Fixing device

Abstract

To provide a fixing device that fits and holds a slide member into a fitting groove part of a fixing pad, and can prevent the occurrence of failure of fixation to a recording material due to projections formed on the slide member.SOLUTION: In a slide member 304 slid with a fixing belt 301, when seen from a width direction intersecting a conveyance direction (arrow X direction), a leading end of a most downstream projection 304b1 projects by "0.4 mm or more and 2 mm or less" (height H) compared with a proximity position 303b1 closest to a fixing nip part at a downstream-side guide part 303b. The slide member 304 is formed with the most downstream projection 304b1 on a substrate 304a so that the distance L between the leading end of the most downstream projection 304b1 and the proximity position 303b1 becomes "less than 3 mm" with respect to the conveyance direction. This can prevent the occurrence of failure of fixation to the recording material due to projections formed on the slide member 304 without impairing separability of the recording material passing through the fixing belt 301.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a fixing device suitable for use in an image forming apparatus using electrophotographic technology, such as a printer, a copier, a facsimile machine, or a multifunction peripheral.

Background Art

[0002] An image forming apparatus includes a fixing device that fixes a toner image on a recording material by applying heat and pressure to the recording material on which the toner image is formed. The fixing device has a rotating endless fixing belt, a fixing pad disposed non-rotatably on the inner peripheral side of the fixing belt, and a pressure roller that abuts against the outer peripheral surface of the fixing belt. In this fixing device, the fixing belt is pressed by the fixing pad and the pressure roller to form a fixing nip portion between the fixing belt and the pressure roller, and when the recording material is sandwiched and conveyed through the fixing nip portion, heat and pressure are applied, so that the toner image is fixed on the recording material.

[0003] However, if the frictional force between the fixing belt and the fixing pad is large, the rotation of the fixing belt is hindered. Therefore, in order to reduce the frictional force between the fixing belt and the fixing pad in the fixing nip portion where the pressure is high, a device provided with a sliding member that slides on the fixing belt has been proposed (Patent Document 1). Recently, in order to reduce the frictional force between the fixing belt and the sliding member, a sliding member having a plurality of convex portions formed on its surface has been used.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, the fixing pad has a concave fitting portion (hereinafter referred to as the fitting groove) into which the sliding member is fitted in order to hold the sliding member. However, conventionally, the protrusions formed on the sliding member made it difficult for the recording material to separate properly from the fixing belt, which could lead to poor fixing of the recording material.

[0006] In view of the above problems, the present invention aims to provide a fixing device that has a configuration in which a sliding member is fitted and held in the fitting groove of the fixing pad, and that can suppress the occurrence of fixing failures to the recording material caused by the recording material becoming difficult to separate from the fixing belt due to a protrusion formed on the sliding member. [Means for solving the problem]

[0007] A fixing device according to one embodiment of the present invention is a fixing device for fixing a toner image formed on a recording material to the recording material, comprising: an endless belt that heats the recording material; a rotating body that contacts the outer circumferential surface of the belt in a pressurizing direction; a pad member that forms a nip portion on the inside of the belt by clamping the belt between itself and the rotating body; and a sliding member that is held by the pad member and slides against the inner circumferential surface of the belt in the nip portion, wherein the rotating body, together with the belt, clamps and conveys the recording material in the conveying direction at the nip portion, and fixes the toner image on the recording material by applying heat and pressure, and the sliding member protrudes toward the rotating body on the side that slides with the belt. Furthermore, the pad member has a plurality of protrusions that slide against the inner circumferential surface of the belt, and the pad member has a guide portion that guides the belt after it has passed the nip portion, and in the state in which the nip portion is formed, the distance in the conveying direction between the downstream end of the tip of the downstreammost protrusion in the direction of rotation of the belt and the upstream end of the guide portion that contacts the inner circumferential surface of the belt in the direction of rotation of the belt is 3.0 mm or less, and the distance in the pressing direction between the tip of the downstreammost protrusion in the direction of rotation of the belt and the upstream end of the guide portion that contacts the inner circumferential surface of the belt in the direction of rotation of the belt is 0.4 mm or more and 2.0 mm or less. Furthermore, another fixing apparatus according to the present invention is a fixing apparatus for fixing a toner image formed on a recording material to the recording material, comprising: an endless belt that applies heat to the recording material; a rotating body that contacts the outer surface of the belt in the direction of pressure; and a pad member that forms a nip portion on the inside of the belt by sandwiching the belt between itself and the rotating body. A heating rotating body is positioned on the inner circumferential surface of the belt at a location different from the nip portion, and heats the belt. The pad member is held by the pad member and comprises a sliding member that slides against the inner circumferential surface of the belt at the nip portion, wherein the sliding member is A plate-shaped base, and from the base Multiple protrusions project toward the rotating body on the side that slides with the belt. and, The pad member and the inner circumferential surface of the belt slide against each other at least downstream of the nip portion in the transport direction of the recording material. Furthermore, the pad member has a guide portion that guides the belt after it has passed the nip portion, and in the state in which the nip portion is formed, the upstream end of the guide portion that contacts the inner circumferential surface of the belt in the direction of rotation of the belt is located in the pressing direction between the downstream end of the base body of the sliding member that slides with the belt in the direction of rotation of the belt and the tip of the downstreammost projection of the plurality of projections in the direction of rotation of the belt. It is characterized by the following: [Effects of the Invention]

