Fixing apparatus and image forming apparatus

Abstract

This suppresses the occurrence of uneven thickness of the lubricant in the axial direction on the inner surface of the rotating body that heats the recording material. [Solution] The heating unit heats a recording material on which a toner image has been formed, and includes a rotatable and cylindrical fixing film 20 and a nip-forming member having a friction portion 83a that rubs against the inner circumferential surface of the fixing film 20; and a pressure roller that faces the fixing film 20 and rotates about a rotation axis extending in the longitudinal direction LD, and forms a fixing nip together with the nip-forming member via the fixing film 20. A lubricant is interposed between the friction portion 83a and the inner circumferential surface of the fixing film 20, and the fixing film 20 has ring-shaped divided conductors 20b1 that are divided in the longitudinal direction LD such that there are gaps between them in the longitudinal direction LD, and the friction portion 83a extends in a direction intersecting the rotation direction Rf of the fixing film 20 and has a groove portion 60 through which the lubricant can pass.

Description

Technical Field

[0001] The present invention relates to a fixing device for fixing a toner image onto a recording material and an image forming apparatus including the same.

Background Art

[0002] Generally, as a fixing device mounted on an electrophotographic copying machine or printer, a fixing device using an electromagnetic induction heating method is known. As such a fixing device, for example, a fixing film having a conductive layer, a magnetic core provided in the internal space of the fixing film, and a spiral coil wound around the magnetic core has been developed (see Patent Document 1). In this fixing device, when an alternating magnetic field is generated by flowing an alternating current through the coil, an eddy current flows through the heating layer of the fixing film due to the principle of electromagnetic induction.

[0003] On the other hand, in a fixing device using an electromagnetic induction heating method, when a damaged part such as a crack or a crack (groove, thin part) occurs in the fixing film, there is a risk that heat generation concentrates at the end of the damaged part and the temperature locally rises (see Patent Document 2). Such local temperature rise may cause image defects such as image unevenness.

[0004] In order to prevent the temperature rise caused by such damaged parts such as cracks and cracks, a fixing device using a fixing film formed by a plurality of divided heating layers in which the heating layer is electrically divided in the axial direction of the rotation axis of the fixing film has been proposed (see Patent Document 3). In this fixing device, by forming a magnetic field in the axial direction of the fixing film, the divided heating layers generate heat by induced current, but since they are divided, the current flowing through each divided heating layer is small. Therefore, even when cracks or cracks occur in the fixing film, the amount of current flowing into the ends of the cracks or cracks can be suppressed, and local temperature rise can be prevented.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] However, the fixing device described in Patent Document 3 may have the following problems. A lubricant such as grease or oil is applied to the inner circumferential surface of the fixing film, and a nip-forming member that slides against this inner circumferential surface is provided. Since the heating layer of the fixing film consists of multiple divided heating layers that are divided in the axial direction, temperature unevenness may occur in the lubricant in the axial direction.

[0007] The viscosity of lubricants generally exhibits temperature characteristics, with viscosity tending to decrease as temperature increases. Therefore, viscosity variations in the lubricant can occur along the axial direction. Furthermore, when the fixing film rubs against the nip-forming member under a predetermined load to hold and transport the recording material, the thickness of the lubricant interposed between them (grease thickness or oil film thickness) depends on the viscosity of the lubricant. In other words, if temperature variations occur in the axial direction due to the divided heat-generating layer of the fixing film, minute variations in the lubricant thickness may also occur. Such variations in lubricant thickness in the axial direction can lead to increased torque in the fixing device, stick-slip, or wear on the inner surface of the fixing film, potentially posing a challenge to extending the lifespan of the fixing device.

[0008] The present invention aims to provide a fixing device capable of suppressing the occurrence of thickness unevenness of the axial lubricant on the inner circumferential surface of a rotating body that heats a recording material, and an image forming apparatus equipped therewith. [Means for solving the problem]

[0009] The fixing device of the present invention is a fixing device for fixing a toner image to a recording material, and comprises a rotating body that is rotatable and formed in a cylindrical shape, a nip portion forming member having a sliding portion that slides against the inner circumferential surface of the rotating body, a heating unit for heating the recording material on which the toner image is formed, and an opposing member that faces the rotating body and rotates about a rotation axis extending in the axial direction, and forms a nip portion together with the nip portion forming member via the rotating body, wherein a lubricant is interposed between the sliding portion of the nip portion forming member and the inner circumferential surface of the rotating body, the rotating body has a plurality of ring-shaped heating elements that are divided in the axial direction so as to have gaps between them in the axial direction, and the sliding portion extends in a direction intersecting the rotation direction of the rotating body and has a groove through which the lubricant can pass.

[0010] Furthermore, the image forming apparatus of the present invention is characterized by comprising an image forming unit that forms a toner image on a recording material, and the fixing device described above. [Effects of the Invention]

[0011] According to the present invention, it is possible to suppress the occurrence of unevenness in the thickness of the lubricant in the axial direction on the inner circumferential surface of a rotating body that heats the recording material. [Brief explanation of the drawing]

[0012] [Figure 1] A schematic diagram showing the printer according to Example 1. [Figure 2] A cross-sectional view showing the fixing device. [Figure 3] (a) is a cross-sectional view showing the region of the fixing film where the conductive layer exists, (b) is a cross-sectional view showing the region of the fixing film where the conductive layer does not exist, and (c) is a cross-sectional view showing the region of the fixing film parallel to the longitudinal direction. [Figure 4] A perspective view showing the fixing film, magnetic core, and excitation coil. [Figure 5] (a) shows a cross-section of the fixing film in the longitudinal direction, a cross-sectional view to explain the magnetic field and the current flowing through the conductive layer, and (b) is a perspective view to explain the magnetic field and the current flowing through the conductive layer. [Figure 6] (a) is a diagram showing the arrangement of the convex portions according to Example 1 as viewed from the pressure roller, and (b) is a diagram showing the arrangement of the divided conductors. [Figure 7] (a) is a diagram showing a cross-section of the convex shape of the convex portion according to Example 1 as viewed from the rotational direction, and (b) is a diagram showing a cross-section of the contact state between the convex portion and the fixing film as viewed from the rotational direction. [Figure 8] It is a diagram showing the arrangement of the convex portions as viewed from the pressure roller, where (a) is a modification of Example 1 and (b) is another modification of Example 1. [Figure 9] It is a diagram showing the arrangement of the convex portions as viewed from the pressure roller, where (a) is Example 2 and (b) is a modification of Example 2. [Figure 10] It is a diagram showing the arrangement of the convex portions as viewed from the pressure roller, where (a) is Example 3 and (b) is a modification of Example 3. [Figure 11] (a) is a cross-sectional view of the fixing device according to Example 4, and (b) is a diagram showing the arrangement of the convex portions of Example 4 as viewed from the pressure roller.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments according to the present disclosure will be described with reference to the drawings. In the present disclosure, the "image forming apparatus" broadly includes not only a single-function printer having only a printing function, but also a copying machine having a copying function, a multifunction machine having a plurality of functions, a large commercial printer, etc., apparatuses that form an image on a recording material.

[0014] Also, in the present disclosure, the "fixing device" broadly includes a device (image heating device) that heats an image (toner image) formed on a recording material by an electrophotographic process or the like and fixes it to the recording material. The fixing device may be arranged to reheat an image that has already been fixed (primarily fixed) to the recording material to impart gloss.

[0015] <Example 1> [Image Forming Apparatus] The overall configuration of the image forming apparatus according to Embodiment 1 of the present disclosure will be described with reference to FIG. 1. FIG. 1 is a cross-sectional view showing a schematic configuration of a laser beam printer (hereinafter referred to as Printer 100) as an example of an image forming apparatus. Printer 100 executes an image forming operation of forming an image on a recording material P based on image information received from an external device such as a personal computer. As the recording material P (recording medium), various sheet materials with different sizes and materials can be used, such as paper such as plain paper and thick paper, sheet materials with surface treatment such as coated paper, sheet materials with special shapes such as envelopes and index papers, plastic films, cloth, etc.

[0016] Printer 100 includes an image forming unit 70 that forms an image (toner image) on the recording material P by an electrophotographic process, and a fixing device 80 that fixes the image on the recording material P.

[0017] The image forming unit 70 includes a photosensitive drum 1 as an image carrier, a charging roller 2 as a charging unit, a laser scanner 3 as an exposure unit, and a developing device 4 as a developing unit. Further, the image forming unit 70 includes a transfer roller 6 as a transfer unit and a cleaner 5 as a cleaning unit. The photosensitive drum 1 is a cylindrical photosensitive member. The developing device 4 includes a container 4a that stores toner as a developer, and a developing roller 4b that carries the toner and supplies it to the photosensitive drum 1.

[0018] In the image forming operation, the photosensitive drum 1 is rotationally driven, and the charging roller 2 uniformly charges the surface of the photosensitive drum 1. The laser scanner 3 irradiates the photosensitive drum 1 with laser light for exposure by receiving a digital image signal generated based on image information by an image processing unit included in Printer 100, and writes an electrostatic latent image corresponding to the image information on the surface of the photosensitive drum 1. The developing device 4 supplies toner to the photosensitive drum 1 and develops the electrostatic latent image into a toner image.

