Fixing device

Abstract

The present invention provides a configuration that can prevent the sliding member 304 from falling off and does not generate excessive stress on the belt 301. [Solution] The pad 303 has a fitting groove 303f for holding the sliding member 304. The fitting groove 303f has a bottom surface 303d and a downstream side surface 303e that faces the downstream end surface 304e of the sliding member 304 in the conveying direction. The pad 303 has a protruding portion 303h upstream of the downstream side surface 303e, which is formed so that when the pressure roller 305 contacts the belt 301 and a nip portion is formed, the protruding portion 303h does not protrude beyond the nip portion side of the sliding member 304. The sliding member 304 is positioned upstream of the protruding portion 303h and has a contact portion 304h that contacts the protruding portion 303h when the pressure roller 305 is in a spaced position away from the belt 301, thereby restricting the movement of the sliding member 304 downstream in the conveying direction.

Description

Technical Field

[0001] The present invention relates to a fixing device for fixing a toner image carried on a recording material to the recording material.

Background Art

[0002] As a fixing device, a configuration is conventionally known in which a nip portion is formed by nip portion forming members such as a belt and a roller and the recording material passing through the nip portion is heated and pressurized (Patent Document 1). In the configuration described in Patent Document 1, a nip portion is formed between the belt and the nip portion forming member by sliding a sliding member on the inner peripheral surface of the belt in the nip portion.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, there is a configuration provided with a holding member for holding the sliding member. In this configuration, a concave portion is formed in the holding member, and the sliding member is held in the concave portion. On the other hand, when the nip portion forming member such as a roller is brought into contact with and separated from the belt, there is a risk that the sliding member may fall out of the concave portion when the nip portion forming member is separated from the belt. And in a state where the sliding member has fallen out of the concave portion, there is a risk that the sliding member may ride on the downstream side of the concave portion of the holding member due to the frictional force received from the belt, resulting in the occurrence of the dropout of the sliding member. When the dropout of the sliding member occurs as described above, there is a risk that problems such as the recording material passing through the nip portion being difficult to peel off from the belt may occur.

[0005] Therefore, in order to prevent the sliding member from falling off, it is conceivable to provide a protrusion further downstream than the downstream side surface of the recess. However, if a protrusion is provided in this way, the protrusion will come into contact with the belt, causing extra stress on the belt.

[0006] The present invention aims to provide a configuration that can suppress the detachment of sliding members and does not generate excessive stress on the belt. [Means for solving the problem]

[0007] One aspect of the present invention is a fixing device for fixing a toner image supported on a recording material to the recording material, comprising: an endless, rotatable belt; a nip portion forming member that contacts the outer circumferential surface of the belt to form a nip portion for clamping and transporting the recording material between itself and the belt; a sliding member that slides against the inner circumferential surface of the belt in the nip portion; and a holding member positioned inside the belt to clamp the sliding member and the belt between itself and the nip portion forming member, with a recess formed on the side facing the nip portion for holding the sliding member, wherein the nip portion forming member is movable between a contact position that contacts the outer circumferential surface of the belt to form the nip portion and a separated position that is separated from the outer circumferential surface of the belt, and the recess has a bottom surface and a downstream side of the bottom surface with respect to the transport direction of the recording material transported in the nip portion The fixing device is characterized by having a downstream side surface facing the downstream end surface in the conveying direction of the sliding member which is formed and held in the recess, the sliding member being held by the holding member so as to be movable away from the bottom surface when the nip portion forming member is in the separated position, the holding member having a protruding portion which protrudes toward the nip portion side upstream of the downstream side surface of the recess in the conveying direction and is formed so as not to protrude toward the nip portion side than the sliding member when the nip portion forming member is in the contact position, and the sliding member being positioned upstream of the protruding portion in the conveying direction and having a contact portion which restricts the sliding member from moving downstream in the conveying direction by contacting the protruding portion when the nip portion forming member is in the separated position. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a configuration that can suppress the detachment of the sliding member and does not generate excessive stress on the belt. [Brief explanation of the drawing]

[0009] [Figure 1] A schematic cross-sectional view of the image forming apparatus according to the embodiment. [Figure 2] (a) A schematic cross-sectional view of the fixing device according to the embodiment, and (b) A schematic diagram showing an enlarged view of part A in (a). [Figure 3] (a) a cross-sectional view and (b) a plan view schematically showing a sliding member according to the embodiment. [Figure 4] A schematic cross-sectional view showing an enlarged view of the vicinity of the nip portion of the fixing device according to the embodiment. [Figure 5] A perspective view of the vicinity of the widthwise end of the fixing pad and sliding member according to the embodiment, as seen from the sliding member side. [Figure 6] This is a schematic cross-sectional view showing an enlarged view of the vicinity of the nip exit in a fixing device according to an embodiment, with the pressure roller separated from the fixing belt. [Figure 7] This is a schematic cross-sectional view showing an enlarged view of the vicinity of the nip exit in the fixing device according to the embodiment, with the pressure roller in contact with the fixing belt. [Figure 8] A schematic cross-sectional view showing an enlarged view of the vicinity of the nip exit in the fixing device according to Comparative Example 1, with the pressure roller separated from the fixing belt. [Figure 9] A schematic cross-sectional view showing an enlarged view of the vicinity of the nip exit in the fixing device according to Comparative Example 2, with the pressure roller in contact with the fixing belt. [Modes for carrying out the invention]

[0010] Embodiments will be described using Figures 1 to 9. First, the schematic configuration of the image forming apparatus of this embodiment will be described using 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. In this embodiment, the image forming units Pa, Pb, Pc, and Pd are arranged in a tandem configuration along the rotation direction of the 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 reading unit (document reader) 2 connected to the image forming apparatus body 3 or an image signal from a host device such as a personal computer that is communicatively connected to the image forming apparatus body 3. Examples of recording materials include paper, plastic film, and sheet materials such as cloth.