[0008] According to the present invention, by fitting a sliding member into a fitting groove of a holding member to hold it in place, it is possible to suppress the occurrence of poor fixing of the recording material due to the recording material becoming difficult to separate from the fixing belt caused by a protrusion formed on the sliding member, with a simple configuration. [Brief explanation of the drawing]

[0009] [Figure 1] A schematic diagram showing a suitable image forming apparatus using the fixing device of this embodiment. [Figure 2] (a) A schematic diagram showing the fixing device, (b) A cross-sectional view showing the fixing belt, pressure roller, and fixing pad unit. [Figure 3] (a) Schematic diagram showing the sliding member, (b) Top view showing the sliding member. [Figure 4] A cross-sectional view showing the vicinity of the fixing nip. [Figure 5] A cross-sectional view showing the vicinity of the exit of the fixing nip portion in this embodiment. [Figure 6] A cross-sectional view showing the vicinity of the exit of the fixing nip section in the comparative example. [Modes for carrying out the invention]

[0010] The fixing device of this embodiment will now be described. First, a schematic configuration of an image forming apparatus suitable for using the fixing device of this embodiment will be described with reference to Figure 1.

[0011] <Image forming apparatus> The image forming apparatus 1 is an electrophotographic full-color printer having four image forming units Pa, Pb, Pc, and Pd, corresponding to four colors: yellow, magenta, cyan, and black. This embodiment is a tandem-type image forming apparatus 1 in which the image forming units Pa, Pb, Pc, and Pd are arranged along the rotation direction of an intermediate transfer belt 204, which will be described later. The image forming apparatus 1 forms a toner image (image) on a recording material in response to an image signal from a document reader 2 connected to the main body 3 of the image forming apparatus 1 or from a host device such as a personal computer that is communicatively connected to the main body 3. Examples of recording materials include paper, plastic film, and sheet materials such as cloth.

[0012] As shown in Figure 1, the image forming apparatus 1 comprises a document reader 2 and a main body 3. The document reader 2 reads a document placed on the document glass 21. Light emitted from the light source 22 is reflected by the document and formed on the CCD sensor 24 via optical system components 23 such as lenses. When this optical system unit is scanned in the direction of the arrow under the control of the reader control unit, it reads the document line by line and converts it into a sequence of electrical signal data. The image signal obtained by the CCD sensor 24 is sent to the main body 3, where the control unit 30 performs image processing according to each image forming unit described later. The control unit 30 also receives external input as an image signal from an external host device such as a print server.

[0013] The main unit 3 of the apparatus comprises multiple image forming units Pa, Pb, Pc, and Pd, and each image forming unit performs image formation based on the image signal described above. That is, the image signal is converted into a laser beam controlled by PWM (pulse width modulation) by the control unit 30. The polygon scanner 31, which acts as an exposure device, scans the laser beam according to the image signal. The laser beam is then irradiated onto the photosensitive drums 200a to 200d, which serve as image carriers for each of the image forming units Pa to Pd.

[0014] The image forming unit Pa forms a toner image of yellow (Y), the image forming unit Pb forms a toner image of magenta (M), the image forming unit Pc forms a toner image of cyan (C), and the image forming unit Pd forms a toner image of black (Bk), each corresponding to the respective color. Since these image forming units Pa to Pd have substantially the same configuration, the following explanation will use the image forming unit Pa, which forms a toner image of yellow (Y), as an example, and the explanations of the other image forming units Pb to Pd will be omitted. In the image forming unit Pa, a toner image is formed on the surface of the photosensitive drum 200a based on the image signal, as described below.

[0015] The charging roller 201a, acting as a primary charger, charges the surface of the photosensitive drum 200a to a predetermined potential, preparing it for electrostatic latent image formation. An electrostatic latent image is formed on the surface of the photosensitive drum 200a, which has been charged to the predetermined potential, by a laser beam from the polygon scanner 31. The developer 202a develops the electrostatic latent image on the photosensitive drum 200a to form a toner image. The primary transfer roller 203a discharges from the back of the intermediate transfer belt 204, applying a primary transfer bias with the opposite polarity to the toner, and transfers the toner image on the photosensitive drum 200a onto the intermediate transfer belt 204. After the transfer, the surface of the photosensitive drum 200a is cleaned by the cleaner 207a.