[0019] Simultaneously with the creation of the toner image, the recording material P is transported. A cassette 7 is retractably stored in the lower part of the printer 100. The cassette 7 is filled with the recording material P. The recording material P stored in the cassette 7 is fed one sheet at a time by the feed roller 8, which acts as the feeding unit, and transported to the transfer nip unit Nt by the transport roller pair 9.

[0020] The transfer roller 6 transfers the toner image from the photosensitive drum 1 to the recording material P at the transfer nip Nt between the photosensitive drum 1 and the transfer roller 6. Any foreign matter, such as residual toner that remains on the photosensitive drum 1 and is not transferred to the recording material P, is removed by the cleaner 5.

[0021] The recording material P that has passed through the transfer nip section Nt is sent to the fixing device 80. The fixing device 80 heats and pressurizes the image (toner image) on the recording material P while transporting it, fixing it to the recording material P. Details of the fixing device 80 will be described later. The recording material P that has passed through the fixing device 80 is discharged to the discharge tray 12 by the discharge roller pair 11.

[0022] In this embodiment, the image forming unit 70 is described as a direct transfer type image forming unit, but it is not limited to this. For example, an intermediate transfer type image forming unit may be used in which a toner image is first transferred from an image carrier to an intermediate transfer body such as an intermediate transfer belt, and the toner image is secondarily transferred from the intermediate transfer body to a recording material. Also, in this embodiment, the image forming unit 70 is described as having a configuration that forms a monochrome image, but it is not limited to this, and it may also have a configuration that creates a color image using multiple colors of toner.

[0023] [Fusing device] The fixing device 80 will now be described. In this embodiment, the fixing device 80 is an electromagnetic induction heating type fixing device. Figure 2 is a cross-sectional view showing the fixing device 80.

[0024] As shown in Figure 2, the fixing device 80 includes a heating unit 81 for heating the recording material P on which the toner image is formed, a pressure roller 82 which is an example of a counter member, and a temperature sensor 85.

[0025] The heating unit 81 includes a fixing film 20, which is an example of a rotatable rotating body; a magnetic field generating unit 21 that forms an alternating magnetic field in the longitudinal direction LD of the fixing film 20; and a nip portion forming member 83. The fixing member and the fixing film 20 as a rotating body are formed from a flexible tubular (endless) film. The fixing film 20 is a fixing member that heats the image on the recording material.

[0026] The magnetic field generating unit 21 includes a magnetic core 30 as a magnetic material and an excitation coil 31 as a coil. When an alternating current flows through the excitation coil 31, an alternating magnetic field is generated, and this alternating magnetic field induces a circumferential current in the conductive layer 20b of the fixing film 20 (see Figure 3(c)).

[0027] The nip-forming member 83 is supported by a support member 86. The support member 86 is a longitudinal member extending in the longitudinal direction LD, and in the rotation direction Rf of the fixing film 20, it contacts the inner circumferential surface of the fixing film 20 upstream and downstream of the nip-forming member 83 to restrict the rotational position. The nip-forming member 83 has a substantially flat sliding portion 83a that rubs against the inner circumferential surface of the fixing film 20, and sandwiches the fixing film 20 between the fixing film 20 and the pressure roller 82, forming a fixing nip portion Nf, which is an example of a nip portion, between the fixing film 20 and the pressure roller 82.

[0028] The material of the nip-forming member 83 is preferably a metal such as aluminum, or a heat-resistant resin such as PPS (polyphenylene sulfide) or LCP (liquid crystal polymer). Furthermore, in order to ensure the sliding properties of the nip-forming member 83 with respect to the fixing film 20, it is preferable to apply a surface treatment or fluororesin coating to the sliding portion 83a. In this embodiment, the nip-forming member 83 uses aluminum as the base material and has been anodized on the sliding portion 83a. The shape of the sliding portion 83a, which is a feature of this embodiment, will be described later.

[0029] The pressure roller 82 faces the fixing film 20 and rotates around a rotation axis extending in the longitudinal direction LD. The pressure roller 82 contacts the nip portion forming member 83 via the fixing film 20, and together with the nip portion forming member 83, forms a fixing nip portion Nf between the pressure roller 82 and the friction portion 83a of the nip portion forming member 83. The pressure roller 82 has a core metal 82a, an elastic layer 82b formed on the outer surface of the core metal 82a, and a release layer 82c formed on the outer surface of the elastic layer 82b. In this embodiment, the outer diameter of the pressure roller 82 is 30 mm.

[0030] A lubricant 84 is interposed between the friction portion 83a of the nip portion forming member 83 and the inner circumferential surface of the fixing film 20. The lubricant 84 is applied to the inner circumferential surface of the fixing film 20. The lubricant 84 is interposed between the friction portion 83a of the nip portion forming member 83 and the inner circumferential surface of the fixing film 20, maintaining good sliding properties between the nip portion forming member 83 and the fixing film 20. As the lubricant 84, a heat-resistant lubricating oil or grease is desirable, and it is preferable to use silicone oil, PFPE (perfluoropolyether), or fluorine grease with a thickener added to PFPE. In this embodiment, a heat-resistant fluorine grease MOLYKOTE HP-300 (product name, DuPont-Toray Specialty Materials) is used as the lubricant 84, and 500 mg is applied to the inner circumferential surface of the fixing film 20.

[0031] The fixing film 20, magnetic core 30, pressure roller 82, and nip-forming member 83 are all longitudinal members whose longitudinal direction LD (see Figure 3(c)) is the axial direction of the rotation axis of the pressure roller 82. In other words, the longitudinal direction LD can also be said to be the generatrix direction or axial direction of the fixing film 20. The lengths of the fixing film 20, magnetic core 30, pressure roller 82, and nip-forming member 83 in the longitudinal direction LD are longer than the maximum width of the recording material P that can be conveyed to the fixing device 80.

[0032] The fixing device 80 has a frame (not shown) that supports both ends of the support member 86 in the longitudinal direction LD. The frame rotatably supports the shaft portion of the core metal 82a of the pressure roller 82 via a bearing member (not shown). The pressure roller 82 is pressed toward the nip portion forming member 83 by a biasing member (not shown), such as a pressure spring. In this embodiment, the biasing member applies pressure to the bearing members provided at both ends of the pressure roller 82 with a total pressure of approximately 196N to 392N (approximately 20kgf to 40kgf). As a result, the elastic layer 82b of the pressure roller 82 is crushed and elastically deformed, and a fixing nip portion Nf of a predetermined width is formed between the surface of the fixing film 20 and the surface of the pressure roller 82.

[0033] In this embodiment, the pressure roller 82 was biased toward the nip-forming member 83, but this is not limited to this. For example, the nip-forming member 83 may be biased toward the pressure roller 82 by a biasing member.

[0034] Next, the fixing film 20 of this embodiment will be described in detail. The fixing film 20 is formed in a cylindrical shape with a diameter of 10 to 100 mm, and in this embodiment, a fixing film 20 with an outer diameter of 30 mm is used. Figure 3(a) is a cross-sectional view showing the region of the fixing film 20 where the conductive layer 20b exists (hereinafter referred to as the heat-generating region), and Figure 3(b) is a cross-sectional view showing the region of the fixing film 20 where the conductive layer 20b does not exist (hereinafter referred to as the non-heat-generating region). Figure 3(c) is a cross-sectional view showing the fixing film 20 parallel to the longitudinal direction LD.

[0035] As shown in Figure 3(c), the fixing film 20 has intermittent heat-generating and non-heat-generating regions along its longitudinal direction LD. That is, the fixing film 20 has alternating heat-generating and non-heat-generating regions along its longitudinal direction LD.

[0036] The fixing film 20 has a layered structure in the heat-generating region, as shown in Figure 3(a), including a base layer 20a, a conductive layer 20b, a protective layer 20c, an elastic layer 20d, and a release layer 20e. The base layer 20a, conductive layer 20b, protective layer 20c, elastic layer 20d, and release layer 20e are laminated in this order from the inner circumferential surface to the outer circumferential surface in the thickness direction of the fixing film 20.

[0037] The base layer 20a is made of a non-magnetic material with high volume electrical resistivity and excellent heat resistance. For example, the base layer 20a can be made of heat-resistant resins such as PI (polyimide) or PAI (polyamide-imide), or fiber-reinforced resins such as CFRP (carbon fiber reinforced polymer) or GFRP (glass fiber reinforced polymer). When a heat-resistant resin is used for the base layer 20a, the thickness of the base layer 20a is preferably such that the strength of the fixing film 20, the sliding properties of the fixing nip Nf, and the rotational stability of the fixing film 20 are easily obtained, and is preferably between 20 μm and 200 μm. In this example, the base layer 20a was made of PI (polyimide), and the thickness of the base layer 20a was set to 50 μm.

[0038] Suitable materials for the conductive layer 20b formed on the outer surface of the base layer 20a include metals with low volume resistivity, such as gold, silver, copper, iron, platinum, tin, SUS, titanium, aluminum, and nickel. In this embodiment, copper with a volume resistivity of 1.7 × 10⁻⁸ Ωm (room temperature) was used for the conductive layer 20b, and the thickness of the conductive layer 20b was set to 3 μm. Note that the volume resistivity and thickness mentioned here are examples and are not limited to these. Furthermore, as shown in Figure 3(c), the conductive layer 20b is formed by a plurality of divided conductors 20b1 (divided conductive layers) that are electrically divided in the longitudinal direction LD. Each divided conductor 20b1 is formed in a ring shape parallel to the rotational direction Rf. The plurality of divided conductors 20b1 are an example of a plurality of heating elements, and are divided in the longitudinal direction LD such that there are gaps between them in the longitudinal direction LD, and heat the fixing film 20.

