing film 25 does not directly contact the stay 22, it is possible to prevent the occurrence of poor fixing. Also, as shown in FIG. 18, since the shape change of the fixing film 25 is suppressed, it is possible to prevent an increase in the biasing force due to an increase in the tolerance angle.

[0166] In the present embodiment, the heater holder 29 has a heater holding portion 290 that holds the heater 20, and an upstream guide portion 291 and a downstream guide portion 292 that are integrally provided on the heater holding portion 290. In the present embodiment, it does not have the protruding guide portion 293 in the fourth embodiment. Also, the stay 22 has an opposing portion 22a similar to the fourth embodiment. In the present embodiment, only one cover 50 is provided. Also, the cover 50 is provided along the upper surface of the stay 22 from upstream of the opposing portion 22a toward the downstream in the sheet conveyance direction DF, and further provided downward along the downstream side surface of the stay. The surface of the cover 50 that contacts the fixing film 25 is a flat surface.

[0167] It is provided between the opposing portion 22a of the stay 22 and the inner peripheral surface on the upstream side of the fixing film 25 in the sheet conveyance direction DF. Thereby, even if the fixing film 25 is deformed, it is possible to prevent the fixing film 25 from directly abutting on the opposing portion 22a. The cover 50 is supported by the stay 22. Also, the cover 50 is made of a material having a lower thermal conductivity than the stay 22, such as resin. Thereby, it is possible to suppress heat from escaping compared to the case where the fixing film 25 directly abuts on the opposing portion 22a.

[0168] As described above, according to the fixing device 6D of the present embodiment, by providing the cover 50, the fixing film 25 is supported from the inside to suppress shape changes, and it is possible to prevent the inner peripheral surface of the fixing film 25 from contacting the opposing portion 22a. As a result, even in a configuration where the amount of deformation of the fixing film 25 tends to increase due to thinning of the fixing film 25 or the like, it is possible to suppress the occurrence of fixing defects and local buckling, and to realize a fixing device capable of corresponding to high speed and long life.

[0169] In the present embodiment, an example in which one cover 50 is arranged on the second side W2 is shown, but the present invention is not limited to this, and a plurality of covers 50 may be arranged. Further, the surface of the cover 50 that contacts the fixing film 25 is not limited to a flat surface, and grooves may be provided for the purpose of reducing the contact area.

[0170] <Sixth Embodiment> Next, a sixth embodiment of the present invention will be described. The sixth embodiment is configured by modifying the second flange 40b of the first embodiment. For this reason, regarding the same configuration as that of the first embodiment, illustration is omitted or the same reference numerals are given in the drawings for explanation.

[0171] In the fourth and fifth embodiments, in order to prevent fixing defects due to contact with the stay 22 and an increase in the local force due to a tolerance angle with the roller portion 26 caused by a shape change of the fixing film 25 due to a temperature rise in the non-paper-passing portion Ar2. However, the local force itself caused by the occurrence of a conveyance speed difference due to a temperature rise in the non-paper-passing portion Ar2 could not be suppressed. Therefore, in the present embodiment, by using the shift flange unit 43 for the second flange 40bE on the second side W2, the local force generated due to a temperature rise in the non-paper-passing portion Ar2 is reduced.

[0172] [Shift Flange Unit] The shift flange unit 43 of the fixing device 6E of the present embodiment will be described with reference to FIGS. 20(a) to 21(b). The shift flange unit 43 includes a second flange 40bE, a support portion 44, and a biasing spring 45. The support portion 44 is fixed to a frame (not shown) of the fixing device 6E. The second flange 40bE is movably engaged with the support portion 44, and a gap with a slight distance G0 in the sheet conveyance direction DF is provided between the second flange 40bE and the support portion 44.

[0173] The second flange 40bE has a regulating surface 41bE facing the end surface of the second side W2 of the fixing film 25 and a guide portion 42bE facing the inner peripheral surface of the end portion of the fixing film 25. When the fixing film 25 moves closer in the width direction W, the end surface of the fixing film 25 abuts against the regulating surface 41bE. The guide portion 42bE also has a function of guiding the inner peripheral surface of the fixing film 25 when the fixing film 25 rotates.

[0174] The second flange 40bE has a convex portion 46 that protrudes on the second side W2 in the width direction W and has a tip surface 46a facing in a direction oblique to the width direction W. The tip surface 46a of the convex portion 46 is inclined such that the second side W1 in the width direction W is upstream in the sheet conveyance direction DF. The support portion 44 has a concave portion 44a that is recessed from the end surface on the first side W1 in the width direction W toward the second side W2 and has a bottom surface 44b facing in a direction oblique to the width direction W. The bottom surface 44b of the concave portion 44a is inclined such that the second side W1 in the width direction W is upstream in the sheet conveyance direction DF. That is, the support portion 44 has the bottom surface 44b of the concave portion 44a as an example of a cam surface, and the second flange 40bE has the tip surface 46a of the convex portion 46 that abuts against and slides on the bottom surface 44b as an example of a slider.