[0016] Also, the toner image on the intermediate transfer belt 204 is conveyed to the next image forming unit, and in the order of Y, M, C, and Bk, the toner images of each color formed in each image forming unit are sequentially transferred, and a four-color image is formed on its surface. And the toner image that has passed through the Bk image forming unit Pd, which is the most downstream in the rotation direction of the intermediate transfer belt 204, is conveyed to the secondary transfer unit T2 composed of the secondary transfer roller pair 205 and 206. And in the secondary transfer unit T2, a secondary transfer electric field with a polarity opposite to that of the toner image on the intermediate transfer belt 204 is applied, so that the toner image is secondarily transferred from the intermediate transfer belt 204 to the recording material.

[0017] The recording material is housed in the cassette 9, and the recording material fed from the cassette 9 is conveyed to the registration unit 208 composed of, for example, a pair of registration rollers and waits in the registration unit 208. Then, the timing of the registration unit 208 is controlled to align the position of the toner image on the intermediate transfer belt 204 with the paper, and the recording material is conveyed to the secondary transfer unit T2.

[0018] The recording material onto which the toner image has been transferred in the secondary transfer unit T2 is conveyed to the fixing device 8, and in the fixing device 8, by being heated and pressurized, the toner image carried on the recording material is fixed to the recording material. The recording material that has passed through the fixing device 8 is discharged to the discharge tray 7. When forming images on both sides of the recording material, after the transfer and fixing of the toner image to the first side (front surface) of the recording material are completed, the recording material is reversed through the reverse conveyance unit 10, and the transfer and fixing of the toner image to the second side (back surface) of the recording material are performed and stacked on the discharge tray 7.

[0019] The control unit 30 controls the entire image forming apparatus 1 as described above. Further, the control unit 30 can perform various settings and the like based on inputs from the operation unit 4 of the image forming apparatus 1. Such a control unit 30 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The CPU controls each unit while reading out a program corresponding to the control procedure stored in the ROM. Also, work data and input data are stored in the RAM, and the CPU performs control by referring to the data stored in the RAM based on the above-mentioned program and the like.

[0020] <Fixing device> Next, the configuration of the fixing device 8 in the present embodiment will be described using FIGS. 2(a) to 4. In the present embodiment, a belt heating type fixing device using an endless belt is adopted. As shown in FIG. 2(a), in the fixing device 8, the recording material is conveyed in the direction from right to left (arrow X direction). In this specification, the width direction (longitudinal direction) refers to the direction intersecting the conveyance direction (lateral direction) of the recording material in the fixing nip portion N, in other words, the direction of the rotation axis of the pressure roller 305.

[0021] The fixing device 8 includes an endless and rotatable fixing belt 301, a pressure roller 305 as a counter member that abuts on the fixing belt 301 and forms a fixing nip portion N together with the fixing belt 301, a heating roller 307, and a fixing pad unit 300.

[0022] <Fixing belt> The fixing belt 301 is provided in a replaceable manner on the fixing pad unit 300. The fixing belt 301 has thermal conductivity and heat resistance, and is formed in a thin-walled cylindrical shape. In this embodiment, as shown in Figure 2(b), the fixing belt 301 has a three-layer structure in which a base layer 301a is formed on the inner circumference, an elastic layer 301b is formed on the outer circumference of the base layer 301a, and a release layer 301c is formed on the outer circumference of the elastic layer 301b. As an example, the base layer 301a is made of polyimide resin (PI) with a thickness of "80 μm", the elastic layer 301b is made of silicone rubber with a thickness of "300 μm", and the release layer 301c is made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) with a thickness of "30 μm". The outer diameter of the fixing belt 301 is set to, for example, "150 mm". This fixing belt 301 is stretched by a heating roller 307 and a fixing pad unit 300.

[0023] <Pressure roller> The pressure roller 305 is rotatably supported on the fixing frame (not shown) of the fixing device 8, and a gear (not shown) is fixed to one end in the width direction. The gear is connected to a drive source (not shown) such as a motor, and the roller is rotationally driven. When the pressure roller 305 rotates, the rotational force of the pressure roller 305 is transmitted to the fixing belt 301 by the frictional force generated at the fixing nip portion N. In this way, the fixing belt 301 rotates in accordance with the pressure roller 305.

[0024] As shown in Figure 2(b), the pressure roller 305 has an elastic layer 305b formed on the outer circumference of the rotating shaft 305c, and a release layer 305a formed on the outer circumference of the elastic layer 305b. As an example, the rotating shaft 305c is made of stainless steel (SUS) with a diameter of 72 mm, the elastic layer 305b is made of conductive silicone rubber with a thickness of 8 mm, and the release layer 305a is made of PFA with a thickness of 100 μm.

[0025] As shown in Figure 2(a), the pressure roller 305 contacts the outer circumferential surface of the fixing belt 301 so as to sandwich the fixing belt 301 between itself and the sliding member 304 (described later), forming a fixing nip section N that grips and transports the recording material in the transport direction (arrow X direction) to fix the toner image onto the recording material. To do this, the pressure roller 305 is pressurized toward the fixing pad unit 300 via the fixing belt 301 by a drive source (not shown). In this embodiment, for example, the pressure roller 305 contacts the fixing belt 301 such that the pressure (NF) in the fixing nip section N is "1600N", the length of the fixing nip section N in the transport direction is "24.5mm", and the length in the width direction is "326mm".