[0039] An example of a method for forming the conductive layer 20b is described below. First, a coating containing the above-mentioned metal fine particles and a polyimide precursor solution is prepared, and this coating is applied to the outer surface of the base layer 20a by means of a blade or screen printing to form a coating film. When applying the coating to the outer surface of the base layer 20a, divisions are formed on the base layer 20a in advance by a general masking process or other method, so that the conductive layer 20b is electrically divided at predetermined intervals in the longitudinal direction LD. Then, the coating film is gradually heated and dried to about 300°C to 500°C to promote imidization, firmly bonding the base layer 20a and the coating film, and forming multiple divided conductors 20b1 that are electrically divided in the longitudinal direction LD. In addition to the above method, the divided conductors 20b1 may also be formed by plating the above-mentioned metal on the outer surface of the base layer 20a and then using methods such as laser etching or chemical etching.

[0040] A protective layer 20c is formed on the outer surface of the conductive layer 20b for the purpose of protecting the divided conductor 20b1. Similar to the base layer 20a, the material of the protective layer 20c should be non-magnetic, have high volume resistivity, and excellent heat resistance. For example, the material of the protective layer 20c could be a heat-resistant resin such as PI (polyimide) or PAI (polyamide-imide), or a fiber-reinforced resin such as CFRP (carbon fiber reinforced polymer) or GFRP (glass fiber reinforced polymer). The thickness of the protective layer 20c should be between 20 μm and 200 μm, which is suitable for obtaining rotational stability of the fixing film 20. In this embodiment, the protective layer 20c was formed from PI (polyimide), and its thickness was 50 μm.

[0041] An elastic layer 20d made of a heat-resistant elastic material such as silicone rubber is formed on the outer surface of the protective layer 20c. In this embodiment, the elastic layer 20d is made of a silicone rubber with good thermal conductivity, and the thickness of the elastic layer 20d is 200 μm.

[0042] Furthermore, a release layer 20e is formed on the outer surface of the elastic layer 20d for the purpose of preventing toner from adhering to the surface of the fixing film 20 and preventing image defects. The release layer 20e is made of a material with excellent non-stick properties, and for example, PFA (tetrafluoroethylene perfluoroalkyl vinyl ether) is preferred. Alternatively, PTFE (polytetrafluoroethylene), FEP (tetrafluoroethylene hexafluoropropylene), ETFE (tetrafluoroethylene ethylene), etc. are preferred as the release layer 20e. In this example, the release layer 20e was formed from PFA, and the thickness of the release layer 20e was set to 15 μm.

[0043] On the other hand, in the non-heat-generating region, the fixing film 20 has a layered structure including a base layer 20a, a protective layer 20c, an elastic layer 20d, and a release layer 20e, as shown in Figure 3(b). In the non-heat-generating region, the fixing film 20 does not have a conductive layer 20b. Details of the division pattern of the conductive layer 20b will be described later.

[0044] In this embodiment, an elastic layer 20d was provided between the protective layer 20c and the release layer 20e, but this is not limited to this. For example, the elastic layer 20d may be omitted, and the protective layer 20c and the release layer 20e may be placed adjacent to each other. A primer layer may also be provided to enhance the adhesion between each layer. Furthermore, a layer constituting the inner surface of the fixing film 20 may be provided on the inner circumference side of the base layer 20a.

[0045] Next, the magnetic core 30 and excitation coil 31 provided in the internal space of the fixing film 20 will be described. Figure 4 is a perspective view showing the fixing film 20, magnetic core 30 and excitation coil 31. The magnetic core 30 has a cylindrical shape extending in the longitudinal direction LD and is positioned approximately in the center of the fixing film 20 by fixing means (not shown). This magnetic core 30 functions as a member that guides magnetic field lines (magnetic flux) generated by the alternating magnetic field of the excitation coil 31 into the internal space of the fixing film 20 and forms a path (magnetic path) for the magnetic field lines.

[0046] The magnetic core 30 is preferably made of a material with low hysteresis loss and high relative permeability. Suitable materials for the magnetic core 30 include, for example, ferromagnetic materials composed of highly permeable oxides or alloys such as calcined ferrite, ferrite resin, amorphous alloys, and permalloy. The magnetic core 30 is formed in a closed shape with a length in the longitudinal LD ​​of, for example, 200 mm to 300 mm. The diameter of the magnetic core 30 is preferably as large as possible in terms of cross-sectional area, within the range that allows it to be housed inside the fixing film 20. In this embodiment, calcined ferrite with a length of 240 mm and a diameter of 15 mm was used for the magnetic core 30. Note that the shape of the magnetic core 30 is not limited to a cylindrical shape; a prismatic shape or other shapes can also be selected.

[0047] In this embodiment, the magnetic core 30 is arranged only within the internal space of the fixing film 20 to form an open magnetic path, but the embodiment is not limited to this. For example, the magnetic core may be arranged outside the fixing film 20 so as to encircle the fixing film 20 to form a closed magnetic path.

[0048] The excitation coil 31 is formed by winding a single copper wire with a diameter of 1 mm to 2 mm, coated with heat-resistant polyamide-imide, around a spiral axis X in a magnetic core 30 with approximately 10 to 30 turns, thereby creating a spiral-shaped section L. The spiral axis X extends almost parallel to the longitudinal direction LD. In the spiral-shaped section L, the spacing between coils (wires) is uniform, and in this embodiment, the number of turns is 18. When a high-frequency current (alternating current) is supplied to the excitation coil 31 from the high-frequency converter 51 via the power supply contacts 31a and 31b, an alternating magnetic field (magnetic field) is generated in the longitudinal direction LD of the fixing film 20.

[0049] [The principle of heat generation in fixing films] The heat generation principle of the fixing film 20 will be explained with reference to Figures 5(a) and 5(b). Figure 5(a) is a cross-sectional view of the fixing film 20 in the longitudinal direction LD, illustrating the relationship between the magnetic field and the current flowing through the conductive layer 20b. Figure 5(b) is a perspective view illustrating the relationship between the magnetic field and the current flowing through the conductive layer 20b. For the sake of simplicity, the protective layer 20c, elastic layer 20d, and release layer 20e are not shown in Figures 5(a) and 5(b).

[0050] Figure 5(a) shows an example in which the magnetic core 30, excitation coil 31, and conductive layer 20b are arranged concentrically from the center of the fixing film 20. In Figure 5(a), magnetic field lines moving in the depth direction are represented by Bin (a circle with an X inside), and magnetic field lines moving in the foreground direction are represented by Bout (a circle with a black dot inside).

[0051] As shown in Figure 5(a), at the moment when the current increases in the direction of arrow I in the excitation coil 31, a magnetic field line Bin is formed in the magnetic path, extending in the depth direction in the figure, and a magnetic field line Bout is formed that returns towards the viewer outside the fixing film 20. When such magnetic field lines are formed, an induced electromotive force is applied to the entire circumferential direction of the conductive layer 20b to cancel out the magnetic field lines, and a current flows in the direction of arrow J that circulates around the conductive layer 20b (hereafter, this current will be called the circumferential current).

[0052] Since the induced electromotive force is applied in the circumferential direction of the conductive layer 20b, the circumferential current flows uniformly within the conductive layer 20b. Furthermore, the magnetic field lines generated from the magnetic core 30 are repeatedly created, annihilated, and reversed in direction by the high-frequency current flowing through the excitation coil 31, so the circumferential current flows while repeatedly being created, annihilated, and reversed in direction in sync with the high-frequency current. When current flows through the conductive layer 20b, Joule heat is generated in the conductive layer 20b due to the electrical resistance of the material (metal) of the conductive layer 20b.

[0053] Since the magnetic field lines generated from the magnetic core 30 are parallel to the longitudinal direction LD of the fixing film 20, the circumferential current flows in the rotational direction of the fixing film 20. Therefore, as shown in Figure 5(b), circumferential current flows in the direction of arrow J in each of the electrically divided conductive layers 20b of the fixing film 20. In this way, in the fixing film 20 of this embodiment, by passing a high-frequency current through the excitation coil 31, an induced current is generated in the divided conductive layers 20b (divided conductors 20b1), causing the conductive layers 20b (divided conductors 20b1) to heat up. That is, the divided conductors 20b1 are conductors that heat up due to the induced electromotive force when an alternating magnetic field is generated.

[0054] [Fixing operation] When the image forming operation of the printer 100 begins, the aforementioned fixing device 80 electromagnetically inductively heats the fixing film 20 using the aforementioned heating principle at a predetermined timing. Also, as shown in Figure 2, the fixing device 80 rotates the pressure roller 82 in the rotational direction Rp by the rotational drive of a motor (not shown). The fixing film 20 rotates in the rotational direction Rf, following the rotation of the pressure roller 82, with the inner circumferential surface of the fixing film 20 in contact with the friction portion 83a of the nip portion forming member 83.

[0055] As shown in Figure 4, the high-frequency converter 51 supplies high-frequency current to the excitation coil 31 via power supply contacts 31a and 31b. The control circuit 50 controls the high-frequency converter 51 based on the temperature detected by the temperature sensor 85 located in the center of the longitudinal LD ​​of the fixing film 20. This allows the fixing film 20 to be heated by electromagnetic induction while maintaining and adjusting the surface temperature to a predetermined target temperature (approximately 150°C to 200°C). Then, as shown in Figure 2, the recording material P carrying the unfixed toner image T (image) is clamped and transported in the fixing nip Nf, thereby applying heat and pressure to the toner image T and fixing the toner image T to the recording material P.