[0175] In addition, in this embodiment, the case where the tip surface 46a of the convex portion 46 is an inclined surface that slides on the bottom surface 44b has been described, but the present invention is not limited to this. For example, the tip of the convex portion 46 may have a curved surface shape or a spherical surface shape, or a rotatable rotating body may be provided to slide with respect to the bottom surface 44b. Further, in this embodiment, the case where a slider is provided on the second flange 40bE and a cam surface is provided on the support portion 44 has been described, but the present invention is not limited to this, and the reverse relationship may also be applicable. That is, either one of the second flange 40bE and the support portion 44 may have a cam surface, and the other of the second flange 40bE and the support portion 44 may have a slider that abuts against and slides on the cam surface.

[0176] When the second flange 40bE and the support portion 44 are combined, the convex portion 46 of the second flange 40bE fits into the concave portion 44a of the support portion 44. With this configuration, the second flange 40bE is slidably held along the concave portion 44a of the support portion 44. The biasing spring 45 is an example of a biasing portion, and is provided between the second flange 40bE and the support portion 44, and is a compression coil spring that biases the second flange 40bE in a direction away from the support portion 44 (the first side W1).

[0177] Next, the operation of the shift flange unit 43 will be described. FIG. 20(a) shows a state when no force is generated toward the fixing film 25. At this time, the biasing spring 45 presses the second flange 40bE toward the first side. At this time, there is a gap between the regulating surface 41bE of the second flange 40b and the end surface of the fixing film 25. Further, there is a gap between the tip surface of the convex portion 46 of the second flange 40bE and the bottom surface of the concave portion 44a of the support portion 44.

[0178] When a force F10 toward the fixing film 25 is generated due to, for example, a temperature increase in the non-paper-passing portion Ar2 in this state, the fixing film 25 abuts against the regulating surface 41bE. When the force F10 toward the fixing film 25 is stronger than the pressing force of the biasing spring 45, the fixing film 25 pushes the regulating surface 41bE toward the support portion 44. When the tip surface of the convex portion 46 of the second flange 40bE reaches the bottom surface of the concave portion 44a of the support portion 44, the tip surface of the convex portion 46 slides along the bottom surface of the concave portion 44a.

[0179] As shown in FIG. 20(b), when the tip surface of the convex portion 46 of the second flange 40bE slides on the bottom surface of the concave portion 44a of the support portion 44 and abuts against the sheet conveyance direction DF, it means that the second flange 40bE has moved upstream by a distance G0 in the sheet conveyance direction DF.

[0180] Here, the position of the second flange 40bE in FIG. 20(a) is defined as the first position, and the position of the second flange 40bE in FIG. 20(b) is defined as the second position. The second flange 40bE is movable between the first position and the second position. The second position is such that the guide portion 42bE is located upstream in the sheet conveyance direction DF from the first position. When the regulating surface 41bE is pressed against the second side W2 by the fixing film 25 when the second flange 40bE is located at the first position, the second flange 40bE moves from the first position to the second position. Also, the position of the regulating surface 41bE when the second flange 40bE is located at the second position is located on the second side W2 from the position of the regulating surface 41bE when the second flange 40bE is located at the first position. Further, the bottom surface 44b and the tip surface 46a guide the second flange 40bE toward the second position by receiving a pressing force that resists the biasing force from the biasing spring 55 when the regulating surface 41bE of the second flange 40bE located at the first position is pressed from the fixing film 25 toward the second side W2. Here, in the present embodiment, the case where the guide portion 42bE and the regulating surface 41bE are integrally formed and move integrally has been described, but the present invention is not limited thereto, and these may be separate members that move independently. In this case, for example, an actuator or the like may be used to move the guide portion 42bE and the regulating surface 41bE independently.

[0181] When the second flange 40bE moves a distance G0 upstream in the sheet conveyance direction DF, the fixing film 25 is displaced upstream by only the distance G0 on the second side W2, creating a tolerance angle with respect to the roller unit 26. Here, with reference to FIG. 15, the effect of the fixing film 25 on the second side W2 being displaced upstream in the sheet conveyance direction DF will be described. In FIG. 15, it is the first side W1 where the fixing film 25 is displaced upstream in the sheet conveyance direction DF. The fixing film 25 receives a force F0 from the roller unit 26, and this force F0 can be decomposed into a component force F2 acting in the longitudinal direction of the fixing film 25 and a component force F1 acting in the short-side direction of the fixing film 25. Therefore, when creating a tolerance angle between the fixing film 25 and the roller unit 26, it can be seen that a component force F2 acts on the fixing film 25 in a direction away from the first flange 40a that has been displaced upstream in the sheet conveyance direction DF.

[0182] FIG. 21(a) is a cross-sectional view taken from above of the state cut along the line I-I of FIG. 12(a) when a letter-sized sheet is continuously fed through in the present embodiment. Since the attracting force due to the temperature rise of the non-paper-feed portion Ar2 does not occur, the shift flange unit 43 is not operating.

[0183] FIG. 21(b) is a cross-sectional view taken from above of the state cut along the line I-I of FIG. 12(a) when an A6-sized sheet is continuously fed through in the present embodiment. Due to the temperature rise of the non-paper-feed portion Ar2, an attracting force acts on the fixing film 25 in a direction pressing against the regulating surface 41bE of the shift flange unit 43.