[0026] <Heating roller> The heating roller 307 is positioned on the inner circumference of the fixing belt 301 and, together with the fixing pad unit 300, tensions the fixing belt 301. The heating roller 307 is formed in a cylindrical shape from a metal such as aluminum or stainless steel, and a halogen heater 306 is disposed inside it as a heat source for heating the fixing belt 301. The heating roller 307 is then heated to a predetermined temperature by the halogen heater 306.

[0027] In this embodiment, the heating roller 307 is formed from, for example, an aluminum pipe with a thickness of "1 mm" and its surface is anodized, from the viewpoint of thermal conductivity. While one halogen heater 306 may be used, it is desirable to have multiple halogen heaters to facilitate temperature distribution control in the direction of the heating roller 307's rotation axis (width direction). Multiple halogen heaters 306 have different light distributions in the width direction, and the lighting ratio is controlled by the control unit 30 (see Figure 1) according to the size of the recording material. In this embodiment, three halogen heaters 306 are arranged. Note that the heating source is not limited to halogen heaters; other heaters capable of heating the heating roller 307, such as carbon heaters, may also be used.

[0028] Furthermore, the heating roller 307 may have a pivot point at one end or near the center in the direction of the rotation axis (width direction) and swing to generate a tension difference between one side and the other side in the width direction of the fixing belt 301, thereby allowing the fixing belt 301 to move in the width direction. That is, depending on the outer diameter accuracy of the heating roller 307 on which it is tensioned and the alignment accuracy with the fixing pad 303 described later, the fixing belt 301 may shift towards one end in the width direction during rotation (so-called belt shift). For this reason, the position (shift position) of the fixing belt 301 in the direction of the rotation axis is controlled by swinging the heating roller 307. In addition, the heating roller 307 may be biased by a spring supported by the frame (not shown) of the fixing device 8 and may also serve as a tension roller that applies a predetermined tension to the fixing belt 301.

[0029] <Fuser pad unit> Next, the fixing pad unit 300 will be described. As shown in Figure 2(a), the fixing pad unit 300 has a fixing stay 302, a fixing pad 303, and a sliding member 304, which are arranged on the inner circumference side of the fixing belt 103. The fixing stay 302 is a rigid member, for example made of metal, that extends in the width direction along the fixing belt 301, and the fixing stay 302 supports the fixing pad 303 on the pressure roller 305 side.

[0030] In this embodiment, the fixing belt 301 is pressed from the inner circumference toward the pressure roller 305 by the fixing pad 303 supported by the fixing stay 302. This creates a fixing nip section N with a wide nip that ensures both the length in the conveying direction and the width direction between the pressure roller 305 and the fixing belt 103. Furthermore, by supporting the resin fixing pad 303 with a more rigid metal fixing stay 302, the deflection of the fixing pad 303 caused by the pressure when pressurized is reduced, and a uniform fixing nip width in the width direction is obtained.

[0031] <Fixing pad> The fixing pad 303, acting as a holding member, is non-rotatably mounted on the inner circumference of the fixing belt 301 and has a fitting groove 303f (see Figure 4) into which a long sliding member 304 can be fitted, and holds the sliding member 304 so as to contact the inner surface of the fixing belt 301. The fixing pad 303 is a resin member that extends in the width direction, and the width of the fixing pad 303 is longer than the width of the recording material of the maximum size in which an image can be formed. The fixing pad 303 is made of a resin with good insulating and heat-resistant properties, such as LCP (liquid crystal polymer resin). The fixing pad 303 is a molded product manufactured by injection molding using a mold from these resins.

[0032] As shown in Figure 4, the fixing pad 303 has, with respect to the transport direction, an upstream guide portion 303c that contacts the fixing belt 301 on the upstream side of the bottom surface 303h of the fitting groove portion 303f, and a downstream guide portion 303b that contacts the fixing belt 301 on the downstream side of the bottom surface 303h. The bottom surface 303h is the surface that contacts the opposite surface 304a2 of the sliding member 304, opposite to the sliding surface (tip of the protrusion). The upstream guide portion 303c guides the fixing belt 301 toward the fixing nip portion N, and the downstream guide portion 303b guides the fixing belt 301 toward the fixing stay 302 so as to move it away from the fixing nip portion N after it has passed through the fixing nip portion N. These upstream guide sections 303c and downstream guide sections 303b are in contact with the fixing belt 301 over the entire paper-feed area through which the largest possible size of recording material capable of image formation in the fixing nip section N passes, in the width direction.