[0056] [Abrasive portion of the nip-forming member] Next, the shape of the friction portion 83a of the nip portion forming member 83 will be described using Figures 6(a) to 7(b). As shown in Figure 6(a), the friction portion 83a has a base surface 90 facing the fixing film 20 and a plurality of protrusions 91 that project from the base surface 90 toward the pressure roller 82 and contact the fixing film 20. In this embodiment, a plurality of protrusions 91 are provided on the base surface 90 of the friction portion 83a, and the spacing between the protrusions 91 in the longitudinal direction LD of the fixing film 20 is made narrower than the pitch of the divided conductors 20b1. The purpose of this is to suppress the occurrence of thickness unevenness in the longitudinal direction LD of the lubricant 84 caused by the divided conductors 20b1 of the fixing film 20 as described above. The configuration of the protrusions 91 will be described in detail below.

[0057] As shown in Figure 3(c), the fixing film 20 of this embodiment has intermittently divided conductors 20b1 in the longitudinal direction LD. That is, heat-generating regions where divided conductors 20b1 are present and non-heat-generating regions where they are not present alternate along the longitudinal direction LD of the fixing film 20, which can cause temperature unevenness. On the release layer 20e side of the fixing film 20 that is in contact with the recording material P, the temperature unevenness caused by the divided conductors 20b1 is thermally diffused in the protective layer 20c and the elastic layer 20d, so image defects caused by temperature unevenness are unlikely to occur in the toner image on the recording material.

[0058] In contrast, on the base layer 20a side that is in contact with the nip portion forming member 83, only the base layer 20a exists between the divided conductor 20b1 and the nip portion forming member 83, so the thermal diffusion effect is small and temperature unevenness is likely to occur. As a result, temperature unevenness is likely to occur in the lubricant 84 that is in contact with the base layer 20a, viscosity unevenness of the lubricant 84 occurs, and as a result there is a risk that thickness unevenness of the lubricant 84 will occur.

[0059] Here, considering the friction between the fixing film 20 and the nip forming member 83 based on the theory of the Stribeck curve, a fluid lubrication state is preferable, where the lubricant 84 is thick and the fluid pressure of the lubricant 84 supports the load. However, as mentioned above, if there are thickness inconsistencies in the lubricant 84, the thin regions of the lubricant 84 are more likely to transition from fluid lubrication to mixed lubrication or boundary lubrication. This can lead to partial direct contact between the fixing film 20 and the nip forming member 83, making it difficult to ensure good sliding properties. In particular, when the printer 100 feeds a large number of sheets and the rotation time of the fixing film 20 is long, the total amount of lubricant 84 decreases. Therefore, if the thickness inconsistencies of the lubricant 84 occur as described above, there is a risk that the torque of the fixing device 80 will increase, stick-slip will occur, or the inner surface of the fixing film 20 will wear down, thus hindering the long lifespan of the fixing device 80.

[0060] Therefore, in this embodiment, in order to suppress the occurrence of thickness unevenness in the lubricant 84 caused by the divided conductor 20b1, a plurality of protrusions 91 are provided on the friction portion 83a of the nip portion forming member 83. As a result, as the fixing film 20 rotates, the protrusions 91 stir the lubricant 84 in the longitudinal direction LD, and smooth out the thickness unevenness of the lubricant 84 in the longitudinal direction LD at the friction portion 83a.

[0061] In this embodiment, the protrusions 91 are formed by embossing. Specifically, the protrusions 91 are formed by chemical etching of the aluminum base material of the nip portion forming member 83. For example, the friction surface 83a is processed by the corrosion action of chemicals on an aluminum base material that has been masked according to the desired shape and arrangement of the protrusions 91. Other methods for forming the protrusions 91 may also be used, such as press working or laser processing. In this embodiment, chemical etching is performed on the aluminum base material to form the desired shape and arrangement of the protrusions 91 on the friction surface 83a, and then anodizing is performed.

[0062] Next, the arrangement of the protrusions 91 on the friction portion 83a of this embodiment will be described in detail using Figure 6(a). Figure 6(a) is a diagram illustrating the arrangement of the protrusions 91 provided on the friction portion 83a of the nip portion forming member 83, and is a view of the friction portion 83a from the pressure roller 82 side. In this embodiment, each of the multiple mountain-shaped protrusions 91 on the friction portion 83a is arranged in an island-like manner, independently spaced apart in the longitudinal direction LD and the rotational direction Rf of the fixing film 20. Each protrusion 91 is formed in a substantially circular shape when viewed from the pressure roller 82 side. As shown in Figure 6(a), the protrusions 91 are arranged at equal intervals with a pitch Lx along the longitudinal direction LD. In this embodiment, the pitch Lx is set to 1000 μm as an example.

[0063] Multiple protrusions 91 are arranged on the fixing film 20 with a shift in the longitudinal direction LD in the rotation direction Rf. As shown in Figure 6(a), the protrusions 91 on the straight line P1 along the longitudinal direction LD are arranged at equal intervals with a pitch Lx, starting from a reference position S0 in the longitudinal direction LD. In contrast, the protrusions 91 on the adjacent straight line P2 in the rotation direction Rf are arranged at equal intervals with a pitch Lx, starting from a position shifted by 3 / 4 Lx (=750 μm) in the longitudinal direction LD from the reference position S0. Furthermore, the protrusions 91 on the straight line P3 are arranged at equal intervals with a pitch Lx, starting from a position shifted by 1 / 4 Lx (=250 μm) in the longitudinal direction LD from the reference position S0. The protrusions 91 along the straight line P4 are arranged at equal intervals with a pitch Lx, starting from a position shifted by 1 / 2 Lx (=500 μm) in the longitudinal direction LD from the reference position S0. Thus, in the sliding portion 83a of this embodiment, four protrusions 91 are periodically arranged, shifted by 1 / 4 Lx (=250 μm) in the longitudinal direction LD along the rotational direction Rf.

[0064] The arrangement of the multiple protrusions 91 is as follows: in line P2, they are positioned at a location shifted by 3 / 4 Lx from the reference position S0; in line P3, they are positioned at a location shifted by 1 / 4 Lx from the reference position S0; and in line P4, they are positioned at a location shifted by 1 / 2 Lx from the reference position S0. However, this is not limited to this arrangement. For example, in line P2, they may be positioned at a location shifted by 1 / 4 Lx from the reference position S0; in line P3, they may be positioned at a location shifted by 1 / 2 Lx from the reference position S0; and in line P4, they may be positioned at a location shifted by 3 / 4 Lx from the reference position S0. Alternatively, other amounts of shift are also acceptable. Furthermore, the number of lines is not limited to four; two or more lines can be arranged with a shift in the longitudinal direction LD.

[0065] In this embodiment, the reason why the protrusions 91 are positioned offset in the longitudinal direction LD along the rotational direction Rf is to agitate the lubricant 84 with the protrusions 91 and eliminate thickness unevenness. If the protrusions 91 are not positioned offset in the longitudinal direction LD along the rotational direction Rf, areas that are always in contact with the protrusions 91 and areas that are not in contact with the protrusions 91 will occur on the inner circumferential surface of the fixing film 20 at a pitch Lx. In the areas that are always in contact with the protrusions 91, the amount of lubricant 84 will be less, and conversely, in the areas that are not always in contact with the protrusions 91, the amount of lubricant 84 will be more. Thus, if the protrusions 91 are not positioned offset in the longitudinal direction LD along the rotational direction Rf, there is a risk that the protrusions 91 will cause thickness unevenness in the lubricant 84. Therefore, in this embodiment, the position of the protrusions 91 is offset in the longitudinal direction LD along the rotational direction Rf.

[0066] Next, the contact area between the shape of the protrusions 91 and the inner circumferential surface of the fixing film 20 will be explained using Figures 7(a) and 7(b). Figure 7(a) is a diagram illustrating the shape of the protrusions 91 when viewed from upstream in the rotation direction Rf of the fixing film 20, and the spacing between adjacent protrusions 91 in the longitudinal direction LD. In Figure 7(a), the cross-sectional shape (P1 cross-section) when the protrusions 91 in Figure 6(a) are cut by a straight line P1 and viewed from upstream in the rotation direction Rf, and the cross-sectional shape (P3 cross-section) when cut by a straight line P3 and viewed from upstream in the rotation direction Rf are shown side by side. As shown in Figure 7(a), mountain-shaped protrusions 91 are provided at equal intervals with a pitch Lx. Comparing the P1 cross-section and the P3 cross-section when viewed from upstream in the rotation direction Rf, the protrusions 91 are offset in the longitudinal direction LD by a spacing of 1 / 4 of the pitch Lx.

[0067] Here, the height h of the protrusion 91 is preferably set to 5 μm to 100 μm depending on the shape of the protrusion 91, taking into consideration the leveling effect of the lubricant 84 and the contact pressure of the protrusion 91 on the inner surface of the fixing film 20. In this embodiment, the height h of the protrusion 91 was set to 20 μm.