[0184] The fixing film 25 is shifted upstream by a distance G0 in the sheet conveyance direction DF while being regulated only on the second side W2 by the second flange 40bE due to the operation of the shift flange unit 43. The fixing film 25 will be separated from the stay 22 by the second flange 40bE and will not come into contact with the stay 22, preventing the occurrence of poor fixing. Also, since the fixing film 25 can form a tolerance angle with respect to the roller unit 26 in a direction canceling out the attracting force due to the temperature rise of the non-paper-feed portion Ar2 by the movement of the second flange 40bE, the attracting force can be reduced.

[0185] [Examples and Comparative Examples] To confirm the effects of this embodiment, a comparative test was conducted using Example 6 of this embodiment, Example 4, and Comparative Example 5. The fixing film 25 used in the comparative test had a base layer 251 with a thickness of 60 μm, an elastic layer 252 with a thickness of 250 μm, and a surface layer 253 with a thickness of 12 μm. This fixing film 25 was incorporated into each configuration, and the fixability when continuously passing 500 sheets of PB PAPER (A6 size, 68 g / cm 2 ) at a speed of 75 sheets per minute and the lateral force applied to the end of the fixing film were evaluated.

[0186] Table 8 shows the evaluation results of fixability and lateral force. The evaluation criteria for fixability were "○ (good)" when there were no problems and "× (poor)" when the fixability was insufficient.

Table 8

[0187] The results of the fixability of Comparative Example 5 and Embodiment 4 are as described in the fourth embodiment. In Example 6, since the fixing film 25 did not come into contact with the stay 22 due to the operation of the shift flange unit 43, the occurrence of fixing defects could be prevented.

[0188] Regarding the lateral force applied to the end of the fixing film 25, the temperature rise of the non-paper-passing part Ar2 was almost the same in all configurations. However, in Comparative Example 5, it was 1.8 kgf, in Example 4 it was 1.1 kgf, and in Example 6 it was 0.5 kgf. In Comparative Example 5, in addition to the lateral force due to the temperature rise of the non-paper-passing part Ar2, a high value was obtained due to the influence of the lateral force generated by the tolerance angle caused by the shape change of the fixing film 25. In Example 4, the lateral force due to the temperature rise of the non-paper-passing part Ar2 was the same as that in Comparative Example 5, but since the shape change in the width direction W of the fixing film 25 was suppressed by the protruding guide part 293, the tolerance angle did not become large, so it could be made lower than in Comparative Example 5. In Example 6, by canceling the lateral force due to the temperature rise of the non-paper-passing part Ar2 with the shift flange unit 43, the lateral force could be further suppressed to be lower than in Example 4.

[0189] As described above, according to the fixing device 6E of the present embodiment, since the shift flange unit 43 is provided on the second side W2, it is possible to reduce the pulling force due to the temperature rise of the non-paper passing portion Ar2. As a result, even in a configuration where the amount of deformation of the fixing film 25 tends to increase due to thinning of the fixing film 25 or the like, it is possible to suppress the occurrence of fixing defects and lateral buckling, and a fixing device capable of coping with high speed and long life can be realized. Further, for example, a fixing film 25 with an even thinner base layer 251 can also be applied, making it possible to reduce costs and the like.

[0190] <Other Embodiments> In addition, in each of the above-described embodiments, the image forming apparatus 100 which is a monochrome laser printer has been described as an example, but the present invention is not limited thereto. For example, the present invention may be applied to an image forming apparatus which is a full-color laser printer.