[0033] <Sliding member> If the frictional force between the fixing belt 301 and the fixing pad 303 is large, the rotation of the fixing belt 301 will be hindered. Therefore, in this embodiment, as shown in Figure 2(a), in order to reduce the frictional force between the fixing belt 301 and the fixing pad 303 in the fixing nip section N where the pressure is high, the fixing pad 303 is provided with a sliding member 304 that slides against the fixing belt 301. The sliding member 304 is held by the fixing pad 303 and is positioned opposite the pressure roller 305 with the fixing belt 301 in between. In this embodiment, the sliding member 304 is held by the fixing pad 303 such that its shorter side is in the conveying direction.

[0034] The sliding member 304 has heat resistance and strength, and while held by the fixing pad 303, it has a sliding surface that contacts the inner circumferential surface of the rotating fixing belt 301 and slides against the fixing belt 301. By interposing the sliding member 304 between the fixing pad 303 and the fixing belt 301, the frictional force between the fixing pad 303 and the fixing belt 301 is reduced, thereby preventing the fixing pad 303 from hindering the rotation of the fixing belt 301. The inner circumferential surface of the fixing belt 301 may be coated with a lubricant to allow the fixing belt 301 to slide smoothly against the sliding member 304. For example, silicone oil can be used as the lubricant.

[0035] As described above, in this embodiment, the sliding member 304 reduces the frictional force with the fixing belt 301. In the sliding member 304 of this embodiment, as shown in Figure 2(b), the sliding surface that slides against the fixing belt 301 is formed in an embossed (recessed) shape.

[0036] The sliding member 304 is formed from a metal such as stainless steel (SUS), copper, or aluminum. In this embodiment, the sliding member 304 is formed from stainless steel (SUS) with a thickness of 1 mm. The sliding member 304 is not limited to metal; it may also be formed from engineering plastics such as polyimide resin (PI), polyetheretherketone resin (PEEK), or LCP (liquid crystal polymer resin).

[0037] As shown in Figures 3(a) and 3(b), the sliding member 304 has a plate-shaped base 304a and a plurality of protrusions 304b that protrude from the base 304a and slide on the fixing belt 301. As shown in Figure 3(a), the protrusions 304b protrude from the surface of the base 304a. The amount of protrusion (height in the Z direction) of the protrusions 304b from the surface of the base 304a is, for example, "250 μm". Also, as shown in Figure 3(b), the protrusions 304b are arranged on the base 304a with approximately the same spacing between adjacent protrusions in the conveying direction and approximately the same spacing between adjacent protrusions in the width direction. The spacing (d) between adjacent protrusions 304b is, for example, "1.4 mm" in both the conveying direction and the width direction.

[0038] Furthermore, a low-friction layer 304c is formed on the surface of the sliding member 304 to reduce the frictional force with the fixing belt 301, using, for example, PTFE (polytetrafluoroethylene resin), PFA, etc. In this embodiment, PTFE with a thickness of "20 μm" is coated on the surface of the base body 304a and the protrusion 304b.

[0039] As shown in Figure 4, in this embodiment, the surface of the sliding member 304 is formed in an uneven manner, and the sliding member 304 slides against the fixing belt 301 with the tip surface of the protrusion 304b. This reduces the contact area between the sliding member 304 and the fixing belt 301, thereby reducing the frictional force with the fixing belt 301. Furthermore, as described above, the surface of the protrusion 304b is coated with a low-friction layer 304c, which also reduces the frictional force with the fixing belt 301.

[0040] As described above, the fixing pad 303 holds the sliding member 304 such that the inner circumferential surface of the fixing belt 301 slides against the tip surface of the protrusion 304b. To do this, the fixing pad 303 has a concave fitting groove 303f formed on the side opposite to the side supported by the fixing stay 302 for fitting and holding the sliding member 304.

[0041] In this embodiment, the sliding member 304 has a first non-formed region 3041 and a second non-formed region 3042 at both ends in the transport direction (short side direction) where no protrusions 304b are formed. The first non-formed region 3041 is a flat region from the downstream end of the base body 304a to the downstreammost protrusion 304b1 formed at the downstream end of the multiple protrusions 304b, with respect to the transport direction. The second non-formed region 3042 is a flat region from the upstream end of the base body 304a to the upstreammost protrusion 304b2 formed at the upstream end of the multiple protrusions 304b, with respect to the transport direction. In this embodiment, with the sliding member 304 held by the fixing pad 303, the first non-formed region 3041 and the second non-formed region 3042 are in contact with the bottom surface 303h of the fitting groove 303f of the fixing pad 303, similar to the base body 304a.

[0042] <Comparative Example> However, in the configuration where the sliding member 304 is fitted and held in the fitting groove 303f of the fixing pad 303, it becomes difficult to properly separate the recording material from the fixing belt 301, which may cause poor fixing of the recording material. This point will be explained with reference to Figure 2(a) and Figure 6. Figure 6 is a cross-sectional view showing the vicinity of the exit of the fixing nip portion N in the comparative example.