[0068] Figure 7(b) shows the contact state between the protrusion 91 and the fixing film 20. Figure 7(b) is a projection of the P3 cross section onto the P1 cross section when viewed from upstream in the rotational direction Rf of the fixing film 20, with the far side of the paper being downstream in the rotational direction Rf. In Figure 7(b), the protrusion 91 is shown enlarged to explain the contact state with the fixing film 20. As shown in Figure 7(b), the protrusion 91 is in contact with the base layer 20a on the inner circumferential surface of the fixing film 20 at the contact surface 91a, which is the leading edge surface on the fixing film 20 side, with a longitudinal width Lc. The protrusion 91 also has an inclined surface 91b that is continuously provided between the contact surface 91a and the base surface 90.

[0069] At this time, the distance La of the region not in contact with the protrusions 91 on the inner circumferential surface of the fixing film 20 is La = 1 / 4Lx - Lc. Adding the P2 and P4 cross-sections to the P1 and P3 cross-sections, when all the protrusions 91 on the friction portion 83a are viewed from upstream in the rotational direction Rf of the fixing film 20, each protrusion 91 is adjacent to one another with a distance La. In this embodiment, since the longitudinal width Lc of the contact surface 91a with the fixing film 20 is 150 μm, the value of the distance La of the region not in contact with the protrusions 91 is 100 μm.

[0070] Figure 6(b) shows the arrangement of segmented conductors 20b1 in the fixing film 20. As shown in Figure 6(b), in the fixing film 20, multiple segmented conductors 20b1 exist intermittently along the longitudinal direction LD at a pitch Lb. In this embodiment, the pitch Lb of the segmented conductors 20b1 was set to 500 μm. That is, multiple segmented conductors 20b1 are arranged in a line along the longitudinal direction LD at a predetermined pitch Lb.

[0071] In this embodiment, the spacing La between adjacent protrusions 91, as viewed from upstream in the rotational direction Rf of the fixing film 20, is set to be narrower than the pitch Lb of the divided conductors 20b1 of the fixing film 20. That is, the spacing La (=100μm) between the protrusions 91, as viewed from upstream in the rotational direction Rf of the fixing film 20, is narrower than the pitch Lb (=500μm) of the divided conductors 20b1 of the fixing film 20. By making the spacing La of the protrusions 91 narrower than the pitch Lb of the divided conductors 20b1, the thickness unevenness of the lubricant 84 caused by the divided conductors 20b1 is smoothed out in the longitudinal direction LD by the protrusions 91 of the friction portion 83a as the fixing film 20 rotates. This makes it possible to eliminate the thickness unevenness of the lubricant 84.

[0072] Here, if the spacing La between the protrusions 91 is wider than the pitch Lb of the divided conductor 20b1, there will be regions where the leveling effect of the protrusions 91 is not sufficiently generated, which may cause localized thickness unevenness of the lubricant 84. In contrast, by making the spacing La between the protrusions 91 narrower than the pitch Lb of the divided conductor 20b1, the leveling effect of the protrusions 91 can be sufficiently generated in all regions. Therefore, it is possible to suppress thickness unevenness of the lubricant 84 caused by the divided conductor 20b1.

[0073] Furthermore, the spacing La between the protrusions 91 as viewed from upstream in the rotational direction Rf of the fixing film 20 may be 0. For example, the pitch Lx in this embodiment may be set to 600 μm or less, and the arrangement of the protrusions 91 may be such that there is no spacing between the protrusions 91 as viewed from upstream in the rotational direction Rf of the fixing film 20. In this case as well, the spacing La between the protrusions 91 as viewed from upstream in the rotational direction Rf of the fixing film 20 can be made narrower than the pitch Lb of the divided conductor 20b1 of the fixing film 20, thereby suppressing thickness unevenness of the lubricant 84 caused by the divided conductor 20b1.

[0074] In this embodiment, the lubricant 84 is agitated and leveled as it flows between adjacent protrusions 91. That is, grooves 60 are formed between the base surface 90 and the multiple protrusions 91, allowing the lubricant 84 to pass through the grooves 60. In this case, if the grooves 60 extend only in the rotational direction Rf, the lubricant 84 will not be sufficiently leveled in the longitudinal direction LD. Therefore, in this embodiment, the grooves 60 are formed in a shape that extends in a direction intersecting the rotational direction Rf of the fixing film 20. As a result, the lubricant 84 guided through the grooves 60 moves in a direction intersecting the rotational direction Rf and is leveled in the longitudinal direction LD. In this embodiment, as shown in Figure 6(a), the area between the base surface 90 and the inclined surface 91b, which is the part of the sliding portion 83a other than the contact surface 91a of the protrusions 91, forms the grooves 60 as a whole. The lubricant 84 is moved by the groove 60 formed in the region between the base surface 90 and the inclined surface 91b.

[0075] Furthermore, in this embodiment, as described above, the spacing La (=100 μm) between the protrusions 91 viewed from upstream in the rotational direction Rf of the fixing film 20 is narrower than the pitch Lb (=500 μm) of the divided conductors 20b1 of the fixing film 20. If this configuration is defined in terms of the grooves 60, then, viewed in the rotational direction Rf, the minimum width (spacing La) of the grooves 60 is smaller than the pitch Lb (=500 μm) of the divided conductors 20b1.

[0076] [Comparison with the comparative example] Next, we will describe the evaluation experiment that confirmed the improvement in durability of this embodiment. The effect was confirmed by comparing the nip-forming member 83 of this embodiment (Embodiment 1), which has a protrusion 91 shown in Figure 6(a) on the abrasive portion 83a, with a nip-forming member without a protrusion 91 on the abrasive portion 83a, which was used as Comparative Example 1. The evaluation experiment was conducted using a paper-feed durability test, and the conditions for the occurrence of stick-slip and the torque value of the fixing device 80 were compared between Comparative Example 1 and Embodiment 1. The details of the durability test will be described below.

[0077] For the paper feeding conditions, GFC-081 (product name, Canon Marketing Japan) was used as the recording material P, and continuous printing was performed at a paper transport speed of 350 mm / sec (throughput of 65 sheets per minute). In the durability test, the occurrence of stick-slip was checked every 50,000 sheets of paper fed. The slower the rotation speed of the fixing film 20, the thinner the lubricant 84 tends to be, and the more likely stick-slip is to occur. Therefore, to check for stick-slip, the fixing unit 80 was driven alone without feeding the recording material P, and the rotation speed of the fixing film 20 was changed to 200, 150, 100, and 50 mm / sec, and it was determined whether or not abnormal noise caused by stick-slip occurred. When driving the fixing unit 80 alone, the temperature control was performed so that the surface temperature of the fixing film 20 was 200°C based on the temperature detected by the temperature sensor 85.

[0078] The durability test results are shown in Table 1. Table 1 shows the occurrence of stick-slip after a predetermined number of sheets have been fed through in Comparative Example 1 and Example 1. × indicates when abnormal noise caused by stick-slip occurred, and ○ indicates when it did not occur. [Table 1]

[0079] As shown in Table 1, in Comparative Example 1, which does not have a protrusion 91 on the friction portion 83a, no stick-slip occurred up to 150,000 sheets. However, after 200,000 sheets were fed, when the fuser 80 was driven at 50 mm / sec, a chattering noise caused by stick-slip was detected. Further testing revealed that after 250,000 sheets, chattering noise caused by stick-slip was detected at speeds below 100 mm / sec, and after 300,000 sheets, it was detected at speeds below 150 mm / sec. When stick-slip occurs in the low-speed range, there is a risk that abnormal noises caused by stick-slip may occur when printing in low-speed mode, such as when printing on thick paper or rough paper, or at the start and stop of the fuser 80.

[0080] In contrast, in Example 1, no abnormal noise caused by stick-slip was observed even at low-speed rotation after 300,000 sheets of paper had been fed through. In this example, it was confirmed that unevenness of the lubricant 84 was suppressed and the occurrence of stick-slip was suppressed by providing protrusions 91 on the friction portion 83a of the nip portion forming member 83 at a narrower interval than the interval between the divided conductive members 20b1 of the fixing film 20.

[0081] Furthermore, a comparison of the torque values ​​of the fixing device 80 was also performed. In Comparative Example 1 and Example 1, when the fixing device 80 was driven independently at 200 mm / sec after 300,000 sheets of paper had been fed through, the torque of the fixing device 80 was measured at 6 kgf·cm in Comparative Example 1, while it was 4 kgf·cm in Example 1. Thus, in this example, the torque value after durability could also be reduced compared to Comparative Example 1, confirming that good sliding properties between the fixing film 20 and the nip portion forming member 83 can be maintained over a long period of time.

[0082] As is clear from the evaluation experiments described above, in this embodiment, the unevenness of the lubricant 84 caused by the segmented conductor 20b1 can be suppressed, thereby reducing the torque value after durability while suppressing the occurrence of stick-slip. Therefore, it is possible to improve the durability of the fixing device 80.

[0083] As described above, in the fixing device 80 of this embodiment, the friction portion 83a has a groove portion 60 that extends in a direction intersecting the rotation direction Rf and through which the lubricant 84 can pass. This equalizes the thickness unevenness of the lubricant 84. In particular, in this embodiment, the groove portion 60 is composed of protrusions 91, and the distance La between adjacent protrusions 91 as viewed from upstream in the rotation direction Rf of the fixing film 20 is made narrower than the pitch Lb of the divided conductors 20b1 of the fixing film 20. This equalizes the thickness unevenness of the lubricant 84, suppresses the occurrence of thickness unevenness of the lubricant 84 in the longitudinal direction LD on the inner circumferential surface of the fixing film 20, and extends the lifespan of the fixing device 80.