[0191] Further, the disclosure of the present embodiment includes the following configuration examples and method examples. (Configuration 1) A fixing device comprising a heating unit for heating a sheet, and a counter roller facing the heating unit and forming a fixing nip together with the heating unit, wherein the toner image carried on the sheet is fixed to the sheet by applying heat and pressure in the fixing nip, One end portion in the width direction intersecting the sheet conveyance direction of the sheet conveyed to the fixing device passes through a predetermined position in the width direction of the fixing nip regardless of the size of the sheet, The counter roller has a roller portion including a base portion and an elastic layer provided around the base portion, When the side where the predetermined position is located with respect to the central portion of the roller portion in the width direction is the first side and the side opposite to the first side is the second side, the roller portion has, in the width direction, a first end portion which is an end portion on the first side and a second end portion which is an end portion on the second side, The thickness of the elastic layer at the second end portion is thinner than the thickness of the elastic layer at the first end portion, A fixing device characterized by the above. (Configuration 2) The maximum outer diameter of the base portion at the second end portion is larger than the maximum outer diameter of the base portion at the first end portion. The fixing device according to Configuration 1, characterized in that. (Configuration 3) The outer diameter of the central portion of the roller portion is smaller than the maximum outer diameter of the first end portion and the maximum outer diameter of the second end portion. The fixing device according to Configuration 1 or 2, characterized in that. (Configuration 4) The maximum outer diameter of the second end portion of the roller portion is larger than the maximum outer diameter of the first end portion. The fixing device according to any one of Configurations 1 to 3, characterized in that. (Configuration 5) The maximum outer diameter of the second end portion is 101% or more and 103% or less of the maximum outer diameter of the first end portion. The fixing device according to Configuration 4, characterized in that. (Configuration 6) The thickness of the elastic layer at the second end portion is 65% or more and 75% or less of the thickness of the elastic layer at the first end portion. The fixing device according to any one of Configurations 1 to 5, characterized in that. (Configuration 7) The roller portion has a release layer provided around the elastic layer. The fixing device according to any one of Configurations 1 to 6, characterized in that. (Configuration 8) In a fixing device that includes a heating unit that heats a sheet, a counter roller that faces the heating unit and forms a fixing nip together with the heating unit, and a biasing unit that biases either one of the heating unit and the counter roller toward the other one of the heating unit and the counter roller, and fixes a toner image carried on the sheet to the sheet by applying heat and pressure in the fixing nip. One end portion in the width direction intersecting the sheet conveyance direction of the sheet conveyed to the fixing device passes through a predetermined position in the width direction of the fixing nip regardless of the size of the sheet. The opposing roller has a roller part including a base part and an elastic layer provided around the base part and having elasticity. When the side where the predetermined position is located with respect to the central part of the roller part in the width direction is defined as the first side and the side opposite to the first side is defined as the second side, the roller part has, in the width direction, a first end part that is the end part on the first side and a second end part that is the end part on the second side. The biasing unit is configured such that the biasing force at the first end part is greater than the biasing force at the second end part. The elastic layer is provided on the first side and has a high-hardness region that is harder than the elastic layer at the central part. A fixing device characterized by the above. (Configuration 9) At least a part of the high-hardness region overlaps with the conveyance region of the smallest-size sheet to be conveyed as viewed from the intersection direction intersecting the sheet conveyance direction and the width direction. The fixing device according to Configuration 8, characterized by the above. (Configuration 10) The elastic layer is provided on the second side and has a low-hardness region that is softer than the elastic layer at the central part. The fixing device according to Configuration 8 or 9, characterized by the above. (Configuration 11) The hardness of the elastic layer in the high-hardness region is 110% or more and 120% or less of the hardness of the elastic layer in the low-hardness region. The fixing device according to Configuration 10, characterized by the above. (Configuration 12) The biasing unit has a first biasing part that biases either one of the heating unit and the opposing roller toward the other one of the heating unit and the opposing roller at the first end part, and a second biasing part that biases either one of the heating unit and the opposing roller toward the other one of the heating unit and the opposing roller at the second end part. The biasing force of the first biasing part is 130% or more and 170% or less of the biasing force of the second biasing part. The fixing device according to any one of configurations 8 to 11, characterized in that... (Configuration 13) The high-hardness region is disposed between the central portion and the predetermined position in the width direction. The fixing device according to any one of configurations 8 to 12, characterized in that... (Configuration 14) In a fixing device comprising a heating unit that heats a sheet, and a counter roller that faces the heating unit and forms a fixing nip together with the heating unit, and fixing a toner image carried on the sheet to the sheet by applying heat and pressure in the fixing nip, One end portion in the width direction intersecting the sheet conveyance direction of the sheet conveyed to the fixing device passes through a predetermined position in the width direction of the fixing nip regardless of the size of the sheet. The heating unit includes an endless rotatable flexible rotating body, a heater disposed in the internal space of the rotating body for heating the rotating body, and a regulating member. The counter roller has a roller portion including a base portion and an elastic elastic layer provided around the base portion. When the side where the predetermined position is located with respect to the central portion of the roller portion in the width direction is defined as the first side and the side opposite to the first side is defined as the second side, the regulating member has a regulating surface that contacts the end surface of the rotating body on the second side in the width direction to regulate the movement of the rotating body to the second side. The rotating body has a base layer and an elastic layer provided around the base layer and containing a filler. The base layer has a protruding portion that protrudes to the second side more than the elastic layer and can contact the regulating surface in the width direction. A fixing device characterized by the above. (Configuration 15) The protruding portion is provided in a region of 70% or more of the end surface of the rotating body on the second side. The fixing device according to configuration 14, characterized in that... (Configuration 16) The protruding amount of the second side of the protruding portion with respect to the elastic layer is 0.1 mm or more and 10 mm or less. The fixing device according to Configuration 14 or 15, characterized by this. (Configuration 17) By the protruding portion coming into contact with the regulating surface, the contact of the elastic layer with the regulating surface is regulated. The fixing device according to any one of Configurations 14 to 16, characterized by this. (Configuration 18) The regulating member has the regulating surface and a guide portion that protrudes in the width direction from the regulating surface toward the rotating body and contacts the inner peripheral surface of the rotating body to guide the rotating body. The fixing device according to any one of Configurations 14 to 17, characterized by this. (Configuration 19) The protruding amount of the second side of the protruding portion with respect to the elastic layer is shorter than the length in the width direction of the guide portion. The fixing device according to Configuration 18, characterized by this. (Configuration 20) The elastic layer is a first elastic layer. The roller portion has a base portion and a second elastic layer having elasticity provided around the base portion. The inner peripheral surface of the base layer is electrically grounded. The end surface on the second side of the protruding portion is provided on the second side rather than the end surface on the second side of the second elastic layer. The fixing device according to any one of Configurations 14 to 19, characterized by this. (Configuration 