[0012] The image forming apparatus 1 comprises an image reading unit 2 and an image forming apparatus body 3. The image reading unit 2 reads a document placed on the document glass 21. Light emitted from a light source 22 is reflected by the document and formed as an image on a CCD sensor 24 via an optical system component 23 such as a lens. By scanning in the direction of the arrow, this optical system unit converts the document into a series of electrical signal data for each line. The image signal obtained by the CCD sensor 24 is sent to the image forming apparatus body 3, where the control unit 30 performs image processing according to each image forming unit, which will be 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 body of the image forming apparatus 3 is equipped with 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] Note that Pa is an image forming unit for yellow (Y), Pb is an image forming unit for magenta (M), Pc is an image forming unit for cyan (C), and Pd is an image forming unit for black (Bk), each forming an image of the corresponding color. Since the image forming units Pa to Pd are substantially the same, the details of the Y image forming unit Pa will be described below, and the descriptions of the other image forming units will be omitted. In the image forming unit Pa, the photosensitive drum 200a has a toner image formed on its surface based on an image signal as described below.

[0015] The charging roller 201a as the primary charger charges the surface of the photosensitive drum 200a to a predetermined potential to prepare for electrostatic latent image formation. An electrostatic latent image is formed on the surface of the photosensitive drum 200a charged to a predetermined potential by a laser beam from the polygon scanner 31. The developing device 202a develops the electrostatic latent image on the photosensitive drum 20o a to form a toner image. The primary transfer roller 203a discharges from the back of the intermediate transfer belt 204 and applies a primary transfer bias of the opposite polarity to the toner, transferring the toner image on the photosensitive drum 200a onto the intermediate transfer belt 204. The photosensitive drum 200a after transfer is cleaned on its surface 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, 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. Then, the toner image that has passed through the Bk image forming unit Pd at the most downstream in the rotation direction of the intermediate transfer belt 204 is conveyed to the secondary transfer unit composed of the secondary transfer roller pair 205 and 206. And in the secondary transfer unit, a secondary transfer electric field of the opposite polarity to the toner image on the intermediate transfer belt 204 is applied, and secondary transfer is performed onto 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.

[0018] The recording material onto which the toner image is transferred by the secondary transfer unit 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 it is stacked on the discharge tray 7.

[0019] Note that the control unit 30 controls the entire image forming apparatus 1 as described above. Also, the control unit 30 can perform various settings based on the input from the operation unit 4 provided in 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 aforementioned 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) and 2(b). In the present embodiment, a belt heating type fixing device using an endless belt is adopted. In FIG. 2(a), the X direction is the conveyance direction of the recording material P (not shown in the figure), the Y direction is the width direction of the recording material intersecting (orthogonal in the present embodiment) with the conveyance direction of the recording material, and the Z direction is the pressurization direction in which the recording material is pressurized at the nip portion N. In the present embodiment, the X direction, the Y direction, and the Z direction are directions orthogonal to each other.

[0021] The fixing device 8 includes a fixing belt (hereinafter referred to as "belt") 301, a stay 302, a fixing pad (hereinafter referred to as "pad") 303, a sliding member 304, a pressure roller 305, a heating roller 307, and the like. The belt 301 is an endless, rotatable heating rotating body. The pressure roller 305, as a nip-forming member, is a pressure rotating body that contacts the outer circumferential surface of the belt 301 and forms a nip portion (fixing nip portion) N that clamps and conveys the recording material between itself and the belt 301. In this embodiment, the pad unit 300 is composed of the stay 302, the pad 303, and the sliding member 304.

[0022] The sliding member 304 slides against the inner circumferential surface of the belt 301 at the nip portion N. The pad 303, acting as a retaining member, is positioned on the inside of the belt 301 so as to sandwich the sliding member 304 and the belt 301 between the pressure roller 305, and a fitting groove portion 303f (see Figure 4, described later) is formed on the side facing the nip portion N as a recess for holding the sliding member 304. The sliding member 304 is positioned so as to cover the outer circumferential surface of the pad 303 on the belt 301 side. The stay 302 is positioned on the inside of the belt 301, on the opposite side of the nip portion N, sandwiching the pad 303, and supports the pad 303. The heating roller 307 is positioned on the inside of the belt 301 so as to tension the belt 301 and heats the belt 301. Each component will be described in detail below.

[0023] The belt 301 is replaceably mounted on the pad unit 300. The belt 301 has thermal conductivity and heat resistance, and is a thin-walled cylindrical shape. In this embodiment, as shown in Figure 2(b), the belt 301 has a three-layer structure with a base layer 301a, an elastic layer 301b on the outer circumference of the base layer 301a, and a release layer 301c on the outer circumference of the release layer. The base layer 301a is, for example, 80 μm thick and made of polyimide resin (PI). The elastic layer 301b is, for example, 300 μm thick and made of silicone rubber. The release layer 301c is, for example, 30 μm thick and made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin. The belt 301 is stretched by the pad unit 300 and the heating roller 307. The outer diameter of the belt 301 is 150 mm in this embodiment.

[0024] 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 belt 301 by the frictional force generated at the nip portion N. In this way, the belt 301 rotates in accordance with the pressure roller 305.