[0043] In the following description, with the sliding member 304 sliding on the fixing belt 301, the height "H" is defined as the difference between the tip of the downstreammost protrusion 304b1 in the transport direction (arrow X direction) of the protrusion 304b and the closest proximity position 303b1 on the downstream guide portion 303b with respect to the protrusion direction of the protrusion 304b (opposite direction to arrow Z), as viewed from the width direction (arrow Y direction). The distance "L" is defined as the distance between the downstream end of the tip of the downstreammost protrusion 304b1 in the transport direction and the proximity position 303b1. The tensioning of the fixing belt 301 by the fixing pad 303 and the sliding member 304 downstream of the fixing nip portion N changes depending on these height "H" and distance "L".

[0044] When the height "H" is less than a predetermined height and the distance "L" is greater than a predetermined distance, the fixing belt 301 cannot be raised steeply after passing the fixing nip section N, making it difficult to ensure the separation performance of the recording material from the fixing belt 301. For example, as shown in Figure 6, when the height "H" is less than a predetermined height, the radius of curvature of the bending section R1 is greater than the radius of curvature of the bending section R2. In this case, the force tensioning the fixing belt 301 at the bending section R2 becomes stronger than the force tensioning the fixing belt 301 at the bending section R1, causing the fixing belt 301 to rotate in a trajectory that is close to the recording material discharged from the fixing nip section N.

[0045] When the fixing belt 301 follows a trajectory close to the recording material, the force separating the recording material from the fixing belt 301 after passing through the fixing nip section N becomes weaker, resulting in undesirable separation performance. This leads to excess heat being applied to the recording material from the fixing belt 301, causing poor toner fixation due to overheating. Furthermore, the recording material that has passed through the fixing nip section N may become warped or deformed due to the heat and pressure applied. In such cases, if the recording material and the fixing belt 301 are close together after passing through the fixing nip section N, there will be areas on the recording material that have passed through the fixing nip section N that are in contact with the fixing belt 301 and areas that are not, resulting in poor fixation such as gloss unevenness.

[0046] Furthermore, as shown in Figure 6, even when the distance "L" is greater than the predetermined distance, the fixing belt 301 rotates in a trajectory that is close to the recording material discharged from the fixing nip section N, just as when the height "H" is less than the predetermined height. Moreover, when the distance "L" is greater than the predetermined distance, the fixing belt 301 tends to flap around. Therefore, even when the distance "L" is greater than the predetermined distance, there is a risk of the fixing failure described above occurring.

[0047] Therefore, in this embodiment, in order to suppress the occurrence of the fixing failure described above, the height "H" is set to be above a predetermined height and the distance "L" is set to be below a predetermined distance, so that the fixing belt 301 rotates in a trajectory that rises steeply after passing through the fixing nip section N. The configuration of this embodiment will be described below with reference to Figure 5. Figure 5 is a cross-sectional view showing the vicinity of the exit of the fixing nip section in this embodiment.

[0048] In this embodiment, the height "H" is "0.4 mm or more and 2 mm or less", and the distance "L" is "3 mm or less". In other words, when the sliding member 304 is sliding on the fixing belt 301, when viewed from the width direction, the tip of the downstreammost projection 304b1 protrudes "0.4 mm or more and 2 mm or less" from the proximity position 303b1 closest to the fixing nip N on the downstream guide portion 303b. Furthermore, the downstreammost projection 304b1 is formed on the base 304a of the sliding member 304 such that the distance (distance "L") between the downstream end of the tip of the downstreammost projection 304b1 and the proximity position 303b1 is "3 mm or less". In this case, the proximity position 303b1 of the downstream guide portion 303b is located at a position where it is retracted in the direction of arrow Z from the tip of the downstreammost projection 304b1.

[0049] As a result, in this embodiment, as can be understood by comparing it with the comparative example shown in Figure 6, the fixing belt 301 does not trace a trajectory close to the recording material, but rather rotates in a trajectory that rises sharply after passing the fixing nip portion N. Therefore, it is possible to secure the force that separates the recording material from the fixing belt 301 after passing the fixing nip portion N, and the desired separation performance can be obtained, thereby suppressing the occurrence of the fixing failure described above. In other words, it is possible to suppress the occurrence of fixing failure on the recording material caused by the protrusions formed on the sliding member 304 without impairing the separability of the recording material that has passed through the fixing belt 301.

[0050] In this embodiment, the height "H" is set to "0.4 mm or more and 2 mm or less" and the distance "L" is set to "3 mm or less" over the entire paper feeding area of ​​the fixing nip section N in the width direction. Therefore, regardless of the size of the recording material, the desired separation performance can be obtained and fixing failures can be suppressed.