21) The base layer is made of a resin material. The fixing device according to any one of Configurations 14 to 20, characterized by this. (Configuration 22) The filler is made of an inorganic material. The fixing device according to any one of Configurations 14 to 21, characterized by this. (Configuration 23) The filler contains ceramic powder, metal oxide powder, or metal powder. The fixing device according to Configuration 22, characterized in that. (Configuration 24) The filler contains alumina, metal silicon, silicon carbide, or zinc oxide, The fixing device according to Configuration 23, characterized in that. (Configuration 25) A fixing device comprising a heating unit for heating a sheet, and an opposing roller facing the heating unit and forming a fixing nip together with the heating unit, wherein the toner image carried on the sheet is fixed to the sheet by applying heat and pressure at the fixing nip. One end portion in the width direction intersecting the sheet conveyance direction of the sheet conveyed to the fixing device passes through a predetermined position in the width direction of the fixing nip regardless of the size of the sheet. The heating unit includes a rotatable endless rotating body having flexibility, a heater disposed in the internal space of the rotating body for heating the rotating body, a first support member disposed in the internal space for supporting the heater, and a second support member disposed in the internal space for supporting the first support member. The opposing roller has a roller portion including a base portion and an elastic layer provided around the base portion. When the side where the predetermined position is located with respect to the central portion of the roller portion in the width direction is the first side and the side opposite to the first side is the second side, the first support member is provided on the first side in the width direction, and a first guide portion capable of guiding the rotating body upstream of the fixing nip in the sheet conveyance direction, and a second guide portion provided on the second side in the width direction and capable of guiding the rotating body upstream of the fixing nip in the sheet conveyance direction. The second support member is disposed at a position spaced apart from the fixing nip more than the first guide portion and the second guide portion in a direction orthogonal to the sheet conveyance direction and the width direction, and has an opposing portion facing the inner peripheral surface on the upstream side of the rotating body in the sheet conveyance direction. In the sheet conveyance direction, the distance from the opposing portion to the upstream end of the second guide portion is longer than the distance from the opposing portion to the upstream end of the first guide portion. A fixing device characterized by the following. (Configuration 26) The first support member is provided on the second side with respect to the width direction, can guide the rotating body upstream of the fixing nip in the sheet conveyance direction, and has a third guide portion provided separately from the second guide portion in the width direction. In the sheet conveyance direction, the distance from the opposing portion to the upstream end of the third guide portion is shorter than the distance from the opposing portion to the upstream end of the second guide portion. The fixing device according to Configuration 25, characterized by the above. (Configuration 27) A fixing device including a heating unit that heats a sheet and an opposing roller that faces the heating unit and forms a fixing nip together with the heating unit, and fixing a toner image carried on the sheet to the sheet by applying heat and pressure at the fixing nip. One end portion in the width direction intersecting the sheet conveyance direction of the sheet conveyed to the fixing device passes through a predetermined position in the width direction of the fixing nip regardless of the size of the sheet. The heating unit includes an endless rotating body having flexibility and being rotatable, a heater disposed in the internal space of the rotating body for heating the rotating body, a first support member disposed in the internal space for supporting the heater, and a second support member disposed in the internal space for supporting the first support member. The opposing roller has a roller portion including a base portion and an elastic layer provided around the base portion. The second support member has an opposing portion facing the inner peripheral surface on the upstream side of the rotating body in the sheet conveyance direction at an end portion on the opposite side of the roller portion with respect to the fixing nip in a direction orthogonal to the sheet conveyance direction and the width direction. The heating unit is a cover disposed on the opposite side of the predetermined position from the central portion of the roller portion with respect to the width direction, and has a cover provided between the opposing portion of the second support member and the inner peripheral surface on the upstream side of the rotating body in the sheet conveyance direction. A fixing device characterized by the above. (Configuration 28) The cover is supported by the second support member, The fixing device according to Configuration 27, characterized in that. (Configuration 29) The cover is made of a material having a lower thermal conductivity than the second support member, The fixing device according to Configuration 27 or 28, characterized in that. (Configuration 30) A fixing device comprising a heating unit for heating a sheet and an opposing roller facing the heating unit and forming a fixing nip together with the heating unit, wherein the toner image carried on the sheet is fixed to the sheet by applying heat and pressure in the fixing nip. In the fixing device, One end portion in the width direction intersecting the sheet conveyance direction of the sheet conveyed to the fixing device passes through a predetermined position in the width direction of the fixing nip regardless of the size of the sheet. The heating unit includes an endless rotatable flexible rotating body, a heater disposed in an internal space of the rotating body for heating the rotating body, and a regulating member. The opposing roller has a roller portion including a base portion and an elastic elastic layer provided around the base portion. When the predetermined position is on the first side with respect to the central portion of the roller portion in the width direction and the side opposite to the first side is the second side, the regulating member contacts an end surface of the rotating body on the second side in the width direction to regulate movement of the rotating body to the second side. A regulating surface, and a guide portion that protrudes in the width direction from the regulating surface toward the rotating body and contacts an inner peripheral surface of the rotating body to guide the rotating body. The regulating member is movable between a first position and a second position where the guide portion is located upstream in the sheet conveyance direction from the first position. When the regulating member is located at the first position, the regulating surface is pressed by the rotating body to the second side, and thus the regulating member moves from the first position to the second position. The fixing device, characterized in that. (Configuration 31) When the regulating member is located at the second position, the position of the regulating surface is located closer to the second side than the position of the regulating surface when the regulating member is located at the first position. The fixing device according to Configuration 30, characterized in that. (Configuration 32) The heating unit includes a support portion that movably supports the regulating member, and a biasing portion that biases the regulating member toward the first side with respect to the support portion. Either one of the regulating member and the support portion has a cam surface. The other of the regulating member and the support portion has a slider that abuts against and slides on the cam surface. The cam surface and the slider guide the regulating member toward the second position when the regulating surface of the regulating member located at the first position receives a pressing force that resists the biasing force from the biasing portion toward the second side from the rotating body. The fixing device according to Configuration 30 or 31, characterized in that. (Configuration 33) The guide portion and the regulating surface are integrally formed. The fixing device according to any one of Configurations 30 to 32, characterized in that. (Configuration 34) An image forming unit that forms a toner image on a sheet, The fixing device according to any one of Configurations 1 to 33 that fixes the toner image formed by the image forming unit to the sheet, and. An image forming apparatus, characterized in that. (Configuration 35) A conveying unit that is disposed upstream of the image forming unit in the sheet conveying direction and conveys the sheet in the sheet conveying direction while moving the sheet in the width direction so that one end portion of the sheet passes through the predetermined position of the fixing nip. The image forming apparatus according to Configuration 34, characterized in that.