[0025] The pressure roller 305 is a roller having a core metal (shaft) 305c, an elastic layer 305b formed on the outer circumference of the core metal 305c, and a release layer 305a formed on the outer circumference of the release layer. The core metal 305c is, for example, made of stainless steel with a diameter of 72 mm. The elastic layer 305b is, for example, made of conductive silicone rubber with a thickness of 8 mm. The release layer 305a is, for example, made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin with a thickness of 100 μm.

[0026] The pressure roller 305 contacts the outer surface of the belt 301 so as to sandwich the belt 301 between itself and the sliding member 304, which will be described later, forming a nip section N that grips and conveys the recording material in the conveying direction (arrow X direction) and fixes the toner image onto the recording material. The fixing device 8 fixes the toner image onto the recording material P while gripping and conveying the recording material P in the nip section N. For this purpose, the pressure roller 305 is pressurized toward the pad unit 300 via the belt 301 by the drive source shown in the figure. In this embodiment, the pressurized force (NF) in the nip section N during image formation is 1600N, and the pressure roller 305 contacts the belt 301 such that the width of the nip section N in the X direction (direction of conveying the recording material) is 24.5 mm and the width in the Y direction (width direction of the recording material) is 326 mm.

[0027] Furthermore, the pressure roller 305 is movable between a contact position in which it abuts the outer surface of the belt 301 to form a nip portion N, and a separated position where it is separated from the outer surface of the belt 301. That is, by moving the pressure roller 305 from the contact position using a drive source (not shown), it is possible to separate it from the belt 301 and release the nip portion N. When recording material is not to pass through the nip portion N, the pressure roller 305 is separated from the belt 301 to avoid a temperature rise in the pressure roller 305.

[0028] The heating roller 307 is positioned inside the belt 301 and, together with the pad unit 300, tensions the 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 belt 301. The heating roller 307 is then heated to a predetermined temperature by the halogen heater 306.

[0029] In this embodiment, the heating roller 307 is formed from, for example, an aluminum pipe with a thickness of 1 mm, from the viewpoint of thermal conductivity. While one halogen heater 306 may suffice, it is desirable to have multiple halogen heaters 306 to control the temperature distribution in the longitudinal direction (rotation axis direction) of the heating roller 307. Multiple halogen heaters 306 have different light distributions in the longitudinal direction, and the control unit 30 (Figure 1) controls the lighting ratio 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; it may be other heaters capable of heating the heating roller 307, such as a carbon heater. The belt 301 is heated by the heating roller 307 heated by the halogen heaters 306, and controlled to a predetermined target temperature according to the type of recording material based on temperature detection by a thermistor (temperature sensing member) (not shown).

[0030] 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 belt 301, thereby allowing the belt 301 to move in the width direction. That is, depending on the outer diameter accuracy of the heating roller 307 on which the tension is mounted and the alignment accuracy with the pad unit 300 described later, the belt 301 may shift towards one end in the width direction during rotation (so-called belt shifting occurs). For this reason, the position (shifting position) of the belt 301 in the direction of the rotation axis is controlled by swinging the heating roller 307. In addition, the heating roller 307 may also serve as a tension roller that applies a predetermined tension to the belt 301 by being biased by a spring supported by the frame (not shown) of the fixing device 8.

[0031] [Pad Unit] Next, the pad unit 300 will be described using Figures 2(a) to 4. The pad unit 300 has a stay 302, a pad 303, and a sliding member 304, which are arranged on the inner circumference side of the belt 301. The stay 302, which acts as a support member, is a rigid member, for example, made of metal, that extends in the width direction along the belt 301. The stay 302 is positioned on the opposite side of the nip portion N, sandwiching the pad 303, and supports the pad 303. In this embodiment, the pad 303, which is supported by the stay 302, is pressed from the outer circumference side of the belt 301 by the pressure roller 305. In this way, a wide nip portion N is formed between the pressure roller 305 and the belt 301, ensuring both the length in the conveying direction and the width direction. Furthermore, by supporting the resin pad 303 with the more rigid metal stay 302, the deflection that occurs in the pad 303 due to the pressure when pressurized is reduced, and a uniform nip width in the width direction is obtained.

[0032] The pad 303, acting as a retaining member, is non-rotatably mounted on the inside of the belt 301 and has a fitting groove 303f as a recess into which a long sliding member 304 can be fitted, and holds the sliding member 304 so as to contact the inner circumferential surface of the belt 301. In this embodiment, the pad 303 is a substantially plate-shaped member that is long along the width direction of the belt 301 (the longitudinal direction intersecting the rotation direction of the belt 301, and the rotation axis direction of the heating roller 307). The width direction length of the pad 303 is longer than the width direction length of the recording material of the maximum size in which an image can be formed. The pad 303 is formed from a resin with good insulating and heat-resistant properties, such as LCP (liquid crystal polymer) resin. The pad 303 is a molded product manufactured by injection molding using a mold from these resins. A sliding member 304 is interposed between the pad 303 and the belt 301. Details of the sliding member 304 will be described later.

[0033] As shown in Figure 4, the fitting groove portion 303f of the pad 303 has a bottom surface 303d and a downstream side surface 303e formed on the downstream side of the bottom surface 303d with respect to the transport direction of the recording material transported in the nip portion, and facing the downstream end surface 304e in the transport direction of the sliding member 304 held in the fitting groove portion 303f. With respect to the transport direction, the pad 303 has an upstream guide portion 303c that abuts the belt 301 on the upstream side of the bottom surface 303d of the fitting groove portion 303f, and a downstream guide portion 303b that abuts the belt 301 on the downstream side of the bottom surface 303d. The bottom surface 303d is the surface that contacts the side opposite to the sliding surface (tip of the protrusion) of the sliding member 304. The upstream guide portion 303c is an upstream guide surface that guides the belt 301 toward the nip portion N. The downstream guide portion 303b is a downstream guide surface that guides the belt 301 toward the stay 302 so as to move it away from the nip portion N after it has passed through the nip portion N. That is, the downstream guide portion 303b is formed downstream in the transport direction from the downstream side surface 303e of the fitting groove portion 303f, and guides the belt 301 toward the downstream side in the rotational direction of the belt 301. These upstream guide portion 303c and downstream guide portion 303b are in contact with the belt 301 over the entire passage area through which the largest size of recording material capable of image formation in the nip portion N passes, in the width direction.