[0084] Furthermore, in the fixing device 80 of this embodiment, the protrusions 91 are arranged in an independent island-like manner in both the longitudinal direction LD and the rotational direction Rf. As a result, the lubricant 84 is moved in a complex manner in multiple directions intersecting the rotational direction Rf between the protrusions 91, and is thoroughly spread.

[0085] In the above-described embodiment, the convex portion 91 is described as having a mountain-like shape with an inclined surface 91b and being approximately circular in shape when viewed from the pressure roller 82, but it is not limited to this. For example, as shown in Figure 8(a), the convex portion 191 in the sliding portion 183a may be convex in shape with a side surface 191b perpendicular to the base surface 190. In this case, the contact surface 191a may be rectangular inclined at 45 degrees with respect to the longitudinal direction LD when viewed from the pressure roller 82. Alternatively, the contact surface 191a may be square in shape, and the convex portions 191 may be arranged with a periodic shift of two rows with respect to the rotational direction Rf.

[0086] Alternatively, as shown in Figure 8(b), the protrusion 291 in the friction portion 283a has a convex shape with a side surface 291b perpendicular to the base surface 290, and the contact surface 291a may have a scale-like shape with a pointed tip in the longitudinal direction LD as viewed from the pressure roller 82, and the other parts rounded. In this case as well, the protrusions 291 may be arranged with a two-row periodic offset with respect to the rotational direction Rf.

[0087] Furthermore, although the arrangement of the protrusions 91 is regular in the embodiment described above, it is not limited to this, and a random arrangement is also possible as long as the distance La between adjacent protrusions 91 as seen in the rotational direction Rf is narrower than the pitch Lb of the divided conductor 20b1. In this case as well, since the distance La between adjacent protrusions 91 as seen in the rotational direction Rf is narrower than the pitch Lb of the divided conductor 20b1, the thickness unevenness of the lubricant 84 can be smoothed out in the same way as in the embodiment described above.

[0088] Furthermore, in the embodiment described above, the divided conductor 20b1 is formed in a ring shape parallel to the rotation direction Rf, but this is not limited to this. For example, the ring-shaped divided conductors 20b1 may be arranged in an inclined manner rather than parallel to the rotation direction Rf. In this case as well, if temperature unevenness occurs in the lubricant 84, it is possible to suppress the temperature unevenness of the lubricant 84 by making the distance La between adjacent protrusions 91 as seen in the rotation direction Rf narrower than the pitch Lb of the divided conductor 20b1.

[0089] Furthermore, although the above-described embodiment describes a configuration in which the aluminum base material of the nip portion forming member 83 is provided with the shape of the protrusion 91, the embodiment is not limited to this. For example, a sliding sheet may be provided between the nip portion forming member 83 and the fixing film 20, and the protrusion 91 described above may be provided on the sliding surface of the sliding sheet that rubs against the fixing film 20. In this case, for example, the sliding sheet may be made of a heat-resistant resin such as PI (polyimide) or PAI (polyamide-imide) in the base layer and coated with a fluororesin on the surface layer, and the desired protrusion 91 may be formed by heat embossing or the like. By fixing such a sliding sheet with the protrusion 91 to the support member 86 on the upstream side of the fixing nip portion Nf and arranging it so that it slides between the fixing film 20 and the nip portion forming member 83, it is also possible to suppress thickness unevenness of the lubricant 84.

[0090] Furthermore, although the above-described embodiment described the case in which a divided conductor 20b1 that generates heat by electromagnetic induction is used as a plurality of heating elements, it is not limited to this. For example, heaters divided in the longitudinal direction LD may be used as a plurality of heating elements.

[0091] <Example 2> Next, Embodiment 2 of the present disclosure will be described. Embodiment 2 is a modification of the arrangement pattern of the protrusions 91 in Embodiment 1. For this reason, the same configuration as in Embodiment 1 will be omitted from the illustration or will be described using the same reference numerals in the figure. This embodiment differs from Embodiment 1, which has an island-like arrangement, in that the protrusions 391 of the sliding portion 383a have a continuous shape. The shape of the protrusions 391 of the sliding portion 383a in this embodiment will be explained using Figure 9(a). Figure 9(a) is a view of the sliding portion 383a from the pressure roller 82 side.

[0092] As shown in Figure 9(a), the sliding portion 383a has a plurality of zigzag-shaped protrusions 391 with respect to the rotational direction Rf. In this embodiment, the protrusions 391 have a continuous shape with an intersection angle with respect to the rotational direction Rf. Specifically, each protrusion 391 has a first straight portion 391c located on one side LD1 of the longitudinal direction LD where the downstream side of the rotational direction Rf is located more than the upstream side, and a second straight portion 391d located on the other side LD2 of the longitudinal direction LD where the downstream side of the rotational direction Rf is located more than the upstream side. The first straight portion 391c and the second straight portion 391d are examples of straight portions and are formed in a straight line extending in a direction that intersects both the longitudinal direction LD and the rotational direction Rf. In this embodiment, grooves 360 are formed between each of the protrusions 391.

[0093] By providing continuous protrusions 391 that intersect the rotation direction Rf of the fixing film 20 in this manner, the lubricant 84 diffuses in the longitudinal direction LD as the fixing film 20 rotates, thereby making it possible to smooth out the thickness unevenness of the lubricant 84. Even with such continuous protrusions 391, the spacing between adjacent protrusions 391 as viewed from upstream of the rotation direction Rf of the fixing film 20 is narrower than the pitch Lb of the divided conductor 20b1, so that there are no regions where the smoothing effect of the protrusions 391 is insufficient.

[0094] Furthermore, in this embodiment, the width Lz of the longitudinal LD ​​at each protrusion 391 is made wider than the pitch Lb of the divided conductors 20b1 of the fixing film 20. This allows the protrusions 391 to be arranged within the fixing nip portion Nf such that at least a portion of them overlaps with the multiple divided conductors 20b1, thereby allowing the lubricant 84 to diffuse beyond the spacing between the divided conductors 20b1. That is, each protrusion 391 is arranged such that at least a portion of it overlaps with two adjacent divided conductors 20b1 when viewed in a direction perpendicular to both the longitudinal LD ​​and the rotational direction Rf. By arranging the continuous protrusions 391 across multiple divided conductors 20b1 in this way, the effect of leveling the thickness unevenness of the lubricant 84 can be improved.

[0095] In this embodiment, the segmented conductors 20b1 are arranged with a gap of 200 μm between them. Therefore, if the width Lz of the longitudinal LD ​​of the protrusion 391 is at least 200 μm, it is possible that it will span multiple segmented conductors 20b1, thus generating a leveling effect. However, if the width Lz of the longitudinal LD ​​is only slightly over 200 μm, it may not span multiple segmented conductors 20b1 depending on the position of the protrusion 391. Therefore, it is preferable to make it wider, for example, wider than the pitch Lb. Furthermore, by making the width Lz of the longitudinal LD ​​wider than the sum of the pitch Lb and the 200 μm gap, it is possible to make it span multiple segmented conductors 20b1 at any position, further improving the leveling effect.

[0096] In this embodiment as well, the friction portion 83a extends in a direction intersecting the rotational direction Rf and has a groove portion 360 through which the lubricant 84 can pass. This helps to even out the thickness unevenness of the lubricant 84. In particular, in this embodiment, the spacing La between adjacent protrusions 391 viewed from upstream in the rotational direction Rf of the fixing film 20 is made narrower than the pitch Lb of the divided conductors 20b1 of the fixing film 20. This evens out the thickness unevenness of the lubricant 84, suppressing the occurrence of thickness unevenness of the lubricant 84 in the longitudinal direction LD on the inner circumferential surface of the fixing film 20, thereby extending the lifespan of the fixing device 80.

[0097] In the example shown in Figure 9(a), the convex portion 391 is described as having four straight sections, but it is not limited to this; it is sufficient to have two or more straight sections. Furthermore, the section may not be straight, but rather curved or other curved shapes, for example.

[0098] In the embodiment described above, the sliding portion 383a was described as having a zigzag-shaped protrusion 391 having multiple straight sections, but it is not limited to this. For example, as shown in Figure 9(b), the sliding portion 483a may have multiple protrusions 491 that are oblique in shape with respect to the rotation direction Rf of the fixing film 20. In this case, the protrusions 491 consist of straight sections formed in a straight line that extends in a direction intersecting both the longitudinal direction LD and the rotation direction Rf. As shown in Figure 9(b), by providing oblique-shaped protrusions 491 that have an intersection angle with respect to the rotation direction Rf of the fixing film 20, it is possible to smooth out the thickness unevenness of the lubricant 84 as the fixing film 20 rotates. In this case, grooves 460 are formed between each of the protrusions 491.

[0099] Furthermore, the protrusions 491 are arranged symmetrically with respect to the center LC of the longitudinal LD ​​of the nip portion forming member 83, and are formed so that the protrusions 491 move closer to the center LC along the rotational direction Rf of the fixing film 20. That is, in the rotational direction Rf, the protrusions 491 have an upstream end 490e and a downstream end 490f, with the downstream end 490f being located closer to the center of the friction portion 483a in the longitudinal LD ​​than the upstream end 490e. By arranging the obliquely shaped protrusions 491 in this way, as the fixing film 20 rotates, the thickness unevenness of the lubricant 84 is evened out, and the lubricant 84 is moved closer to the center LC of the longitudinal LD. As a result, the amount of lubricant 84 that leaks out from both ends of the longitudinal LD ​​of the fixing film 20 is reduced, and the amount of lubricant 84 on the inner surface of the fixing film 20 can be maintained over a long period of time, resulting in further improved durability.