Explanation of Signs

[0192] 6: Fixing device / 19: Oblique correction device (conveyor section) / 20: Heater / 22: Stay (second support member) / 22a: Opposing section / 25: Fixing film (rotating body) / 26: Roller section / 26a: First end / 26b: Second end / 29, 29C: Heater holder (first support member) / 40b: Flange (restricting member) / 44: Support section / 44b: Bottom surface (cam surface) / 45: Biasing spring (biasing section) / 46a: Tip surface (slider) / 48... Biasing unit / 48a: First pressurizing spring (first biasing section) / 48b: Second pressurizing spring (second biasing section) / 50: Cover / 60: Heating unit / 61: Opposing roller / 140: Image forming section / 251: Base layer / 252: Elastic layer (first elastic layer) / 254: Protrusion / 254a: End surface / 261: Base section / 262: Elastic layer (second elastic layer) / 263: Release layer / 291: Upstream guide member (first guide section) / 291a: Upstream guide member (third guide section) / 293: Protruding guide section (second guide section) / N2: Fixing nip / P0: Paper passing reference position (predetermined position) / PC: Central section / S: Sheet / T: Toner image / W: Width direction / W1: First side / W2: Second side

Claims

1. A fixing device comprising a heating unit for heating a sheet, and a counter roller facing the heating unit and forming a fixing nip together with the heating unit, and fixing a toner image carried on the sheet to the sheet by applying heat and pressure in the fixing nip, wherein one end portion in the width direction intersecting the sheet conveyance direction of the sheet conveyed to the fixing device passes through a predetermined position in the width direction of the fixing nip regardless of the size of the sheet, the counter roller has a roller portion including a base portion and an elastic layer provided around the base portion, when the side where the predetermined position is located with respect to the central portion of the roller portion in the width direction is defined as the first side and the side opposite to the first side is defined as the second side, the roller portion has a first end portion which is an end portion on the first side and a second end portion which is an end portion on the second side in the width direction, the thickness of the elastic layer at the second end portion is thinner than the thickness of the elastic layer at the first end portion, characterized in that it is a fixing device.

2. The maximum outer diameter of the base portion at the second end portion is larger than the maximum outer diameter of the base portion at the first end portion, characterized in that it is the fixing device according to Claim 1.

3. The outer diameter of the central portion of the roller portion is smaller than the maximum outer diameter of the first end portion and the maximum outer diameter of the second end portion, characterized in that it is the fixing device according to Claim 1.

4. The maximum outer diameter of the second end portion of the roller portion is larger than the maximum outer diameter of the first end portion, characterized in that it is the fixing device according to Claim 1.

5. The maximum outer diameter of the second end portion is 101% or more and 103% or less of the maximum outer diameter of the first end portion, characterized in that it is the fixing device according to Claim 4.

6. The thickness of the elastic layer at the second end portion is 65% or more and 75% or less of the thickness of the elastic layer at the first end portion, characterized in that it is the fixing device according to Claim 1.

7. The roller portion has a release layer provided around the elastic layer, characterized in that it is the fixing device according to Claim 1.

8. A heating unit for heating a sheet, a counter roller facing the heating unit and forming a fixing nip together with the heating unit, and a biasing unit for biasing either one of the heating unit and the counter roller toward the other one of the heating unit and the counter roller. In a fixing device for fixing a toner image carried on a sheet by applying heat and pressure in the fixing nip, One end portion in the width direction intersecting the sheet conveyance direction of the sheet conveyed to the fixing device passes through a predetermined position in the width direction of the fixing nip regardless of the size of the sheet. The counter roller has a roller portion including a base portion and an elastic layer provided around the base portion. When the side where the predetermined position is located with respect to the central portion of the roller portion in the width direction is defined as the first side and the side opposite to the first side is defined as the second side, the roller portion has a first end portion which is an end portion on the first side and a second end portion which is an end portion on the second side in the width direction. The biasing unit is configured such that the biasing force at the first end portion is greater than the biasing force at the second end portion. The elastic layer is provided on the first side and has a high hardness region having a higher hardness than the elastic layer at the central portion. A fixing device characterized by the above.