[0034] [Sliding member] If the frictional force between the belt 301 and the pad 303 is large, the rotation of the belt 301 will be hindered. Therefore, in this embodiment, as shown in Figure 4, in order to reduce the frictional force between the belt 301 and the pad 303 in the nip section N where the pressure is high, the pad 303 is provided with a sliding member 304 that slides against the belt 301. The sliding member 304 is held by the pad 303 and positioned opposite the pressure roller 305 with the belt 301 in between. In this embodiment, the sliding member 304 is held by the pad 303 such that its shorter side is in the conveying direction.

[0035] The sliding member 304 has heat resistance and strength, and while held by the pad 303, it has a sliding surface that contacts the inner circumferential surface of the rotating belt 301 and slides against the belt 301. By interposing the sliding member 304 between the pad 303 and the belt 301, the frictional force between the pad 303 and the belt 301 is reduced, so that the pad 303 does not hinder the rotation of the belt 301. The inner circumferential surface of the belt 301 may be coated with a lubricant to allow the belt 301 to slide smoothly against the sliding member 304. For example, silicone oil can be used as the lubricant.

[0036] As described above, in this embodiment, the sliding member 304 reduces the frictional force with the belt 301. In the sliding member 304 of this embodiment, as shown in Figure 2, a plurality of protrusions are formed on the sliding surface that slides against the belt 301. The sliding member 304 is formed using a metal such as stainless steel (SUS), copper, or aluminum. Since the sliding member 304 comes into contact with the heated belt 301, it is desirable that it has a small heat capacity. Therefore, in this embodiment, the sliding member 304 is formed using stainless steel (SUS) with a thickness of "1 mm". Note that the sliding member 304 is not limited to metal, but may also be formed using engineering plastics such as polyimide resin (PI), polyetheretherketone resin (PEEK), or LCP (liquid crystal polymer resin).

[0037] The detailed configuration of the sliding member 304 is shown in Figures 3(a) and 3(b). Figure 3(a) is a cross-sectional view of the sliding member 304 when cut in the conveying direction, and Figure 3(b) is a plan view of the sliding member 304 as seen from the contact surface side between the belt 301 and the sliding member 304. The sliding member 304 is fixed to the stay 302 via a pad 303 by fastening members such as stepped screws 308 (Figure 5), as will be described in more detail later. The sliding member 304 consists of a plate-shaped base 304a and a sliding layer 304c. Multiple protrusions (convex portions) 304b are formed on the side of the base 304a that slides against the belt 301, projecting toward the inner circumferential surface of the belt 301. The sliding layer 304c is provided so as to cover the surface of the base 304a that slides against the belt 301 (including the multiple protrusions 304b).

[0038] As shown in Figure 3(a), the multiple protrusions 304b are provided so as to project from the base body 304a toward the inner circumferential surface of the belt 301. The amount of protrusion (height in the Z direction) of the multiple protrusions 304b from the surface of the base body 304a is, for example, "250 μm". Also, as shown in Figure 3(b), the multiple protrusions 304b and 304d are integrally formed from the same material as the base body 304a, and multiple protrusions are arranged in the direction of transport of the recording material in the nip section N (X direction) and in the width direction of the recording material (Y direction) intersecting the transport direction. The distance (spacing) d between the centers of adjacent protrusions 304b in the transport direction, and the distance (spacing) d between the centers of adjacent protrusions 304b in the width direction, are 1.25 mm or more, preferably 1.4 mm or more. In this embodiment, in order to ensure uniform sliding properties with the belt 301, the spacing between the multiple protrusions 304b is the same in the conveying direction and the width direction, and the spacing d of each is set to 1.4 mm.

[0039] By providing multiple protrusions 304b on the sliding surface of the sliding member 304 that slides against the belt 301, the contact area between the sliding member 304 and the belt 301 is reduced, thereby lowering the sliding resistance between the sliding member 304 and the belt 301. The sliding layer (low friction layer) 304c is preferably a coating agent such as a fluororesin (PTFE (polytetrafluoroethylene), PFA, etc.) to achieve low friction. In this embodiment, the sliding member 304 is formed by coating the surface of a substrate 304a containing multiple protrusions 304b with PTFE with a thickness of 20 μm.

[0040] As shown in Figure 4, in this embodiment, a convex shape is formed on the surface of the sliding member 304, and the sliding member 304 slides against the belt 301 with the tip surfaces of the multiple protrusions 304b. This reduces the contact area between the sliding member 304 and the belt 301, thereby reducing the frictional force with the belt 301. Furthermore, since the surface of the multiple protrusions 304b is coated with the sliding layer 304c as described above, this also reduces the frictional force with the belt 301.

[0041] [Holding of sliding members] As described above, the pad 303 holds the sliding member 304 such that the inner circumferential surface of the belt 301 slides against the tip surfaces of the multiple protrusions 304b. In this embodiment, a concave fitting groove 303f is formed on the side of the pad 303 opposite to the side supported by the stay 302 for fitting and holding the sliding member 304. The sliding member 304 is held by the pad 303 so as to be movable away from the bottom surface 303d of the fitting groove 303f when the pressure roller 305 is in a separated position.