[0100] Furthermore, in such diagonally shaped protrusions 491, it is preferable that each protrusion 491 is arranged to span across a plurality of segmented conductors 20b1 within the fixing nip portion Nf. That is, it is preferable to provide the diagonally shaped protrusions 91 such that the width Lg of the longitudinal LD ​​of the protrusion 491 within the fixing nip portion Nf is wider than the pitch Lb of the segmented conductors 20b1 of the fixing film 20.

[0101] Even in the convex portions 491 shown in Figure 9(b), the spacing La between adjacent convex portions 491, as viewed from upstream in the rotational direction Rf of the fixing film 20, is made narrower than the pitch Lb of the divided conductors 20b1 of the fixing film 20. This smooths out thickness variations in the lubricant 84, suppressing the occurrence of thickness variations in the lubricant 84 in the longitudinal direction LD on the inner circumferential surface of the fixing film 20, thereby extending the lifespan of the fixing device 80.

[0102] In the example shown in Figure 9(b), the convex portion 491 is described as being straight, but it is not limited to this and may be curved or other shapes.

[0103] <Example 3> Next, Embodiment 3 of the present disclosure will be described. Embodiment 3 is a modification of the arrangement pattern of the protrusions 91 in Embodiment 1. For this reason, the same configuration as in Embodiment 1 will be omitted from the illustration or will be described using the same reference numerals in the figure. In this embodiment, the protrusions 591 of the sliding portion 583a are not uniform, but are arranged in a way that changes along the longitudinal direction LD, which is different from Embodiment 1 in that the arrangement does not change. The shape of the protrusions 591 of the sliding portion 583a in this embodiment will be described using Figure 10(a). Figure 10(a) is a view of the sliding portion 583a from the pressure roller 82 side.

[0104] As shown in Figure 10(a), the sliding portion 583a has a plurality of mountain-shaped second protrusions 591A located in the central region D1 of its longitudinal direction LD, and a plurality of oblique-shaped first protrusions 591B located in the end region D2 of the end of the longitudinal direction LD. The second protrusions 591A are located closer to the center of the sliding portion 583a than the first protrusions 591B in the longitudinal direction LD, and have a different shape from the first protrusions 591B. The first protrusions 591B have a shape that extends toward the center of the sliding portion 583a in the longitudinal direction LD as it moves toward the rotational direction Rf. These first protrusions 591B are located closer to the end of the sliding portion 583a than to the center of the sliding portion 583a in the longitudinal direction LD. In this embodiment, the first protrusions 591B are located furthest from the center of the sliding portion 583a in the longitudinal direction LD among the plurality of protrusions 591.

[0105] By providing a diagonally shaped first protrusion 591B in the end region D2, leakage of lubricant 84 from the end of the longitudinal direction LD of the fixing film 20 can be suppressed. Furthermore, by providing a mountain-shaped second protrusion 591A in the central region D1, concentration of the lubricant 84 in the center of the longitudinal direction LD can be suppressed. In this way, by varying the shape and arrangement of the protrusions 591 along the longitudinal direction LD, rather than making them uniform in the friction surface 583a, it is possible to obtain secondary effects such as preventing leakage of the lubricant 84 and optimizing its distribution, in addition to the effect of leveling out thickness variations of the lubricant 84.

[0106] In this embodiment as well, the friction portion 83a extends in a direction intersecting the rotational direction Rf and has a groove through which the lubricant 84 can pass. This helps to even out the thickness variations of the lubricant 84. In particular, in this embodiment, the spacing La between adjacent protrusions 591 viewed from upstream in the rotational direction Rf of the fixing film 20 is made narrower than the pitch Lb of the divided conductors 20b1 of the fixing film 20. This evens out the thickness variations of the lubricant 84, suppressing the occurrence of thickness variations of the lubricant 84 in the longitudinal direction LD on the inner circumferential surface of the fixing film 20, and thus extending the lifespan of the fixing device 80.

[0107] Furthermore, as shown in Figure 10(b), the shape of the protrusions 691 may be changed to match the region of the fixing film 20 where the segmented conductors 20b1 are present. Figure 10(b) shows the relationship between the region of the fixing film 20 where the segmented conductors 20b1 are present and the region of the friction portion 683a where the protrusions 691 are present.

[0108] When the recording material P passes through the fixing device 80, heat is not removed from the recording material P in the non-paper-passing area, resulting in a temperature rise in the non-paper-passing area where the temperature of the fixing film 20 is higher than in the paper-passing area. To suppress this temperature rise in the non-paper-passing area, if the divided conductor 20b1 is not provided at the end of the fixing film 20 in the longitudinal direction LD as shown in Figure 10(b), temperature unevenness of the lubricant 84 will not occur at that end. Therefore, the protrusion 91 is provided in the region D3 where the divided conductor 20b1 is present, but it is not necessary to provide the protrusion 91 in the region D4 where the divided conductor 20b1 is not present.

[0109] Furthermore, if the spacing between the segmented conductors 20b1 of the fixing film 20 is not constant in the longitudinal direction LD, the shape and arrangement of the protrusions 691 may be changed in the longitudinal direction LD according to the spacing between the segmented conductors 20b1. In this way, the shape and arrangement of the protrusions 691 may be changed in the longitudinal direction LD depending on the arrangement of the segmented conductors 20b1 in the fixing film 20 and the corresponding purpose. The combinations of shapes and arrangements of the protrusions 691 and the areas to be changed when changing in the longitudinal direction LD are not limited to those described above, and it is preferable to combine and arrange protrusions 91 of various shapes according to the purpose.

[0110] <Example 4> Next, Embodiment 4 of the present disclosure will be described. Embodiment 4 is a modification of the arrangement pattern of the protrusions 91 in Embodiment 1. For this reason, the same configuration as in Embodiment 1 will be omitted from the illustration or will be described using the same reference numerals in the figures. In this embodiment, the protrusions 791 of the sliding portion 783a are not uniform, but rather arranged in a way that changes along the rotational direction Rf, which is different from Embodiment 1 in that the arrangement does not change. The shape of the protrusions 791 of the sliding portion 783a in this embodiment will be described using Figures 11(a) and (b). Figure 11(a) shows a schematic cross-sectional view of the fixing device 780 and the nip force distribution within the fixing nip portion Nf.

[0111] In this embodiment, the cross-sectional shape of the nip-forming member 783 differs from that of Embodiment 1. The thickness of the nip-forming member 83 increases toward the downstream side in the rotational direction Rf of the fixing film 20, and the base surface 790 is inclined to protrude toward the pressure roller 82. By using a nip-forming member 783 with this shape, it is possible to generate a high nip force in, for example, region Sp downstream of the fixing nip portion Nf, as shown in the nip force distribution of the fixing nip portion in the figure. Here, nip force refers to the force that the friction portion 783a receives from the pressure roller 82, regardless of the presence or absence of a protrusion, and is a different concept from pressure per unit area. By applying a high nip force downstream of the fixing nip portion Nf in this way, the toner of the recording material P can be efficiently deformed and melted when it has softened sufficiently, thereby improving fixing performance. In other words, the base surface 790 has a shape in which the amount of protrusion toward the pressure roller 82 in the region Sp (second position), which is located downstream of the upstream part in the rotational direction Rf (first position), is greater than the amount of protrusion toward the pressure roller 82 in the upstream part (first position) in the rotational direction Rf.

[0112] On the other hand, in the fixing nip portion Nf, in the region Sp where there is a locally high nip force, the pressing force on the inner surface of the fixing film 20 by the protrusion 791 of the nip portion forming member 783 is strong, which may accelerate wear of the inner surface of the fixing film 20. Therefore, in this embodiment, as shown in Figure 11(b), the arrangement of the protrusion 791 is not uniform in the friction portion 783a, but changes along the rotational direction Rf of the fixing film 20.

[0113] Figure 11(b) shows the friction portion 783a as viewed from the pressure roller 82 side. In this embodiment, as in Embodiment 1, a plurality of mountain-shaped protrusions 791 are provided on the friction portion 783a, but the height of the protrusions 791 in the region Sp, which has a high nip force in the rotational direction Rf of the fixing film 20, is lower than the height of the protrusions 791 in other regions. That is, the amount of protrusion of the protrusions 791 from the base surface 790 in region Sp is smaller than the amount of protrusion of the protrusions 791 from the base surface 790 in the upstream portion. In this way, by making the height of the protrusions 791 in the region Sp, which has a locally high nip force, lower than in other regions, it is possible to suppress wear on the inner circumferential surface of the fixing film 20.

[0114] In this embodiment, the height of the protrusions 791 is changed, but this is not the only way to do so. The shape of the protrusions 791, the spacing between them, etc., may be changed to suppress wear on the inner circumferential surface of the fixing film 20 in region Sp. For example, the total contact area of ​​the protrusions 791 that contact the fixing film 20 may be made larger in region Sp compared to other regions. Furthermore, the protrusions 791 may not be provided in region Sp at all.