9. At least a part of the high hardness region overlaps the conveyance region of the smallest size sheet to be conveyed when viewed from the intersecting direction intersecting the sheet conveyance direction and the width direction. The fixing device according to claim 8, characterized by the above.

10. The elastic layer is provided on the second side and has a low hardness region having a lower hardness than the elastic layer at the central portion. The fixing device according to claim 8, characterized by the above.

11. The hardness of the elastic layer in the high hardness region is 110% or more and 120% or less of the hardness of the elastic layer in the low hardness region. The fixing device according to claim 10, characterized by the above.

12. The biasing unit has a first biasing portion for biasing either one of the heating unit and the counter roller toward the other one of the heating unit and the counter roller at the first end portion, and a second biasing portion for biasing either one of the heating unit and the counter roller toward the other one of the heating unit and the counter roller at the second end portion. The biasing force of the first biasing portion is 130% or more and 170% or less than the biasing force of the second biasing portion. The fixing device according to claim 8, characterized in that.

13. The high hardness region is disposed between the central portion and the predetermined position in the width direction. The fixing device according to claim 8, characterized in that.

14. A fixing device comprising a heating unit that heats a sheet, and an opposing roller that faces the heating unit and forms a fixing nip together with the heating unit, and fixing a toner image carried on the sheet to the sheet by applying heat and pressure in the fixing nip. One end portion in the width direction intersecting the sheet conveyance direction of the sheet conveyed to the fixing device passes through a predetermined position in the width direction of the fixing nip regardless of the size of the sheet. The heating unit includes an endless rotatable flexible rotating body, a heater disposed in an internal space of the rotating body for heating the rotating body, and a regulating member. The opposing roller has a roller portion including a base portion and an elastic elastic layer provided around the base portion. When the side where the predetermined position is located with respect to the central portion of the roller portion in the width direction is the first side and the side opposite to the first side is the second side, the regulating member has a regulating surface that contacts an end surface on the second side of the rotating body in the width direction to regulate movement of the rotating body to the second side. The rotating body has a base layer and an elastic layer provided around the base layer and containing a filler. The base layer has a protruding portion that protrudes to the second side more than the elastic layer and can contact the regulating surface in the width direction. A fixing device characterized by that.

15. The protruding portion is provided in an area of 70% or more of the end surface on the second side of the rotating body. The fixing device according to claim 14, characterized in that.

16. The protruding amount of the protruding portion to the elastic layer on the second side is 0.1 mm or more and 10 mm or less. The fixing device according to claim 14, characterized in that.

17. The protruding portion regulates contact of the elastic layer with the regulating surface by contacting the regulating surface. The fixing device according to claim 14, characterized in that.

18. The regulating member has a regulating surface and a guide portion that protrudes in the width direction from the regulating surface toward the rotating body and contacts the inner peripheral surface of the rotating body to guide the rotating body. The fixing device according to claim 14, characterized in that.

19. The protruding amount of the second side of the protruding portion with respect to the elastic layer is shorter than the length of the guide portion in the width direction. The fixing device according to claim 18, characterized in that.

20. The elastic layer is a first elastic layer. The roller portion has a base portion and a second elastic layer having elasticity provided around the base portion. The inner peripheral surface of the base layer is electrically grounded. The end surface of the second side of the protruding portion is provided on the second side rather than the end surface of the second side of the second elastic layer. The fixing device according to claim 14, characterized in that.

21. The base layer is made of a resin material. The fixing device according to claim 14, characterized in that.

22. The filler is made of an inorganic material. The fixing device according to claim 14, characterized in that.

23. The filler includes ceramic powder, metal oxide powder, or metal powder. The fixing device according to claim 22, characterized in that.

24. The filler includes alumina, metal silicon, silicon carbide, or zinc oxide. The fixing device according to claim 23, characterized in that.

25. A fixing device that includes a heating unit that heats a sheet and an opposing roller that faces the heating unit and forms a fixing nip together with the heating unit, and fixes a toner image carried on the sheet to the sheet by applying heat and pressure in the fixing nip. In the fixing device, One end portion in the width direction intersecting the sheet conveyance direction of the sheet conveyed to the fixing device passes through a predetermined position in the width direction of the fixing nip regardless of the size of the sheet. The heating unit has an endless rotating body that is rotatable and has flexibility, a heater that is disposed in the internal space of the rotating body and heats the rotating body, a first support member that is disposed in the internal space and supports the heater, and a second support member that is disposed in the internal space and supports the first support member. The opposing roller has a roller portion including a base portion and an elastic layer having elasticity provided around the base portion. When the side where the predetermined position is located with respect to the central portion of the roller portion in the width direction is defined as the first side and the side opposite to the first side is defined as the second side, the first support member is provided on the first side in the width direction and has a first guide portion capable of guiding the rotating body upstream of the fixing nip in the sheet conveyance direction, and a second guide portion provided on the second side in the width direction and capable of guiding the rotating body upstream of the fixing nip in the sheet conveyance direction. The second support member is disposed at a position spaced apart from the fixing nip more than the first guide portion and the second guide portion with respect to the orthogonal direction orthogonal to the sheet conveyance direction and the width direction, and has an opposing portion facing the inner peripheral surface on the upstream side of the rotating body in the sheet conveyance direction. In the sheet conveyance direction, the distance from the opposing portion to the upstream end of the second guide portion is longer than the distance from the opposing portion to the upstream end of the first guide portion. A fixing device characterized by the above.