[0042] Figure 5 is a partial perspective view illustrating the relationship between the pad 303 and the sliding member 304. The belt 301, not shown in Figure 5, contacts and slides with the sliding member 304 in the area indicated by B in the figure. The sliding member 304 is fastened to the stay 302 by stepped screws 308, which act as fastening members, on the outer side in the width direction of the area in which it slides with the belt 301.

[0043] A mounting portion 304k is provided at the widthwise end of the base 304a of the sliding member 304. The mounting portion 304k is formed by bending the end of the base 304a toward the opposite side of the belt 301, and then bending it outward in the widthwise direction, thereby creating a step relative to the base 304a. A slit 304j is also formed in the mounting portion 304k, and the mounting portion 304k is fastened to the stay 302 by inserting a stepped screw 308 into this slit 304j and then screwing the stepped screw 308 into a screw hole formed in the stay 302.

[0044] As described above, the mounting portion 304k has a step relative to the base 304a of the sliding member 304, and is fastened to the stay 302 at a position further in the height direction from the belt 301 than the base 304a. Here, the height direction is perpendicular to the transport direction of the recording material and perpendicular to the width direction, which is the Z direction as described above. By forming the mounting portion 304k with a step relative to the base 304a in this way, it becomes possible to attach the stepped screw 308 at a position away from the belt 301, and it becomes possible to assemble and detach the belt 301 to the pad unit 300 without removing the stepped screw 308.

[0045] Furthermore, the sliding member 304 is fastened to the stay 302 by a stepped screw 308 via a slit 304j formed in the mounting portion 304k, with a gap in the height direction. That is, by using a stepped screw 308 as the fastening member for the sliding member 304 to the stay 302, the sliding member 304 can move in the height direction relative to the stay 302 by the amount of the gap between the stepped screw 308 and the mounting portion 304k. In addition, the stepped screw 308 is loosely fitted into the slit 304j, fastening it to the stay 302 with a gap in the transport direction and width direction of the recording material. Therefore, the sliding member 304 can move in the transport direction and width direction relative to the stay 302 by the amount of the gap between the stepped screw 308 and the slit 304j.

[0046] The reason why the sliding member 304 is made movable relative to the stay 302 in the height, transport, and width directions is that the pad 303 and the sliding member 304 are made of different materials and have different coefficients of thermal expansion. For example, when the fixing device 8 is used, the belt 301 is heated, causing the temperature of the pad 303 and the sliding member 304 to rise, and each component to expand due to thermal expansion. In this embodiment, the difference in thermal expansion at this time is absorbed by the above configuration. The tolerances of the sliding member 304, pad 303, and stay 302 are also absorbed by the above configuration. Note that if the sliding member 304 is secured to the pad 303 so that there is some play in the height direction, the sliding member 304 does not need to be fastened to the stay 302.

[0047] When the nip portion N is formed, that is, when the pressure roller 305 is positioned in contact with the surface, the belt 301 slides against the multiple protrusions 304b of the sliding member 304 as the pressure roller 305 rotates. As a result, the sliding member 304 receives a frictional force from the belt 301 in a direction toward the downstream side with respect to the conveying direction of the recording material. At this time, since the sliding member 304 is fastened to the stay 302 so as to be movable in the conveying direction of the recording material, the frictional force received from the belt 301 causes the sliding member 304 to move toward the downstream side in the conveying direction of the recording material, and the downstream end face 304e of the sliding member 304 comes into contact with the downstream side surface 303e of the fitting groove portion 303f formed in the pad 303 (see Figure 4). This determines the position of the sliding member 304 relative to the pad 303 in the conveying direction of the recording material. In other words, when the pressure roller 305 is in contact with the sliding member 304, the downstream end face 304e and the downstream side surface 303e of the fitting groove 303f come into contact, thereby restricting the sliding member 304 from moving downstream in the conveying direction. Note that even when the nip portion N is formed, the downstream end face 304e and the downstream side surface 303e do not need to come into contact if the protruding portion 303h and the contact portion 304h, which will be described later, are in contact.

[0048] As shown in Figure 4, the downstream side surface 303e of the fitting groove 303f is formed continuously with the downstream guide portion 303b, with a circular arc-shaped corner portion 303k in between. This allows the belt 301 to continuously contact and be guided by the sliding member 304 and the pad 303. Specifically, with the pressure roller 305 in contact with the belt, the belt 301 is stretched between the multiple protrusions 304b of the sliding member 304 and the downstream guide portion 303b. In this embodiment, the curvature of the belt 301, which is curved by the corner of the protrusion 304b located furthest downstream in the direction of transport of the recording material, causes the recording material to peel away from the belt 301.

[0049] [Prevention of sliding member detachment] Next, the configuration for preventing the sliding member 304 from falling off in this embodiment will be explained using Figures 6 and 7 in addition to Figure 5 described above. Figure 6 is a cross-sectional view of the vicinity of the exit of the nip portion N when the pressure roller 305 is separated from the outer circumferential surface of the belt 301 and the nip portion N is released. Figure 7 is a cross-sectional view of the vicinity of the exit of the nip portion N when the pressure roller 305 is in contact with the outer circumferential surface of the belt 301 and the nip portion N is formed.

[0050] As described above, the sliding member 304 is held with a gap in the height direction relative to the pad 303 to avoid expansion deformation due to thermal expansion. Therefore, when the nip portion N is released, the sliding member 304 may maintain contact with the belt 301 and move away from the pad 303. That is, as the pad 303 separates from the belt 301, the belt 301 bends away from the pad 303 due to gravity, and the sliding member 304 falls relative to the pad 303 by gravity by the amount of the gap between the mounting portion 304k of the sliding member 304 and the stepped screw 308.