[0115] Furthermore, in this embodiment, the height of the protrusions 791 is lower only in the region Sp having a high nip force than in other regions, resulting in two overall height levels for the protrusions 791. However, this is not limited to this, and instead of changing the height of the protrusions 791 only in region Sp, the height, shape, spacing, etc. of the protrusions 791 may be changed in stages according to the nip force distribution within the fixing nip portion Nf. For example, if the nip force distribution changes in the rotational direction Rf of the fixing film 20, as in this embodiment, the height of the protrusions 791 may be lowered along the rotational direction Rf of the fixing film 20 as the nip force increases. Also, if the nip force changes with respect to the longitudinal direction LD, the shape and arrangement of the protrusions 791 may be changed according to the nip force distribution in the longitudinal direction LD. In this way, by changing the height, shape, spacing, etc. of the protrusions 791 according to the nip force distribution within the fixing nip portion Nf, it is possible to prevent wear of the inner surface of the fixing film 20 by the protrusions 791.

[0116] In this embodiment as well, the friction portion 83a extends in a direction intersecting the rotational direction Rf and has a groove through which the lubricant 84 can pass. This helps to even out the thickness variations of the lubricant 84. In particular, in this embodiment, the spacing La between adjacent protrusions 791 viewed from upstream in the rotational direction Rf of the fixing film 20 is made narrower than the pitch Lb of the divided conductors 20b1 of the fixing film 20. This evens out the thickness variations of the lubricant 84, suppressing the occurrence of thickness variations of the lubricant 84 in the longitudinal direction LD on the inner circumferential surface of the fixing film 20, and thus extending the lifespan of the fixing device 80.

[0117] Furthermore, the disclosure of this embodiment includes the following configuration examples and method examples. (Composition 1) In a fixing device that fixes a toner image onto a recording material, A heating unit comprising a rotatable and cylindrical rotating body, and a nip-forming member having a sliding portion that rubs against the inner circumferential surface of the rotating body, for heating a recording material on which a toner image has been formed, The opposing member, which faces the rotating body and rotates about a rotation axis extending in the axial direction, and which forms a nip portion together with the nip portion forming member via the rotating body, A lubricant is interposed between the sliding portion of the nip portion forming member and the inner circumferential surface of the rotating body. The rotating body has a plurality of ring-shaped heating elements that are divided in the axial direction so as to have gaps between them in the axial direction. The sliding portion extends in a direction intersecting the rotational direction of the rotating body and has a groove through which the lubricant can pass. A fixing device characterized by the following features. (Configuration 2) The sliding portion has a base surface facing the rotating body and a plurality of protrusions that project from the base surface toward the opposing member and contact the rotating body. The groove is formed between the base surface and the plurality of protrusions. The fixing device according to configuration 1, characterized by the above. (Composition 3) Each of the aforementioned multiple protrusions is independently arranged with spacing between them in the axial direction and the rotational direction. The fixing device according to configuration 2, characterized in that... (Composition 4) Each of the aforementioned multiple protrusions has a linear portion that is formed in a straight line and extends in a direction that intersects both the axial direction and the rotational direction. The fixing device according to configuration 2, characterized in that... (Composition 5) Each of the aforementioned multiple protrusions has an upstream end and a downstream end in the direction of rotation. The downstream end of the protrusion is located closer to the center of the sliding portion in the axial direction than the upstream end. A fixing device according to configuration 2 or 4, characterized by the above. (Composition 6) Each of the plurality of protrusions is arranged such that, when viewed in a direction perpendicular to both the axial direction and the rotational direction, at least a portion of it overlaps two adjacent heating elements. A fixing device according to any one of configurations 2 to 5, characterized by the above. (Composition 7) The plurality of heating elements are arranged in a line at a predetermined pitch in the axial direction, When viewed in the rotational direction, the minimum width of the groove is smaller than the predetermined pitch. A fixing device according to any one of configurations 2 to 6, characterized by the above. (Composition 8) The plurality of protrusions each have a first protrusion that extends toward the center of the sliding portion in the axial direction as it moves toward the rotational direction, The first protrusion is positioned in the axial direction closer to the end of the sliding portion than to the center of the sliding portion. A fixing device according to any one of configurations 2 to 7, characterized by the above. (Composition 9) The first protrusion is positioned among the plurality of protrusions at the position furthest from the center of the sliding portion in the axial direction. The fixing device according to configuration 8, characterized by the above. (Composition 10) The plurality of protrusions are positioned closer to the center of the sliding portion than the first protrusion in the axial direction, and each has a second protrusion with a different shape from the first protrusion. The fixing device according to configuration 8 or 9, characterized by the above. (Composition 11) The base surface has a shape in which the amount of protrusion toward the opposing member at the second position, which is located downstream of the first position in the rotational direction, is greater than the amount of protrusion toward the opposing member at the first position. The amount of the protrusion of the convex portion from the base surface at the second position is smaller than the amount of the protrusion of the convex portion from the base surface at the first position. A fixing device according to any one of configurations 2 to 10, characterized by the above. (Composition 12) The aforementioned heating element is a conductor that generates heat due to an induced electromotive force when an alternating magnetic field is generated. A fixing device according to any one of configurations 1 to 11, characterized by the features described above. (Composition 13) The aforementioned multiple protrusions are formed by embossing. A fixing device according to any one of configurations 1 to 12, characterized by the features described above. (Composition 14) An image forming unit that forms a toner image on the recording material, A fixing device comprising any one of configurations 1 to 13, An image forming apparatus characterized by the following features. [Explanation of Symbols]

[0118] 20: Fixing film (rotating body) / 20b1: Divided conductor (heating element) / 60, 360, 460: Groove section / 70: Image forming section / 80: Fixing device / 81: Heating unit / 82: Pressure roller (opposing member) / 83: Nip section forming member / 83a, 183a, 283a, 383a, 483a, 583a, 683a, 783a: Friction section / 84: Lubricant / 90, 190, 290, 790: Base surface / 91, 191 ,291,391,491,591,691,791: protrusion / 100: printer (image forming apparatus) / 391c: first straight section (straight section) / 391d: second straight section (straight section) / 490e: upstream end / 490f: downstream end / 591A: second protrusion / 591B: first protrusion / Lb: pitch (predetermined pitch) / LD: longitudinal direction (axial direction) / Nf: fixing nip section (nip section) / P: recording material / Rf: rotational direction

Claims

1. In a fixing device that fixes a toner image onto a recording material, A heating unit comprising a rotatable and cylindrical rotating body, and a nip-forming member having a sliding portion that rubs against the inner circumferential surface of the rotating body, for heating a recording material on which a toner image has been formed, The opposing member, which faces the rotating body and rotates about a rotation axis extending in the axial direction, and which forms a nip portion together with the nip portion forming member via the rotating body, A lubricant is interposed between the sliding portion of the nip portion forming member and the inner circumferential surface of the rotating body. The rotating body has a plurality of ring-shaped heating elements that are divided in the axial direction so as to have gaps between them in the axial direction. The sliding portion extends in a direction intersecting the rotational direction of the rotating body and has a groove through which the lubricant can pass. A fixing device characterized by the following features.

2. The sliding portion has a base surface facing the rotating body and a plurality of protrusions that project from the base surface toward the opposing member and contact the rotating body. The groove is formed between the base surface and the plurality of protrusions. The fixing device according to feature 1.

3. Each of the aforementioned multiple protrusions is independently arranged with spacing between them in the axial direction and the rotational direction. The fixing device according to feature 2.

4. Each of the aforementioned multiple protrusions has a linear portion that is formed in a straight line and extends in a direction that intersects both the axial direction and the rotational direction. The fixing device according to feature 2.

5. Each of the aforementioned multiple protrusions has an upstream end and a downstream end in the direction of rotation. The downstream end of the protrusion is located closer to the center of the sliding portion in the axial direction than the upstream end. The fixing device according to feature 2.

6. Each of the plurality of protrusions is arranged such that, when viewed in a direction perpendicular to both the axial direction and the rotational direction, at least a portion of it overlaps with two adjacent heating elements. The fixing device according to feature 2.

7. The plurality of heating elements are arranged in a line at a predetermined pitch in the axial direction, When viewed in the rotational direction, the minimum width of the groove is smaller than the predetermined pitch. The fixing device according to feature 2.

8. The plurality of protrusions each have a first protrusion that extends toward the center of the sliding portion in the axial direction as it moves toward the rotational direction, The first protrusion is positioned in the axial direction closer to the end of the sliding portion than to the center of the sliding portion. The fixing device according to feature 2.

9. The first protrusion is positioned among the plurality of protrusions at the position furthest from the center of the sliding portion in the axial direction. The fixing device according to feature 8.

10. The plurality of protrusions are positioned closer to the center of the sliding portion than the first protrusion in the axial direction, and each has a second protrusion having a different shape from the first protrusion. The fixing device according to feature 8.

11. The base surface has a shape in which the amount of protrusion toward the opposing member at the second position, which is located downstream of the first position in the rotational direction, is greater than the amount of protrusion toward the opposing member at the first position. The amount of the protrusion of the convex portion from the base surface at the second position is smaller than the amount of the protrusion of the convex portion from the base surface at the first position. The fixing device according to feature 2.

12. The aforementioned heating element is a conductor that generates heat due to an induced electromotive force when an alternating magnetic field is generated. The fixing device according to feature 1.

13. The aforementioned multiple protrusions are formed by embossing. The fixing device according to feature 1.

14. An image forming unit that forms a toner image on the recording material, A fixing device according to any one of claims 1 to 13, comprising An image forming apparatus characterized by the following features.

Images