26. The first support member is provided on the second side in the width direction and is capable of guiding the rotating body upstream of the fixing nip in the sheet conveyance direction, and has a third guide portion provided separately from the second guide portion in the width direction. In the sheet conveyance direction, the distance from the opposing portion to the upstream end of the third guide portion is shorter than the distance from the opposing portion to the upstream end of the second guide portion. The fixing device according to claim 25, characterized by the above.

27. A fixing device including a heating unit that heats a sheet and an opposing roller that faces the heating unit and forms a fixing nip together with the heating unit, and fixes a toner image carried on the sheet to the sheet by applying heat and pressure at the fixing nip. One end portion in the width direction intersecting the sheet conveyance direction of the sheet conveyed to the fixing device passes through a predetermined position in the width direction of the fixing nip regardless of the size of the sheet. The heating unit includes an endless rotating body having flexibility and capable of rotating, a heater disposed in the internal space of the rotating body for heating the rotating body, a first support member disposed in the internal space for supporting the heater, and a second support member disposed in the internal space for supporting the first support member. The opposing roller has a roller portion including a base portion and an elastic layer provided around the base portion. The second support member has a facing portion facing the inner peripheral surface on the upstream side in the sheet conveyance direction of the rotating body at an end portion on the opposite side of the roller portion with respect to the fixing nip in an orthogonal direction orthogonal to the sheet conveyance direction and the width direction. The heating unit is a cover disposed on the side opposite to the predetermined position with respect to the central portion of the roller portion in the width direction, and has a cover provided between the facing portion of the second support member and the inner peripheral surface on the upstream side in the sheet conveyance direction of the rotating body. A fixing device characterized by the above.

28. The cover is supported by the second support member. The fixing device according to claim 27, characterized in that.

29. The cover is made of a material having a lower thermal conductivity than the second support member. The fixing device according to claim 27, characterized in that.

30. A fixing device including a heating unit that heats a sheet, and a counter roller that faces the heating unit and forms a fixing nip together with the heating unit, and fixes a toner image carried on the sheet to the sheet by applying heat and pressure at the fixing nip. One end portion in the width direction intersecting the sheet conveyance direction of the sheet conveyed to the fixing device passes through a predetermined position in the width direction of the fixing nip regardless of the size of the sheet. The heating unit includes an endless rotatable flexible rotating body, a heater disposed in the internal space of the rotating body for heating the rotating body, and a regulating member. The counter roller has a roller portion including a base portion and an elastic elastic layer provided around the base portion. When the side where the predetermined position is located with respect to the central portion of the roller portion in the width direction is the first side and the side opposite to the first side is the second side, the regulating member has a regulating surface that contacts the end surface on the second side in the width direction of the rotating body to regulate the movement of the rotating body to the second side, and a guide portion that protrudes in the width direction from the regulating surface toward the rotating body and contacts the inner peripheral surface of the rotating body to guide the rotating body. The regulating member is movable between a first position and a second position where the guide portion is located upstream in the sheet conveyance direction from the first position, and moves from the first position to the second position when the regulating surface is pressed by the rotating body to the second side when located at the first position. A fixing device characterized by the above.

31. When the regulating member is located at the second position, the position of the regulating surface is located on the second side rather than the position of the regulating surface when the regulating member is located at the first position. The fixing device according to claim 30, characterized in that.

32. The heating unit includes a support portion that movably supports the regulating member, and a biasing portion that biases the regulating member toward the first side with respect to the support portion. Either one of the regulating member and the support portion has a cam surface. The other of the regulating member and the support portion has a slider that abuts against and slides on the cam surface. The cam surface and the slider guide the regulating member toward the second position when the regulating surface of the regulating member located at the first position receives a pressing force that resists the biasing force from the biasing portion toward the second side from the rotating body. The fixing device according to claim 30, characterized in that.

33. The guide portion and the regulating surface are integrally formed. The fixing device according to claim 30, characterized in that.

34. An image forming unit that forms a toner image on a sheet; The fixing device according to any one of claims 1 to 33 that fixes the toner image formed by the image forming unit to the sheet. An image forming apparatus, characterized in that.

35. A conveying unit that is disposed upstream of the image forming unit in the sheet conveying direction and conveys the sheet in the sheet conveying direction while moving the sheet in the width direction so that one end portion of the sheet passes through the predetermined position of the fixing nip. The image forming apparatus according to claim 34, characterized in that.

Images