[0051] At this time, if the sliding member 304, which is a thin plate about 1 mm thick, falls out of the fitting groove 303f, the frictional force received from the belt 301 may cause the sliding member 304 to ride up onto the downstream guide portion 303b of the pad 303. The belt 301 is guided along the corners of the multiple protrusions 304b of the sliding member 304 and the downstream guide portion 303b to separate the recording material on which the toner image has been formed. Therefore, there is a concern that riding up may cause abnormalities such as poor separation of the recording material. For this reason, in this embodiment, a protruding portion (restricting portion) 303h is provided on the downstream side of the pad 303 in the transport direction, projecting toward the nip portion. By bringing the protruding portion 303h into contact with the contact portion (downstream end) 304h formed on the downstream side of the sliding member 304 in the transport direction, the movement of the sliding member 304 downstream in the transport direction is restricted even if it falls.

[0052] Specifically, the pad 303 has a protruding portion 303h that protrudes toward the nip portion on the upstream side in the conveying direction from the downstream side surface 303e of the fitting groove portion 303f, and is formed so as not to protrude toward the nip portion beyond the sliding member 304 when the pressure roller 305 is in contact position (the state in Figure 7). On the other hand, the sliding member 304 is positioned upstream of the protruding portion 303h in the conveying direction and has a contact portion 304h that, when the pressure roller 305 is in a separated position (the state in Figure 6), comes into contact with the protruding portion 303h, thereby restricting the movement of the sliding member 304 toward the downstream side in the conveying direction.

[0053] In this embodiment, as shown in Figure 5, the sliding member 304 has a notch 304g cut out from the downstream end to the upstream side with respect to the conveying direction. A part of the notch 304g, specifically the edge of the edge forming the notch 304g that faces downstream in the conveying direction, is designated as the contact portion 304h. The notch 304g is formed at the downstream end of the sliding member 304 in the conveying direction and at the end in the width direction. In other words, by cutting out the downstream end of the base body 304a of the sliding member 304 in the conveying direction and at the end in the width direction, a contact portion 304h that can contact the protrusion 303h is formed upstream of the downstream end face 304e of the sliding member 304. Such a contact portion 304h is provided outside the region where the multiple protrusions 304b are formed with respect to the width direction.

[0054] On the other hand, the protrusion 303h formed on the pad 303 is located at the end of the pad 303 in the width direction and is positioned downstream in the conveying direction from a part of the notch 304g which is the contact portion 304h. That is, the protrusion 303h is positioned to enter the notch 304g formed on the sliding member 304. Furthermore, the height of the fitting groove portion 303f of the protrusion 303h from the bottom surface 303d (the height distance between the bottom surface 303d and the tip of the protrusion 303h) is greater than the height of the upstream end of the downstream guide portion 303b in the conveying direction from the bottom surface 303d (the height distance between the bottom surface 303d and the upstream end of the downstream guide portion 303b in the conveying direction). As a result, even if the nip portion N is released and the sliding member 304 falls from the fitting groove portion 303f, the protrusion 303h can be positioned to more reliably contact the contact portion 304h.

[0055] In this embodiment, a notch 304g is formed at the downstream end of the sliding member 304, and a contact portion 304h, which is part of the notch 304g, is brought into contact with a projection 303h formed on the pad 303. This restricts the movement of the sliding member 304 even if it falls out of the fitting groove 303f and tries to move downstream in the conveying direction. In other words, the detachment of the sliding member 304 can be suppressed. In the above example, a notch 304g was formed on the sliding member 304 to provide the contact portion 304h, but for example, a through hole or groove into which the projection 303h can enter may be formed on a part of the sliding member 304 at a position corresponding to the upstream side in the conveying direction of the downstream side surface 303e of the pad 303, and the inner wall of the through hole or groove may be used as the contact portion 304h.

[0056] Furthermore, the aforementioned notches 304g are formed to cut out the corners at both ends in the width direction of the sliding member 304 and at the downstream end in the conveying direction. Similarly, the protrusions 303h are formed at both ends in the width direction on the downstream side of the pad 303 as a continuous shape from the downstream guide portion 303b. Therefore, at both ends in the width direction of the sliding member 304, the contact portion 304h, which is part of the notches 304g, comes into contact with the protrusions 303h of the pad 303, thereby restricting the sliding member 304 from moving downstream in the conveying direction even if it falls.

[0057] On the other hand, as shown in Figure 7, when the nip portion N is formed, the sliding member 304 is pressed in the direction of the pad 303 by the pressure roller 305 via the belt 301. As described above, the protruding portion 303h is formed so as not to protrude toward the nip portion side than the sliding member 304 when the pressure roller 305 is in contact position (the state in which the nip portion N is formed). In this embodiment, a notch portion 304g is formed at the end of the sliding member 304 within the range in which it slides with the belt 301, and the contact portion 304h is formed upstream of the downstream side surface 303e of the sliding member 304 in the direction of transporting the recording material.

[0058] Here, it is conceivable to form the notch 304g outside the range in which it slides with the belt 301, but in this case, the widthwise length of the sliding member 304 would increase. Furthermore, in order to prevent interference with other members located outside the widthwise direction of the sliding member 304, it would be necessary to position the other members even further outside in the widthwise direction, which could result in the device becoming larger. For this reason, in this embodiment, the notch 304g is formed within the range in which the belt 301 and the sliding member 304 slide. Therefore, the protruding portion 303h that contacts the contact portion 304h of the notch 304g is also located within the range in which the belt 301 and the sliding member 304 slide. Accordingly, in this embodiment, the protruding portion 303h is formed upstream in the conveying direction of the downstream side surface 303e of the pad 303, so that when the nip portion N is formed, the protruding portion 303h does not contact the inner circumferential surface of the belt 301 that is stretched between the multiple protrusions 304b and the downstream guide portion 303b.