[0051] <Regarding non-forming areas> Incidentally, if the heights of the multiple protrusions 304b on the sliding member 304 are not approximately uniform, uneven pressure will occur at the fixing nip portion N, causing poor fixing of the recording material. The difference in height of the protrusions 304b that causes poor fixing is, for example, about 20 μm to 50 μm. To prevent poor fixing of the recording material caused by the height of such protrusions 304b, the sliding member 304 is inspected by measuring the height of the multiple protrusions 304b using a non-contact inspection device, such as a laser scan device. The non-contact inspection device measures the height of the protrusions 304b with a line-scan type sensor (called a scan sensor) using laser light and compares the measured value with a reference value specified in a pre-prepared protrusion shape profile. If the difference between the measured value and the reference value is within a predetermined range (for example, 15 μm or less), the sliding member 304 is judged to be a good product. Sliding members 304 that are not judged to be good products are not used.

[0052] When the sliding member 304 is formed from a base material such as stainless steel, warping may occur in the width direction (longitudinal direction), starting from the center, due to the precision of the base material and residual stress during processing. The height difference due to warping between the width direction end and the center varies from one sliding member 304 to another, but is, for example, about "2 mm". If the sliding member 304 is warped, it is difficult to accurately measure the height of the protrusion 304b using the non-contact inspection device described above. Therefore, it is necessary to correct the warping of the sliding member 304 before measuring the height of the protrusion 304b. To correct the warping of the sliding member 304, the sliding member 304 is fixed (clamped) between a surface plate and a clamping member, as described later. If the thickness of the base body 304a is, for example, "1.0 mm", the clamping force (CF) by the clamping member (not shown) required to correct the warping of the sliding members (404, 304) is set to about "2 to 4 N".

[0053] In this embodiment, the height of the protrusion 304b can be measured with the curvature of the sliding member 304 corrected by clamping the first non-formed region 3041 and the second non-formed region 3042 (see Figure 4). The first non-formed region 3041 and the second non-formed region 3042 are formed to lengths (L1, L2) such that they can be clamped without interfering with the protrusion 304b in the transport direction. For example, the first non-formed region 3041 is formed to a length "L1" of "0.5 mm" or more in the short direction (transport direction) from one downstream end of the base body 304a. Similarly, the second non-formed region 3042 is formed to a length "L2" of "0.5 mm" or more in the short direction (transport direction) from the other upstream end of the base body 304a. This makes it possible to measure the height of the protrusion 304b with high accuracy while the curvature of the sliding member 304 is corrected.

[0054] Furthermore, in order to securely clamp the sliding member 304 and correct its warping, it is preferable that the length of the first non-formed area 3041 and the second non-formed area 3042 in the transport direction be 1.0 mm or more. In addition, it is preferable that the first non-formed area 3041 and the second non-formed area 3042 be formed over the entire width (entire longitudinal) of the sliding member 304.

[0055] Furthermore, in the case of the sliding member 304 of this embodiment, as shown in Figure 4, the first non-formed area 3041 and the second non-formed area 3042 are formed outside the range of the fixing nip portion N so as not to come into contact with the fixing belt 301. Therefore, even if minute scratches or dents occur in the first non-formed area 3041 and the second non-formed area 3042 due to being pressed by the clamping member, it will not affect the fixing of the toner image to the recording material in any way.

[0056] As described above, from the viewpoint of ensuring secure clamping to the sliding member 304, the transport direction lengths (L1, L2) of the first non-forming region 3041 and the second non-forming region 3042 should be long, preferably 0.5 mm or more, and more preferably 1.0 mm or more. However, if the transport direction lengths (L1, L2) of the first non-forming region 3041 and the second non-forming region 3042 are longer than necessary, the transport direction length of the fixing nip section N (see Figure 2(a)) will be shortened, making it easier for uneven pressure to occur. To address this, it is conceivable to lengthen the sliding member 304 itself to secure the transport direction length of the fixing nip section N, but this is costly and difficult to adopt as it would enlarge the fixing device 8. Furthermore, depending on the transport direction lengths (L1, L2) of the first non-forming region 3041 and the second non-forming region 3042, the distance from the downstream end of the fixing nip section N to the upstream end of the separation plate (not shown) will be long. The separation plate is positioned downstream of the fixing device 8 to separate the recording material that has passed through the fixing nip section N from the fixing belt 301. However, this is undesirable because it makes it difficult to separate the recording material from the fixing belt 301.

[0057] In view of the above, the transport direction lengths of the first non-formed region 3041 and the second non-formed region 3042 are set to "2.0 mm" or less. In summary, the transport direction lengths (L1, L2) of the first non-formed region 3041 and the second non-formed region 3042 are "0.5 mm or more and 2.0 mm or less", preferably "1.0 mm or more and 1.5 mm or less". Note that the transport direction length (L1) of the first non-formed region 3041 is smaller than the distance "L" mentioned above (L1 <L)。

[0058] <Other Embodiments> Furthermore, the above-described embodiment is not limited to a configuration in which the fixing belt 301 is heated, but can also be applied to a configuration in which a belt-shaped pressure belt is used instead of the pressure roller 305, and this pressure belt is heated by a heating heater or the like. [Explanation of Symbols]