[0059] Specifically, the protruding portion 303h of the pad 303 is formed upstream of the downstream guide portion 303b in the conveying direction, so as to face the contact portion 304h of the sliding member 304. Furthermore, because the contact portion 304h is formed upstream of the downstream side surface 303e in the conveying direction, the contact portion 304h is positioned away from the downstream guide portion 303b. As a result, it becomes possible to position the protruding portion 303h and the contact portion 304h further back from the trajectory of the belt 301, which is formed by stretching between the multiple protrusions 304b and the downstream guide portion 303b. This suppresses contact between the protruding portion 303h and the belt 301, thereby suppressing stress on the belt 301 such as deformation and pressure concentration due to contact.

[0060] [Arrangement of protruding parts] In this embodiment, as described above, the sliding member 304 is fastened to the stay 302 via a stepped screw 308 with a gap between them. Therefore, when forming the nip portion N, the frictional force received by the sliding member 304 from the belt 301 causes the downstream end face 304e to come into contact with the downstream side surface 303e of the pad 303. As a result, a continuous pressure distribution is formed in the short direction of the nip portion N, which is a suitable arrangement to prevent image defects caused by a decrease in nip pressure.

[0061] On the other hand, at the end of the pad 303 where the protrusion 303h is provided, a notch 304g is formed in the sliding member 304 to form a contact portion 304h that abuts against the protrusion 303h, thus creating a gap between the pad 303 and the sliding member 304. Here, if the notch 304g is formed within the region (passage region) through which the recording material passes the nip portion N, a gap will exist between the pad 303 and the sliding member 304 within this passage region. In this case, pressure may escape in this gap, or water vapor generated by heating the recording material may accumulate in this gap, potentially affecting the image fixed to the recording material as it passes through the nip portion N and causing image defects. Therefore, it is desirable that the protrusion 303h and the contact portion 304h be positioned at the longitudinal end and outside the maximum width of the recording material that can be handled by the fixing device 8.

[0062] In other words, in this embodiment, the protrusion 303h is provided outside the region through which the largest recording material passes the nip portion N, with respect to the width direction. In this embodiment, with respect to the width of the largest recording material passing through the fixing device 8, which is 330.2 mm, the protrusion 303h and the contact portion 304h are formed outside the width direction, beyond a position 170 mm from the center in the width direction of the recording material.

[0063] [Comparative Example] Next, the configurations of Comparative Examples 1 and 2, which illustrate the effects of this embodiment, will be described using Figures 8 and 9. Comparative Example 1, shown in Figure 8, is an example in which the pad 303A does not have a configuration to restrict the detachment of the sliding member 304A, and the sliding member 304A detaches and rides up onto the downstream guide portion 303b of the pad 303A. In contrast to the configuration of this embodiment described above, Comparative Example 1 has no protruding portion 303h formed on the pad 303A and no contact portion 304h formed on the sliding member 304A. The other configurations are the same as those of this embodiment described above. Figure 8 is a cross-sectional view illustrating the positional relationship between the pad 303A and the sliding member 304A when the pressure roller 305 is separated from the belt 301 and the nip portion N is released.

[0064] When the nip portion N is released, the sliding member 304A separates from the bottom surface 303d of the pad 303A. At this time, due to the frictional force from the belt 301, the downstream end surface 304e of the sliding member 304A moves further downstream in the conveying direction than the arc-shaped corner portion 303k which is continuous with the downstream side surface 303e of the fitting groove portion 303f formed in the pad 303A. If the nip portion N is formed again in this state, the sliding member 304A cannot return to the fitting groove portion 303f and will fall off by riding on the downstream guide portion 303b downstream of the corner portion 303k.

[0065] In contrast, in this embodiment, when the nip portion N is released, the protrusion 303h formed on the pad 303 comes into contact with the contact portion 304h of the sliding member 304, thereby positioning the downstream end face 304e of the sliding member 304 upstream in the conveying direction from the corner portion 303k, which has a circular arc cross-section. As a result, even when the nip portion N is released, it becomes possible to suppress the sliding member 304 from falling off.

[0066] Next, Comparative Example 2 will be described. Comparative Example 2, shown in Figure 9, is an example in which the protrusion 303h of the pad 303B is formed at a position that abuts against the downstream end face 304e of the sliding member 304B. In Comparative Example 2, unlike the configuration of the embodiment described above, the position of the protrusion 303h of the pad 303B is provided downstream in the conveying direction from the downstream side surface 303e of the fitting groove 303f, and the abutment portion 304h is not formed on the sliding member 304B, and the protrusion 303h is in contact with the downstream end face 304e of the sliding member 304B. The other configurations are the same as those of the embodiment described above. Figure 9 is a cross-sectional view to explain the positional relationship between the pad 303B and the sliding member 304B when the pressure roller 305 is in contact with the belt 301 and the nip portion N is formed.

[0067] In Comparative Example 2, the end of the downstream side surface 303e of the pad 303B is extended toward the nip portion N to form a protrusion 303h, which is brought into contact with the downstream end surface 304e of the sliding member 304B, thereby preventing the sliding member 304B from falling out of the fitting groove portion 303f. However, because the protrusion 303h is located downstream in the conveying direction from the downstream side surface 303e, when the nip portion N is formed, the protrusion 303h comes into contact with the inner circumferential surface of the belt 301, which can cause stress such as stress concentration due to local deformation of the belt 301, potentially leading to a shortened lifespan of the belt 301.

[0068] In contrast, in this embodiment, by forming the protrusion 303h on the upstream side in the conveying direction relative to the downstream side surface 303e, it becomes possible to position the protrusion 303h with a gap between it and the belt 301, which is guided by the multiple protrusions 304b of the sliding member 304 and the downstream guide portion 303b of the pad 303. This suppresses excessive stress on the belt 301. Thus, in this embodiment, the detachment of the sliding member 304 can be suppressed, and the generation of excessive stress on the belt 301 can be suppressed.

[0069] <Other Embodiments> In the above-described embodiment, a configuration was described in which the sliding member 304 is fitted inside the fitting groove 303f of the pad 303. However, as long as the relationship between the protruding portion 303h and the contact portion 304h is as described above, a configuration in which a member is sandwiched between the pad 303 and the sliding member 304 is also acceptable. [Explanation of symbols]

[0070] 8. Fixing device 301... belt 302...Stay (support member) 303... Pad (retaining member) 303b... Downstream guide section (downstream guide surface) 303d...bottom 303e...downstream side 303f... Fitting groove (recess) 303h...Protrusion 304...Sliding member 304b...Protrusion 304e...Downstream end face 304g... Notched section 304h...Contact part 305... Pressure roller (nip forming member) 306...Halogen heater (heat source) 307...Heating roller 308... Stepped screw (fastening component)

Claims

1. A fixing device for fixing a toner image supported on a recording material to the recording material, An endless, rotatable belt, A nip-forming member that contacts the outer surface of the belt and forms a nip portion that grips and transports the recording material between itself and the belt, A sliding member that slides against the inner circumferential surface of the belt in the nip portion, The belt comprises a holding member positioned on the inside of the belt so as to sandwich the sliding member and the belt between the nip portion forming member, and having a recess formed on the side facing the nip portion for holding the sliding member, The nip-forming member is movable between a contact position in which it abuts the outer circumferential surface of the belt to form the nip, and a separated position where it is spaced away from the outer circumferential surface of the belt. The recess has a bottom surface and a downstream side surface formed on the downstream side of the bottom surface with respect to the transport direction of the recording material transported by the nip portion, and facing the downstream end surface of the sliding member held in the recess in the transport direction. The sliding member is held by the holding member so as to be movable away from the bottom surface when the nip portion forming member is in the separated position. The holding member has a protrusion that protrudes toward the nip portion on the upstream side in the conveying direction from the downstream side of the recess, and is formed so as not to protrude toward the nip portion from the sliding member when the nip portion forming member is in the contact position. The sliding member is positioned upstream of the protrusion in the conveying direction and has a contact portion that, when the nip portion forming member is in the separated position, contacts the protrusion, thereby restricting the sliding member from moving downstream in the conveying direction. A fixing device characterized by the following features.

2. The sliding member is restricted from moving downstream in the conveying direction when the nip-forming member is in the contact position, and the downstream end face and the downstream side surface of the recess come into contact with each other. The fixing device according to feature 1.

3. The sliding member has a notch cut out from the downstream end toward the upstream end with respect to the conveying direction, The aforementioned contact portion is part of the aforementioned notch portion, The aforementioned protrusion is located downstream in the conveying direction from a portion of the aforementioned notch. The fixing device according to feature 1.

4. The notch is formed at the downstream end of the sliding member in the conveying direction and at the end in the width direction intersecting the conveying direction. The fixing device according to feature 3.

5. The aforementioned protrusion is provided at the end of the retaining member with respect to the width direction. The fixing device according to feature 4.

6. The retaining member is formed downstream of the downstream side of the recess in the conveying direction and has a downstream guide surface that guides the belt downstream in the rotational direction of the belt. The height of the protruding portion from the bottom surface is greater than the height of the upstream end of the downstream guide surface from the bottom surface in the conveying direction. The fixing device according to feature 1.

7. A support member is positioned on the opposite side of the nip portion, sandwiching the aforementioned holding member, and supports the aforementioned holding member. The device further comprises a fastening member that fastens the sliding member to the support member in a manner that has a gap in the height direction perpendicular to the transport direction and perpendicular to the width direction intersecting the transport direction. The fixing device according to feature 1.

8. The fastening member fastens the sliding member to the support member with a gap in the transport direction and the width direction, respectively. The fixing device according to feature 7.

9. The aforementioned protrusion is provided outside the region through which the largest size recording material passes, with respect to the width direction intersecting the transport direction. The fixing device according to feature 1.

10. The sliding member has a plurality of protrusions on the side that slides against the belt, which are provided to project toward the inner circumferential surface of the belt. The fixing device according to feature 1.

11. The retaining member is formed downstream of the downstream side of the recess in the conveying direction and has a downstream guide surface that guides the belt downstream in the rotational direction of the belt. The aforementioned protrusions are formed so as not to contact the inner circumferential surface of the belt that is stretched between the plurality of protrusions and the downstream guide surface when the nip portion forming member is in the contact position. The fixing device according to claim 10.

12. The contact portion is provided outside the region where the plurality of protrusions are formed, with respect to the width direction intersecting the transport direction. The fixing device according to claim 10.

13. The nip-forming member is a pressure roller that applies pressure to the belt toward the sliding member. The fixing device according to feature 1.

14. A heating roller that contacts the inner circumferential surface of the belt, The system further comprises a heat source for heating the heating roller. The fixing device according to feature 1.

Images