[0059] 8... Fixing device, 301... Fixing belt, 303... Holding member (fixing pad), 303b... Guide part (downstream guide part), 303f... Fitting groove part, 303h... Bottom surface, 304... Sliding member, 304a... Base body, 304b (304b1)... Protrusion, 304c... Low friction layer, 305... Opposing member (pressure roller), 3041... Non-formed area (first non-formed area), 3042... Non-formed area (second non-formed area), N... Fixing nip part

Claims

1. A fixing device for fixing a toner image formed on a recording material to the recording material, A belt that is endless and applies heat to the recording material, A rotating body that contacts the outer surface of the belt in the pressurizing direction, A pad member that forms a nip portion by sandwiching the belt between itself and the rotating body on the inside of the belt, The system includes a sliding member that is held by the pad member and slides against the inner circumferential surface of the belt at the nip portion, The rotating body, together with the belt, grips and conveys the recording material in the conveying direction at the nip portion, and fixes the toner image on the recording material by applying heat and pressure. The sliding member has a plurality of protrusions that project toward the rotating body on the side that slides with the belt and slide with the inner circumferential surface of the belt. The pad member has a guide portion that guides the belt after it has passed the nip portion. In the state in which the nip portion is formed, the distance in the conveying direction between the downstream end of the tip of the downstreammost projection among the plurality of projections in the direction of belt rotation and the upstream end of the guide portion that contacts the inner circumferential surface of the belt in the direction of belt rotation is 3.0 mm or less. The distance in the pressing direction between the tip of the downstreammost projection among the plurality of projections in the direction of belt rotation and the upstream end of the guide portion that contacts the inner circumferential surface of the belt in the direction of belt rotation is 0.4 mm or more and 2.0 mm or less. A fixing device characterized by the following features.

2. The pad member holds the sliding member over the entire width direction intersecting the transport direction. The fixing device according to feature 1.

3. The pad member has a fitting groove for fitting and holding the sliding member. The fixing device according to claim 1 or 2.

4. The sliding member is held by the pad member such that its shorter side is the conveying direction, and at both ends in the shorter side, there is a non-formed area in which the protrusion is not formed and does not come into contact with the belt, extending from each end in the shorter side by 0.5 mm to 2.0 mm. The fixing device according to any one of claims 1 to 3.

5. The non-formed region is formed over the entire area of ​​the sliding member with respect to the width direction intersecting the transport direction. The fixing device according to feature 4.

6. The sliding member has a low-friction layer that reduces the frictional force between the plurality of protrusions and the belt. The fixing device according to any one of claims 1 to 5.

7. The aforementioned pad member is made of resin, The sliding member is made of metal. The fixing device according to any one of claims 1 to 6.

8. A fixing device for fixing a toner image formed on a recording material to the recording material, A belt that is endless and applies heat to the recording material, A rotating body that contacts the outer surface of the belt in the pressurizing direction, A pad member that forms a nip portion by sandwiching the belt between itself and the rotating body on the inside of the belt, A heating rotating body is positioned on the inner circumferential surface of the belt at a location different from the nip portion, and heats the belt. The system includes a sliding member that is held by the pad member and slides against the inner circumferential surface of the belt at the nip portion, The sliding member has a plate-shaped base and a plurality of protrusions that project from the base toward the rotating body toward the side that slides with the belt, At least downstream of the nip portion in the transport direction of the recording material, the pad member and the inner circumferential surface of the belt slide against each other. The pad member has a guide portion that guides the belt after it has passed the nip portion. In the state in which the nip portion is formed, the upstream end of the guide portion that contacts the inner circumferential surface of the belt in the direction of rotation of the belt is located in the pressing direction between the downstream end of the base body of the sliding member that slides with the belt in the direction of rotation of the belt and the tip of the downstreammost projection of the plurality of projections in the direction of rotation of the belt. A fixing device characterized by the following features.

9. Upstream of the nip portion in the direction of transport of the recording material, the pad member and the inner circumferential surface of the belt slide against each other. The fixing device according to feature 8.

10. The pad member holds the sliding member over the entire width direction intersecting the transport direction. The fixing device according to feature 8.

11. The sliding member has a low-friction layer that reduces the frictional force between the plurality of protrusions and the belt. The fixing device according to feature 8.

12. The base has a plurality of protrusions that slide on the inner circumferential surface of the belt at the nip portion. The fixing device according to feature 8.

13. The aforementioned pad member is made of resin, The base of the sliding member is made of metal. The fixing device according to feature 12.

14. The sliding member has a low-friction layer on the surface of the base body that reduces the frictional force between the plurality of protrusions and the belt. The fixing device according to feature 13.

15. The heating rotating body has a plurality of heating sources inside it. The fixing device according to feature 8.

16. The plurality of heating sources are halogen heaters. The fixing device according to claim 15.

17. The substrate has a thickness of 1 mm. The fixing device according to feature 12.

18. The sliding member has higher heat resistance and strength than the pad member. The fixing device according to feature 8.

19. The inner circumferential surface of the belt is coated with a lubricant. The fixing device according to feature 8.

Images